Amitriptyline and imipramine poisoning

Tricyclic antidepressant poisoning: an evidence-based consensus guideline for out-of-hospital management

A review of U.S. poison center data for 2004 showed over 12,000 exposures to tricyclic antidepressants (TCAs). A guideline that determines the conditions for emergency department referral and prehospital care could potentially optimize patient outcome, avoid unnecessary emergency department visits, reduce healthcare costs, and reduce life disruption for patients and caregivers. An evidence-based expert consensus process was used to create the guideline. Relevant articles were abstracted by a trained physician researcher. The first draft of the guideline was created by the lead author. The entire panel discussed and refined the guideline before distribution to secondary reviewers for comment. The panel then made changes based on the secondary review comments. The objective of this guideline is to assist poison center personnel in the appropriate prehospital triage and management of patients with suspected ingestions of TCAs by 1) describing the manner in which an ingestion of a TCA might be managed, 2) identifying the key decision elements in managing cases of TCA ingestion, 3) providing clear and practical recommendations that reflect the current state of knowledge, and 4) identifying needs for research. This guideline applies to ingestion of TCAs alone. Co-ingestion of additional substances could require different referral and management recommendations depending on their combined toxicities. This guideline is based on the assessment of current scientific and clinical information. The panel recognizes that specific patient care decisions may be at variance with this guideline and are the prerogative of the patient and the health professionals providing care, considering all the circumstances involved. This guideline does not substitute for clinical judgment. Recommendations are in chronological order of likely clinical use. The grade of recommendation is in parentheses. 1) Patients with suspected self-harm or who are the victims of malicious administration of a TCA should be referred to an emergency department immediately (Grade D). 2) Patients with acute TCA ingestions who are less than 6 years of age and other patients without evidence of self-harm should have further evaluation including standard history taking and determination of the presence of co-ingestants (especially other psychopharmaceutical agents) and underlying exacerbating conditions, such as convulsions or cardiac arrhythmias. Ingestion of a TCA in combination with other drugs might warrant referral to an emergency department. The ingestion of a TCA by a patient with significant underlying cardiovascular or neurological disease should cause referral to an emergency department at a lower dose than for other individuals. Because of the potential severity of TCA poisoning, transportation by EMS, with close monitoring of clinical status and vital signs en route, should be considered (Grade D). 3) Patients who are symptomatic (e.g., weak, drowsy, dizzy, tremulous, palpitations) after a TCA ingestion should be referred to an emergency department (Grade B). 4) Ingestion of either of the following amounts (whichever is lower) would warrant consideration of referral to an emergency department: an amount that exceeds the usual maximum single therapeutic dose or an amount equal to or greater than the lowest reported toxic dose. For all TCAs except desipramine, nortriptyline, trimipramine, and protriptyline, this dose is >5 mg/kg. For despiramine it is >2.5 mg/kg; for nortriptyline it is >2.5 mg/kg; for trimipramine it is >2.5 mg/kg; and for protriptyline it is >1 mg/kg. This recommendation applies to both patients who are naïve to the specific TCA and to patients currently taking cyclic antidepressants who take extra doses, in which case the extra doses should be added to the daily dose taken and then compared to the threshold dose for referral to an emergency department (Grades B/C). 5) Do not induce emesis (Grade D). 6) The risk-to-benefit ratio of prehospital activated charcoal for gastrointestinal decontamination in TCA poisoning is unknown. Prehospital activated charcoal administration, if available, should only be carried out by health professionals and only if no contraindications are present. Do not delay transportation in order to administer activated charcoal (Grades B/D). 7) For unintentional poisonings, asymptomatic patients are unlikely to develop symptoms if the interval between the ingestion and the initial call to a poison center is greater than 6 hours. These patients do not need referral to an emergency department facility (Grade C). 8) Follow-up calls to determine the outcome for a TCA ingestions ideally should be made within 4 hours of the initial call to a poison center and then at appropriate intervals thereafter based on the clinical judgment of the poison center staff (Grade D). 9) An ECG or rhythm strip, if available, should be checked during the prehospital assessment of a TCA overdose patient. A wide-complex arrhythmia with a QRS duration longer than 100 msec is an indicator that the patient should be immediately stabilized, given sodium bicarbonate if there is a protocol for its use, and transported to an emergency department (Grade B). 10) Symptomatic patients with TCA poisoning might require prehospital interventions, such as intravenous fluids, cardiovascular agents, and respiratory support, in accordance with standard ACLS guidelines (Grade D). 11) Administration of sodium bicarbonate might be beneficial for patients with severe or life-threatening TCA toxicity if there is a prehospital protocol for its use (Grades B/D). 12) For TCA-associated convulsions, benzodiazepines are recommended (Grade D). 13) Flumazenil is not recommended for patients with TCA poisoning (Grade D).

