Deaths may occur from overdosage with this class of drugs. As the management is complex and changing, it is recommended that the physician contact a poison control center for current information on treatment. Signs and symptoms of toxicity develop rapidly after tricyclic antidepressant overdose; therefore, hospital monitoring is required as soon as possible.
Manifestations: Should overdosage with topical application of Zonalon (doxepin)
Cream occur, the signs and symptoms may include: cardiac dysrhythmias, severe
hypotension, convulsions, and CNS depression, including coma. Changes in the
electrocardiogram, particularly in QRS axis or width, are clinically significant
indicators of tricyclic antidepressant toxicity.
Other signs of overdose may include: confusion, disturbed concentration, transient
visual hallucinations, dilated pupils, agitation, hyperactive reflexes, stupor,
drowsiness, muscle rigidity, vomiting, hypothermia, hyperpyrexia, or any of
the symptoms listed under ADVERSE REACTIONS.
General: Obtain an ECG and immediately initiate cardiac monitoring.
Protect the patient's airway, establish an intravenous line and initiate gastric
decontamination. A minimum of six hours of observation with cardiac monitoring
and observation for signs of CNS or respiratory depression, hypotension, cardiac
dysrhythmias and/or conduction blocks, and seizures is strongly advised. If
signs of toxicity occur at any time during this period, extended monitoring
is recommended. There are case reports of patients succumbing to fatal dysrhythmias
late after overdose; these patients had clinical evidence of significant poisoning
prior to death and most received inadequate gastrointestinal decontamination.
Monitoring of plasma drug levels should not guide management of the patient.
Cardiovascular: A maximal limb-lead QRS duration of > /=0.10 seconds
may be the best indication of the severity of the overdose. Intravenous sodium
bicarbonate should be used to maintain the serum pH in the range of 7.45 to
7.55. If the pH response is inadequate, hyperventilation may also be used. Concomitant
use of hyperventilation and sodium bicarbonate should be done with extreme caution,
with frequent pH monitoring. A pH > 7.60 or a pCO 2 < 20 mm Hg is undesirable.
Dysrhythmias unresponsive to sodium bicarbonate therapy/hyperventilation may
respond to lidocaine, bretylium or phenytoin.
Type 1A and 1C antiarrhythmics are generally contraindicated (e.g., quinidine,
disopyramide, and procainamide).
In rare instances, hemoperfusion may be beneficial in acute refractory cardiovascular instability in patients with acute toxicity. However, hemodialysis, peritoneal dialysis, exchange transfusions, and forced diuresis generally have been reported as ineffective in tricyclic antidepressant poisoning.
CNS: In patients with CNS depression, early intubation is advised because
of the potential for abrupt deterioration. Seizures should be controlled with
benzodiazepines, or if these are ineffective, other anticonvulsants (e.g., phenobarbital,
Physostigmine is not recommended except to treat life-threatening symptoms that have been unresponsive to other therapies, and then only in consultation with a poison control center.
Pediatric Management: The principles of management of child and adult
overdosages are similar. It is strongly recommended that the physician contact
the local poison control center for specific pediatric treatment.
Because doxepin HCl has an anticholinergic effect and because significant plasma levels of doxepin are detectable after topical Zonalon (doxepin) Cream application, the use of Zonalon (doxepin) Cream is contraindicated in patients with untreated narrow angle glaucoma or a tendency to urinary retention.
Zonalon (doxepin) Cream is contraindicated in individuals who have shown previous sensitivity to any of its components.