Famprofazone, a major ingredient of Gewolen, is an analgesic that has been demonstrated to be metabolized to methamphetamine (MA) and amphetamine (AM) following administration. Therefore, a famprofazone user may be interpreted as an illicit MA abuser in Taiwan because the user's urine tested positive for MA. The purpose of this study was to investigate whether the concentration of MA metabolized from a single dose of Gewolen users would offend the official controlled substance regulation and be identified as MA-positive. Subjects (n = 6) received 25 mg of famprofazone and collected all urine specimens at certain timed intervals for 48 h after drug administration. The urine specimens were screened by immunoassay and then confirmed by gas chromatography-mass spectrometry (GC-MS). The highest concentration of amphetamines by immunoassay was 1954 ng/mL, and 18.8% of the urine specimens' amphetamines concentrations exceeded 500 ng/mL. The MA and AM concentrations by GC-MS analysis of these urine specimens ranged from 901 to 2670 ng/mL and 208 to 711 ng/mL, respectively. These urine specimens were interpreted as MA-positive (>or= 500 ng/mL MA and >or= 100 ng/mL AM), according to the official test methods of Taiwan. The MA positive results appeared within 2-34 h. It is therefore clearly possible to misinterpret the legitimate famprofazone user as an MA abuser in Taiwan.

No abstract