OPHTHALMIC ANTIMICROBIALS

Alison Clode, DVM, DACVO

Port City Veterinary Referral Hospital Portsmouth, New Hampshire

New England Equine Medical and Surgical Center Dover, New Hampshire Overview

• Interpretation of efficacy

• Mechanisms of resistance

• Antibacterial agents • Mechanism of action • Applications in ophtho

• Antifungal agents • Mechanism of action • Applications in ophtho Interpretation of Efficacy – in vitro

1. MIC = minimum inhibitory concentration • Lowest concentration of that inhibits growth of a specific organism

2. MBC = minimum bactericidal concentration • Lowest concentration of an antibiotic at which bacteria are killed

3. Breakpoint • Antibiotic concentration dividing susceptible and resistant • MIC < breakpoint à S • MIC ≥ breakpoint à I, R

Interpretation of Efficacy – in vivo

4. PK/PD = (what the body does to the drug) pharmacodynamics (what the drug does to the body)

5. Susceptible = bacteria inhibited by usually achievable concentrations of antibiotic when recommended dose used for particular site of infection

6. Intermediate = bacteria inhibited in sites were antibiotic is physiologically concentrated or when higher-than-normal dosage can be used

7. Resistant = bacteria not inhibited by usually achievable concentrations of antibiotic with normal dosing schedules or when microbial resistance mechanisms are likely Interpretation of Efficacy

• Indices utilized: • T > MIC = % time plasma concentration is above MIC • Cmax/MIC = max plasma concentration relative to MIC • AUC/MIC = plasma concentration time curve (duration of drug exposure) relative to MIC

• Determined by various animal models

www.rxkinetics.com Time- versus Concentration-Dependent

www.slideshare.net Mechanisms of Resistance

• Intrinsic to the bacteria

• Acquired by the bacteria Acquired Mechanisms of Resistance

1. Modification of the antibiotic

2. Preventing antibiotic from reaching target

3. Modification of the target Acquired Mechanisms of Resistance

1. Modification of the antibiotic

• Enzyme-induced damage to antibiotic à inactive antibiotic

• Enzyme-induced acetylation, adenylation, phosphorylation of antibiotic à alter affinity of antibiotic for target

Acquired Mechanisms of Resistance

2. Prevent antibiotic from reaching target

• Preventing intracellular drug accumulation

• Alteration of porin channels à reduced drug entry

• Production of active efflux pumps à reduced drug retention Acquired Mechanisms of Resistance

3. Modification of target by altering:

• Binding proteins • Ribosomes • Chromosomes • Cell physiology Acquired Mechanisms of Resistance

• Vertical gene transfer = transfer of R-conferring gene to progeny

• Horizontal gene transfer = sharing of R-conferring DNA among bacteria • Same or different strains

• Transformation = DNA uptake from environment • Transduction = DNA transfer by viruses • Conjugation = plasmid exchange via cell-to-cell contact Antibacterial Agents Antibacterial Agents

• Mechanisms of action = disruption of:

1. Cell wall synthesis 2. Cell membrane integrity 3. Protein synthesis 4. Folate metabolism 5. DNA synthesis Bacterial Cell Wall

• Main component = peptidoglycan • PS + peptide crosslinks • Formed by transpeptidases (penicillin binding proteins)

• Gram positive: • Thick cell wall with greater peptidoglycan content and teichoic acid • Cytoplasmic membrane

Bacterial Cell Wall

• Main component = peptidoglycan • PS + peptide crosslinks • Formed by transpeptidases (penicillin binding proteins)

• Gram negative: • Outer membrane of LPS and phospholipids • Thinner cell wall with lesser peptidoglycan content • Cytoplasmic membrane 1. Cell Wall Synthesis Inhibitors

• Penicillins

•

• Bacitracin

• Glycopeptides Penicillins – Structure and function

thiazolidine ring • Side chain: • Spectrum side chain • Susceptibility to destruction • Pharmacokinetic properties

