Rx Update: April 2002
Mary Ross, R.Ph., M.B.A., Barbara Mutnick, R.Ph., M.H.P., Joan
Murhammer, R.Ph., Pharmacotherapy Evaluation and Consultation
Service, Department of Pharmaceutical Care
Peer Review Status: Internally Reviewed
The manufacturer of droperidol (Inapsine®), an agent used to reduce the incidence of nausea and vomiting associated with surgical and diagnostic procedures, recently issued a "black box" warning after reports of QT prolongation and torsades de pointes were received in patients treated with droperidol. QT prolongation and torsades de pointes are serious cardiac conditions that may result in fatal arrhythmias. QT prolongation has been reported at doses at or below recommended droperidol doses. Case reports have occurred in patients with no known prior risk factors for QT prolongation, and some have been fatal. Some of the risk factors for the development of prolonged QT syndrome include congestive heart failure, bradycardia, use of a diuretic, cardiac hypertrophy, hypokalemia, hypomagnesemia, or administration of another drug known to increase the QT interval.
A number of other drugs are known to increase QT interval in some patients. These include antiarrhythmics such as amiodarone, disopyramide, dofetilide, flecainide, ibutilide, procainamide, quinidine, and sotalol. The antipsychotics (e.g., chlorpromazine, haloperidol, mesoridazine, quetiapine, risperidone, thioridazine, and ziprasidone) have also been shown to cause QT prolongation. Antibiotics with QT prolongation warnings include the macrolides (e.g., clarithromycin and erythromycin), and the fluoroquinolones (e.g., gatifloxacin, levofloxacin, moxifloxacin, and sparfloxacin). There are other commonly used drugs that increase risk of QT prolongation (e.g., fluoxetine, fosphenytoin, imipramine, naratriptan, paroxetine, salmeterol, sertraline, sumatriptan, and venlafaxine).
All patients receiving droperidol treatment must have 12-lead ECG monitoring before administration of droperidol. If it is determined that a patient has a prolonged QT interval (QTc greater than 440 msec for males and QTc greater than 450 msec for females), droperidol should NOT be administered. ECG monitoring should continue during administration and for 2 to 3 hours after completing therapy to monitor for the development of arrhythmias.
Therefore, droperidol should not be administered to patients with known or suspected prolonged QT interval. Due to its potential for serious proarrhythmic effects and death, droperidol should be reserved for use in the treatment of patients who fail to show an acceptable response to other adequate treatments. Prescribers should weigh the risks and benefits of therapy before initiating droperidol.
BENZOCAINE SPRAY
Benzocaine is a topical anesthetic agent used to provide rapid anesthesia to mucous membranes. The recommended dose of benzocaine 20% spray (Hurricaine®) is a 1/2 second spray; this delivers 30 mg of benzocaine. The product is poorly labeled with regard to dosing, and it is difficult to administer just a 1/2 second dose. Exceeding this duration of spray can be hazardous and result in methemoglobinemia. If cyanosis develops in a patient after the application of benzocaine, methemoglobinemia should be considered. Due the risk of accidental overdose, benzocaine spray is not permitted to be used as a "bedside" medication.