The purpose of this study is to compare 2 single doses of ivermectin as tablets with 2 single applications of malathion 0.5% lotion (Days 1 and 8) in clearing head lice, in patients who have recently used standard head lice treatments without success.

Head lice infestation occurs frequently, primarily in children 3 to 11 years of age. In recent years an increasing prevalence of lice infestation in schools, day care centres, and summer day camps is believed to be partly due to increasing lice resistance to currently available standard treatments for pediculosis (infestation with lice). There is a need for new effective backup treatments for this common condition of head lice infestation. This is a double-blind, randomized, parallel-group, study in several clinical centres comparing ivermectin as tablets to malathion 0.5% lotion in the treatment of head lice. All enrolled patients participate in the primary phase of the study up to the Day 15 evaluation. Patients who are still infested with lice at Day 15 (treatment failures) will enter an extension phase and be treated in a double-blind, fashion with the opposite treatment (ie ivermectin or malathion). The study hypothesis is that ivermectin will be more effective than malathion in clearing head lice infestation , as measured by the proportion of patients who are lice-free at Study Day 15.

Inclusion Criteria:

• Head lice infestation confirmed by detection combing by study staff
• previous (within 6 weeks) use of a topical insecticide product
• minimum 15kg weight
• providing informed consent

Exclusion Criteria:

• pregnant or nursing patients
• households with 7 or more infested patients
• households where there are other known infested household members not participating
• head lice treatment within 2 weeks of entry
• active scalp infection
• any difficulty with combing assessment
• patient from region endemic for certain parasitic worm diseases