Bromocriptine has been shown to be a mechanism-based inhibitor of CYP3A4 in vitro. It is most probably not an inducer or inhibitor of CYP enzymes in vivo. Risk for gastrointestinal adverse events in the form of constipation, vomiting and diarrhoea motivates vigilance against insufficient intake of food, especially of carbohydrate.

Bromocriptine is a dopamine receptor agonist and ergot peptide derivative.

Bromocriptine is indicated for the treatment of Parkinsons disease, inhibition of lactation for medical reasons, hyperprolactinaemia, menstrual cycle disorders and female infertility, prolactinomas, acromegaly, premenstrual symptoms and benign breast disease. Common side effects that can be potentially porphyrinogenic through reduction in carbohydrate intake and that also can be confused with an acute porphyria attack are constipation, vomiting and nausea. Other common side effects are headache, dizziness and drowsiness.

Bromocriptine is extensively metabolised by CYP3A4 (SPC) to lysergic acid and peptides. It is a potent inhibitor of CYP3A4 in vitro (SPC) and has been reported to be a mechanism-based inhibitor of CYP3A4 in human liver microsomes (Zhou 2009). Bromocriptine inhibits the metabolism of tacrolimus, a CYP3A4 substrate (Norsk legemiddelhåndbok), and increase the exposure of tacrolimus in vitro (Christians 2002), but no quantitative assessment of this inhibition was given. An oral dose of 5 mg of bromocriptine results in a Cmax of 0.465 ng/ml (SPC and Wynalda 1997) or 0.7 nM. The maximal dose is 30 mg/day (SPC) which indicates that it will most probably not exceed 100 nM, the concentration needed to activate PXR and induce CYP enzymes. Wynalda (1997) also states that the plasma concentration of bromocriptine is too low to expect it to significantly inhibit or induce the metabolism of other drugs. Bromocriptine is not listed as an inducer or mechanism-based inhibitor of any major CYP enzymes (FDA, Hisaka 2010, Isoherranen 2009 and Pelkonen 2008) and no drug-drug interaction with bromocriptine as a perpetrator has been reported in the literature.

Bromocriptine is listed as unsafe for use in acute porphyria because it has been shown to be porphyrinogenic in animals or in vitro systems (Moore 1997). Bromocriptine is listed as unsafe for use in acute porphyrias (Gorchein 1995).