• β-lactam: • Function • Bind transpeptidase à inhibit formation of peptide linkages between polysaccharides à inhibit formation of peptidoglycan β-lactam Penicillins – Resistance

1. β-lactamase production • à hydrolysis of β-lactam ring

• Occurs extracellularly in G+ • Occurs between cell membrane and wall in G-

• Induced by drug binding to bacterial cell wall or • Constitutively produced by bacteria

www.wiley.com Penicillins – Resistance

2. Alter transpeptidases • Penicillins unable to bind to and inactivate transpeptidase

• ‘MRSA’

www.wiley.com Penicillins – Classes

• Effective versus G+

• Resistant to penicillinase

• Extended spectrum

• Anti-pseudomonal Penicillins

Effective versus G+

Penicillin G (parenteral) Penicillin V

1. Highly susceptible to β-lactamases à poor activity versus Staph aureus and Staph epidermidis

2. Ineffective versus altered transpeptidases à poor activity versus , viridans streptococci

Penicillins

Resistant to penicillinases

Methicillin Oxacillin Cloxacillin Dicloxacillin Nafcillin

1. Structural modifications à increased efficacy versus β- lactamase-producing Staph aureus, Staph epidermidis

2. Resistance now due to altered transpeptidases

Penicillins

Extended spectrum Ampicillin (+/- sulbactam)

Amoxicillin (+/- clavulanate)

1. Penicillins inactivated by β-lactamases when not in combo

2. Irreversible inactivation of β-lactamases by sulbactam and clavulanate

3. Ineffective versus altered transpeptidases

Penicillins

Anti-pseudomonal activity

Carbenicillin Ticarcillin (+/- clavulanate) Piperacillin (+/- tazobactam) Mezlocillin

Also effective versus Proteus and Enterobacter Cephalosporins – Structure and Function

dihydrothiazine ring • Side chains: side chain • Spectrum/classification • Susceptibility to destruction • Pharmacokinetic properties

• β-lactam: • Function • Bind transpeptidase à inhibit formation of peptide linkages between polysaccharides à inhibition of peptidoglycan formation β-lactam side chain Cephalosporins – Resistance

1. Destruction by β-lactamases

• Cephalosporins less susceptible than penicillins • S. aureus produces penicillinases • G- bacteria produce β-lactamases • Extended spectrum β-lactamases (E. coli, Pseudomonas, etc.)

* Zapun A, et al., FEMS Microbiol Rev 2008 Cephalosporins – Resistance

2. Alteration of transpeptidases • Cephalosporins unable to bind to and inactivate enzyme • Less common for cephalosporins than for penicillins • ‘MRSA’

* Zapun A, et al., FEMS Microbiol Rev 2008 Cephalosporins

First generation Second Third generation Fourth generation generation Drugs Cephalexin Ceftazidime Cefepime Cefazolin Cefoxitin Cefotaxime Cefadroxil Cefaclor Ceftriaxone Cephradine Cefprozil Cefixime Cefotetan Cefdinir

Other Good G+ activity Good G+ activity Modest G+ Good G+ activity activity Modest G- activity Improved G- Good G- activity activity Improved enteric Increasing G- activity resistance of Streptococcus Ceftazidime has pneumoniae to excellent activity cefazolin versus

Penicillins and Cephalosporins in Ophtho

• No commercially available topical ophthalmic preparations

• Systemic administration: • Orbital disease • Adnexal disease • Limited use in ocular surface disease • Staph and Strep resistance (penicillins) • Strep resistance (cephalosporins) • Limited use in endophthalmitis Bacitracin

• Interrupts transporter molecule à inhibits movement of peptidoglycan precursor from cytoplasm to cell wall

