Influence of P-glycoprotein inhibition on the distribution of the tricyclic antidepressant nortriptyline over the blood-brain barrier

The distribution of the antidepressant drug nortriptyline (NT) and its main metabolite E-10-hydroxy-nortriptyline (E-10-OH-NT) across the blood-brain barrier was considered in relation to inhibition of the multidrug transporter P-glycoprotein (P-gp). Rats received NT in doses of 25 mg/kg orally, 10 mg/kg i.p. or 25 mg/kg i.p. Half the rats were treated with the P-glycoprotein inhibitor cyclosporine A (CsA) (200 mg/kg) 2 h prior to NT administration, and the other half served as a control group. NT and the metabolite were extracted from brain and serum by liquid-liquid extraction and analysed by HPLC with UV-detection. The brain to serum ratio of NT was increased in the CsA treated groups (22.3-26.8) compared with the control groups (16.5-22.7), the difference being statistically significant in two of the three experiments (p<0.05). Increased brain-serum ratios were also found for E-10-OH-NT, but the differences were not statistically significant. These results suggest that inhibition of P-gp by CsA increases the accumulation of NT in the brain. Administration of the antipsychotic drug risperidone (0.5 mg/kg s.c.), which is a P-gp substrate, instead of CsA did not exert any measurable influence on the blood-brain ratio of NT concentrations. In conclusion, the results show that drug-drug interaction at P-gp may influence the intracerebral NT concentration, but apparently, a major inhibition of P-gp is necessary to attain a measurable effect.

Are one or two dangerous? Tricyclic antidepressant exposure in toddlers

Tricyclic antidepressants (TCA), increasingly prescribed for multiple indications in children and adults, are responsible for many pediatric poisonings. Though the majority of TCA exposures in this age group remain asymptomatic, several reports in the English language literature reveal significant morbidity as well as fatalities in toddlers, primarily from imipramine and desipramine. These few cases indicate that doses of 10-20 mg/kg (one to two pills) have the potential for toxicity and fatalities. More recent studies have focused on the relative safety of small exposures suggesting that with doses less than 5 mg/kg the patient may be safely observed at home. Though further studies are necessary to determine the exact dosing that places the child at risk, the authors recommend a 6-h Emergency Department observation period for children who ingest more than 5 mg/kg of most TCAs, as clinical toxicity becomes evident within this time frame.

Excess fatality from desipramine and dosage recommendations

Higher case fatality rates (CFR) were previously reported from desipramine than for 3 other tricyclic antidepressants (TCAs): amitriptyline, nortriptyline, and imipramine. The database of the American Association of Poison Control Centers (AAPCC) Toxic Exposure Surveillance System (TESS) for the 20 years 1983-2002 was used to evaluate the CFR of desipramine and the other TCAs. The CFR of desipramine was 2.25-, 2.31-, and 2.62-fold the CFR for amitriptyline, nortriptyline, and imipramine, respectively (P < 0.001). Mechanisms of desipramine toxicity and its dosage recommendations are discussed. Desipramine and nortriptyline have higher distribution volumes and erythrocyte/plasma ratios than their parent compounds imipramine and amitriptyline. This implies lower therapeutic plasma levels and reduced doses for desipramine and nortriptyline compared with their parent compounds. Such adjustments have been done for nortriptyline, but not for desipramine. The authors suggest that the high CFR of desipramine might be reduced by lowering its dose, therapeutic plasma level, and maximal pill content.

Population pharmacokinetic analysis of mirtazapine

OBJECTIVE

Mirtazapine belongs to the new generation of antidepressants that is commonly used in clinical routine. Therefore, we feel it mandatory to control compliance in the context of non-response, adverse events or other clinical situations by means of plasma concentration measurements. While controlled clinical studies have evaluated the effect of individual covariates on the pharmacokinetics of mirtazapine, our analysis aims to identify covariates within a naturalistic clinical setting.

METHODS

We performed non-linear mixed-effects modelling with data from 65 depressed inpatients whose plasma concentrations were measured weekly during their stay in hospital. Each patient's age, height, weight, co-medication, alcohol, coffee and cigarette consumption, weekly serum creatinine concentrations, liver enzyme activity, blood pressure and pulse was noted. From 49 patients, the genotype of cytochrome P450 (CYP) isoenzymes 2D6, 2C9 and 2C19 was analysed.

