Principles of antibiotic therapy

Outline

• Introduction • Pathogens • Danger of overuse • Selection and administration of antibiotics• Methods of administration of antibiotics

Introduction Chemical substances produced by microorganism that has the capacity to inhibit

growth or destroy bacteria

Bactericidal Bacteriostatic

• Inhibits cell wall synthesis• Inhibits protein synthesis• Inhibits nucleic acid synthesis • Inhibits cell membrane synthesis

Bactericidal Bacteriostatic

Penicillins Chloramphenicol

Cephalosporin Erythromycin

Vancomycin Clindamycin

Gentamicin Sulfonamides

Pathogens

Gram positive and Gram negative Aerobic and anaerobic

Gram positive cocci Gram negative rodsPenicillins, cephalosporins and Vancomycin

Aminoglycosides, cephalosporins

Erythromycin, clindamycin ,chloramphenicol and tetracycline

Chloramphenicol and tetracycline

Chloramphenicol

• First line treatment of bacterial conjunctivitis(broad spectrum)

• Bacteriostatic antibiotic which inhibits protein synthesis

• Streptococci, Pneumococci and Corynebacteria

• 0.5% drops and a one percent ointment

Fluoroquinolones • Ciprofloxacin, ofloxacin(2nd generation)• Levofloxacin( 3rd generation)• Moxifloxacin, Gatifloxacin( fourth generation)• Efficacious against Gram positive and Gram

negative bacteria, particularly staphylococci• Low toxicity• Enzymic inhibition of bacterial DNA

production( DNA gyrase)• Deposit of whitish material in the base of corneal

ulcers which can make monitoring of the progress of the disease more difficult.

Penicillins

• Benzylpenicillin,Procaine penicillin, Benzathine penicillin ,Phenoxymethyl penicillin, Cloxacillin,Ampicillin/amoxicillin

• Bactericidal and inhibit cell wall synthesis• Low toxicity

Cephalosporins

• 1st generation: cefazolin, cephalexin( gram positive cocci)

• 2nd generation: cefaclor, cefuroxime sodium( gram positive and negative)

• 3rd generation: cefotaxime sodium, ceftizoxime(gram negative bacilli)

• Bactericidal and Inhibit cell wall synthesis• Allergic reaction, neutropenia and

thrombocytopenia

Aminoglycosides

• Gentamicin(0.3%), Kanamycin, Neomycin(0.3-0.5%), Streptomycin, Tobramycin(1%), amikacin

• Bactericidal and inhibit protein synthesis• Oto-toxicity and nephrotoxicity

Macrolides

• Erythromycin, Clarithromycin, Azithromycin

• Inhibits protein synthesis

Danger of overuse1.Hypersensitivity • Skin eruptions • Painful swollen joints, asthma and

fever• Anaphylactic shock

2. Drug toxicity• Aplastic anemia

3. Bacterial resistance 4. Alteration of normal bacterial flora

Selection and administration of antibiotics

1. Nature of the offending organism and its sensitivity to antibiotic

2. Nature of the disease, seriousness and location

3. General health, sensitivities and allergies of the patient

Methods of administration of antibiotics

• Topical • Subconjunctivally• Intracamerally• Systematically

Topical

• Conjunctivitis• Superficial corneal ulcers

Systematic antibiotics

• Intraocular infections• Infections of the orbit• Severe conjunctivitis• Severe corneal ulcers

Subconjunctival injections

• Severe intraocular infections• Severe corneal ulcers

Intracamerally

• Bacterial endophthalmitis

Summary

• Introduction • Pathogens • Danger of overuse • Selection and administration of antibiotics• Methods of administration of antibiotics

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