In a randomized trial in 115 children 2-13yo randomized to 1% permethrin repeated at 1wk if necessary plus either oral trimethoprim-sulfamethoxazole (10mg/kg/d divided BID x 10d) vs. placebo was ass'd with sig. higher cure rate at 4wks (92.5% vs. 72%).  Probable mechanism is that TMP-SMX-containing blood sucked by the louse kills bacteria in the gut of the louse that produce B-vitamins (Peds. 107:e30, 2001--JW)