| Nimotop tablets should not be administered concomitantly with Nimotop solution. Drugs that affect nimodipine Nimodipine is metabolised via the cytochrome P450 3A4 system, located both in the intestinal mucosa and in the liver. Drugs that are known to either inhibit or induce this enzyme system may, therefore, alter the first pass or the clearance of nimodipine. The extent as well as the duration of interactions should be taken into account when administering nimodipine together with the following drugs: The concomitant use of oral nimodipine and rifampicin or cytochrome P450 3A4 system-inducing antiepileptic drugs such as phenobarbital, phenytoin or carbamazepine is contraindicated (see section 4.3 contraindications). The efficacy of Nimotop tablets could be reduced if these drugs are administered concomitantly. Upon co-administration with the following inhibitors of the cytochrome P450 3A4 system the blood pressure should be monitored and, if necessary, an adaption in the nimodipine dose should be considered (see section 4.2 Posology and method of administration):- macrolide antibiotics (e.g. erythromycin)- anti-HIV protease inhibitors (e.g. ritonavir)- azole anti-mycotics (e.g. ketoconazole)- nefazodone. Although no formal interaction studies have been performed to investigate the potential interaction between nimodipine and these drugs the potential for drug interaction and increased nimodipine plasma concentrations cannot be excluded. (See section 4.4 Special warnings and precautions for use). Azithromycin, although structurally related to the class of macrolide antibiotics, is void of CYP3A4 inhibition. Concurrent twice daily administration of 30mg nimodipine and daily administration of 20mg of the antidepressant fluoxetine to elderly patients resulted in an increase in nimodipine plasma levels, a reduction in fluoxetine levels and a trend towards increased norfluoxetine levels. The daily dose used in patients with subarachnoid haemorrhage is four times the daily dose used in this trial, and as a steady state norfluoxetine level was not achieved, the clinical significance of this interaction in the treatment of aneurysmal subarachnoid haemorrhage (aSAH) is uncertain. Concurrent three times daily administration of 30mg nimodipine and three times daily administration of 10mg of the antidepressant nortriptyline to elderly patients resulted in a slight decrease in nimodipine plasma levels with no effect on nortriptyline plasma levels. The daily dose used in patients with subarachnoid haemorrhage is four times the daily dose used in this trial, thus the clinical significance of this interaction in the treatment of aneurysmal subarachnoid haemorrhage (aSAH) is uncertain. The simultaneous administration of nimodipine with the anticonvulsant valproic acid or the H2-antagonist cimetidine can lead to an increase in the plasma concentration of nimodipine. Based on experience with the calcium-antagonist, nifedipine, co-administration of quinupristin/dalfopristin may lead to increased plasma concentrations of nimodipine.Effects of nimodipine on other drugs Animal studies have shown that when nimodipine and zidovudine are administered concomitantly, the AUC for zidovudine was increased, and the volume of distribution and clearance rate decreased. The clinical relevance of this interaction is unknown, but since the side-effects profile of zidovudine is known to be dose-related, this interaction should be considered in patients receiving nimodipine and zidovudine concomitantly.Other types of interaction Blood pressure lowering drugs Nimodipine may increase the blood pressure lowering effect of concomitant antihypertensives, such as diuretics, beta-blockers, ACE inhibitors, A1-antagonists, other calcium antagonists, alpha-adrenergic blocking agents, PDE5 inhibitors and alpha-methyldopa. If a combination of this type proves unavoidable particularly careful monitoring of the patient is necessary. The intake of grapefruit juice is not recommended in combination with nimodipine as it can result in increased plasma nimodipine concentrations due to the inhibition of the oxidative metabolism of dihydropyridines. As a consequence, the blood pressure lowering effect may be increased. This effect may last for at least 4 days after the last ingestion of grapefruit juice. Interactions shown not to exist A study examining the effects of 90mg nimodipine (in divided doses) on elderly patients receiving haloperidol did not show evidence of potential interactions. It is unclear whether this study is relevant to use in subarachnoid haemorrhage because of the higher dose of nimodipine used. Concomitant administration of oral nimodipine and diazepam, digoxin, glibenclamide, indometacin, ranitidine and warfarin did not reveal any potential for mutual interaction. | |