Penicillin G, Amoxicillin, Ampicillin: Key Drugs in the Class

Penicillins are beta-lactam antibiotics used for bacterial infections. Learn the mechanism, indications, side effects, interactions, and clinical monitoring.

Penicillin's Overview

Penicillins are beta-lactam antibiotics that treat bacterial infections. They are effective and safe. The main drug is penicillin G. Amoxicillin and ampicillin are also used often.

Medications in the class.

• Penicillin G (prototype)

• Penicillin V

• Amoxicillin

• Ampicillin

• Cloxacillin

• Piperacillin (extended-spectrum)

Mechanism of Action

Penicillins block bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs). This stops peptidoglycan cross-linking, causing cell death. They are bactericidal.

Classifications

Penicillins are not divided into formal generations but have groups.

1. Natural Penicillins (Penicillin G, Penicillin V)

2. Aminopenicillins (ampicillin, amoxicillin)

3. Penicillinase-resistant penicillins (Cloxacillin, Oxacillin)

4. Extended-Spectrum Penicillins (Piperacillin, Ticarcillin)

Indications (When Used)

• Streptococcal infections (pharyngitis, pneumonia, endocarditis)

• Doctors prefer penicillin G for treating syphilis.

• Meningitis (from susceptible organisms)

• Otitis media, sinusitis (amoxicillin)

• Skin and soft tissue infections

• Community-acquired pneumonia (based on sensitivity)

Contraindications (When Not to Use)

• Known hypersensitivity to penicillin.

• Severe allergic history (anaphylaxis).

• Caution in renal impairment (adjust the dose).

Side Effects

• Allergic reactions (rash, urticaria, anaphylaxis)

• Gastrointestinal issues (diarrhea, nausea)

• Rare: hemolytic anemia, interstitial nephritis, and seizures (in high doses)

Drug Interactions

• Methotrexate: increased toxicity (due to lower renal clearance).

• Some debate whether oral contraceptives might become less effective.

• Aminoglycosides work together, but you shouldn’t mix them in the same IV solution.

• Probenecid: raises penicillin levels (blocks renal excretion).

Antidote

There's no specific antidote for penicillin overdose. Management is supportive. Use epinephrine for anaphylaxis. Hemodialysis may help in severe cases.

Monitoring for Complications

• Observe for allergic reactions, especially with the first doses.

• Monitor renal function in patients with kidney issues.

• Watch for superinfections like Clostridium difficile colitis during prolonged use.

Penicillins are crucial antibiotics, providing broad use with low toxicity. Monitoring allergies and drug interactions is key to safe use.