The concomitant use of alcohol or other CNS depressants may have an additive effect. Warn patients accordingly.
The prolonged ingestion of barbiturates gives rise to enzyme induction. This increases the rate of metabolism of certain drugs, including oral anticoagulants and oral contraceptives, thus reducing their effectiveness.
See also phenobarbital monograph.
The concomitant use of cytochrome P450 3A (CYP3A) inhibitors such as macrolide antibiotics (e.g. troleandomycin, erythromycin, clarithromycin), HIV protease or reverse transcriptase inhibitors (e.g. ritonavir, indinavir, nelfinavir, delavirdine) or azole antifungals (e.g. ketoconazole, itraconazole, voriconazole) and BELLERGAL Spacetabs must be avoided. since this can result in an elevated exposure to ergotamine and ergot toxicity (vasospasm and ischemia of the extremities and other tissues). Ergot alkaloids have also been shown to be inhibitors of CYP3A. No pharmacokinetic interactions involving other cytochrome P450 isoenzymes are known.
Concurrent use of vasoconstrictor agents including preparations containing ergot alkaloids, sumatriptan and other 5HT1 receptor agonists, and nicotine (e.g. heavy smoking) must be avoided since this may result in enhanced vasoconstriction .
Visual disturbances, dry mouth, flushing, drowsiness may occur. In children, behavioural disturbances and cognitive impairment may occur, due to the presence of phenobarbital.
Paraesthesia (e.g. numbness, tingling), pain and weakness in the extremities or peripheral vasoconstriction may occur. If ergotamine containing drugs are used excessively over years, they may induce fibrotic changes, in particular of the pleura and the retroperitoneum. There have also been rare reports of fibrotic changes of the cardiac valves.
Owing to its vasoconstrictor properties ergotamine may cause precordial pain, myocardial ischemia or, in rare cases, infarction, even in patients with no known history of coronary heart disease.
