Therapeutic drug monitoring of tricyclic antidepressants in everyday clinical practice

Data about therapeutic drug monitoring (TDM) of psychotropic medications are often obtained from samples of highly selected individuals, who may not be representative for the average psychiatric patient. These data therefore may have limitations with regard to their transferability to everyday clinical practice. Therefore studies under naturalistic conditions are important to clarify the full clinical relevance of TDM. We retrospectively evaluated all TDM-analyses of the tricyclic antidepressants (TCA) amitriptyline and clomipramine during a 12-month period in an unselected sample of patients in a standard clinical setting. We especially examined the relationship between serum levels on one hand and clinical response and adverse effects on the other hand. In patients with amitriptyline, responders showed a significantly higher serum level than non-responders, whereas in patients with clomipramine a serum level within the recommended therapeutic range was associated with clinical response. We also found significantly higher serum concentrations in patients with adverse effects compared to patients without adverse effects in the clomipramine group. No such relationship could be shown in patients treated with amitriptyline. Our results suggest that therapeutic ranges in naturalistic settings in some ways differ from those obtained in controlled clinical settings and that TDM studies in everyday clinical practice are necessary and beneficial.

Definition, assessment, and staging of treatment-resistant refractory major depression: a review of current concepts and methods

OBJECTIVE

Up to 15% of depression patients eventually present with treatment-resistant or refractory depression (TRD), a condition that causes significant social and economic burdens. Our paper aims to summarize the current medical literature on the conceptual and methodologic issues involved in the definition, assessment, and staging of TRD.

METHOD

We reviewed the recently published medical literature to identify papers that specifically discuss TRD. For this, we searched MEDLINE, EMBASE, and PsycINFO for potentially relevant English-language articles published between January 1996 and June 2006.

RESULTS

Recent methodologic and conceptual advances have contributed to the achievement of an acceptable level of theoretical consensus on the general meaning of TRD. Accordingly, depression is usually considered resistant or refractory when at least 2 trials with antidepressants from different pharmacologic classes (adequate in terms of dosage, duration, and compliance) fail to produce a significant clinical improvement. Regarding diagnostic assessments, an accurate and systematic evaluation should be made to elicit the potential role of several contributing factors, such as medical and psychiatric comorbidity.

CONCLUSION

Recently, 3 staging methods for TRD have been described, but they currently require extensive empirical support. Future research on TRD should include prospective studies addressing the validity of the proposed criteria, the impact of depression comorbid with other psychiatric disorders and (or) physical conditions, and the possible predictors o treatment outcome. There is an important and clear need for studies that empirically test current definitions, assessment strategies, and staging methods of TRD.

Blood-brain barrier penetration and pharmacokinetics of amitriptyline and its metabolites in p-glycoprotein (abcb1ab) knock-out mice and controls

In earlier studies with P-gp (abcb1) knock-out mice, we showed that P-gp exports the antidepressants citalopram, paroxetine, venlafaxine and amitriptyline and its metabolites across the blood-brain barrier, thereby reducing cerebral bioavailability of some substances up to 9 times. The present study investigated the pharmacokinetics of amitriptyline and whether abcb1ab double knock-out mice metabolize amitriptyline and its metabolites differently. P-gp knock-out mice and controls received a s.c. injection of 10mug amitriptyline/g of body weight. The animals were sacrificed after 30, 60, 120 and 240min and concentrations of amitriptyline and its metabolites were measured with HPLC in brain, plasma, liver, kidney, spleen, lung, muscle, fat and ovaries. Cerebral concentrations of amitriptyline and its metabolites were higher in P-gp-deficient mice compared to controls. No significant group effect was found for spleen, liver, lung, kidney and fat tissue. The results of our study indicate that amitriptyline and its metabolites are substrates of P-gp. Overall pharmacokinetics between knock-outs and controls were very similar. This confirms the validity of the P-gp knock-out model and allows for a continued research of the interactions between P-gp, the blood-brain barrier and CNS substances such as antidepressants, neuroleptics and others.

