Introduction Terminal complement amplification is hypothesized to be a key contributor to the clinical manifestations of severe coronavirus disease 2019 (COVID-19). Ravulizumab, a humanized monoclonal antibody that binds with high affinity to complement protein C5 and inhibits terminal complement activation, is being evaluated as a treatment for COVID-19-related severe pneumonia, acute lung injury, and acute respiratory distress syndrome in an ongoing phase 3 randomized controlled trial (ALXN1210-COV-305). To address the overactivation of terminal complement in severe COVID-19 compared to the diseases in which ravulizumab is currently approved, a modified dosing regimen was adopted. This analysis evaluates preliminary pharmacokinetic/pharmacodynamic data to confirm the modified dosing regimen. Methods Weight-based ravulizumab doses were administered on days 1, 5, 10, and 15. Serum levels of ravulizumab and free C5 were measured before and after administration of ravulizumab and any time on day 22. Free C5 levels 175 μg/mL, the concentration above which C5 is completely inhibited. Results Twenty-two patients were included in this evaluation. At baseline, mean C5 concentration was 240 ± 67 μg/mL. In all patients and at all individual timepoints after the first dose was administered, ravulizumab concentrations remained > 175 μg/mL and free C5 concentrations remained, Plain Language Summary While many people have no or mild COVID-19 symptoms, a small number of people become very sick and require hospitalization in intensive care units. One part of their immune system, known as complement, overreacts and attacks the lungs and other organs. Researchers are looking for a way to keep the immune system from attacking the body instead of protecting it. Ravulizumab is a medication currently used to do this in other diseases. Ravulizumab is being studied to see if it can reduce the destructive and deadly effects of the coronavirus infection. In this evaluation, ravulizumab effectively reduced complement in patients with severe COVID-19.