Classification
In the pharmacotherapy of Parkinson's disease, bromocriptine is classified as a dopaminergic system stimulant, specifically a direct dopamine receptor agonist.
For differential diagnosis, it is important to distinguish it from other classes:
- Levodopa — a dopamine precursor.
- Selegiline — an MAO-B inhibitor.
- Amantadine — a drug that enhances dopamine release (and acts as an NMDA receptor blocker).
- Trihexyphenidyl — a central anticholinergic agent (suppresses the cholinergic system).
Mechanism of Action
The drug is a non-selective $D_1$ and $D_2$ receptor agonist, but exhibits the highest specific activity toward $D_2$ receptors.
Unlike levodopa, which requires metabolic conversion to dopamine to cross the blood-brain barrier, bromocriptine directly stimulates postsynaptic dopamine receptors in the CNS.
Pharmacological Effects
The effects of the drug depend strictly on the localization of the stimulated receptors:
- Antiparkinsonian effect: Mediated via stimulation of $D_2$ receptors in the neostriatum.
- Endocrine effect: Stimulation of pituitary $D_2$ receptors leads to reduced hormone release from the anterior pituitary.
- Effect on the prolactin axis: Normally, the hypothalamus exerts dual control over lactation, with dopamine acting as the primary inhibitory factor. Bromocriptine mimics this effect, suppressing lactogenic hormone (prolactin) secretion.
- Effect on the somatotropic axis: The drug is also capable of reducing growth hormone (GH) secretion.
Indications
The drug is used in both neurology and endocrinology:
- Parkinson's disease: Prescribed primarily in combination with levodopa. This combination is justified when levodopa monotherapy is insufficiently effective or when the "on-off" phenomenon develops.
- Hyperprolactinemic states: Prolactin-dependent amenorrhea, galactorrhea.
- Lactation: Used for the medical suppression of physiological lactation.
- Acromegaly: Prescribed to suppress growth hormone (GH) when surgical treatment is not feasible.
Comparison with Other Dopamine Agonists
Other drugs in this class are used in modern clinical practice:
- Pramipexole: Stimulates $D_2$ and $D_3$ receptors. Considered more effective than bromocriptine and can be used either as monotherapy or combined with levodopa.
- Cabergoline (Dostinex): A modern selective $D_2$ receptor agonist. It features a significantly longer duration of action (hypoprolactinemic effect persists for 7–28 days). At therapeutic doses, it suppresses only pituitary lactotrophs, and only at high doses does it cause central stimulation effects.
Adverse Effects and Contraindications
The adverse effects of bromocriptine are directly linked to the distribution of dopamine receptors in the body:
- Chemoreceptor trigger zone of the emetic center: Nausea and vomiting.
- Cerebral cortex: Psychotic reactions (delusions, hallucinations).
- Extrapyramidal system: Dyskinesias.
- Peripheral circulation: Orthostatic reactions, as well as peripheral arterial vasospasm, which can lead to calf muscle cramps.
- Other: Dry mouth, constipation.
Contraindications: Severe arterial hypertension, occlusive vascular diseases, Huntington's chorea.