Date of report 29 Oct 2021

Reported case interaction between
Etravirine and TACROLIMUS

A 57-year-old White British male attended our clinic for rationalisation of his antiretroviral regimen following MDT discussion. The patient was on Lamivudine 100mg OD, Etravirine 200mg BD, Raltegravir 400mg BD and Maraviroc 300mg BD. He was consistently virologically suppressed with a CD4 count of 269 cells mm3 (30%). He was highly treatment experienced with extensive drug resistance (see table 1).

Table 1: Summary of drug resistance mutations

His past medical history included liver transplantation secondary to alcoholic liver disease. Amongst his list of co-medications, he took tacrolimus 2mg OD for transplant rejection and itraconazole 100mg BD for oesophageal candidiasis prophylaxis.

His ARV regimen was simplified to Doravirine 100mg BD, Dolutegravir 50mg OD and Maraviroc 150mg BD. The removal of etravirine, a moderate CYP3A4 inducer, warranted close monitoring of tacrolimus levels to prevent drug-related toxicity (see table 2). Concomitant administration of potent CYP3A4 inhibitor itraconazole made prediction of drug level changes more difficult.

Table 2: Tacrolimus level monitoring post-antiretroviral switch

Following completion of post-switch monitoring, a 75% tacrolimus dose reduction was required to maintain therapeutic drug levels. This demonstrates the significance of the enzyme inducing effects of etravirine, even in the presence of a potent CYP3A4 inhibitor. The change in levels from day 7 to 35 suggests that enzyme deinduction follows a prolonged time course following etravirine discontinuation.