OIA1015 PENICILLINS

Penicillin

A β-lactam antibiotic that inhibits bacterial cell wall synthesis.

β-Lactam Ring

A four-membered cyclic amide essential for antibacterial activity.

Peptidoglycan

A polymer of sugars and amino acids that forms bacterial cell walls.

Transpeptidation

The cross-linking reaction in peptidoglycan synthesis inhibited by penicillin.

Penicillin-Binding Proteins (PBPs)

Enzymes involved in bacterial cell wall synthesis targeted by penicillin.

Inhibition of Transpeptidase

Penicillin binds PBPs, blocking peptidoglycan cross-linking, leading to cell lysis.

Activation of Autolysins

Induces self-destruction of bacterial cell walls.

Bactericidal Action

Effective only on actively growing bacteria.

Penicillins

E.g., Penicillin G, Amoxicillin, Methicillin

Cephalosporins

E.g., Ceftriaxone, Cephalexin.

Carbapenems

E.g., Imipenem, Meropenem.

Monobactams

E.g., Aztreonam.

Natural Penicillins

Penicillin G, Penicillin V.

Active against Gram-positive bacteria (e.g., Streptococcus).

Anti-Staphylococcal Penicillins

Methicillin, Nafcillin, Oxacillin, Cloxacillin.

Resistant to β-lactamases.

Extended-Spectrum Penicillins

Ampicillin, Amoxicillin.

Better Gram-negative coverage.

Anti-Pseudomonal Penicillins

Piperacillin, Ticarcillin.

Active against Pseudomonas aeruginosa.

β-Lactamase Production

Bacteria produce enzymes that hydrolyze β-lactam rings (e.g., Staphylococcus aureus).

Alteration of PBPs

Methicillin-Resistant Staphylococcus aureus (MRSA) modifies PBPs, reducing penicillin binding.

Efflux Pumps

Some bacteria actively pump penicillin out of the cell.

Reduced Permeability

Gram-negative bacteria modify porins, blocking penicillin entry.

Clavulanic Acid

Inhibits β-lactamases, combined with Amoxicillin.

Sulbactam

Combined with Ampicillin to extend bacterial coverage.

Tazobactam

Used with Piperacillin for broader activity.

Gram-Positive Bacteria

Streptococcus, Staphylococcus (except MRSA).

Gram-Negative Cocci

Neisseria gonorrhoeae.

Spirochetes

Treponema pallidum (syphilis).

Limited Gram-Negative Bacilli Activity

Enterobacteriaceae, Pseudomonas require extended-spectrum penicillins.

Absorption

Penicillin V is acid-stable (oral).

Penicillin G is acid-sensitive (IM/IV use).

Distribution

Well-distributed, crosses placenta but not the CNS (unless inflamed meninges).

Metabolism

Minimal hepatic metabolism, except Nafcillin and Oxacillin.

Excretion

Primarily renal elimination via tubular secretion.

Syphilis Treatment

Penicillin G is the drug of choice.

Streptococcal Infections

Pharyngitis, rheumatic fever prophylaxis.

Endocarditis

Penicillin G for Streptococcus viridans.

Pseudomonas Infections

Piperacillin-Tazobactam.

Hypersensitivity Reactions

Rash, anaphylaxis, angioedema.

Stevens-Johnson Syndrome (SJS)

Severe allergic reaction affecting the skin and mucous membranes.

Gastrointestinal Disturbances

Diarrhea, disruption of gut flora.

Neurotoxicity

Seizures at high doses, especially in renal impairment.

Nephritis & Hematologic Effects

Methicillin-associated interstitial nephritis.

Coagulation defects with high-dose piperacillin.