RESULTS

The clearance of CYP2D6 intermediate metabolisers was reduced by 26% compared with extensive metabolisers. No other factor significantly influenced the clearance of these patients.

CONCLUSION

The variability of mirtazapine plasma concentrations in clinical routine is caused to a relevant degree by CYP2D6. This should be taken into account when therapeutic drug monitoring is carried out to check treatment adherence or when a special clinical situation, such as co-morbidity and add-on medication, demands careful dosing of this drug.

Transdermal delivery of imipramine hydrochloride: Development and evaluation (in vitro andin vivo) of reservoir gel formulation

The in vitro permeation studies of imipramine hydrochloride (IMH) reported earlier from our laboratory showed that a combination of menthol (2.5% w/v) and oleic acid (2.5% w/v) worked well in terms of safety and efficacy. The main objective of this study was to evaluate the in vivo performance of this combination; in order to do that, penetration enhancers were incorporated in a hydro-alcoholic gel of hydroxypropylmethyl cellulose along with IMH and used as the drug matrix in a reservoir transdermal patch. A stability study of IMH gel was performed at 40 degrees C/75% RH for 2 months. The results of this study indicate that gels of IMH stored at 40 degrees C/75% RH turned yellow brown in 2 months and the small change in viscosity of gel at 40 degrees C/75% RH had an insignificant effect on the release rate of IMH from the gel (p>0.05). The in vivo performance of the gel was tested in rats using a reservoir transdermal patch, which consisted of a backing membrane, drug matrix and retaining membrane with an area of 12.5 cm2. Plasma concentrations of 3 microg/ml of IMH were achieved and in a histopathological study 24 h occlusion was found to be safe.

Single and multiple dose pharmacokinetic evaluation of a transdermal delivery system of imipramine hydrochloride

The transdermal route provides an attractive alternative to the presently used peroral therapy with tricyclic antidepressants due to the avoidance of first-pass metabolism and the associated side effects. In this investigation an earlier developed transdermal delivery system (TDS) of imipramine hydrochloride (CAS 113-52-0; IMH) was evaluated with respect to dose proportionality at three different dose levels. Linearity was observed with the lower doses. For the prediction of in vivo plasma levels, various pharmacokinetic parameters such as alpha, beta, volume of distribution, and AUC0-infinity. were determined by single dose intravenous administration (2 mg/kg). The lowest dose was selected for the multiple dose study taking into consideration the issues of stability, safety, therapeutic range and linearity of pharmacokinetics. At all dose levels the experimental plasma values were significantly lower than predicted levels (p < 0.05) but 30-50 fold higher than the therapeutic range with no significant difference at different dose levels. The plasma levels obtained by repeated application were comparable to that obtained in the single dose study. In addition, IMH exhibited dose proportional pharmacokinetics at the higher doses (above 50 mg/day). The developed TDS was able to maintain steady-state plasma levels for the entire duration of the multiple dose study.

Impact of CYP2D6 intermediate metabolizer alleles on single-dose desipramine pharmacokinetics

This study utilized cytochrome P450 2D6 (CYP2D6) genotypes to explain variability of desipramine pharmacokinetics in a cohort of non-poor metabolizer individuals. In an interaction study utilizing desipramine as a probe, genotyping for the CYP2D6*3, *4, *5 and *6 alleles was used to screen out CYP2D6 poor metabolizers. Individuals were categorized according to these and additional alleles (CYP2D6*2, *9, *10, *17, *41 and x2). Genotypes of individuals heterozygous for two or three of *2, *17 and *41 alleles were confirmed by molecular haplotyping. Pharmacokinetic parameters of desipramine were analysed according to CYP2D6 category. Molecular haplotyping was necessary to definitively categorize four of 16 individuals. A subject who had unusually high plasma elimination half-time, exposure and metabolic ratios carried an intermediate metabolizer (IM) *9 allele in combination with a non-functional allele. This combination has a population frequency of less than 1 : 200. Individuals with *1/*1, *1/*2 and *2/*2 genotypes had lower than average plasma elimination half-time, exposure and metabolic ratios. For desipramine, additional genotyping of CYP2D6 IM alleles helped define subgroups of the CYP2D6-positive cohort. This suggests that genotyping for IM alleles will aid in interpretation of clinical trials involving CYP2D6 substrates. Due to the diversity of IM alleles, molecular haplotyping may be necessary to fully characterize CYP2D6 genotype-phenotype relationships.

