Interaction between Midodrine and Ranolazine
Moderate Metabolism

ID DDInter1213 and DDInter1570
Interaction Coadministration with ranolazine may increase the plasma concentrations of drugs that are substrates of the CYP450 2D6 isoenzyme. Ranolazine has been shown in vitro to be an inhibitor of CYP450 2D6. However, concomitant use of ranolazine with other drugs that are metabolized by CYP450 2D6 such as tricyclic antidepressants and antipsychotics has not been studied.
Management Caution is advised if ranolazine must be used concurrently with medications that undergo metabolism by CYP450 2D6, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever ranolazine is added to or withdrawn from therapy.
References
Alternative for Midodrine C01C
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Alternative for Ranolazine C01E

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.