Influence of CYP2D6 polymorphism on the pharmacokinetics and pharmacodynamics of tolterodine

• Published in: Clinical pharmacology and therapeutics 1998-05, Vol.63 (5), p.529-539
• Main Authors: Brynne, Niclas, Dalén, Per, Alván, Gunnar, Bertilsson, Leif, Gabrielsson, Johan
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cholinergic system; Medical sciences; Neuropharmacology; Neurotransmitters. Neurotransmission. Receptors; Pharmacology. Drug treatments
• ISSN: 0009-9236; 1532-6535
• DOI: 10.1016/S0009-9236(98)90104-7

Objective To determine whether cytochrome P450 2D6 (CYP2D6) is involved in the metabolism of tolterodine by investigating potential differences in pharmacokinetics and pharmacodynamics (heart rate, accommodation, and salivation) of tolterodine and its 5‐hydroxymethyl metabolite between poor metabolizers and extensive metabolizers of debrisoquin (INN, debrisoquine). Methods Sixteen male subjects (eight extensive metabolizers and eight poor metabolizers) received 4 mg tolterodine by mouth twice a day for 8 days followed by a single intravenous infusion of 1.8 mg tolterodine for 30 minutes after a washout period. Doses were given as the tartrate salt. The pharmacokinetics of tolterodine and 5‐hydroxymethyl metabolite were determined, and the pharmacodynamics were measured. Results The mean systemic clearance of tolterodine was significantly lower (p < 0.001) among poor metabolizers (9.0 ± 2.1 L/hr) compared with extensive metabolizers (44 ± 13 L/hr), resulting in a fourfold longer elimination half‐life (p < 0.001). The terminal half‐life of the 5‐hydroxymethyl metabolite (2.9 ± 0.4 hours) was slightly longer than that of the parent compound (2.3 ± 0.6 hours) among extensive metabolizers, but the 5‐hydroxymethyl metabolite was undetectable in the serum of poor metabolizers. Only minor differences in pharmacodynamic effects after tolterodine dosage were observed between the groups. Tolterodine caused a similar decrease in salivation in both panels. The decrease occurred when the concentration of unbound tolterodine and 5‐hydroxymethyl metabolite among extensive metabolizers was comparable with that of tolterodine among poor metabolizers. Conclusions Tolterodine is extensively metabolized by CYP2D6 with high specificity. Despite the effect on pharmacokinetics, the CYP2D6 polymorphism does not appear to be of great importance in the antimuscarinic effect, probably because of the additive action of parent drug and active metabolite. Clinical Pharmacology & Therapeutics (1998) 63, 529–539; doi: