Effects of several tricyclic antidepressants on the hemodynamics and myocardial contractility of the anesthetized dogs

Inhibition of G protein-activated inwardly rectifying K+ channels by various antidepressant drugs

G protein-activated inwardly rectifying K+ channels (GIRK, also known as Kir3) are activated by various G protein-coupled receptors. GIRK channels play an important role in the inhibitory regulation of neuronal excitability in most brain regions and the heart rate. Modulation of GIRK channel activity may affect many brain functions. Here, we report the inhibitory effects of various antidepressants: imipramine, desipramine, amitriptyline, nortriptyline, clomipramine, maprotiline, and citalopram, on GIRK channels. In Xenopus oocytes injected with mRNAs for GIRK1/GIRK2, GIRK2 or GIRK1/GIRK4 subunits, the various antidepressants tested, except fluvoxamine, zimelidine, and bupropion, reversibly reduced inward currents through the basal GIRK activity at micromolar concentrations. The inhibitions were concentration-dependent with various degrees of potency and effectiveness, but voltage- and time-independent. In contrast, Kir1.1 and Kir2.1 channels in other Kir channel subfamilies were insensitive to all of the drugs. Furthermore, GIRK current responses activated by the cloned A1 adenosine receptor were similarly inhibited by the tricyclic antidepressant desipramine. The inhibitory effects of desipramine were not observed when desipramine was applied intracellularly, and were not affected by extracellular pH, which changed the proportion of the uncharged to protonated desipramine, suggesting its action from the extracellular side. The GIRK currents induced by ethanol were also attenuated in the presence of desipramine. Our results suggest that inhibition of GIRK channels by the tricyclic antidepressants and maprotiline may contribute to some of the therapeutic effects and adverse side effects, especially seizures and atrial arrhythmias in overdose, observed in clinical practice.

Imipramine, mianserine and maprotiline block delayed rectifier potassium current in ventricular myocytes

Imipramine, mianserine and maprotiline are three widely used antidepressant drugs with different chemical structure. In the present work we have studied the effects of these drugs on the delayed rectifier potassium current (I(K)) in myocytes isolated from rat ventricle. The delayed rectifier potassium current, responsible for action potential termination, is blocked by all of the three drugs I(K)studied in a state-independent manner. Imipramine and mianserine block I(K)in a 1 : 1 drug-receptor interaction, whereas maprotiline shows a negative cooperativity in the interaction between the channel complex and drug molecules.

Effects of clomipramine hydrochloride on heart rate and rhythm in healthy dogs

OBJECTIVE

To determine the effects of clomipramine hydrochloride on heart rate and rhythm in dogs.

ANIMALS

17 healthy Beagles.

PROCEDURES

In experiment 1, 8 dogs received placebo or clomipramine (20 mg/kg of body weight, q 24 h, PO) for 7 days in a 2-way crossover design. In experiment 2, 9 dogs were evaluated for 48 hours before and 24 hours after oral administration of clomipramine (4 or 12 mg/kg) in a 2-way crossover design. Electrocardiogram and heart rate were monitored continuously by use of telemetry.

RESULTS

A significant diurnal rhythm in heart rate was detected; minimum values were recorded at night. Administration of 20 mg of clomipramine/kg induced a significant reduction in heart rate, with peak effect achieved approximately 12 hours after dosing. Administration of 4 or 12 mg of clomipramine/kg did not result in significant changes in heart rate. Sinoatrial and second-degree atrioventricular block and ventricular escape beats were observed during periods of slow heart rate in more dogs that received clomipramine (3 to 4 of 8 dogs), compared with dogs that received placebo (1 to 2 of 8 dogs), but this difference was not significant.

CONCLUSIONS AND CLINICAL RELEVANCE

Short-term administration of clomipramine induced benign cardiovascular effects in dogs rather than the potentially dangerous arrhythmias or tachycardia reported following administration of tricyclic antidepressants to humans. Precautions regarding cardiovascular effects may not be needed for the use of clomipramine in healthy dogs.

Cardiac electrophysiological effects of citalopram in guinea pig papillary muscle comparison with clomipramine

The effect of citalopram, a selective serotonin reuptake inhibitor (SSRI) antidepressant, was studied on cardiac action potential configuration and compared with that of the tricyclic antidepressant (TCA) clomipramine. Conventional microelectrode techniques were used in right ventricular papillary muscle preparations of the guinea pig. Citalopram caused a concentration-dependent (10-100 microM) shortening of action potential duration (APD), depression of plateau and overshoot potential, and reduction of maximum velocity of depolarization (V(max)). No significant changes in resting membrane potential were observed. Similar results were obtained with clomipramine; however, reduction of V(max) and overshoot was more pronounced with clomipramine, whereas citalopram caused relatively greater shortening of APD. Effects of both drugs were partly reversible. The results indicate that the SSRI antidepressant citalopram, similarly to TCA compounds, alters cardiac action potential configuration in guinea pig ventricular muscle, probably owing to inhibition of cardiac Na(+) and Ca(2+) channels. Differences in cardiac side effects of the two drugs may be related to their different actions on cardiac action potential configuration.

Metabolism of tricyclic antidepressants

1. Despite the considerable advances in the treatments available for mood disorders over the past generation, tricyclic antidepressants (TCAs) remain an important option for the pharmacotherapy of depression. 2. The pharmacokinetics of TCAs are characterized by substantial presystemic first-pass metabolism, a large volume of distribution, extensive protein binding, and an elimination half-life averaging about 1 day (up to 3 days for protriptyline). 3. Clearance of tricyclics is dependent primarily on hepatic cytochrome P450 (CYP) oxidative enzymes. Although the activities of some P450 isoenzymes are largely under genetic control, they may be influenced by external factors, such as the concomitant use of other medications or substances. Patient variables, such as ethnicity and age, also affect TCA metabolism. The impact of gender and related reproductive issues is coming under increased scrutiny. 4. Metabolism of TCAs, especially their hydroxylation, results in the formation of active metabolites, which contribute to both the therapeutic and the adverse effects of these compounds. 5. Renal clearance of the polar metabolites of TCAs is reduced by normal aging, accounting for much of the increased risk of toxicity in older patients. 6. Knowledge of factors affecting the metabolism of TCAs can further the development and understanding of newer antidepressant medications.

