Secnidazole

Secnidazole is a long-acting nitroimidazole given as a single oral dose for bacterial vaginosis, trichomoniasis, giardiasis and amoebiasis. Its half-life of about 17 to 29 hours allows once-only dosing, which helps adherence.

Classification. Nitroimidazole.

Mechanism. The nitro group is reduced in anaerobic organisms, producing free radicals that break DNA; bactericidal and antiprotozoal.

Spectrum. Gardnerella and vaginal anaerobes, Trichomonas vaginalis, Entamoeba histolytica, Giardia lamblia and anaerobic bacteria. Helicobacter pylori resistance is common.

Pharmacokinetics. Well absorbed orally. Half-life 17 to 29 hours. Low protein binding. Hepatic metabolism with renal excretion.

Single dose; maximum 2 g.

Adults, oral.

• Bacterial vaginosis: 2 g as a single dose.
• Trichomoniasis: 2 g as a single dose, with simultaneous partner treatment.
• Giardiasis: 2 g as a single dose.
• Intestinal amoebiasis: 2 g as a single dose; invasive amoebiasis or liver abscess 2 g once daily for 3 days, followed by a luminal agent.

Children. Giardiasis and amoebiasis 30 mg/kg as a single dose (maximum 2 g). Not advised under 2 years.

Alternatives. Metronidazole, tinidazole.

Contraindications. Nitroimidazole hypersensitivity; alcohol during treatment and for 72 hours after; blood dyscrasias (relative).

Adverse effects. Metallic taste, nausea, vomiting, headache, abdominal pain, vulvovaginal candidiasis. Serious: peripheral neuropathy and seizures (rare), hypersensitivity, leucopenia.

Interactions. Alcohol (disulfiram-like); warfarin (INR rise); lithium; disulfiram; busulfan.

Common prescribing errors. Alcohol use after dosing, no partner treatment in trichomoniasis, and no luminal agent after invasive amoebiasis.

Special groups. - Pregnancy: use only when necessary; avoid in the first trimester where possible. Breastfeeding: avoid for 96 hours after the dose (discard milk). - Older adults: usual dose. - Kidney impairment: no adjustment. - Liver impairment: use with caution. - Region: used in East Africa mainly for amoebiasis, giardiasis and vaginal infection.

Administration. Take with food. Granules can be sprinkled on a soft food such as yoghurt or porridge and eaten within 30 minutes.

Baseline and monitoring. - Baseline: medication review, alcohol history, pregnancy status. - During treatment: symptom review at 7 to 14 days; test of cure for trichomoniasis in selected settings.

Stop rules. Not applicable for single doses; avoid further dosing if severe hypersensitivity or neurological symptoms appear.

Referral and escalation. Refer for persistent or recurrent infection after treatment, and for amoebic abscess.