Beta Lactam Antibiotics
BETA LACTAM ANTIBIOTICS:
are the most popularly used antibiotics. They are any antibiotic agent that contains a β-lactam chain in the molecular structure. Penicillin is the prototype drug and once was a cure for almost anything. Sir Alexander Fleming discovered Penicillin. It was a miracle discovery in history of Mankind.
Mechanism of Action:
– Interfere with the synthesis of bacterial cell wall
– Inhibit transpeptidases so that cross linking does not take place
– When susceptible bacteria divide in the presence of it- cell wall deficient forms are produced resulting in the lysis of bacterial cell
– Peptidoglycan cell wall is unique to bacteria and it is non toxic to man
– Gram positive bacteria have higher susceptibility to PnG
Penicillin G (Benzyl Penicillin):
– Narrow spectrum; gram positive
– Majority of gram negative bacilli, M.tuberculosis, ricketsiae, chlamydiae, virus insensitive
– Resistance:
- Inherent: PBPs located deeper under lipoprotein where PnG is unable to penetrate
- Penicillinase: opens the beta lactam ring
- Penicillin tolerant but not penicillin destroying like pneumococci
– Pharmacokinetics:
- Acid labile: gastric acid
- Low oral absorption and rapid and complete absorption from i.m site
- Plasma t1/2 30 minutes
- Poor CSF and serous cavity penetration but increased in inflammation
- Rapid renal excretion (GFR-10 % and rest tubular secretion)
- Tubular secretion blocked by Probenecid: higher and longer lasting plasma concentration
– Preparation and Dose:
- Sodium Penicillin G injection
- Repository Penicillin G injection
- Procaine Penicillin G
- Benzathine Penicillin G
– Adverse Effects:
- Local irritancy and direct toxicity: pain at im site, nausea, thrombophlebitis, mental confusion, muscular twitchings, convulsions, bleeding, hallucinations, CNS stimulation
- Hypersensitivity: Urticaria, fever, wheezing, edema, serum sickness
- Superinfections
- Jarisch Herxheimer reaction
Semisynthetic Penicillins:
- Acid resistant alternative: Phenoxymethyl penicillin (Penicillin V)
- Penicillinase Resistant: Methicillin, Cloxacillin
- Extended Spectrum:
- Aminopenicillin: Amoxycillin, Ampicillin, Bacampicillin
- Carboxypenicillin: Carbenicillin, Tircarcillin
- Ureidopenicillin: Poperacillin, Mezlocillin
- Beta- lactamase inhibitor: Clavulanic acid, Sulbactam, Tazobactam