Effect of Topical Gatifloxacin 0.3% & Ciprofloxacin 0.3% in The Treatment Of Bacterial Corneal Ulcer
Cornea is the outermost coat of the eyeball, which is the most vital part for vision. It has tremendous optical importance in the visual function. It is the main part of refractive media that contributes about 74% of total diopteric power of normal human eye (John E. Stuphen et al. 2007-8). So the corneal health and disease are not less important than that of any vital organ of the body. The cornea has some anatomical and physiological specialties with which it can function without any interruption throughout life. In spite of these specialties the cornea frequently becomes diseased and corneal ulcer is one of the top of the list of corneal disease. So we should give great importance when it becomes diseased.
The avascular, clear anatomical structure of the cornea, with its specialized micro environment predispose to potential alteration and destruction by invading microorganism by virulence factor and host response factors (C. Stephen Foster, 2005). Bacterial Corneal ulcer is a common sight threatening condition. A wide variety of bacterial species can cause microbial corneal ulcer. The common organisms are Streptococcus pneumonae, Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa and Enterobactereriace. Uncommon organisms are N. gonorrhoae, N. meningitides, Moraxella species, Haemophilus species, Mycobacteriam spp. & Corynebacteriam spp. (C. Stephen Foster, 2005).
Bacterial corneal ulcer has the potential to progress rapidly to corneal perforation. Even small axial lesion can cause surface irregularity & scar that can lead to significant loss of vision. (Jack J. Kanski, 2007). The objective of therapy in bacterial corneal ulcer is rapidly to eliminate the infective organism, reduce the inflammatory response, prevent structural damage to the cornea and promote healing of the epithelial surface. (Jones DB.1979). A large number of active antimicrobial drugs available for the treatment of bacterial corneal ulcer a greater choice for cure with less drug related toxicity while providing alternative choices despite the continuing emergence of drug resistant pathogenic organisms (C. Stephen Foster, 2005).
Different antimicrobial agent used in the treatment of bacterial corneal ulcer are penicillins, cephalosporins, other ?-lactum antibiotics, glycopeptides, aminoglycosides, macrolides, tetracyclines, chloramphenicol and fluoroquinolones.
Fluoroquinolones block bacterial DNA synthesis by inhibiting bacterial tropoisomerase II (DNA gyres) and tropoisomerase IV. Inhibition of DNA gyres prevents the relaxation of positively super coiled DNA that is required for normal transcription and replication. Inhibition of tropoisomerase IV interferes with separation of replicated chromosomal DNA into the respective daughter cells during cell division (Betan G. Katzung, 2007) Nalidixic acid, the first member of quinolone, then newer generation of fluoroquinolones discovered to expand the antibacterial spectrum greatly. Newer generation of fluoroquinolones have been obtained by the slight modification of previous generation fluoroquinolones side chain. Fluoroquinolones those commonly used as topical solution are ciprofloxacin, levofloxacin, lomifloxacin, gatifloxacin and moxifloxacin. Their high potency and generally excellent activity against the most frequent gram positive and gram negative ocular pathogens, bactericidal mode of action bioavailability & biocompatibility make fluoroquinolones an excellent initial choice of topical therapy of bacterial keratitis(C. Stephen Foster, 2005).
In treating patient with ciprofloxacin crystalline white precipitate were observed in the area of epithelial ulceration and this crystalline precipitate reduces the activeconcentration of drug in the stroma at the site of infection(O’ Brien et al. 1993). Such crystalline deposition has the potential disadvantage of decreasing visualization of the stromal infiltrate immediately deep to the precipitate for clinical monitoring of the therapeutic progress, there is evidence that ciprofloxacin precipitation may also prevent or delay re-epithelization of a corneal defect(Kanellopoulos AJ et al. 1994). In addition to these, their widespread use has lead to emergence of resistance in many bacterial species.
In vitro study indicated that fourth generation fluoroquinolones appear to cover bacterial resistance to the second and third generation fluoroquinolones, and were more potent than the second and third generation fluoroquinolones for gram-positive bacteria, and are equally potent for gram-negative bacteria (Mather R. et al 2002). But the MICs are statistically higher for the second generation fluoroquinolone resistant Staphylococci than for the second generation fluoroquinolone susceptible Staphylococci (Aparna Duggirala et al. 2007). Gatifloxacin 0.3% offers improved activity against gram-positives, improved activity against atypical and retained activity against gram-negatives, the gram-positive pathogens, which were resistant to the previous generations of fluoroquinolones, are now susceptible. (Francis S. 2004).
Low MICs and higher tissue concentrations are necessary for effective therapy as well as guarding against antibiotic resistance. Potentially, a million bacteria may exist on the eyelids or in large bacterial infiltrates and abscesses. Bacterial resistance to the second generation fluoroquinolones (ciprofloxacin and ofloxacin) can occur with a single genetic mutation. This means that one bacteria in ten million can develop resistance to a second-generation fluoroquinolone antibiotic. However, the fourth generation fluoroquinolones (moxifloxacin and gatifloxacin) were developed to resist spontaneous mutations that convey antibiotic resistance (Drlica K. A 2001 & Courvalin P. 2000). It generally takes two genetic mutations for resistance to occur with fourth generation fluoroquinolones. This means that one bacteria in ten trillion can develop resistance to fourth-generation fluoroquinolone antibiotics. Even in the instance of ocular infection, a bacterial load of one trillion is not probable to be reached.
