Toxicology Brief: Baclofen overdose in dogs - Veterinary Medicine
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Toxicology Brief: Baclofen overdose in dogs


VETERINARY MEDICINE


Treatment

Because of the potential for a rapid onset of clinical signs, decontamination is best attempted under veterinary supervision. Emesis is contraindicated in symptomatic animals. Activated charcoal with a cathartic is recommended; however, repeated doses of activated charcoal have not been proved to be beneficial. Avoid magnesium-based cathartics, as they may compound central nervous system depression.4 Gastric lavage may be considered in cases of large ingestions, but take care to ensure that anesthesia does not compound central nervous system depression. Using short-acting induction agents such as propofol or thiopental sodium followed by inhalant anesthesia is preferred, and the airway must be protected.

Because of baclofen's low protein-binding and urinary excretion, its elimination may be enhanced through fluid diuresis.4 Fluid therapy will also help maintain blood pressure, protect the kidneys from myoglobinuria (secondary to tremors or seizures), and may aid in reducing cardiac arrhythmias.4 Cardiac monitoring with electrocardiography is recommended, and refractory arrhythmias should be treated as needed. Hypothermia is common in comatose or recumbent patients, so thermoregulation is important.

Ventilatory support is a prime concern, and endotracheal intubation and positive pressure mechanical ventilatory support may be needed for an extended time in severe cases. Monitor for aspiration in comatose animals. The use of central nervous system respiratory stimulants is of questionable value.4 Flumazenil and physostigmine have been used in people with baclofen toxicosis, with varying results.6 Experimental studies of baclofen toxicosis in rats have failed to consistently produce positive outcomes when flumazenil was used, and the drug can cause serious adverse effects (seizures).6 Phaclofen is a baclofen reversal agent that has been used experimentally, but it is not commercially available.6

Diazepam (0.5 to 1 mg/kg slowly intravenously, to effect) is the drug of choice for baclofen-induced seizures.4 Propofol or isoflurane may be considered in cases that are refractory to diazepam. Take care when administering long-acting barbiturates or other agents that produce profound or prolonged central nervous system depression in animals experiencing seizures. Cyproheptadine hydrochloride (1.1 mg/kg orally or rectally, as needed) has been used with some success to reduce the vocalization or disorientation seen in some animals (ASPCA APCC Database: Unpublished data, 1994-2004).

Hypoglycemia, hypokalemia, and elevated serum creatine phosphokinase, L-lactate dehydrogenase, and aspartate transaminase activities have occasionally been reported in people with baclofen toxicosis, so obtain baseline serum chemistry profile, acid-base balance, and electrolyte values.6 Continue to monitor these values and correct any abnormalities until signs have resolved. Baclofen concentrations can be determined in urine and serum, although they are considered of minimal benefit in managing clinical cases of toxicosis.4

Prognosis

Resolution of clinical signs may take several days in severe cases, but if adequate ventilatory support is available, the prognosis is generally good. Animals experiencing seizures have a more guarded prognosis. After a patient has recovered from baclofen toxicosis, no residual central nervous system effects are expected. No specific gross or histopathologic lesions would be expected in animals that die of skeletal muscle relaxant toxicosis.

"Toxicology Brief" was contributed by Tina Wismer, DVM, DABVT, DABT, ASPCA Animal Poison Control Center, 1717 S. Philo Road, Suite 36, Urbana, IL 61802. The department editor is Petra A. Volmer, DVM, MS, DABVT, DABT, College of Veterinary Medicine, University of Illinois, Urbana, IL 61802.


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Source: VETERINARY MEDICINE,
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