Effects of imipramine, an uptake inhibitor, on double-peaked constrictor responses to periarterial nerve stimulation in isolated, perfused canine splenic arteries

Using a cannula insertion method, periarterial nerve electrical stimulations were performed at 1 and 10 Hz in the isolated, perfused canine splenic artery. Electrical nerve stimulation readily caused double-peaked vasoconstrictions. The 1st-peak response at 1 Hz was not influenced by treatment with imipramine but the 2nd one was significantly enhanced by it. The 2nd-peak response was markedly blocked by prazosin. An additional treatment with alpha,beta-methylene ATP, a P2X-purinoceptor desensitizer, abolished electrical stimulation-induced vascular responses that remained. At 10 Hz, the responses to electrical stimulation were not significantly influenced by imipramine. On the other hand, the imipramine treatment inhibited the tyramine-induced vasoconstriction but potentiated the noradrenaline-induced one. ATP-induced responses were not modified by imipramine. From these results, it is concluded that 1) the 1st-peaked constriction is mainly due to a P2X-purinoceptor-dependent mechanism, 2) the 2nd one is mainly due to an alpha1-adrenoceptor-dependent mechanism, and 3) presynaptic uptake mechanisms may perform an important role in the regulation of vascular reactivity, especially at a low frequency.

Cardiovascular effects of therapeutic doses of tricyclic antidepressants in children and adolescents

OBJECTIVE

Tricyclic antidepressants (TCAs) play an important role in the treatment of pediatric psychiatric disorders. Despite widespread clinical use, concerns about their possible cardiovascular risk have arisen following several published reports of sudden death associated with their use in children. Accordingly, available evidence concerning TCA-associated cardiovascular effects in children and adolescents was surveyed.

METHOD

A systematic literature search from 1967 to 1996 identified relevant pediatric studies that evaluated cardiovascular effects of TCAs.

RESULTS

Twenty-four studies involving 730 children and adolescents given imipramine, amitriptyline, desipramine, or nortriptyline were found. TCA treatment was associated with minor increases in systolic and diastolic blood pressure, in heart rate, and in the electrocardiographic (ECG) conduction parameters, PR, QRS, and QTc. Holter ECG monitoring and exercise testing also revealed minor treatment effects. Some ECG changes related to specific TCAs emerged. Few age-related ECG differences in TCA-treated children, adolescents, or adults were detected. Associations of ECG abnormalities and relatively higher serum TCA levels were found.

CONCLUSION

TCA treatment in children and adolescents, like that in adults, is associated with cardiovascular changes of uncertain, but probably minor, clinical significance. More information is needed on the contribution of other physiological conditions on the cardiovascular system during exposure to TCAs. Guidelines for using TCAs in children and adolescents are presented.

Cyclic antidepressant toxicity in children and adolescents

We retrospectively evaluated the clinical and laboratory findings of all patients admitted to our facility during a 6.5-year period with a history of cyclic antidepressant ingestion (CAD). Outcome parameters [admission CAD concentration, arterial pH, and corrected QT (QTc) and QRS intervals] used in adult populations to predict morbidity after CAD ingestion were applied to our study population. During the study period, 45 patients (mean +/- SD age of 11.8 +/- 5.6 years) were admitted with CAD ingestion. Conduction delays were present in 17 patients, 9 of whom had QTc intervals greater than 0.43 seconds. Seven patients had generalized seizures; 7 required mechanical ventilation; 14 had Glasgow Coma Scores of 8 or lower on presentation; and one required pharmacologic support for hypotension. In our cohort, the mean admission serum CAD concentration was 461.5 +/- 477.4 ng/mL. Correlations were found between the arterial pH, the QRS interval, the QTc interval, and the admission CAD serum concentration. In an analysis of three subsets of patients (i.e., those with seizures, coma, and respiratory insufficiency), only patients who presented with seizures were found to have a significant prolongation in the QRS and QTc intervals. Pediatric patients who have ingested CADs and present with seizures would appear to be at increased risk for having conduction delays, cardiac dysrhythmias, and, presumably, attendant morbidity and mortality associated with an ingestion.

Magnesium potentiates imipramine toxicity in the isolated rat heart

STUDY OBJECTIVE

To study the effect of magnesium on cardiac function and hemodynamics during imipramine toxicity.

DESIGN

After stabilization, isolated, beating rat hearts were perfused with Krebs-Henseleit bicarbonate buffer (KHB) solution containing 2.0 mg/L imipramine (IMIP) and 2.4 mEq [Mg2+] until toxicity, defined as 25% widening of the ventricular depolarization duration (VDD). Experiments were performed at either constant coronary perfusion pressure or flow.

SETTING

Animal research laboratory of a large, urban hospital.

MEASUREMENTS

Heart rate, VDD, left ventricular pressure and +/- dP/dt, and coronary flow.

INTERVENTIONS

On onset of toxicity, KHB+IMIP was switched to either control (KHB+IMIP), magnesium (KHB+IMIP+4.0 or 6.0 mEq/L [Mg2+]), or hypertonic alkaline treatment (165 mEq/L [Na+], pH 7.55).

RESULTS

At a constant coronary perfusion pressure of 100 mm Hg, magnesium at 6.0 mEq produced significant decreases in heart rate, left ventricular pressure, +dP/dt, and increase in VDD versus control. With coronary flow held constant, magnesium reduced left ventricular pressure and +dP/dt but not heart rate or VDD. Incidences of electromechanical dissociation and asystole were higher with magnesium versus control. Hypertonic alkaline treatment tended to improve all parameters in constant pressure and constant flow experiments.

CONCLUSION

Magnesium potentiates IMIP-induced negative inotropic effects and cardiac conduction defects in isolated rat hearts.

