Gender-related efficacy difference to an extended duration formulation of topical N,N-diethyl-m-toluamide (DEET)

A clinical trial (n = 120, 60 males and 60 females) was conducted to assess the efficacy of an extended duration tropical insect/arthropod repellent ( EDTIAR) topical formulation of N,N-diethyl-m-toluamide (DEET). The amount o f EDTIAR (mean +/- confidence interval), applied by participants in accorda nce with label directions, was not significantly different between females (3.66 +/- 0.32 mg/cm(2)) and males (3.35 +/- 0.33 mg/cm(2)). There also was no significant difference in the number of Anopheles stephensi mosquitoes biting the control arm of females or males at 0, 3, 6, 9, and 12 hr. While gender had no effect on feeding, the time of day did effect mosquito feedin g with fewer mosquitoes feeding in the afternoon than in the morning or eve ning. The percent protective efficacy at 0, 3, 6, 9, and 12 hr was 100.0, 9 9.3, 92.8, 79.7 and 66.3 for females, and 100.0, 100.0, 97.6, 91.9, and 77. 5 for males. These data are inconsistent with the EDTIAR label claim that t he repellent provides 95% or greater protection against mosquitoes for 12 h r or more under normal use conditions. The results of a multivariate regres sion analysis indicated that 1) protection decreased linearly as time after application of repellent increased (P < 0.001), 2) individuals who applied higher doses of repellent were better protected against mosquito bites (P < 0.001), 3) females experienced significantly less protection over time th an did males (P = 0.005), and 4) the estradiol concentration in the blood h ad no effect on efficacy of the repellent (P = 0.110).