Drug Interactions between hydroxychloroquine and Phenergan with Dextromethorphan

GENERALLY AVOID: Hydroxychloroquine (HCQ) can cause dose-related prolongation of the QT interval. Theoretically, coadministration with other agents that can prolong the QT interval may result in additive effects and increased risk of ventricular arrhythmias including torsade de pointes and sudden death. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such advanced age, congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s). In a retrospective study of electronic health records analyzing QTc prolongation risk in patients on HCQ alone or with other QT-prolonging drugs, a statistically significant QTc interval increase of 18 ms was observed in the HCQ monotherapy group. No significant QTc increase was found in patients taking HCQ with the evaluated QT-prolonging medications. However, this result may have been influenced by factors such as varying patient sensitivity to QT-prolonging drugs across treatment sites, and differences in HCQ exposure duration prior to QTc measurement in combination therapy cases. QT prolongation has also been reported with chloroquine, with an increased risk reported at higher doses.

MANAGEMENT: Coadministration of hydroxychloroquine or chloroquine with other drugs that can prolong the QT interval should generally be avoided, particularly in patients with baseline QT prolongation (e.g., QTc >=500 msec) or congenital long QT syndrome. Close monitoring of QTc interval, electrolyte levels, and renal and hepatic function is recommended if concomitant use is required, and benefits are anticipated to outweigh the risks. Electrolyte abnormalities should be corrected prior to initiating treatment with hydroxychloroquine. Patients should be advised 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. Because both hydroxychloroquine and chloroquine are eliminated slowly from the body (e.g., terminal half-life of hydroxychloroquine is 40-50 days), potential drug interactions may persist for several weeks to months after their discontinuation.

MONITOR: Central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients. Sedation and impairment of attention, judgment, thinking, and psychomotor skills may increase.

MANAGEMENT: During concomitant use of these drugs, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. Cautious dosage titration may be required, particularly at treatment initiation. Ambulatory patients should be counseled to avoid hazardous activities requiring 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.

MONITOR: Coadministration with CYP450 2D6 inhibitors may increase the plasma concentrations of dextromethorphan in patients who are extensive metabolizers of this isoenzyme (approximately 93% of Caucasians and more than 98% of Asians and individuals of African descent). The proposed mechanism is inhibition of the CYP450 2D6-mediated O-demethylation of dextromethorphan. Increased plasma concentrations increase the risk of dextromethorphan-related adverse effects (e.g., agitation, confusion, tremor, insomnia, diarrhea, and respiratory depression) and serotonin syndrome. Coadministration of dextromethorphan (60 mg orally, once) with the CYP450 2D6 inhibitor panobinostat (20 mg orally once a day on days 3, 5, and 8) in 14 patients with advanced cancer had a highly variable effect on dextromethorphan levels, increasing the peak plasma concentration (Cmax) of dextromethorphan by 20% to 200%, and total systemic exposure (AUC 0 to infinity) by 20% to 130%, compared to dextromethorphan given alone. The moderate CYP450 2D6 inhibitor asunaprevir, given at 200 mg twice daily, also increased Cmax and AUC of a single 30 mg dose of dextromethorphan by 2.7- and 3.9-fold, respectively, in 17 study subjects.

MANAGEMENT: Caution should be exercised if these drugs must be used together. Patients should be monitored for signs of dextromethorphan adverse effects (e.g., agitation, confusion, tremor, insomnia, diarrhea, and respiratory depression) and serotonin syndrome, and advised to notify their health care professional if these adverse effects develop or worsen. Dose reduction of dextromethorphan may also be required.