• G+ • Staphylococcus •

• Administered topically (ointment) • Nephrotoxicity • May be administered IM in very few approved situations • Poor transcorneal penetration • “Allergen of the Year” 2003

www.ccbcmd.edu Glycopeptides

• Bind D-Ala-D-Ala terminal portion of peptidoglycan precursor à peptidoglycan precursor unavailable for cell wall formation à decreased cell wall growth + decreased cell wall rigidity

vancomycin Glycopeptides

• Strong activity vs G+ • Drug of choice for MRSA, penicillin- resistant Strep pneumoniae

• Most G- are resistant

• Vancomycin • Teicoplanin

vancomycin Glycopeptides – Resistance

1. Alterations of the antibiotic target

• VanA resistance: • Reduced affinity via alteration of terminal amino acid residues of peptidoglycan precursor (D-Ala-D-Ala à D-Ala-D-Lac)

• VanC resistance: • Steric hindrance caused by substitution (D-Ala-D-Ala à D-Ala-D- Ser)

Glycopeptides – Resistance

2. Altered antibiotic penetration

• Inability to penetrate bacterial membrane (G- organisms)

• Intrinsic resistance Glycopeptides – Resistance Glycopeptides – Resistance

Enterococcal spp that are resistant to vancomycin but require vancomycin presence to grow have been isolated…

Vancomycin presence induces resistance mechanisms….

This is VERY BAD… Vancomycin – Ocular Application

• Reaches therapeutic AH levels when applied topically (50 mg/ml)

• Effective versus corneal infections with MRSA and MRSE

• Associated with cystoid macular edema when used intracamerally during cataract surgery

• Non-toxic to the retina at 1 mg dose • in combination with amikacin or ceftazadime for endophthalmitis

* Alster Y, et al., BJO 2000 ** Sotozono C, et al., Cornea 2002 *** Penha FM, et al., Ophthalmic Res 2010 Teicoplanin – Ocular Application

• Alternative therapy for MRSA infections • No vitreal penetration when administered topically • Poor vitreal penetration when administered IV 2. Cell Membrane Disruptors

• Polymyxin B

• Gramicidin

• Similarities between bacterial and human cell membranes limit use Polymyxin B

• Detergent/surfactant • Disrupts cell membrane phospholipids à increased permeability à cell death • Positively charged drug binds negatively charged LPS layer • Binds to and inactivates endotoxin

• G- activity good • Effective versus Pseudomonas • Not effective versus Proteus • G+ activity poor • Thick cell membrane • Absence of LPS

• Neurotoxic, nephrotoxic Gramicidin

• Functions as membrane channel • Alters permeability • Selective movement of monovalent cations and water

• Stable in solution • Predominantly G+ activity

• Hemolysis when administered systemically, therefore topical administration only

www.physics.usyd.edu.au 3. Protein Synthesis Disruptors

• Aminoglycosides

• Tetracyclines

•

• Chloramphenicol

• Oxazolidinones Protein Synthesis – Short Version

• Translation = mRNA à protein • Ribosomes • 50S subunit + 30S subunit = 70S prokaryotic ribosome • 40S subunit + 60S subunit = 80S eukaryotic ribosome

• Peptidyl transferase • Enzymatic function of ribosome to create peptide bonds between adjacent amino acids

www.wikipedia.com Protein Synthesis Disruptors

Target = 30S

Amino- Tetracyclines glycosides Protein Synthesis Disruptors

Target = 30S

Amino- Tetracyclines glycosides

• G- aerobes (Pseudomonas, Proteus, Klebsiella, E. coli, Enterobacter) • Some Staphylococcus spp. • Neomycin generally not effective versus Pseudomonas Aminoglycosides – MOA

• Positively charged • Bind negatively-charged LPS of G- outer membrane • Bind negatively-charged rRNA

• Hydrophilic • Poor lipid membrane penetration

• Different AG have variable specificity for different regions, leading to different spectrum of activity Aminoglycosides – MOA

1. Bind outer membrane (electrostatic) 2. Diffuse into periplasmic space 3. Transport into cytoplasm (oxygen-dependent) 4. Bind 16s rRNA of 30S subunit (energy-dependent) 5. mRNA misreading à missense, premature stop codons

