The combination abuse of MDMA and methamphetamine changed the kinetics of drugs (e.g. MDMA) in brain, and the releases of monoamines such as dopamine increasingly. Thereby, the influences of the drugs on brain caused by MDMA with methamphetamine seemed to be more serious than when a sole administration of MDMA.
3,4-Methylenedioxymethamphetamine (MDMA) and methamphetamine often cause serious adverse effects (e.g., rhabdomyolysis, and cardiac disease) following hyperthermia triggered by release of brain monoamines such as dopamine and serotonin. Therefore, evaluation of brain monoamine concentrations is useful to predict these drugs’ risks in human. This study aimed to evaluate risks of co-administration of MDMA and methamphetamine, both of which are abused frequently in Japan, based on drug distribution and monoamine level in the rat brain. Rats were allocated to three groups: (1) sole MDMA administration (12 or 25 mg/kg, intraperitoneally), (2) sole methamphetamine administration (10 mg/kg, intraperitoneally) and (3) co-administration of MDMA (12 mg/kg, intraperitoneally) and methamphetamine (10 mg/kg, intraperitoneally). We monitored pharmacokinetic and pharmacodynamic variables for drugs and monoamines in the rat brain. Area under the curve for concentration vs. time until 600 min from drug administration (AUC0–600) increased from 348.0 to 689.8 μg min/L for MDMA and from 29.9 to 243.4 μM min for dopamine in response to co-administration of methamphetamine and MDMA compared to sole MDMA (12 mg/kg) administration. After sole methamphetamine or that with MDMA administration, AUC0–600 of methamphetamine were 401.8 and 671.1 μg min/L, and AUC0–600 of dopamine were 159.9 and 243.4 μM min. In conclusion, the brain had greater exposure to MDMA, methamphetamine and dopamine after co-administration of MDMA and methamphetamine than when these two drugs were given alone. This suggests co-administration of MDMA with methamphetamine confers greater risk than sole administration, and that adverse events of MDMA ingestion may increase when methamphetamine is co-administered.