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AIDSinfo Drug Database

AIDSinfo Drug Database

Drugs by class



Carrageenan  Audio icon

Other Names: Carraguard, lambda carrageenan, PC-515
Drug Class: Microbicides
Registry Number: 9000-07-1 (CAS)
Chemical Name: Carrageenan
Chemical Class: Natural Products, Marine Saccharides
Company: Population Council Center for Biomedical Research
Phase of Development: Phase III. In a Phase II clinical study, carrageenan vaginal gel was found to be ineffective as a topical microbicide for preventing HIV infection.

(Compound details obtained from ChemIDplus Advanced1, NIAID Therapeutics Database2, Antiviral Research article3, and The Population Council, Inc. News Release4)

What is an investigational drug?

An investigational drug is one that is under study and is not approved by the U.S. Food and Drug Administration (FDA) for sale in the United States. Medical research studies are conducted to evaluate the safety and effectiveness of an investigational drug. These research studies are also called clinical trials. Once an investigational drug has been proven safe and effective in clinical trials, FDA may approve the drug for sale in the United States.

What is carrageenan?

Carrageenan (brand name: Carraguard) is an investigational drug that has been studied to prevent sexual transmission of HIV and other sexually transmitted infections (STIs). It is a type of drug product called a topical microbicide. Topical microbicides are products that are applied to the vagina or rectum (such as gels, films, or creams) or inserted into the vagina (such as vaginal rings) to prevent getting STIs, such as HIV infection.5 

Topical microbicides can also be referred to as topical pre-exposure prophylaxis (PrEP) products.5,6 PrEP means using a medicine before possible exposure to a virus or bacteria to reduce the risk of becoming infected with the virus or bacteria. Topical microbicides to prevent HIV infection are designed to work close to where they are applied and near to where HIV might enter the body (through the vagina or rectum).6,7 They may prevent HIV transmission in a number of ways. For example, topical microbicides for HIV might:

  • inactivate HIV or other pathogens (also called disease-causing micoorganisms);
  • strengthen the body’s normal defenses;
  • block HIV from attaching to healthy cells susceptible to infection;
  • prevent HIV infection from spreading to other cells that are healthy.5

Carrageenan works by blocking HIV from attaching to susceptible, healthy cells. Carrageenan belongs to a group of drugs called polyanion-based entry inhibitors.3 Polyanion-based entry inhibitors interact through an electrostatic association with the surface of viruses such as HIV. The interaction between the negatively charged surface of a polyanion-based entry inhibitor and HIV’s positively charged surface may prevent HIV from attaching to, entering, or infection healthy cells.3,8,9
Carrageenan is currently in a gel form. The gel has been studied for vaginal use.10

How are clinical trials of investigational drugs conducted?

Clinical trials are conducted in phases. Each phase has a different purpose and helps researchers answer different questions.11 

  • Phase I trials: Researchers test an investigational drug in a small group of people (20–80) for the first time. The purpose is to evaluate its safety and identify side effects.
  • Phase II trials: The investigational drug is administered to a larger group of people (100–300) to determine its effectiveness and to further evaluate its safety.
  • Phase III trials: The investigational drug is administered to large groups of people (1,000–3,000) to confirm its effectiveness, monitor side effects, compare it with standard or equivalent treatments, and collect information that will allow the investigational drug to be used safely.11

In most cases, an investigational drug must be proven safe and effective in a Phase III clinical trial to be considered for approval by FDA for sale in the United States. Some drugs go through FDA’s accelerated approval process and are approved before a Phase III clinical trial is complete. After a drug is approved by FDA and made available to the public, researchers track its safety in Phase IV trials to seek more information about the drug’s risks, benefits, and optimal use. 11

In what phase of testing is carrageenan?

Carrageenan vaginal gel has been studied in Phase III clinical trials.2

Carrageenan vaginal gel was found to be ineffective for preventing HIV infection in a Phase III clinical study.4


What are some studies on carrageenan?

