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Drugs

Tenofovir (microbicide)

Other Names: GS-1278, PMPA gel, TFV gel, tenofovir 1% gel, tenofovir gel Drug Class: Microbicides
Molecular Formula: C9 H14 N5 O4 P
Registry Number: 147127-20-6 (CAS) Chemical Name: [(1R)-2-(6-aminopurin-9-yl)-1-methyl-ethoxy]methylphosphonic acid Chemical Class: Purine Nucleotides Organization: Gilead Sciences, Inc. Phase of Development: Tenofovir vaginal gel is in Phase III development. Other tenofovir-based microbicide products are in earlier phases of study.

Chemical Image:

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tenofovir

tenofovir

Molecular Weight: 287.2146

(Compound details obtained from ChemIDplus Advanced,1 NIAID Therapeutics Database,2 and ClinicalTrials.gov3-7)

Pharmacology


Mechanism of Action: Microbicide; nucleoside reverse transcriptase inhibitor. HIV-specific topical microbicides formulated with ARV drugs, such as tenofovir, are being developed as a pre-exposure prophylaxis (PrEP) strategy to prevent the sexual transmission of HIV. ARV-based topical microbicides are designed to inhibit the infection process at the vaginal or rectal mucosa and directly interfere with the HIV replication cycle.8-11

Tenofovir, an adenosine nucleoside monophosphate (nucleotide) analog, is intracellularly phosphorylated to the active metabolite tenofovir diphosphate (TFV-DP). TFV-DP competitively inhibits the activity of HIV reverse transcriptase and causes DNA chain termination.10,12 Tenofovir, formulated as a microbicide, has primarily been studied for preventing sexually transmitted HIV; secondarily, it has been studied for its potential impact on preventing other sexually transmitted infections, such as HSV-2.3

Several different tenofovir-based microbicide products have been studied in clinical trials.3-7 The tenofovir vaginal gel is the furthest along in development, with a completed Phase III efficacy study (FACTS 001; NCT01386294). Results from this trial found that the gel did not protect women from acquiring HIV and that product adherence was an important factor in the overall results of the trial.3,13 A Phase II study on tenofovir rectal gel has been completed (MTN-017; NCT01687218).4  

Half-life (T½): When given as a single oral dose of tenofovir DF, tenofovir has a plasma elimination half-life of approximately 17 hours and an intracellular half-life that is greater than 60 hours.10

In a study of tenofovir vaginal gel in macaques, the estimated intracellular half-life of tenofovir in vaginal lymphocytes was 25 hours. In comparison, with orally dosed tenofovir DF in macaques, the tenofovir intracellular half-life in PBMCs was 49 hours.14 

In a study that compared rectally applied tenofovir gel to oral tenofovir DF, the tenofovir plasma half-life was at least 5 hours shorter with single and multiple rectal dosing than with single oral dosing.15

Metabolism/Elimination: Tenofovir is not a CYP substrate. Approximately 70 to 80% of an intravenously administered dose of tenofovir is recovered in the urine as unchanged drug. Tenofovir is eliminated renally.10

Resistance: In the CAPRISA 004 trial (NCT00441298), which evaluated tenofovir 1% vaginal gel, no resistance mutations related to tenofovir, thymidine analog mutations (TAMs), or mutations conferring multi-NRTI resistance were detected among HIV seroconverters.16

In the VOICE trial (NCT00705679), which assessed the effectiveness of a topical HIV prevention method (tenofovir 1% vaginal gel) and 2 different oral HIV prevention methods (tenofovir DF and emtricitabine/tenofovir DF [Truvada]), 1 participant in the Truvada group who underwent HIV-1 seroconversion 11 months after enrollment developed the M184V HIV resistance mutation.17

In the context of suboptimal use of microbicides, an in vitro study examined the effects of suboptimal concentrations of tenofovir, dapivirine, and dapivirine plus tenofovir on the development of drug-resistant HIV over 25 weeks. Results indicated that suboptimal doses of dapivirine alone permitted the emergence of more reverse transcriptase mutations than did the suboptimal doses of dapivirine plus tenofovir or the suboptimal doses of tenofovir alone. Suboptimal concentrations of tenofovir alone resulted in the development of 1 NRTI mutation, K65R. Drug-resistant virus selected with suboptimal doses of dapivirine plus tenofovir demonstrated resistance to nevirapine, but it remained susceptible to lamivudine and stavudine.18


Clinical Trials


Reduced glycerin tenofovir 1% gel - intrarectal

Study Identifiers: MTN-017; NCT01687218
Sponsor: CONRAD
Phase: II
Study Purpose: The purpose of this study was to evaluate the safety and acceptability of reduced glycerin tenofovir 1% gel applied rectally versus oral Truvada.
Study Population: Participants were HIV-uninfected men and transgender women.
Dosing: Participants were randomized to 1 of 6 groups. Groups differed by the order in which each study product was used. All participants received the following study products for 8 weeks each, with a 1-week washout between products:

  • Reduced glycerin tenofovir 1% gel applied rectally and once daily
  • Reduced glycerin tenofovir 1% gel applied rectally, used within 12 hours prior to receptive anal intercourse (RAI) and as soon as possible within 12 hours after RAI; no more than 2 doses used in a 24-hour period (dosing strategy also known as BAT24)
  • Truvada taken orally and once daily.4,19-22

Selected Study Results:



Tenofovir 1% gel - intravaginal

Study Identifiers: (1) CAPRISA 004; NCT00441298 (2) CAPRISA 008; NCT01691768 and (3) CAPRISA 009; NCT01387022
Sponsor: Centre for the AIDS Programme of Research in South Africa
Phase: CAPRISA 004 was a Phase IIb trial.
Study Purpose: The purpose of CAPRISA 004 was to assess the safety and effectiveness of tenofovir 1% vaginal gel for preventing HIV infection in women. CAPRISA 008 and 009 were open-label follow-on studies.
Study Population: Participants in CAPRISA 004 were HIV-uninfected, sexually active women in South Africa.
Dosing: CAPRISA 004 participants were randomly assigned to either tenofovir 1% gel (vaginal formulation) or placebo. Participants were instructed to use the study product within 12 hours prior to intercourse and as soon as possible within 12 hours after intercourse, with no more than 2 doses used in a 24-hour period (dosing strategy also known as BAT24).

