Measurement of serum drug levels in the assessment of antidepressants

Monitoring of tricyclic antidepressant plasma levels and clinical response: a review of the literature. Part I

Part I of this paper presents a comprehensive review of plasma level monitoring of tricyclic antidepressants (TCAs) and their relationship to clinical response to antidepressant therapy. Imipramine, nortriptyline, amitriptyline, clomipramine and desipramine are the most widely studied TCAs in this regard. Typical therapeutic plasma concentration ranges are suggested for some of these agents, although a consensus is lacking.

Structural and concentration effects on the deposition of tricyclic antidepressants in human hair

In order to elucidate the possibility of a long-term compliance analysis the hair samples of 56 patients, who were under a permanent treatment with tricyclic antidepressants, were analyzed for amitriptyline, clomipramine, doxepine, imipramine and maprotiline as well as their nor-metabolites. The hair concentrations varied between 0.4 and 40 ng/mg with no strong difference between the five drugs. In comparison to the therapeutic plasma levels described in literature the nor-metabolites always accumulate less in hair than drugs. No correlation was found between the hair concentration and the daily dose. The investigation of the full hair length in 3-cm sections for several examples of all five drugs shows that they can be detected in normally kept hair at least 1 year after intake.

Drug monitoring of clomipramine and desmethylclomipramine in depressed patients using a new liquid chromatographic assay

A method has been developed for the quantitative analysis of clomipramine and its major metabolite desmethylclomipramine in plasma, using normal phase chromatography with UV detection at 254 nm. This rapid (6 min) and highly sensitive methodology (detection limits 0.5 ng/mL and 2 ng/mL for clomipramine and desmethylclomipramine, respectively; S/N = 3, 0.001 aufs) allows pharmacokinetic studies and drug monitoring of the two compounds. Using the described methodology we report an application which involved 10 depressed inpatients.

Clinical pharmacokinetics of clomipramine

Clomipramine is a tricyclic antidepressant medication widely used in Western Europe. Its pharmacokinetics have been studied essentially in healthy volunteers. By combining published information obtained during observational studies, it has been possible to derive a fairly precise picture of the behaviour of both parent compound and main metabolite (demethyl-clomipramine) in humans. Clomipramine can be compared with amitriptyline or imipramine so far as its physicochemical properties are concerned. As a consequence, its pharmacokinetic profile is also similar to that observed for these 2 drugs. Clomipramine is well absorbed from the gastrointestinal tract, but undergoes an important first-pass metabolism to demethyl-clomipramine which is pharmacologically active and participates in both therapeutic and unwanted effects. Protein binding is high, and the apparent volume of distribution is very large (i.e. greater than 1000L). After reaching the systemic circulation, clomipramine is further biotransformed into demethyl-clomipramine, and both active principles are hydroxylated to metabolites which are further conjugated before being excreted in urine. Hydroxylation of parent drug and metabolite is under polymorphic genetic control by the same cytochrome P450 as debrisoquine and sparteine. The apparent elimination half-life of clomipramine is about 24h and that of demethyl-clomipramine, 96h. Accordingly, the time to reach steady-state for both active moieties is in general around 3 weeks. Various pathological or environmental factors influence the behaviour of clomipramine and demethyl-clomipramine. Patients genetically deficient in hydroxylation accumulate demethyl-clomipramine at high concentrations that can produce serious side effects and/or nonresponse. The same is true for the coadministration of neuroleptics, in particular phenothiazines. Smoking induces demethylation, whereas long term alcohol intake appears to reduce this metabolic pathway. Finally, age usually diminishes both demethylation and hydroxylation, leading to a lower daily dose of clomipramine in most elderly patients. Studies relating blood concentrations of clomipramine and demethyl-clomipramine are conflicting. However, analysis of the available information indicates that blood concentrations lower than 150 micrograms/L are usually associated with nonresponse, whereas those above 450 micrograms/L seldom lead to an improvement in the efficacy of therapy. As a consequence clomipramine, like the other tricyclics, is an antidepressant with a fairly narrow therapeutic range. This property, combined with a high interindividual variability, makes this class of drugs ideal candidates for blood concentration monitoring.

Antidepressive effect of amitriptyline treatment with plasma drug levels controlled within three different ranges

Seventy-four depressed patients were treated with amitriptyline for 4-6 weeks. Their doses were individually adjusted to maintain the sum of the plasma levels of amitriptyline (AT) and nortriptyline (NT) within one of three different ranges, randomly allocated. Allowance was made for individual plasma binding of the drugs. In the 50 patients between 25 and 65 years of age, the antidepressive response at low plasma drug levels was somewhat poorer than at medium or high levels, which were equally effective. In this age group an association was found between outcome and the individual rate of AT metabolism, expressed as "reciprocal clearance" (RC), the steady-state plasma concentration of AT plus NT divided by the daily AT dose. Good antidepressive outcome was associated with high RC. The implications of these findings for patient treatment and for the interpretation of other studies are discussed. The 18 patients between 65 and 80 years of age showed no significant differences between the effectiveness of treatment at different plasma drug levels, and no significant associations between outcome and RC.

