Ospen (Phenoxymethylpenicillin)

Phenoxymethylpenicillin is used to treat infections caused by susceptible Gram‑positive bacteria, particularly in the respiratory and ear‑nose‑throat pathways.

• Acute otitis media: reduces the bacterial load and alleviates symptoms.
• Streptococcal pharyngitis: shortens the duration of sore throat and prevents complications.
• Community‑acquired pneumonia: helps eradicate the causative organisms and improves lung function.
• Skin and soft‑tissue infections: assists in clearing the infection and limits spread.
• Rheumatic fever prophylaxis: maintains suppression of streptococcal colonisation.
• Dental abscess prevention: supports infection control post‑dental procedures.

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

Phenoxymethylpenicillin may cause a range of adverse reactions, most of which are mild and reversible.

Common Side Effects

• Nausea: mild stomach upset often resolves without treatment.
• Diarrhea: loose stools that typically improve after therapy ends.
• Rash: transient skin redness or itching.
• Vaginal candidiasis: mild yeast infection in some women.
• Elevated liver enzymes: temporary increase detected in blood tests.

Serious or Rare Side Effects

• Anaphylaxis: severe, potentially life‑threatening allergic reaction.
• Stevens‑Johnson syndrome: rare skin blistering disorder.
• Hemolytic anemia: destruction of red blood cells.
• Clostridioides difficile infection: severe colitis following gut flora disruption.
• Serum sickness‑like reaction: fever, rash, joint pain after exposure.

Phenoxymethylpenicillin should be used with caution in specific clinical situations.

• Allergy assessment: verify no known hypersensitivity to penicillins.
• Renal function: adjust dose in patients with impaired kidney function.
• Hepatic function: monitor liver enzymes in patients with liver disease.
• Concomitant antibiotics: avoid simultaneous use with bacteriostatic agents.
• Pregnancy and lactation: weigh benefits against potential risks.
• Store at below 25°C: keep in the original packaging, protect from moisture and light.

Phenoxymethylpenicillin can interact with several other medicines, requiring monitoring or avoidance.

Major Interactions (Avoid)

• Oral contraceptives: may reduce efficacy, consider backup method.
• Methotrexate: increased toxicity risk.
• Probenecid: raises penicillin levels, risk of toxicity.

Moderate Interactions (Monitor Closely)

• Bacteriostatic antibiotics (e.g., tetracyclines): may antagonize effect.
• Warfarin: potential alteration of INR.
• Allopurinol: rare skin reactions may be enhanced.