Binding of 3H-metronidazole in olfactory, respiratory and alimentary epithelia in rats

Clarifying busulfan metabolism and drug interactions to support new therapeutic drug monitoring strategies: a comprehensive review

INTRODUCTION

Busulfan (Bu) is an alkylating agent with a limited therapeutic margin and exhibits inter-patient variability in pharmacokinetics (PK). Despite decades of use, mechanisms of Bu PK-based drug-drug interactions (DDIs), as well as the negative downstream effects of these DDIs, have not been fully characterized. Areas covered: This article provides an overview of Bu PK, with a primary focus on how known and potentially unknown drug metabolism pathways influence Bu-associated DDIs. In addition, pharmacogenomics of Bu chemotherapy and Bu-related DDIs observed in the stem cell transplant clinic (SCT) are summarized. Finally the increasing importance of Bu therapeutic drug monitoring is highlighted. Expert opinion: Mechanistic studies of Bu metabolism have shown that in addition to GST isoenzymes, other oxidative enzymes (CYP, FMO) and ABC/MDR drug transporters likely contribute to the overall clearance of Bu. Despite many insights, results from clinical studies, especially in polypharmacy settings and between pediatric and adult patients, remain conflicting. Further basic science and clinical investigative efforts are required to fully understand the key factors determining Bu PK characteristics and its effects on complications after SCT. Improved TDM strategies are promising components to further investigate, for instance DDI mechanisms and patient outcomes, in the highly complex SCT treatment setting.

The effect of metronidazole on busulfan pharmacokinetics in patients undergoing hematopoietic stem cell transplantation

Busulfan (Bu) is an important component of some myeloablative regimens prior to stem cell transplantation (SCT). Over the last few years it has been shown that other drugs administered concomitantly can influence Bu pharmacokinetics. In the present study, we compared Bu concentrations (trough levels) in three groups of patients. Group A (n=5) received metronidazole as graft-versus-host disease prophylaxis during Bu treatment. Group B (n=9) received Bu only for 2 days followed by 2 days of Bu and metronidazole. Group C (n=10) was a control group that received Bu without metronidazole. The mean Bu levels for Group A receiving metronidazole during conditioning was significantly (P<0.001) higher (948+/-280 ng/ml), compared to those observed in the control group (507+/-75 ng/ml). In Group B, the administration of metronidazole resulted in a significant (P<0.001) increase in Bu levels (807+/-90 ng/ml) during the last 2 days, compared to 452+/-68 ng/ml during the first 2 days. In Group A, one patient died with multiorgan failure, three experienced veno-occlusive disease (VOD) and one developed hemorrhagic cystitis. Elevated liver transaminases (AST, ALT) and bilirubin were detected in all Group A patients. In Group B, six patients had elevated liver function tests but no VOD was observed. We conclude that metronidazole should not be administered simultaneously with Bu to avoid the high plasma levels of Bu, which may lead to severe toxicity and/or treatment related mortality.