Interaction between quinupristin/dalfopristin and cyclosporine

OBJECTIVE: To describe a case of a drug interaction between cyclosporine and quinupristin/dalfopristin (QND). CASE SUMMARY: A patient who had undergone a kidney transplant and was receiving chronic cyclosporine therapy was treated with the investigational streptogramin antibiotic QND. Baseline trough cyclosporine concentrations ranged from 80 to 105 ng/mL. Two and 3 days after initiation of QND therapy, trough cyclosporine concentrations increased to 261 and 291 ng/mL, respectively. Following discontinuation of QND, the cyclosporine blood concentration decreased and the dosage was subsequently increased to the previous regimen. DISCUSSION: A patient's cyclosporine blood concentration tripled 3 days after initiating therapy with QND,A one-third reduction in the cyclosporine dosage was required. QND was the most likely cause for the change in cyclosporine blood concentrations, probably due to inhibition of cyclosporine metabolism. This represents the first published case of an interaction between cyclosporine and QND. CONCLUSIONS: Frequent monitoring of cyclosporine concentrations with attention to the need for dosage modification is recommended when initiating or discontinuing QND therapy.