AstraZeneca Plc (AZN) has lifted allocation limits for blood-pressure medicine Toprol XL that were put in place to ensure supply of the drug after problems at two generic drug makers caused a shortage that began late last year.

The shortage has become a windfall for the London-based drug giant, which has ramped up production enough to alleviate any supply concerns about both the branded version and an authorized generic it makes for Par Pharmaceutical Cos. (PRX). All versions and dosages are now available in all quantities, the U.S. Food and Drug Administration said Friday.

"Anybody who may have had trouble getting the product should be able to find it at their local pharmacy," said AstraZeneca spokesman Blair Hains.

The drug was once a big U.S. seller for AstraZeneca, bringing in sales of $1.4 billion in 2006, the last year before it went generic. But the shortage has reinvigorated sales.

For the three months ended March 31, sales of Toprol XL rose to $176 million, compared to $295 million for all of 2008.

Since November, sales of branded Toprol have more than tripled - from about 51,000 total weekly prescriptions in early November to about 162,000 as of the end of April, according to SDI, a drug-data research firm.

Sales of a generic version, called metoprolol succinate, have consistently dropped in that same period - falling to about 428,000 prescriptions a week from 812,000 in November.

But 98% of that market is the AstraZeneca-authorized generic that previously had only a third of generic sales.

Total prescriptions of both versions have dropped 32% since early November, as patients likely sought alternatives in order to ensure they could get the medicine. 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.

Regardless, AstraZeneca is clearly benefiting from the shortage and there is no sign of when other suppliers will return to the market.

Last year, Sandoz, the generic unit of Novartis AG (NVS), recalled six million bottles of generic Toprol XL after the FDA 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 in January and recalled most products already on the market, including Toprol, as it deals with an FDA investigation.

"Sandoz continues to work with the U.S. FDA on our remediation efforts for our Wilson, North Carolina, facility and believes that we are on schedule to meet all the commitments made to FDA. At this stage, we cannot comment on our plans to reintroduce metoprolol succinate to market," a Sandoz spokeswoman said in a statement.

Watson Pharmaceuticals Inc. (WPI) has an application pending with the FDA on its own generic version of Toprol. During a recent conference call, the company wouldn't speculate on the timeline for approval, but said it is preparing to launch the drug.

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