OBJECTIVE

This study consisted of 2 phases: development of a liquid chromatography-tandem mass spectrometry (LC/MS) method for determination of memantine in human plasma and characterization of single-dose and multiple-dose pharmacokinetic profiles of memantine in healthy Chinese volunteers using the LC/MS method.

METHODS

An analytic method of LC/MS for determination of memantine in human plasma was developed and validated and was applied to this single-center, open-label, single-dose and multiple-dose pharmacokinetic study conducted in healthy native Chinese volunteers. Subjects were randomized to receive a single dose of 5, 10, or 20 mg of memantine to study the linear characteristics of pharmacokinetics, or a multiple dose of 5 mg once daily for 14 days to study the drug accumulation. The pharmacokinetic parameters calculated included C(max), T(max), AUC, t(1/2),mean residence time (MRT), maximum steady-state plasma concentration (C(ssmax)), minimum steady-state plasma concentration ((ssmin)), average steady-state plasma concentration (C(ssav)), and fluctuation percentage (DF). All values were expressed as mean (SD). Sequential blood samples were collected from 0 to 360 hours for single-dose pharmacokinetic determinations after the dose on day 1; in the multiple-dose pharmacokinetic arm, the sequential blood samples were also obtained from 0 to 360 hours on day 14 after collecting the predose samples at 0 hour on days 11, 12, and 13. Memantine concentrations in plasma were determined by LC/MS method. A calibration curve was constructed by 7 memantine concentrations and processed by least-squares linear regression analysis (w=1/x(2)). Safety assessments, including adverse events (AEs), were performed at all study visits.

RESULTS

The LC/MS method for determination of memantine in human plasma was developed and validated. The standard calibration curve for spiked human plasma containing memantine was linear in the concentration range of 0.2 to 200.0 ng/mL. The correlation coefficient was greater than 0.9960 (n = 6). The lower limit of quantification for memantine in human plasma was 0.2 ng/mL, and the intraday and interday coefficients of variation were all lower than 15%. The mean recoveries of the 0.4, 20.0, and 180.0 ng/mL levels were 78.87%, 81.55%, and 81.98%, respectively. The coefficients of variation were all lower than 15% after being treated at room temperature for 24 hours, for 45 days at -40 degrees , and within 3 freeze-and-thaw cycles in plasma samples. Forty native Chinese subjects (10 [5 men, 5 women] subjects per group; mean [SD] age, 21.6 [1.6] [range, 19-27] years; weight, 63.0 [7.7] [range, 52-82] kg; height, 170.0 [7.0] [range, 155-185] cm) were enrolled in the study. After single-dose oral administration, the main pharmacokinetic parameters found for memantine at doses of 5, 10, and 20 mg were as follows: C(max), 6.20 (0.75), 11.60 (1.95), and 25.34 (8.34) ng/mL, respectively; T(max), 5.70 (1.64), 6.00 (1.33), and 6.89 (1.41) h; AUC(0-t), 486.19 (80.00), 889.32 (239.49), and 1772.91 (784.07) ng x h/mL; AUC(0-infinity), 540.05 (89.68), 932.07 (230.82), and 1853.29 (776.85) ng x h/mL; t(1/2), 66.86 (11.75), 63.57 (12.58), and 62.06 (9.26) h; and MRT, 99.37 (16.96), 91.73 (18.16), and 89.56 (13.77) h. The main pharmacokinetic parameters found for memantine at doses of 5 mg once daily for 14 days were as follows: T(max), 6.80 (2.46) h; C(ssmax), 19.69 (2.00) ng/mL; C(ssmin), 12.76 (2.80) ng/mL; C(ssav), 16.10 (2.46) ng/mL; t(1/2), 64.57 (15.78) h; MRT, 93.17 (23.38) h; AUC(ss),386.37 (59.00) ng x h/mL; and DF, 44.47% (15.27%). One female subject withdrew from the study after a single 20-mg dose due to an AE (dizziness and vomiting); no other subjects experienced an AE.

CONCLUSIONS

In these healthy Chinese subjects, the t(1/2) and MRT values were fixed and did not increase following the increased dose, and the AUC(infinity) and C(max) values increased following the increasing dosage of memantine. Linear pharmacokinetics was found at doses from 5 to 20 mg. The multiple-dose pharmacokinetic parameters (other than C(max)) were nearly similar compared with the single-dose administration. The maximum plasma concentration of memantine after multiple-dose administration was greater than that after a single-dose administration, suggesting memantine accumulation with multiple-dose administration of 5 mg and requiring further confirmation in larger studies.