Roxithromycin

Roxithromycin is a macrolide with longer half-life than erythromycin, used for upper and lower respiratory, skin and genital infection in many countries but not in the United States.

Classification. Macrolide.

Mechanism. Binds the 50S ribosomal subunit and blocks protein synthesis.

Spectrum. Streptococci, pneumococci (macrolide resistance common), MSSA, Moraxella, Legionella, Mycoplasma, Chlamydia and Bordetella pertussis. Not active against Enterobacterales, Pseudomonas or most Haemophilus.

Pharmacokinetics. Oral bioavailability about 50%, reduced by food. Half-life about 12 hours. Mainly faecal elimination; about 7% excreted in urine. Weaker CYP3A4 inhibition than erythromycin or clarithromycin.

No loading dose. Maximum 300 mg daily.

Adults. 150 mg every 12 hours or 300 mg once daily for 5 to 10 days, taken 15 to 30 minutes before meals. - Pharyngitis, sinusitis, bronchitis, atypical pneumonia, uncomplicated skin infection. - Non-gonococcal urethritis and chlamydial infection (alternative): 150 mg every 12 hours for 10 days.

Children. 5 to 8 mg/kg/day in 2 divided doses; maximum 300 mg daily.

Alternatives. Azithromycin, clarithromycin, doxycycline, amoxicillin.

Contraindications. Hypersensitivity to macrolides; co-administration with ergot alkaloids; history of QT prolongation.

Adverse effects. Nausea, abdominal pain, diarrhoea, rash. Serious: QT prolongation, cholestatic hepatitis, severe skin reactions, Clostridioides difficile infection, exacerbation of myasthenia gravis.

Interactions. Ergot alkaloids (contraindicated); simvastatin and lovastatin (avoid); warfarin (INR rise); digoxin; ciclosporin; theophylline; midazolam; QT-prolonging drugs.

Common prescribing errors. Taking with food, using it for Haemophilus infection, and giving it with ergot alkaloids or QT-prolonging drugs.

Special groups. - Pregnancy: avoid unless needed. Breastfeeding: low milk levels; acceptable with monitoring. - Older adults: usual dose. - Kidney impairment: severe impairment (creatinine clearance under 10 mL/min) consider 150 mg once daily. - Liver impairment: severe cirrhosis halve the dose to 150 mg daily. - Region: availability in East Africa is variable.

Formulations. Tablets 150 mg and 300 mg; dispersible tablets for children where supplied.

Baseline and monitoring. - Baseline: medication review, liver tests in liver disease. - During treatment: liver tests if therapy exceeds 2 weeks; ECG in high-risk patients.

Stop rules. Stop for jaundice, syncope or palpitations, or severe skin reaction.

Referral and escalation. Refer for treatment failure at 48 to 72 hours or suspected resistant atypical infection.