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Chapter: Modern Medical Toxicology: Neurotoxic Poisons: Anticonvulsants and Antiparkinsonian Drugs

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Bromocriptine - Antiparkinsonian Drug

Bromocriptine is an ergot derivative with potent dopaminergic agonist action (high affinity for the D2 receptor site).

Bromocriptine

Bromocriptine is an ergot derivative with potent dopaminergic agonist action (high affinity for the D2 receptor site). 

Uses

·              Bromocriptine is indicated for treatment of dysfunctions associated with hyperprolactinaemia, acromegaly to reduce serum growth hormone, and for idiopathic or postencepha-litic Parkinson’s disease.

·              It is no longer indicated for the treatment of suppression of physiological post-partum lactation; the FDA (USA) is of the opinion that bromocriptine may cause a serious adverse effect in post-partum women.

Toxicokinetics

The drug is well absorbed on oral administration and peak plasma levels are reached in about 2 hours. The plasma half-life of bromocriptine is approximately 6 to 8 hours. The volume of distribution is 1 to 4 L/kg, and plasma protein binding is to the extent of 96%. Liver is the main site of metabolism and the main route of excretion is biliary. Less than 0.1% is excreted unchanged.

Mode of Action

Bromocriptine is a synthetic ergoline and a direct dopamine D2 agonist stimulant. Some of its activity includes inhibi-tion of the release of prolactin by the pituitary, resulting in decreased plasma prolactin concentrations. Bromocriptine, as a dopamine agonist, occupies dopaminergic receptors in the pituitary gland to inhibit prolactin secretion. The D2 receptor sites show properties related to dopaminergic behavioural and endocrine responses.

Adverse Effects

·              Nausea, vomiting, vertigo, postural hypotension, nasal congestion, constipation, and mood disturbances.

·              Less common problems include headache, dryness of mouth, mydriasis, hallucinations, digital vasospasm, eryth- romelalgia,* and bladder disturbances.

·              Diplopia, dyskinesia, anginal pain, and ergotism have also been reported.

·              Long-term therapy may result in pleural effusion, pleural and pulmonary fibrosis, retroperitoneal fibrosis, and pleu- ritic chest pain.

·              Hypothermia, hypertension, myocardial infarction, stroke, and seizures have been reported in postpartum women who were given bromocriptine for lactation suppression.

·              Sudden discontinuation can result in hyperpyrexia.

Drug Interactions

·              Bioavailability of bromocriptine is increased if it is given along with erythromycin.

·              Alcohol reduces tolerance to bromocriptine and vice versa.

·              Bromocriptine has been reported to sensitise patients to acute dystonic crisis following administration of a neuro- leptic. Dopamine antagonists, such as the neuroleptics or leptic. Dopamine antagonists, such as the neuroleptics or C

·              dopamine agonists when given concurrently. Life-threatening symptoms of seizures, cerebral vasospasm, ventricular tachycardia and cardiac dysfunction have been reported when bromocriptine was combined with sympa- thomimetics.

Clinical (Toxic) Features

·              Drowsiness, vertigo, postural hypotension, sweating, hallucina-tions, agitation, convulsions, nausea, and vomiting. Dyskinesias may occur.

Treatment

·      Gastric lavage can be done if the patient is seen within a short time post-ingestion (upto 2 to 3 hours). Activated charcoal may not be beneficial.

·      Rest of the treatment involves supportive and symptomatic measures. Most cases of overdose with bromocriptine appear minimal and treatable with supportive care.

·      Monitor CNS changes for possible dyskinesias or seizures. Specific treatment for dyskinesias primarily includes reduc-tion of dosage and supportive care.

·      If the patient is hyperactive, administer diazepam 10 to 20 mg orally to adults, (no more than 0.1 mg/kg in children).

·      Blood pressure and ECG must be followed up in sympto-matic patients.

·      Because of the significant protein binding of bromocriptine, haemodialysis is not expected to be of benefit.

 

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