Studies in animal models suggest that dexamethasone acts on the glucocorticoid receptor-rich bilateral nucleus tractus solitarius (i.e., the vomiting center), but not the area postrema.
However, like other intravenous drugs containing phosphate esters, dexamethasone has been associated with perineal burning and itching when injected in awake patients.
Apepitant inhibits CYP 3A4 activity. this doubles the plasma concentration of dexamethasone.
Given that dexamethasone has high (80%) oral bioavailability, and that aprepitant also increases the peak plasma concentration and half-life of dexamethasone, aprepitant’s inhibition of CYP 3A4 activity probably plays alarger rolein systemic rather than first-pass clearance of dexamethasone.
Therefore doses of dexamethasone that are coadministered with aprepitant should be reduced by half to maintain dexamethasone plasma concentrations that are similar to regimens without aprepitant.
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