Determination of plasma bupropion and its relationship to therapeutic effect

An analytical method to determine the concentration of bupropion in human plasma has been developed using a deuterium-labeled analog as internal standard and selected ion monitoring applied to an extract of plasma samples taken as part of a clinical trial of this antidepressant. In all, 15 depressed outpatients were randomly assigned to bupropion in a double-blind study which included weekly evaluation of their clinical condition. A good correlation was found between the results obtained by this assay and by a radioimmunoassay technique currently in use. While no simple correlation between plasma concentration and therapeutic improvement was noted, the majority of subjects showed mild to marked amelioration of symptoms and those having mean concentrations above 35 ng ml-1 had significant improvement in their test scores. Interpretation of the mass spectra of both the labeled and unlabeled drug revealed an apparent violation of the 'even-electron rule'.

Strategies for the drug treatment of depression

Antidepressants are a useful addition to a physician's therapeutic armamentarium, but because they are used to treat disorders of diverse and largely unknown cause, there is a much greater element of chance associated with their use than with the use of many other types of drugs (e.g., antibiotics and analgesics). Nevertheless, empirically derived treatment schemes, applied systematically, increase the odds of a favourable response and are preferred to haphazard prescribing. To date, no one antidepressant has been shown to be more effective than any other, although the newer agents are alleged to be faster acting, more specific and less toxic than the established drugs. However, generally, such claims have not been proven clinically. Unless there are overwhelming contraindications (e.g., intolerable side effects, an idiosyncratic response or coexisting cardiac disease) the established agents, with their proven efficacy, are preferred initially.

". . . and a small dose of an antidepressant might help"

My association with the psychosurgical unit now carrying out over 80 per cent of these operations in Britain affords an unusual opportunity to assess the management of treatment-resistant affective disorders by a large number of psychiatrists from various parts of the country. The psychiatrists likely to refer patients for psychosurgery would be expected to be those more inclined to use psychotropic medication and physical treatments in general. Nonetheless, our experience is unequivocally of a widespread under-use of antidepressants. Most referral letters state that ‘… just about every antidepressant has been tried …’, but it is rare for the maximum dose of each drug used to be quoted. The letters suggest that with resistant illnesses the prescription of a series of drugs one after another at the usual doses is the therapeutic strategy, rather than giving one drug only in progressively increasing amounts to the limit of tolerance. Of course, the doses recommended by drug companies are understandably cautious and sometimes excessively so. For example, MIMS (November 1982) gives for “Anafranil” (Geigy); “More severe cases, 75 mg daily or more if necessary” and for “Surmontil” (M & B) “50–75 mg as single dose”.

Plasma levels and clinical response with imipramine in a study comparing efficacy with mianserin and nomifensine

1 The comparative antidepressant efficacy of 150 mg imipramine, 60 mg mianserin and 150 mg nomifensine was studied in 45 depressed patients in a six week double-blind investigation. 2 In the efficacy analysis of 41 patients completing the study there was no overall significant difference in efficacy between the groups. Individual group comparisons showed no significant difference in response between mianserin and nomifensine, and mianserin and imipramine. There was a significant (z = 1.99, P less than 0.05) improved response in the imipramine compared with the nomifensine treated group. The imipramine treated group were significantly older. 3 No significant plasma concentration/clinical response relationships were demonstrated with nomifensine, mianserin, imipramine or desipramine. 4 Plasma level monitoring of imipramine recommended by some investigators does not seem to be appropriate.

Antidepressive effect and pharmacokinetics of amitriptyline with consideration of unbound drug and 10-hydroxynortriptyline plasma levels

In 27 inpatients with primary affective disorder the urinary excretion of 3-methoxy-4-hydroxyphenylglycol (MHPG) was measured prior to a 4-week treatment with 150 mg amitriptyline (AT)/day. Ratings according to the Hamilton depression scale were performed before therapy and repeated after 2 and 4 weeks. Plasma levels of AT, nortriptyline (NT), and E-10-hydroxynortriptyline (OHNT) were assayed weekly, and binding of AT to plasma proteins was determined in one sample. Better therapeutic results were obtained at intermediate, as compared to low and high concentrations of AT or AT plus NT. Independent evaluation of AT and metabolite levels revealed that patients with AT of 50--125 ng/ml responded particularly well when NT did not exceed 95 ng/ml or when NT plus OHNT was below 150 ng/ml. Outside this "therapeutic window' the outcome was markedly poorer. Interindividual variation of AT binding was much smaller than variation of total concentrations. Evaluation of free, instead of total levels did not help to clarify the relationship between clinical and pharmacokinetic variables. Plasma levels within the optimal ranges were found in more patients with high than with low MHPG excretion. The free fraction of OHNT in plasma of healthy subjects was about 35%.