Clinical Pharmacology considerations and drug-drug interactions with
long-acting cabotegravir and rilpivirine relevant to a sub-Saharan
Africa
Abstract
Long-acting injectable (LAI) cabotegravir and rilpivirine for HIV
treatment and LAI cabotegravir for pre-exposure HIV prophylaxis are
being rolled out in a multitude of countries worldwide. Due to the
prolonged exposure, it can be challenging to undertake ‘traditional’
pharmacokinetic studies and current guidance is derived from their oral
equivalents or physiologically-based pharmacokinetic studies. This
review aims to consider pharmacokinetic characteristics of cabotegravir
and rilpivirine and describe anticipated drug-drug interactions (DDIs)
with frequent concomitant medications in African settings. Relevant
comedications were identified from the WHO 2021 List of Essential
Medicines. All original human and physiologically-based pharmacokinetic
studies published in English on PubMed, discussing DDIs with LAI
cabotegravir and rilpivirine prior to April 2023, were reviewed. The
Liverpool HIV interaction database was also reviewed. LAI cabotegravir
and rilpivirine have half-lives of 6-12 and 13-28 weeks, respectively.
Cabotegravir is primarily metabolised by UDP-glucuronyltransferase
(UGT)-1A1 and rilpivirine by cytochrome P450 (CYP)-3A4. LAI cabotegravir
and rilpivirine themselves exhibit low risk of perpetrating interactions
with comedications as they do not induce or inhibit the major drug
metabolising enzymes. However, they are victims of DDIs relating to the
induction of their metabolising enzymes by concomitantly administered
medication. Noteworthy contraindicated comedications include rifamycins,
carbamazepine, phenytoin, flucloxacillin and griseofulvin, which induce
CYP3A4 and/or UGT1A1, causing clinically-significant reduced
concentrations of rilpivirine and/or cabotegravir. In addition to
virologic failure, subtherapeutic concentrations resulting from DDIs can
lead to emergent drug resistance. Clinicians should be aware of
potential DDIs and counsel people receiving LAI cabotegravir/rilpivirine
appropriately to minimise risk.