AstraZeneca (NYSE:AZN) went over a small patent cliff, but its competitors were nice enough to throw it some climbing gear. The company registered a pretty solid quarter thanks to the help, but be careful, Fools -- that rope isn't looking too secure.

Revenue was up 9% year over year at constant currencies, but three points of that came from the growth of heart drug Toprol XL. Both Novartis (NYSE:NVS) and KV Pharmaceutical stopped selling generic versions of the drug because of production issues.

It's a nice bonus for AstraZeneca, but it won't last forever. Novartis is supposed to have its plant inspected by the Food and Drug Administration this quarter, but it isn't saying exactly when it'll resume shipping the product. KV Pharmaceutical's problems are pretty severe and the timeline for the FDA giving it the green light remains unclear.

AstraZeneca also benefited from Mylan (NASDAQ:MYL) not launching its generic version of prostate cancer drug Casodex in the second quarter as expected. Mylan started shipping the drug this month, so sales of Casodex will start falling beginning this quarter.

Other than those issues to watch out for in the coming quarters, AstraZeneca looks pretty strong. Crestor, its cholesterol drug, had an outstanding quarter, with sales up 33% at constant currencies. U.S. prescriptions for the drug are growing faster than the overall statin market, suggesting that doctors taking patients off Merck's (NYSE:MRK) and Schering-Plough's (NYSE:SGP) Vytorin are probably favoring Crestor over Pfizer's (NYSE:PFE) Lipitor.

The company could have more good news about its growth prospects fairly soon. Today is the PDUFA date for its diabetes drug Onglyza, which it'll sell with Bristol-Myers Squibb (NYSE:BMY). I'm not convinced that Onglyza, which is fairly similar to Merck's Januvia, will be able to capture much of the diabetes market, but as AstraZeneca knows, every little bit helps -- even when it's help from a competitor.

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Pfizer is a Motley Fool Inside Value recommendation. Novartis is a Global Gains selection. Try any of our Foolish newsletters today, free for 30 days.

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.