Comparative evaluation of the acute effects of oxygen free radicals on myocardial contractility in anesthetized dogs with those occurring in the early stages of splanchnic artery occlusion and hemorrhagic shock

Oxygen free radicals are cytotoxic and generated in excessive quantities during reoxygenation of ischemic organs. It has been demonstrated that oxygen free radicals impair cardiac contractile mechanisms in in vitro studies as well as depress myocardial contractility in in vivo experiments. The objectives of the present studies are to evaluate alterations in cardiac contractility and hemodynamics in two canine models of shock, namely, Wigger's model of hemorrhage and splanchnic artery occlusion (SAO) model. The data obtained in these models are comparatively evaluated with that caused by oxygen free radicals. Pentobarbital anesthetized dogs were instrumented to record blood pressure, heart rate, left ventricular pressure, (LVP & LVEDP) and LVdp/dt. Contractility index was evaluated as max dp/dt.p. In the Wigger's model, during the period of hemorrhage or after reinfusion of the shed blood despite marked variations in preload and afterload, index of contractility was not altered. Similarly, in the SAO model also, during the period of occlusion or after release, contractility index was not depressed. However, in both the models, after reinfusion of the blood (Wigger's) or after release of splanchnic arteries, there were gradual deteriorations of stroke volume, cardiac output, and arterial blood pressure. In contrast, after generation of free radicals by exogenous administration of xanthine plus xanthine oxidase, cardiac contractility was significantly depressed leading to decreases in stroke volume, cardiac output, and blood pressure. Using identical procedures to evaluate contractility, we have demonstrated that the initial depression of myocardial contractility was not the causative factor for circulatory failure in the two models of shock.(ABSTRACT TRUNCATED AT 250 WORDS)

Clomipramine in the elderly: tolerance and plasma levels

Five elderly, treatment-resistant, depressed, female patients were closely monitored in a research setting during treatment with clomipramine. Plasma clomipramine levels were determined to establish a steady state. Elderly patients (67 to 80 years old) reached a therapeutic steady state at doses lower than that reported for midlife patients. Overall, clomipramine was well tolerated in this group. Depression, measured by the Hamilton Rating Scale for Depression, decreased 42%, and the frequency of somatic complaints, measured by the Rating Scale for Side Effects, declined by 57%. Clomipramine is specifically indicated for the treatment of obsessive-compulsive disorder and may be an alternative for elderly depressed patients, provided that lower doses and plasma clomipramine monitoring are used.

Cyclic antidepressant overdose: a review of current management strategies

Cyclic antidepressant (CA) overdose can produce life-threatening seizures, hypotension, and dysrhythmias. It accounts for up to half of all overdose-related adult intensive care unit admissions and is the leading cause of death from drug overdose in patients arriving at the emergency department alive. Several factors contribute to the significant morbidity and mortality associated with CA overdose. First, CAs are widely prescribed and are dispensed to patients at increased risk for attempting suicide. Second, drugs of this class generally have a low therapeutic toxic ratio. Third, in the majority of fatal cases, the patient dies before reaching a hospital. Finally, and of greatest significance for the clinician, the presenting signs and symptoms of CA overdose may be missed by the physician, even in cases of severe toxicity. Therefore, CAs must be considered early in any case of suspected overdose, and all such cases should be managed as potentially fatal ones. The following case demonstrates the current approach to the patient with significant CA toxicity.

Imipramine blocks rapidly activating and delays slowly activating K+ current activation in guinea pig ventricular myocytes

Imipramine is a tricyclic antidepressant drug that also exhibits antiarrhythmic effects and whose clinical spectrum of activity is similar to that of quinidine. It has been previously demonstrated that imipramine inhibits the aggregate time-dependent outward K+ current (IK). IK is composed of at least two components: a slowly activating La(3+)-resistant delayed rectifying current (IK,s) and a rapidly activating La(3+)-sensitive current (IK,r). To assess the effects of imipramine on IK,r and IK,s, single guinea pig ventricular myocytes were studied using the nystatin-perforated patch-clamp technique in the absence and in the presence of La3+. Imipramine inhibited IK,r and IK,s in a concentration-dependent manner. The effects of imipramine on the aggregate time-dependent outward current were more marked than those on IK,s alone. Thus, 1 mumol/L imipramine decreased the tail currents elicited on return to -30 mV after long depolarizing pulses (5 seconds, from -40 to +50 mV) in the absence and in the presence of La3+ by 27 +/- 4% and 15 +/- 3% (n = 6), respectively. Moreover, the inhibition induced by imipramine was greater after short (0.5-second) pulses than after 5-second depolarizing pulses, both in the absence and in the presence of La3+ (53 +/- 3% and 30 +/- 5%, respectively; n = 6; P < .05). Imipramine did not significantly modify either the activation midpoint or the slope factor of the aggregate IK and IK,s activation curves. The reduction of IK,s by imipramine was voltage dependent and was more marked at negative membrane potentials. In the presence of 1 mumol/L imipramine, the ratio of tail current to time-dependent current remained constant at 0.37 +/- 0.03, regardless of the test pulse duration at +50 mV. Thus, the envelope-of-tails test was satisfied in the presence of 1 mumol/L imipramine, which indicates that imipramine, at this concentration, blocks IK,r. Imipramine (1, 5, and 10 mumol/L) had no effect on the kinetics of the later phase of IK activation but delayed the beginning of the activation of IK,s by 62 +/- 22, 74 +/- 23, and 155 +/- 53 milliseconds in the presence of 1, 5, and 10 mumol/L imipramine, respectively. These results suggest that imipramine preferentially blocks rapidly activating K+ channels. In addition, experiments performed in the presence of 30 mumol/L La3+ suggest that the drug preferentially binds, but maybe not exclusively, to a closed state of the slowly activating K+ channel.

Electrocardiographic effects of desipramine and 2-hydroxydesipramine in children, adolescents, and adults treated with desipramine

OBJECTIVE

To assess the developmental effects of desipramine (DMI) treatment on the electrocardiogram (ECG), we investigated serum concentrations of DMI ([DMI]), and its major active metabolite 2-hydroxydesipramine ([OHDMI]) and ECG parameters.

METHODS

ECGs and [DMI] and [OHDMI] were analyzed from 50 children, 39 adolescents, and 30 adult psychiatric patients receiving DMI.

RESULTS

There were modest overall correlations between [DMI], [OHDMI], or [OHDMI+DMI], and the PR and QRS intervals when data from all 119 subjects were pooled. Within the pediatric age groups there were no significant associations between serum drug levels and heart rate or conduction intervals; and in all subjects with ECG abnormalities, there were some findings of higher [DMI], [OHDMI], and [OHDMI+DMI].

CONCLUSIONS

These findings indicate that only modest associations of [DMI] and [OHDMI] with ECG conduction intervals were found, and are not likely to be clinically significant in any of the age groups studied. Compared with adults, children and adolescents do not appear to be at increased risks for ECG changes related to DMI treatment or to circulating concentrations of [DMI] or [OHDMI].