The cardiovascular effects of antidepressants

This monograph comprises a review of the cardiovascular effects of the various types of antidepressant drugs in clinical use. The frequency, severity and clinical importance of these effects are placed in perspective. Most antidepressants can cause changes in blood pressure. Both the tricyclic type (TCA) and the monoamine oxidase inhibitors (MAOIs) can produce postural hypotension which may be dose-limiting. In addition, the MAOIs may be associated with severe hypertension when amine-containing foods or medicines are ingested. It is unlikely that therapeutic doses of any available antidepressant drug could impair cardiac contractility. Typical TCAs can cause abnormalities of cardiac conduction and arrhythmias, but this affects less than 5% of patients, mostly to a clinically insignificant extent. Newer compounds such as lofepramine, mianserin, trazodone and viloxazine seem safer in this respect. Reports of an association between therapeutic use of TCAs and sudden death are far from convincing. Overdosage with the MAOIs, lithium and carbamazepine is dangerous but not common; overdose with a TCA is a major source of morbidity and mortality. Lofepramine, mianserin and trazodone are relatively safe in overdose. The use of various antidepressants in patients with hypertension, cardiac failure, angina pectoris, myocardial infarction, or cardiac arrhythmias is discussed and guidelines suggested for the selection and use of antidepressant medication.

Poisoning due to tricyclic antidepressant overdosage. Clinical presentation and treatment

Tricyclic antidepressants are among the commonest causes of both non-fatal and fatal drug poisoning in the world. Their toxicity is due to effects on the brain, the heart, the respiratory system and the parasympathetic nervous system. Symptoms usually appear within 4 hours of an overdose and all but the most seriously poisoned patients recover within 24 hours. The most common clinical features are dry mouth, blurred vision, dilated pupils, sinus tachycardia, pyramidal neurological signs, and drowsiness. In severe poisoning, there may be coma, convulsions, respiratory depression, hypotension and a wide range of electrocardiographic (ECG) abnormalities. The most frequent findings on the ECG are prolongation of the PR and QT intervals; the tracing may resemble bundle branch block or supraventricular or ventricular tachycardias. Treatment of poisoning due to the tricyclic antidepressants is essentially supportive, there being insufficient evidence at present to recommend the use of methods to increase elimination of the drug from the body. Gastric aspiration and lavage should be performed if more than 750 mg of drug have been taken. There must be regular monitoring for hypoxia, acidosis and hypokalaemia and these complications should be corrected enthusiastically. Convulsions should be treated with diazepam or chlormethiazole. Muscular paralysis and artificial ventilation should be employed if anticonvulsants are ineffective. Hypotension should be treated firstly by fluid replacement and then with sympathomimetic agents (dopamine or dobutamine). Antiarrhythmic drugs should only be employed if there is evidence of circulatory failure which fails to respond to correction of hypotension. Sodium bicarbonate infusions should be given to cardiotoxic patients who are acidotic and are worth trying even if the patient is not acidotic. Although physostigmine salicylate will reverse most of the features of tricyclic antidepressant poisoning, its effects are short-lived in serious toxicity and it can produce dangerous side effects; physostigmine should therefore be reserved for those patients who have complications of coma or who have resistant cardiotoxicity or convulsions. Drug screening and quantitative determination of tricyclic antidepressant serum concentrations are useful in a minority of patients who have severe, unusual or prolonged symptoms.

Fatal maprotiline intoxication

We report a fatal case of drug toxicity associated with torsade de pointes following an overdose of the tetracyclic antidepressant, maprotiline (Ludiomil). Tissue and plasma levels were obtained at autopsy and are noted. In addition, the cardiovascular effects, pharmacokinetics, and toxicity of maprotiline are reviewed and compared with that of tricyclic antidepressants.

