Advice issued by the Australian Advisory Committee on Medicines. Thiopurines (azathioprine, mercaptopurine, tioguanine) People with a deficiency in the thiopurine methyltransferase (TPMT) gene have greater susceptible to serious thiopurine toxicities (myelosuppression and luekopenia). However, after considering the evidence to hand carefully, it was decided that there is little evidence to suggest that genetic testing (to determine TPMT status reduces toxicity in practice at the population level, and that routine/mandatory testing was not recommended.
The committee also considered another critical safety issue, this time relating to gabapentinoid drugs (gabapentin, pregabalin, topiramate). The committee noted a significant extent of off-label use, and that a safety signal for harmful and hazardous had been detected. The issues include development of tolerance, using higher doses than prescribed, drug-seeking behaviour and intentional and accidental poisonings.