Nortriptyline plasma levels and therapeutic response

Phase 1 Clinical Trials of Small Molecules: Evolution and State of the Art

BACKGROUND

Phase 1 studies comprise the first exposure of a promising new chemical entity in healthy volunteers or, when appropriate, in patients. To assure a solid foundation for subsequent drug development, this first step must carefully assess the safety and tolerance of a new compound and often provide some indication of potential effect, so that a safe dose or dose range can be confidently selected for the initial Phase 2 efficacy study in the target patient population.

METHODS

This review was based on a literature search using both Google Scholar and PubMed, dated back to 1970, using search terms including "healthy volunteers", "Phase 1", and "normal volunteers", and also based on the authors' own experience conducting Phase 1 clinical trials. This paper reviews the history of Phase 1 studies of small molecules and their rapid evolution, focusing on the critical single and multiple dose studies, their designs, methodology, use of pharmacokinetic and pharmacodynamic modeling, application of potentially helpful biomarkers, study stopping criteria, and novel study designs.

RESULTS

We advocate for determining the safe dose range of a new compound by conducting careful dose escalation in a well-staffed inpatient setting, defining the maximally tolerated dose (MTD) by reaching the minimally intolerated dose (MID). The dose immediately below the MID is then defined as the MTD. This is best accomplished by using appropriately screened patients for the target indication, as patients in many CNS indications often tolerate doses differently than healthy non-patients. Biomarkers for safety and pharmacodynamic measures can also assist in further defining a safe and potentially effective dose range for subsequent clinical trial phases.

CONCLUSION

Phase 1 studies can yield critical insights into the pharmacology of a new compound in man and offer perhaps the only development period in which the dose range can be safely and thoroughly explored. Phase 1 studies often contain multiple endpoint objectives, the reconciliation of which can present a dilemma for drug developers and study investigators alike, but which can crucially determine whether a compound can survive to the next step in the drug development process.

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.

Exploratory Biomarker Study of the Triple Reuptake Inhibitor SEP-432 Compared to the Dual Reuptake Inhibitor Duloxetine in Healthy Normal Subjects

INTRODUCTION

SEP-432 is a triple monoamine reuptake inhibitor of norepinephrine (NE), serotonin (5-HT), and dopamine (DA), based on in vitro binding studies. We sought evidence that SEP-432 engages these monoamine systems by measuring concentrations of monoamines and/or their main metabolites in cerebrospinal fluid (CSF) and plasma and comparing results to duloxetine, a dual reuptake inhibitor of NE and 5-HT.

METHODS

Eighteen healthy normal subjects received either SEP-432 (300 mg/day), duloxetine (60 mg/day), or placebo for 14 days in-clinic (double blind) with CSF and plasma collections at baseline (single lumbar puncture) and Day 14 (24-h CSF and plasma collection). Concentrations of monoamines and their metabolites, as well as pharmacokinetic concentrations of SEP-432 and metabolite, were quantified by liquid chromatography-tandem mass spectrometry.

RESULTS

Compared to placebo in the Day 14 area under the curve 24-h (AUC0-24 h ) analysis, SEP-432 significantly (P < 0.05) decreased the NE metabolite dihydroxyphenylglycol (DHPG) in CSF and plasma, decreased 5-HT in plasma, and did not affect DA metabolites, while duloxetine had significant effects on DHPG and 5-HT. Time-matched baseline to Day 14 biomarker comparisons confirmed these findings.

CONCLUSION

CSF monoamine biomarkers confirmed central NET activity for SEP-432 and duloxetine's dual reuptake inhibition.

Personalized psychopharmacology for the affective disorders and schizophrenia: where is the evidence?

Individualized medicine is the ultimate aim of many medical specialties. Attempts to individualize psychopharmacology have focused on the genetic polymorphisms of neurotransmitter- and CNS-related genes. While there have been numerous reports on the discovery of possible genetic differences in various psychiatric disorders, clinical psychopharmacology has not yet significantly benefited from such data. At present, individualized psychopharmacology in practice is still largely the choice of drugs with the least side effects for a particular patient.

Evaluation of an integrated in vitro–in silico PBPK (physiologically based pharmacokinetic) model to provide estimates of human bioavailability