Therapeutic tricyclic antidepressant drug monitoring in younger and older depressive patients

The present study shows the evaluation of clinical state and serum level of tricyclic antidepressants in thirty-eight depressive younger and elderly patients during 8-week observation. We observed no statistically significant differences, neither in psychometric scale scores nor in drug serum levels in both groups of patients.

Distribution of antidepressants between plasma and red blood cells

OBJECTIVE

The distribution of different antidepressants between plasma and red blood cells (RBCs) or between water and erythrocyte membranes (ghosts) has not been sufficiently compared so far.

MATERIALS AND METHODS

Distribution of seven antidepressants (amitriptyline, nortriptyline, imipramine, desipramine, didesmethylimipramine, dothiepin, and citalopram) was measured in vitro in small volumes of blood or erythrocyte membrane suspension using radiolabeled drugs. Blood samples were taken from healthy subjects.

RESULTS

The distribution of antidepressants between plasma and RBCs is strongly affected by temperature; however, it does not depend on the antidepressant concentration in the range of their therapeutic concentrations. The data analysis proved that the ratio of RBCs to plasma volume concentrations is the suitable parameter characterizing antidepressant distribution in whole blood. Significantly higher ratios of RBCs to plasma concentrations were found for demethylated metabolites of tricyclic antidepressants and in the case of citalopram. Citalopram showed the highest accumulation in intact RBCs and at the same time the lowest binding to isolated membranes. The binding of drugs to isolated erythrocyte membranes was much higher than in whole blood.

CONCLUSION

The concentration ratio of antidepressant in RBCs and in plasma is sensitive not only to the binding properties of plasma proteins and cell membranes, but also to changes in drug molecule, both in aminopropyl chain and in aromatic rings. This ratio is to a large extent characteristic of a particular antidepressant.

Sequence-based CYP2D6 Genotyping in the Korean Population

For clinical application of pharmacogenetic tests, quantitative prediction of enzyme activity based on accurate determination of genotype is essential. There has been limited information available on the genetic polymorphism of CYP2D6 in the Korean population. In this study, CYP2D6 genotypes were assessed in 400 Korean subjects. Twenty-eight different CYP2D6 alleles and 35 genotypes were detected. On the basis of the genotype determined, the frequency of poor metabolizers and ultrarapid metabolizers were 0.22% and 1.25%, respectively. The CYP2D6 activity expected in regard to different allele combinations varies widely within the extensive and intermediate metabolizer groups. The frequencies of CYP2D6*10 and CYP2D6*5 were 45.00% and 6.13%, respectively. CYP2D6*10xN was found in 4 out of 9 cases with a CYP2D6 duplication. Fifteen heterozygotes for *41 were noted. In addition, the authors measured plasma concentrations of 16 healthy volunteers after administration of nortriptyline and identified the impact of the CYP2D6 genotype on nortriptyline metabolism. This is the first large-scale study to examine the genetic polymorphism of CYP2D6 using sequence-based genotyping in an Asian population. Our results further the understanding of CYP2D6 pharmacogenetics and could be helpful for future clinical studies in the Asian population.

Pharmacokinetics of desipramine HCl when administered with cinacalcet HCl

OBJECTIVE

In vitro work has demonstrated that cinacalcet is a strong inhibitor of cytochrome P450 isoenzyme (CYP) 2D6. The purpose of this study was to evaluate the effect of cinacalcet on CYP2D6 activity, using desipramine as a probe substrate, in healthy subjects.

METHODS

Seventeen subjects who were genotyped as CYP2D6 extensive metabolizers were enrolled in this randomized, open-label, crossover study to receive a single oral dose of desipramine (50 mg) on two separate occasions, once alone and once after multiple doses of cinacalcet (90 mg for 7 days). Blood samples were obtained predose and up to 72 h postdose.

