Pharmacokinetic parameters, safety and drug-drug interactions of mirtazapine and tizanidine, combined in the new original drug Dorsumio®

Objective: to study the pharmacokinetic parameters and safety of Dorsumio® (mirtazapine + tizanidine, extended-release tablets, 15 mg + 6 mg, JSC Valenta Pharm, Russia) taken once by healthy volunteers in comparison with Calixta®, a monocomponent drug (INN: Mirtazapine, filmcoated tablets, 30 mg, Belupo, Drugs and Cosmetics d.d., Republic of Croatia) and Sirdalud® MR (INN: Tizanidine, modified-release capsules, 6 mg, Novartis Pharma AG, Switzerland) with an evaluation of their drug interactions when taken concomitantly or separately.Material and methods. A two-stage, randomized, comparative cross-over study of the pharmacokinetics and safety of the complex drug Dorsumio® was conducted. In the first stage, volunteers alternated between taking one or two tablets of the study drug in two administration periods; in the second stage, subjects alternated between taking the reference monodrugs Calixta® and Sirdalud® MR alone and in a joint combination in three administration periods. A total of 38 volunteers were randomized into the study, of which 14 subjects participated in the first and 24 in the second stage of the study. Quantitative levels of mirtazapine and tizanidine were determined by high-performance liquid chromatography with tandem mass spectrometry. Based on the data obtained, the main pharmacokinetic parameters reflecting the bioavailability of each drug were calculated, and the mutual influence of their combination on pharmacokinetics was also studied. During the study, vital signs and laboratory parameters of the subjects were monitored, and the occurrence of adverse events (AEs) and serious AEs was recorded.Results. A two-fold increase in the dose of the combination drug Dorsumio® resulted in a comparable increase in the pharmacokinetics of the individual drugs. There was no significant reciprocal effect of mirtazapine and tizanidine on their pharmacokinetic parameters. In one of the subjects participating in the second stage of the study, two mild side effects were registered after the joint use of Calixta® and Sirdalud® MR that did not require medical intervention and resolved on their own without health consequences.Conclusion. There were no differences in the safety profile of the combined use of mirtazapine and tizanidine in the form of a free or fixed combination. It was shown that the investigated drug combination had no mutual influence on the pharmacokinetics of the individual components.