PK express module is a physiologically based model of first pass metabolism, which integrates in vitro data with an in silico physiologically based pharmacokinetic (PBPK) model to predict human bioavailability (F(H)). There are three required inputs: FDp (Fraction dose absorbed, final parameter from iDEA absorption module), protein binding (fu) and disappearance kinetics in human hepatocytes. Caco-2 permeability, aqueous solubility (at multiple pH's), estimated dose and chemical structure are inputs required for the estimation of FDp (Norris et al., 2000; Stoner et al., 2004) and were determined for all compounds in our laboratory or obtained from literature. Protein binding data was collected from literature references and/or Pfizer database. Human hepatocyte data was generated in-house using an automated human hepatocyte method (using Tecan Genesis Workstation) as described previously (). Sixteen compounds (commercial and Pfizer compounds) were chosen to evaluate the PK express model and the bioavailability predicted from the module was compared with known clinical endpoints. For majority of the 16 compounds (approximately 80%), the PK express model F(H) values were comparable to the known human bioavailability (F(H)) (within 23.7 units of the known human (true) F, except for PF 3, PF 4, PF 6). In conclusion, the PK express model integrates a number of key readily available discovery parameters and provides estimates of human performance by integrating in silico and experimental variables built on a physiological based pharmacokinetic model. Information from this model in conjunction with other ADME data (e.g., P450 inhibition) will enable progression of most promising compounds for further in vivo PK and/or efficacy studies.

Is dose escalation of antidepressants a rational strategy after a medium-dose treatment has failed? A systematic review

BACKGROUND

Maximizing the dose of antidepressants is widely recommended in cases of non-response to medium-dose treatment. However, scientific evidence supporting high-dose treatment is scarce. Systematic studies comparing dose escalation with alternative strategies for refractory depression (i. e. augmentation or change of compound) are lacking. The aim of this publication is to review available direct and indirect evidence concerning dose increase of antidepressants after a medium-dose trial has failed.

METHOD

We performed a systematic literature search of Medline (1966-2003) and reviewed studies and publication references for available evidence.

DATA SOURCES AND STUDY SELECTION

Studies of the following types were included: 1) dose increase studies in treatment refractory patients, 2) comparative dose studies, 3) therapeutic drug monitoring studies.

RESULTS

Available data suggest differential efficacy of various pharmacological classes at more than medium-dosage. Direct evidence shows no increase of efficacy with high-dose selective serotonin reuptake inhibitor (SSRI) treatment; however, indirect evidence suggests enhanced therapeutic efficacy with high-dose tricyclic antidepressants. Few clinical data show ultra-high-dose treatment with the irreversible monoamine-oxidase-(MAO-) inhibitor tranylcypromine to be effective for refractory depression. Data concerning other selective compounds are insufficient to allow any definitive conclusion on the benefit of high-dose treatment.

CONCLUSIONS

Based on available data highdose antidepressant treatment of patients refractory to medium-dose treatment is recommended for tricyclic compounds but not for SSRI. Some data suggest beneficial efficacy of ultra-high doses of the irreversible MAOI tranylcypromine. Research on other substance groups is limited and inconclusive. Prospective studies comparing dose escalation with alternative strategies for treatment of non-responding patients are needed.

Validation of a semi-automated human hepatocyte assay for the determination and prediction of intrinsic clearance in discovery

An automated high throughput human hepatocyte assay has been established with a 96-well format using a Tecan Genesistrade mark Workstation. Validation of this assay was performed with nine commercially available compounds and an additional 10 Pfizer compounds with varying hepatic extraction ratios (E(H)) ranging from 0.02 to approximately 1. The incubation conditions in the automated assay are readily and precisely controlled and cell viability of over 80% was achieved in the automated assay further confirming its utility for absorption, distribution, metabolism, and excretion (toxicity) (ADME (T)) screening. The results of the nine commercial compounds correlate with both manually executed (R(2)=0.97) and literature reported experimental results (R(2)=0.93). Overall, measured E(H)s were within two-fold of the literature values for approximately 90% of the 19 compounds tested. Additionally, good inter- and intra-day reproducibility was observed for all the 19 compounds. In conclusion, an automated and robust assay suitable for simultaneously testing up to 48 compounds with multiple time points has been validated. Throughput of 192 compounds per run can be achieved using 384-well plates to meet increasing needs in drug discovery. Currently, this automated assay is used to support early discovery profiling towards lead optimization of various discovery targets/programs.

Management of psychiatric disorders in patients infected with human immunodeficiency virus

Psychiatric disorders increase the risk of acquiring human immunodeficiency virus (HIV) and increase morbidity from HIV-related illness by impeding treatment. The response to highly active antiretroviral therapies is impaired by poor patient adherence, a substantial component of which is related to mental illness and substance use disorders. The recognition of psychiatric disorders in most HIV clinics is an issue of utmost importance. We outline diagnostic and treatment issues for major depression, bipolar disorder, personality disorder, substance use disorders, and demoralization as seen in patients with HIV. Our experience at the Johns Hopkins Moore (HIV) Clinic has led us to conclude that treatment of these disorders greatly improves patient adherence to treatment and outcomes of HIV infection.

