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Toxicity varies between patients; tolerance will develop with chronic use. Features of poisoning are to be expected after ingestion of 1 g in adults.
Symptoms: Drowsiness, dysarthria, ataxia, nystagmus and disinhibition. There may also be coma, cardiovascular collapse, cardiac arrest, hypotension, hypotonia, hyporeflexia, rhabdomyolysis, hypothermia, and respiratory depression.
Barbiturates decrease gut motility, which may lead to slow onset and worsening of symptoms or cyclical improvement and worsening of symptoms.
Treatment: Treatment of barbiturate overdosage is primarily supportive. An adequate airway should be maintained, with assisted respiration and administration of oxygen as needed. Vital signs and fluid balance should be monitored. If the patient is conscious and has not lost the gag reflex, emesis may be induced with ipecac syrup, care should be taken to prevent pulmonary aspiration of vomitus.
After vomiting is completed, activated charcoal in a glass of water or sorbitol may be administered to prevent absorption and increase excretion of the barbiturate. Activated charcoal (50 g for an adult, 10-15 g for kids under 5 years) can be considered if >10 mg/kg body weight of drug has been ingested within 1 hour, provided airway can be protected. Repeat dose activated charcoal is the best method of enhancing elimination of phenobarbitone in symptomatic patients.
If emesis is contraindicated, gastric lavage may be performed with a cuffed endotracheal tube in place with the patient face down. Activated charcoal should be left in the stomach and a saline cathartic may be administered.
Charcoal haemoperfusion is the treatment of choice for the majority of patients with severe barbiturate poisoning who fail to improve or who deteriorate despite good supportive care.
Fluid therapy and other standard treatment of shock should be administered if necessary.
A vasopressor may be required if hypotension occurs. If renal function is normal, forced diuresis may help to eliminate the barbiturate. Alkalinization of the urine increases renal excretion of some barbiturates, especially phenobarbitone. Treat rhabdomyolysis with urinary alkalinisation.
Fluid or sodium overload should be avoided, especially if cardiovascular status is decreased although hemodialysis or hemoperfusion is not recommended as a routine procedure, it may be used in severe barbiturate poisoning or if the patient is anuric or in shock or in cases of acute renal or severe hyperkalaemia. Chest physiotherapy should be administered.
In severe hypotension, dopamine or dobutamine can be used.
If pneumonia is suspected, appropriate care should be taken to prevent hypostatic pneumonia, decubiti, aspiration and other complications that may occur with altered states of consciousness.
