The Impact of Infection and Inflammation on Drug Metabolism, Active Transport, and Systemic Drug Concentrations in Veterinary Species.

Within human medicine, it is recognized that the pharmacokinetics (PK) of many compounds can be altered by the presence of inflammation or infection. Research into the reason for these changes has identified pathways that can influence drug absorption, clearance, and tissue distribution. In contrast, far less is known about these relationships within the framework of veterinary medicine. Rather, most of the PK data generated in veterinary species employs healthy subjects, raising the question of whether these studies are founded on an assumption that healthy animal PK reflect that of the diseased animal population. Accordingly, there is a need to explore the PK changes that might be overlooked in studies that recruit only healthy animals to assesses drug PK. To meet this objective, we surveyed the published literature for studies focusing on the impact of disease on the dose-exposure relationships in food-producing and companion animal species. We found that, consistent with humans and laboratory species, both up- and downregulation of the various cytochrome isoenzymes and/or transporters have occurred in response to an increase in inflammatory mediators. These findings suggest that, as observed in human medicine, the potential for differences in the drug PK in healthy versus animal patients points to a need for acquiring a greater understanding of these changes and how they may influence the dose-exposure-response relationships of veterinary pharmaceuticals. SIGNIFICANCE STATEMENT: This review delivers a much-needed summary of published information that provides insights into how disease and inflammation can influence the appropriateness of extrapolating laboratory-based dose-exposure-response relationships to what will occur in the actual veterinary patient. As part of this review, we also examine some of the method-associated issues to be considered when assessing the reported nature and magnitude of these changes.

CYP-mediated therapeutic protein-drug interactions: clinical findings, proposed mechanisms and regulatory implications.

Therapeutic proteins (TPs) may affect the disposition of drugs that are metabolized by cytochrome P450 (CYP) enzymes, as is evident from a review of data in recently published literature and approved Biologic License Applications. Many TPs belonging to the cytokine class appear to differentially affect CYP activities. Cytokine modulators may affect CYP enzyme activities by altering cytokine effects on CYP enzymes. The alteration in CYP enzyme activities seems to result from changes in transcription factor activity for CYP enzyme expression or changes in CYP enzyme stability, which have been observed during altered immunological states such as infection and inflammation. Human growth hormone also appears to differentially affect CYP activities through unknown mechanisms. Because TP-drug interaction research is an evolving area, limited information is available during drug development on TP-drug interactions mediated by CYP inhibition or induction. The authors of this review suggest that effort be made to understand TP-drug interactions for the safe and effective use of TPs in combination with small-molecule drugs.

Sprycel for chronic myeloid leukemia and Philadelphia chromosome-positive acute lymphoblastic leukemia resistant to or intolerant of imatinib mesylate.

PURPOSE: On June 28, 2006, the U.S. Food and Drug Administration approved dasatinib (Sprycel; Bristol-Myers Squibb), a new small-molecule inhibitor of multiple tyrosine kinases, for the treatment of adults with chronic phase, accelerated phase, or myeloid or lymphoid blast phase chronic myeloid leukemia (CML) or Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL) with resistance or intolerance to prior therapy including imatinib. This summary reviews the database supporting this approval. EXPERIMENTAL DESIGN: Four single-arm multicenter studies supported the efficacy and safety of dasatinib. The primary efficacy end point in chronic phase CML was major cytogenetic response. The primary end point in accelerated phase, myeloid phase, and lymphoid blast phase CML, and Ph(+) ALL was major hematologic response. RESULTS: The four studies combined enrolled 445 patients. In patients with chronic phase CML, the major cytogenetic response rate was 45% with a complete cytogenetic response rate of 33%. Major hematologic response rates in patients with accelerated phase CML, myeloid CML, lymphoid blast CML, and Ph(+) ALL were 59%, 32%, 31%, and 42%, respectively. Median response durations in chronic phase, accelerated phase, and myeloid phase CML had not been reached. The median durations of major hematologic response were 3.7 months in lymphoid blast CML and 4.8 months in Ph(+) ALL. Common toxicities with dasatinib included myelosuppression, bleeding, and fluid retention. CONCLUSIONS: This report describes the Food and Drug Administration review supporting the approval of dasatinib for CML and Ph(+) ALL based on the rates and durability of cytogenetic and hematologic responses.

Approval summary: nelarabine for the treatment of T-cell lymphoblastic leukemia/lymphoma.

