Drug Interactions between aprepitant and Synalgos-DC

MONITOR: Coadministration with aprepitant or its prodrug, fosaprepitant, may increase the plasma concentrations of drugs that are primarily metabolized by CYP450 3A4. The mechanism is decreased clearance due to inhibition of CYP450 3A4 activity by aprepitant. According to the manufacturer, administration of the CYP450 3A4 substrate dexamethasone (20 mg orally on day 1 and 8 mg on days 2 through 5) in combination with aprepitant (125 mg single dose on day 1 and 80 mg/day on days 2 through 5) resulted in a 2.2-fold increase in dexamethasone systemic exposure (AUC) on days 1 and 5. Similarly, aprepitant increased the AUC of methylprednisolone (125 mg intravenously on day 1 and 40 mg orally on days 2 and 3) by 1.34-fold on day 1 and 2.5-fold on day 3. The effect of aprepitant on the pharmacokinetics of CYP450 3A4 substrates is expected to be greater when the substrates are administered orally as opposed to intravenously and may be altered following prolonged administration.

MANAGEMENT: Caution is advised when aprepitant or fosaprepitant is used concomitantly with drugs that undergo metabolism by CYP450 3A4, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever aprepitant or fosaprepitant is added to or withdrawn from therapy. Chronic, continuous use of aprepitant for prevention of nausea and vomiting is not recommended because it has not been studied and because the drug interaction profile may change during long-term use.

One study has reported that coadministration of caffeine and aspirin lead to a 25% increase in the rate of appearance and 17% increase in maximum concentration of salicylate in the plasma. A significantly higher area under the plasma concentration time curve of salicylate was also reported when both drugs were administered together. The exact mechanism of this interaction has not been specified. Physicians and patients should be aware that coadministration of aspirin and caffeine may lead to higher salicylate levels faster.