Bacteriology & Antibiotics

Pharmacology of antibiotics

The term antibiotic is now generally used to include antimicrobial substances produced by chemical means as well as those produced by micro-organisms. They may be either bacteriostatic or bacteriocidal. A bacteriostatic antibiotic inhibits the growth and replication of bacteria thereby giving the body's natural defence mechanisms time to become effective in overcoming an infection. In the majority of cases, and particularly in patients whose natural resistance is lowered by disorders of the immune system, it is preferable to choose a bacteriocidal agent. The first bacteriocidal antibiotic was penicillin G. Knowledge of how the body handles a drug, in particular an understanding of absorption, distribution and excretion, helps to provide rational dose regimes which give therapeutic concentrations but keep adverse reactions to a minimum. The two important features of the structure of penicillin are the (3-lactam ring and the side-chain. Alterations in the side-chain give rise to differences in resistance to gastric acid and variation in antibacterial spectrum. In general, increasing the length of the side-chain increases resistance to gastric acid and increases the antibacterial spectrum.