• Also bind to and disrupt cell membrane Aminoglycosides – Resistance

1. Alteration of AG à decreased affinity for ribosome

• AME (aminoglycoside modifying enzymes) • Mutational pressure induced by exposure of bacteria to AG à resistance genes within normal bacterial enzymes à modification of AG • Transferred by plasmids or transposons • Methylation of binding site on AG à decreased binding to ribosome à decreased function of AG

• Most common resistance method • Results in high-level resistance • Resistance not predictable among different AG due enzyme variability

* Shakil S, et al., J Biomed Sci 2008 Aminoglycosides – Resistance

2. Reduced intracellular drug concentration • Bacterial efflux pumps • Energy-dependent • Constitutively expressed à low-level, intrinsic resistance • Substrate-induced or mutation-induced overexpression à increased resistance

• Altered outer membrane permeability • Decreased inner membrane transport • Drug trapping

* Shakil S, et al., J Biomed Sci 2008 Aminoglycosides – Resistance

3. Enzyme-induced alteration of ribosome

• Normal bacterial enzymes

• Alter shape of ribosome à alter contact of AG with ribosome à decreased function of AG

* Shakil S, et al., J Biomed Sci 2008 AGs – Toxicity

• Positive charge increases toxicity • Nephrotoxicity • Concentration in proximal tubule epithelial cells à disrupt tubule fxn à cation-wasting in • Ototoxicity • Localization in hair cells à cell death • Localize in the cochlea, spiral ganglion neurons, organ of Corti • Neuromuscular blockade

• Affinity for rRNA of prokaryotes is only ~10X greater than for eukaryotes Aminoglycosides in Ophthalmology

• Topical: • Neomycin – not considered effective versus Pseudomonas • Gentamicin • Tobramycin • Combination with β-lactam for improved G+ spectrum – must be applied separately! • As a class, noted to have deleterious effects on corneal wound healing • Delayed reepithelialization, punctate epithelial erosions, corneal ulceration, chemosis

• Intravitreal: • Amikacin – less toxic than gentamicin, may be used in combination with vancomycin (G+ spectrum) for endophthalmitis Protein Synthesis Disruptors

Target = 30S

Amino- Tetracyclines glycosides

Rickettsia spp Borrelia spp Chlamydophila spp Mycoplasma spp Moraxella spp Brucella spp Some Staphylococcus and Streptococcus spp. Generally not effective versus Pseudomonas Tetracyclines – Mechanism

1. Enter bacterial cell • Outer membrane porins (G-) à passive diffusion through inner cell membrane • Active transport across cytoplasmic membrane (G+)

2. Inhibit binding of tRNA to mRNA-ribosome complex • 16S subunit of 30S ribosome • Reversible

• Weak binding to eukaryotic ribosomes minimizes toxicity www.antibioticsinfo.org

Tetracyclines – Resistance

Acquisition of tet genes by bacteria

Speer et al., Clin Microbiol Rev, 1992 Tetracyclines – Resistance

1. Efflux pumps

2. Ribosomal protection proteins • Block binding of TCN to ribosome • Bind to and distort ribosome to still allow t-RNA binding • Bind to ribosome and dislodge TCN

3. Enzymatic inactivation (rare) • Addition of acetyl group to drug

Thaker M, et al., Cell Mol Life Sci 2010 D’Costa VM, et al., Science, 2006 Tetracyclines

Short acting Intermediate acting Long acting (t½ 6-8 hours) (t½ 12 hours) (t½ 16 hours) Tetracycline Demeclocycline Doxycycline (1st gen) (2nd gen)

Oxytetracycline Minocycline (1st gen) (2nd gen)

Bonus Properties of TCNs

• Anticollagenase activity • Inhibit MMPs • Bind zinc and calcium ions within enzyme catalytic domain • Likely irreversible • May (or may not) modulate MMP expression