Nortriptyline blood levels and clinical outcome: meta-analysis of published studies

INTRODUCTION: An optimum range has been suggested for nortriptyline blood levels, above or below which patients respond poorly or do not respond at all to treatment. METHODS: A meta-analysis of published studies was performed to verify the existence of an optimal blood concentration range or therapeutic window in nortriptyline-treated depression patients. A MEDLINE search through the years 1970-1999 was carried out to identify original papers and review articles. Data concerning blood levels and percentage improvement were obtained concerning all included pacients. Univariate and multivariate analyses were performed for data comparison. Possible confounding variables, such as pre-treatment, setting (in or outpatients), and duration of treatment were also evaluated. RESULTS: From the 22 published studies found, only six of them with patients' individual data were included. We found an optimal range for nortriptyline concentrations (OR= 2.25, 95% CI = 1.15 to 4.39, p= 0.02). CONCLUSIONS: There may be a biphasic relationship of efficacy to plasma concentrations of nortriptyline, with a therapeutic window between 46 to 236 ng/ml.

Steady-state plasma levels of nortriptyline and its hydroxylated metabolites in Japanese patients: impact of CYP2D6 genotype on the hydroxylation of nortriptyline

The authors investigated the impact of the CYP2D6 genotype on steady-state concentrations of nortriptyline (NT) and its metabolites, trans-10-hydroxynortriptyline (EHNT) and cis-10-hydroxynortriptyline in a Japanese population of psychiatric patients. Forty-one patients (20 men and 21 women) were orally administered nortriptyline hydrochloride. The allele frequencies of the CYP2D6*5 and CYP2D6*10 were 4.9% and 34.1%, respectively. Significant differences in NT concentrations corrected for dose and weight were observed between the subjects with no mutated alleles and those with one mutated allele (mean +/- SD for no mutated alleles vs. one mutated allele: 70.3 +/- 25.4 vs. 98.4 +/- 36.6 ng/mL x mg(-1) x kg(-1); t = 2.54, dcf = 33, p < 0.05) and between the subjects with no mutated alleles and two mutated alleles (no mutated alleles vs. two mutated alleles: 70.3 +/- 25.4 vs. 147 +/- 31.1 ng/mL x mg(-1) x kg(-1); t = 5.87, df = 19, p < 0.0001). Also, a significant difference in the NT/EHNT ratio, which is representative of the hydroxylation ratio of NT, was observed between the subjects with no mutated alleles and those with two mutated alleles (no mutated alleles vs. two mutated alleles: 0.82 +/- 0.30 vs. 2.71 +/- 0.84; t = 7.86, df = 19, p < 0.0001). Multiple regression analysis showed that the number of mutated alleles of CYP2D6, which was the only significant factor, accounted for 41% and 48% of the variability in log(NT corrected for dose and weight) and log(NT/EHNT), respectively.

Therapeutic drug monitoring of psychotropic medications

Therapeutic drug monitoring (TDM) of a number of psychotropic medications has proven to be of value, enabling minimization of the limitations of considerable genetic variability in their metabolism and the high rates of poor compliance with many psychiatric disorders. Therapeutic ranges have been established for lithium, some of the tricyclic antidepressants, and clozapine. TDM has also been shown to be useful in avoiding toxicity (as many psychotropics have narrow therapeutic indices), particularly that due to interactions with other compounds.

Significance of monitoring plasma levels of amitriptyline, and its hydroxylated and desmethylated metabolites in prediction of the clinical outcome of depressive state

The clinical significance of monitoring the plasma levels of amitriptyline and its metabolites in prediction of the clinical outcome of depressive episode was investigated in 49 inpatients. Discriminant analysis of drug concentrations (at two weeks after initiation of drug treatment) and clinical outcome revealed that increasing the plasma levels of amitriptyline, cis-isomers of hydroxylated metabolites (Z-10-hydroxyamitriptyline and Z-10-hydroxynortriptyline) predicted a better clinical outcome, while increasing of plasma levels of nortriptyline and trans-isomers of hydroxylated metabolites (E-10-hydroxyamitriptyline and E-10-hydroxynortriptyline) were shown to predict a poor clinical outcome in the depressive episode of the subjects, and that clinical outcome of approximately 73% of the subjects could be correctly predicted.

Monitoring of plasma clozapine levels and its metabolites in refractory schizophrenic patients

Plasma concentrations of clozapine and its metabolites desmethylclozapine and clozapine N-oxide were measured in 61 patients with refractory schizophrenia. Before the initiation of clozapine, each patient was given haloperidol (HL) up to 60 mg/day for at least 4 weeks without improvement. Patients were then given a fixed dose of clozapine 400 mg/day. Patients were assessed with the Brief Psychiatric Rating Scale (BPRS) at baseline before HL therapy, at the end of HL at 6 weeks, before clozapine, and after 6 weeks of clozapine therapy. Clozapine and its metabolites were measured by high-performance liquid chromatography with ultraviolet detection. The mean plasma concentrations of clozapine, desmethylclozapine, and clozapine N-oxide were 598 +/- 314, 281 +/- 140, and 90 +/- 29 ng/ml, respectively. The mean decrease in the total BPRS scores from baseline clozapine to the 6-week treatment period was 11 +/- 4. Clinical improvement was noted to occur in most patients with clozapine plasma levels > 300 ng/ml. Improvement diminished in patients with clozapine plasma levels > 700 ng/ml. The most common adverse effects were sedation and hypersalivation. Significant correlations between plasma clozapine concentrations and adverse side effects were not found.

