Mechanism of Action
: Microbicide; polyanion-based entry inhibitor. Carbopol 974P is a negatively charged, high molecular weight, crosslinked, polyacrylic acid. It is the major nonaqueous component in BufferGel.5,6,7
As a buffering agent, Carbopol 974P releases hydrogen ions (the active ingredient in BufferGel), which prevents an increase in vaginal pH normally caused by the alkalinizing effects of semen. By maintaining a normally acidic vaginal pH below 5.0 in the presence of semen, Carbopol 974P is thought to potentially inactivate or inhibit a broad spectrum of pathogens, including HIV.7,8,9
Carbopol 974P has demonstrated virucidal and spermicidal activity in vitro
Formulated as BufferGel, Carbopol 974P has been studied as a microbicide for preventing the transmission of HIV infection and other sexually transmitted infections and as a contraceptive product to be used in conjunction with a diaphragm.6,10,11
In addition, the combination of Carbopol 974P microbicide gel used with a diaphragm-like device called the Duet cervical barrier was theorized and tested as a potential strategy for preventing sexually transmitted infections.12
Note: Carbopol 974P microbicide gel was found to be ineffective for preventing HIV infection in a Phase II/IIb clinical study.
Dosing in Clinical Trials
Carbopol 974P microbicide gel is applied intravaginally.
Phase II/IIb (HIV-uninfected women)
- HPTN 035: Safety and Effectiveness Study
Carbopol 974P microbicide gel (BufferGel), 0.5% PRO-2000 gel, hydroxyethylcellulose (HEC) placebo gel, or no intervention (no gel); gels were applied within 1 hour before vaginal intercourse. (Mean follow-up period was 20.4 months.)4,6
Additional studies (Phase I) of Carbopol 974P microbicide gel have also been completed.
In the Phase II/IIb study of Carbopol 974P microbicide gel and PRO-2000 gel used in a coitally dependent manner for approximately 20 months by more than 3000 women, the vaginal use of both gels was determined to be safe. Adverse event rates were similar across all four study arms, with no significant differences in local and systemic events. (Study arms included a placebo gel arm and a no-gel arm.) The four study arms had similar overall incidence rates of deep epithelial disruption, infections with certain sexually transmitted organisms (i.e., Neisseria gonorrheae
, Chlamydia trachomatis
, Trichomonas vaginalis
, and Treponema pallidum
), and bacterial vaginosis.4
Drug interactions related to Carbopol 974P microbicide gel use are currently unknown.
. United States National Library of Medicine. ChemIDplus Advanced
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. National Institute of Allergy and Infectious Diseases (NIAID). NIAID ChemDB, HIV Drugs in Developmen
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. Stone A, Jiang S. Microbicides: stopping HIV at the gate
. 2006 Aug 5;368(9534):431-3. Last accessed on February 17, 2014.
. Abdool Karim SS, Richardson BA, Ramjee G, et al. Safety and Effectiveness of BufferGel and 0.5% PRO2000 Gel for the Prevention of HIV Infection in Women
. 2011 Apr 24;25(7):957-66. Last accessed on February 17, 2014.
. Mayer K, Peipert J, Fleming T, et al. BufferGel: results of the first phase I study of a novel vaginal microbicide
. Abstract presented at: 12th International AIDS Conference; June 28 – July 3, 1998; Geneva, Switzerland. Abstract 33158. Last accessed on February 17, 2014.
. National Institute of Allergy and Infectious Diseases (NIAID). Phase II/IIb Safety and Effectiveness Study of the Vaginal Microbicides BufferGel and 0.5% PRO 2000/5 Gel (P) for the Prevention of HIV Infection in Women
. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on December 11, 2003. NLM Identifier: NCT00074425. Last accessed on February 17, 2014.
. Mayer KH, Peipert J, Fleming T, et al. Safety and Tolerability of BufferGel, a Novel Vaginal Microbicide, in Women in the United States
. Clin Infect Dis
. 2001 Feb 1;32(3):476-82. Last accessed on February 17, 2014.
. Olmsted SS, Khanna KV, Ng EM, et al. Low pH immobilizes and kills human leukocytes and prevents transmission of cell-associated HIV in a mouse model
. BMC Infect Dis
. 2005 Sep 30;5:79. Last accessed on February 17, 2014.
. Nutan, Gupta SK. Microbicides: a new hope for HIV prevention
. Indian J Med Res
. 2011 Dec;134(6):939-49. Last accessed on February 17, 2014.
. Barnhart KT, Rosenberg MJ, MacKay HT, et al. Contraceptive efficacy of a novel spermicidal microbicide used with a diaphragm: a randomized controlled trial
. Obstet Gynecol
. 2007 Sep;110(3):577-86. Last accessed on February 17, 2014.
. Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). A Randomized, Controlled Trial of the Efficacy, Safety, and Acceptability of BufferGel
. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on August 1, 2003. NLM Identifier: NCT00065858. Last accessed on February 17, 2014.
. Montgomery ET, Woodsong C, Musara P, et al. An acceptability and safety study of the Duet® cervical barrier and gel delivery system in Zimbabwe
. J Int AIDS Soc
. 2010 Aug 5;13:30. Last accessed on February 17, 2014.
Last Reviewed: February 17, 2014
Last Updated: April 25, 2014