Interaction between Cilostazol and Siponimod
Major Synergy

ID DDInter379 and DDInter1676
Interaction Due to its significant bradycardic effects, the risk of QT prolongation and torsade de pointes arrhythmia may be increased during initiation of siponimod treatment in patients receiving drugs that prolong the QT interval.
Management Siponimod has not been studied in patients receiving drugs that can prolong the QT interval. Because bradycardia and AV block are recognized risk factors for QT prolongation and torsade de pointes arrhythmia, treatment with siponimod should generally not be initiated in patients who are concurrently treated with QT prolonging drugs with known arrhythmogenic properties.
References
Alternative for Cilostazol B01A
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Alternative for Siponimod L04A
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Potential Metabolism Interactions

Substrate-Substrate Interaction:If more than one drug is metabolized by the same CYP, it is possible that its metabolism is inhibited because of the competition between the drugs. That means, it can be useful to lower the dosage of the drugs in the drug-cocktail because they remain longer in the organism than in monotherapy.
Inhibitor-Inhibitor Interaction:Combining two or more inhibitors of one CYP, should be compensated by lowering the dosage of these drugs because the metabolism is reduced and the drugs remain longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.
Inhibitor-Substrate Interaction:Combining drugs that have inhibitory effect and are substrates of one particular CYP, should be compensated by lowering the dosage. They rest longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.