In a Phase III study, the safety and effectiveness of carrageenan microbicide gel was compared with that of a placebo gel. (A placebo is an inactive drug that is identical in appearance to the active drug being studied.) Over 6000 HIV-uninfected women were instructed to apply the gels vaginally and within 1 hour before vaginal intercourse. Participants used the gels for up to 2 years.10,12

In this study, carrageenan microbicide gel was not effective in preventing sexually transmitted HIV infection in women. Adherence to gel use during each sex act was noted to be only approximately 42%. (Adherence means using a medicine exactly as prescribed.) In terms of safety, carrageenan microbicide gel was determined to be safe when applied vaginally.4,10

What side effects might carrageenan cause?

In the Phase III study discussed under the previous question, no concerning side effects associated with carrageenan microbicide gel were reported.4,10 

Information on possible side effects of the drug is not complete. If testing of carrageenan microbicide gel continues, additional information on possible side effects will be gathered.

Where can I get more information about clinical trials studying carrageenan?

More information about carrageenan-related research studies is available from the AIDSinfo database of study summaries. Click on the title of any trial in the list to see the trial summary and more information about the study.

I am interested in participating in a clinical trial of carrageenan. How can I find more information about participating in a clinical trial?

Participating in a clinical trial can provide benefits. For example, a volunteer participant can benefit from new research treatments before they are widely available. Participants also receive regular and careful medical attention from a research team that includes doctors and other health professionals. However, clinical trials may also involve risks of varying degrees, such as unpleasant, serious, or even life-threatening side effects from the treatment being studied.11

Your health care provider can help you decide whether participating in a clinical trial is right for you. For more information, visit NIH Clinical Research Trials and You.



1. United States National Library of Medicine. ChemIDplus Advanced. Last accessed on March 13, 2014.

2. National Institute of Allergy and Infectious Diseases (NIAID). NIAID ChemDB, HIV Drugs in Development. Last accessed on March 13, 2014.

3. Pirrone V, Wigdahl B, Krebs FC. The rise and fall of polyanionic inhibitors of the human immunodeficiency virus type 1. Antiviral Res. 2011 Jun;90(3):168-82. Last accessed on March 13, 2014.

4. The Population Council, Inc.: News Release, dated February 18, 2008. Trial Shows Anti-HIV Microbicide Is Safe, but Does Not Prove It Effective. Last accessed on March 13, 2014.

5. National Institute of Allergy and Infectious Diseases (NIAID). Topical Microbicides. Last accessed on March 13, 2014.

6. Shattock RJ, Rosenberg Z. Microbicides: Topical Prevention against HIV. Cold Spring Harb Perspect Med. 2012 Feb;2(2):a007385. Last accessed on March 13, 2014.

7. Cranage M, Sharpe S, Herrera C, et al. Prevention of SIV Rectal Transmission and Priming of T cell Responses in Macaques after Local Pre-Exposure Application of Tenofovir Gel. PLoS Med. 2008 Aug 5;5(8):e157; discussion e157. Last accessed on March 13, 2014.

8. International Partnership for Microbicides (IPM) website. Glossary: Polyanion. Last accessed on March 13, 2014.

9. Garg AB, Nuttall J, Romano J. The future of HIV microbicides: challenges and opportunities. Antivir Chem Chemother. 2009;19(4):143-50. Last accessed on March 13, 2014.

10. Skoler-Karpoff S, Ramjee G, Ahmed K, et al. Efficacy of Carraguard for prevention of HIV infection in women in South Africa: a randomised, double-blind, placebo-controlled trial. Lancet. 2008 Dec 6;372(9654):1977-87. Last accessed on March 13, 2014.

11. National Institutes of Health (NIH). NIH Clinical Research Trials and You. Last accessed on March 13, 2014.

12. The Population Council, Inc. Phase III Study of the Efficacy and Safety of the Microbicide Carraguard in Preventing HIV Seroconversion in Women (Population Council Protocol 322): Summary. Last accessed on March 13, 2014.


Last Reviewed: March 13, 2014

Last Updated: April 25, 2014

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