Tinidazole for Protozoal Disease

Tinidazole is a nitroimidazole with a longer half life than metronidazole, allowing single-dose or short-course treatment of giardiasis, amoebiasis and trichomoniasis. It is often better tolerated and more convenient than metronidazole. It shares the disulfiram-type reaction with alcohol.

Class. Antiprotozoal; 5-nitroimidazole.

Mechanism. Reduced inside anaerobic organisms to reactive intermediates that damage DNA and kill the organism.

Pharmacokinetics. Oral bioavailability over 90%. Half life 12 to 14 hours. Metabolised by CYP3A4; excreted in urine and faeces.

Giardiasis. 2 g orally as a single dose (children 3 years and over: 50 mg/kg, maximum 2 g).

Intestinal amoebiasis. 2 g once daily for 3 days (children 50 mg/kg daily for 3 days, maximum 2 g).

Amoebic liver abscess. 2 g once daily for 3 to 5 days (children 50 mg/kg daily for 3 days), followed by a luminal agent (paromomycin 25 to 35 mg/kg daily in three doses for 7 days).

Trichomoniasis. 2 g single dose; treat partners.

Loading dose, maintenance dose and titration. Not applicable. Maximum: 2 g daily.

Main alternative. Metronidazole.

Contraindications. Hypersensitivity to nitroimidazoles; first trimester of pregnancy; blood dyscrasia; neurological disease.

Serious adverse effects. Peripheral neuropathy, seizures, severe skin reactions, QT prolongation and neutropenia (rare).

Common adverse effects. Metallic taste, nausea, vomiting, abdominal pain and headache.

Interactions. Alcohol: avoid during treatment and for 3 days after; warfarin effect rises; lithium and ciclosporin levels rise; CYP3A4 inducers lower levels.

Common prescribing errors. Prescribing in the first trimester, forgetting a luminal agent after amoebic liver abscess, and combining with alcohol.

Special groups. - Pregnancy: avoid in the first trimester; use in the second and third trimesters only if needed. - Breastfeeding: avoid during treatment and for 3 days after. - Children: from 3 years. - Older adults: usual dose. - Kidney impairment: no adjustment; give after haemodialysis. - Liver impairment: caution in severe disease.

Formulations. Tablets 500 mg.

Administration. With food; crush and mix with food for children.

Baseline. Diagnosis by stool microscopy or antigen where available, pregnancy status, alcohol history.

Monitoring. Clinical response at 48 to 72 hours.

Stopping thresholds. Stop for neuropathy, seizures or severe skin reaction.

Referral and escalation. Specialist or surgical review for liver abscess that is large or not responding.