• Inhibit IL-1 synthesis

• Inhibit activated B cell function

• Inhibit NO synthesis via LPS activation

Golub LM, et al., J Dent Res 1987 Smith VA, et al., Br J Ophthalmol 2004 Solomon A, et al., Invest Ophthalmol Vis Sci 2000 Kuzin II, et al., Int Immunol 2001 D’Agostino P, et al., Eur J Pharmacol 1998 Tetracyclines in Ophthalmology

Federici, Pharmacological Research, 2011 Protein Synthesis Disruptors

Target = 50S

Macrolides CHPC Oxazolidinones Protein Synthesis Disruptors

Target = 50S

Macrolides CHPC Oxazolidinones

G+ cocci Erythromycin Chlamydophila spp, Mycoplasma spp, Borrelia spp Clindamycin Increased G- spectrum (azithromycin) Azithromycin Etc.. Enterococci resistant Streptococcus spp developing resistance Macrolides – Mechanisms

1. Prevent formation of peptide bond between adjacent amino acids 2. Premature dissociation of peptidyl-tRNA complex from ribosome 3. Inhibit ribosomal translocation 4. May also affect ribosome assembly

• binding to 50S ribosome is reversible

• Accumulate within leukocytes

faculty.ccbcmd.edu Macrolides – Resistance

• Resistance: • Acquired ribosomal alterations

• Drug-inactivating enzymes (rare)

• Efflux pumps (rare) Protein Synthesis Disruptors

Target = 50S

Macrolides CHPC Oxazolidinones

G+ G- Rickettsia spp, Chlamydophila spp, Mycoplasma spp Spirochetes

Pseudomonas spp are resistant Chloramphenicol – Mechanism

1. High lipid solubility à diffusion across cell membrane 2. Inhibition of peptidyl transferase à inhibition of protein elongation Chloramphenicol – Resistance

1. Reduced membrane permeability • Low-level resistance • Most common

2. Enzymatic inactivation • High-level resistance • Prevents binding to ribosome

3. Mutation of 50S ribosomal subunit • Rare Chloramphenicol – Side Effects

• Dose-related bone marrow suppression • Due to inhibition of mitochondrial synthesis • Reversible with discontinuation • Does not predict development of aplastic anemia

• Idiosyncratic aplastic anemia • Not dose-related • Weeks to months after discontinuation of therapy • Irreversible Dose-Related Bone Marrow Suppression

• Inhibition of mitochondrial protein synthesis à mild BM hypocellularity, anemia, neutropenia, thrombocytopenia

• 0.5% ophthalmic solution • Four times daily x 7 days à total dose < 19 mg • Four times daily x 14 days à total dose < 33 mg • No measurable serum levels in either group (< 1 mg)

• Estimated total dosage for toxicity = 30 mg • Estimated total exposure duration for toxicity = 18 days

Walker et al., Eye, 1998 Aplastic Anemia

intestinal bacteria systemic absorption CHPC dehydro-CHPC

DNA damage in bone marrow cells nitroso-derivatives of CHPC 20X increased cytotoxicity Aplastic Anemia

intestinal bacteria systemic absorption CHPC dehydro-CHPC

DNA damage in bone marrow cells nitroso-derivatives of CHPC 20X increased cytotoxicity

Genetic susceptibility? 1. Increased ability to form nitroso-derivatives 2. Increased sensitivity of bone marrow cell DNA 3. Decreased ability to bone marrow cell DNA to repair itself Aplastic Anemia

Lam et al, Hong Kong Med J, 2002 Aplastic Anemia

Possible association between ocular CHPC and aplastic anemia – the absolute risk is very low (Br J Clin Pharmacol 1998)

145 patients with aplastic anemia 1226 age- and sex-matched controls 3 affected and 5 controls used ocular CHPC preparation Aplastic Anemia

Possible association between ocular CHPC and aplastic anemia – the absolute risk is very low (Br J Clin Pharmacol 1998)

