| Summary: | 碩士 === 慈濟大學 === 藥理暨毒理學研究所 === 96 === In a recent national sport competition in Taiwan, our laboratory found several positive cases on mephentermine and phentermine. One of the athletes claimed that medications had been taken for treating stomach pain prior to the game and the medications were presented to the doping control authority. Results of laboratory investigation found that Stoin was contained in one of the medications administered by the athlete. Stoin contains oxethazaine and has been used clinically as a topical anesthetic. Oxethazaine may convert to mephentermine and phentermine by the body’s metabolism. These drugs are prohibited in sports by the World Anti-Doping Agency.
Excretion studies were carried out on five healthy volunteers who orally consumed oxethazaine (5 mg), mephentermine (10 mg) and phentermine (10 mg) at different times with one week apart. Urine samples were collected at various times and analyzed using gas chromatography-mass spectrometry (GC-MS). The results were as follows: (1) The mass spectrum of mephentermine showed a base peak of m/z 168 with characteristic ions at m/z 110 and 91; phentermine showed a base peak of m/z 154 with characteristic ions at m/z 132 and 91. (2) The metabolic profiles showed that the concentrations of mephentermine and phentermine reached a peak between 2 hr to 24 hr when mephentermine was ingested and between 2 hr to 12 hr when oxethazaine was administrated. (3) The metabolic profiles revealed that the concentrations of phentermine reached a peak at approximately 24 hr, between 2 hr to 12 hr and between 2 hr to 24 hr following administration of mephentermine, oxethazaine and phentermine, respectively. (4) The cumulative amount of mephentermine metabolite (mean±S.D. = 9.3±4.9 mg) in urine was greater than that in phentermine (mean±S.D. = 2.7±2.1 mg), when mephentermine was administrated. However, this relationship was reversed with phentermine (mean±S.D. = 1.2±0.8 mg) greater than mephentermine (mean±S.D. = 0.5±0.3 mg), when oxethazaine was administrated. (5) When phentermine was ingested, only the unchanged parent drug was found in the urine. (6) According to this investigation, it was very likely that the athletes had taken oxethazaine-contained medication prior to the competitions.
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