A comparison of the in vitro susceptibility patterns and the MICs of gatifloxacin and moxifloxacin (fourth-generation fluoroquinoloncs) with ciprofloxacin and ofloxacin (second-generation fluoroquinolones) and levofloxacin (third-generation fluoroquinolone) using bacterial keratitis isolates was conducted. The fourth-generation fluoroquinolones did, however, demonstrate increased susceptibility for S. aureus isolates that were resistant to ciprofloxacin, levofloxacin, and ofloxacin. The MICs of 8-methoxy fluoroquinolones were statistically lower than the MICs of second-generation fluoroquinolones for all gram-positive bacteria tested.
The fourth generation fluoroquinolones did, however, demonstrate increased susceptibility for Staphylococcus aureus isolates that were resistant to CIP, LEV and OFX. In general, CIP demonstrated the lowest MICs for gram-negative bacteria. The MICs for fourth-generation fluoroquinolones were statistically lower than the second-generation fluoroquinolones for all gram-positive bacteria tested. Comparing the two fourth-generation fluoroquinolones, MOX demonstrated lower MICs for most gram-positive bacteria, whereas GAT demonstrated lower MICs for most gram-negative bacteria. Based on in vitro testing, the fourth-generation fluoroquinolones may offer some advantages over those currently available for the treatment of bacterial keratitis.
So in this study we tried to find out a drug for the treatment of bacterial corneal ulcer that is effective as well as have no adverse effect, can be used as mono therapy, available, cheap in Bangladesh context.
Justification of the study:
Corneal ulcer is a serious sight-threatening condition which can result in permanent loss of vision if appropriate treatment is not instituted promptly. Unfortunately due to emergence of resistance in many bacterial species to many topical antibiotics it became difficult to treat corneal ulcer. Newer fluoroquinolones will overcome this problem.
Gatifloxacin, a fourth generation fluoroquinolone, has shown excellent in vitro activity against most pathogens responsible for ocular infections including corneal ulcer. Hitherto, there is no published studies in Bangladesh comparing gatifloxacin with ciprofloxacin or older fluoroquinolones for the treatment of bacterial corneal ulcer. We aimed to compare the bacteriologic and clinical efficacy of gatifloxacin and ciprofloxacin in the treatment of bacterial corneal ulcer.
Topical gatifloxacin 0.3% eye drops is more effective than ciprofloxacin 0.3% eye drops in the treatment of bacterial corneal ulcer.
Objectives of this study
To compare the efficacy of topical gatifloxacin 0.3% eye drops and ciprofloxacin 0.3% eye drops in the treatment of bacterial corneal ulcer.
To find out the symptoms and signs in both groups following treatment.
To determine the ulcer healing rate in both groups.
To assess the bacteriologic and clinical efficacy of gatifloxacin and ciprofloxacin in the treatment of bacterial corneal ulcer.
REVIEW OF LITERATURE
Related previous work:
A study was published in Am J Ophthalmol. 2006; 141(2):282-286, that was conducted by Parmar P. et al: in the Institute of Ophthalmology, Joseph Eye Hospital, Tiruchirapalli, India. They showed that a significantly higher proportion of ulcers in the GAT group exhibited complete healing compared with those in the CIP group (39 eyes [95.1%] vs 38 [80.9%]; P = .042). Gatifloxacin demonstrated a significantly better action than ciprofloxacin against gram-positive cocci in vitro (P < .001) and the percentage of ulcers caused by these pathogens that healed in the GAT group was significantly better than in the CIP group (P = .009).
Another study was conducted by Harold Jensen et al; Journal of ocular pharmacology and therapeutics Volume 21, Number 1, 2005. In their result all eyes showed evidence of infection by 48 hours post-inoculation with 36 of 41 eyes (87.8%) exhibiting moderate-to-severe keratitis. All eyes exhibited corneal healing by day 15, with no significant differences among groups. Three of 4 groups receiving gatifloxacin tended to have smaller fluorescein retention area scores than did the ciprofloxacin group. No eyes tested positive for Pseudomonas at the end of the study. No corneal precipitates were found following as many as 48 doses/day of gatifloxacin. The most important finding of this study was that gatifloxacin 0.3% ophthalmic solution at the least frequently administered dosing regimen is as effective as ciprofloxacin 0.3%. Other finding is consistent with lower toxicity against cultured human cells of gatifloxacin, compared to ciprofloxacin, especially after exposure to ultraviolet light (Yamamoto, T. Tsurumaki Y. Takei M. et al. 2001). In conclusion they state that ophthalmic gatifloxacin 0.3% is at least as effective as ciprofloxacin at healing corneal ulcers infected with Pseudomonas aeruginosa when gatifloxacin is administered less frequently than ciprofloxacin. Trends favored gatifloxacin in fluorescein retention scores.
Another study was conducted by Pragya Parmar MS et al; in the Institute of Ophthalmology, Joseph Eye Hospital, Tiruchirapalli, India & was published in Clinical and Experimental Ophthalmology 2003,- 3 1: 44-47. They showed that Pneumococcal keratitis accounted for 33.3% of bacterial keratitis. Most cases presented with non-severe keratitis (77.5%). Co-existing sac pathology was more frequent in pneumococcal ulcers as compared to non-pneumococcal bacterial ulcers (50% vs 9%, P< 0.001). Characteristic clinical features enabling an accurate clinical diagnosis were found in 27.5% and lanceolate diplococci on Gram’s stain were identified in 76% of cases. In vitro testing showed a high susceptibility to cephazolin and cipro-floxacin. All patients received ciprofloxacin as first-line therapy. Eighty per cent responded well with complete healing of the ulcer. A second drug was required in 8.5%. They found ciprofloxacin to be effective clinically in treating these ulcers with 80% of ulcers responding well to ciprofloxacin alone. Ciprofloxacin has the added advantage of being commercially available and is thus less prone to contamination or loss of efficacy. It is also more economical. In conclusion they state that ciprofloxacin therapy can be effective in the treatment of pneumococcal keratitis.
