A TANG Shiu Kin Hospital doctor slipped into a coma and died after swallowing a lethal mixture of drugs, her brother said yesterday. Medical sources said a post-mortem examination on 28-year-old Dr Amy Kwok Shuk-wa had shown traces of methadone, codeine and other restricted drugs. ''Maybe a mixture of medicines caused her death,'' Herby Kwok, 26, said. Mr Kwok was speaking publicly for the first time on the death last year of his elder sister, a Chinese University graduate in medicine and surgery. Dr Kwok, who lived with her parents and brother in their Wong Tai Sin flat, graduated in 1990 and had worked at Tang Shiu Kin in Wan Chai since early 1992. ''Our family was just informed that it was an overdose of medicine. We're not exactly sure what it was,'' Mr Kwok said. He said his sister had returned home after finishing her usual daytime shift at Tang Shiu Kin. She fell asleep and ''everything seemed normal'' until the family discovered she had fallen into a coma the next morning. ''We rushed her to the [Queen Elizabeth] hospital and she died there,'' he said. Queen Elizabeth Hospital chief executive, Dr York Chow, confirmed Dr Kwok had died in the intensive care unit after failing to regain consciousness. Mr Kwok said the family was trying to push aside unanswered questions about his sister's death. ''It's upsetting and depressing to push ahead to find out,'' he said. ''I'm sceptical about the [overdose], but I can't explain it.'' Hospital Authority spokesman Dr Lawrence Lai said Dr Kwok worked as a medical officer at Tang Shiu Kin up until her death.