Drug interactions between Firmagon and tamoxifen
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GENERALLY AVOID: Long-term androgen deprivation therapy can prolong 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 a single, active-controlled, clinical study comparing abarelix to LHRH (luteinizing hormone releasing hormone) agonist plus nonsteroidal antiandrogen therapy, both therapies were found to prolong the mean Fridericia-corrected QT interval (QTcF) by more than 10 msec from baseline. In approximately 20% of patients in both groups, there were either changes from baseline QTc of greater than 30 msec or end-of-treatment QTc values exceeding 450 msec. Similar results were observed in two other Phase 3 studies with abarelix and the active-control treatments. In a randomized, active-controlled trial comparing degarelix to leuprolide, three patients (<1%) in the pooled degarelix group and four patients (2%) in the leuprolide 7.5 mg group had a QTcF of 500 ms or greater. From baseline to end of study, the median change was 12.3 msec for degarelix and 16.7 msec for leuprolide. Investigators believe that long-term androgen deprivation is responsible for these changes, as testosterone has been found to shorten ventricular repolarization. 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 as 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).
MANAGEMENT: The benefits of androgen deprivation therapy 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 periodic monitoring of electrocardiograms and electrolytes should be considered.
- "Product Information. Vantas (histrelin)." Endo Pharmaceuticals (formally Indevus Pharmaceuticals Inc), Lexington, MA.
- "Product Information. Zoladex (goserelin)." Zeneca Pharmaceuticals, Wilmington, DE.
- "Product Information. Eligard (leuprolide)." Sanofi Winthrop Pharmaceuticals, New York, NY.
Drug Interaction Classification
The classifications below are a guideline only. The relevance of a particular drug interaction to a specific patient is difficult to determine using this tool alone given the large number of variables that may apply.
|Major||Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.|
|Moderate||Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.|
|Minor||Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.|
Do not stop taking any medications without consulting your healthcare provider.
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