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ESSAY ON CLASSES OF ANTIBIOTICS, THEIR MODES OF ACTION, ADVERSE EFFECTS, CONTRAINDICATIONS, AND CLINICAL USES

INTRODUCTION

ANTIBIOTICS ARE A DIVERSE GROUP OF CHEMOTHERAPEUTIC AGENTS, EITHER DERIVED FROM MICROORGANISMS OR PRODUCED SYNTHETICALLY, WHICH EITHER INHIBIT THE GROWTH (BACTERIOSTATIC) OR K...

ESSAY ON CLASSES OF ANTIBIOTICS, THEIR MODES OF ACTION, ADVERSE EFFECTS, CONTRAINDICATIONS, AND CLINICAL USES

INTRODUCTION

ANTIBIOTICS ARE A DIVERSE GROUP OF CHEMOTHERAPEUTIC AGENTS, EITHER DERIVED FROM MICROORGANISMS OR PRODUCED SYNTHETICALLY, WHICH EITHER INHIBIT THE GROWTH (BACTERIOSTATIC) OR KILL (BACTERICIDAL) BACTERIA. THEIR DISCOVERY REPRESENTS A PIVOTAL ADVANCEMENT IN MODERN MEDICINE, DRAMATICALLY REDUCING MORTALITY FROM BACTERIAL INFECTIONS. THE RATIONAL SELECTION OF AN ANTIBIOTIC IS PREDICATED ON A COMPREHENSIVE UNDERSTANDING OF ITS PHARMACOLOGICAL PROPERTIES, INCLUDING ITS MECHANISM OF ACTION, SPECTRUM OF ACTIVITY, POTENTIAL TOXICITIES, AND SPECIFIC CLINICAL INDICATIONS. THIS ESSAY DELINEATES THE MAJOR CLASSES OF ANTIBIOTICS, ELUCIDATING THEIR MODES OF ACTION, ADVERSE EFFECTS, CONTRAINDICATIONS, AND CLINICAL USES, WITH SPECIFIC EXAMPLES AND DOSAGES.

1. BETA-LACTAM ANTIBIOTICS

THIS IS THE LARGEST AND MOST IMPORTANT CLASS OF ANTIBIOTICS, CHARACTERIZED BY A BETA-LACTAM RING IN THEIR MOLECULAR STRUCTURE. THEIR PRIMARY MECHANISM IS THE INHIBITION OF BACTERIAL CELL WALL SYNTHESIS.

· A. PENICILLINS
· MODE OF ACTION: THEY IRREVERSIBLY INHIBIT PENICILLIN-BINDING PROTEINS (PBPS), ENZYMES CRITICAL FOR THE FINAL STAGES OF PEPTIDOGLYCAN CROSS-LINKING IN THE BACTERIAL CELL WALL. THIS LEADS TO OSMOTIC INSTABILITY AND CELL LYSIS (BACTERICIDAL).
· ADVERSE EFFECTS: HYPERSENSITIVITY REACTIONS RANGE FROM MACULOPAPULAR RASHES TO LIFE-THREATENING ANAPHYLAXIS (CROSS-REACTIVITY BETWEEN ALL BETA-LACTAMS IS ~1-10%). GASTROINTESTINAL DISTURBANCES (NAUSEA, DIARRHEA, PSEUDOMEMBRANOUS COLITIS) ARE COMMON. HIGH DOSES, ESPECIALLY IN RENAL IMPAIRMENT, CAN CAUSE NEUROTOXICITY (SEIZURES, ENCEPHALOPATHY).
· CONTRAINDICATIONS: A HISTORY OF IMMEDIATE-TYPE (TYPE I) HYPERSENSITIVITY (E.G., ANAPHYLAXIS, ANGIOEDEMA, URTICARIA) TO ANY BETA-LACTAM ANTIBIOTIC IS A STRONG CONTRAINDICATION.
· CLINICAL USES AND EXAMPLES:
· NATURAL PENICILLINS (PENICILLIN G, PENICILLIN V): DRUG OF CHOICE FOR STREPTOCOCCUS PYOGENES (PHARYNGITIS, SCARLET FEVER), SYPHILIS (TREPONEMA PALLIDUM), AND MENINGOCOCCAL CARRIER STATE.
· DOSAGE: PENICILLIN G (AQUEOUS CRYSTALLINE) - 12-24 MILLION UNITS/DAY IV IN DIVIDED DOSES 4-6 HOURLY FOR SERIOUS INFECTIONS. PENICILLIN V - 250-500MG ORALLY EVERY 6-8 HOURS.
· PENICILLINASE-RESISTANT PENICILLINS (CLOXACILLIN, DICLOXACILLIN, FLUCLOXACILLIN): SPECIFICALLY DESIGNED TO RESIST STAPHYLOCOCCAL BETA-LACTAMASES. USED FOR SUSPECTED OR CONFIRMED METHICILLIN-SENSITIVE STAPHYLOCOCCUS AUREUS (MSSA) INFECTIONS.
· DOSAGE: CLOXACILLIN - 250-500MG ORALLY EVERY 6 HOURS; 1-2GM IV EVERY 6 HOURS.
· AMINOPENICILLINS (AMOXICILLIN, AMPICILLIN): EXTENDED SPECTRUM INCLUDING SOME GRAM-NEGATIVE BACILLI LIKE E. COLI AND H. INFLUENZAE. USED FOR OTITIS MEDIA, SINUSITIS, RESPIRATORY TRACT INFECTIONS, AND URINARY TRACT INFECTIONS (UTIS). AMPICILLIN IS USED FOR LISTERIA MENINGITIS AND ENTEROCOCCAL ENDOCARDITIS.
· DOSAGE: AMOXICILLIN - 500MG ORALLY EVERY 8