Background: Tuberculosis (TB) is the leading cause of death in human immunodeficiency virus (HIV)-infected people worldwide. Currently there are no studies examining the use of Rifabutin (RBN) and Dolutegravir (DTG) in co-infected persons. This is a case series of 4 co-infected patients receiving both agents who underwent Pharmacokinetic (PK) analysis. Methods and Results: This is a retrospective chart review study of four patients diagnosed with both HIV and TB, receiving RBN and DTG and undergoing therapeutic drug monitoring. All 4 cases had lower than expected DTG concentrations at least once, including those on the current recommended dose of DTG with RBN, and even those receiving higher doses. Conclusions: Given the frequency of low DTG and RBN concentrations, therapeutic drug monitoring (TDM) for these drugs is advisable. Prospective clinical studies are needed to further determine the PK interactions between RBN and DTG, and virologic response to treatment.