Drug Interactions between dextromethorphan / promethazine and nilutamide

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.

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GENERALLY AVOID: Long-term androgen deprivation therapy (ADT) can prolong the QT interval. Coadministration of ADT with other agents that may prolong the QT interval could also result in additive effects and an increased risk of ventricular arrhythmias including torsade de pointes and sudden death. The risk may be increased in patients with certain underlying risk factors like congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). Studies in young men have shown that endogenous serum testosterone levels are inversely associated with QTc (QT interval corrected for heart rate) duration. Clinical trials in men with low serum testosterone levels have reported testosterone administration being associated with a shortening of QTc. Likewise, studies using ADT have shown that it may prolong the QT interval; however, this effect may vary by drug, dose, or even each drug class that can be used to reduce testosterone levels. A clinical study comparing abarelix to a luteinizing hormone-releasing hormone agonist plus nonsteroidal antiandrogen therapy found that both therapies prolonged the mean Fridericia-corrected QT interval (QTcF) by more than 10 msec from baseline. Approximately 20% of patients in both groups had either changes from baseline QTc of >30 msec or end-of-treatment QTc values >450 msec. Similarly, a study comparing degarelix to leuprolide found that approximately 20% of patients on each drug had QT/QTc intervals >450 msec after 1 year of treatment. From baseline to end of study, the median change in QTcF was 12.3 msec for degarelix and 16.7 msec for leuprolide. Some drugs used to lower testosterone levels may also have other side effects that can predispose a patient to QT prolongation and torsade de pointes. For example, inhibitors of 17 alpha-hydroxylase/C17,20-lyase (CYP17) like abiraterone may cause hypokalemia as a result of increased mineralocorticoid levels. Clinical data on ADT prolonging the QT interval in women and children are lacking.

MANAGEMENT: The benefits of androgen deprivation therapy (ADT) should be carefully assessed against the potential risk in patients receiving other drugs known to prolong the QT interval. Electrolyte abnormalities should be corrected prior to initiating therapy, and monitoring of electrocardiograms and electrolytes may be advisable. The manufacturer's labeling as well as current clinical guidelines should be consulted for monitoring recommendations.

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