Cardiac arrhythmias and ECG abnormalities in tricyclic antidepressant overdose

Tricyclic antidepressant overdose is widely felt to be associated with cardiac arrhythmias which may occur without warning, sometimes late in the clinical course. For this reason, many institutions routinely monitor cardiac rhythm in such patients for up to 72 h. A retrospective study was carried out to analyze the clinical course of such patients with emphasis on cardiac complications. Thirty-eight cases of TCA overdose were reviewed. Fourteen patients (36.9%) were classified as lethargic or stuporous on admission while 23 (60.5%) were either comatose or semicomatose, nine requiring endotracheal intubation. Patients were continuously monitored an average of 60 h after admission. Admission ECG's were abnormal in a high number of cases, most common abnormalities being sinus tachycardia (43%) and intraventricular conduction defects (24%). Ventricular ectopy was less common (7.8%). ECG abnormalities, with the exception of sinus tachycardia and infrequent PVC's were associated with a severely depressed sensorium and disappeared with neurological improvement, usually in 24 h. No arrhythmias were noted after the patient had become alert. Overall mortality was 2.6%, with no deaths in the adult populations. After a search of the literature, we conclude that intensive care unit monitoring is not indicated for prolonged periods once the patient has otherwise recovered from his acute complications of drug overdose.

Comparison of single-dose pharmacokinetics of imipramine and maprotiline in the elderly

Pharmacokinetic profiles of imipramine and a newer tetracyclic antidepressant, maprotiline, were studied in elderly (75-83 years of age) subjects who were given a single oral dose of 125 and 175 mg, respectively, of these drugs. The apparent elimination half-life of imipramine was 20.8-34.9h (means 26.4h), its biovailability (F) was 40-64% (means 57%), and the apparent plasma clearance was from 0.27-0.57h/kg (mean 0.41h/kg). Maprotiline had a longer half-life (mean 31.5h range 20.6-51.8h, but its bioavailability (mean 50%) and plasma clearance (mean 0.49h/kg) values were in the range similar to those seen after imipramine. It appears that the elimination half-life of imipramine is longer and its plasma clearance is markedly reduced in elderly subjects when compared to values reported in young adults. Subjective clinical side effects were minimal with the two drugs. However, alterations in heart rate, blood pressure, or electrocardiogram occurred in all subjects. This suggests that caution should be exercised before initiating and during the treatment of elderly patients with these antidepressant drugs.

The electrocardiographic and antiarrhythmic effects of imipramine hydrochloride at therapeutic plasma concentrations

The electrocardiographic effects of imipramine hydrochloride at therapeutic plasma concentrations were determined in 44 depressed patients during a 6-week clinical outcome study of depression. During each week of the protocol, i.e., 2 weeks of control and 4 weeks of drug treatment, a standard 12-lead ECG, high-speed, high-fidelity ECG tracings, and a 24-hour continuous ECG recording were obtained. PR, QRS, and QTc intervals, T-wave amplitude, heart rate and frequency of ventricular premature depolarizations (VPDs) were measured. The plasma concentration of imipramine and desmethylimipramine was measured three times a week. Imipramine prolonged the PR (p less than 0.001), QRS (p less than 0.001) and QTc (p less than 0.001) intervals, increased the heart rate (p less than 0.001) and lowered T-wave amplitude (p less than 0.05) during the 4 weeks of treatment. No patient developed high-grade atrioventricular block or severe intraventricular conduction abnormalities. In addition, imipramine had a potent antiarrhythmic action in patients who were recovering from depression. Ten of 11 patients who had more than 10 VPDs/hour had 90% or greater arrhythmia suppression during antidepressant treatment with imipramine at plasma concentrations ranging from 100--302 ng/ml.

Non-monoamine oxidase inhibitor antidepressants and epilepsy: a review

The literature dealing with the convulsant effects of the antidepressant drugs of the non-monoamine oxidase inhibitor variety is reviews. It is concluded that most of these drugs do lower the seizure threshold and may precipitate seizures even at normal therapeutic doses. The pathophysiology of antidepressant-induced seizures is discussed, and attention is drawn to biochemical differences in those antideprssants that have the least epileptogenic potential or may even be anticonvulsant. The clinical difficulties regarding administration of antidepressant drugs to epileptic patients are mentioned, and some practical advice is offered.

