In HIV patients a Lop/Rit dose of 400/100 mg twice a day produces peak Lop concentrations of 9.8 ± 3.7 mg/L, has a mean Lop trough concentration of 5.2 mg/L. Rit peak concentrations are 0.9 mg/L, trough concentrations 0.1 mg/L. In this study, we describe the pharmacokinetics of Lop/Rit in a cohort of hospitalized patients with COVID-19. Overall the reported pharmacokinetics of Lop and Rit at a 400 mg/100 mg 12 hourly dose in noncritical care patients are relatively consistent and suggests that the treatment failure of Lop/Rit in clinical trials is unlikely to be related to pharmacokinetic factors. B Dear Editor: b Although Lopinavir/Ritonavir (Lop/Rit) is now known not to be an effective treatment for hospitalized patients with COVID-19, it was widely used clinically in early 2020.[1] Lop is a viral protease inhibitor, whereas Rit acts to increase its half-life. [Extracted from the article]