Basic Information
ID DDInter458 and DDInter1088
Interaction Coadministration with drugs that inhibit the P-glycoprotein (P-gp) efflux transporter may increase the concentrations of loperamide in plasma and central nervous system (CNS). Inhibition of P-gp in the intestine increases the systemic absorption of loperamide, while inhibition in the blood brain barrier facilitates loperamide entry into the CNS. Opioid and other adverse effects may be enhanced.
Management Caution is recommended if loperamide is used with potent P-gp inhibitors. Particular caution is advised when drugs that inhibit other pathways of loperamide elimination (CYP450 2C8; CYP450 3A4) are also used, since they may act synergistically with P-gp inhibitors to increase loperamide concentrations. Patients should be counseled to not exceed the recommended dosage and frequency or duration of use of loperamide, and to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope. If loperamide-induced cardiotoxicity is suspected, promptly discontinue loperamide and initiate therapy to manage and prevent cardiac arrhythmias and adverse outcomes. Electrical pacing or cardioversion may be necessary if torsade de pointes persists despite pharmacotherapy. "
References [1] US Food and Drug Administration "FDA warns about serious heart problems with high doses of the antidiarrheal medicine loperamide (Imodium), including from abuse and misuse. Available from: URL: http://www.fda.gov/downloads/Drugs/DrugSafety/UCM505108.pdf." ([2016, Jun 7]): [2] Adachi Y, Suzuki H, Sugiyama Y "Quantitative evaluation of the function of small intestinal P-glycoprotein: comparative studies between in Situ and in Vivo." Pharm Res 20 (2003): 1163-9 [3] Sadeque AJ, Wandel C, He H, Shah S, Wood AJ "Increased drug delivery to the brain by P-glycoprotein inhibition." Clin Pharmacol Ther 68 (2000): 231-7 [4] Crowe A, Wong P "Potential roles of P-gp and calcium channels in loperamide and diphenoxylate transport." Toxicol Appl Pharmacol 193 (2003): 127-37 [5] Eggleston W, Clark KH, Marraffa JM "Loperamide abuse associated with cardiac dysrhythmia and death." Ann Emerg Med 69 (2017): 83-6 [6] Warrington SJ, Ankier SI, Turner P "Evaluation of possible interactions between ethanol and trazodone or amitriptyline." Neuropsychobiology 15 (1986): 31-7 [7] "Product Information. Fycompa (perampanel)." Eisai Inc, Teaneck, NJ. [8] "Product Information. Rexulti (brexpiprazole)." Otsuka American Pharmaceuticals Inc, Rockville, MD. [9] Gilman AG, Rall TW, Nies AS, Taylor P, eds. "Goodman and Gilman's the Pharmacological Basis of Therapeutics. 8th ed." New York, NY: Pergamon Press Inc. (1990): [10] Bailey DG, Dresser GK "Natural products and adverse drug interactions." Can Med Assoc J 170 (2004): 1531-2 [11] Ho PC, Ghose K, Saville D, Wanwimolruk S "Effect of grapefruit juice on pharmacokinetics and pharmacodynamics of verapamil enantiomers in healthy volunteers." Eur J Clin Pharmacol 56 (2000): 693-8 [12] Fuhr U, Muller-Peltzer H, Kern R, et al. "Effects of grapefruit juice and smoking on verapamil concentrations in steady state." Eur J Clin Pharmacol 58 (2002): 45-53 [13] Arayne MS, Sultana N, Bibi Z "Review: grape fruit juice - drug interactions." Pak J Pharm Sci 18 (2005): 45-57 [14] McAllister RG, Jr "Clinical pharmacology of slow channel blocking agents." Prog Cardiovasc Dis 25 (1982): 83-102 [15] "Product Information. Covera-HS (verapamil)." Searle, Skokie, IL. [16] Bailey DG, Malcolm J, Arnold O, Spence JD "Grapefruit juice-drug interactions. 1998." Br J Clin Pharmacol 58 (2004): S831-40; discussion S841-3 [17] Zaidenstein R, Dishi V, Gips M, Soback S, Cohen N, Weissgarten J, Blatt A, Golik A "The effect of grapefruit juice on the pharmacokinetics of orally administered verapamil." Eur J Clin Pharmacol 54 (1998): 337-40 [18] Pillai U, Muzaffar J, Sandeep S, Yancey A "Grapefruit juice and verapamil: a toxic cocktail." South Med J 102 (2009): 308-9
Alternative for Cyclosporine L04A
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Alternative for Loperamide A07D
Opium Diphenoxylate Difenoxin
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.