The role of plasma concentrations in the use of tricyclic antidepressant drugs

Clinical response to tricyclic antidepressants in functional bowel disorders is not related to dosage

BACKGROUND

As shown in the per protocol analysis of a recent randomized, controlled trial, when tolerated, Desipramine (DES) is effective over placebo (PLA) in treating moderate-to-severe functional bowel disorders (FBD). Clinical experience suggests that the benefit from tricyclic antidepressants (TCA) in FBD can be achieved at doses lower than those used to treat major depression. Within psychiatry, when using higher dosage of TCAs, plasma levels can be used to adjust daily dosage to optimize a treatment response. However, in FBD, it is not known whether plasma levels at the lower dosage are similarly related to a clinical response.

AIM

To determine in treating FBD, whether DES blood levels or dose taken can predict a clinical response.

METHODS

As part of a study of 12 wk of antidepressant and psychological treatment in 431 patients with FBD at UNC and U of Toronto, we studied those participants who completed treatment (per protocol analysis) taking DES (N = 97, dose 50-150 mg/day) or pill placebo (PLA) (N = 55 1-3 pills/day). The primary outcome measure was defined as a composite score (Satisfaction with Treatment, McGill Pain Questionnaire, Global Well-being, and IBS-QOL). The composite score was correlated with: (i) DES plasma levels at week 6, and (ii) number of pills taken over the duration of the 12-wk treatment period. In addition, we also compared DES dose with DES plasma levels.

RESULTS

There was a modest correlation between mean DES dose at weeks 5 and 6 and DES blood level at week 6 (R = 0.2 p < 0.07). However, there were no significant correlations between the composite score either with DES dose or with DES blood levels.

CONCLUSIONS

Detectable blood levels of DES are associated with a clinical response in FBD. However, with dosages up to 150 mg, there is no relationship between total dose or plasma level and the clinical response.

Simultaneous determination of antidepressant drugs and metabolites by HPLC. Design and validation of a simple and reliable analytical procedure

An analytical procedure suitable for routine use has been developed and validated for the simultaneous separation and quantification of most of the antidepressant drugs (bicyclic, tricyclic and tetracyclic) and their metabolites in human serum by reversed-phase high performance liquid chromatography with ultraviolet detection. The method has good sensitivity and specificity, without the need for long and complex extraction procedures. The results obtained with three different analytical columns were compared and an improvement in specificity by selection of column and detection wavelength used was achieved.

Determination of metapramine, imipramine, trimipramine and their major metabolites in plasma by reversed-phase column liquid chromatography

The determination of metapramine, imipramine, trimipramine and their desmethyl metabolites after alkaline diethyl ether extraction from plasma is achieved by column liquid chromatography using two internal standards and mu Bondapak C18 column. Elution is carried out isocratically at 1 or 0.6 ml min-1 with two mixtures of acetonitrile-potassium dihydrogen phosphate-distilled water (45:55:10 for metapramine and its metabolites; 45:50:5 for imipramine, trimipramine and their metabolites). Detection is monitored by absorption at 254 nm. The detection limit is less than 5 ng ml-1 for each compound. The coefficients of variation (within-day and day-to-day) for the eight compounds are less than 11.3%. Interference from several possible co-medications is discussed. The technique can be used for routine therapeutic monitoring of the antidepressants as well as analytical toxicology. However, the three antidepressants cannot be analysed simultaneously by this method because metapramine requires a different elution system and imipramine interferes with monodesmethyltrimipramine (retention times 8.90 and 8.60 min, respectively).