| Pharmacodynamic interactions At the Pharmacodynamic level cases of serotonin syndrome with citalopram and moclobemide and buspirone have been reported.Contraindicated combination: MAO-inhibitorsThe simultaneous use of citalopram and MAO-inhibitors can result in severe side effects, including the serotonin syndrome (see section 4.3). Cases of serious and sometimes fatal reactions have been reported in patients receiving an SSRI in combination with a monoamine oxidase inhibitor (MAOI), including the irreversible MAOI selegiline and the reversible MAOIs linezolid and moclobemide and in patients who have recently discontinued an SSRI and have been started on a MAOI.Some cases presented with features resembling serotonin syndrome. Symptoms of an active substance interaction with a MAOI include: agitation, tremor, myoclonus and hyperthermia.PimozideCo administration of a single dose of pimozide 2mg to subjects treated with racemic citalopram 40mg/day for 11 days caused an increase in AUC and Cmax of pimozide, although not consistently throughout the study. The co-administration of pimozide and citalopram resulted in a mean increase in the QTc interval of approximately 10 msec. Due to the interaction noted at a low dose of pimozide, concomitant administration of citalopram and pimozide is contraindicated.Combinations requiring precaution for use Selegiline (selective MAO B inhibitor)A pharmacokinetic/pharmacodynamic interaction study with concomitantly administered citalopram (20mg daily) and selegiline (10mg daily) (a selective MAO B inhibitor) demonstrated no clinically relevant interactions. The concomitant use of citalopram and selegiline (in doses above 10mg daily) is not recommended.Serotonergic medicinal products:Lithium and tryptophanNo pharmacodynamic interactions have been found in clinical studies in which citalopram has been given concomitantly with lithium. However there have been reports of enhanced effects when SSRIs have been given with lithium or tryptophan and therefore the concomitant use of citalopram with these medicinal products should be undertaken with caution. Routine monitoring of lithium levels should be continued as usual.The 5-HT effect of serotonergic drugs such as tramadol and sumatriptan may be potentiated by selective serotonin re-uptake inhibitors (SSRIs). Until further information is available, the simultaneous use of citalopram and 5-HT agonists, (sumatriptan and other triptans) is not recommended (see section 4.4).HaemorrhageCaution is warranted for patients who are being treated simultaneously with anticoagulants, medicines that affect the function of thrombocytes, such as NSAIDs, acetylsalicylic acid, dipyridamole, and ticlopidine or other medicines (e.g. atypical antipsychotics, phenothiazines, tricyclic depressants) that can increase the risk of haemorrhage (see section 4.4).NeurolepticsExperience with citalopram has not revealed any clinically relevant interactions with neuroleptics. However, as with other SSRIs, the possibility of a pharmacodynamic interaction cannot be excluded.St John's WortUndesirable effects may be more common during concomitant use of citalopram and herbal preparations containing St John's wort (Hypericum perforatum) due to dynamic interactions (see section 4.4). Pharmacokinetic interactions have not been investigated.ECT (electroconvusive therapy)There are no clinical studies establishing the risks or benefits of the combined use of electroconvulsive therapy (ECT) and citalopram (see section 4.4).AlcoholNo pharmacodynamic or pharmacokinetic interactions have been demonstrated between citalopram and alcohol. However, the combination of citalopram and alcohol is not advisable. Medicinal products including QT prolongation or hypokalaemia/hypomagnesaemiaCaution is warranted for concomitant use of other QT interval prolonging medicines or hypokalaemia/hypomagnesaemia inducing drugs as they, like Citalopram, also prolong the QT interval.Medicinal products lowering the seizure thresholdSSRIs can lower the seizure threshold. Caution is advised when concomitantly using other medicinal products capable of lowering the seizure threshold (e.g. antidepressants (tricyclics, SSRIs), neuroleptics (phenothiazines, thioxanthenes and butyrophenones), mefloquin, bupropion and tramadol).Desipramine, imipramineIn a pharmacokinetic study no effect was demonstrated on either citalopram or imipramine levels, although the level of desipramine, the primary metabolite of imipramine was increased. When desipramine is combined with citalopram, an increase of the desipramine plasma concentration has been observed. A reduction of the desipramine dose may be needed.Pharmacokinetic interactions Biotransformation of citalopram to demethylcitalopram is mediated by CYP2C19 (approx. 