Evaluation of the effects of dopexamine, a novel DA1 receptor and beta 2-adrenoceptor agonist, on cardiac function and splanchnic circulation in a canine model of hemorrhagic shock

In the present studies, the efficacy of dopexamine hydrochloride, a novel DA1-receptor and beta 2-adrenoceptor agonist in preventing deterioration of cardiovascular function in a canine model of hemorrhagic shock was investigated. Pentobarbital-anesthetized dogs were allowed to bleed into a height-regulated reservoir and the hypotensive state (about 40 mmHg) was maintained for a period of 150 min. Subsequently, blood was reinfused and recoveries in various hemodynamic variables were monitored for an additional period of 120 min. Either aqueous solvent or dopexamine HCl was randomly selected for i.v. infusion beginning 30 min before reinfusion of the blood and until the termination of the experiment. In the solvent-treated control group, various cardiovascular variables such as cardiac output, stroke volume, celiac and superior mesenteric arterial blood flows progressively declined to 50% or less of the basal values; these changes were associated with sustained increases in the regional as well as systemic vascular resistances. Dopexamine infusion lowered vascular resistances and facilitated recoveries in various hemodynamic variables to 80% to 100% of the basal values after reinfusion of the shed blood. With the exception of a transient inotropic effect during reinfusion in the dopexamine treated group, there were no essential alterations in the myocardial contractility, during the hypotensive state and/or after reinfusion of the blood. Hence, the results indicate that the efficacy of dopexamine to reduce vascular resistance by actions at DA1-receptors and beta 2-adrenoceptors would account for its ability to improve myocardial performance (secondary to reductions in afterload) and restoration of mesenteric and celiac hemodynamics.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental changes in serum concentrations of desipramine and 2-hydroxydesipramine during treatment with desipramine

Steady-state serum concentrations of desipramine (DMI) and its metabolite, 2-hydroxydesipramine (OHDMI), were measured in 40 children, 36 adolescents, and 27 adult psychiatric patients. The authors predicted that younger patients would show more efficient elimination of DMI, with greater amounts of OHDMI. OHDMI averaged 52% lower than DMI. DMI per weight-corrected dose (ng/mL: mg/kg) rose significantly with maturation, from 50 in children and 56 in adolescents to 91 in adults. Contrary to expectation, OHDMI per DMI dose also rose with age, from 17 in children and 20 in adolescents to 26 in adults. It was concluded that: (1) similar mg/kg doses of DMI result in lower DMI and OHDMI in children; (2) children metabolize both DMI and OHDMI more rapidly than adults; and (3) children do not have high circulating concentrations of OHDMI.

Effects of imipramine on the transient outward current in rabbit atrial single cells

1. The effects of imipramine on action potential characteristics and transient outward potassium current (It) of rabbit isolated atrial myocytes were studied using the whole-cell configuration of the patch-clamp technique. 2. Imipramine, 3 microM, decreased action potential amplitude and lengthened the action potential duration measured at 50% of repolarization, whereas it did not modify the final phase of repolarization or the resting membrane potential. These results are similar to those reported in multicellular rabbit atrial preparations. 3. Imipramine, 0.1-100 microM, induced a concentration-dependent inhibition of the peak amplitude of It, a shortening of the time to peak current and an increase in the inactivation rate. The acceleration of the current inactivation is to a major extent responsible for the decrease in the integral of the outward current measured at 50 ms after the start of the pulse. 4. The drug-induced block of It was not associated with changes in the voltage-dependence of the steady-state inactivation curve or in the process of recovery from inactivation of the current. Extrapolation to zero block shows that imipramine did not block It before its activation at the onset of the depolarization. These results suggested that imipramine does not affect the inactivated or the resting state of It channels. 5. It is concluded that in rabbit isolated atrial cells, imipramine inhibits It and that this effect is responsible for the lengthening of the action potential duration produced by this drug.

Imipramine and 2-hydroxyimipramine: comparative cardiotoxicity and pharmacokinetics in swine

The hemodynamic, cardiographic, and initial pharmacokinetic characteristics of the de novo administration of the 2-hydroxymetabolite (2-OH-IMI) of imipramine (IMI), compared with its parent was studied in a swine preparation. Cardiac output, arterial pressure, and the continuous electrocardiogram were assessed after the intravenous administration of the drug or its metabolite. Plasma, sampled over 120 min and CSF sampled at 60 min were analyzed by reverse phase HPLC with spectroflurometric detection. Equilibrium dialyses were performed on plasma sampled at 60 min. 2-OH-IMI, in doses of 5-6 mg/kg, compared to dosages of IMI up to 8.5 mg/kg, produced a significantly greater incidence of life-threatening arrhythmias, and caused profound and significant decreases in blood pressure and cardiac output. 2-OH-IMI had a smaller volume of distribution (Vd) and shorter half-life. CNS penetration, as estimated by CSF/plasma ratios, was significantly greater for 2-OH-IMI. These phenomena were partly accounted for by significantly less protein binding for the hydroxymetabolite. It is concluded that 2-OH-IMI has increased penetrance into the CNS despite a smaller Vd and that it is significantly more cardiotoxic than its parent.

Determination of imipramine, desipramine and their hydroxy metabolites by reversed-phase chromatography with ultraviolet and coulometric detection

A reversed-phase high-performance liquid chromatographic method is described which analyzes imipramine, desipramine and their corresponding 2-hydroxy metabolites with sequential ultraviolet and coulometric detection from a single common extraction step, so that a wider dynamic range of plasma concentrations can be measured requiring smaller sample volumes. Applicability is broader including single-dose pharmacokinetic studies as well as steady-state concentrations. The extraction procedure gives excellent recoveries for imipramine, desipramine and their metabolites (mean +/- S.D.): ultraviolet detection, imipramine 99.5 +/- 0.68%, desipramine 100 +/- 0.0%, 2-hydroxyimipramine 97.8 +/- 3.5% and 2-hydroxydesipramine 93.1 +/- 4.22%; coulometric detection, imipramine 97.5 +/- 1.9%, desipramine 98.3 +/- 1.2%, 2-hydroxyimipramine 90.3 +/- 4.0% and 2-hydroxydesipramine 86.6 +/- 7.5%.

