Abstract
Objective. To determine the role of cytochrome P450 (CYP)2C19 in N-demethylation of amitriptyline (AT) in healthy Chinese subjects.
Methods. One hundred and one subjects were genotyped for CYP2C19 using polymerase chain reaction-restriction fragment length polymorphism analysis. Twelve unrelated adult men (19.7±0.6 years, 61.8±3.8 kg) were chosen and orally given a single dose of 50 mg AT, and the blood samples were drawn from a forearm vein at 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 24, 48, 72, and 96 h after AT administration. Plasma concentrations of AT and nortriptyline (NT) were determined using high-performance liquid chromatography with an ultraviolet detector.
Results. The mean area under the plasma concentration–time curve (AUCAT) of CYP2C19 poor metabolizers (PMs, n=6) was significantly higher than that of CYP2C19 extensive metabolizers (EMs, n=6) (2207±501 ng/ml·h–1 vs 1596±406 ng/ml·h–1, P<0.05). In contrast, the mean AUCNT(0–∞) of PMs was significantly lower than that of EMs (294±70 ng/ml·h–1 vs 684±130 ng/ml·h–1, P<0.0001). Other pharmacokinetic parameters such as clearance, half-life, maximum plasma concentration, and time to peak plasma concentration showed no significant difference between PMs and EMs (0.41±0.12 l /h·kg–1 vs 0.50±0.15 l /h·kg–1, 25.0±6.2 h vs 24.1±4.4 h, 96±25 ng/ml vs 75±27 ng/ml, 4.0±1.4 h vs 3.7±1.5 h, respectively).
Conclusion. The genetic defects of CYP2C19 have a significant effect on AT pharmacokinetics, and CYP2C19 plays an important role in N-demethylation of AT in vivo at a clinically therapeutic dose.