Population pharmacokinetics and pharmacodynamics: potential use for gathering dose-concentration-response

The population approach is a general term covering different aspects of kinetic and dynamic data collected mainly from drug-treated patients and new techniques allowing evaluation of sparse observations from each subject. Such data originate from clinically relevant conditions and can give information on several qualities of a drug. An example is given with the tricyclic antidepressant nortriptyline for which the kinetics and the concentration-effect relationship have been thoroughly documented previously with conventional techniques. We have evaluated retrospective data from a therapeutic drug monitoring service using a nonparametric population kinetic method (NPML) that allows description of kinetic outliers and nonlinear relationships between kinetic parameters and covariates. In addition, drug interactions, nonlinear kinetics and dosing habits were studied with other techniques corroborating previous results and adding new information. The concentration-effect relationship could not be evaluated from our data as information on efficacy and adverse effects was of too low quality. However, several controlled studies have defined a therapeutic concentration interval and a discussion on dosing strategies is based on this interval. Collection of sparse data in patients during phases II-IV of drug development as a complement to conventional studies is highly recommendable.

Population pharmacokinetics of nortriptyline during monotherapy and during concomitant treatment with drugs that inhibit CYP2D6--an evaluation with the nonparametric maximum likelihood method

Therapeutic drug monitoring data for nortriptyline (674 analyses from 578 patients) were evaluated with the nonparametric maximum likelihood (NPML) method in order to determine the population kinetic parameters of this drug and their relation to age, body weight and duration of treatment. Clearance of nortriptyline during monotherapy exhibited a large interindividual variability and a skewed distribution. A small, separate fraction with a very high clearance, constituting between 0.5% and 2% of the population, was seen in both men and women. This may be explained by the recent discovery of subjects with multiple copies of the gene encoding the cytochrome-P450-enzyme CYP2D6, which catalyses the hydroxylation of nortriptyline. However, erratic compliance with the prescription may also add to this finding. A separate distribution of low clearance values with a frequency corresponding to that of poor metabolizers of CYP2D6 (circa 7% in Caucasian populations) could not be detected. Concomitant therapy with drugs that inhibit CYP2D6 resulted in a major increase in the plasma nortriptyline concentrations. This was caused by a decrease in nortriptyline clearance, whereas the volume of distribution was unchanged. The demographic factors age and body weight had a minor influence on the clearance of nortriptyline which was also unaffected by the duration of treatment.

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.

Clinical significance of plasma levels of clomipramine, its hydroxylated and desmethylated metabolites: prediction of clinical outcome in mood disorders using discriminant analysis of therapeutic drug monitoring data

We measured the plasma concentrations of clomipramine and its metabolites, N-desmethylclompiramine, 8-hydroxy-N-desmethylclomipramine, 8-hydroxyclomipramine in 65 depressed patients with subtypes of DSM-III-R mood disorders receiving clomipramine hydrochloride. There were large interindividual variations in the concentrations of the parent and each of the metabolic compounds, though the overall correlations between drug concentrations and daily doses of clomipramine were highly significant. Metabolic ratios for both desmethylation and hydroxylation varied by 15-35-fold interindividually. Discriminant analysis of the data from drug concentrations and scores of Global Assessment of Functioning revealed that it is useful to monitor the concentrations of both desmethylated and hydroxylated metabolites in order to predict the clinical effects of clomipramine.

Are you recognizing depression in your patients?

Major depression is a prevalent condition that causes significant morbidity and mortality. Diagnosis may be complicated in depressed patients who offer a medical symptom as their chief complaint. Once the diagnosis is established, treatment is relatively straightforward. In prescribing an antidepressant, consideration should be given to the patient's previous response to medications, the documented efficacy of various agents, their side-effect profiles, and their potential for toxicity. Although the more severe and complicated cases should be referred to a psychiatrist, most depressed patients can be treated by their primary care physician.

Psychotropic drug use in the medically ill. Part II

Underlying medical illness and drug interactions may make the use of psychotropic agents problematic in some physically ill patients. This overview, published in two parts, discusses six major classes of psychotropic medications (cyclic antidepressants, monoamine oxidase inhibitors, benzodiazepines, neuroleptics, lithium, psychostimulants, and carbamazepine) and examines their use in the setting of specific types of medical illnesses (e.g., cardiovascular, pulmonary, hepatic, and renal disease). Practical considerations in using psychotropic medications in medical-surgical patients--particularly those who are elderly or medically debilitated--will receive special emphasis.