NMDA receptors in the intermediolateral column of the spinal cord mediate sympathoexcitatory cardiac responses elicited from the ventrolateral medullary pressor area

Microinjections of L-glutamate into the intermediolateral column of the spinal cord (IML) at T1-T3 produced increases in heart rate (predominantly from the right IML) and myocardial contractility (predominantly from the left IML). Maximum responses were elicited from T2 segment. At this site, microinjections of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA), quisqualic acid, kainic acid and N-methyl-D-aspartic acid (NMDA) produced dose-dependent increases in heart rate and contractility which were blocked by kynurenate (a non-selective excitatory amino acid receptor antagonist). D-2-Aminophosphonoheptanoate (DAP-7) blocked the effects of NMDA but not kainic acid, quisqualic acid and AMPA. Bilateral microinjections of kynurenate (2 nmol) and DAP-7 (5 nmol) into the IML at T1-T3 significantly decreased the baseline values for contractility index and blocked the usual increase in contractility induced by unilateral microinjections of L-glutamate (1.77 nmol) into the ventrolateral medullary pressor area (VLPA). These observations suggest that: (1) a tonic excitatory input, involving an NMDA-like amino acid as a transmitter, is present in the IML at T1-T3 and (2) the stimulation of VLPA neurons results in the release of an NMDA-like excitatory amino acid in the IML at this level.

Sudden death in children receiving Norpramin: a review of three reported cases and commentary

The 1990 "package insert" for Norpramin, the Merrell Dow Pharmaceuticals Inc., brand of desipramine, was changed to include the following statement in the Adverse Reactions section, "There has been a report of an 'acute collapse' and 'sudden death' in an eight-year-old (18 kg) male, treated for two years for hyperactivity. There have been additional reports of sudden death in children." The purpose of this commentary is to review what is known about the three reported cases of sudden death and to discuss the implications of these tragedies for children receiving treatment with tricyclic drugs.

Toxicological findings after fatal amitriptyline self-poisoning

A case of fatal self-poisoning with amitriptyline is reported. Both the drug and its metabolite nortriptyline were quantified in several post-mortem tissues and fluids, including vitreous humor. Results are discussed in the light of the existing literature.

Relative effects of different spinal autonomic nuclei on cardiac sympathoexcitatory function

Mean arterial pressure and heart rate were monitored in immobilized and artificially ventilated male Wistar rats either anesthetized with pentobarbital or decerebrated at midcollicular level. The rate of increase in the left ventricular pressure was also monitored in order to compute contractility index. L-glutamate (1.77 nmole) was microinjected (10 nl) into the following autonomic nuclei of the spinal cord at C8 to T4 levels: 1) intermediolateral column (IML), 2) n. intercalatus spinalis (IC) and 3) n. intercalatus pars paraependymalis (ICpe); this region is commonly known as the central autonomic area (CA). The site of microinjection was marked by injection of a dye; these studies suggested that microinjections of glutamate into the IML are likely to encompass the neurons in the nucleus (n.) intermediolateralis thoracolumbalis pars principalis (ILp) and n. intermediolateralis thoracolumbalis pars funicularis (ILf). Sympathoexcitatory cardiac responses to glutamate microinjections were elicited from T1 to T3 levels; these responses could not be evoked at C8 and T4 levels. In each of these segments, maximum responses were obtained from the IML while the responses evoked from the IC and the CA were minimal. These results suggest that at T1 to T3 levels of the spinal cord, IML is the main cell group regulating sympathetic cardiac function; CA and IC may play a relatively minor role in this function.

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.

Evidence for altered desipramine disposition in methadone-maintained patients treated for cocaine abuse

Plasma concentrations of desipramine (DMI) and its 2-hydroxy metabolite (OHDMI) were compared among 72 patients being treated with desipramine for either depression (n = 39) or cocaine abuse (n = 33). Eleven cocaine abusers who were concurrently maintained on methadone had a significantly lower ratio of DMI dose to plasma concentration (0.9) than the depressives (2.2) or nonmethadone cocaine abusers (2.0). Their OHDMI/DMI ratios were significantly lower (0.19) than for either the other 22 cocaine abusers (0.39) or the depressed (0.50) patients. This difference was not due to DMI dosage. Although the underlying mechanism cannot be determined from these plasma studies, possible reduced hydroxylation of DMI in methadone patients suggests the need for DMI plasma monitoring.

Microinjections of cholinergic agonists into the intermediolateral cell column of the spinal cord at T1-T3 increase heart rate and contractility

Cardiovascular responses to the microinjections of cholinergic agonists into the intermediolateral cell column (IML) of the spinal cord at T1-T3 level were studied. Mean arterial pressure (MAP), heart rate (HR), the rate of increase in the left ventricular pressure (dp/dt) and contractility index (CI) were monitored in immobilized and artificially ventilated male Wistar rats either anesthetized with pentobarbital or decerebrated at mid-collicular level. Microinjections (20 nl) of carbachol (110-660 pmol) into the right IML elicited a marked increase in HR and a small increase in CI. A marked increase in the CI with relatively little effect on the HR was observed when carbachol was injected into the left IML. The cardioacceleratory effects of carbachol, but not those of L-glutamate, were blocked by prior microinjections of scopolamine (18 nmol) into the IML. Intravenous injections of chlorisondamine (a ganglion blocker) also blocked these effects of carbachol. Spinal transections at C4 or T6 level did not alter these responses. Microinjections of acetylcholine (0.01-1 nmol) into the right IML also produced tachycardic effects. The responses to acetylcholine were blocked by prior injections of a muscarinic receptor blocker (atropine hemisulfate, 0.2 nmol). Microinjections of a selective M2 muscarinic receptor agonist, cis-methyldioxolane (CD; 0.2-0.8 nmol), but not those of a relatively selective M1 receptor agonist (McN-A343; 2-3 nmol), into the right IML elicited an increase in HR. Previous microinjections of a selective competitive M2 receptor antagonist (AFDX-116; 0.8 nmol), but not those of a potent selective M1 receptor antagonist (pirenzepine; 2 nmol), into the IML blocked the effects of CD. Nicotine (0.25-1 nmol) when injected into the right IML also produced positive chronotropic effects. These responses were blocked by prior microinjections of hexamethonium (5 nmol). The above-mentioned results suggest that cholinoceptive neurons, interneurons or terminals are located in the areas of IML which control cardiac functions. Muscarinic as well as nicotinic receptors are present in this area. Muscarinic receptors are predominantly of the M2 type. The physiological significance of the presence of cholinergic receptors in this area in controlling cardiac functions remains to be established.

