Pharmacokinetic and Pharmacodynamic Study of Tenofovir 1% Gel

Inclusion Criteria: * Age 18-50 years, inclusive; * General good health (by volunteer history and per investigator discretion) without any clinically significant systemic disease (including, but not limited to, significant liver disease/hepatitis, gastrointestinal disease, kidney disease, thyroid disease, osteoporosis or bone disease, and type 2 diabetes); * Currently having regular menstrual cycles, if not on hormonal (including continuous) contraception, by volunteer report and per investigator discretion; * History of Pap smears and follow-up consistent with American Congress of Obstetricians and Gynecologist (ACOG) practice guideline #109 (see study manual) or willing to undergo a Pap smear at Visit 1. (Note: See study manual for clarification of eligibility criteria specific to Pap smear results.) * Willing to abstain from the use of any vaginal product other than the study gel including spermicides, lubricants, vaginal hygiene products, contraceptive intravaginal ring, diaphragms, and cervical caps (non-hormonal IUC if used as her method of contraception, is allowed) for the duration of the study; * In a monogamous relationship for at least the last four months with a male partner, at least 18 years old with no known risks for STIs, and not known to be HIV positive, who is willing and able to comply with the study requirements, and with whom condoms are not typically used; * Protected from pregnancy by sterilization of either partner, use of combination oral contraceptives or patch for at least two cycles, or non-hormonal intrauterine contraception throughout the study. Continuous oral contraceptives are allowable if the patient is at low risk for breakthrough bleeding; * Vaginal and cervical anatomy that, in the opinion of the investigator, lends itself to easy genital tract sample collection; * Negative urine pregnancy test; and * Willing to give voluntary consent, sign an informed consent form and comply with study procedures as required by the protocol. Exclusion Criteria: * History of hysterectomy; * Currently pregnant or within two calendar months from the last pregnancy outcome. Note: If recently pregnant must have had at least two spontaneous menses since pregnancy outcome; * Use of Depo-Provera in the last 120 days; * Currently breastfeeding or having breastfed an infant in the last two months, or planning to breastfeed during the course of the study; * History of sensitivity/allergy to any component of the study product, topical anesthetic, or allergy to both silver nitrate and Monsel's solution; * In the last six months, diagnosed with or treated for any STI or pelvic inflammatory disease. Note: Women with a history of genital herpes or condylomata who have been asymptomatic for at least six months may be considered for eligibility; * Symptomatic vulvovaginal candidiasis, Nugent score greater than equal to 7 at screening or symptomatic bacterial vaginosis (BV) at Visit 2, or symptomatic urinary tract infection (UTI); * Positive test for Trichomonas vaginalis, Neisseria gonorrhea or Chlamydia trachomatis; * Deep epithelial genital findings such as abrasions, ulcerations, and lacerations, or vesicles suspicious for a sexually transmitted infection; * Positive test for HIV; * Positive test for Hepatitis B surface antigen (HBsAg); * Known bleeding disorder that could lead to prolonged or continuous bleeding with biopsy; * Chronic or acute vulvar or vaginal symptoms (pain, irritation, spotting, etc.); * Known current drug or alcohol abuse which could impact study compliance; * Grade 1 or higher laboratory abnormality, per the August 2009 update of the DAIDS Table for Grading the Severity of Adverse Events; * Systemic use in the last two weeks or anticipated use during the study of drugs on a daily basis that may reduce renal function (e.g., ibuprofen) or liver function (e.g., Tylenol®), or that may affect anti-HSV activity (e.g., acyclovir or valacyclovir) of any of the following: corticosteroids, antibiotics, antifungals, antivirals (e.g. acyclovir or valacylovir) or antiretrovirals (e.g. Viread®). Note: Participants should avoid nonsteroidal anti-inflammatory drugs (NSAIDs) except for treatment of dysmenorrhea during menses. Participants may use Tylenol® on an as-needed but not daily basis during the study * Participation in any other investigational trial (device, drug, or vaginal trial)within the last 30 days for this study or planned participation in any other investigational trial during the study; * History of gynecological procedures (including genital piercing) on the external genitalia, vagina or cervix within the last 14 days; and * Abnormal finding on laboratory or physical examination or a social or medical condition which, in the opinion of the investigator, would make participation in the study unsafe or would complicate interpretation of data.