Action Mechanism of action

Indications Cons Pros/activity

Penicillin and cephalosporins

Cell wall When penicillin and PBP react, the B lactamase ring opens irreversibly and penicillin covalently binds to active site PBP inhibiting enzymic activity involved in peptidoglycan cross linking formation. This weakens structural integrity and makes cell more susceptible to autolytic enzymes.

Broad spectrum antibiotic used systemically

Penicillin V- Common oral antibioticOther examples: ampicillin, amoxicillin, pipericillin (p.a), fluclox-acillin (resistant ring)

Not absorbed through ocular barriers

High incidence of allergic reactions.

Type 1 and type 4 hypersensitivity reactions in penicillin and 1st gen cephalosporins: uticaria, angiodema, SJS

Side effects: nausea, diarrhoea

Adverse effects: neurotoxicity, vit k deficiency, bleeding (Cephalosporins C/I haemophiliacs)

B lactamase ring target for bacterial resistance – B lactamases

Broad spectrum+Ve and –Ve

Bacitracin Cell wall Prevents the movement of the precursor of peptidoglycan from moving to cell wall – inhibiting cell wall synthesis

Topical skin ointments

Nephrotoxicity +Ve and N.Gonorrheae

Bacteria have low resistance

Vacomycin Cell wall Binds to mucopeptide precursor of peptidoglycan preventing synthesis of cell wall

Ototoxic- can cause deafness

Bacteria have lowResistanceMRSA

+Ve

Polymixin B Cell membranepermeability

Detergent- disrupts phospoholipid membrane- Makes cell leaky

Topical use only

Maxitrol- dexamethasone

Used prophylactically when cornea and conjuc. Compromised

Neuro/nephrotoxic -Ve: P.aeruginosa

Gramicidin Cell membrane permeability

Detergent Sufradex

prophylactically

+Ve (except bacilli) and –Ve

Aminoglycosides Protein synthesis

Binds irreversibly to 30s subunit of ribosomes causes kink in mRNA causes misreading of mRNA

Gentamicin, Tobramycin, Neomycin(combination with steroid)

Resistance- mutations in ribosomal binding site, enzymic modification,

+ve and –Ve including p.a (except neomycin)

preventing the production of functional proteins

decrease uptake into the cell

Not active against MRSA

Otoxicity, nephrotoxicity (not normally topical)

Hypersensitivitycommon

Tetracycline Protein synthesis

Physically blocks tRNA from attaching to mRNA-ribsome complex

Resistance: efflux out of cell, mutations of 30s subunit, decreased penetration through cell wall

Chelates calcium- affect teeth and bone growth (rare with topical use)

Active against +ve and –ve (no p.a)

-chlamydiae

Chloramphenicol

P MED

Protein synthesis Binds to 50s subunit inhibiting peptide bond formation between aa on tRNA molecules

Broad spec Resistance:plasma encoded transferase

Avoid if family history of blood disorders; can cause aplastic anemia leading to angranulocytosis (rare with topical use)

Active against +ve and –ve (no p.a)

-chlamydiae

Macrolides Protein synthesis Binds to 50s subunit reversibly preventing movement of ribosome along mRNA-preventing translation of mRNA

Azyter- only ocular prep-single use

Resistance: Esterases breakdown anitobiotic, active efflux, mutation of binding site via methylation

+ve and some –ve

Fusidic acid

Level 1

Protein synthesis Binds to EF-G preventing aa linking

Fucithalmic -1% viscous drops(BKC and EDTA)

Broad spec

Resistance:alterations to EF-G gene

+ve and –ve

Fluoroquinolones DNA Bind to alpha subunit of DNA gyrases prevent supercoiling of DNA

Ofloaxin- 0.3% multidose +BKCLevofloxin- 0.5% single dose and multidoseCiprofloxin (white reversible deposits)

Resistance:Altered alpha subunit of DNA gene, alter porins decrease uptake

+ve and –Ve

Systemic and local side effects-rare hypersensivity, well tolerated/comfortable

Propamide and dibromopropamide

Interferes with building blocks of DNA

Inhibits uptake of purine nucleotides prevents DNA,RNA, protein synthesis

Broad specAvailable OTCBrolene eyedrops

Not as effective and chloramphenicol

Resistance:alter permease transport

+ve and –ve

Systemic and local side effects

Level 1 system -rare hypersensivity, well tolerated/comfortable

Sulph-on-amidies Metabolism Compete with PABA preventing synthesis of folic acid

Resistance: cell wall permeability

Systemic: SJSLocal: rare hypersensitivity reactions

-ve and +ve

Trimethoprim Metabolism Inhibits dihydrofolate reductase involved in synthesis of folic acid

Not for ocular use

Minimal side effects

Resistance: altered affinity to dihydrofolate reductase

1st line

chloramphenicol

2nd line

Fusidic acid

3rd line (GP; SP, IP)

Ofloxacin; ciprofloxacin; gentomicin

4th line (Ophthamologist only)

Cefuroxime ophthalmic solution (fridge required)