A double-blind placebo controlled study of desipramine in the treatment ADD: II. Serum drug levels and cardiovascular findings

In a 6-week study of children and adolescents with attention deficit disorder with hyperactivity (ADDH) in which desipramine (DMI) was highly effective and well tolerated, the mean maximal daily oral dose in the DMI-treated patients (N = 31) was 4.6 +/- 0.2 mg/kg. Additional data were obtained for 27 placebo nonresponders given DMI openly for 6 additional weeks following a nearly identical protocol and mean daily doses (total N = 58). Individual serum drug concentration varied widely at a given dose. The overall median serum DMI level was 152 ng/ml and in 6 of 56 cases with assayed serum (DMI), the level exceeded 500 ng/ml. Serum tended to be higher with older age and greater clinical improvement. Only small, clinically unimportant but statistically significant increases in diastolic blood pressure, heart rate, and electrocardiographic conduction parameters occurred. DMI-treated patients showed higher incidence during DMI treatment of sinus tachycardia and ECG evidence of intraventricular conduction defect (IVCD) of the right bundle branch block type, with two of these patients developing complete IVCD. Increases in ventricular rate and in ECG conduction parameters, as well as the incidence of IVCD, were higher in patients attaining serum levels of DMI above the median. These findings suggest that, although treatment with DMI at daily doses above 3.5 mg/kg may be needed in some cases of childhood ADDH, such doses require caution and monitoring of serum drug levels and ECG when they are used in the pediatric population.

Clinical pharmacokinetic considerations in the elderly. An update

There are numerous studies of drug handling in the elderly, but it is difficult to assess the significance of changes seen in vitro, or after single-dose administration, because they are often compensated by other mechanisms at steady-state. However, a knowledge of these studies is important as the results alert the investigator to possible treatment problems. The high incidence of adverse drug reaction in the elderly population leaves no doubt that improvements in therapy are needed. Research has been directed at seeking patterns of abnormality in the elderly on which to base recommendations for alterations in dosage regimens. The major shortcoming of this approach has been the failure to distinguish between the effect of chronological age on drug pharmacokinetics, and drug kinetics in elderly people with multiple pathology. The latter concern appreciates the variety of factors involved and the importance of treating each patient as an individual: presentation of mean data is confusing and misleading. The objective of drug treatment in any age group, but particularly in the elderly, is to administer the smallest possible dose which gives adequate therapeutic benefit throughout the entire dosage interval with the minimum of side effects. For most drugs the safe starting dose in the elderly is one-third to half that recommended in the young. Vigilance for potential side effects with plasma concentration monitoring, if available, should help keep toxicity to a minimum. When other medications are added or changed, the possibility of interaction should be anticipated. Methods for individualisation of dosage regimens and the use of sustained-release formulations in the elderly are discussed. Dosage alteration in the elderly in terms of reduced dose frequency, rather than dose size, may help improve compliance. A knowledge of the pharmacokinetics of a drug helps determine which approach will be most beneficial.

Cardiac responses to the microinjections of excitatory amino acids into the intermediolateral cell column of the rat spinal cord

Sympathoexcitatory cardiovascular responses to the microinjections of L-glutamate into the intermediolateral cell column (IML) of the upper thoracic cord (C8 to T4) were studied. Mean arterial pressure (MAP), heart rate (HR), the rate of increase in the left ventricular pressure (dP/dt) and contractility index were monitored in immobilized and artificially ventilated male Wistar rats anesthetized with pentobarbital or isoflurane. On the right side, microinjections (10-20 nl) of L-glutamate (0.9-1.77 nmol in 0.9% sodium chloride solution, pH 7.4) into the IML at T2 level produced marked tachycardiac responses with relatively small changes in contractility. On the left side, similar microinjections produced marked increase in dP/dt and contractility index with relatively small increase in HR. On either side, the responses were smaller at T1 and T3 level and absent at C8 and T4 level. No changes in blood pressure were observed with microinjections of L-glutamate on either side. Microinjections of N-methyl-D-aspartic acid (NMDA), 1-100 pmol, into the IML elicited responses similar to those of L-glutamate. These amino acids failed to evoke any response when microinjected into the adjacent areas (e.g. 0.5 mm lateral or medial to the IML). The effects of glutamate and NMDA in the IML were blocked by microinjections of glutamic acid diethylester (GDEE) and D-2-amino-7-phosphonoheptanoic acid (D-AP7), respectively. Control microinjections of physiological saline into the IML produced no responses. These results indicate that excitatory amino acids, in small doses and volumes, can be used to identify cardiac sympathoexcitatory neuronal pools in the IML. This preparation may prove useful in characterizing pharmacological actions of various putative neurotransmitters in this region of the spinal cord.

Late death in tricyclic antidepressant overdose revisited

We report a late death following the ingestion of amitriptyline. A 46-year-old woman presented to the emergency department with coma, hypotension, tachycardia, and a prolonged QRS interval after the ingestion of a large quantity of Elavil. She was managed with aggressive supportive care, multiple doses of oral charcoal, and charcoal hemoperfusion. The patient's ECG and hemodynamic status returned to normal within 24 hours. Despite an apparent total recovery, she suddenly sustained a cardiorespiratory arrest and died 33 hours after ECG normalization (at 57 hours after admission). This case brings into question the feasibility of ceasing ECG monitoring in tricyclic antidepressant overdoses once the ECG has stabilized, especially in patients with a history of chronic usage. A possible explanation for late sequelae is the myocardial cell binding and depressant effect of preexisting therapeutic TCA medication.

Desipramine plasma concentration and therapeutic response in elderly depressives: a naturalistic pilot study

This naturalistic pilot study of desipramine hydrochloride treatment in elderly DSM III diagnosed depressives demonstrated that therapeutic response was related to desipramine plasma levels and that a desipramine plasma concentration of 200 nmol/l significantly differentiated responders from non-responders. Plasma concentrations of 2-Hydroxydesipramine were not related to therapeutic response. This finding suggests that monitoring of desipramine plasma levels has utility in certain clinical situations. Further fixed dosage studies are necessary to confirm these initial results.