PURPOSE: To describe the clinical studies, chemistry manufacturing and controls, and clinical pharmacology and toxicology that led to Food and Drug Administration approval of nelarabine (Arranon) for the treatment of T-cell acute lymphoblastic leukemia/lymphoblastic lymphoma. EXPERIMENTAL DESIGN: Two phase 2 trials, one conducted in pediatric patients and the other in adult patients, were reviewed. The i.v. dose and schedule of nelarabine in the pediatric and adult studies was 650 mg/m2/d daily for 5 days and 1,500 mg/m2 on days 1, 3, and 5, respectively. Treatments were repeated every 21 days. Study end points were the rates of complete response (CR) and CR with incomplete hematologic or bone marrow recovery (CR*). RESULTS: The pediatric efficacy population consisted of 39 patients who had relapsed or had been refractory to two or more induction regimens. CR to nelarabine treatment was observed in 5 (13%) patients and CR+CR* was observed in 9 (23%) patients. The adult efficacy population consisted of 28 patients. CR to nelarabine treatment was observed in 5 (18%) patients and CR+CR* was observed in 6 (21%) patients. Neurologic toxicity was dose limiting for both pediatric and adult patients. Other severe toxicities included laboratory abnormalities in pediatric patients and gastrointestinal and pulmonary toxicities in adults. CONCLUSIONS: On October 28, 2005, the Food and Drug Administration granted accelerated approval for nelarabine for treatment of patients with relapsed or refractory T-cell acute lymphoblastic leukemia/lymphoblastic lymphoma after at least two prior regimens. This use is based on the induction of CRs. The applicant will conduct postmarketing clinical trials to show clinical benefit (e.g., survival prolongation).

Modeling and simulation of adherence: approaches and applications in therapeutics.

Partial adherence with a prescribed or randomly assigned dose gives rise to unintended variability in actual drug exposure in clinical practice and during clinical trials. There are tremendous costs associated with incomplete and/or improper drug intake-to both individual patients and society as a whole. Methodology for quantifying the relation between adherence, exposure and drug response is an area of active research. Modeling and statistical approaches have been useful in evaluating the impact of adherence on therapeutics and in addressing the challenges of confounding and measurement error which arise in this context. This paper reviews quantitative approaches to using adherence information in improving therapeutics. It draws heavily on applications in the area of HIV pharmacology.

A pharmacokinetic-pharmacodynamic model for the quantitative prediction of dofetilide clinical QT prolongation from human ether-a-go-go-related gene current inhibition data.

BACKGROUND: QT prolongation is an important biomarker of the arrhythmia torsades de pointes and appears to be related mainly to blockade of delayed inward cardiac rectifier potassium currents. The aim of this study was to quantify the relationship between in vitro human ether-a-go-go-related gene (hERG) potassium channel blockade and the magnitude of QT prolongation in humans for the class III antiarrhythmic dofetilide. METHODS: The in vitro affinity and activity of dofetilide were determined in recombinant cell cultures expressing the hERG channel, and the QT-prolonging effect of dofetilide was assessed in 5 clinical studies (80 healthy volunteers and 17 patients with ischemic heart disease). A population pharmacokinetic-pharmacodynamic analysis of the in vitro and in vivo data was performed in NONMEM by use of the operational model of pharmacologic agonism to estimate the efficiency of transduction from ion channel binding to Fridericia-corrected QT response. RESULTS: A 3-compartment pharmacokinetic model with first-order absorption characterized the time course of dofetilide concentrations. On the basis of an in vitro potency of 5.13 ng/mL for potassium current inhibition and predicted unbound dofetilide concentrations, the estimated transducer ratio (tau) of 6.2 suggests that the QT response plateaus before currents are fully blocked. In our study population, 10% hERG blockade corresponds to a QT prolongation of 20 ms (95% confidence interval, 12-32 ms). With long-term dofetilide administration, tolerance develops with a half-life of 4.7 days. CONCLUSIONS: The current mechanism-based pharmacokinetic-pharmacodynamic model quantified the relationship between in vitro hERG channel blockade and clinical QT prolongation for dofetilide. This model may prove valuable for assessing the risk of QT prolongation in humans for other drugs that selectively block the hERG channel on the basis of in vitro assays and pharmacokinetic properties.

Estimating treatment effect in the presence of non-compliance measured with error: precision and robustness of data analysis methods.

Non-compliance with the nominal prescribed dosage causes unintended variability in actual drug exposure during clinical trials. In the ideal case that compliance is not a confounder, and it is known--hence actual dosage is known--true dose-response can be validly estimated. Measuring compliance presents a challenge, however. A simulation study of the case that dosage history questionnaires (C(Q)--usually over-optimistic estimates of actual compliance) are available in all subjects enrolled in a clinical trial, but accurate compliance measurements (C--e.g. from electronic medication event monitors), are only available in a (random) fraction of subjects is reported. It reveals that a 'Maximum Penalized Marginal Likelihood' (MPML) method which uses all compliance data, effectively calibrating C(Q) to C, is superior to other methods which use only one compliance measure, or both, or neither (neither = ITT, intention to treat, which assumes actual dosage equals nominal dosage), but do not calibrate. MPML yields the most precise estimates of dose-response over widely varying clinical trial designs, extremes in quality and quantity of compliance information, and a range of drug effect sizes. It is most beneficial when compliance data are sparse and maintains good performance even when its key assumptions are somewhat violated.