Psychotropic drug use in the medically ill: Part I

Underlying medical illness and drug interactions may make the use of psychotropic agents in some physically ill patients problematic. This overview, published in two parts, discusses six major classes of psychotropic medications (cyclic antidepressants, monoamine oxidase inhibitors, benzodiazepines, neuroleptics, lithium, psychostimulants, and carbamazepine) and examines their use in the setting of specific types of medical illnesses (e.g., cardiovascular, pulmonary, hepatic, and renal disease). Practical considerations in using psychotropic medications in medical-surgical patients, particularly those who are elderly or medically debilitated, receive special emphasis. In part I, the use of cyclic antidepressants, monoamine oxidase inhibitors, benzodiazepines, and buspirone are discussed.

The pharmacokinetics of tricyclic antidepressant drugs in the elderly

Antidepressants, especially tricyclic agents (TCAs), are increasingly used in geriatric patients since depression is a common mood disorder in the elderly and the size of elderly population is increasing. Notwithstanding the importance of kinetics to better use of drugs, its study in the elderly (regarding TCAs) is not sufficiently developed. The present paper briefly reviews the available data on amitriptyline, nortriptyline, protriptyline, imipramine, desipramine and clomipramine kinetics in the elderly.

Factors affecting the delay of antidepressant effect in responders to nortriptyline and phenelzine

Seventy-six elderly depressed patients who had responded to either nortriptyline or phenelzine after a trial of up to 3 months were examined. The mean week of response was nearly 6 weeks. Patients who were more severely depressed took longer to respond. Patients with endogenous depression responded sooner on nortriptyline than did patients with nonendogenous depression. For patients on nortriptyline, lower plasma levels in the early weeks of treatment may delay response while differences in platelet monoamine oxidase inhibition in the early weeks of treatment do not appear to affect week of response for patients on phenelzine.

Plasma levels and effects of nortriptyline in geriatric depressed patients

Pharmacokinetic, therapeutic effects, and side effects of nortriptyline were studied in geriatric depressed patients treated with a standard dose of 150 mg/day. Plasma levels and elimination half-life of nortriptyline were no different in geriatric patients than younger patients. The antidepressant therapeutic effects of nortriptyline appeared to be similar in geriatric patients as in younger depressed patients. Geriatric patients experienced few subjective side effects of nortriptyline. Overall, the drug produced no clinically significant changes in several parameters of the EKG, and no geriatric patient experienced tachycardia on nortriptyline. Nortriptyline did induce significant orthostatic hypotension in the systolic component, but not in the diastolic component. However, the orthostatic hypotension produced by nortriptyline was not greater in geriatric patients than in younger patients treated with the same dose.

Comparative efficacy and safety of MAOIs versus TCAs in treating depression in the elderly

This comprehensive study investigated both the role of antidepressant drugs in the treatment of affective disorders of later life and their safety with careful clinical and pharmacological monitoring. A 7-week double-blind comparison was made of the efficacy and safety of nortriptyline (a tricyclic), phenelzine (a monoamine oxidase inhibitor), and placebo. The results indicated a response rate of approximately 60% for both nortriptyline and phenelzine versus a 13% response rate for placebo. Anticholinergic side effects were more frequently reported in the nortriptyline group. Orthostatic symptoms were reported with similar frequency in both drug groups. Overall, both drugs were well tolerated.

The antiarrhythmic effect of nortriptyline in cardiac patients with ventricular premature depolarizations

The effect of nortriptyline against ventricular arrhythmias was determined in 16 cardiac patients with 30 or more ventricular premature depolarizations per hour. Nortriptyline was administered orally, 0.5 mg/kg body weight per day, and increased by 0.5 mg/kg per day every third day until ventricular premature depolarizations were suppressed (greater than or equal to 80%), adverse effects occurred or a total daily dose of 3.5 mg/kg per day was given. Each patient had daily 24 hour continuous electrocardiograms, 12 lead standard electrocardiograms and physical examination; blood pressure was measured in the supine and standing position four times a day. Each patient also had radionuclide angiography at rest to measure ejection fraction before and at the effective or maximal dose. Thirteen patients (81%) had an antiarrhythmic response and 11 met the study criterion of at least 80% improvement. Doses ranged from 50 to 200 mg/day (mean 111 +/- 45), steady state plasma concentration ranged from 46 to 410 ng/ml (mean 153 +/- 96) and half-life of elimination of nortriptyline was 4 to 22 hours (mean 13 +/- 4). Administration of nortriptyline did not depress mean ejection fraction (before 42 +/- 12%, after 41 +/- 12%); it was associated with an orthostatic decrease in systolic blood pressure (mean -13 +/- 13 mm Hg). Nortriptyline is an effective antiarrhythmic agent which may be given twice a day even in patients with impaired ventricular function.

