The Advertising Standards Authority has rejected a complaint that pharmaceutical giant Bayer has been trying to disparage generic drugs and create doubts about their safety.

It said a statement in Bayer advertorial that there were "questions" about nifedipine's bioequivalence were factual and in the public interest.

Nifedipine, sold under the brand names Adalat, Nifedical, and Procardia, is used for treating chest pain resulting from coronary artery spasm.

The complaint was lodged by the National Association of Pharmaceutical Manufacturers (NAPM) over an article in the March 2008 edition of the Medical Chronicle.

The advertorial said generic drugs were supposed to demonstrate bioequivalence with their brand name counterparts, and health care professionals therefore assumed that these products were interchangeable.

It said new studies however raised questions about the bioequivalence of generic nifedipine products, and that at least two generics tested were not able to prove bioequivalence.

Bioequivalence means that before a generic drug can be sold, the manufacturer must prove that it has the same strength as the brand name medication, and affects people the same way within the same time frame.

If a generic passes these tests, it is said to be bioequivalent to the original brand name drug.

The NAPM complained Bayer had misrepresented facts and that the "questions" did not apply to the South African market, as the studies related to testing in Europe on European products, which were neither registered nor marketed in South Africa.

In response, Bayer submitted an opinion from Prof Brian Rayner of the University of Cape Town's department of medicine, who said there was no record of anything published in the medical literature in South Africa on nifedipine.

"In the absence of local information we have to use information published elsewhere," he wrote.

"These papers were both published in prestigious, peer-reviewed international journals."

The advertorial, he said, was neither dishonest nor misleading.

The ASA said it was satisfied Rayner's comments adequately supported the claims made in the advertorial.