Drug-induced liver injury secondary to increased levonorgestrel exposure in a patient taking ritonavir

We report the first published case of a drug induced liver injury (DILI) presumed secondary to a drug-drug interaction between ritonavir and levonorgestrel progestogen-only emergency contraception (POEC). Our patient is a 25-year-old female living with human immunodeficiency virus (HIV), taking antiretroviral therapy (ART) containing tenofovir alafenamide/emtricitabine and darunavir/ritonavir. She was found to have elevated transaminases at a routine clinic appointment consistent with hepatocellular DILI. Further investigation found the most likely cause of this was a drug-drug interaction (DDI) between the ritonavir component of her ART and recent use of levonorgestrel POEC 3 days earlier. Evidence suggests that ritonavir increases levonorgestrel exposure, yet our patient received double the usual dose as per dispensing guidance at the time. We review the pharmacokinetics of ritonavir-levonorgestrel DDIs and highlight the need for consistent guidelines on this topic.