Clonidine interaction in amitriptyline poisoning

Clinical Course, Therapy, Outcome and Analytical Data in Amitriptyline and Combined Amitriptyline/Chlordiazepoxide Overdose

A total of 103 cases of amitriptyline (AT) overdose (group 1) and 81 cases of overdose with a fixed combination of AT and chlordiazepoxide (CDE) (group 2), treated at our Intensive Care Unit or reported to our Poison Information Center between 1985-1990, were evaluated with respect to clinical course, symptoms and outcome, as well as efficacy of therapy. The mean amount of AT was considerably higher in group 1 compared to group 2 (13 mg kg-1 vs 7.7 mg kg-1 ). The most frequent symptoms in both groups were impaired consciousness, anticholinergic symptoms, seizures, arrhythmia and hypotension. Respiratory insufficiency necessitated respirator therapy in 63 of the patients. Two patients in group 1 and one patient in group 2 did not survive.

Therapy included primary detoxification by gastric lavage and repeated administration of activated charcoal. In four of eight patients with cardiac conduction disturbances, hypertonic sodium bicarbonate led to a significant reduction in QRS duration and AV interval. Physostigmine was effective in eight of 14 patients with pronounced anticholinergic symptoms. No effect was observed in the other six patients. Haemoperfusion, which was performed in five patients, led to rapid improvement of coma after initiation of therapy in four patients. The clinical efficacy of haemoperfusion in AT overdose despite the high volume of distribution of AT deserves further investigation.

The rather high average overdose of AT implies that large package sizes of AT were available to the patients. A major step towards prevention of serious AT overdose would be the prescription of package sizes containing a total amount of less than 500 mg AT.

Different analytical methods (enzyme immunoassay, fluorescence polarization immunoassay, and gas chromatography/mass spectrometry) for rapid detection of AT and its metabolites in plasma and urine were evaluated. Commercially available immunoassays like EMIT and ADX were highly reliable and sensitive in the detection of AT overdose. Five previously unknown metabolites or derivatives of AT could be detected in cases of AT overdose with the aid of a gas chromatography/mass spectrometry screening procedure.

Effect of calcium chloride and 4-aminopyridine therapy on desipramine toxicity in rats

BACKGROUND

Hypotension is a major contributor to mortality in tricyclic antidepressant overdose. Recent data suggest that tricyclic antidepressants inhibit calcium influx in some tissues. This study addressed the potential role of calcium channel blockade in tricyclic antidepressant-induced hypotension.

METHODS

Two interventions were studied that have been shown previously to improve blood pressure with calcium channel blocker overdose. CaCl2 and 4-aminopyridine. Anesthetized rats received the tricyclic antidepressant desipramine IP to produce hypotension, QRS prolongation, and bradycardia. Fifteen min later, animals received CaCl2, NaHCO3, or saline. In a second experiment, rats received tricyclic antidepressant desipramine IP followed in 15 min by 4-aminopyridine or saline.

RESULTS

NaHCO3 briefly (5 min) reversed hypotension and QRS prolongation. CaCl2 and 4-aminopyridine failed to improve blood pressure. The incidence of ventricular arrhythmias (p = 0.004) and seizures (p = 0.03) in the CaCl2 group was higher than the other groups.

CONCLUSION

The administration of CaCl2 or 4-aminopyridine did not reverse tricyclic antidepressant-induced hypotension in rats. CaCl2 therapy may possibly worsen both cardiovascular and central nervous system toxicity. These findings do not support a role for calcium channel inhibition in the pathogenesis of tricyclic antidepressant-induced hypotension.

Effects of epinephrine and norepinephrine on hemodynamic parameters and arrhythmias during a continuous infusion of amitriptyline in rats

Epinephrine and norepinephrine were evaluated in treatment of hemodynamic compromise in amitriptyline intoxication. One hundred and one male Wistar rats were monitored hemodynamically during amitriptyline intoxication and given one of three infusion rates (0.1, 0.5 or 5.0 mg/kg/min) of either epinephrine or norepinephrine. Sixteen rats served as controls and received only glucose after intoxication. Amitriptyline intoxication lowered mean arterial pressure, heart rate, left ventricular max dP/dt, and increased left ventricular end-diastolic pressure. All doses of norepinephrine and the two higher doses of epinephrine increased mean arterial blood pressure and left ventricular max dP/dt. Heart rate increased with both drugs, more with epinephrine, but not beyond pre-intoxicated levels at any dose. Left ventricular end-diastolic pressure was unaltered by both drugs. Malignant arrhythmias appeared in 7% of all animals, whereas a progressive decline of cardiac contractility caused cardiac arrest in 36% of all animals. This suggests that myocardial depression is the aspect most likely to cause death. At intermediate doses epinephrine resulted in significantly fewer arrhythmias and lower mortality compared to norepinephrine. We conclude that epinephrine and norepinephrine each appeared effective in reversing amitriptyline-induced hemodynamic alterations. Epinephrine had fewer arrhythmogenic properties than norepinephrine and may be preferable to norepinephrine.