RESULTS

Fourteen subjects completed both treatment arms. Relative to desipramine alone, mean AUC and C(max) of desipramine increased 3.6- and 1.8-fold when coadministered with cinacalcet. The t (1/2,z) of desipramine was longer when desipramine was coadministered with cinacalcet (21.0 versus 43.3 hs). The t (max) was similar between the regimens. Fewer subjects reported adverse events following treatment with desipramine alone than when receiving desipramine with cinacalcet (33 versus 86%), the most frequent of which (nausea and headache) have been reported for patients treated with either desipramine or cinacalcet.

CONCLUSION

This study demonstrates that cinacalcet is a strong inhibitor of CYP2D6. These data suggest that during concomitant treatment with cinacalcet, dose adjustment may be necessary for drugs that demonstrate a narrow therapeutic index and are metabolized by CYP2D6.

Biowaiver Monographs for Immediate Release Solid Oral Dosage Forms: Amitriptyline Hydrochloride**This paper reflects the scientific opinion of the authors and not the policies of regulating agencies

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing amitriptyline hydrochloride are reviewed. Its therapeutic uses, its pharmacokinetic properties, the possibility of excipient interactions and reported BE/bioavailability (BA) problems are also taken into consideration. Literature data indicates that amitriptyline hydrochloride is a highly permeable active pharmaceutical ingredient (API). Data on the solubility according to the current Biopharmaceutics Classification System (BCS) were not fully available and consequently amitriptyline hydrochloride could not be definitively assigned to either BCS Class I or BCS Class II. But all evidence taken together, a biowaiver can currently be recommended provided that IR tablets are formulated with excipients used in existing approved products and that the dissolution meets the criteria defined in the Guidances.

[Therapeutic drug monitoring: A pharmacotherapeutic tool in psychiatry]

Therapeutic drug monitoring (TDM) is used increasingly for managing psychiatric outpatients, where the preanalytic error risk is high. Blood samples must be collected under steady-state conditions immediately before ingestion of the morning dose or before the next injection. In order to interpret the plasma levels accurately, age, gender, ethnicity, compliance, drug dosage, renal and hepatic function and comedication incl. smoking habits and diet (esp. caffeine intake and consumption of grapefruit juice) have to be taken into account. If in doubt, aberrant plasma levels should be confirmed by a second control under optimized conditions. Pharmacogenetic testing enables the identification of abnormal metabolizers. TDM and pharmacogenetic tests are useful tools to improve pharmacotherapy by preventing dose-dependent adverse drug events, optimizing dosage during long-term treatment and identifying ultrarapid metabolizers and malcompliance.

Inter- and intraindividual pharmacokinetic variations of mirtazapine and its N-demethyl metabolite in patients treated for major depressive disorder: a 6-month therapeutic drug monitoring study

Mirtazapine pharmacokinetic (PK) data from patients on long-term treatment for major depression have never been investigated. For this reason, in a large naturalistic outpatient study (prospective, multicenter, open-labeled, and noncomparative) conducted in Sweden in the period 2000-2002, one of the main objectives was to outline the inter- as well as intraindividual PK variance of mirtazapine and demethylmirtazapine serum concentrations in a patient cohort treated up to 6 (optionally 12) months. A total of 192 male and female outpatients aged 18 years or older were included. Serum samples of mirtazapine and demethylmirtazapine were collected, by the means of therapeutic drug monitoring, at weeks 1, 4, 8, and 24 (52). Altogether 683 serum samples were analyzed. A pronounced interindividual variability of mirtazapine and demethylmirtazapine, and the demethylmirtazapine/mirtazapine ratio was seen. The coefficient of variation was about 38%, 33%, and 36%, respectively. The intraindividual variation over time was low, about 20% on all variables. At the population level, no accumulation of mirtazapine, demethylmirtazapine, or change of the demethylmirtazapine/mirtazapine ratio was observed over time. Women had significantly higher dose-corrected concentrations of mirtazapine and demethylmirtazapine and demethylmirtazapine/mirtazapine ratio than men. Patients above 65 years of age had higher concentrations than their younger counterparts. Among patients with adverse events, lower demethylmirtazapine concentrations were observed than in patients with no adverse events. Patients on multiple drug treatment had higher dose-corrected mirtazapine and demethylmirtazapine serum concentrations than patients taking only mirtazapine. Weight and BMI had a significant negative correlation with demethylmirtazapine concentrations and with the demethylmirtazapine/mirtazapine ratio. Continued efforts are warranted to perform PK studies in a natural clinical setting to learn and understand inter- and intraindividual PK variances in real patients treated for longer periods of time. For mirtazapine as well as for most antidepressant drugs only relatively short term PK is available. To help clinicians improve their treatment of patients with major depressive disorder, the possible implications on the PK with a long-term treatment are important to study.

