Persistent impairment of clomipramine demethylation in recently detoxified alcoholic patients

Population pharmacokinetics of clomipramine, desmethylclomipramine, and hydroxylated metabolites in patients with depression receiving chronic treatment: model evaluation

Because metabolites play a major role in the clinical response to clomipramine, the objective of the current study was to develop a population model and evaluate its performance to describe the pharmacokinetic profiles of clomipramine (C) and its active metabolites desmethylclomipramine (DC), 8-hydroxy-clomipramine (OHC) and 8-hydroxy-desmethylclomipramine (OHDC). A first sample of 14 patients served for development of a 2-molecule C and DC model, which was shown to provide reasonable estimates of AUC-based clearances, as well as precise estimation of interindividual variability. Simulated data, generated to mimic a semi-rich sampling design and chronic treatment with clomipramine, indicated that clearance estimation was feasible under routine treatment conditions. A second sample of 30 patients, recruited prospectively and followed for a median 4-week period, was used to extend the 2-molecule model to a 4-molecule model. Goodness-of-fit assessment revealed that model-predicted concentrations were reasonably close to observed concentrations for a majority of patients. Interindividual variability was 50% to 60% for hydroxylation and desmethylation clearances, and residual variability was 30%. The proposed model incorporates much of what is known about the metabolism of clomipramine and may valuably integrate the influence of genetic and environmental factors on each metabolic pathway.

Status epilepticus associated with the combination of valproic acid and clomipramine

An epileptic patient well controlled on valproic acid (VPA) developed a prolonged episode of status epilepticus 12 days after initiation of 75 mg of clomipramine (CMI) to treat depression. Serum level of VPA in the emergency room was unchanged from her previous levels; serum level of CMI was very elevated despite the relatively small dose of CMI. A pharmacokinetic interaction between VPA, an enzyme inhibitor, and CMI has not been described but seemed to have occurred in this patient. Decreased metabolism of CMI and its metabolites, increased free CMI fraction, and precipitation of a nonlinear saturation kinetic state has been described when CMI was used concomitantly with other highly protein-bound, enzyme-inhibiting compounds. This case provides reasonable evidence that the combination of VPA and CMI may result in elevation of levels of CMI and possibly of its metabolites and may precipitate seizures in patients with an underlying predisposition. The elevated serum level of CMI at the time of the seizures, despite the relatively small oral dose of the drug, suggests that VPA may have inhibited its metabolism and/or elimination.

Pharmacokinetic optimisation of therapy with newer antidepressants

Since the early 1950s, when imipramine was first introduced, a whole series of antidepressants with differences in structures, neurochemical effects and pharmacokinetics have been developed. Structurally or functionally, they have been classified as tricyclic antidepressants (TCAs), tetracyclic antidepressants, monoamine oxidase inhibitors (MAOIs), or selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors (SSRIs). In addition, there is a series of antidepressants with unique structures. Many of the newer TCAs appear to have shorter half-lives than the standard TCAs (e.g. imipramine), allowing for the possibility of a more rapid response, but requiring the drugs to be given in multiple daily doses, which may reduce patient compliance. The short time to peak plasma concentration (tmax) can also lead to rapid onset of adverse effects. The tetracyclic antidepressants have longer elimination half-lives (t1/2) than the TCAs, but there is only very minimal evidence for a relationship between drug concentrations in the blood and clinical response. The triazolopyridines, like the newer TCAs, show pharmacokinetic evidence for rapid onset of adverse effects and the need for multiple daily doses due to short tmax and t1/2. The newer MAOIs are a significant addition to therapy, as the rapid binding action of these medications increases their safety margin with regard to tyramine interactions. Further information in this area is required. In addition, moclobemide has pharmacokinetic features that are clinically beneficial (e.g. aging and renal dysfunction have little effect on the elimination of the drug), but also features that are not beneficial (e.g. nonlinear pharmacokinetics). Among the SSRIs, there are a range of t1/2 values for the parent drugs, from relatively short t1/2 values of less than 24 hours (paroxetine, fluvoxamine) to among the longest found (e.g. 2 days for fluoxetine). Only 2 of the agents (sertraline and citalopram) have linear pharmacokinetics, and 1 drug has nonlinear pharmacokinetics within the usual therapeutic range (fluvoxamine). Once a therapeutic blood concentration is established, linearity is helpful in avoiding the small dose changes and repeated rechecking of concentrations of medications that would be required for those agents with nonlinear pharmacokinetics. Sertraline stands out as having the best effects on behaviour among all antidepressants. However, fluoxetine and fluvoxamine are least likely to penetrate into breast milk. All 3 of the structurally unique newer antidepressants [amfebutamone (bupropion), viloxazine venlafaxine] have relatively short tmax values (1 to 2 hours), which may relate to the early onset of adverse effects. Amfebutamone has the benefits of linear pharmacokinetics with potential for defined therapeutic blood concentrations, lack of effect of liver enzymes on metabolism of the drug, and lack of significant effects of either aging or hepatic dysfunction on elimination of the drug. Thus, the antidepressants best suited for pharmacokinetic optimisation of therapy are the following: desipramine, sertraline, fluvoxamine, citalopram and amfebutamone.

Involvement of CYP2D6, CYP3A4, and other cytochrome P-450 isozymes in N-dealkylation reactions

Metabolic N-dealkylation is a commonly observed biotransformation with tertiary and secondary amine drugs and related N-alkylated amides, but surprisingly little is known about the cytochrome P-450 isozymes involved in these dealkylation reactions. In this review, evidence is provided that supports the involvement of various P-450 isozymes, but especially CYP3A4 and other isozymes of the CYP3A subfamily. Although CYP2D6 is generally not considered to be capable of catalyzing the N-dealkylation of basic drugs, some examples of the involvement of this important isozyme in N-dealkylation reactions are identified. Procedures used to identify individual P-450 isozymes involved in N-dealkylation reactions are discussed.