Intravitreal Antibiotics
Intravitreal antibiotic is the current standard of care in infectious endophthalmitis of any cause. The vitreous is a transparent gelatinous avascular body rich in collagen and hyaluronic acid; it provides a good culture medium for microorganisms to proli
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Intravitreal Antibiotics Sharat Hegde and Avinash Pathengay
Intravitreal antibiotic is the current standard of care in infectious endophthalmitis of any cause. The vitreous is a transparent gelatinous avascular body rich in collagen and hyaluronic acid; it provides a good culture medium for microorganisms to proliferate. In order to eliminate infection in endophthalmitis, antibiotics must reach the intraocular space and adjacent ocular tissues in adequate levels so as to reach above the minimum inhibitory concentration (MIC). Static and dynamic ocular barriers (blood-ocular barrier) that form a part of natural protective mechanisms of the eye impede the penetration of systemically and topically administered antibiotics. Various factors are responsible for poor penetration of topical and systemic antibiotics: The tear film dilutes topically instilled medicines [1]. Low molecular weight drugs undergo systemic absorption from the conjunctival capillaries, and hence, bioavailability decreases [2]. Tight junctions in corneal epithelium lead to poor paracellular drug penetration especially for ionic drugs [3]. Systemically administered drugs easily gain access to the choroidal extravascular space, but thereafter distribution into the intraocular space via the retinal pigment epithelium (RPE) impedes the further access into the ocular cavity [4]. An intravitreal injection bypasses the blood-retinal barrier as drug is injected directly into the vitreous cavity. Thus, antibiotics delivered through the intravitreal route achieve a higher drug concentration for prolonged periods of time [5].
History of Intravitreal Antibiotics Injection of intravitreal antibiotics dates back to around 1940s when Sallmann et al. injected penicillin in a rabbit eyes with traumatic endophthalmitis [6]. Intravitreal antibiotic era was heralded when Peyman and associates (1970s) conducted S. Hegde, M.S. • A. Pathengay, F.R.C.S. (*) LV Prasad Eye Institute, Vishakhapatnam, India e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2018 T. Das (ed.), Endophthalmitis, https://doi.org/10.1007/978-981-10-5260-6_21
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experimental studies on endophthalmitis-induced rabbits and established the recommended doses of various intravitreal antibiotics [7, 8]. Later, many experimental studies were conducted on small animals and nonhuman primate models to establish the mechanisms of drug clearance and safety doses of intravitreal antibiotics [9]. The class of drug, mechanism of action, and susceptible organisms to the antimicrobials are mentioned in Table 21.1. Table 21.1 Class of drug, mechanism of action, and susceptibility of the commonly used antimicrobials in endophthalmitis Drug Amikacin
Class of drug Aminoglycoside
Amphotericin B
Polyene antibiotics
Ceftazidime
Third-generation cephalosporin
Cefazolin
First-generation cephalosporin
Ciprofloxacin
Fluoroquinolones
Imipenem
Carbapenem
Piperacillin/ tazobactam
Beta-lactam antibiotics
Vancomycin
Glycopeptide
Voriconazole
Triazoles
Mechanism o
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