Dose selection of siltuximab for multicentric Castleman's disease.

PURPOSE: Siltuximab is a monoclonal antibody that binds to interleukin (IL)-6 with high affinity and specificity; C-reactive protein (CRP) is an acute-phase protein induced by IL-6. CRP suppression is an indirect measurement of IL-6 activity. Here, modeling and simulation of the pharmacokinetic (PK)/pharmacodynamic (PD) relationship between siltuximab and CRP were used to support dose selection for multicentric Castleman's disease (CD). METHODS: PK/PD modeling was applied to explore the relationship between siltuximab PK and CRP suppression following intravenous siltuximab infusion in 47 patients with B cell non-Hodgkin's lymphoma (n = 17), multiple myeloma (n = 13), or CD (n = 17). Siltuximab was administered as 2.8, 5.5, or 11 mg/kg q2wks, 11 mg/kg q3wks, or 5.5 mg/kg weekly. Simulations of studied or hypothetical siltuximab dosage regimens (15 mg/kg q4wks) were also performed to evaluate maintenance of CRP suppression below the cutoff value of 1 mg/L. RESULTS: A two-compartment PK model and an inhibitory indirect response PD model adequately described the serum siltuximab and CRP concentration-time profiles simultaneously. PD parameter estimates were physiologically plausible. For all disease types, simulations showed that 11 mg/kg q3wks or 15 mg/kg q4wks would reduce serum CRP to below 1 mg/L after the second dose and throughout the treatment period. CONCLUSIONS: PK/PD modeling was used to select doses for further development of siltuximab in multicentric CD. The dosing recommendation was also supported by the observed efficacy dose-response relationship. CRP suppression in the subsequent randomized multicentric CD study was in agreement with the modeling predictions.

Medication use and medical comorbidity in patients with chronic hepatitis C from a US commercial claims database: high utilization of drugs with interaction potential.

BACKGROUND: With the advent of the direct-acting antiviral agents, significant drug-drug interaction (DDI) potential now exists for patients treated for chronic hepatitis C virus (HCV) infection. However, little is known about how often patients with HCV infection use medications that may interact with newer HCV treatments, especially those with cytochrome P450 3A (CYP3A) DDI potential. METHODS: Using a large US commercial insurance database, medication use and comorbidity burden were examined among adult patients with a chronic HCV diagnosis from 2006 to 2010. Medications were examined in terms of total number of prescription claims, proportion of patients exposed, and DDI potential with the prototypical CYP3A direct-acting antiviral agents boceprevir and telaprevir, for which data were available. RESULTS: Patient comorbidity burden was high and increased over the study period. Medication use was investigated in 53 461 patients with chronic HCV. Twenty-one (53%) of the top 40 most utilized medications were classified as having interaction potential, with 62% of patients receiving at least one of the top 22 interacting medications by exposure. Of these, 59 and 41% were listed in a common DDI resource but not in medication-prescribing information, 77 and 77% had not been investigated in DDI studies, 41 and 36% did not have clear recommendations for DDI management, and only 14 and 23% carried a recommendation to avoid coadministration for boceprevir and telaprevir, respectively. CONCLUSION: Practitioners may expect a medication with CYP3A DDI potential in two-thirds of patients with HCV and may expect almost one-half of the most frequently used medications to have CYP3A DDI potential. However, DDI potential may not be reflected in prescribing information.