Plasma tyrosine/neutral amino acid ratio correlated with clinical response to nortriptyline in endogenously depressed patients

Ratios in plasma of tryptophan (Trp) and tyrosine (Tyr) to other large neutral amino acids were determined in 26 endogenous depressives before and after treatment with nortriptyline in doses adequate to achieve a steady-state serum level between 70 and 130 ng/ml, i.e., within the recommended therapeutic range. Pretreatment plasma Trp ratio and Tyr ratio were normal and did not change significantly during treatment. The plasma Trp and Tyr concentrations and the plasma Trp ratio showed no significant association with the therapeutic response. However, the pretreatment plasma Tyr ratio correlated significantly and directly with the final Hamilton rating score, and inversely with the per cent reduction of Hamilton rating score. Moreover, depressives with plasma Tyr ratio below the normal mean showed significantly greater clinical improvement than patients with higher plasma Tyr ratio with comparable serum nortriptyline levels. Evidence has been presented that biochemical variables in depressed patients are important determinants of clinical improvement following pharmacotherapeutic treatment. Moreover, the results suggest that the plasma Tyr ratio may be a guideline for antidepressant response to nortriptyline.

Therapeutic monitoring of psychotherapeutic drugs: role of the clinical laboratory

Therapeutic monitoring of drugs is a well established clinical tool. However, the state of the art is somewhat less advanced for drugs used in psychiatry than it is for other classes of drugs, for several reasons. Most psychotherapeutic drugs have large volumes of distribution and achieve relatively low plasma concentrations following therapeutic doses. Many have one or more active metabolites. While psychotherapeutic drugs act through biochemical mechanisms, they are used to treat clinical syndromes which may be heterogeneous in their biochemical pathogenesis. As a consequence, the analytical methodologies are often complex and not always reliable; well-controlled clinical studies are difficult to perform; the therapeutic ranges have been difficult to establish. Despite these limitations, prudent and selective monitoring of serum drug concentrations, particularly of the tricyclic antidepressants, can be helpful in clinical management.

Plasma nortriptyline and clinical response in depression

Plasma levels of nortriptyline below 50 ng/ml or above 150 ng/ml have been reported to yield results inferior to intermediate levels. In the present study, patients with uncomplicated primary, nonbipolar depression were randomly assigned to 12 weeks of treatment with NT alone or with cognitive therapy. Nine of 35 patients had mean NT plasma levels less than 50 ng/ml. Five of them improved clinically to the criterion level of less than or equal to 7 on the Hamilton Rating Scale for Depression. This improvement rate was not at all different from that of patients with mean plasma levels within the presumed therapeutic window. The upper limit of 150 ng/ml was not tested. This study is presented in the hope of reviving the apparently dormant search for optimal therapeutic plasma levels of antidepressants.

Determination of citalopram, amitriptyline and clomipramine in plasma by reversed-phase high-performance liquid chromatography

The determination of citalopram, amitriptyline, clomipramine and their desmethyl metabolites after alkaline diethyl either extraction from plasma is achieved by high-performance liquid chromatography using two internal standards and mu Bondapak C18 as stationary phase. Elution is carried out isocratically at 0.5 or 1 ml/min with a mixture of acetonitrile-potassium dihydrogen phosphate-distilled water (45:50:5). Detection is monitored by absorption at 254 nm. The detection limit is less than 5 ng/ml for each compound. The coefficients of variation are between 1.3% and 9.4% for 8-360 ng/ml. Interference from 22 possible co-medications is discussed. The technique can be used for therapeutic monitoring of these antidepressants as well as in analytical toxicology.

Seizures with antidepressants: an in vitro technique to assess relative risk

The relative potential of various antidepressants to induce seizures while being used at therapeutic doses was studied by examining their action on spike activity in perfused guinea pig hippocampal slices. Within the range of concentration studied, imipramine, amitriptyline, nortriptyline, maprotiline, and desipramine tended to increase spike activity in a descending order of effect. Doxepin and nomifensine increased spike activity at lower concentrations, but reduced it at higher concentrations. Protriptyline and trimipramine reduced spike activity with increasing concentrations, whereas mianserin and viloxazine had little effect at any concentration. These findings are discussed in light of previous clinical and laboratory reports, and the clinical implications of these findings are presented. Finally, results with the antidepressants are compared with those previously observed with neuroleptics. On the basis of this comparison and a review of clinical reports, the assumption that neuroleptics have greater epileptogenic potential than antidepressants is questioned.

