5-Nitroimidazole refractory giardiasis is common in Matanzas, Cuba and effectively treated by secnidazole plus high-dose mebendazole or quinacrine: a prospective observational cohort study

Abstract Objective To evaluate the effectiveness and tolerability of secnidazole combined with high-dose mebendazole for treatment of 5-nitroimidazole resistant giardiasis. Method Adults with microscopically verified Giardia intestinalis monoinfection attending a secondary level hospital in Matanzas City, Cuba were prospectively included into a cohort. A recently introduced treatment ladder consisting of metronidazole as first line, followed by secnidazole, tinidazole, secnidazole plus mebendazole and quinacrine as 2nd to 5th line treatment was used. Adverse events and treatment success were determined by questioning and microscopy on concentrated stool samples, respectively on days 3, 5 and 7 after end of treatment. If G. intestinalis were detected on day 3, 5 or 7 the infection was classified as refractory and no further microscopy was done. Results 456 patients were included. Metronidazole, 500 mg three times daily for 5 days, cured 248/456 (54%) patients. A single two gram secnidazole dose as second line treatment cured 50/208 (24%) patients. A single two gram tinidazole dose as third line treatment cured 43/158 (27%) patients. Three rounds of 5-nitroimidazole therapy thus cured 341/456 (75%) patients. Secnidazole plus mebendazole (200 mg every 8 hours for 3 days) cured 100/115 (87%) of nitroimidazole refractory infections. Quinacrine cured the remaining 15 patients. All treatments were well tolerated. Conclusions 5-Nitroimidazole refractory giardiasis was common indicating that an alternative first line treatment may be needed. Retreatment of metronidazole refractory giardiasis with an alternative 5-nitroimidazole was suboptimal indicating cross-resistance. Mebendazole plus secnidazole were well tolerated and effective for the treatment of 5-nitroimidazole refractory G. intestinalis infection in this setting.