M J Bharathi, R Ramakrishnan, R Meenakshi, et al. published in Br J Ophthalmol 2006 90: 1271-1276 Microbiological diagnosis of infective keratitis: comparative evaluation of direct microscopy and culture results showed bacterial pathogens isolated from corneal scrapes of 1151 eyes with infective keratitis treated at a tertiary eye care referral centre in south india.
Table 1. comparative evaluation of direct microscopy and culture results showed bacterial pathogens isolated from corneal scrapes of 1151 eyes with infective keratitis:
|Bacterial isolates||Pure isolates||Mixed with other bacteria||Mixed with fungal spp||Total no. of bacterial isolates (%)|
|Streptococcus pneumonia||417||7||14||438 (36.03)|
|Staphylococcus aureus||36||10||0||46 (3.78)|
|Miccrococcus spp||6||0||0||6 (0.49)|
|?-Haemolytic streptococci||46||5||2||53 (4.36)|
|?-Haemolytic streptococci||6||0||6 (0.49)|
|Non-haemolytic streptococci||9||0||9 (0.74)|
|2||Gram-positive bacilli||33||22||2||57 (4.69)|
|Bacillus spp||12||15||0||27 (2.22)|
|Corynebacterium spp||21||7||2||30 (2.47)|
|Moraxella spp||9||9 (0.74)|
|Neisseria spp||3||3 (0.25)|
|4||Aerobic actinomycetes||39||7||46 (3.78)|
|Nocarcia spp||39||7||46 (3.78)|
|5||Gram-negative bacilli||245||36||39 1||321 (26.40)|
|Pseudomonas spp||173||29||36 1||239(19.65)|
|Proteus spp||6||6 (0.49)|
|Alcaiigens spp||6||6 (0.49)|
|Hoemophllus spp||6||6 (0.49)|
|Acinetobacter spp||6||6 (0.49)|
|E coll||4||4 (0.33)|
|Serratia spp||3||3 (0.25)|
|Total number of isolates(%)||1004(82.57)||130 (10.69)||81 (6.66)||1216(100)|
In the diagnosis of bacterial keratitis, the sensitivity of Gram stain (100%) obtained in this study was higher than that reported by Sharma S, Kuntmoto DY, Goplnathan U, et al. 2002 in early keratitis (36%) and also in advanced keratitis (40.9%). Asbell and Stenson Asbell P, Stenson S.1982 reported 67.0% sensitivity of Gram stain in the detection of bacteria in the US, and Dunlop AA, Wright ED, Howiader SA, et al. 1994 reported 62.0% detection in Bangladesh. The results of this analysis indicate that Gram stain has a vital role in the diagnosis of bacterial keratitis.
Rookaya Mather MD et al: Am J Ophthalmol 2002; 133:463-466 showed the differences in the susceptibility patterns and the potencies of fourth generation FQs (gatifloxacin-GAT and moxifloxacin-MOX) were compared with third generation (levofloxacin-LEV) and second generation FQs (ciprofloxacin-CIP and ofloxacin-OFX). That was an Experimental laboratory investigation. This in-vitro study in testing endophthalmitis isolates suggests that the fourth generation fluoroquinolones are more potent than the second and third generation fluoro-quinolones for gram-positive bacteria and are equally as potent for gram-negative bacteria. Furthermore, the fourth generation fluoroquinolones appear to cover second and third generation fluoroquinolone resistance among Staphylococcal species (Stroman DW et.al. 2001). In conclusion they states that this in vitro study indicated that fourth generation FQs appear to cover bacterial resistance to the second and third generation FQs, were more potent than the second and third generation FQs for gram-positive bacteria, and are equally potent for gram-negative bacteria. Clinical studies will need to confirm these results.
Stephen V. Scoper Virginia Eye Consultants, Norfolk, Virginia, USA in the study of Review of Third and Fourth Generation Fluoroquinolones in Ophthalmology: In- Vivo Efficacy, which was published in Adv Ther. 2008;25(10);979-994 states that the five in-vitro studies demonstrated that moxifloxacin and gatifloxacin are statistically more potent than levofloxacin against Gram-positive organisms and similar in potency in most cases of Gram-negative bacteria. In-vivo animal models testing moxifloxacin or gatifloxacin against levofloxacin 0.5% (no clinical trials testing the efficacy of levofloxacin 0.5% have yet been published) demonstrated that fourth- generation agents were superior to third-generation levofloxacin 0.5% for prophylaxis of Gram-positive bacteria induced infections and were equal to, or better than, levofloxacin 0.5% for the treatment of Gram-negative infections. Fourth-generation agents have increased, potency against Gram-positive bacteria compared with levofloxacin, while maintaining similar potency against Gram-negative bacteria.
Gatifloxacin and Moxifloxacin: An In Vitro Susceptibility Comparison to Levofloxacin, Ciprofloxacin, and Ofloxacin Using Bacterial Keratitis isolates performed by Kowalski RP, Dhaliwal DK, Karenchak LM, et al. was published in Am J Ophthalmol 2003; 136: 500-505. They found that for most keratitis isolates, there were no susceptibility differences among the five fluoroquinolones. The fourth-generation fluoroquinolones did, however, demonstrate increased susceptibility for Staphylococcus aureus isolates that were resistant to CIP, LEV and OFX. In general, CIP demonstrated the lowest MICs for gram-negative bacteria. The MICs for fourth-generation fluoroquinolones were statistically lower than the second-generation fluoroquinolones for all gram-positive bacteria tested. Comparing the two fourth-generation fluoroquinolones, MOX demonstrated lower MICs for most gram-positive bacteria, whereas GAT demonstrated lower MICs for most gram-negative bacteria. In conclusion they states that based on in vitro testing, the fourth-generation fluoroquinolones may offer some advantages over those currently available for the treatment of bacterial keratitis. Clinical studies will be required to confirm these results.