A case report of a poor metabolizer of CYP2D6 presented with unusual responses to nortriptyline medication

We present a case with decreased metabolic activity of CYP2D6, a cytochrome P450 enzyme catalyzing the metabolism of nortriptyline (NT). Conventional dosage regimen led to toxic plasma concentration of NT and adverse effects such as dry mouth, constipation, and dizziness in this case with genotype CYP2D6*5/*10B. This case suggests the clinical usefulness of pharmacogenetic testing in individualized dosage adjustments of NT.

Treatment-resistant panic disorder

A substantial number of patients with panic disorder and agoraphobia may remain symptomatic after standard treatment (including selective serotonin reuptake inhibitors, tricyclic antidepressants, benzodiazepines, or irreversible monamine oxidase inhibitors). In this review, recommendations for the treatment of patients with panic disorder and agoraphobia who do not respond to these drugs are provided. Nonresponse to drug treatment could be defined as a failure to achieve a 50% reduction on a standard rating scale after a minimum of 6 weeks of treatment in adequate dose. When initial treatments have failed, the medication should be changed to other standard treatments. In further attempts at treatment, drugs should be used that have shown promising results in preliminary studies, such as venlafaxine. Combination treatments may be used, such as the combination of an selective serotonin reuptake inhibitor and a benzodiazepine. Psychological treatments such as cognitive-behavioral therapy have to be considered in all patients, regardless whether they are nonresponders or not. According to existing studies, a combination of pharmacologic treatment with cognitive-behavioral therapy can be recommended.

Two Cases Involving Clomipramine Intoxication

Clomipramine and its active metabolite norclomipramine were identified and quantitated in multiple tissues recovered from two postmortem cases using liquid chromatography-mass spectrometry. In both cases clomipramine toxicity was assessed primarily upon levels determined from brain samples. This communication supplements the database on clomipramine and norclomipramine by providing quantitative determinations of both parent drug and metabolite in multiple tissues. A literature search revealed a paucity of data on clomipramine and norclomipramine levels in general and a total absence of documented brain levels. In patients who have undergone long-term tricyclic antidepressant (TCA) therapy, blood and liver analysis alone may not be sufficient to establish toxicity. Such patients can sequester substantial amounts in liver, a concern because the TCAs are subject to significant postmortem redistribution. When conducting postmortem investigations, the inclusion of brain determination provides valuable information in assessing the magnitude of toxicity in cases involving clomipramine and its active metabolite norclomipramine.

Pharmacokinetic interaction after joint administration of zinc and imipramine in forced swim test in mice

Recent preclinical and clinical data indicate beneficial role of zinc in the antidepressant treatment. To evaluate the mechanism of interaction between zinc and antidepressants, in the present study we examined the brain zinc, imipramine and desipramine concentrations in mice treated with combinations of zinc and imipramine and subjected to the forced swim test. We have chosen doses of zinc (10 mg/kg) and imipramine (15 mg/kg) which we have previously found to be ineffective in the forced swim test when given alone. However, when administered jointly, a significant reduction in the immobility time in this test was demonstrated. In the present study, we demonstrated a significant ca. 60% reduction in the brain desipramine and non-significant reduction (ca. 40%) in brain imipramine concentrations in the group of animals treated with zinc plus imipramine compared with animals treated with imipramine alone. The brain zinc concentration in the zinc plus imipramine group was reduced when compared with the group treated with zinc or imipramine alone. Since there was no increase in brain imipramine/desipramine or zinc brain concentration after combined zinc and imipramine treatment, the data suggest that pharmacodynamic rather than pharmacokinetic interaction between zinc and imipramine is responsible for behavioral effect in the forced swim test.

