ANTIBIOTICS

The selection of antibiotic therapy for an infection requires a knowledge of: 1The infecting organism, including the pathogen most likely to be present in given clinical or geographical circumstances 2The local patterns of antimicrobial resistance in common pathogens 3 An understanding of the pharmacokinetics of the antimicrobials selected 4 The physiology of the patient, metabolic upset, renal or hepatic dysfunction, age and available routes of administration. The clinical history should determine the systems of the body most likely to be involved in disease. Figure 6.3 (p. 133) shows common pathogens found in different systems.Figure 6.3p. 133 The Selection of Antibiotic

ENDOGENOUS INFECTIONS-RESERVOIRS OF INFECTIONS IN ADULTS The human body is in contact with many potentially infectious agents: bacteria, viruses, fungi or protozoa. Most are harmless colonisers causing no clinical upset but forming a natural reservoir of potential infection in the human host

Common Infecting Organisms.

Selection of Antibiotics Identification of Infecting organism

Empirical treatment Prior to Identification of Organism 1.The Acutely Ill patient 2. Selecting a Drug

C.Determining the Antimicrobial Susceptibility of the Organism Bacteriostatic vs Bacteriocidal MIC MBC D. Effect of Site of Infection on Therapy: Blood Brain Barrier Lipid solubility of drug Mol wt Protein Binding

E. Patient Factors Immune system Renal dysfunction Hepatic dysfunction Poor perfusion Age Pregnancy Lactation F. Drug Safety G. Cost of therapy

Route of Administration Determination of Rational Dosing 1 Concentration dependent killing 2. Post antibiotic effect

SITES OF MICROBIAL ACTION

Chemotherapeutic Spectra Narrow Extended Broad Combination of Antimicrobials Advantages Disadvantages

DRUG RESISTENCE 1.Genetic alteration Spontaneous mutation DNA transfer of drug resistence 2. Altered expression of proteins in drug resistant organisms Modification of target sites Decreased accumulation Enzyme inactivation

PROPHYLACTIC ANTIBIOTICS Rheumatic heart disease Dental work in pts with valves, prosthesis TB Surgery Pregnant mother - zidovudine

COMPLICATIONS OPF ANTIBIOTIC THERAPY Hypersensitivity Direct toxicity Superinfections

Inhibitors of Cell Wall Synthesis

PENICILLIN

PENICILLIN G

Extended Penicillins ORAL - Amoxycillin IV -Ampicillin Wider range Broken down by penicillinase Combined with penicillinanse (BETA LACTAMASE) inhibitors - Clavulanic acid Sulbactam Tazobactam Augmentin- Amoxy+sulbactam

Anti Staphylococcal Penicillins Oral & Not inactivated by penicillinases ( BETA LACTAMASE )‏ Cloxacillin Dicloxacillin Flucloxacillin

ADVERSE EFFECTS OF PENICILLINS

Stability of penicillins to acid & penicillinases

CEPHALOSPORINS

OTHER BETA LACTAM ANTIBIOTICS- CARBAPENEMS& MONOBACTAMS

OTHER CELL WALL INHIBITORS- VANCOMYCIN SIDE-EFFECTS