Pemirolast

A mast cell initiating an allergic reaction. Source: Wikimedia Commons

Other Names

Pemirolast is sold under the name Alamast. It is made by Santen and marketed by Vistakon Pharmaceuticals.

Uses/Indications

Pemirolast is used to soothe the itchy eyes associated with allergies. It is not used to treat eyes that have been irritated by contact lenses.

How Pemirolast is Taken

Pemirolast is available as a 10-ml solution of 0.1% of pemirolast, the active ingredient. One to two drops are instilled (applied) into the eye four times a day during allergy season. The drops are squeezed out into the sac below the eye.

How Pemirolast Works

Allergic reactions are caused by the release of histamine and proteins from mast cells. Pemirolast is a mast cell stabilizer. It prevents the release of histamine and the other cellular products that promote allergic reactions. The cellular mechanism underlying these effects is not clear, but it may be related to the prevention of calcium entry into the cells. Pemirolast also reduces the number of cells recruited into the eye to promote the allergic reaction.

How the Body Affects Pemirolast

Even though pemirolast is instilled in the eye, a very small amount is released into the circulation. The half-life of pemirolast, the time required for the concentration of the drug to be reduced by half, is approximately 4.5 hours. The metabolism of pemirolast is not clear, and 10%-15% of Alamast is excreted unchanged in the urine.

Side Effects

Side effects of pemirolast are generally mild. Some studies suggest that it is better tolerated than other eye drops for soothing irritated eyes. Some common side effects associated with pemirolast use include the following:

• Headache
• Cold or flu-like symptoms
• Rhinitis (stuffy nose)
• Burning sensation in the eye immediately following instillation

Risks and Precautions

Pemirolast is not used in red eyes that are covered by contact lenses. It is not used to treat irritation due to contact lenses. Contact lenses should be removed before using pemirolast because a preservative used in the eye drops can be absorbed into soft contact lenses. The lenses can be placed into the eye approximately 10 minutes after using pemirolast.

Administration of very high concentrations of pemirolast causes birth defects in test animals. The effects during pregnancy in humans, however, are not known. Accordingly, pemirolast is only used during pregnancy if the benefits justify the risk. Whether pemirolast crosses into breast milk is not known.

Research

Pemirolast has been reported to reduce itching within a few days. However, sometimes it takes up to four weeks before the benefits of pemirolast are seen. An analysis of two clinical trials found that the number of days without itchy eyes was lower in the patients given pemirolast compared to those given a placebo.^[1] In a study comparing pemirolast with another mast cell stabilizer, nedocromil, 58% of pemirolast-treated and 28% of nedocromil-treated patients experienced symptoms of allergies at work or school.^[2] In addition, the volunteers receiving pemirolast reported fewer eye-related side effects, such as burning.

External Links

Vistakon: Alamast Main Page

EyeUpdate.com: Ocular Allergy Treatment

References

1. ↑ Abelson MB, Berdy GJ, Mundorf T, Amdahl LD, Graves AL; Pemirolast study group. Pemirolast potassium 0.1% ophthalmic solution is an effective treatment for allergic conjunctivitis: a pooled analysis of two prospective, randomized, double-masked, placebo-controlled, phase III studies. J Ocul Pharmacol Ther 2002 Oct;18(5):475-88. Abstract
2. ↑ Shulman DG. Two mast cell stabilizers, pemirolast potassium 0.1% and nedocromil sodium 2%, in the treatment of seasonal allergic conjunctivitis: a comparative study. Adv Ther 2003 Jan-Feb;20(1):31-40. Abstract