Table 2. Median minimum inhibitory concentrations (MICs; µg/mL) of bacterial keratitis isolates to fluoroquinolones.
|Moxifloxacin||Gatifloxacin||Levofloxacin||Potency by rank|
|Staphylococcus aureus FQR||25||1.5||4||16||mox>gat>lev|
|Staphylococcus aureus FQS||25||0.032||0.094||0.19||mox>gat>lev|
|Coag-neg Staphylococcus FQR||10||2.5||3||64||mox=gat>Iev|
|Coag-neg Staphylococcus FQS||10||0.064||0.125||0.19||mox>gat>lev|
|Pseudomonas aeruginosa FQR||12||Resistant to all fluoroquinolones|
|Pseudomonas aeruginosa FQS||25||0.5||0.25||0.38||gat>lev>mox|
Note: analysis ranked, all MICs from lowest to highest and compared the antibiotics by analysis of variance (ANOVA) of the ranks (not the actual MICs) using Duncan’s multiple comparisons at p<0.05 significance. Coag-neg = coagulase-negative; FQR = fluoroquinolone-resistant (ciprofloxacin and ofloxacin); FQS = fluoroquinolone-sensitivc (ciprofloxacin and ofloxacin).
In the study: Activity of newer fluoroquinolones against gram-positive and gram-negative bacteria isolated from ocular infections: An in vitro comparison conducted by Aparna Duggirala, MSc; Joveeta Joseph, MSc; Savitri Sharma, MD; Rishita Nutheti, MSc; Prashant Garg,MD; Taraprasad Das, MS published in Indian J Ophthalmology 2007;55;15-9 They found that for gram-positive isolates, median MICs of fourth generation fluoroquinolones were lower than second generation. The median MIC was lowest for gatifloxacin and moxifloxacin (0.094 µg/ml) in ciprofloxacin-susceptible isolates of gram-positive bacteria. For ciprofloxacin-susceptible gram-negative bacteria, the median MIC of ciprofloxacin (0.19 ug/ml) was significantly lower than ofloxacin, levofloxacin, gatifloxacin and moxifloxacin (1.5, 0,5, 0.5 and 2 µg/ml respectively). Ciprofloxacin-resistant isolates of gram-positive bacteria showed higher MIC of levofloxacin, moxifloxacin and gatifloxacin though they remained susceptible to them. None of the fluoroquinolones were effective against ciprofloxacin-resistant gram-negative bacteria. Overall, for gram-positive bacteria, median MICs of levofloxacin, moxifloxacin and gatifloxacin were below ciprofloxacin, the MIC of gatifloxacin and moxifloxacin was equal for gram- positive bacteria. In conclusions: Levofloxacin, gatifloxacin and moxifloxacin are statistically more effective against gram-positive bacteria, the latter two being equally effective. Ciprofloxacin remains the most effective fluoroquinolone against gram-negative bacteria.
Anatomy & Physiology of Cornea
We obtain more than 80% of our information from the external world by means of visual function. The cornea serves as the gateway into the eye for external images. The cornea is a transparent avascular tissue that is exposed to the external environment. The anterior corneal surface is covered by the tear film, and the posterior surface is bathed directly by the aqueous humor. The transparent cornea is continuous with the opaque sclera and the semi-transparent conjunctiva. The adult human cornea measures 11 to 12mm horizontally and 10 to 11 mm vertically. It is approximately 0.5 mm thick at the center, and its thickness increases gradually towards the periphery, where it is about 0.7 mm thick. The curvature of the corneal surface is not constant, being greatest at the center and smallest at the periphery. The radius of curvature is between 7.5 and 8.0 mm at the central 3mm optical zone of the cornea where the surface is almost spherical. The refractive power of the cornea is 40 to 44 diopters and constitutes about two-thirds of the total refractive power of the eye. The optical properties of the cornea are determined by its transparency, surface smoothness, contour, and refractive index. Corneal transparency is mostly attributable to the arrangement of collagen fibers in the stroma.
The structure of the cornea is relatively simple compared with that of other parts of the body. Cornea is composed of five layers in the microscopic section. They are arranged from before backwards as follows:
The corneal epithelium is composed of nonkeratinized, stratified squamous epithelial cells. The thickness of the corneal epithelium is approximately 50 µm, which is about 10% of the total thickness of the cornea and is constant over the entire corneal surface
An acellular membrane-like zone known as Bowman’s layer, or Bowman’s membrane, is the interface between the corneal epithelium and stroma.
The stroma constitutes the largest portion, more than 90%, of the cornea. Many characteristics of the cornea, including its physical strength, stability of shape, and transparency, are largely attributable to the anatomic and biochemical properties of the stroma.
Descemet’s membrane is the basement membrane of the corneal endothelium. The thickness of this layer is 8 to 10 µm. Descemet’s membrane is composed mostly of collagen type IV and laminin (Fitch J.M. et al: 1990) but also contains fibronectin (Suda T, et al: 1981 & Fujikawa LS, et al: 1981). Descemet’s membrane does not regenerate.
A single layer of corneal endothelial cells covers the posterior surface of Descemet’s membrane in a well-arranged mosaic pattern.
Maintenance of Normal Corneal integrity
Maintenance of corneal structure is crucial for the physiological functions of this tissue in refraction and bio-defense. Corneal epithelial cells renew rapidly and continuously to maintain the layered structure of the epithelium. The centripetal movement of corneal epithelial cells has been well demonstrated as has the fact that only the basal epithelial cells are capable of proliferation. Epithelial migration is the initial step in the resurfacing of epithelial defects (Binder PS et al: 1980).
