Neuroleptics and other centrally-active dopamine antagonists, such as sulpiride or metoclopramide, may diminish the effectiveness of ropinirole and, therefore, concomitant use of these drugs with REQUIP PD 24 HOUR should be avoided.
There is no pharmacokinetic interaction between ropinirole and L-dopa or domperidone which would necessitate dosage adjustment of these drugs. No interaction has been seen between ropinirole and other drugs commonly used to treat Parkinson's disease.
In a study in parkinsonian patients receiving concurrent digoxin, no interaction was seen which would require dosage adjustment.
Ropinirole is principally metabolised by the cytochrome P450 enzyme CYP1A2. A pharmacokinetic study in Parkinson's patients revealed that ciprofloxacin increased the Cmax and AUC of ropinirole by approximately 60% and 84%, respectively. Hence, in patients already receiving REQUIP PD 24 HOUR, the dose of REQUIP PD 24 HOUR may need to be adjusted when drugs known to inhibit CYP1A2, e.g. ciprofloxacin, enoxacin or fluvoxamine, are introduced or withdrawn.
A pharmacokinetic interaction study in Parkinson's patients between ropinirole and theophylline, as representative of substrates of CYP1A2, revealed no change in the pharmacokinetics of either ropinirole or theophylline. Hence, changes in ropinirole pharmacokinetics following co-administration with other substrates of CYP1A2 are not expected.
Increased plasma concentrations of ropinirole have been observed in patients treated with high doses of oestrogens. In patients already receiving hormone replacement therapy (HRT), REQUIP PD 24 HOUR treatment may be initiated in the normal manner. However, if HRT is stopped or introduced during treatment with ropinirole, dosage adjustment may be required.
No information is available on the potential for interaction between ropinirole and alcohol. As with other centrally active medications, patients should be cautioned against taking REQUIP PD 24 HOUR with alcohol.
Smoking is known to induce CYP1A2 metabolism, therefore, if patients stop or start smoking during treatment with REQUIP PD 24 HOUR, adjustment of dose may be required.