Bristol-Myers Squibb said it has recalled 64 million tablets of the blood pressure medicine Avalide in the United States and Puerto Rico due to the potential for reduced effectiveness.

The move, which Bristol-Myers said was undertaken as a precautionary measure, marked the second major recall in less than four months of the medicine co-marketed with French drugmaker Sanofi-Aventis.

In September, Bristol-Myers recalled 62 lots, or 60 million tablets, of the drug manufactured in Puerto Rico. The new recall involved 65 lots of Avalide manufactured in plants in Humacal, Puerto Rico and Evansville, Indiana, the company said.

Avalide is a combination pill comprised of the drugs irbesartan, which is sold under the brand name Avapro, and hydrochlorothiazide, a generic diuretic.

The recall was not announced publicly but communicated via letters to wholesalers and healthcare professionals, Bristol-Myers said.

Reuters first learned of the recall from a doctor.

The problem detected was the same that led to the previous recall, a potential variability in levels of the less-soluble form of the active ingredient irbesartan.

As with the September recall, the problem suggests the possibility of reduced efficacy, although the company has not turned up evidence of reduced effectiveness, nor have there been any reports of safety problems or patient harm, Bristol-Myers spokeswoman, Christina Trank said.

The affected Avalide doses were 150/12.5 milligrams, 300/12.5 mg, 300/25 mg and blister sample packs of 300/25 mg. The first number represents the irbesartan dose.

The recall did not involve stand-alone Avapro, the company said.

For the first nine months of 2010, Bristol-Myers reported combined worldwide sales of Avalide and Avapro of $924 million.

Since the September recall, Trank said the company had developed more sensitive testing methods to detect a less soluble form of the active ingredient and the new testing revealed the need for a further recall.

Patients who have purchased Avalide from the recalled lots can contact their prescribing doctor, pharmacy or Bristol-Myers customer relations, Trank said.