It performs two major functions. As a component of the body surface, it separates self from the environment and is responsible for protecting the eye from infection and injury. As an optical structure, it provides the majority of the refractive power to the eye and it must remain optically clear and refract light regularly for acute vision.
Bacterial Corneal Ulcer
Infection of the Cornea
Infection of the ocular surface involves four processes: access of the microbe to the ocular surface, attachment of the microbe to the ocular surface, penetration of the microbe through the corneal epithelium, and subsequent growth of the organism.
An ulcer is defined as a local epithelial defect with excavation of tissue. There are several mechanisms that contribute to stromal melting and loss. The production of elastase and alkaline phosphatase by Pseudomonas and hyaluronidase by Staphylococcus aureus are a few such examples. Other mechanisms of stromal loss are common to ulcers resulting from any etiology. First, breakdown of the corneal epithelium is a prerequisite for development of stromal melting and tissue loss. Several papers have documented that healthy corneal epithelium not only prevents stromal degradation and loss, but also is a prerequisite for stromal healing (Smelser G: 1960 & Weimar V: 1960) Second, most ulcers are associated with a marked inflammatory response. Typically, the inflammatory response is characterized by dense neutrophil infiltration, but other leukocytes play significant roles. The contribution of neutrophils to corneal ulceration has been demonstrated in several animal models. Physical blockade of infiltrating leukocytes in models of corneal injury that induce corneal ulceration in control animals prevents ulceration (Kenyon KR et al:1979). Similarly, systemic depletion of neutrophils can prevent corneal ulceration in guinea pigs (Foster CS et al: 1982). A third and final common mechanism of corneal ulceration is enzymatic degradation of extracellular matrix as part of the normal remodeling of tissues and during tissue repair.
The accurate incidence of bacterial keratitis is not known. It is estimated that 30000 cases of microbial keratitis occur in the US annually (Pepose JS 1992). An estimated 10 to 30 individuals per 100000 contact lens wearers develop ulcerative keratitis annually in the US (MacRae S 1991 & Poggio EC 1989). Similar estimates for Great Britain show approximately 1500 annual cases of microbial keratitis from all causes (Dart JKG 1993). Epidemiological information of developing countries is lacking. Bacterial keratitis is a leading cause of corneal blindness in developing nations.
There are four principal groups of bacteria that are most frequently responsible (Jones DB. 1979). Micrococcaceaee (Staphylococcus,Micrococcus), the Streptococcus species, the Pseudomonas species, and the Enterobactcriaceae (Citrobtacter, Klebsiella, Enterobacter, Serratia, Proteus). However, virtually any bacteria can potentially cause keratitis under certain favorable conditions. Differences were reported in isolates from patients with suppurative keratitis from Ghana and southern India, both of which are at similar tropical latitudes (Leck AK, et al.2002).
Perhaps the most important defense barrier for the cornea is an intact epithelial layer. Most corneal infections result from trauma to the corneal epithelium. Alteration of any of the local or systemic defense mechanisms may also predispose the host to corneal infection. Eyelid abnormalities, abnormalities of the preocular tear film, lacrimal drainage obstruction, the inappropriate use of topical antibiotics & use of topical corticosteroids are major risk factors for bacterial keratitis.
The pathogenesis of ocular infectious disease is determined by the intrinsic virulence of the microorganism, the nature of the host response, and the anatomic features of the site of the infection (O’Brien TP et al.1996). The intrinsic virulence of an organism relates to its ability to invade tissue, resist host defense mechanisms, and produce tissue damage (Jones DB et al. 1978). Penetration of exogenous bacteria into the corneal epithelium typically requires a defect in the surface of the squamous epithelial layer. By virtue of specialized enzymes and virulence factors, a few bacteria, such as N. gonorrhoeae, N. meningitidis, C. diphtheriae, Shigella, and Listeria, may directly penetrate corneal epithelium to initiate stromal suppuration.
Certain bacteria exhibit differential adherence to corneal epithelium. The adherence of S. aureus, S. pneumoniae, and P. aeruginosa to ulcerated corneal epithelium is significantly higher than that of other bacteria and may account in part for their frequent isolation (Reichert R 1984).
Bacteria adhere to injured cornea (Hazlett LD, et al.1987), to exposed corneal stroma (Stern GA et al. 1982), or to immature non-wounded cornea (Hazlett LD, et al. 1986). The corneal epithelial receptors for Pseudomonas species are glycoproteins (Hazlett LD, et al. 1992 & Rudner XL, et al. 1992).
In addition to organism factors, host lysosomal enzymes and oxidative substances produced by neutrophils, keratocytcs, and epithelial cells may significantly contribute to the destruction caused by Pseudomonas keratitis (Steuhl KP, et al.1987).
Once corneal infection is established, there are no absolutely specific clinical symptoms to confirm infection or exclusively distinctive biomicroscopic signs to distinguish the responsible organism(s). Because of the rich innervation of the cornea, the most common symptom of inflammatory lesions of the cornea is pain. Movement of the eyelids over ulcerated corneal epithelium intensifies the pain. Keratitis is usually accompanied by a variable decrease in vision, reflex tearing, photophobia, and blepharospasm are common and sometime purulent discharge. The conjunctiva may be variably hyperemic and a nonspecific papillary reaction may vary in intensity, depending on the severity of the keratitis. The preocular tear film in bacterial keratitis can be observed by slit-lamp microscopy to contain inflammatory cells and debris. Ipsilateral lid edema may be variably observed with bacterial keratitis.
