Do CYP3A and ABCB1 genotypes influence the plasma concentration and clinical outcome of donepezil treatment?

PURPOSE: The aim of our study was to evaluate the impact of CYP3A4, CYP3A5, and ABCB1 polymorphisms on donepezil disposition and clinical outcome. METHODS: Fifty-four Italian patients diagnosed with probable mild to moderate Alzheimer's disease, treated with donepezil (37 patients 5 mg/day, 17 patients 10 mg/day) were genotyped for CYP3A4 (*1B, *3, and *4), CYP3A5 (*2, *3, and *6) and ABCB1 (3435C>T, 2677G>T/A, and 1236C>T) polymorphisms. All patients were evaluated for the degree of cognitive impairment with Mini Mental State Examination (MMSE) screening test at baseline (before treatment) and after at least 3 months of donepezil treatment at stable dose, when the drug plasma levels were measured. RESULTS: Three patients carried one detrimental CYP3A4 allelic variant, and 12 carried one functional CYP3A5*1 allele. No statistically significant association was found between CYP3A4 or CYP3A5 genotypes and plasma donepezil concentrations, or between genotypes and clinical response (as measured by change in MMSE score). Nine ABCB1 haplotypes were observed, the most common being 1236C/2677G/3435C (46%) and 1236T/2677T/3435T (41%). Patients homozygous for the T/T/T haplotype had slightly though not significantly lower plasma donepezil concentration-to-dose ratios than those carrying other genotypes [median (95% CI) 0.18 (0.13-0.45) vs. 0.31 (0.30-0.44) mg/l/mg/kg, respectively]. These patients also showed a slightly better clinical response (as measured by change in MMSE score) than the other genotype groups [median (95% CI) 0 (-1.3 to 3.3) vs. -1.0 (-2.1 to 0.0), respectively]. CONCLUSIONS: Our data suggest that the CYP3A4 and CYP3A5 polymorphisms are unlikely to influence donepezil metabolism and/or clinical outcome. On the other hand, the ABCB1 polymorphisms may play a role in donepezil disposition and clinical outcome.

Impact of the CYP2D6 polymorphism on steady-state plasma concentrations and clinical outcome of donepezil in Alzheimer's disease patients.

OBJECTIVE: The aims of this study were to evaluate the impact of the CYP2D6 polymorphism on both the steady-state plasma concentrations (Cp) and the clinical outcome of donepezil, a selective acetylcholinesterase inhibitor used in the treatment of Alzheimer's disease (AD). METHODS: Forty-two patients of Caucasian ethnicity affected by probable AD were included in the study. All had been receiving therapy with donepezil for at least 3 months: 31 patients with 5 mg/day and 11 patients with 10 mg/day. The CYP2D6 genotype was analysed, and donepezil Cp was measured by using high-performance liquid chromatography. RESULTS: On the basis of their CYP2D6 genotype, 30 patients could be classified as homozygous extensive metabolizers (EM), 10 as heterozygous EM and 2 as ultrarapid metabolizers (UM). No poor metabolizer was found. The dose and body weight-corrected median donepezil Cp were slightly, though not significantly, lower in homozygous than in heterozygous EM (0.33 vs. 0.41 ng/ml/mg/kg, respectively). The latter group consistently showed a better clinical response to treatment, as measured by change in Mini-Mental State Examination score (median: 1.40 vs. -1.30, respectively). UM patients had lower Cp than EM patients and showed no clinical improvement. CONCLUSIONS: Our preliminary data suggest that the CYP2D6 polymorphism influences both donepezil metabolism and therapeutic outcome and that a knowledge of a patient's CYP2D6 genotype together with donepezil concentration measurements might be useful in the context of improving the clinical efficacy of donepezil therapy.