Therapeutic Drug Monitoring of Rivastigmine and Donepezil Under Consideration of CYP2D6 Genotype-Dependent Metabolism of Donepezil.

BACKGROUND

The efficacy of acetylcholinesterase inhibitors (AChE-I) might depend on blood concentration. While rivastigmine metabolism is independent of the cytochrome P450 system, its isoenzymes, especially CYP2D6, metabolize donepezil. polymorphisms can cause altered enzyme activity resulting in lower or higher than expected drug concentrations of donepezil.

OBJECTIVE

We investigated correlations between clinical efficacy and serum concentrations of rivastigmine and donepezil under special consideration of genotype or gene dose-dependent metabolism of donepezil.

METHODS

Serum concentrations of donepezil and rivastigmine were measured by liquid chromatography - tandem mass spectrometry (LC-MS/MS). Real-time quantitative polymerase chain reaction (PCR) and allele-specific PCR were performed to assess genotype and gene dose.

RESULTS

Patients treated with rivastigmine (n=28) or donepezil (n=48) were included in the study. Both gene dose and metabolism type significantly predicted the level of donepezil serum concentration (p=0.019 and p=0.013, respectively). In the rivastigmine group, changes of the word list delayed recall subtest before treatment and under stable medication were significantly associated with rivastigmine serum levels (β=0.465; p=0.018). Drug serum concentrations were outside the recommended range in a substantial percentage of participants, which might have contributed to poor correlations between changes in cognitive measures and drug concentrations. Donepezil serum concentrations significantly depended on gene dose.

CONCLUSION

Testing AChE-I serum concentration should be considered in patients without clinical response to treatment or those with severe side effects. Patients with donepezil drug levels outside the recommended range might additionally profit from genotyping or treatment with an AChE-I independent of CYP metabolism.