Cardiotoxicity of tricyclic antidepressants in primary cultures of rat myocardial cells

Primary cultures of myocardial cells were used to evaluate the cardiotoxic potential of various tricyclic antidepressants (TCAs). Lactate dehydrogenase (LDH) leakage, cellular viability, and beating rates were measured to compare the cardiotoxicity of amitriptyline, desipramine, imipramine, and nortriptyline. Tricyclic antidepressants were added to the cultures to give final concentrations of 1 X 10(-5), 1 X 10(-4), and 1 X 10(-3) M. Treatments lasted 1 and 4 h. All TCAs tested caused significant release of LDH and decreased cellular viability when added at 1 X 10(-3) M for 1 and 4 h. Amitriptyline was the only compound that caused significant LDH release 4 h after exposure to lower doses. Decreased viability was observed 4 h after exposure to all TCAs at a concentration of 1 X 10(-4) and 1 X 10(-3) M. Arrhythmias were observed 1 h after exposure to 1 X 10(-5) and 1 X 10(-4) M amitriptyline. All doses of amitriptyline inhibited beating 4 h after exposure. Imipramine, desipramine, and nortriptyline at a concentration of 1 X 10(-5) M decreased the beating rates of cultured myocytes 1 and 4 h after exposure. Arrhythmias and/or total inhibition of beating were observed when the cultures were exposed to higher concentrations of these compounds. Based on these data, the rank order of cardiotoxicity was amitriptyline greater than imipramine = desipramine greater than nortriptyline.

A collection of therapeutic, toxic and fatal blood drug concentrations in man

In order to assess the significance of drug concentrations measured in clinical and toxicological investigations, it is essential that good collections of data are readily available. As a guide to interpreting findings, the present work provides a compilation of therapeutic, toxic and fatal blood concentration ranges of 298 drugs of interest to clinical pharmacologists, clinical toxicologists, and forensic toxicologists. Wherever possible, ranges are expressed concisely in terms of the maximum blood concentrations which account for 10, 50 and 90% of the data collected. They provide easy access to the most reliable information which relates the blood drug concentration to the biological response it produces. Where appropriate, the different toxic effects of a drug and/or the different degrees of severity of toxic symptoms associated with different drug levels are clearly defined. The original sources of all data used are provided to allow the analyst to obtain further analytical, pharmacokinetic and toxicological information should this be necessary. Those factors (e.g. age, capacity for drug metabolism, drug interactions, etc) which can modify the relationship between a drug concentration and the response it produces are briefly discussed.

Nortriptyline plasma levels and clinical response in patients with familial pure unipolar depression and blunted TRH tests

We studied the efficacy of nortriptyline (NT) when given in doses which produce tricyclic antidepressant (TCA) levels within the proposed therapeutic "window" in a select patient group to assess the "window" hypothesis in a group of patients that was biologically homogeneous with respect to the TRH test and clinically homogeneous with respect to RDC, DSM III, and Winokur criteria. Pharmacokinetic and dose differences were controlled for by administering a NT dose-prediction test, giving the indicated dose, allowing levels to reach steady state and changing the dose, if necessary, to maintain NT levels within the range of 90-130 ng/ml. Using this protocol nine of ten patients responded to NT. This rate of response for a severely depressed patient group is comparable to response data for ECT and recent European data using regular NT levels to change doses of NT and assess appropriate NT trial duration.

Relationship between the plasma concentration of clomipramine and desmethylclomipramine in depressive patients and the clinical response

Thirty one in-patients suffering from depression were treated orally with clomipramine (C1) at various dosage, for 28 days, after a "wash-out" period of three days. In 17 patients receiving 75 mg per day of C1, steady state plasma levels of C1 were reached at Day 14, and steady state plasma levels of its active metabolite, desmethylclomipramine (DMC1), were reached at Day 21. In contrast, in 7 other patients receiving a dosage increasing to 150 mg per day at Day 7, mean plasma levels of C1 and DMC1 continued to rise during the entire treatment period. At the steady state, a correlation was found between C1 dosage expressed as mg kg body weight and the plasma concentration of C1 and DMC1. Factors such as tobacco and alcohol consumption seem to modify the C1/DMC1 ratio. A comparison of clinical response with plasma levels of C1, DMC1 and C1 + DMC1 showed a significant negative linear correlation.

Nortriptyline therapy in elderly patients: dosage prediction from plasma concentration at 24 hours after a single 50 mg dose

Ten depressed elderly female patients in hospital (mean age 82 years) received a single oral dose of 50 mg nortriptyline prior to commencing treatment with this drug. The nortriptyline concentration in a plasma sample obtained 24 hours afterwards was used to predict the daily dose required to achieve a steady-state concentration within the range of 50-150 micrograms. l-1. The mean daily dose prescribed was 50 mg (range 20-100 mg). These dosage regimes provided a mean observed steady-state nortriptyline concentration of 104 micrograms. l-1, with a range of 76-180 microgram. l-1 (S.D. 30 microgram. l-1). Use of this prediction test can prevent the development of toxic plasma concentrations and enhance the possibility of therapeutic success.

Pharmacokinetic linearity of desipramine hydrochloride

The pharmacokinetic linearity of two single oral doses of desipramine hydrochloride was examined in a parallel study involving 30 subjects. Fourteen subjects received 75 mg (3 x 25 mg) of desipramine hydrochloride, and 16 subjects received 150 mg (1 x 150 mg). An open one-compartment model with a lag time to the start of absorption was used to examine the pharmacokinetic linearity. The results of the study suggest that the kinetics are linear in the dose range studied.

