Experimental comparing of lipophilicity of opioid antagonists

Introduction. The high lipophilicity of synthetic opioids determines their abnormally high toxicity in comparison with natural opiates. The need to develop medical treatment of poisoning with such substances validates the task to study experimentally the logP partition coefficients of narcotic analgesics and their antagonists in standardized conditions close to the conditions of a living organism. Material and methods. The lipophilicity of pharmacological agents was determined in accordance with the principles of GOST 32474-2013. “Methods of testing chemical products that pose a threat to the environment. The determination of the n-octanol/water partition coefficient by high-performance liquid chromatography”, using the selected calibration dependence of the lipophilicity values on the logarithm of the retention factor of the substances studied. Results. The HPLC method has been proposed to determine the logP value of opioid antagonists using selected reference pharmacological agents. The method has revealed a linear dependence of the logP of CNS-active pharmacological agents on the logarithm of their retention factor in the chromatographic column, which allowed to determine the logP value of a number of opioid receptor antagonists and a model representative of synthetic opioids in one experiment. Limitations. The calibration dependence of the lipophilicity value on the logarithm of the retention factor of the studied substances has been obtained using reference logP values of a limited number of reference substances. Conclusion. When conducting pharmacological studies, using the HPLC method for the definition of logP provides high reproducibility of measurement conditions close to the conditions of a living organism and allows to compare the results obtained. Thus, the correlation of the logP values, found by the HPLC method, has showed a ten times lower lipophilicity of naloxone relative to fentanyl. The largest value of logP, among the studied opioid receptor antagonists used in clinical practice, was found for nalmefene.