Giardiasis: Treatment

The drug of first choice is tinidazole (Fasigyn®), 2 grammes to be taken in one dose. This gives a cure rate of 90 to 95%. Metronidazole may also be used, but produces more side effects. Ornidazole (Tiberal®) 500 mg b.i.d. is an alternative, but is best given for 5 days. Alcohol should be avoided since there may be an antabuse effect. Other nitro-imidazoles are also sometimes used: secnidazole (Flagentyl®), nimorazole (Naxogyn®). Resistance to nitro-imidazoles is increasing. Mepacrine (quinacrine, atebrine) is an old drug (3 x 100 mg/day orally for 5 days) which gives good results if tinidazole fails. It is a yellow product and may cause a jaundice-like skin discoloration, which the patient should be warned about beforehand. It may also cause haemolysis if there is severe G6PD deficiency. Albendazole has also proved effective in vitro, but produces varying results in vivo. It is quite expensive. Paromomycin (Humatin®, Gabbroral®) is an aminoglycoside which has very low absorption when taken orally and is thus active in the intestinal lumen. However, there is quite a high relapse rate (25%).

In therapy-resistant giardiasis the questions should be considered as to whether

(1) compliance is failing,

(2) if there may be re-infection (e.g. via an asymptomatic cyst carrier), or

(3) immunodeficiency, including IgA-deficiency,

(4) possibly the presence of a duodenal diverticulum (mechanical reason for relapse) or

(5) whether this is genuine problem of resistance. There is in-vitro cross-resistance between the different nitro-imidazoles. If symptoms persist,

(6) long-term lactase deficiency or

(7) bacterial overgrowth in the small intestine with possible inactivation of nitro-imidazoles by Gram-negative bacteria should be considered.

Category: Medicine Notes