Sequestration of amitriptyline by liposomes

We study the uptake of amitriptyline, which is a common cause of overdose-related fatalities, in aqueous solutions by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes and liposomes composed of a mixture of DMPC and 1,2-dioleoyl-sn-glycero-3-[phospho-rac(1-glycerol)] (DOPG) lipids. The effect of drug concentration, liposomal charge, pH, salt, and protein presence on the drug uptake is investigated using two different methodologies, a precipitation and a centrifugation method. Furthermore, the time scale of the drug uptake is studied through qualitative observations at high pH and through conductivity measurements at neutral pH and found to be <5 s. The results of the quantitative studies show that the fractional drug uptake decreases with increasing drug concentration, and for a given concentration it increases with the pH and decreases in the presence of salt. We find that a larger amount of drug is sequestered by negatively charged liposomes (those containing DOPG) than liposomes with no net charge (DMPC). We speculate that the mechanism of drug uptake is due to both electrostatic interactions as well as hydrophobic effects. The fractional uptake by DMPC:DOPG in a 70:30 ratio is as high as 95% in water and about 90% in physiological buffer. The fractional uptake is also measured in presence of 2% (w/w) bovine serum albumin (BSA), which is approximately the protein concentration in the intercellular fluid. In presence of protein the fractional uptakes by 70:30 DMPC:DOPG liposomes and 50:50 DMPC:DOPG liposomes are 82 and 90%, respectively, at 125 muM drug amitriptyline. In the absence of liposomes, 67% of the drug is taken up by the protein in a 2% (w/w) BSA, 125 muM amitriptyline solution. Thus, addition of 50:50 DMPC:DOPG liposomes reduces the free drug concentration by a factor of about 3.5, making them attractive candidates for drug detoxification.

Rates of In Vivo Methylation of Desipramine and Nortriptyline

Routine monitoring of an 81-year-old man receiving treatment with nortriptyline for generalized anxiety disorder and depression revealed plasma concentrations of both amitriptyline and nortriptyline. In humans, the tricyclic antidepressant (TCA) tertiary amines imipramine and amitriptyline are typically metabolized by demethylation to the secondary active metabolites desipramine and nortriptyline, respectively. However, to our knowledge, methylation of secondary amine TCAs has been reported in only one case report of nortriptyline overdose and in two studies involving desipramine. In a retrospective analysis of patients from five Veterans Affairs medical centers, the rate of methylation of desipramine and nortriptyline was 8.9 % (five of 56 patients) and 14.6% (36 of 247), respectively. Possible explanations for methylation include genetic polymorphisms in cytochrome P450 metabolizing enzymes, polymorphism of amine N-methyltransferase enzyme, drug-drug interactions, smoking, and alcohol consumption. However, the mechanism by which methylation occurs is unclear and warrants further investigation. Awareness of the phenomenon could help in discouraging repeated laboratory tests and unnecessary adjustments of drug therapies, resulting in cost savings and better patient outcomes.