The hallmark clinical signs that are distinctive for suspected infectious keratitis include an ulceration of the epithelium with suppurative stromal inflammation that is either focal or diffuse. The presence of diffuse cellular infiltration in the adjacent stroma and an anterior chamber cellular reaction is highly suggestive for infectious keratitis. The anterior chamber reaction may range from mild flare and cells to severe layered hypopyon formation.
The hypopyon in bacterial keratitis is usually sterile when Descemet’s membrane is intact. Certain characteristic clinical features may be suggestive of specific corneal pathogens, although clinical observation alone should not replace laboratory investigation with corneal scrapings for smears and culture (Liesegang TJ 1988, Ogawa GSH ,1994 & Arffa RC).
Gram-positive cocci typically cause localized, round or oval ulcerations with grayish-white stromal infiltrates having distinct borders and minimal surrounding epithelial edema. Staphylococcal keratitis is more frequently encountered in compromised corneas, such as with bullous keratopathy, chronic herpetic keratitis, keratoconjunctivitis sicca, ocular rosacea, or atopic keratoconjunctivitis.
After trauma, S.pneumoniae keratitis may present with a deep, oval, central stromal ulceration having serpiginous edges. There is typically dense stromal abscess formation with radiating folds in descemet’s membrane and moderate accompanying stromal edema.
Gram-negative corneal infection typically follows a rapid-paced inflammatory destructive course or, alternatively, a less commonly encountered, slowly progressive indolent ulceration. P. aeruginosa has the most distinctive clinical course after corneal infection. There is a loss of corneal transparency with adjacent peripheral inflammatory epithelial edema and a “ground-glass” stromal appearance.
Histopathologic analysis of bacterial keratitis discloses distinct stages of progressive infiltration, active ulceration, regression, and healing (Ogawa GSH, et al. 1994). The progressive stage includes adherence and entry of the organism, diffusion of toxins and enzymes, and resultant tissue destruction. In the second stage, active ulceration, the clinical severity varies with the virulence of the organism and toxin production.
The third or regressive stage is characterized by an improvement in the clinical signs and symptoms. The natural host defense mechanisms predominate and humoral and cellular immune defenses combine with antibacterial therapy to retard bacterial replication, promote phagocytosis of the organism and cellular debris, and halt destruction of stromal collagen.
In the regression phase, a distinct demarcation line may appear as the epithelial ulceration and stromal infiltration consolidate and the edges become rounded.
In the final phase or healing stage, the epithelium resurfaces the central area of ulceration and the necrotic stroma is replaced by scar tissue produced by fibroblasts.
Based on the presenting clinical history, antecedent risk factors, predisposing ocular and systemic diseases, and distinctive clinical signs, an index of clinical suspicion for infectious keratitis versus a nonmicrobial process is formulated.
Clearly, laboratory diagnosis of ocular infection by definitive culturing is the gold standard of clinical management. Standard laboratory procedures can usually recover most organisms by stain or culture (Wilhelmus KR, et al 1994). With special clinical circumstances, more selective diagnostic techniques and culture media may be indicated. Stains
The Gram stain is the most widely used standard microbiologic stain and its results have been advocated as a guide to the initiation of treatment of bacterial keratitis. Gram stain classifies bacteria into two major groups based on distinct differences in the cell wall. Gram-positive bacteria retain the gentian violet-iodine complex and appear blue-purple. Gram-negative bacteria lose the gentian violet iodine complex with the decolorization step and appear pink when counterstained with safranin. The Giemsa stain may be useful in distinguishing bacteria from fungi. It uses eosin, methylene blue, and azure dyes. With the Giemsa technique, bacteria appear dark blue. Fungal hyphae absorb the stain and generally appear purple or blue. The Giemsa stain identifies normal and inflammatory cells. In addition to bacteria and fungi, identification of chlamydial inclusion bodies and the cysts and trophozoites of Acanthamoeba species may be facilitated with Giemsa stain.
Culture on standard bacteriologic media remains the gold standard for diagnosis of suspected bacterial keratitis (Wilhelmus KR, et al 1994).
Antimicrobial Susceptibility Testing
Effective antimicrobial therapy embodies the idea of selective toxicity and requires that the antimicrobial agent reach the site of corneal infection in sufficient concentration to inhibit and preferably kill the causative microorganism, while causing minimal to no toxicity to the host (Amsterdam D.1992). Standard disk diffusion or microdilution techniques are the preferred laboratory methods for antimicrobial susceptibility testing of bacterial ocular isolates (National Committee for Clinical Laboratory Standards, 1993, Neuman MA, et al. 1998 & Sahm DF, et al. 1988).
Corneal trauma may result in inoculation of organisms deep into the stroma. With deep suppurative strornal keratitis, a vertical or oblique incision can allow sampling using a sterile needle or minispatula (Wilhelmus KR, et al 1994).
In general, because of the potential rapid destruction of corneal tissue that may accompany bacterial keratitis, if there is a clinical suspicion suggestive of a bacterial pathogen, the patient should be treated appropriately for bacterial keratitis until a definitive diagnosis is established. The objective of therapy in bacterial keratitis is rapidly to eliminate the infective organism, reduce the inflammatory response, prevent structural damage to the cornea, and promote healing of the epithelial surface (Jones DB. 1979).
The large number of active antimicrobial drugs available to the treating clinician offers the patient with bacterial keratitis a greater chance for cure with less drug-related toxicity while providing alternative choices despite the continuing emergence of drug-resistant pathogenic organisms.
After Fleming’s announcement of his discovery of penicillin (Fleming A.1929), 10 years elapsed before it was established as a major chemotherapeutic agent (Chain E,1940 & Abraham EP, et al.1941). Most strains of S. aureus produce beta-lactamase and are resistant. Penicillin-resistant Neisseria strains, especially penicillinase-producing N. gonorrhoeae, were introduced. Thus, penicillin is no longer recommended for empirical therapy.
