Date of report: 27 Feb 2020
Reported case interaction between
 Efavirenz and Orlistat

FLS Science

Drugs suspected to be involved in the DDI

Drug A
Efavirenz (Victim)
Daily Dose
600 (mg)
Dose adjustment performed
No
Administration Route
Oral
Start date
Unknown
End date
Unknown
Drug B
Orlistat (Perpetrator)
Daily Dose
180 (mg)
Dose adjustment performed
No
Administration Route
Oral
Start date
Unknown
End date
Unknown

Complete list of drugs taken by the patient

Antiretroviral treatment
Emtricitabine/Tenofovir-DF
Efavirenz
Complete list of all comedications taken by the patient, included that involved in the DDI
Orlistat

Clinical case description

Gender
Female
Age
39
eGFR (mL/min)
>60
Liver function impairment
No
Description
HIV patient treated with efavirenz who voluntarily decided to buy over‐the‐counter (OTC) orlistat to lose body weight. Virological failure with mean HIV RNA of 101,810 copies/mL. TDM revealed suboptimal efavirenz concentrations during orlistat therapy (<150 ng/mL) compared with after orlistat discontinuation (3795 ng/mL). This case was published by Gervasoni C, et al in J Antimicrob Chemother. 2016 Jun;71(6):1739-41

Outcome

Loss of efficacy

Drug Interaction Probability Scale (DIPS)

Score
7 - Probable

Editorial Comment

Orlistat reduces dietary fat absorption and may affect the absorption of antiretrovirals (especially if lipophilic). Although there are no specific data in this combination available, orlistat should only be used with efavirenz if separated by 4-5 hours. [Note: this interaction is not specific for atazanavir, but for any medication taken with orlistat.]