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.

Electrocardiogram changes and therapeutic desipramine and 2-hydroxy-desipramine concentrations in elderly depressives

ECG parameters in elderly depressed in-patients were assessed during routine desipramine treatment. Significant changes (prolonged PR and PRS intervals and a decreased QTc interval) were found, related only to steady state concentrations of desipramine's major metabolite--2-hydroxy-desipramine. Potentially clinically significant changes developed in 40% of the patients. All serum drug concentrations were within therapeutic limits. Previous assurances about desipramines's cardiac safety in the elderly may need to be re-evaluated.

Tricyclic antidepressant overdose

Overdose of a tricyclic antidepressant is a serious and all-too-frequent occurrence. The diagnosis must be considered in known or suspected overdoses, and signs such as a dry axilla, tachycardia, and wide QRS must be specifically sought. Management depends upon support of vital functions and a thorough understanding of the pharmacology of the drug. Emptying the gastrointestinal tract with ipecac or lavage and hastening elimination with activated charcoal and a cathartic are extremely important measures. Cardiac arrhythmias generally respond to sodium bicarbonate, and seizures respond to intravenous diazepam. Neither physostigmine nor dialysis are considered to be treatments of choice. As in other overdoses, counseling to prevent ingestions is more than worth "a pound of the cure."

Hemodynamic and electrocardiographic effects of fluoxetine and its major metabolite, norfluoxetine, in anesthetized dogs

The cardiovascular effects of the selective serotonin uptake inhibitor, fluoxetine, and its N-desmethyl metabolite, norfluoxetine, were studied in anesthetized dogs during constant iv infusion of supratherapeutic doses (0.1 mg/kg/min for 50 min). Fluoxetine and norfluoxetine did not significantly affect mean blood pressure, pulmonary artery wedge pressure, or heart rate compared to a corresponding vehicle group. Cardiac output fell 15 to 20% during fluoxetine infusion due to nonsignificant decreases in both heart rate (10%) and stroke volume (5 to 10%). In contrast, the tricyclic antidepressant agent, amitriptyline, infused at the same dose, decreased both mean pressure and systemic vascular resistance (20%) and increased heart rate (20%). Pulmonary wedge pressure rose by 35%, and stroke volume fell by 20% suggesting impaired ventricular contractility. Both intramyocardial and infranodal conduction was slowed during amitriptyline infusion as indicated by increases in the QRS duration, and the PQ and HV interval. Fluoxetine and norfluoxetine had no influence on cardiac impulse conduction velocity as assessed by either surface or intracardiac conduction indices. Plasma concentrations of fluoxetine, norfluoxetine, and amitriptyline reached during infusion ranged from 1.0 to 2.5 micrograms/ml. Platelet [3H]serotonin uptake was inhibited by 95% during infusion of fluoxetine and about 75% during infusion of norfluoxetine or amitriptyline. These observations indicate that large iv doses of fluoxetine or norfluoxetine lack prominent cardiodepressant effects in dogs, suggesting a greater margin of safety for fluoxetine compared to tricyclic antidepressant drugs.

Steady-state levels of imipramine and its metabolites: significance of dose-dependent kinetics

Seventeen hospitalized patients (age 39-66 years), received a loading dose of 100 mg imipramine HCl and then 50 mg b.i.d. The 12-h plasma concentration at steady-state varied between 40-637 nmol/l for imipramine, 49-1148 nmol/l for desipramine and 89-1603 nmol/l for imipramine + desipramine. Guided by plasma level monitoring, a final therapeutic plasma level between 548-910 nmol/l for imipramine + desipramine was achieved (therapeutic dose range: 50-400 mg/day). Mean time to reach the therapeutic level was 19 days. The mean 2-OH-imipramine/imipramine ratio was 0.24 and mean 2-OH-desipramine/desipramine ratio was 0.56. There was a significant intrapatient correlation between the two ratios, both during 100 mg imipramine/d and at the therapeutic dose level. A low ratio was associated with high imipramine and particularly with a high desipramine level. Well defined steady state levels were established at two different dose levels in 12 patients and at three dose levels in 5 patients. With increasing dose there was a marked and disproportionate rise in the desipramine level and to some extent in the imipramine level. Saturation of imipramine and desipramine hydroxylation appeared to be responsible for the dose-dependent kinetics. Concomitant treatment with levomepromazine and perphenazine in one patient resulted in a significant rise both in imipramine and desipramine concentration, apparently due to inhibition of the hydroxylation. Eleven out of twelve endogenously depressed patients responded completely to treatment, whereas the response was poor in the non-endogenously depressed patients despite optimal drug levels.

The effect of experimentally-induced renal failure on accumulation of bupropion and its major basic metabolites in plasma and brain of guinea pigs

Dosage regimen adjustments because of poor renal function are often assumed to be unnecessary for extensively metabolized antidepressants. This assumption is being increasingly questioned in recognition of the role of active drug metabolites. The purpose of this study was to assess the steady-state accumulation of the new antidepressant bupropion and its three major basic metabolites in guinea pigs, with and without experimentally-induced renal failure. Two groups of guinea pigs were treated by intraperitoneal (IP) implantation of mini-osmotic pumps containing bupropion hydrochloride. Immediately after surgery, one group of animals received an injection of uranyl nitrate. After 4 days, all animals were sacrificed by decapitation following blood removal by cardiac puncture. Analysis of plasma and brain samples by high performance liquid chromatography (HPLC) for concentrations of bupropion (BUP) and its major basic metabolites, the erythro-amino alcohol (EB), the threo-amino alcohol (TB) and the hydroxy metabolite (HB) revealed greater accumulation of BUP, TB, and HB in plasma and brain of the animals with renal failure compared to controls. No difference was found between groups in the concentrations of the EB metabolite. As the guinea pig shows a BUP and metabolite plasma concentration profile similar to that seen in human studies, these results suggest that further studies of bupropion and its major metabolites are warranted in patients with impaired renal function to assess possible excessive drug and metabolite accumulation.