Like the penicillins, cephalosporins contain a ?-lactam ring that is necessary for antibacterial activity. Cephalosporins are generally well tolerated, with hyper-sensitivity reactions being the most common systemic adverse effects. They are particularly well tolerated with topical ocular application. But all beta-lactam antibiotics are somewhat unstable in solution, which may limit their activity with topical application for bacterial keratitis (Lambert HP, et al.1983).
Vancomycin is a glycopeptide antibiotic with activity against penicillin-resistant staphylococci.
Aminoglycosides are principally active against aerobic and facultative gram-negative bacilli.
Erythromycin has a relatively broad spectrum of activity, especially against most gram-positive and some gram-negative bacteria. .
The most recent class of antibacterial agents to receive FDA approval for the indication of therapy of bacterial keratitis are the fluoroquinolone compounds. The fiuoroquinolones were serendipitously discovered in 1962, during the purification of chloroquine. Nalidixic acid, the first member of the quinolone class. The fluoroquinolones are rapidly bactericidal in action and exert their effects by variably inhibiting the action of bacterial DNA gyrase, an enzyme essential for bacterial DNA synthesis (Smith JT. 1986, Courtright JB,1988 & Hooper DC,1988). The commercially available fluoroquinolones (ciprofloxacin, norfloxacin, ofloxacin, gatifloxacin, and moxifloxacin) for topical ophthalmic use have similar antimicrobial spectra that include most aerobic gram-negative and some gram-positive bacteria. Although there has been evidence for development of resistance to fluoroquinolones based on in vitro susceptibility testing among ocular isolates, until recently there have-been no clinically significant observations of fluoro-quinolone resistance with topical therapy for keratitis. However, clinical cases of bacterial keratitis exhibiting resistance to ciprofloxacin treatment have been reported (Snyder ME, 1992 & Maffett M, 1993). Topical ciprofloxacin (3 mg/mL) and ofloxacin (3 mg/mL) were found to penetrate well into stromal tissue and to be effective in eradicating Pseudomonas organisms compared with controls (O’Brien TP,1988 & Gritz DC,1992). Based on its excellent activity in experimental bactetial ketatitis, topical ciprofloxacin therapy for bacterial keratitis in humans was assessed in an open-label, nonrandomized clinical trial initially (Leibowitz HM, et al.1991). In this noncomparative treatment trial, ciprofloxacin 0.3% topical solution was found to be highly effective in therapy of acute bacterial keratitis and reasonably well tolerated by the ocular surface. Crystalline white ciprofloxacin precipitates were observed in the area of epithelial ulceration in 16% of patients (Leibowitz HM, et al. 1991). Such crystalline drug precipitation occurs with higher frequency in eyes treated with ciprofloxacin than in those treated with norfloxacin of ofloxacin, consistent with differences in fluoroquinolone compound pH solubility profiles (Essepian JP,1995). Comparative pharmacokinetic data suggest that this precipitation may reduce the active concenttation of drug in the stroma at the site of infection (O’Brien TP,1993). Such crystalline deposition has the potential disadvantage of decreasing visualization of the stromal infiltrate immediately deep to the precipitate for clinical monitoring of therapeutic progress. There is evidence that ciprofloxacin precipitation may also prevent or delay reepithelialization of a corneal defect (Kanellopoulos AJ, 1994). The crystalline corneal precipitates of ciprofloxacin usually spontaneously resolve with cessation of therapy.
Expanded-spectrum fluoroquinolones have a greater activity, especially against gram-positive pathogens (Fugimaki K,1988, Fernandas PB,1988 & Gargallo D, Morris M, Coll R, et al.1988). A comparison of the in vitro susceptibility patterns and the MICs of gatifloxacin and moxifloxacin (fourth-generation fluoroquinoloncs) with eiprofloxacin and ofloxacin (second-generation fluoroquinolones) and levofloxacin (third-generation fluoroquinolone) using bacterial keratitis isolates was conducted. The fourth-generation fluoroquinolones did, however, demonstrate increased susceptibility for S. aureus isolates that were resistant to ciprofloxacin, levofloxacin, and ofloxacin. The MICs of 8-methoxy fluoroquinolones were statistically lower than the MICs of second-generation fluoroquinolones for all gram-positive bacteria tested. A study to assess the effectiveness of a fourth-generation fluoroquinolone for prophylaxis against multiple drug-resistant staphylococcal keratitis after lamellar keratectomy in a rabbit model was conducted (Tungsiripat T, et al.2003). The fourth-generation fluoroquinolone, gatifloxacin, is an effective prophylaxis against the development of keratitis after lamellar keratectomy in rabbits with an organism resistant to methicillin, levofloxacin, and ciprofloxacin (Tungsiripat T, et al.2003). In summary, there is considerable experimental and clinical experience with the use of fluoroquinolone solutions for therapy of ocular infections . Their high potency and generally excellent activity against the most frequent gram-positive and gram-negative ocular pathogens, bactericidal mode of action, bioavailability, and biocom-patibility make fluoroquinolones an excellent initial choice for the topical therapy of bacterial keratitis.
Routes of Administration
One of the fundamental principles of pharmacotherapy is to maximize the amount of drug that reaches the site of action so that sufficient concentrations are achieved to cause a beneficial therapeutic effect (O’Brien TP, 1995). Topical application is the mainstay of ocular drug delivery systems and the topical route is the preferred method of application of antibiotics in therapy for bacterial keratitis (Shell JW. 1982, Lesar TS, 1985 & Barza M. 1989). Eye-drops are the most common route of antibiotic delivery to the eye. Other topical preparations, including ointments, gels, and sustained-release vehicles, are used to achieve higher concentrations of antibiotics in the corneal stroma. Fluoroquinolone antibiotics may be effective at their commercial concentrations in therapy for bacterial keratitis given their relatively high potency (O’Brien TP, 1995, Leibowitz HM, et al. 1991 & Hyndiuk RA, et al.1996).
