U.S. regulators have granted approval for the drug Ranexa in the treatment of chronic angina.

Angina causes chest pain because of an insufficient supply of oxygen to the heart.

The Food and Drug Administration (FDA) has approved Ranexa for patients for whom other anti-anginal drugs have not been effective, and has recommended it be used in combination with other treatments, such as beta blockers or nitrates.

According to the drug company CV Therapeutics, they were concerned that the FDA might approve the drug for an even more restricted group of patients.

It is estimated that of the 6.4 million Americans with chronic angina, 25% have become resistant to existing drugs, so the company stands to do well with Ranexa.

The drug should be available in pharmacies in late March, and will be the first drug developed in-house by the California-based biotechnology company to reach the market, and will give patients access to a new angina therapy for the first time in years.

Approval for Ranexa has suffered from long delays because of safety issues and the company is apparently conducting a 6,500-patient study of the drug as a treatment for acute coronary syndrome.

Positive results from that study, due late this year or early 2007, may be used to apply for FDA approval for Ranexa as a first-line therapy for angina.

Acute coronary syndrome occurs when a plaque inside a coronary artery suddenly ruptures and blocks blood flow to the heart muscle.