The Food and Drug Administration said that an analysis of many studies on cholesterol-lowering drugs known as statins, have not shown any increase of amyotrophic lateral sclerosis, or ALS, a condition also known as Lou Gehrig's disease.

According to IMS Health, a health-care information company, cholesterol-lowering drugs are the top-selling class of drugs in terms of overall sales, with more than 220 million prescriptions written in the U.S. last year. These include Pfizer Inc.'s (PFE) Lipitor, AstraZeneca PLC's (AZN) Crestor, and Merck & Co.'s (MRK) Zocor sold generically as simvastatin , and Bristol-Myers Squibb Co's Pravachol, available generically as pravastatin.

A review of 41 long-term controlled clinical trials were conducted after the FDA received numerous reports of Lou Gehrig's disease in patients who were treated with statins. The researchers found that during long term clinical trials, out of 64,000 patients who were treated with statins only nine were diagnosed with the fatal neurodegenerative disease, ALS. The figures for the placebo group were 10 out of 56,000 said the report published Monday in the journal Pharmacoepidemiology and Drug Safety.

"The results show no increased incidence of the disease in patients treated with a statin compared with placebo," an FDA statement said.

The FDA estimates one to two people per 100,000 suffer from ALS, a neurological disease involving nerve cells that control muscles and affects a person's ability to move, talk, eat and breathe, that is eventually fatal.

Mark Avigan, a director in the FDA's pharmacovigilance division said, "While the FDA finds the lack of an increase in the incidence of amyotrophic lateral sclerosis (ALS) in patients treated with statins in clinical trials reassuring, given the extensive use of this class of drugs and the serious nature of ALS, continued study of this issue is warranted."

The FDA said results from another study by researchers at Stanford University and the health insurer Kaiser Permanente should be available in six to nine months, and added they were also considering additional studies of their own.

Donna Huang spokeswoman for AstraZeneca said upwards of 13 million patients worldwide have been prescribed the drug, she said and the company's own monitoring and reviews of medical literature "has not identified a causal relationship between ALS and the use of Crestor."