[Functional state of the dopaminergic system of the brain on a background of different doses of amitriptiline]

The aim of the work is study of adsorbtion dynamics of amitriptiline on the surface of erythrocytes and to compare the obtained data with the character of pharmacokinetics and pharmacodynamics of amitriptiline in plasma. With the method of PLC the adsorb gas was been analyzed. The drag was administered to adult drugs and the blood sampled were collected following 10, 20, 60 min. and 4,0; 6,0 and 8,0 hours after the injection. In the supernatants from the erythrocytes and in the blood plasma the dopaminergic systems has been analyzed. Our data proved the ability of amitriptiline to adsorb on the surface of erythrocytes. Its concentration in the supernatant washed from the surface of erythrocytes and in the blood were not the same. It may be connected with the character and quantity of functional groups located on the surface of erythrocytes.

Tricyclic antidepressant poisoning : cardiovascular toxicity

Tricyclic antidepressants remain a common cause of fatal drug poisoning as a result of their cardiovascular toxicity manifested by ECG abnormalities, arrhythmias and hypotension. Dosulepin and amitriptyline appear to be particularly toxic in overdose. The principal mechanism of toxicity is cardiac sodium channel blockade, which increases the duration of the cardiac action potential and refractory period and delays atrioventricular conduction. Electrocardiographic changes include prolongation of the PR, QRS and QT intervals, nonspecific ST segment and T wave changes, atrioventricular block, right axis deviation of the terminal 40 ms vector of the QRS complex in the frontal plane (T 40 ms axis) and the Brugada pattern (downsloping ST segment elevation in leads V1-V3 in association with right bundle branch block). Maximal changes in the QRS duration and the T 40 ms axis are usually present within 12 hours of ingestion but may take up to a week to resolve. Sinus tachycardia is the most common arrhythmia due to anticholinergic activity and inhibition of norepinephrine uptake by tricyclic antidepressants but bradyarrhythmias (due to atrioventricular block) and tachyarrhythmias (supraventricular and ventricular) may occur. Torsade de pointes occurs uncommonly. Hypotension results from a combination of reduced myocardial contractility and reduced systemic vascular resistance due to alpha-adrenergic blockade. Life-threatening arrhythmias and death due to tricyclic antidepressant poisoning usually occurs within 24 hours of ingestion. Rapid deterioration is common. Level of consciousness at presentation is the most sensitive clinical predictor of serious complications. Although a QRS duration >100 ms and a rightward T 40 ms axis appear to be better predictors of cardiovascular toxicity than the plasma tricyclic drug concentration, they have at best moderate sensitivity and specificity for predicting complications.

Prediction of drug-drug interactions for AUCoral of high clearance drug from in vitro data: utilization of a microtiter plate assay and a dispersion model

The purpose of this study was to propose a new method to predict in vivo drug-drug interactions (DDIs) for a high clearance drug from in vitro data. As the high clearance drug, NE-100 (N, N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride) was used. First, approach based on I(u)/K(i) value was used for the prediction of DDIs between NE-100 and concomitant drugs. When the K(i) values (K(i-cal)) obtained from the microtiter plate (MTP) assay and the reported K(i) values (K(i-rep)) for these drugs were used to predict increases at levels of NE-100 AUC(oral) (AUC(oral) ratio), the AUC(oral) ratios from the I(u)/K(i-cal) correlated with those from the I(u)/K(i-rep). This result suggests that the K(i-cal) from the MTP assay can be used for prediction of DDIs instead of the K(i-rep) value. Second, a new approach combining the inhibition rate (R) calculated from the MTP assay and two physiological models was used to predict DDIs. When the AUC(oral) ratios of NE-100 by various drugs were predicted using the R value and the well-stirred model, the ratios were similar to those predicted using the I(u)/K(i). However, after co-administration of drugs such as quinidine, propafenone and thioridazine (potent inhibitors of CYP2D6), the NE-100 AUC(oral) ratios predicted from the dispersion model was much greater than those from well-stirred model. This result shows that application of the dispersion model to the prediction method using the R value might sensitively and precisely predict the increased levels of AUC(oral) by DDIs for high clearance drug, compared with the prediction method using I(u)/K(i) value.