145 patients with aplastic anemia 1226 age- and sex-matched controls 3 affected and 5 controls used ocular CHPC preparation

BMJ, 1998

426 patients with aplastic anemia 3118 age- and sex-matched controls 0 affected and 7 controls used CHPC eye drops Aplastic Anemia

Possible association between ocular CHPC and aplastic anemia – the absolute risk is very low (Br J Clin Pharmacol 1998)

145 patients with aplastic anemia 1226 age- and sex-matched controls 3 affected and 5 controls used ocular CHPC preparation Relative risk = < 1: 1,000,000

BMJ, 1998

426 patients with aplastic anemia 3118 age- and sex-matched controls 0 affected and 7 controls used CHPC eye drops Protein Synthesis Disruptors

Target = 50S

Macrolides CHPC Oxazolidinones

Predominantly G+ aerobes and anaerobes Including methicillin- and vancomycin-resistant strains Some G- activity (anaerobes) Poor activity versus G- aerobes Oxazolidinones – MOA

• Bind 23S subunit of 50S ribosome à non-functional initiation complex portion of 70S ribosome

• Inhibits translocation

• May also decrease bacterial virulence factors and increase phagocytosis at sub-MIC concentrations

Oxazolidinones – Resistance

• Alteration of target ribosomal binding site

• Development low due to: • Synthetic nature of compounds • Unique method of inhibiting bacterial protein synthesis • Multiple genes encode binding site to 23S ribosomal subunit • Difficult to select for linezolid-resistant strains in vitro

• Risk factors for development of resistance: • Lengthy or repeated course of therapy • Use in presence of foreign bodies

• Reversal of resistance has been reported following discontinuation of antibiotic Oxazolidinones – Toxicity

• GI suppression • Reversible thrombocytopenia and anemia • Neuropathy Oxazolidinones in Ophthalmology

• Topical administration • 0.2% penetrates into rabbit anterior segment • 0.2% successfully treated humans with vancomycin-resistant or vancomycin-intolerant bacterial

• Intravitreal administration • Effective in experimental model of S. aureus endophthalmitis in rabbits (30 mg once) • No retinal toxicity

• Oral administration • Achieves levels >MIC for common organisms in human AH and VH following single oral dose Saleh et al., JCRS 2010 Tu et al., AJO 2013 Saleh et al., IOVS 2012 George et al., JOPT 2010

4. Folate Metabolism Disruptors

• Sulfonamides

•

• Pyrimethamine Folate Metabolism Disruptors

• Folate • Necessary for DNA and RNA synthesis and maintenance • Mammals acquire folate (or folic acid) in food • Bacteria must synthesize folate

• MOA = enzyme inhibition • Dihydropteroate synthetase • Sulfonamides • Dihydrofolate reductase • Trimethoprim • Pyrimethamine (primarily antiprotozoal) Folate Metabolism Disruptors

• Resistance: 1. Overproduction of PABA by bacteria 2. Decreased enzyme affinity for drug 3. Decreased bacterial permeability of drug 4. Increased inactivation of drug by bacteria

• If resistant to one , resistant to all Sulfonamide Toxicity – KCS

• Direct toxic effect on lacrimal acinar cells • N-containing pyridine and pyrimidine rings • Dose-dependent or idiosyncratic

• 15-25% incidence in dogs treated with sulfas • May develop months to years after discontinuation • May be reversible upon discontinuation

• Other systemic toxicity signs variable (i.e., hepatotoxicity) Barnett K, et al., Human Toxicol 1987 Trepanier L. J Vet Pharm Therapeutics 2004 Trepanier L, et al. J Vet Intern Med 2003 5. DNA Synthesis Disruptors

• Fluoroquinolones

DNA Synthesis – Very Short Version

• II (DNA • Topoisomerase IV gyrase) • ParC + ParE • gyrA + gyrB

• Unlinks newly formed DNA strands • Relaxes positive supercoils • Relaxes positive supercoils that accumulate ahead of that accumulate ahead of DNA polymerase during DNA polymerase during DNA replication DNA replication

