High levels of tricyclic antidepressants in conventional therapy: determinant factors

The incidence of potentially toxic serum levels (greater than or equal to 400 ng/ml) was analyzed in a group of 196 monitored patients on a standard dosage regimen (75-225 mg/day) of several antidepressants: imipramine, amitriptyline, nortriptyline, maprotiline and clomipramine. Mean incidence was 12%. The maximum antidepressants serum levels in these patients ranged from 403 to 1,776 ng/ml. The drug/metabolite ratio was 1.5 +/- 0.7. Only in 23% of the cases did the clinical symptoms allow us to suspect the presence of potentially toxic serum levels. The factors that may contribute to the appearance of high serum levels were analyzed; these are: association of neuroleptic agents to the antidepressant therapy, advanced age and administration of doses above 2.5 mg/kg/day. In 64% of the patients, the clinical criteria suggested the need for a reduction in the dose, with a mean value of 42%.

Site dependence of drug concentrations in postmortem blood--a case study

A 25-year-old female died from a suicidal overdose of imipramine, acetaminophen, codeine, diphenhydramine, and ethanol. Blood samples from ten segregated arterial and venous sites, twenty-four tissue samples, cerebrospinal fluid, vitreous humor, and bile were analyzed. Imipramine and desipramine, which were highly concentrated in the liver and lungs, each showed marked site dependent differences in blood concentrations. The highest concentrations were in pulmonary venous blood and the lowest in peripheral venous blood. Imipramine concentrations in the ten blood samples differed by as much as 760% (range 2.1 to 16.0 mg/L). Blood desipramine concentrations ranged from 1.4 to 10.6 mg/L. In contrast, blood concentrations of acetaminophen differed by less than 20% (55 to 65 mg/L) and blood ethanol concentrations ranged from 151 to 175 mg/100 mL. Blood concentrations of diphenhydramine ranged from 0.34 to 2.07 mg/L and codeine from 0.33 to 0.89 mg/L. The data illustrates that a marked site dependent variability in postmortem blood concentrations exists for some drugs but not others.

Analysis of 2-hydroxyimipramine in an imipramine-related fatality

A fatality following ingestion of the tricyclic antidepressant imipramine (Novopramine), acetaminophen, and ethyl alcohol is described. Imipramine, desipramine, acetaminophen, and 2-hydroxyimipramine were quantitated by high performance liquid chromatography, and ethyl alcohol by gas liquid chromatography. Concentrations of imipramine, desipramine, 2-hydroxyimipramine, and acetaminophen were: in blood--9.0, 1.1, 3.9, and 11 mg/L; in urine--92, 14, and 42 mg/L (acetaminophen not quantitated in urine). Ethyl alcohol concentration in blood was less than 10 mg/dL and 105 mg/dL in the urine by headspace gas chromatography. These findings are compared to previous reports of imipramine-related fatalities. To our knowledge, this is the first fatality reported involving imipramine where analysis included quantitation of 2-hydroxyimipramine in blood and urine.

[Munchausen syndrome induced as recurrent imipramine poisoning]

A nine-year-old girl with Munchausen syndrome by proxy is reported. She had been admitted to different hospitals for 17 times in the last seven years. Clinical complaint were complex neurological symptoms and the first diagnosis was acute intermittent porphyria. It was demonstrated later that this symptoms were due to imipramine poisoning given by her mother.

Imipramine poisoning in a child: lack of efficacy of resin hemoperfusion

A three-year-old boy ingested up to 1,500 mg of the tricyclic antidepressant imipramine (Tofranil). He entered our facility within two hours of discovery, and multiple resuscitative efforts, which proved unsuccessful, followed. Resin hemoperfusion was used in an effort to remove imipramine from the systemic circulation. Serum concentrations of imipramine and its major metabolite desipramine were determined from serum drawn before, during, and after hemoperfusion. Serum concentrations of imipramine and desipramine did not change appreciably. No improvement in the clinical condition was noted during the hemoperfusion period, which was due in part to the fact that our patient was clinically brain dead upon arrival in our intensive care unit. Our subsequent literature review documents that this case represents the first reported use of hemoperfusion in a pediatric tricyclic antidepressant ingestion, hemoperfusion removes an insignificant portion of the total amount of tricyclic antidepressant ingested, and some pediatric literature misleadingly suggests that hemoperfusion may be useful in such patients. Physicians treating tricyclic antidepressant ingestion cases should avoid using hemoperfusion; standard supportive care remains the essential management response.

Hyperpyrexia following psychotropic drug overdose

A case of overdose of tricyclic antidepressants associated with severe pyrexia is reported in a patient taking monoamine oxidase inhibitors, and its management described. The similarities to and differences from the malignant hyperpyrexia syndrome are discussed.