Determination of tianeptine in human plasma using high-performance liquid chromatography with fluorescence detection

A new, selective and sensitive high-performance liquid chromatography (HPLC) method with fluorimetric detection was developed for the determination of tianeptine (TIA) in human plasma using solid phase extraction (SPE) procedures. The method is based on the derivatization of TIA with 4-chloro-7-nitrobenzofurazan (NBD-Cl) in borate buffer of pH 8.5 to yield a yellow, fluorescent product. The HPLC separation was achieved on a Phenomenex C(18) column (250 mm x 4.6 mm) using a mobile phase of acetonitrile-10mM orthophosphoric acid (pH 2.5) (77:23, v/v) solvent system at 1 mL/min flow rate. Gabapentin (GA) was used as the internal standard. The fluorometric detector was operated at 458 nm (excitation) and 520 nm (emission). The assay was linear over the concentration range of 5-300 ng/mL. The detection limit (LOD) was found to be 2 ng/mL. The mean recovery was determined to be 88.6%. The proposed method was applied for pharmacokinetic study of 12.5mg TIA in a healthy volunteer.

Prolonged clinical effects in modified-release amitriptyline poisoning

BACKGROUND

Tricyclic antidepressant poisoning is often associated with significant cardiovascular and central nervous system toxicity. Effective treatment includes the use of appropriate gastric decontamination techniques, the administration of sodium bicarbonate, and meticulous supportive care. Tricylcic antidepressant toxicity typically lasts 24-48 hours following a significant overdose.

CASE REPORT

We describe a case of tricyclic antidepressant poisoning where significant clinical toxicity (QRS prolongation, metabolic acidosis) was observed for up to 4 days following ingestion of a modified-release preparation of amitriptyline. Successful patient recovery was associated with the use of multidose activated charcoal and repeated administration of intravenous sodium bicarbonate.

CONCLUSIONS

Clinicians should be aware of the potential for prolonged tricyclic toxicity in patients who have ingested modified-release amitriptyline in overdose. Gastric decontamination techniques such as multidose activated charcoal and whole bowel irrigation should be considered where there is evidence of ongoing tricyclic antidepressant absorption or clinical toxicity following ingestion of a modified-release preparation. These interventions may be indicated for prolonged periods (greater than 36 hours) post ingestion.

Association between plasma interleukin-18 levels and liver injury in chronic hepatitis C virus infection and non-alcoholic fatty liver disease

There is significant upregulation of interleukin-18 (IL-18) expression in viral infectious diseases and in some chronic hepatic diseases, especially (i) hepatitis C virus (HCV) infection, (ii) HCV infection with persistently normal ALT levels (PNAL), and (iii) non-alcoholic fatty liver disease (NAFLD). The aim of this study was a better understanding of the implications of plasma IL-18 levels in the above-mentioned liver diseases. Thirty-four patients with HCV infection, 13 with NAFLD, and 10 controls were enrolled. The HCV-RNA and HCV-genotypes and the serum or plasma levels of IL-18, aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyltranspeptidase (gamma-GT), alkaline phosphatase, total cholesterol, triglycerides, alpha(1)-fetoprotein, and ferritin were evaluated. Patients with HCV showed higher levels of IL-18 than the NAFLD patients (p <0.01) and the controls (p <0.005). Patients with NAFLD showed higher values of body mass index and liver disease parameters, compared to HCV-infected subjects or controls. These data confirm previous reports of enhanced expression of IL-18 in patients with HCV and NAFLD, compared to healthy subjects, and suggest that IL-18 is important as a marker of liver diseases.

Placental passage of tricyclic antidepressants

BACKGROUND

The use of antidepressants during pregnancy continues to garner considerable attention, though there are limited investigations that have sought to quantify fetal exposure.

METHODS

Maternal and umbilical cord sera were collected at delivery from ten women taking nortriptyline and seven taking clomipramine. Placental passage was calculated as the ratio of umbilical cord to maternal serum concentration. Obstetrical outcome data were gathered from subjects at delivery.

