What side effect is bromocriptine (dopamine agonist) therapy least likely to cause: dyskinesias, retroperitoneal fibrosis, gynaecomastia, hypotension, or Raynaud's phenomenon?

Bromocriptine Side Effects: Gynaecomastia is Least Likely

Among the listed side effects, gynaecomastia is the least likely to be caused by bromocriptine therapy. In fact, bromocriptine, as a dopamine agonist, typically reduces prolactin levels and is used to treat conditions associated with hyperprolactinemia, including gynaecomastia 1.

Common Side Effects of Bromocriptine

Bromocriptine, a dopamine receptor agonist, is associated with several well-documented side effects:

1. Dyskinesias

• Bromocriptine can cause dyskinesias, particularly when used in Parkinson's disease
• This effect may be related to dopamine receptor stimulation, particularly D1 receptors 2

2. Hypotension

• Postural hypotension is a common side effect of bromocriptine therapy
• This is mentioned as one of the initial adverse effects that may wear off over time 3
• Hypotension is a recognized side effect of dopamine agonists, occurring slightly more often in intervention arms of clinical trials 1

3. Raynaud's Phenomenon

• Digital vasospasm (Raynaud's phenomenon) is documented with bromocriptine use, particularly at higher doses 4
• This is related to the ergot-derived nature of bromocriptine

4. Retroperitoneal Fibrosis

• Retroperitoneal fibrosis is a recognized complication of ergot-derived dopamine agonists like bromocriptine 2, 5
• This appears to be a class effect of ergot-derived dopamine agonists related to stimulation of serotonin 5-HT2B receptors 2
• Case reports document serious complications including ureteric strictures and renal insufficiency requiring surgical intervention 5

Why Gynaecomastia is Least Likely

Bromocriptine actually treats rather than causes gynaecomastia:

• Bromocriptine is a dopamine agonist that suppresses prolactin secretion 6
• It is specifically used to treat hyperprolactinemia, which can cause gynaecomastia in males 4, 3
• The drug allows for "satisfactory return of sexual and reproductive function in 90% of patients" with hyperprolactinemia 4
• Current guidelines recommend dopamine agonists as first-line therapy for prolactinomas, with cabergoline being preferred over bromocriptine due to better efficacy and fewer side effects 1

Clinical Implications

When prescribing bromocriptine:

• Start with low doses during evening meals and gradually increase to minimize side effects like nausea and hypotension 3
• Monitor for signs of fibrotic complications, including dyspnea, cough, fatigue, leg edema, and symptoms of urinary obstruction 5
• Consider non-ergot dopamine agonists (pramipexole, ropinirole) which have lower risk of fibrotic complications 2
• Be aware that withdrawal of bromocriptine therapy is associated with reversal of its beneficial effects in most patients 6

Pitfalls to Avoid

• Don't confuse bromocriptine's therapeutic effect (reducing gynaecomastia) with its side effect profile
• Don't overlook the potential for serious fibrotic complications with long-term use
• Don't miss early signs of retroperitoneal fibrosis, which may present as asymmetric leg edema or urinary symptoms
• Be aware that modern guidelines often prefer cabergoline over bromocriptine due to its better tolerability and sustained activity 3