Plasma concentrations and cardiotoxic effects of desipramine and protriptyline in the rat

1 Desipramine and protriptyline were administered to anaesthetized rats by two consecutive intravenous infusions in order to obtain a peak level (first infusion) followed by lower steady state concentrations (second infusion) (Wagner, 1974). Theoretical plasma level time courses were confirmed experimentally.2 Desipramine and protriptyline were measured in atria and ventricles. Increasing infusion rates led to proportional increases in plasma and atrial concentrations. The tissue/medium ratio ranged from 57 to 21 for desipramine and from 43 to 11 for protriptyline according to the time of determination during infusions.3 Heart rate changes, deviation of the electrical axis of the heart and prolongation of atrioventricular conduction were recorded at fixed times during infusion.4 Positive chronotropic effects were noted at plasma concentrations ranging from 0.035 to 0.1 mug/ml for desipramine and from 0.04 to 1.2 mug/ml for protriptyline. At higher plasma concentrations the positive chronotropic effect decreased and bradycardia developed. Both drugs induced right rotation of the electrical axis of the heart. Threshold plasma levels giving 40 degrees rotation were 1.35 mug/ml (desipramine) and 1.75 mug/ml (protriptyline). Atrioventricular conduction was prolonged at threshold plasma concentrations of 2.2 mug/ml for desipramine and 3.6 mug/ml for protriptyline.5 Desipramine is more cardiotoxic than protriptyline. This difference is discussed in relation to the plasma and heart concentration of the two drugs.

Assessment of cardiovascular side effects of therapeutic doses of tricyclic anti-depressant drugs

An assessment of the side effects of therapeutic doses of tricyclic anti-depressant drugs was attempted in 32 patients with depressive illness. The patients studied had no evidence of clinical heart disease or hypertension and were not receiving any other drugs. Moderate increase in heart rate and mild prolongation of atrioventricular conduction occurred. No significant effect on the corrected QT interval or blood pressure was found. There was no correlation between the increased heart rate, prolongation of the atrioventricular conduction time (PR interval) and plasma nortriptyline levels measured in 20 out of 32 patients.

Amitriptyline and imipramine poisoning in children

The increasing number of children admitted to this hospital with poisoning by tricyclic antidepressants is causing concern. Of 60 children admitted between January 1966 and July 1973, half were admitted in the last 18 months. In 60% of these patients the tricyclic compounds had been prescribed for nocturnal enuresis. One child aged 2 years and 4 months died of imipramine poisoning. It is imperative that all children with poisoning by tricyclic compounds, irrespective of the dosage, are admitted to hospital for continuous cardiac monitoring. Cardiac arrhythmias induced in children by amitriptyline and imipramine are prominent and dangerous.In the earlier years of this survey the antidepressants taken by children had usually been prescribed for adults, but recently they have been increasingly prescribed as a treatment for enuresis in children themselves. Medicine for a trivial complaint is unlikely to be regarded by parents as potentially dangerous and practitioners should therefore warn them accordingly; if, indeed, the transient effect of these potentially dangerous drugs upon the average case of bed-wetting in childhood can be justified.

Tachyarrhythmia in severe imipramine overdose controlled by practolol

A 2½-year-old boy, comatose and having fits after an overdose of imipramine, suffered a respiratory and cardiac arrest from which he was successfully resuscitated. A severe tachyarrhythmia was well controlled by intravenous practolol, and it is suggested that practolol is the drug of choice in this situation.

Treatment of severe imipramine poisoning

Two cases are described which illustrate the successful use of diazepam and lignocaine in the management of severe poisoning by the tricyclic antidepressant group of drugs. A routine for the management of such cases is set out.

Cardiac abnormalities in poisoning with tricyclic antidepressants

Of 80 consecutive admissions to a general hospital for drug overdose, 10 had taken one or other of the tricyclic antidepressants. All 10 had abnormalities of cardiac conduction as shown by prolonged Q-T(e) intervals, and eight had S-T segment and T-wave changes. Five of the 10 patients had arrhythmias and two of these died. Continuous electrocardiographic monitoring is recommended in patients with overdosage of tricyclic antidepressants.

Electrocardiographic changes in amitriptyline poisoning

In imipramine and amitriptyline poisoning the electrocardiographic abnormalities comprise arrhythmias, widening of the QRS complex, and marked changes in die S-T segment. These features were found to be of value in the differential diagnosis of unknown poisoning. The unusual configuration of qR with raised S-T segment in V1, simulating myocardial infarction, was seen in one of our patients and has been noted in four cases reported by other workers.

Myocardial damage in amitriptyline and nortriptyline poisoning

Two cases of self-poisoning with amitriptyline and one with nortriptyline are described. The patients showed transient E.C.G. changes and two had a rise in the serum enzymes usually associated with myocardial necrosis.