Electrophysiological effects of desmethylimipramine and desmethyldoxepin on canine cardiac Purkinje fibers

Although the tricyclic antidepressant drugs imipramine and doxepin exert similar direct electrophysiological effects on cardiac cells, toxic cardiac arrhythmias and conduction disturbances are much more commonly associated with imipramine than doxepin in clinical use. To ascertain if this discrepancy could be due to different cellular electrophysiological actions of active metabolites of imipramine and doxepin, the effects of desmethylimipramine (DMI) and desmethyldoxepin (DMD) on isolated, superfused, canine cardiac Purkinje fibers were studied by glass microelectrodes and programmed stimulation. At a concentration of 50 ng/ml neither DMI nor DMD affected the resting membrane potential (RMP), action potential amplitude (Amp), maximum upstroke velocity of phase 0 (Vmax), action potential duration to repolarization to 50 and 100% of the amplitude (APD50, APD100), effective refractory period (ERP), or conduction velocity (CV). At 250 ng/ml neither drug affected Amp, APD100, or CV; both compounds reduced APD50 by 10 to 15%; and DMD but not DMI caused small reductions of RMP, Vmax, and ERP. At 1000 ng/ml neither DMI nor DMD affected RMP but both caused more marked reductions of APD50 (31 to 35%) and ERP (21 to 23%). At this concentration both substances also reduced Amp by 6 to 7%, Vmax by 28 to 35%, APD100 by 7 to 12%, and CV by 15 to 25%. These effects of DMI and DMD are similar to those produced by the parent drugs. Differences in cardiotoxicity between imipramine and doxepin in clinical use are probably not due to different direct cellular electrophysiological effects of the circulating demethylated metabolites of these drugs.

The metabolism and excretion of [14C]imipramine in an experimental hepatitis

The effect of experimental hepatitis, induced by i.p. D-galactosamine, on the metabolism and excretion of [14C]imipramine in the rat is reported. The major consequence was an increase of the conjugated metabolites of imipramine excreted in urine, resulting in a four-fold increase in 2-hydroxyimipramine glucuronide and two-fold increases in 2-hydroxydesmethylimipramine glucuronide and 10-hydroxyimipramine glucuronide. The total excretion of 14C-labelled metabolites in urine of galactosamine-treated rats was 69% dose compared with 37% in untreated animals. Faecal excretion of [14C]imipramine metabolites was lowered from 68% dose in untreated animals to 27% in animals with induced hepatitis. Induction of a galactosamine hepatitis decreased markedly the biliary excretion of imipramine metabolites in bile duct-cannulated rats; 80% dose was excreted in bile in normal rats, and 35.5% in rats with hepatitis. Plasma clearance of imipramine, after i.v. dosage, was decreased by 60% and clearance of metabolites (excluding imipramine) by 40%, in galactosamine hepatitis; the pharmacokinetics changed from a two- to a single-compartment system reflecting decreased extraction and/or metabolism, by the liver. The clinical implications of these findings are discussed in relation to the hazard attending the use of imipramine in patients suffering from liver disease.

Cerebral and blood pharmacokinetics of imipramine and its active metabolites in the pregnant rat

A single IP dose of imipramine (IMI) was administered to pregnant rats. Whole blood, plasma, and brain concentrations of IMI, desipramine (DMI), and their 2-hydroxylated metabolites were separated by high-pressure liquid chromatography and quantified by fluorescence detection. IMI and DMI rapidly appeared in brain tissue in concentrations greatly exceeding those in whole blood and plasma. The much higher concentration and longer persistence of DMI in brain compared to IMI suggests that the predominant central effects from administered IMI result from biotransformation to DMI. The metabolite: "parent" area under the curve ratios for the hydroxylated metabolites indicate that their contribution to the pharmacologic effects of IMI and DMI are probably negligible.

The analysis and disposition of imipramine and its active metabolites in man

Single oral and intramuscular (i.m.) doses of imipramine (IMI) were administered to four normal males. Serum and urine concentrations of IMI, desipramine (DMI) and their unconjugated 2-hydroxy metabolites were measured by high-pressure liquid chromatography (HPLC). Urinary conjugated 2-hydroxy metabolites were also measured after enzyme hydrolysis. Computer analysis of serum concentration and urinary excretion rate data allowed confirmation of drug and metabolite kinetics, and calculation of pharmacokinetic parameters. The rapid appearance of the metabolites in serum indicates that sequential first-pass metabolism of IMI involves both hydroxylation and demethylation. However, the dose-normalized areas under the serum concentration-time curves indicate that the fractions of the doses converted to metabolites were similar after both routes of IMI administration. Similar total fractions of the i.m. and oral doses recovered in urine indicate complete absorption of the oral doses. Inclusion of the metabolites increased the apparent availability of active components after oral IMI from 22%-50% to 45%-94%. Both the 2-hydroxy metabolites exhibited formation rate-limited kinetics, whereas DMI kinetics were elimination rate-limited. The t1/2 of IMI and 2-hydroxyimipramine (2-OH-IMI) was 6-18 h, while that of DMI and 2- hydroxydesipramine (2-OH-DMI) was 12-36 h. The t1/2 of these compounds was 1.5-2 times longer after the i.m. doses. The metabolite/parent ratios and the disposition of the individual metabolites confirm findings that chronic dosing results in only limited accumulation of hydroxy metabolites.

Quantification of imipramine and its major metabolites in whole blood, brain, and other tissues of the rat by liquid chromatography

An assay procedure is presented using high-performance liquid chromatography and fluorescence detection for simultaneous determination of imipramine, desipramine, and their 2-hydroxylated metabolites in whole blood and various tissues of the rat. By modifying methods previously described for plasma, we have developed an assay method for sensitive, reproducible quantitation of these compounds in rat plasma, whole blood, brain, liver, and fetus. Increasing the volume of the extraction solvent (20% butanol in hexane) increased recovery of imipramine and desipramine to greater than 90% for all tissues examined. No interfering peaks were observed for any of the tissues studied. Addition of n-butylamine as a modifier to the mobile phase decreased the retention of all four compounds and decreased peak tailing of the demethylated compounds. The total elution time was less than 15 min. Using these methods the coefficient of variation for all four compounds was generally less than 5% for each of the five tissues examined. The calibration curves were linear for standard concentrations of 25-2,000 ng/ml spiked tissue homogenate. This method has sufficient sensitivity and specificity for use in pharmacokinetic studies of imipramine.