Treatment of haemodynamic and electrocardiographic side-effects resulting from imipramine toxicity in rats and dogs

This study was designed to analyze the effects of carbocromene and dipyridamole on the haemodynamic and electrocardiographic side-effects resulting from imipramine infusion in anaesthetised rats and dogs. Imipramine was infused at 1 mg/kg/min until cardiac failure and vascular collapse terminated the experiment at 21 +/- 2.3 min in rats and at 29.5 +/- 2.1 min in dogs. This was characterized by hypotension, bradycardia, intraventricular conduction delay, cardiac tachyarrhythmia and A-V block. Carbocromene (4 mg/kg i.v., followed by 80 micrograms/kg/min) protected the animals against heart failure. This was associated with delayed hypotension and negative inotropy, and lower incidence of heart block. Survival time increased to 37 +/- 1.5 min (P less than 0.05), and 54.2 +/- 2.6 min (P less than 0.02) in rats and dogs, respectively. Dipyridamole (0.5 mg/kg i.v., followed by 80 micrograms/kg/min) failed to decrease imipramine toxicity as judged by the haemodynamic and electrocardiographic parameters and did not alter survival time of imipramine controls. These results suggest that carbocromene is an effective treatment for imipramine-induced cardiovascular collapse and cardiac arrhythmias, the beneficial effects being largely due to metabolic and membrane stabilizing effects. Carbocromene has both therapeutic and prophylactic value and appears to be superior to dipyridamole therapy.

Dopamine and isoproterenol in imipramine intoxication in the dog

Artificially ventilated anesthetized dogs were given imipramine 7.5 mg/kg/hr i.v. In the first group (n = 6) mechanical cardiac activity was no longer detectable after a cumulative dose of 20.0 +/- 6.6 mg/kg (mean +/- sd). When aortic flow had decreased to 75% of its initial value, in a second group (n = 5) of experiments dopamine 10 micrograms/kg/min and in a third group (n = 5) isoproterenol 1 microgram/kg/min were administered i.v.. The doses of dopamine and isoproterenol were doubled when aortic flow had again decreased to 75% and 100%, respectively, of the original values. Cardiac mechanical activity was not detectable after a cumulative dose of 43.8 +/- 13.3 in the dopamine and 42.5 +/- 8.0 mg imipramine/kg in the isoproterenol group. These values differed significantly from that in the reference group (both 0.01 greater than p greater than 0.001). In the first group plasma imipramine concentrations at the end of the experiments were 3.06 +/- 0.66, in the second 3.36 +/- 0.66 and in the third 3.32 +/- 1.10 mg/1. Desipramine concentrations were 0.078 +/- 0.06, 0.162 +/- 0.076 and 0.383 +/- 0.09 mg/1 respectively. Dopamine induced a hemodynamic profile of low output and high pressure and isoproterenol one of low pressure and high output. It is concluded that dopamine combined with isoproterenol might be effective in counteracting the cardiodepressant action of imipramine.

The treatment of tricyclic antidepressant overdose with repeated charcoal

Activated charcoal given repeatedly through a nasogastric tube to three patients in coma from amitriptyline overdose greatly accelerated tricyclic elimination: the apparent half-life fell below 10 hours for each patient to as low as 4 hours. This contrasts with extended half-lives for amitriptyline elimination averaging 36.8 hours and regularly over 60 hours previously reported for overdoses treated without repeated charcoal. The enterohepatic recirculation of amitriptyline and nortriptyline appears to be a major influence on keeping their blood levels up. In one case, intravenous diazepam inhibited tricyclic elimination.

Use of sodium bicarbonate to treat tricyclic antidepressant-induced arrhythmias in a patient with alkalosis

Sodium bicarbonate has been recommended for the treatment of arrhythmias induced by tricyclic antidepressants. It is unclear, however, whether this therapy is effective only in the presence of acidosis. A case is presented in which there was an immediate response to sodium bicarbonate in three episodes of ventricular tachycardia despite the presence of alkalosis on two of the three occasions. Given the poor response to conventional therapy of arrhythmias induced by tricyclic antidepressants the use of sodium bicarbonate may be reasonable even in the presence of alkalosis. However, in the presence of pre-existing respiratory or metabolic alkalosis, such therapy is not without risk, and it is suggested that it be reserved for life-threatening situations when the arrhythmia has failed to respond to hyperventilation or antiarrhythmics or both.