[N-methyl-11C]Mirtazapine for positron emission tomography neuroimaging of antidepressant actions in humans

RATIONALE

Many actions of antidepressant drugs cannot yet be studied using positron emission tomography (PET) neuroimaging due to lack of suitable radioligands. We believe that mirtazapine, radiolabeled with C-11, might be suitable for PET neuroimaging of alpha2-adrenoceptors in selected regions of the living human brain.

OBJECTIVE

To determine the regional central biodistribution and pharmacokinetics of [N-methyl-11C]mirtazapine in humans.

METHODS

Five healthy volunteers received an intravenous injection of [N-methyl-11C]mirtazapine for evaluating its metabolism, biodistribution and pharmacokinetics.

RESULTS

[N-methyl-11C]Mirtazapine entered the brain readily, with initial clearance from blood to tissue (K1) ranging from 0.31 ml/ml/min in amygdala to 0.54 ml/ml/min in thalamus. The rate of metabolism of [N-methyl-11C]mirtazapine in the bloodstream was relatively slow, with 20-40% of [11C]-derived radioactivity still present as parent compound at 60 min post-injection. The clearance of [N-methyl-11C]mirtazapine from the tissue compartment (k2') ranged from a low of 0.03 min(-1) in amygdala to a high of 0.06-0.07 min(-1) in thalamus and cerebellum. The volume of distribution (Ve') of [N-methyl-11C]mirtazapine was markedly greater in hippocampus and amygdala (11.3-12.0) than in cerebellum (6.7), with intermediate levels in the thalamus (9.4).

CONCLUSIONS

[N-methyl-11C]Mirtazapine has suitable properties for PET neuroimaging. We envision [N-methyl-11C]mirtazapine as a molecular probe for PET imaging of antidepressant actions at sites such as alpha2-adrenoceptors in the living human brain.

Challenging the neuronal MIBG uptake by pharmacological intervention: effect of a single dose of oral amitriptyline on regional cardiac MIBG uptake

PURPOSE

Imaging with metaiodobenzylguanidine (MIBG) is used for the assessment of neuronal dysfunction in various cardiovascular disorders. Although valuable information is obtained by resting MIBG imaging, it is conceivable that competitive interference with the re-uptake mechanism would exaggerate MIBG defects and might unmask subclinical neuronal dysfunction. Tricyclic antidepressants, such as amitriptyline, have been reported to significantly increase cardiac MIBG washout and inhibit uptake into presynaptic neurons. This study was undertaken to assess whether a single oral dose of amitriptyline could influence cardiac MIBG distribution.

METHODS

Six patients (aged 62-81 years; four males, two females) who had demonstrated a normal cardiac MIBG scan during work-up for movement disorders were studied. The patients underwent a second 123I-MIBG study after oral administration of 25 mg amitriptyline within 1 week. Single-photon emission computed tomography images were acquired at 4 h to assess the regional distribution of MIBG, after generation of polar maps and employing a 20-segment model. Mean percentage of peak activity was calculated for each segment at rest and after amitriptyline administration.

RESULTS

After amitriptyline administration, there was a decrease in regional MIBG uptake in 10+/-4 segments per patient [62/120 segments (52%): 37 segments with a 5-10% decrease, 25 segments with a >10% decrease]. This change was statistically significant in lateral (P=0.003), apical (P<0.0001) and inferior (P=0.03) regions.

CONCLUSION

A single oral dose of amitriptyline can induce changes in the uptake and retention of cardiac MIBG, indicating the feasibility of use of pharmacological intervention in cardiac neurotransmission imaging.

