A doctor wrongly prescribed a diabetes drug to three patients - a potentially fatal error that put two of the patients in hospital. The Health Department said initial inquiries showed that the error was caused by a faulty blood glucose meter. The doctor was named as Li Ming who has a clinic in Luen Wo Hui, Fanling. The incident was revealed by William Chui Chun-ming, the Society of Hospital Pharmacists president, after the Poison Information Centre issued a poison alert to healthcare professionals. Chui, who said the Health Department should have made the incident known as other people may have been affected, said: "We call on patients who have visited this clinic and their family members to check what medications they were prescribed." Warning signs include dizziness or patients may fall unconscious. Misuse of diabetes medications - in this case Gliclazide which lowers blood sugar levels - could even cause death, he said. Blood sugar meters were intended for use by diabetics to monitor blood sugar levels and were not meant to be used by doctors for diagnosis instead of blood tests, added Chui. Li said last night that he had used an old meter after the batteries on his usual meter died. "I was misled by the machine. I express my deepest apologies," said Li, a doctor for 20 years. He admitted blood tests offered a more accurate diagnosis but the patients involved had a record of high blood glucose levels and were showing similar symptoms; he wanted to prescribe medication that day. He has since bought a new machine. The two patients hospitalised over the Easter weekend were aged 72 and 85. Both are said to be in stable conditions. The third patient did not take the drug.