 

CAPRISA 008 was an open-label follow-on study that provided previous CAPRISA 004 participants with tenofovir gel. The study assessed product safety and the effectiveness of gel provision through family planning services. Participants were instructed to use tenofovir gel according to the BAT24 dosing strategy.

CAPRISA 009 was an open-label follow-on study designed to evaluate if use of tenofovir gel impacted the efficacy of tenofovir-containing ART in women who acquired HIV during CAPRISA 004 or CAPIRSA 008.

Selected Study Results:

 

Study Identifiers: MTN-003; VOICE trial; NCT00705679
Sponsor: National Institute of Allergy and Infectious Diseases (NIAID)
Phase: IIb
Study Purpose: The purpose of this study was to assess the safety and effectiveness of oral tenofovir DF (Viread), oral Truvada, and tenofovir 1% vaginal gel for the prevention of HIV infection in women.
Study Population: Participants were HIV-uninfected, sexually active women in South Africa, Uganda, and Zimbabwe.
Dosing: Participants were randomized to 1 of the following 5 groups:

  • Tenofoivr DF 300 mg plus Truvada placebo, both taken orally and once daily
  • Truvada 200 mg/300 mg plus tenofovir DF placebo, both taken orally and once daily
  • Tenofovir DF placebo plus Truvada placebo, both taken orally and once daily
  • Tenofovir 1% gel (vaginal formulation) applied once daily
  • Vaginal placebo gel applied once daily.17,28-30
Selected Study Results:

 

Study Identifiers: FACTS 001; NCT01386294
Sponsor: CONRAD
Phase: III
Study Purpose: The purpose of this study was to assess the safety and effectiveness of tenofovir 1% vaginal gel for preventing HIV infection and HSV-2 infection in women.
Study Population: Participants were HIV-uninfected, sexually active women in South Africa.
Dosing: Participants were randomly assigned to either tenofovir 1% gel (vaginal formulation) or placebo. Participants were instructed to use the study product according to the BAT24 dosing strategy.3,13,31
Selected Study Results:


Additional clinical trials of tenofovir 1% vaginal or rectal gels have been completed. One example is the Phase I MTN-007 study (NCT01232803), which tested the safety and acceptability of reduced glycerin tenofovir 1% gel for rectal use. Another example is the Phase I CHARM-01 and CHARM-02 studies (NCT01575405 and NCT01575418), which evaluated the safety, acceptability, and pharmacokinetics of 3 gel formulations used rectally: a vaginal formulation, a reduced glycerin vaginal formulation, and a rectal-specific formulation.32-37 Other forms of tenofovir-based microbicides in early development include vaginal tablets, vaginal films, and intravaginal rings.5-7,38-41


Adverse Events


In the MTN-017 study (NCT01687218), which compared rectally applied reduced glycerin tenofovir 1% gel with oral Truvada, the gel was reported to be safe, with the majority of adverse events (AEs) being minor. Grade 2 or higher AE rates in the gel groups were similar to the rates in the oral Truvada group.4,20,21

In the CAPRISA 004 study (NCT00441298), tenofovir 1% vaginal gel that was used over a 30-month period by women demonstrated no evidence of increased renal, hepatic, pregnancy-related, or genital AEs when compared with placebo. Mild and self-limiting diarrhea was reported more frequently in the tenofovir gel group than in the placebo group.16

In the VOICE trial (NCT00705679), elevations in serum creatinine levels (all mild, except 1) occurred more frequently among participants in the oral Truvada group than among participants in the oral placebo group. No other significant differences in safety concerns were noted in the study.17


Drug Interactions


Drug interactions related to topical tenofovir gel are currently unknown. An in vivo drug interaction study of tenofovir 1% vaginal gel and 3 commonly used vaginal products was completed.42


References


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  3. CONRAD. A Phase III, Multi-Centre, Randomized Controlled Trial to Assess the Safety and Effectiveness of the Vaginal Microbicide 1% Tenofovir Gel in the Prevention of Human Immunodeficiency Virus Type 1 Infection in Women, and to Examine Effects of the Microbicide on the Incidence of Herpes Simplex Virus Type 2 Infection. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on June 28, 2011. NLM Identifier: NCT01386294. Available at: https://www.clinicaltrials.gov/ct2/show/NCT01386294. Last accessed on May 2, 2017.
  4. CONRAD. A Phase 2 Randomized Sequence Open Label Expanded Safety and Acceptability Study of Oral Emtricitabine/Tenofovir Disoproxil Fumarate Tablet and Rectally-Applied Tenofovir Reduced-Glycerin 1% Gel. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on August 27, 2012. NLM Identifier: NCT01687218. Available at: https://www.clinicaltrials.gov/ct2/show/NCT01687218. Last accessed on May 2, 2017.
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  7. Albert Einstein College of Medicine, Inc. Phase 1 safety and pharmacokinetic study of a polyurethane tenofovir disoproxil fumarate vaginal ring in sexually active women (TDF IVR-002). In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on April 22, 2016. NLM Identifier: NCT02762617. Available: https://www.clinicaltrials.gov/ct2/show/NCT02762617. Last accessed on May 2, 2017.
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Last Reviewed: May 2, 2017