Understanding Hyperprolactinemia
Prolactin is a hormone produced by the pituitary gland, a small gland at the base of the brain. While it's most known for its role in enabling milk production (lactation) after childbirth, it affects many bodily functions. Hyperprolactinemia is a condition characterized by abnormally high levels of prolactin in the blood. Normal levels are typically under 25 ng/mL for women and 15 ng/mL for men. Elevated levels can result from various causes, including pregnancy, certain medications, an underactive thyroid, or, most commonly, a benign pituitary tumor called a prolactinoma.
Symptoms of high prolactin differ between sexes but often impact reproductive health.
- In women: Symptoms can include irregular or absent menstrual periods, infertility, milky discharge from the nipples when not pregnant or breastfeeding (galactorrhea), and menopausal symptoms like vaginal dryness.
- In men: Symptoms may manifest as erectile dysfunction, decreased libido, breast enlargement (gynecomastia), and reduced muscle mass or body hair. If the cause is a large tumor (macroadenoma), it can also press on surrounding tissues, leading to headaches and vision problems. Untreated, chronically high prolactin can lead to bone density loss (osteoporosis) due to suppressed estrogen and testosterone production.
The Primary Treatment: Dopamine Agonists
The most common and effective medical treatment for hyperprolactinemia involves a class of drugs called dopamine agonists. The secretion of prolactin from the pituitary gland is primarily regulated by dopamine, a chemical messenger in the brain. Dopamine acts as an inhibitory signal, telling the pituitary gland to stop producing prolactin.
Dopamine agonists work by mimicking the effects of natural dopamine. They bind to specific sites on the prolactin-producing cells in the pituitary gland called dopamine D2 receptors. This action 'tricks' the body into thinking there is more dopamine present, which powerfully suppresses prolactin production and secretion. As prolactin levels fall, symptoms of hyperprolactinemia typically improve, and these medications can also shrink the size of prolactinoma tumors.
FDA-Approved Dopamine Agonists
Two main dopamine agonists are FDA-approved and widely used to lower prolactin levels:
- Cabergoline: Often considered the first-line treatment, cabergoline is a long-acting dopamine agonist. It is generally more effective at normalizing prolactin levels and has a more favorable side effect profile compared to bromocriptine. Its long half-life allows for less frequent administration, which can improve patient compliance. Studies show cabergoline normalizes prolactin in 80-90% of cases.
- Bromocriptine (Parlodel, Cycloset): This is an older dopamine agonist that has been used for decades. It is also effective but generally requires more frequent administration and is associated with a higher incidence of side effects, particularly nausea and dizziness. Despite this, bromocriptine is still a valuable option, especially for patients planning pregnancy, due to a more extensive safety record in that context.
Other Dopamine Agonists
- Quinagolide (Norprolac): This is a non-ergot derived dopamine agonist that is effective in lowering prolactin levels and is an option for patients who do not tolerate bromocriptine. It is not currently approved for use in the United States but is available in Canada and several European countries.
Comparison of Prolactin-Lowering Drugs
| Feature | Cabergoline | Bromocriptine | Quinagolide |
|---|---|---|---|
| Drug Class | Dopamine D2 Receptor Agonist (Ergot derivative) | Dopamine D2 Receptor Agonist (Ergot derivative) | Dopamine D2 Receptor Agonist (Non-ergot) |
| Efficacy | 80-90% normalization of prolactin | 60-80% normalization of prolactin | Effective, especially in bromocriptine-intolerant patients |
| Administration Frequency | Typically once or twice weekly | Typically once or twice daily, in divided administrations | Typically once daily |
| Common Side Effects | Nausea, headache, dizziness, fatigue | Nausea, vomiting, dizziness, postural hypotension | Nausea, headache, dizziness, fatigue |
| Tolerability | Generally better tolerated | Higher rate of side effects, leading to discontinuation in more patients | Better tolerated than bromocriptine |
| Use in Pregnancy | Used, but less data than bromocriptine | Preferred choice due to extensive safety data | Should not be used if pregnancy is desired |
Side Effects and Management
Common side effects of dopamine agonists include nausea, dizziness, headache, and constipation. These effects are often dose-dependent and can be minimized by starting with a very low dose and gradually increasing it under medical supervision. Taking the medication with food or at bedtime can also help reduce gastrointestinal upset.
More rarely, these medications have been associated with impulse control disorders, such as compulsive gambling or shopping. High administrations of cabergoline, typically those used for Parkinson's disease, have been linked to a risk of heart valve damage, but this risk is considered minimal at the lower administrations used for hyperprolactinemia.
Conclusion
Pharmacological treatment is the cornerstone of managing hyperprolactinemia. Dopamine agonists, particularly cabergoline and bromocriptine, are highly effective at lowering prolactin levels by mimicking the brain's natural inhibitory signals. Cabergoline is often the first choice due to its superior efficacy and tolerability. Treatment decisions should be made in consultation with a healthcare provider to weigh the benefits against potential side effects and tailor the therapy to the individual's specific condition, symptoms, and life goals, such as pregnancy. Regular monitoring of prolactin levels and any potential side effects is crucial for successful long-term management.
For more information, you can visit the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