38%), CYP3A4 (approx. 31%) and CYP2D6 (approx. 31%) isoenzymes of the cytochrome P450 system. The fact that citalopram is metabolised by more than one CYP means that inhibition of its biotransformation is less likely as inhibition of one enzyme may be compensated by another. Therefore co-administration of citalopram with other medicinal products in clinical practice has very low likelihood of producing pharmacokinetic medicinal product interactions.Influence of other medicinal products on the pharmacokinetics of citalopram Pharmacokinetic interactions based on plasma-protein binding should not be expected. Citalopram is a weak inhibitor of CYP2D6. Although clinically relevant medicinal interactions with citalopram are unusual, an interaction cannot be excluded if citalopram is administered simultaneously with another medicinal product that is metabolised by CYP2D6. CimetidineCimetidine, a known enzyme-inhibitor, caused a slight rise in the average steady-state citalopram levels. Caution is therefore recommended when administering high doses of citalopram in combination with high doses of cimetidine. Co-administration of escitalopram (the active enantiomer of citalopram) with omeprazole 30mg once daily (a CYP2C19 inhibitor) resulted in moderate (approximately 50%) increase in the plasma concentrations of escitalopram. Thus, caution should be exercised when used concomitantly with CYP2C19 inhibitors (e.g. omeprazole, esomeprazole, fluvoxamine, lansoprazole, ticlopidine) or cimetidine. A reduction in the dose of escitalopram may be necessary based on monitoring of undesirable effects during concomitant treatment.There is no pharmacokinetic interaction between lithium and citalopram. However, there have been reports of enhanced serotonergic effects when SSRIs were administered in combination with lithium or tryptophan. Co-administration with ketoconazole (potent CYP3A4 inhibitor) did not change the pharmacokinetics of citalopram.FoodThe absorption and other pharmacokinetic properties of citalopram have not been reported to be affected by food.Effects of citalopram on other medicinal products Escitalopram (the active enantiomer of citalopram) is an inhibitor of the enzyme CYP2D6. Caution is recommended when citalopram is co-administered with medicinal products that are mainly metabolised by this enzyme, and that have a narrow therapeutic index, e.g. flecainide, propafenone and metoprolol (when used in cardiac failure), or some CNS acting medicinal products that are mainly metabolised by CYP2D6, e.g. antidepressants such as desipramine, clomipramine and nortriptyline or antipsychotics like risperidone, thioridazine and haloperidol. Dosage adjustment may be warranted. A pharmacokinetic/pharmacodynamic interaction study with concomitant administration of citalopram and metoprolol (a CYP2D6 substrate) showed a twofold increase in metoprolol concentrations, but no statistically significant increase in the effect of metoprolol on blood pressure and heart rate in healthy volunteers.Citalopram and demethylcitalopram are negligible inhibitors of CYP2C9, CYP2E1 and CYP3A4, and only weak inhibitors of CYP1A2, CYP2C19 and CYP2D6 as compared to other SSRIs established as significant inhibitors. Levomepromazine, digoxin, carbamazepineThus no change or only very small changes of no clinical importance were observed when citalopram was given with CYP1A2 substrates (clozapine and theophylline), CYP2C9 (warfarin), CYP2C19 (imipramine and mephenytoin), CYP2D6 (sparteine, imipramine, amitriptyline, risperidone) and CYP3A4 (warfarin, carbamazepine (and its metabolite carbamazepine epoxid) and triazolam.No pharmacokinetic interaction was observed between citalopram and levomepromazine or digoxin (indicating that citalopram neither induces nor inhibits P-glycoprotein). | |