Therapeutic monitoring of cyclosporine following pediatric bone marrow transplantation: problems with sampling from silicone central venous lines.

Blood concentrations are commonly used to guide dosing requirements of cyclosporine, due to large variations in pharmacokinetics both between and within individuals. Bone marrow transplant patients at The Hospital for Sick Children are prescribed intravenous cyclosporine as part of the posttransplant immunosuppression protocol. Sampling for blood concentration measurement is generally done via a single-lumen central venous line (CVL). Cyclosporine concentrations sampled by this route were compared with concentrations in peripheral capillary samples taken concurrently. Results from the CVL blood were substantially higher despite appropriate flushing of the CVL between the end of the infusion and the time of sample collection. This discrepancy disappeared once the patient was converted to oral cyclosporine. We conclude that the sampling error is due to drug adsorbed to the silicone CVL catheters during intravenous administration and displaced during blood sample collection.