P-glycoprotein reduces the ability of amitriptyline metabolites to cross the blood brain barrier in mice after a 10-day administration of amitriptyline

P-glycoprotein (P-gp) is a 170-kDa membrane protein and the gene product of the multiple drug resistance (MDR1 or ABCB1) gene. It constitutes an important part of the blood-brain barrier and actively exports a number of molecules across the blood-brain barrier back into the vascular space, subsequently reducing central nervous system (CNS) bioavailability of these substances. The aim of the present study was to investigate the pharmacokinetics of amitriptyline and its metabolites in P-gp (also called mdr1ab or abcb1ab) knockout mice and controls after a long-term adminstration for 10 days. Knockout mice and controls received s.c. injections of amitriptyline (10 microg/g bodyweight) twice daily for 10 days. After 10 days, the animals were sacrificed and the concentrations of amitriptyline and nortriptyline and both their E-10-OH and Z-10-OH metabolites were measured with high-performance liquid chromatography in the cerebrum, plasma, spleen, kidney, testes, lung, liver, muscle and fat. Except for amitriptyline, the brain concentrations of all other examined substances were significantly higher in the P-gp knockout mice. Compared to controls, concentrations of nortriptyline were 2.6-fold higher, E-10-OH-nortriptyline 10-fold higher, Z-10-OH-nortriptyline seven-fold higher, E-10-OH-amitriptyline two-fold higher and Z-10-OH-amitriptyline five-fold higher. The present study confirms that P-gp plays an important role in the interaction between CNS drugs and the blood-brain barrier. Without P-gp at the blood-brain barrier, the brain concentrations of the substances were up to 10-fold higher, showing that P-gp plays an active role in exporting CNS drugs out of the brain. Recent clinical studies showing different side-effects in patients with P-gp polymorphisms confirm the clinical importance of these findings.

Systemic absorption of amitriptyline and buspirone after oral and transdermal administration to healthy cats

A prospective study was performed to determine the relative availability of buspirone and amitriptyline after oral and transdermal routes of administration in 6 adult cats. For topical administration, drugs were compounded in a transdermal organogel containing pluronic and lecithin (PLO). Using a crossover design, each cat received a single dose of amitriptyline (5 mg) and buspirone (2.5 mg) by the transdermal and oral route of administration with at least a 2-week washout interval between drug treatments. Blood samples were obtained at 0, 0.5, 1, 2, 4, 6, 8, 10, and 12 hours after drug administration for determination of plasma drug concentrations. Plasma concentrations of immunoreactive amitriptyline and buspirone were determined using commercial enzyme-linked immunosorbent assay (ELISA) tests. Systemic absorption of amitriptyline and buspirone administered by the transdermal route was poor compared with the oral route of administration. Until supporting pharmacokinetic data are available, veterinarians and cat owners should not rely on the transdermal route of administration for treating cats with amitriptyline or buspirone.

Effect of the novel anxiolytic drug deramciclane on cytochrome P 450 2D6 activity as measured by desipramine pharmacokinetics

BACKGROUND

In vitro findings have indicated that the novel anxiolytic drug, deramciclane, is an inhibitor of the cytochrome P(450) (CYP) 2D6 enzyme and co-administration of deramciclane and the CYP2D6 probe drug desipramine is possible in clinical practice.

OBJECTIVE

To evaluate the effects of deramciclane on CYP2D6 activity as measured by desipramine pharmacokinetics and pharmacodynamics using paroxetine as a positive control for CYP2D6 inhibition.

METHODS

Fifteen healthy subjects received either 60 mg deramciclane, 20 mg paroxetine or matched placebo for 8 days in randomized order in this double-blind, cross-over study. On day 8 of each study phase, the subjects received a 100-mg single dose of desipramine. Desipramine and its CYP2D6-dependent metabolite, 2-OH-desipramine, concentrations were measured for 240 h. Measurement of secretion of saliva, Visual Analogue Scale assessment of dryness of mouth and tiredness were carried out on day 7 and day 8 to assess the pharmacodynamic consequences of deramciclane or paroxetine co-administration with desipramine.

RESULTS

Repeated administration of deramciclane doubled the AUC of desipramine ( P<0.001), while paroxetine caused a 4.8-fold increase in the AUC of desipramine ( P<0.001). Significant correlations were observed with paroxetine (r(s)=0.84, P<0.001) and deramciclane (r(s)=0.51, P=0.0498) concentrations and the magnitude of increase of desipramine AUC. Both deramciclane and paroxetine decreased the formation of 2-OH-desipramine in the first-pass phase. The AUC ratio of 2-OH-desipramine/desipramine was decreased by 39% ( P<0.001) by deramciclane and by 74% ( P<0.001) by paroxetine. There were no changes in the secretion of saliva during co-administration of desipramine with deramciclane compared with placebo.