Selection of Antibiotic Therapy
The objective for initial antibiotic selection in therapy for bacterial keratitis is rapid elimination of the corneal pathogen. The selection of an antimicrobial agent or agents with a broad spectrum of activity, including the most likely gram-positive and gram-negative corneal pathogens, is desirable.
The fluoroquinolone class of antibiotics possesses potent bactericidal activity against the broad spectrum of gram-negative aerobic bacteria and many gram-positive bacteria, including penicillinase-producing and methicillin-resistant staphylococci. The fluoroquinolones have been shown in several independent clinical trials to provide as safe and effective therapy for acute bacterial keratitis as combination fortified antibiotic treatment (O’Brien TP, 1995 & Hyndiuk RA, et al.1996).
Because of the rich innervation of the cornea, ulcerative keratitis is frequently accompanied by significant pain. Pain control with acetaminophen or other analgesics topical cycloplegic agents to relieve ciliary spasm, alleviate pain, and prevent the formation of synechiae. Elevated intraocular pressure should be monitored and treated with a topical ?-adrenergic blocker or topical or oral carbonic anhydrase inhibitors as required for control. After eradication of the causative bacteria, patching may be applied to assist re-epetheliazation. Therapeutic soft bandage contact lenses may be a useful adjunct to assist epithelial healing. The precise role and the timing of adjunctive topical corticosteroid use in the therapy of bacterial keratitis are controversial. Cryotherapy may be useful in selected cases of focal peripheral corneal ulcerations or in Pseudomonas sclerokeratitis (Codere F, 1981 & Eiferman RA.1979). The application of tissue adhesive (isobtityl cyanoacry-late or orher analogs) has been recommended in progressive stromal keratolysis, thinned dcscemetoceles, or small, perforated infectious ulcerations. Excimer laser photoablative treatment of microbial keratitis has been investigated in experimental animal models (Gottsch JD,1991 & Serdarevic O, et al.1985). If there is a large perforation or a residual necrotic cornea, a therapeutic penetrating keratoplasty may be indicated (Kirkness CM, 1991).
MATERIALS AND METHODS:
8.1 Research Approach
This prospective study was carried out on 112 patients attended at eye out patient department of Mymensingh Medical College Hospital, Mymensingh & BNSB, Mymensingh. All informations were collected in a predesigned structured data collection sheets. Finally we evaluated only 100 patients and they were considered as study sample.
8.2 Study design
A prospective study.
8.3 Study population:
Patients with clinically diagnosed bacterial corneal ulcer, age between two years to seventy years and irrespective of sex were selected as study population.
8.4 Place of study
Department of Ophthalmology, Mymensingh Medical College Hospital, Mymensingh & BNSB, Mymensingh .
8.5 Period of study
The study was carried out from 1st July 2008 to 31st December 2009, a period of one year & 6 months.
8.6 Sample size
A total number of 100 patients who were clinically diagnosed as bacterial corneal ulcer were included in this study.
Sample size determination:
The sample size was determined by following formula
Sample size n = z2 pq/r2
Here z = 1.96 for 95% confidence level
p = prevalence rate.
q = 1 – p
r = error limit.
As we did not find any prevalence rate of bacterial corneal ulcer in Bangladesh
We may consider
P = 50% = 0.5
q = 1-p = 1-.5 =.5
r = error limit
If we take error limit as 10% of prevalence rate then
r = .05
So sample number
N = (1.96)2 ×0.5 ×0.5/ (0.05)2
So required sample number is 384. But for time limitation, logistic support and availability of the patient the effective number of sample was reduced to 100.
8.7 Sampling method
8.8 Ethical consideration:
Prior to the commencement of this study, the research protocol was approved by the thesis committee (Local Ethical committee). Objectives of the study along with its procedure, alternative treatment methods, risks and benefits of this study were explained to the patients in easily understandable local language and then informed written consent was taken from each patient/guardian. It was assured that all informed and records would be kept confidential and the procedure was helpful for both the physicians and the patients in making better case management.
8.9 Sample source
Sample was taken from the patients attended at eye out patient department of Mymensingh Medical College Hospital, Mymensingh & BNSB, Mymensingh with clinical diagnosis of corneal ulcer .
8.10 Grouping of patients:
Group A: 50 Patients treated with topical gatifloxacin 0.3% eye drops.
Group B: 50 Patients treated with topical ciprofloxacin 0.3% eye drops.
8.11 Inclusion criteria:
ü Clinically diagnosed an acute bacterial corneal ulcer of at least 1mm in size.
8.12 Exclusion criteria:
Ø Bilateral corneal ulcer or one eyed patient.
Ø Presence of fungi on direct microscopy.
Ø Presence of uncontrolled systemic disease, pregnant or lactating women.
Ø A history of hypersensitivity to fluoroquinolones and related compounds.
After taking consent of the patients following informations were recorded in a data base chart:
· History and clinical examination including general, systemic and ophthalmological examination.
· Clinical and laboratory investigations.
Name, age, sex, address, chief complaints, predisposing factors, history of past illness, treatment and drug history.
Ocular examination were carried out by using – Snellen’s chart, E. chart, Torchlight,
slit lamp biomicroscope, ophthalmoscope etc.
Following points were noted:
Visual acuity – Unaided, with pinhole and with lens.
Ocular adenaxae particularly eyelids, eyelashes, lacrimal sac regions.
Careful measurement and documentation of objective parameters of corneal ulcer.*
Lens and vitreous condition.