HPLC-ED-MEPS analysis of methadone in dried blood spots after microwave-assisted extraction

Opioid replacement therapy with long-acting opioids is the most effective approach to counteract heroin dependence, a worldwide health and social problem affecting the lives of millions of people. Since its introduction in the 1960s, methadone ((RS)-6-(dimethylamino)-4,4-diphenylheptan-3-one, MTD), a synthetic full µ-opioid receptor agonist, has been the treatment of choice for opioid addiction. However the outcome of the pharmacological therapy with MTD is highly variable depending on different factors, such as individual metabolism. Thus, it is important to accurately determine blood levels of MTD to optimize the dosage in the patient and to monitor possible abuse of the drug. Nowadays, clinical laboratories are constantly confronted with the increasing demand for higher sample throughput, thus shorter analysis times; it is advisable to have at disposal high-sensitivity and low-cost methods to determine blood levels of MTD in heroin addicted patients. A rapid isocratic reversed-phase high-performance liquid chromatographic method (RP-HPLC) with coulometric detection has been developed for the determination of MTD in dried blood spot (DBS) and human plasma samples. Furthermore the aim of this study was to evaluate the reliability of dried blood spot specimens in the determination of MTD levels in whole blood from heroin addicted patients. Advantages of DBS technique include short collection time, low invasiveness, ease and low cost of sample collection, transport and storage. The clean-up of DBS was performed by means of an original MEPS (microextraction by packed sorbent) procedure after a microwave-assisted extraction of the drug with acetonitrile. Promising results were obtained in terms of extraction yield and sensitivity. Assays are in progress in order to completely validate the method.