CONCLUSION

Although deramciclane seems to be a weaker inhibitor of CYP2D6 than paroxetine, dose adjustment of drugs metabolized by CYP2D6 may be needed when used concomitantly with deramciclane.

Enteral Drug Absorption in Patients with Short Small Bowel

Drug therapy may become difficult when a significant amount of the small intestine is resected, as happens in patients with a short small bowel. Drug absorption from the gastrointestinal tract is altered in these patients; however, this effect is variable in patients and differs with each drug. Literature regarding clinical outcomes of normal or alternative administration routes in patients with a short small bowel is limited. We explored what is written about the normal absorption of commonly used drugs and what difference the resection of different but substantial parts of the small intestine makes. Changes in the gastrointestinal tract after resection of >50% of the small intestine causes malabsorption of macronutrients and micronutrients, and may alter the drug absorption process. The metabolic activity of the abundantly present intestinal lactobacilli can also affect the enteral drug absorption in patients with short small bowel as this results in the production of lactic acid, gaseous CO(2), ethanol and an increased bile acid deconjugation. Accelerated intestinal luminal transit time causes a reduction in absorption of certain antimicrobial agents, digoxin, hydrochlorothiazide, ciclosporin, cimetidine, mesalazine (5-aminosalicylic acid), oral contraceptives and levothyroxine. Gastric hypersecretion and lack of sufficient contact time with the intestinal mucosa in patients with short small bowel leads to insufficient absorption of drugs such as omeprazole. Successful treatment with warfarin, tricyclic antidepressants, metronidazole, fluconazole, procainamide, sotalol and pindolol are reported in several studies. Many different factors cause this variability in drug absorption in such patients. Monitoring the serum drug concentration in these patients may ease dealing with the management problems.

Potential and Practical Adrenomedullary PET Radiopharmaceuticals as an Alternative to m-Iodobenzylguanidine: m-(ω-[18F]Fluoroalkyl)benzylguanidines

To investigate adrenomedullary radiopharmaceuticals for positron emission tomography (PET), we have developed no-carrier-added m-(omega-[18F]fluoroalkyl)benzylguanidines. m-(omega-[18F]Fluoroalkyl)benzylguanidines were prepared in two steps starting from N,N'-bis(tert-butyloxycarbonyl)-N' '-(omega-methanesulfonyloxyalkyl)benzylguanidines in 20-30% radiochemical yields (decay corrected for 100 min) and with high radiochemical purity (>97%) and shown to be stable (>90%) in an in vitro metabolic stability assay. The binding of m-(3-[18F]fluoropropyl)benzylguanidine ((18F]3) to SK-N-SH human neuroblastoma cells was temperature dependent, and binding levels at 4 degrees C were reduced to half of that at 37 degrees C, which was similar to the reduction rate observed for [123I]MIBG. Tissue distribution studies in mice showed the highest uptake in the adrenals (%ID/g = 27.2 +/- 5.0%) with relatively high uptake in the myocardium (%ID/g = 9.3 +/- 0.5%). The results suggest that this radiotracer holds promise as a useful adrenomedullary radiopharmaceutical for PET imaging.

Trimipramine pharmacokinetics after intravenous and oral administration in carriers of CYP2D6 genotypes predicting poor, extensive and ultrahigh activity

OBJECTIVE

The tricyclic antidepressant trimipramine is one of the drugs with the most pronounced differences in pharmacokinetics caused by the CYP2D6 genetic polymorphism. However, the effect of CYP2D6 genotype on steady state kinetics and on bioavailability has not been studied so far. In addition, we were interested in trimipramine pharmacokinetics in genetically defined ultra rapid metabolizers.

METHODS

We studied intravenous and multiple dose oral application of 50 mg trimipramine in five, seven, and three healthy volunteers with CYP2D6 genotypes predicting deficient, highly active and ultrarapid metabolism. The latter group included carriers of one wild-type and one duplication allele. Trimipramine and desmethyltrimipramine concentrations were measured by HPLC over a time interval of 72 h after intravenous and after one oral application.

