Ospen (Phenoxymethylpenicillin)

Phenoxymethylpenicillin is a narrow‑spectrum penicillin that targets infections caused by susceptible Gram‑positive organisms.

• Acute tonsillitis: reduces symptom duration and bacterial load.
• Scarlet fever: eliminates Streptococcus pyogenes and prevents complications.
• Early‑stage rheumatic fever prophylaxis: helps prevent recurrence.
• Minor skin infections: treats localized streptococcal infections.
• Otitis media (middle‑ear infection): aids in bacterial clearance.

• Phenoxymethylpenicillin inhibits bacterial cell‑wall synthesis by binding to penicillin‑binding proteins, which blocks the cross‑linking of peptidoglycan strands. This disruption weakens the bacterial wall, leading to osmotic lysis and death of susceptible Gram‑positive organisms.

Phenoxymethylpenicillin is generally well tolerated, but adverse reactions can occur.

Common Side Effects

• Nausea: mild gastrointestinal upset.
• Diarrhea: loose stools, often transient.
• Rash: mild skin erythema.
• Vaginal candidiasis: yeast overgrowth in some women.
• Elevated liver enzymes: mild, reversible changes.

Serious or Rare Side Effects

• Anaphylaxis: severe, potentially life‑threatening allergic reaction.
• Stevens‑Johnson syndrome: rare severe skin reaction.
• Hemolytic anemia: immune‑mediated red‑cell destruction.
• Serum sickness‑like reaction: fever, rash, arthralgia.
• Clostridioides difficile infection: severe colitis following disruption of gut flora.

When prescribing Phenoxymethylpenicillin, clinicians should consider several safety aspects.

• Allergy history: avoid in patients with known penicillin hypersensitivity.
• Renal function: adjust dose in severe impairment.
• Hepatic function: monitor if pre‑existing liver disease exists.
• Concomitant oral contraceptives: advise possible reduction in efficacy.
• Age considerations: use caution in neonates and the elderly.
• Store at below 25°C: keep in the original packaging, protect from moisture and direct sunlight.

Phenoxymethylpenicillin may interact with other medicines, requiring attention to avoid reduced efficacy or increased toxicity.

Major Interactions (Avoid)

• Methotrexate: increased risk of myelosuppression.
• Oral anticoagulants (e.g., warfarin): enhanced anticoagulant effect.

Moderate Interactions (Monitor Closely)

• Oral contraceptives: possible reduction of hormonal effectiveness.
• Probenecid: may increase penicillin plasma levels.
• Allopurinol: heightened risk of rash.
• Tetracyclines: antagonistic effect on bacterial killing.
• Non‑steroidal anti‑influmatic drugs (NSAIDs): increased risk of renal impairment.