Drug Interaction Report

MONITOR CLOSELY: Coadministration of ketamine with other central nervous system (CNS) depressants, including alcohol, may result in profound sedation, respiratory depression, coma, and death. In addition, opioid analgesics, barbiturates, and benzodiazepines may prolong the time to complete recovery from anesthesia.

MANAGEMENT: During concomitant use of ketamine with other CNS depressants, including alcohol, close monitoring of neurologic status and respiratory parameters, including respiratory rate and pulse oximetry, is recommended. Dosage adjustments should be considered according to the patient's clinical situation. 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.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of ketamine. Use in combination may result in additive central nervous system (CNS) depression and/or impairment of judgment, thinking, and psychomotor skills.

GENERALLY AVOID: Coadministration of oral ketamine with grapefruit juice may significantly increase the plasma concentrations of S(+) ketamine, the dextrorotatory enantiomer of ketamine. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Inhibition of hepatic CYP450 3A4 may also contribute. When a single 0.2 mg/kg dose of S(+) ketamine was administered orally on study day 5 with grapefruit juice (200 mL three times daily for 5 days) in 12 healthy volunteers, mean S(+) ketamine peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 2.1- and 3.0-fold, respectively, compared to administration with water. In addition, the elimination half-life of S(+) ketamine increased by 24% with grapefruit juice, and the ratio of the main metabolite norketamine to ketamine was decreased by 57%. The pharmacodynamics of ketamine were also altered by grapefruit juice. Specifically, self-rated relaxation was decreased and performance in the digit symbol substitution test was increased with grapefruit juice, but other behavioral or analgesic effects were not affected.

MANAGEMENT: Patients receiving ketamine should not drink alcohol. Caution is advised when ketamine is used in patients with acute alcohol intoxication or a history of chronic alcoholism. Following anesthesia with ketamine, patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination, such as driving or operating hazardous machinery, for at least 24 hours and until they know how the medication affects them. Patients treated with oral ketamine should also avoid consumption of grapefruit and grapefruit juice during treatment. Otherwise, dosage reductions of oral ketamine should be considered.

ADJUST DOSING INTERVAL: Concomitant use of some oral medications may reduce the bioavailability of orally administered iron, and vice versa.

Food taken in conjunction with oral iron supplements may reduce the bioavailability of the iron. However, in many patients intolerable gastrointestinal side effects occur necessitating administration with food.

MANAGEMENT: Ideally, iron products should be taken on an empty stomach (i.e., at least 1 hour before or 2 hours after meals), but if this is not possible, administer with meals and monitor the patient more closely for a subtherapeutic effect. Some studies suggest administration of iron with ascorbic acid may enhance bioavailability. In addition, administration of oral iron products and some oral medications should be separated whenever the bioavailability of either agent may be decreased. Consult the product labeling for specific separation times and monitor clinical responses as appropriate.