AA Pharma Bromocriptine Mechanism of Action

Pharmacotherapeutic Group: Prolactin Inhibitor, Growth Hormone Suppressant in Acromegaly, Adjunctive Medication in Parkinson's Disease.
Pharmacology: AA PHARMA BROMOCRIPTINE (bromocriptine mesylate) is a dopaminomimetic ergot derivative with D₂ type dopamine receptor agonist activity, and has also D₁ dopamine receptor antagonist properties. The dopaminomimetic activity of bromocriptine in the striatum is considered responsible for the clinical benefits seen in selected patients with Parkinson's Disease, when low doses of the drug are gradually added to levodopa therapy in patients on long-term treatment who develop late side effects of levodopa or no longer respond to the medication.
Excessive dopaminomimetic drive may, however, provoke psychotic and other adverse reactions. It inhibits the release and synthesis of prolactin by acting directly on the prolactin secreting cells of the anterior pituitary.
In patients with acromegaly, apart from lowering prolactin and elevated levels of growth hormone, bromocriptine has a beneficial effect on clinical symptoms and on glucose tolerance.
In man, bromocriptine is rapidly absorbed after oral administration with an absorption half-life of approximately 0.3 hours. The amount absorbed is about 65-95% of the oral dose. About 7% of the dose reaches the systemic circulation unchanged, due to a high hepatic extraction rate and first pass metabolism. The plasma protein binding amounts to 96%. Bromocriptine is extensively metabolized by the liver. Only traces of the unchanged compound are found in urine, together with 2 major metabolites. Unchanged drug represents about 10-15% of peak levels of radioactivity in plasma measured after a single dose of labelled drug. The active parent drug and the metabolites are primarily excreted via the liver, with only 6% being eliminated via the kidney. In plasma, the elimination half-life was between 2 to 8 hours for the parent drug and 50 to 70 hours for the metabolite after single oral doses.
The extreme variability in GI tract absorption and the extensive and individually variable first-pass metabolism are responsible for the broad variability in plasma concentrations of bromocriptine and, in part, for the variability in dose response.
A comparative bioavailability study was performed using normal healthy volunteers. The rate and extent of absorption after a single 7.5 mg dose of AA PHARMA BROMOCRIPTINE 2.5 mg tablets and PARLODEL 2.5 mg tablets was measured and compared. The results are summarized as follows: (See table).

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