INTERACTION BETWEEN QUINUPRISTIN DALFOPRISTIN AND CYCLOSPORINE/

OBJECTIVE: To describe a case of a drug interaction between cyclospori ne and quinupristin/dalfopristin (QND). CASE SUMMARY: A patient who ha d 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 10 5 ng/mL. Two and 3 days after initiation of QND therapy, trough cyclos porine concentrations increased to 261 and 291 ng/mL, respectively. Fo llowing discontinuation of QND, the cyclosporine blood concentration d ecreased and the dosage was subsequently increased to the previous reg imen. 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 t he change in cyclosporine blood concentrations, probably due to inhibi tion of cyclosporine metabolism. This represents the first published c ase of an interaction between cyclosporine and QND. CONCLUSIONS: Frequ ent monitoring of cyclosporine concentrations with attention to the ne ed for dosage modification is recommended when initiating or discontin uing QND therapy.