AstraZeneca (AZN) has effectively filled the supply gap following a shortage in the generic version of its blood pressure medicine Toprol XL after two drug makers stopped supplying the drug in recent months.

The London-based drug giant says it has ramped up production of both the branded version and an authorized generic it makes for Par Pharmaceutical Cos. (PRX). The drug was once a big U.S. seller for AstraZeneca, but sales have plummeted since it went generic in 2007. The company's U.S. sales of Toprol dropped to $295 million in 2008 after hitting $1.4 billion in 2006.

An AstraZeneca spokesman acknowledged that the increased sales of the drug will have a positive business benefit, but declined to elaborate. Toprol is not a high-priced product, with an average cost of about $33 a month for the branded version.

Last year, Sandoz, the generic unit of Novartis AG (NVS), recalled 6 million bottles of generic Toprol XL after the Food and Drug Administration sent a warning letter about the factory in North Carolina that makes the pills.

Another supplier of the drug, K-V Pharmaceutical Co. (KVA, KVB), stopped manufacturing and shipping all of its products last month and recalled most products already on the market, including Toprol, as it deals with an FDA investigation.

Since November, sales of branded Toprol have almost doubled - from about 51,000 total prescriptions a week in early November to about 124,000, according to Verispan, a drug-data research firm.

Sales of a generic version have dropped to 616,000 prescriptions from 812,000 in the same timeline, but that market is now dominated by the AstraZeneca-authorized generic that previously had a third of generic sales.

Total prescriptions of both versions have dropped 14% since early November, as patients likely sought alternatives. Toprol contains a warning from the FDA about the dangers of abruptly stopping treatment, so patients who couldn't find the medicine would need to switch treatments.

The AstraZeneca spokesman said that its product is now in the distribution pipeline and any current shortages of the drug should be short-lived.

The company is allocating its supply to customers to order to ensure that there is enough of the drug. The move could result in smaller volume shipments for the time being, he said.

AstraZeneca said it is in contact with the FDA about supplying the drug to the public, but it has no contact with the generic companies and doesn't know when more supply could come on the market.

Officials from Sandoz weren't immediately available for comment.

Watson Pharmaceuticals Inc. (WPI) has an application pending with the FDA on its own generic version of Toprol.

-By Thomas Gryta, Dow Jones Newswires; 201-938-2053; thomas.gryta@dowjones.com