RESULTS

The placental passage ratio of nortriptyline and its active metabolite, cis-10-hydroxynortriptyline, were .68 +/- .40, 1.40 +/- 2.40, respectively. Clomipramine and desmethylclomipramine ratios were .60 +/- .50, .80 +/- .60. Obstetrical complications, such as pre-term delivery and pregnancy induced hypertension, were increased compared to the national average.

CONCLUSIONS

The in vivo ratios of umbilical cord to maternal serum drug concentrations demonstrate considerable fetal exposure and differ greatly from previous results utilizing ex vivo perfusion.

In vitro release of clomipramine HCl and buprenorphine HCl from poly adipic anhydride (PAA) and poly trimethylene carbonate (PTMC) blends

Controlled drug-delivery technology is concerned with the systematic release of a pharmaceutical agent to maintain a therapeutic level of the drug in the body for modulated and/or prolonged periods of time. This may be achieved by incorporating the therapeutic agent into a degradable polymer vehicle, which releases the agent continuously as the matrix erodes. In this study, poly trimethylene carbonate (PTMC), an aliphatic polycarbonate, and poly adipic anhydride (PAA), an aliphatic polyanhydride, were synthesized via melt condensation and ring-opening polymerization of trimethylene carbonate and adipic acid, respectively. The release of clomipramine HCl and buprenorphine HCl from discs prepared with the use of PTMC-PAA blends in phosphate buffer (pH 7.4) are also described. Clomipramine HCl and buprenorphine HCl were both used as hydrophilic drug models. Theoretical treatment of the data with the Peppas model revealed that release of clomipramine HCl (5%) in devices containing 70% PTMC or more followed a Fickian diffusion model. However, the releases of buprenorphine HCl (5%) in the same devices were anomalous. For devices containing 50% and more PAA, surface erosion may play a significant role in the release of both molecules.

Imipramine dose in relation to therapeutic plasma level: are clinical trials using imipramine as a positive control flawed?

RATIONALE

Imipramine has often been used as positive control in studies investigating the efficacy of new antidepressants. Imipramine-controlled studies in general employ a fixed-dose design. It is unclear how many patients would achieve effective plasma levels with such a design.

OBJECTIVES

The objectives of this study were to assess the range of doses necessary to attain a therapeutic plasma level in the imipramine arms of two double-blind, fixed-plasma-level studies and to compare them with doses administered in efficacy studies with imipramine as a positive control.

METHOD

During two double-blind studies, imipramine doses were adjusted to a predefined fixed plasma level. Here we report an analysis of the range of doses necessary to attain that level in the imipramine arms of the studies. We also computed the cumulative percentage of patients with therapeutic plasma levels (> or = 200 ng/ml) at various imipramine doses in order to compare them with doses administered in efficacy studies with imipramine as a positive control.

RESULTS

Target plasma levels were attained with a mean daily dose of 248 mg, with a dose range of 50-450 mg. We calculated a possible increase in efficacy of imipramine of about 20% if doses had been adjusted to therapeutic plasma levels in clinical trials using it as a positive control.

CONCLUSIONS

The absence of significant differences in efficacy between selective serotonin re-uptake inhibitors (SSRIs) and imipramine in these trials is at least in part due to improper dosing of the latter; imipramine with therapeutic drug monitoring may be more effective than SSRIs.

Impact of the CYP2D6 ultra-rapid metabolizer genotype on doxepin pharmacokinetics and serotonin in platelets

INTRODUCTION

CYP2D6 gene duplication causing ultrafast metabolism is one reason for failure in responding to CYP2D6-metabolized antidepressants. We studied the effect of the CYP2D6 duplication genotype on doxepin pharmacokinetics and platelet serotonin uptake and concentrations.