The pharmacokinetics of nortriptyline in patients with chronic renal failure

1 The pharmacokinetics of single oral doses of nortriptyline were studied in twenty patients with chronic renal failure, eight of whom were receiving treatment with haemodialysis. 2 The median nortriptyline half-life was 25.2 h (range 14.5-140.0 h) and the median nortriptyline clearance was 32.3 l/h (range 8.1-122.0 l/h). 3 No differences were observed between the dialysed and non-dialysed groups. 4 Comparisons of nortriptyline half-life and clearance between the patients and groups of physically healthy subjects revealed no significant differences. 5 There was no significant linear correlation between age and either of these measurements. In the twelve patients not receiving haemodialysis there was no correlation between nortriptyline clearance and glomerular filtration rate. 6 Chronic renal failure is not associated with a significant alteration in nortriptyline metabolism as measured by its half-life or clearance, but the drug should nonetheless be used with caution, and monitored whenever possible. However, the marked inter-individual differences observed in nortriptyline half-life and clearance in patients with chronic renal failure may not be solely responsible for their unpredictable response to tricyclic antidepressant therapy, and other possible contributory factors are discussed.

Fluphenazine pharmacokinetics and therapeutic response

We conducted a double-blind study of therapeutic outcome versus mean steady-state levels in 29 newly admitted schizophrenic and schizoaffective patients who were treated with a constant dose of fluphenazine HCI over a 2-week period. both an upper and lower end of the therapeutic window were suggested by three nonresponders whose plasma levels were above 2.8 ng per ml and by two nonresponders and one partial responder whose plasma levels were below 0.2 ng per ml. The mean terminal half-life of fluphenazine (+ or - SD) was 16.4 + or - 13.3 h. We found that concomitant use of benztropn mesylate during the initial 4 weeks of fluphenazine treatment did not significantly alter fluphenazine plasma levels.

Evaluation of the cytotoxicity of tricyclic antidepressants in primary cultures of rat hepatocytes

Primary cultures of hepatocytes from postnatal Sprague-Dawley rats were grown in arginine-deficient, ornithine-supplemented medium to inhibit fibroblastic overgrowth and to selectively isolate relatively pure cultures of parenchymal hepatocytes. This system of primary cultures of rat hepatocytes was utilized to evaluate the cytotoxicity of certain tricyclic antidepressant drugs (TCAs). The compounds tested were chosen to represent two distinct chemical classifications of TCAs: the dibenzazepine derivatives, imipramine (1) and desipramine (D), and the dibenzocycloheptadiene derivatives, amitriptyline (A) and nortriptyline (N). The study also allowed direct comparison of the parent tertiary amines, A and I, and their respective demethylated pharmacologically active metabolites, N and D. The hepatotoxicity of the compounds was determined by measuring leakage of cytoplasmic enzymes, lactate dehydrogenase (LDH) and glutamic-pyruvic transaminase (GPT), into the culture medium and by assessing cell viability by the trypan blue dye exclusion test. LDH leakage was a more sensitive index of early cellular injury in this study. The compounds demonstrated a dose- and time-dependent order of toxicity; their hepatotoxicity potency was ranked as A = N greater than D greater than I.

Efficacy of desipramine in endogenomorphically depressed patients

This study was designed to test the hypothesis that there are 2 biochemical subgroups of 'endogenously' depressed patients--serotonin-deficient and noradrenalin-deficient groups--which respond differently to antidepressants depending on relative blockade of serotonin vs. norepinephrine (NE) reuptake. Patients with pervasive anhedonia and autonomy of depressed mood (endogenomorphic depressives) were treated first with the noradrenergic agent desipramine (DMI), then, if still depressed, such patients were randomized double-blind to continued DMI or clomipramine (CMI), a primarily serotonergic agent. Of 34 such endogenomorphically depressed patients 2 responded during a placebo period and 5 dropped out. Of 27 patients completing at least 4 weeks of DMI (mean maximum daily dose 283 mg, range 100-400 mg/d), 23 (85.2%) responded. With only 4 nonresponders, the second, or CMI, part of the study had to be abandoned. Since DMI strongly blocks neuronal reuptake of catecholamines with little effect on serotonin reuptake, these results suggest that endogenomorphic depressives may have a relatively homogeneous catecholamine deficiency. Alternatively, DMI may exert its effect by a mechanism other than blockade of EN reuptake. Eleven of the endogenomorphically depressed patients also met Research Diagnostic Criteria for situational depression (reactive). Ten of these 11 responded to DMI suggesting that presence or absence of a precipitant may be irrelevant in predicting response to tricyclic antidepressants in endogenomorphic depressions. Mean blood levels drawn at equivalent DMI dose were 238 ng/ml (range, 48-712) for responders, and 352 ng/ml (range, 160-877) for non-responders, indicating that patients appear to respond to DMI across a wide range of blood levels and suggesting the absence of a narrow therapeutic window.