Magnesium therapy for torsades de pointes

This is the first report of the successful use of magnesium sulfate (MgSO4) in 3 consecutive patients with torsades de pointes (TdP). In 1 patient, TdP was induced by a combination of quinidine and amiodarone, in the second by procainamide, and in the third by an overdose of imipramine. The QT intervals before TdP were 0.70, 0.64 and 0.56 second, respectively. A bolus of 1.0 to 2.0 g MgSO4 25% abolished the TdP in all 3 patients; but in the third patient, because of recurrent TdP, a second bolus of 1.0 g and a continuous 24-hour infusion of 1.0 mg/min were administered, preventing TdP. There was no immediate shortening in the QT interval in any patient after MgSO4. Magnesium can be given safely even in patients with acute myocardial infarction, angina pectoris or systemic hypertension, conditions in which isoproterenol is contraindicated; it can be applied faster than temporary cardiac pacing; and its use for TdP appears worthy of additional trials.

External ophthalmoplegia, alpha and spindle coma in imipramine overdose: case report and review of the literature

A 13-year-old boy with imipramine overdose developed seizures, respiratory arrest, and coma. Abnormalities of oculovestibular reflexes, electroencephalograms, and brainstem auditory evoked potentials were monitored in relation to measurements of drug levels. An alpha-coma electroencephalographic pattern evolved into one evidencing spindle coma and eventually into a normal pattern. Prolonged brainstem auditory evoked potentials also normalized as coma and oculocephalic reflex abnormalities resolved. In spite of the history that suggested hypoxic damage, the absence of reflex eye movements in a comatose patient and the presence of alpha- and spindle-coma electroencephalographic patterns, even with prolonged brainstem auditory evoked potentials, are not reliable prognostic indicators in tricyclic drug overdose.

[Prolonged high plasma imipramine levels after acute intoxication (author's transl)]

A case of severe intoxication by tricyclic antidepressants with persistence during 14 days of abnormally high plasma imipramine levels is reported. The various factors capable of maintaining plasma imipramine at a high level are discussed. They include mechanical factors (intestinal absorption), ventilation under positive end-expiratory pressure, alterations of hepatic metabolism by other drugs such as metronidazole or cimetidine, and changes in tissue distribution. Attention is drawn to the risks inherent in the various treatments used against acute intoxications and in combined chemotherapy during intensive care generally. When such drugs are necessary, the plasma levels of those with higher toxicity should be monitored.

Hemoperfusion for imipramine overdose: elimination of active metabolites

The serum concentrations of imipramine and its pharmacologically active metabolites were followed during resin hemoperfusion for imipramine overdose. The initial serum concentration of 2-hydroxy-imipramine plus 2-hydroxy-desipramine was 13.3% of the total tricyclic antidepressant level (imipramine + desipramine + hydroxymetabolites). Despite high extraction ratio (greater than or equal to 0.75) and clearances (130--180 mL/min) for both imipramine and its metabolites, the calculated amount of drug removed was small. Only 0.91% of the estimated dose ingested was removed as imipramine, 0.52% as desipramine, and 0.33% as hydroxylated metabolites. While the hydroxylated metabolites of imipramine may contribute to its toxicity, it is unlikely that the small amount removed can explain reports of apparent clinical benefit from hemoperfusion.

The influence of physostigmine on respiratory and circulatory changes caused by overdoses of orphenadrine or imipramine in the rat

Orphenadrine or imipramine were given intravenously as an infusion to spontaneously breathing, anaesthetized rats until respiratory arrest, the primary cause of death for both drugs. Intravenous injections of physostigmine did not prolong survival. Artificial ventilation prolonged survival for orphenadrine and imipramine by about a factor 3 and the rats died from cardiogenic shock. The cardiotoxic properties of orphenadrine and imipramine express themselves as a progressing disturbance in stimulus formation and conduction, a decrease in dP/dt max and increase in left ventricular end-diastolic pressure and a decrease in cardiac output caused by the progressing decrease of heart rate. An intravenous injection of physostigmine did not prolong survival and had no favourable effect on the cardiotoxicity caused by orphenadrine and imipramine. Although physostigmine may be useful in the treatment of the anticholinergic syndrome it has, at least in the rat, no favourable effect on the respiratory insufficiency, due to overdoses of orphenadrine and imipramine. Moreover it is not effective in antagonizing the cardiotoxic effects of orphenadrine or imipramine.

Treatment of imipramine overdose in children

Enuresis is a common problem often treated effectively with imipramine hydrochloride. The usefulness of this therapy carries with it, however, the risk of accidental overdose by younger siblings of these enuretic patients. Traditional support measures are effective in the treatment of the mild to moderate overdose, while separate symptomatic treatment of seizures and cardiac arrhythmias is possible as outlined herein. Physostigmine offers a single alternate treatment which is effective in the full panorama of life-threatening manifestations of an imipramine overdose.