A NEW drug may bring relief to hundreds of Hong Kong men who are suffering prostate trouble. The drug, called Proscar, is the first to address the root cause of benign prostate hyperplasia (BPH), a condition in which the prostate gland enlarges, squeezing the urethra and eventually hindering the flow of urine. The condition is a symptom of ageing and affects half of all men over 60. European studies show that a quarter of men who live to the age of 80 are likely to undergo surgery for BPH. According to Dr John Trachtenberg, director of the Prostate Centre of Toronto Hospital, Canada, many of these men suffered symptoms that bothered them so much that their lives were badly affected. Symptoms included anything from having to get up to go to the toilet four or five times a night to incontinence. Some men actually became reclusive because they were so embarrassed by the problem. In about five per cent of cases the condition was so severe that sufferers could not urinate at all or developed kidney problems. Dr Trachtenberg, who is in Hong Kong for a symposium on the issue, said surgery to correct BPH cost the United States more than US$3 billion (HK$23.23 billion) each year - and was the single biggest item in the 1992 Medicare budget. While there were no figures for the number of sufferers in Hong Kong, about 255 of the 5,000 operations performed at Princess Margaret Hospital each year were for BPH, according to its chief of services, Dr Chan Yau-tung. Proscar works by suppressing the hormone which causes the prostate to swell. A three-year study of 1,645 men in North America and Europe found that a five milligram pill each day relieved symptoms in 60 per cent of men. The prostate gland shrank by an average of 27 per cent in all patients, while 40 per cent of patients said their urine flow rate increased by one-third. Dr Trachtenberg said the results were ''statistically better'' than the one-year placebo trial - although about 50 per cent of this group also claimed their symptoms were relieved. However, he said all studies on BPH showed a strong initial placebo effect that declined over time. A year's supply of Proscar, which is manufactured by Merck Sharp & Dohme, costs about $4,000.