RESULTS

Both bioavailability and systemic clearance significantly depended on CYP2D6 genotype with a linear gene dose relationship. Mean bioavailability was 44, 16 and 12% in carriers of zero, two and three active genes of CYP2D6, respectively, and the corresponding data for systemic clearance were 12.0, 24.2, and 30.3 l/h. Consequently, the mean total oral clearances were 27.3, 151, and 253 l/h in poor, extensive and ultrarapid metabolizers.

CONCLUSIONS

High bioavailability combined with low systemic clearance of trimipramine in poor metabolizers of CYP2D6 substrates results in a very high exposure to trimipramine with the risk of adverse drug reactions. On the other hand, the extremely high systemic and presystemic elimination may result in sub-therapeutic drug concentrations in carriers of CYP2D6 gene duplications with a high risk of poor therapeutic response.

Age-dependent antidepressant pharmacogenomics: polymorphisms of the serotonin transporter and G protein beta3 subunit as predictors of response to fluoxetine and nortriptyline

In 169 depressed patients randomized to treatment with either fluoxetine or nortriptyline, we examined whether polymorphisms of the serotonin transporter and the G protein beta3 subunit influenced response to these antidepressants. For depressed patients under the age of 25 yr the T allele of the G protein beta3 subunit was associated with a markedly poorer response to nortriptyline, while serotonin transporter polymorphisms did not predict antidepressant response. However, in patients 25 yr or older, the G protein beta3 polymorphisms did not predict antidepressant response, while the s,s genotype of the serotonin transporter was associated with a poorer response to both fluoxetine and nortriptyline. These differential pharmacogenetic predictors of antidepressant response by age, may provide clues to understanding the discontinuities in pharmacological responsiveness of child/adolescent and adult depressive disorders.

Determination of mirtazapine in human plasma by liquid chromatography

A rapid high-performance liquid chromatographic method for the quantitation of mirtazapine in human plasma is presented. The method is based on a liquid-liquid extraction and reversed-phase chromatography with fluorimetric detection. The separation was performed on a Luna microm C(18)(2) 50 x 4.6 mm I.D. column using an isocratic elution. Zolpidem hemitartrate was used as the internal standard. The between-day precision expressed by relative standard deviation was less than 5% and inaccuracy does not exceed 6%. A low limit of quantitation (1.5 ng/ml) and a short time of analysis (4 min) makes this assay suitable for pharmacokinetic studies.

Are gender differences important for the clinical effects of antidepressants?

OBJECTIVE

Gender differences in antidepressant treatment response, side effects, dropout rates, and plasma concentrations were examined in patients with major and predominantly melancholic depression.

METHOD

The study included a subgroup of 292 inpatients (96 men, 196 women) from three Danish double-blind, randomized, controlled trials. All patients completed a 5-week treatment period and fulfilled the DSM-III or DSM-III-R criteria for major depression. Clomipramine (150 mg/day) was the reference treatment, and comparable treatments were citalopram (40 mg/day), paroxetine (30 mg/day), and moclobemide (400 mg/day). Assessments were performed by using the 17-item Hamilton Depression Rating Scale and the Udvalg for Kliniske Undersøgelser Side Effect Rating Scale. In a subgroup of 110 patients, weekly measurements of clomipramine plasma concentrations were obtained. Nonparametric statistical tests and multiple linear and logistic regression models were used for statistical evaluations.

RESULTS

Both genders had similar remission rates (Hamilton depression scale score <8) when treated with clomipramine and had significantly higher remission rates with clomipramine than with the comparable treatments. The plasma concentrations of clomipramine were significantly higher for female than for male patients. No gender differences were found in posttreatment Hamilton depression scale scores, nor did the therapeutic effects of treatment depend on gender. Rates of dropout and side effects were similar for men and women. No relationship between plasma concentrations, gender, and therapeutic outcome was found.

CONCLUSIONS

In a group of patients with major and predominantly melancholic depression, differentiation according to gender was not important in treatment with common antidepressants. Women appeared to have higher plasma concentrations of tricyclic antidepressants than men. The consequences of this difference for clinical effects are unclear. Gender-specific recommendations for dosing of tricyclic antidepressants may be considered.