Concomitant administration of multiple drugs frequently causes severe pharmacokinetic or pharmacodynamic drug–drug interactions (DDIs) resulting in the possibility of enhanced toxicity and/or treatment failure. The activity of cytochrome P450 (CYP) 3A4 and P-glycoprotein (P-gp), a drug efflux pump sharing localization and substrate affinities with CYP3A4, is a critical determinant of drug clearance, interindividual variability in drug disposition and clinical efficacy, and appears to be involved in the mechanism of numerous clinically relevant DDIs, including those involving dexamethasone. The recent increase in the use of high doses of dexamethasone during the COVID-19 pandemic have emphasized the need for better knowledge of the clinical significance of drug–drug interactions involving dexamethasone in the clinical setting. We therefore aimed to review the already published evidence for various DDIs involving dexamethasone in vitro in cell culture systems and in vivo in animal models and humans.

Inflammatory labyrinthitis is defined as a fluctuant vestibulo-cochlear syndrome associated with an impairment of the blood-labyrinthine barrier (BLB) on delayed FLAIR MRI sequences. Systemic and intratympanic corticosteroids are the gold standard treatment but their effect is frequently insufficient. The objective is here to determine whether infliximab could be of value in the treatment of bilateral inflammatory labyrinthitis. A retrospective monocentric study was conducted between January 2013 and December 2021. All patients included in the study were affected with a bilateral vestibulo-cochlear syndrome associated with bilateral blood-labyrinthine barrier impairment. Patients were administered infliximab at the dose of 5 mg/kg every 6 weeks for 6 months. Audiometry, MRI with delayed FLAIR sequences on the labyrinth, and corticosteroid doses still required were assessed both before and after treatment with infliximab was completed. Pure-tone average (PTA) was the primary outcome. The secondary outcomes were the speech recognition threshold (SRT), the Dizziness Handicap Inventory (DHI) score, and the corticosteroid (CS) dose. A total of nine patients including five men and four women were enrolled in the study. Thirteen ears were analyzed. After a 6-month period of treatment, the mean PTA (54 ± 24 db versus 66 ± 22 db; p = 0.027), SRT (54 ± 37 db versus 66 ± 32 db; p = 0.041) and DHI score (27 ± 15 versus 9 ± 2; p = 0.032) significantly improved. After the 6-month treatment period, the mean CS dose decreased from 38 ± 33 to 6 ± 5 mg/day (p = 0.003). We conclude that infliximab substantially improves the vestibulo-cochlear function in patients with bilateral inflammatory labyrinthitis and could be of value in corticosteroid-dependent cases.