1. Tetracyclines and Chloramphenicol (broad spectrum antibiotics)

2. Source- Soil actinomycetes Chlortetracycline- introduced in 1948 Divided into three groups: Group I- Tetracycline Chlortetracycline Oxytetracycline Group II- Demeclocycline Methacycline Lymecycline

5. 2. Most gram positive bacilli- Clostridia, Listeria & Corynebacteria are inhibited but not Mycobacteria . 3. Sensitive gram negative bacilli- H.ducreyi,V .cholerae, Yersinia pestis etc. 4. Spirochetes 5. Rickettsiae and Chlamydiae are highly sensitive 6. Entamoeba histolytica and plasmodia - at high concentration

7. Group I Tetracycline(T) Oxytetracycline (oxyT) Group II Demeclocycline (Deme) Group III Doxycycline(Doxy) Minocycline(Mino) Source T- semisynthetic OxyT- S.rimosus S.aureofaciens Doxy- semisynthetic Mino- semisynthetic Potency Low Intermediate High Intestinal absorption T- intermediate OxyT- intermediate intermediate Complete, no interference by food Plasma protein binding OxyT- Low T- intermediate High High Elimination Rapid renal excretion Partial metabolism, Slower renal excretion Doxy- faeces Mino- urine and bile Plasma 6-10 hrs 16-18 hrs 18-24 hrs Dosage 250-500 mg QID or TDS 300-600 mg BD 200 mg initially, 100-200 mg OD

8. Group I Tetracycline(T) Oxytetracycline (oxyT) Group II Demeclocycline (Deme) Group III Doxycycline(Doxy) Minocycline(Mino) Alteration of intestinal flora Marked Moderate Least Incidence of diarrhoea High Intermediate Low Phototoxicity Low Highest Low Specific toxicity OxyT-less tooth discolouration More phototoxic Doxy-low renal toxicity

12. CHLORAMPHENICOL Source- Streptomyces venezuelae in 1947 Mechanism of action- inhibits bacterial protein synthesis By interferring with transfer of elongating peptide chain to the newly attached aminoacyl-tRNA at the ribosome-mRNA complex. It binds to 50S ribosome Probably by acting as peptide analogue, it prevents formation of peptide bonds