• Bacterial enzyme only • Not present in all bacteria Fluoroquinolones – MOA

1. Enter bacterial cell • Porin- and LPS-mediated (G-) • Lipophilicity (G+)

2. Bind to enzyme à interrupt DNA stabilization à inhibit DNA synthesis • DNA gyrase target for G- • Topoisomerase IV target for G+

• Spectrum depends upon substituents added to core structure

www.pharmainfo.net Fluoroquinolones – Resistance

• Low-level resistance = in vitro determination that may not correlate with clinical failure due to ability to achieve greater local concentrations • Single-step mutants

• High-level resistance = in vitro determination that is more likely to correlate with clinical failure due to inability to achieve appropriate local concentrations • Multi-step mutants • Due to repeated exposure to sub-lethal concentrations of FQN Fluoroquinolones – Resistance

Chromosome-mediated (mutational)

1. Mutations in genes encoding protein targets of FQNs • Mutation in gyrA à low-level resistance • Mutation in parC à moderate-level resistance • Second mutation in gyrA à high-level resistance • Second mutation in parC à highest-level resistance

2. Mutations causing reduced drug accumulation • Decreased uptake • Decreased expression of porins (G-) • Increased efflux • Upregulation of efflux pumps Fluoroquinolones – Resistance

Plasmid-mediated

1. Qnr • Encodes protein that protects from antibiotic • Results in low-level resistance

2. Enzymatic inactivation • Alters antibiotic structure à inactivation of antibiotic • In combination with Qnr à higher-level resistance

3. QepA • Gene encoding for efflux pump Fluoroquinolones – Avoiding Resistance

• Low-level resistance: • Maintain drug concentrations above mutant prevention concentration • Generally several-fold higher than minimum inhibitory concentration

• High-level resistance: • Avoid repeated exposure to low levels of FQN • Avoid intermittent FQN exposure • Avoid tapering FQN

• Newer FQN: • Structural features confer less resistance potential • Structural features increase ocular tissue concentrations • MICs generally lower Fluoroquinolones in Ophthalmology

Generation First Second Third Fourth (quinolone) Drugs

Spectrum G- G- G- G- Some G+ Some G+ G+

Other Weak versus Improved versus Efficacy Pseudomonas Pseudomonas versus MRSA, resistant Increasing Pseudomonas resistance of strains Strep pneumoniae 4th Generation Fluoroquinolones

• Moxifloxacin • Gatifloxacin • Besifloxacin (formulated for ophthalmic use)

• Balanced inhibition of DNA gyrase and topoisomerase IV • Strong Gram+ activity, strong anaerobic activity, retain Gram- activity • Labeled for bacterial • Clinical efficacy in bacterial keratitis, post-operative endophthalmitis, etc. • No difference in tolerability, adverse events

O’Brien, Adv Thera, 2012 Majmudar, Cornea, 2014 Garg Asia Pac J Ophth 2015 Etc… Fluoroquinolones in Vet Ophthalmology

• [Ofloxacin] > [ciprofloxacin] in canine AH • [Moxifloxacin] > [ciprofloxacin] in equine AH • [Moxifloxacin] > [ciprofloxacin] in equine tears, cornea, and AH

• Increased resistance of β-hemolytic Streptococcus to ciprofloxacin in dogs Fluoroquinolones – Side Effects

• Corneal cytotoxicity in vitro • Delayed wound healing in vivo • 1.5% levo > 0.5% moxi > 0.3% gati > 0.5% levo

• Corneal precipitates

• Endothelial damage with intraocular injection • Concentration-dependent Summary

• Important to understand the mechanisms of bacterial resistance • Significantly increasing understanding of these mechanisms via genomics • Appropriate selection of antibiotic in ophthalmology depends upon spectrum of action and toxicities