Pharmacokinetics And Relative Bioavailability Of Lorazepam In Healthy Volunteers

Objective Lorazepam belongs to benzodiazepine drug, which is used clinically as ananxiolytic, as a treatment for status epilepticus, preoperatively, and as an adjunct for nausea management. It is difficult to determinate concentration of lorazepam in human plasma for low dose and low concentration. The present study was performed with the goal of investigation in particular the pharmacokinetics of lorazepam injection and bioavailability of lorazepam tablets.Methods1. Volunteers and study designNine healthy Chinese volunteers (4 male and 5 female) were given a single intramuscular dose (4mg) of the lorazepam injection. A single oral dose (3mg) of the standard formulation and the tested formulation were respectively given to other 18 volunteers in randomized cross-over test. Informed consent was obtained from the subjects after explaining the nature and purpose of the study. The protocol was approved by the Ethics committee in Zhengzhou University.Approximately 4ml blood samples were drawn into heparinized tubes before (Oh) and at 0.33, 0.67, 1.0, 1.5, 2, 3, 4, 6, 8, 12, 24, 48, 60 h after dosing. The blood samples were centrifuges at 3000 rpm for 15 min, plasma was separated and kept frozen at -20℃.2. Determination of lorazepam in plasmaThe concentration of lorazepam in plasma was determined by HPLC. (1) Chromatographic conditions: The chromatographic column of Hypersil C18 was used. The mobile phase consisted of methanol-acetonitrile-water(20 : 40 : 40) and the flow rate was 1 mL min~-1. The detection wavelength was 230 run. Internal standard method was used and internal standard was diazepam. (2) Sample preparation : To lml plasma in a 10ml test tube, 20ul diazepam(2.5mg L~-1) and 100ul NaOH (2M) were added and extracted with 5ml ether. (3)Standard curve: To blank plasma, lorazepam standard solutions was added to obtain lorazepam standard concentrations : 3.125, 6.25, 12.5, 25, 50, 100g L~-1. All calibration samples were taken through the extraction procedure. The standard curve was plotted using the ratio of the peak areas of lorazepam and diazepam versus various lorazepam concentrations.3. Data analysisEstimation and calculation of pharmacokinetic parameters were performed using 3P97 software. The peak plasma concentration (Cmax) and the time needed to reach this maximum concentration (Tmax) were directly obtained from observed values. Statistical analyses of the parameters were performed by ANOVA, and AUC, Cmax and Tmax were analyzed statistically by two one-sided /-test.Results1. RP-HPLC Determination of Lorazepam Concentration in PlasmaThe retention time of lorazepam and diazepam were 6.4 min and 12.7 min,respectively. The standard curves of lorazepam was linear in the concentration range of 3.125-100 ug L~-1 Recoveries were more than 90 %. Both Intra-day RSD and inter-day RSD were less than 15 %.2. Pharmacokinetics of lorazepam injection in Chinese healthy volunteersTo study pharmacokinetics of lorazepam injection in 9 young healthy Chinese volunteers. The lorazepam concentrations in plasma were determined by HPLC after a single intramuscular dose(4mg) of the lorazepam injection. The concentration-time curves of the formulations fitted to one-compartment open model. The Tmaxwas (2.78 ±0.83) h,Cmax was (56.16±18.78) ug -L"1,T1/2ke was (16.85±3.46 )h, TI/2ka was(0.95+0.83)h, V/F was (77.5±18.9)L, CL/F was (3.3 + 1.1) L/h, AUC'O was (1251 ±438) ug ? h ? L"1,AUC; (1383+489) ^g ? h ? L"\ respectively.3. Relative Bioavailability of Lorazepam Tablets in Healthy VolunteersThe lorazepam concentrations in plasma were determined by HPLC after a single oral dose of the standard formulation and the tested formulation were respectively given to 18 volunteers in randomized cross-over test. The concentration-time curves of two formulations fitted to a one-compartment open model. The Cmax were (36.9 ±9.1) P g 'L^and (38.2±10.2) u g ?L'1,Tmax were (2.5±0.7) hand(2.5+0.7)h,Ti/2ke were (15.8 ±3.0) h and (15.4+2.8) h, AUQm were (579±176) u g ? h ? L"'and (586±194) u g ? h ? I/1, AUCo— were (702 + 163) and (699 ± 198) U g ? h ? L'Vespectively.The pharmacokinetic parameters obtained from our studies showed no significant difference between two formulations(P>0.05). The relative bioavailability was(102.7±14.0)% of tested formulation. The results of statistical analysis suggest that the two formulations be bioequivalent.Conclusions1. Compared western, both Cmax and AUC^'m Chinese are higher, which suggest thatChinese should use different regimen of lorazepam injection.2. The results of statistical analysis suggest that the two formulations be bioequivalent.