Famprofazone use can be misinterpreted as methamphetamine abuse.

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.

Famprofazone as the source of methamphetamine and amphetamine in urine specimen collected during sport competition.

During a sport competition event in Taiwan, one urine specimen was found positive for both methamphetamine (2688 ng/mL) and amphetamine (462 ng/mL). The specimen donor claimed that she had taken Gewolen (a nonprescription drug manufactured in Taiwan) for treating abdominal pain and the medication was presented. Laboratory investigation confirmed that Gewolen contains famprofazone, which is known to metabolize to methamphetamine and amphetamine and is included in the prohibited list of the World Anti-Doping Agency. Study on the excretion profiles of three volunteers ingesting 50 mg famprofazone produced the following patterns similar to that observed in the case specimen: (a) the ratio of methamphetamine to amphetamine was approximately 6 to 1; (b) d- and l-enantiomers of both methamphetamine and amphetamine were present, while the amount of l-methamphetamine was 3-4-fold greater than its counterpart. The data suggested that famprofazone (as the ingredient of Gewolen) was likely the source of the prohibited drugs found in the case specimen.