METHODS

Pharmacokinetics of trans (E)- and cis (Z)-doxepin and N-desmethyldoxepin were analyzed after a single dose of 75 mg doxepin in 11 ultrafast metabolizers (UM), 11 extensive metabolizers (EM) and 3 poor metabolizers (PM), identified by genotyping for CYP2D6 alleles *2, *3, *4, *5, *6, *9, *10, *35, *41 and specific analyses to characterize gene duplication. Platelet serotonin concentrations were measured by HPLC.

RESULTS

A trend for lower AUC of the active principle (sum of doxepin and N-desmethyldoxepin) in UMs versus EMs was detected (575 versus 1,000 nmol h/l, P=0.07), mainly due to the differences in desmethyldoxepin concentrations (P=0.003). Stereoselective analysis showed a significant effect of the UM genotype on (E)-doxepin pharmacokinetic parameters whereas those of (Z)-doxepin did not differ between the CYP2D6 genotype groups. The 75-mg doxepin dose had no effect on platelet serotonin concentration and uptake, but serotonin concentrations in platelets were significantly higher in UM in comparison to the EM and PM groups. At baseline, these concentrations were 462, 399, and 292 ng/10 platelets in UM, EM and PM (P<0.0001 for trend).

CONCLUSIONS

At the same dose, internal exposure to doxepin differed by more than ten-fold between the CYP2D6 genotype groups. CYP2D6 may have an effect on platelet serotonin explained by salvage pathways of 5-methoxytryptamine to serotonin mediated by CYP2D6; however, this finding requires further confirmatory experiments.

Tissue distribution of mirtazapine and desmethylmirtazapine in a case of mirtazapine poisoning

An ingestion of an unknown quantity of mirtazapine in a suicide attempt leading to death is described. Sertraline and amitriptyline have been co-ingested. Because mirtazapine is reported to be relatively safe in overdose, body fluids and tissues were investigated for both mirtazapine and desmethylmirtazapine by high-pressure liquid chromatography/tandem mass spectrometry following liquid-liquid extraction. The limit of detection was sufficiently low to also apply the assay in pharmacokinetic studies. The levels of amitriptyline and nortriptyline were very low (38 and 19 ng/mL femoral venous blood) and the amount of sertraline in blood taken from the femoral vein (880 ng/mL) was considerably lower than those seen in overdosage. Accumulation of mirtazapine and N-desmethylmirtazapine was evident in fluids and tissues involved in enterohepatic circulation and excretion. The concentration determined in a brain sample suggests a contribution of the metabolite to the drug's pharmacodynamic activity. Based on literature data, significant adverse or synergistic effects among the drugs detected as well as adverse reactions such as a serotonin reaction appeared less probable. Mirtazapine exhibits alpha(1)-antagonistic properties on the cardiac-vascular system and may cause hyponatraemia. In the face of the cardiac findings at autopsy and the lack of an apparent cause of death, these effects of mirtazapine may have initiated a process leading to death.

The Use of Tricyclic Antidepressants and Selective Serotonin Reuptake Inhibitors in Women Who Are Breastfeeding

Postpartum depression is a well-recognized psychiatric condition that has gained increased attention over the past decade due to several nationally publicized tragedies. Medical management of this condition in women who are breastfeeding provides a unique challenge to health care professionals who may seek to maintain a fine balance between limiting the infant's exposure to hormone-altering drugs and maintaining the benefits of breastfeeding. No controlled trials have examined antidepressant therapy in nursing women; however, numerous case reports and case series have been published. Relatively few serious adverse effects have been reported. Although tricyclic antidepressants have been the treatment of choice in the past, selective serotonin reuptake inhibitors are gaining popularity due to their superior safety profiles. Of all the agents reviewed in the literature, sertraline was the most prescribed, and no adverse effects were reported. Therefore, this agent would be a good first choice for treatment-naive women. For treatment of postpartum depression in women with a history of successfully treated depression, the most practical approach may be to continue therapy with the previously effective agent. Treatment should be maintained at the lowest effective dosage to minimize infant exposure. Both mother and child should be closely monitored; in addition, collaboration between the prescribing physician and the child's pediatrician is essential.