- Female participants must have a negative serum pregnancy test at screening and a negative urine pregnancy test on the morning of the challenge and use effective birth control during the entire study period. Methods of effective birth control include: complete abstinence, the use of a licensed hormonal method, intrauterine device, barrier method plus spermicide, or having sexual relations exclusively with a vasectomized partner. Appropriate barrier methods include condoms, cervical sponge, and diaphragm. Females who are not of childbearing potential are defined as those who are physiologically incapable of becoming pregnant, including any female with tubal ligation or who is postmenopausal. For purposes of this study, postmenopausal status will be defined as absence of menses for at least 1 year.