Antibacterials
Antibiotics are the substances produced by microorganisms, which suppress the growth of or kill other microorganisms at very low concentrations.
Mechanism of action | Spectrum | Mechanism of resistance | Adverse effects | |
Penicillin | Bactericidal Inhibit TRANSPEPTIDASE so that crosslinking of bacterial cellwall is lost. | Narrow spectrum Gram positive and few gram negative and anaerobic bacteria | Tolerance Penicillinase production | Local irritation Hypersensitivity JARISCH HERSCHEIMER REACTION in syphilis patients Super infection Hemolytic anemia |
Cephalosporin | Bactericidal Inhibit cellwall synthesis | Mixed spectrum I gen: gram positive. II gen: gram negative, few gram positive bacteria III, IV, V gen: gram negative, enterpbacteriaceae, Pseudomonas, weakly gram positive | Increased efflux Impermeability to antibiotics Elaboration of beta lactamase | Pain Diarrhea Nephrotoxicity Neutropenia, thrombocytopenia Disulfiram like reaction |
Tetracycline | Bacteriostatic Binds with 30s ribosomes, inhibits protein synthesis | Broad Spectrum Gram positive, gram negative bacteria Rickettsia Mycoplasma Actinomycetes Spirochetes Protozoans like E. histolytica | Pumping out the tetracyclines Ribosomal protection Enzymatic inactivation | Renal damage Anti anabolic effect Phototoxicity Diabetes insipidus Hepatic damage Fanconi syndrome Vestibular toxicity |
Chloramphenicol | Bacteriostatic Binds with 50s ribosomes, inhibit protein synthesis | Broad spectrum Gram positive, gram negative bacteria Spirochetes Rickettsia Mycoplasma Salmonella etc | Inactivation by Acetyl transferase enzyme | Bone marrow suppression Hypersensitivity Super infection Gray baby syndrome |
Macrolide | Bacteriostatic but at high dose, bactericidal Inhibit protein synthesis | Narrow spectrum Gram positive bacteria | Increased efflux Erythromycin esterase production Ribosomal protection Cross resistance | Motilin receptor agonist - diarrhea Allergy CVS: QT prolongation, ventricular arrhythmia Reversible ototoxicity |
Sulfonamide | Bacteriostatic Competitively inhibit union of PABA with pteridine leading to inhibitioj of folic acid synthesis | Narrow spectrum Strep. pyogenes H. influenza V. cholerae H. ducreyi | Adapt alternative mechanism for folate synthesis Increased PABA synthesis | Aplastic anemia Bilirubin displacement Crystalluria, hematuria Rashes SLE Hemolytic in G6PD deficiency |
Cotrimoxazole | Bactericidal Fixed dose of TRIMETHOPRIM and SULFAMETHOXAZOLE in the ratio of 1:5 | S typhi Sulfonamide resistant strains of Staph. aureus Kelbsiella, Enterobacter Yersinia P. jiroveci Gonococci Meningococci etc. | Alternative pathway of folate mechanism Plasmid mediated acquisition of DHFRase | Nausea, vomitting Stomatitis Headache Folate def. C/I in pregnancy, renal disease |
Fluoroquinolone | Bactericidal Inhibit DNA gyrase, topoisomerase IV - inhibiting DNA replication | Wide range of organisms | Due to chromosomal mutation Reduced affinity for fluorosquinolones | GI Distress Headache, dizziness Seizures C/I pregnancy, tendonitis in adults |
Aminoglycoside | Bactericidal Bind to 30s and 50s ribosomes and freeze initiation | Narrow spectrum | Ribosomal protection Mutation Decreased efficiency of transport mechanism (not seen in amikacin, netilmycin) | Nephrotoxicity Allergy Neurotoxic Ototoxic |
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