Interaction between Diltiazem and Finasteride
Moderate Metabolism

ID DDInter561 and DDInter736
Interaction Coadministration with diltiazem may increase the plasma concentrations of drugs that are substrates of the CYP450 3A4 isoenzyme. The mechanism is decreased clearance due to inhibition of CYP450 3A4 activity by diltiazem.
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Management Caution is advised if diltiazem must be used concomitantly with medications that undergo metabolism by CYP450 3A4, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever diltiazem is added to or withdrawn from therapy.
References
Alternative for Diltiazem C05A
Triamcinolone (topical)
Betamethasone (topical)
Triamcinolone (nasal)
Prednisolone (ophthalmic)
Procaine
Tetracaine
Tetracaine (topical)
Zinc sulfate
Hydrocortisone (ophthalmic)
Betamethasone
Fluorometholone (ophthalmic)
More
Alternative for Finasteride D11A
Ivermectin (topical)
Alitretinoin (topical)
Ivermectin
Glycopyrronium
Dupilumab
Pimecrolimus
Glycopyrronium (topical)
Magnesium sulfate
Brimonidine
Diclofenac (ophthalmic)
Aminobenzoic acid
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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.