Drug Interaction Report

MONITOR CLOSELY: 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. For example, when 16 mg of loperamide was administered to 8 healthy subjects with 600 mg of quinidine, a potent P-gp inhibitor, mean loperamide systemic exposure (AUC) increased by 2.5 fold and respiratory response to carbon dioxide decreased. High plasma levels of loperamide, including through abuse or misuse, has been associated with serious and potentially fatal cardiac adverse events such as syncope, cardiac arrest, and arrhythmia related to prolongation of the QT interval. According to the FDA, the agency received reports of 48 cases of serious heart problems associated with use of loperamide from when it was first approved in 1976 through 2015. Thirty-one of these cases resulted in hospitalizations, and 10 patients died. The serious heart problems occurred mostly in patients who were using loperamide dosages that were much higher than recommended in an attempt to achieve euphoria, prevent opioid withdrawal, or treat diarrhea. In the most severe cases, individuals self-treated with dosages ranging from 70 to 1600 mg/day, or 4 to 100 times the recommended dosage. In other cases, patients were taking the recommended dosage, but with concomitant interacting drugs that caused an increase in loperamide levels. There have been additional cases of serious heart problems associated with loperamide use reported in the medical literature.

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. In many of the reported cases of loperamide-induced cardiotoxicity, standard antiarrhythmic drugs were ineffective, and electrical pacing or cardioversion was necessary.

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GENERALLY AVOID: Coadministration of tacrolimus and cyclosporine may increase the risk and severity of nephrotoxicity due to additive effects on the kidney. Clinical experience indicates that the combination is associated with increased renal toxicity as evidenced by increased serum creatinine and decreased glomerular filtration rate. In vitro and animal data also suggest that tacrolimus may inhibit the intestinal first-pass metabolism of cyclosporine via CYP450 3A4, resulting in significantly increased bioavailability of the latter.

MANAGEMENT: To avoid undue nephrotoxicity, tacrolimus and cyclosporine should not be used simultaneously. Tacrolimus or cyclosporine should be discontinued for at least 24 hours prior to initiating the other. In the presence of elevated tacrolimus or cyclosporine concentrations, dosing with the other drug usually should be further delayed.

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MONITOR CLOSELY: 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. For example, when 16 mg of loperamide was administered to 8 healthy subjects with 600 mg of quinidine, a potent P-gp inhibitor, mean loperamide systemic exposure (AUC) increased by 2.5 fold and respiratory response to carbon dioxide decreased. High plasma levels of loperamide, including through abuse or misuse, has been associated with serious and potentially fatal cardiac adverse events such as syncope, cardiac arrest, and arrhythmia related to prolongation of the QT interval. According to the FDA, the agency received reports of 48 cases of serious heart problems associated with use of loperamide from when it was first approved in 1976 through 2015. Thirty-one of these cases resulted in hospitalizations, and 10 patients died. The serious heart problems occurred mostly in patients who were using loperamide dosages that were much higher than recommended in an attempt to achieve euphoria, prevent opioid withdrawal, or treat diarrhea. In the most severe cases, individuals self-treated with dosages ranging from 70 to 1600 mg/day, or 4 to 100 times the recommended dosage. In other cases, patients were taking the recommended dosage, but with concomitant interacting drugs that caused an increase in loperamide levels. There have been additional cases of serious heart problems associated with loperamide use reported in the medical literature.

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. In many of the reported cases of loperamide-induced cardiotoxicity, standard antiarrhythmic drugs were ineffective, and electrical pacing or cardioversion was necessary.

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GENERALLY AVOID: Administration with grapefruit juice (compared to water or orange juice) has been shown to increase blood concentrations of cyclosporine with a relatively high degree of interpatient variability. The mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits.

GENERALLY AVOID: Administration with red wine or purple grape juice may decrease blood concentrations of cyclosporine. In 12 healthy volunteers, 12 ounces total of a merlot consumed 15 minutes prior to and during cyclosporine administration (single 8 mg/kg dose of Sandimmune) decreased cyclosporine peak blood concentration (Cmax) and systemic exposure (AUC) by 38% and 30%, respectively, compared to water. The time to reach peak concentration (Tmax) doubled, and oral clearance increased 50%. Similarly, one study were 12 healthy patients were administered purple grape juice and a single dose of cyclosporine showed a 30% and a 36% decrease in cyclosporine systemic exposure (AUC) and peak blood concentration (Cmax), respectively. The exact mechanism of interaction is unknown but may involve decreased cyclosporine absorption.

MONITOR: Food has been found to have variable effects on the absorption of cyclosporine. There have been reports of impaired, unchanged, and enhanced absorption during administration with meals relative to the fasting state. The mechanisms are unclear. Some investigators found an association with the fat content of food. In one study, increased fat intake resulted in significantly increased cyclosporine bioavailability and clearance. However, the AUC and pharmacodynamics of cyclosporine were not significantly affected, thus clinical relevance of these findings may be minimal.

MANAGEMENT: Patients receiving cyclosporine therapy should be advised to either refrain from or avoid fluctuations in the consumption of grapefruits and grapefruit juice. Until more data are available, the consumption of red wine or purple grape juice should preferably be avoided or limited. All oral formulations of cyclosporine should be administered on a consistent schedule with regard to time of day and relation to meals so as to avoid large fluctuations in plasma drug levels.

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GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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ADJUST DOSING INTERVAL: Consumption of food has led to a 27% decrease in the bioavailability of orally administered tacrolimus.

MANAGEMENT: Tacrolimus should be administered at least one hour before or two hours after meals.

GENERALLY AVOID: Grapefruit juice has been reported to increase tacrolimus trough concentrations. Data are limited, but inhibition of the CYP450 enzyme system appears to be involved.

MANAGEMENT: The clinician may want to recommend that the patient avoid ingesting large amounts of grapefruit juice while taking tacrolimus.

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