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By Tan Ee Lyn

HONG KONG, June 1 (Reuters) - Hong Kong doctors are over prescribing a slimming drug to women desperate to lose weight, pharmacists said on Friday, warning its misuse could increase the risk of stroke.

The generic drug phentermine, an appetite suppressant that acts on the central nervous system, has a chemical structure similar to that of the stimulant amphetamine and causes side effects including high blood pressure, palpitations and insomnia.

The U.S. FDA approves phentermine only for people who are obese, or with a Body Mass Index (BMI) of 30 and over. It must also be accompanied by exercise and proper diet control.

Pharmacists in Hong Kong say some family doctors have been loosely prescribing phentermine since 2004, even to women who obviously do not need to lose weight.

Phentermine is prescribed two times more than a close alternative, sibutramine, which is patented and costlier, but which is considered safer and has fewer side-effects, according to the Society of Hospital Pharmacists of Hong Kong.

"We found out that family doctors are prescribing phentermine irrationally. It's moving in the direction of abuse," said William Chui, education director at the society.

The society said between 6,000 and 10,000 people on average were using phentermine, now off patent after first being approved by the FDA in 1959, in Hong Kong each day.

To fight the side-effects, some doctors prescribe other drugs to lower blood pressure and heart rate and help patients sleep.

"Many doctors prescribe phentermine and then long-acting sleeping pills to fix the symptoms. Such sleeping pills can result in dependency. That's unethical, especially when patients know nothing about drugs," Chui said.

"They also prescribe anti-hypertensive drugs to lower blood pressure which has been raised by the phentermine."

SIDE -EFFECTS

Chui warned of dire consequences.

"Phentermine affects blood pressure and heart rate. If you have potential cardiovascular disease, it will worsen your condition. It can worsen your arrhythmia, and if your blood pressure increases, you can suffer from a stroke," he said.

This practice came to light in 2004 when patients turned up in government hospitals complaining of various side-effects.

Twelve people were admitted to hospital in the past year and some of them needed emergency treatment. In one instance, a woman was found to have been prescribed both phentermine and sibutramine.

"When this is done, it could have very severe side-effects, including death," Benjamin Kwong, president of the Pharmaceutical Society of Hong Kong, told a news conference.

Sibutramine is known by its brand, Reductil. Phentermine is off-patent and costs a fraction of the patented sibutramine.

Phentermine was part of a weight loss drug combo known as "fen-phen" (fenfluramine and phentermine) which was wildly popular during a diet craze in the United States in the 1990s.

But the Food and Drug Administration banned fenfluramine, and a related drug, dexfenfluramine, in 1997 after studies linked them to heart valve damage. Fenfluramine and dexfenfluramine were made by Wyeth <WYE.N>, which continues to be hounded by liability claims. Phentermine remains on the market.

The slimming craze has taken Asia by storm over the last decade. Classified as health products, many brands of diet pills and teas -- some containing controlled substances -- are readily available in supermarkets in the region and on the Internet.

Chui said doctors prescribe more phentermine because it's cheaper and gives faster results.

"GPs don't prescribe sibutramine because phentermine's response is very quick. You can reduce up to 6 kg in 2-3 weeks. But Reductil cuts 2-4 kg in 1-2 months. That's a huge difference. When you have quick fixes, you attract business," he said.

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