A 2007 Cochrane review on scabies treatment identified 11 trials that evaluated permethrin for treating scabies.1 In 2 trials, 140 patients were randomized to receive either 200 mcg/kg of oral ivermectin or overnight application of 5% topical permethrin. Topical permethrin was superior to oral ivermectin with failure rates at 2 weeks of 8% and 39%, respectively (number needed to treat [NNT]=4; risk ratio [RR]=4.61; 95% confidence interval [CI], 2.07-10.26).
Two trials compared 5% topical permethrin with 10% topical crotamiton in 194 patients with follow-up at 28 days. Permethrin was superior to crotamiton with failure rates of 6% and 26%, respectively (NNT=6; RR=0.24; 95% CI, 0.10-0.55).
Five trials with 753 patients compared topical permethrin, 2.5% to 3.5%, with topical 1% lindane, but heterogeneity precluded pooling all the studies. In the 3 studies (554 patients) that were comparable, topical 3.5% permethrin was superior to lindane after a single application of each with failure rates of 9% and 15%, respectively (NNT=17; RR=0.59; 95% CI, 0.37-0.95).
Two trials that compared permethrin with topical benzyl benzoate (53 patients) and natural synergized pyrethrins (40 patients) showed no difference in treatment failures, but the trials were small and lacked sufficient statistical power.
Four additional studies included in the review compared crotamiton with lindane (100 patients), lindane with sulfur (68 patients), benzyl benzoate with sulfur (158 patients), and benzyl benzoate with natural synergized pyrethrins (240 patients). None demonstrated superiority, but all were small studies.1 A single small trial of 55 patients that compared oral ivermectin 200 mcg/kg with placebo showed failure rates at one week of 21% and 85%, respectively (NNT=2; RR=0.24; 95% CI, 0.12-0.51).1
Topical permethrin vs oral ivermectin
A 2014 systematic review of 5 studies included 2 new studies done after the 2007 Cochrane review.2 The new RCTs compared a single application of 5% topical permethrin with a single dose or 2 doses of oral ivermectin given 2 weeks apart. No statistically significant differences were found in these studies.2 Both underpowered studies favored topical permethrin, however.
The P value was .42 in one study of 242 adults and children, and this trial showed a clinical cure rate at 2 weeks of 93% using topical permethrin vs 86% using oral ivermectin.2
The other study of 120 adults and children didn’t report a P value or identify statistically significant differences between topical permethrin and oral ivermectin.2 This study reported a clinical cure rate of 87% with topical permethrin, 78% with a single dose of oral ivermectin, and 67% with 2 doses of oral ivermectin 2 weeks apart.2