Morbidity is increased in patients undergoing hematopoietic stem cell transplantation when drug-drug interactions lead to unexpected outcomes. These interactions occur as a result of exposure to complicated medical regimens with drugs with narrow therapeutic windows and high toxicity profiles. In this report, we review the available evidence and possible mechanisms of the most clinically relevant drug interactions, including those involving inhibitors and inducers of the P450 isoenzyme system. We identify key interactions that should be familiar to any physician caring for patients after hematopoietic stem cell transplantation. We discuss drug metabolism in children and in the elderly and examine how age-related differences in metabolism make complicate drug regimens in these populations. A better understanding of these interactions and the responsible mechanisms will promote efficient delivery of the safest medical regimens to patients undergoing hematopoietic stem cell transplantation.
Summary. The success in achieving therapeutic international normalized ratio (INR) targets in the control of warfarin using a whole-blood point-of-care testing (POCT) monitor (CoaguChek) in a community clinic was compared with hospital laboratory coagulometer prothrombin time (PT) testing in a randomized crossover study. Forty-six patients were randomized into two groups. At each visit, capillary blood was taken for the POCT monitor and venous blood for the laboratory coagulometer. In Group 1, for 6 months, dosage was based on the CoaguChek and for the second 6 months on the coagulometer. In the second group, the order was reversed. Dosages were determined using the dawn ac computer programme. Success was assessed by the percentage of time patients were maintained within the INR targets. Agreement between laboratory and monitor INR, and patient satisfaction were also assessed. Results with the POCT monitor compared well with the hospital coagulometer. Time in INR target range between the groups was similar, with 60AE9% on the POCT monitor and 59AE3% with the laboratory coagulometer in Group 1 and in Group 2, respectively, 64AE3% and 63AE4% with no significant difference in mean INR. An INR above 4AE0 gave some discrepant results. International Sensitivity Index calibrations of the two test systems indicated that the INRs were dependable. Patient questionnaires showed greater satisfaction with community POCT monitoring.
Sirolimus is increasingly used in transplantation for prevention and treatment of graft-versus-host disease and organ rejection. Voriconazole is contraindicated when used concomitantly with sirolimus because of a substantial increase in sirolimus drug exposure with unadjusted dosing, but voriconazole is also considered the best initial treatment of invasive aspergillosis and other fungal infections. Patients who received voriconazole and sirolimus concomitantly were identified by a review of the medical records of all allogeneic hematopoietic stem cell recipients at our institution from September 1, 2002, to June 1, 2005. Data including baseline characteristics, indications for both drugs, and potential adverse effects were evaluated. Eleven patients received voriconazole and sirolimus concomitantly for a median of 33 days (range, 3-100 days). In 8 patients whose sirolimus dose was initially reduced by 90%, trough sirolimus levels were similar to those obtained before the administration of voriconazole; no obvious significant toxicity from either drug was observed during coadministration. Serious adverse events were observed in 2 patients in whom sirolimus dosing was not adjusted during voriconazole administration. Sirolimus and voriconazole may be safely coadministered if there is an empiric initial 90% sirolimus dose reduction combined with systematic monitoring of trough levels.
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