Drug Interactions between Innovar and Lufyllin-EPG

MONITOR CLOSELY: The use of droperidol has been associated with QT interval prolongation, torsade de pointes and other serious arrhythmias, and sudden death. The concurrent administration of agents that can produce bradycardia, a known risk factor for QT interval prolongation, such as benzodiazepines and opiates, particularly intravenous opiates, may increase the risk of QT interval prolongation. In addition, hypotensive effects and central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking droperidol with benzodiazepines or opiates, especially in elderly or debilitated patients.

MANAGEMENT: Extreme caution and close monitoring are recommended if droperidol must be administered concomitantly with other bradycardic drugs. The dosage of droperidol should be individualized and titrated to the desired effect. Routine vital sign and ECG monitoring is recommended. When droperidol is used in combination with benzodiazepines or opiates, patients should be monitored for potentially excessive or prolonged CNS or respiratory depression as well as severe hypotension. 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 doctor if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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GENERALLY AVOID: Barbiturates may potentiate the central nervous system (CNS) depressant effects of opioids. Concomitant use may result in profound sedation, respiratory depression, coma, and death. On the other hand, some barbiturates can also induce the hepatic metabolism of opioids that are metabolized by CYP450 3A4 such as butorphanol, fentanyl, hydrocodone, methadone and oxycodone, resulting in enhanced clearance. Reduced analgesic efficacy or withdrawal symptoms may occur in patients maintained on their opioid regimen following the addition of a barbiturate. Conversely, discontinuation of the barbiturate may increase plasma concentrations of the opioid and potentiate the risk of overdose and fatal respiratory depression.

MANAGEMENT: The use of opioids in conjunction with other CNS depressants such as barbiturates should generally be avoided unless alternative treatment options are inadequate. If coadministration is necessary, the dosage and duration of each drug should be limited to the minimum required to achieve desired clinical effect, and patients should be closely monitored for signs and symptoms of CNS and respiratory depression. Particular caution is advisable when a barbiturate is added to or withdrawn from therapy in patients receiving opioids that are CYP450 3A4 substrates, as there may be an increased risk of withdrawal symptoms (e.g., restlessness, insomnia, sweating, lacrimation, or rhinorrhea) following initiation of the barbiturate and overdose following discontinuation. A dosage adjustment for one or both drugs may be required.

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MONITOR: Theoretically, potent CYP450 3A4 inducers may decrease serum concentrations of butyrophenones such as benperidol or droperidol. This interaction has been reported for haloperidol. In an observational study of 12 schizophrenic patients taking oral haloperidol, the administration of rifampin for 28 days reduced haloperidol plasma levels by a mean of 70%, and scores in the Brief Psychiatric Rating Scale (BPRS) were increased. However, clinical data are lacking for benperidol or droperidol. In addition, butyrophenones may lower the seizure threshold. Central nervous system- and/or respiratory-depressant effects may also be additively or synergistically increased in patients taking droperidol or benperidol with certain other drugs that cause these effects, especially in elderly or debilitated patients.

MANAGEMENT: The potential for diminished neuroleptic effects of droperidol or benperidol should be considered during coadministration with potent CYP450 3A4 inducers. Pharmacologic response to these medications should be monitored more closely whenever a CYP450 3A4 inducer is added to or withdrawn from therapy, and the droperidol or benperidol dosage adjusted as necessary. Patients taking potent CYP450 3A4 inducers that are anticonvulsants should be monitored for loss of seizure control. Additionally, when droperidol or benperidol are used in combination with other drugs that cause CNS and/or respiratory depression, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. 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 doctor if they experience seizures or excessive CNS effects that interfere with their normal activities.

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Ephedrine-methylxanthine combinations are used for the treatment of asthma but the efficacy of the combination has been questioned. This combination may lead to increased xanthine side effects. The mechanism is unknown, but may be related to synergistic pharmacologic effects. Patients using this combination should be closely monitored for side effects such as nausea, vomiting, tachycardia, nervousness, or insomnia. If side effects are noted, the dosage of the xanthine may need to be decreased.

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