Moving Beyond Maximum Tolerated Dose for Targeted Oncology Drugs: Use of Clinical Utility Index to Optimize Venetoclax Dosage in Multiple Myeloma Patients

Exposure-response analyses of venetoclax in combination with bortezomib and dexamethasone in previously treated patients with multiple myeloma (MM) were performed on a phase Ib venetoclax dose-ranging study. Logistic regression models were utilized to determine relationships, identify subpopulations with different responses, and optimize the venetoclax dosage that balanced both efficacy and safety. Bortezomib refractory status and number of prior treatments were identified to impact the efficacy response to venetoclax treatment. Higher venetoclax exposures were estimated to increase the probability of achieving a very good partial response (VGPR) or better through venetoclax doses of 1,200 mg. However, the probability of neutropenia (grade ≥3) was estimated to increase at doses >800 mg. Using a clinical utility index, a venetoclax dosage of 800 mg daily was selected to optimally balance the VGPR or better rates and neutropenia rates in MM patients administered 1-3 prior lines of therapy and nonrefractory to bortezomib.

Pharmacokinetics and tolerability of paritaprevir, a direct acting antiviral agent for hepatitis C virus treatment, with and without ritonavir in healthy volunteers

AIMS

Paritaprevir is a direct acting antiviral agent for use as part of a multidrug hepatitis C virus infection treatment regimen. To characterize the pharmacokinetics, safety, and tolerability of paritaprevir and determine an optimal dosing regimen for subsequent evaluations, clinical studies were conducted with paritaprevir alone or with ritonavir, a cytochrome P450 3A4 inhibitor anticipated to increase paritaprevir exposure.

METHODS

Two phase 1, double-blind, placebo-controlled, parallel group studies were conducted in healthy volunteers (NCT00850044 and NCT00931281). Single dose study participants (n = 87) were randomized to one time administration of either paritaprevir or placebo, or paritaprevir with ritonavir or placebo. Participants (n = 38) enrolled in the multiple dose study received paritaprevir with ritonavir or placebo once or twice daily for 14 days. Pharmacokinetics, safety and tolerability were assessed throughout the study treatment periods.

RESULTS

After single or multiple dose administration, paritaprevir displayed non-linear pharmacokinetics, with maximum plasma concentration and area under the plasma concentration-time curve increasing in a greater than dose proportional manner. Concomitant administration of 100 mg ritonavir increased paritaprevir exposure from a 300 mg dose approximately 30- to 50-fold and extended paritaprevir half-life. The tolerability of paritaprevir was similar with or without ritonavir. Asymptomatic, transient increases in bilirubin were observed but were not associated with abnormalities in other liver function tests.

CONCLUSIONS

Paritaprevir exhibits non-linear pharmacokinetics with greater than dose proportional increases in exposure after single or multiple dosing. Co-administration with ritonavir increases paritaprevir exposure and half-life without adversely influencing tolerability.

Plasma and urine pharmacokinetics of niacin and its metabolites from an extended-release niacin formulation

OBJECTIVE

To characterize plasma and urine pharmacokinetics of niacin and its metabolites after oral administration of 2,000 mg of extended-release (ER) niacin in healthy male volunteers.

METHODS

Niacin ER was administered to 12 healthy male subjects following a low-fat snack. Plasma was collected for 12 h post dose and was analyzed for niacin, nicotinuric acid (NUA), nicotinamide (NAM) and nicotinamide-N-oxide (NNO). Urine was collected for 96 h post dose and analyzed for niacin and its metabolites, NUA, NAM, NNO, N-methylnicotinamide (MNA) and N-methyl-2-pyridone-5-carboxamide (2PY).

RESULTS

Mean niacin Cmax and AUC(0-t) values were 9.3 microg/ml and 26.2 microg x h/ml and were the highest of all analytes measured. Peak niacin and NUA levels occurred at 4.6 h (median) while tmax for NAM and NNO were 8.6 and 11.1 h, respectively. The mean plasma terminal half-life for niacin (0.9 h) and NUA (1.3 h) was shorter as compared to NAM (4.3 h). Urine recovery of niacin and metabolites accounted for 69.5% of the administered dose; only 3.2% was excreted as niacin. The highest recovery was for 2PY (37.9%), followed by MNA (16.0%) and NUA (11.6%). Mean half-lives for 2PY and MNA calculated in urine were 12.6 and 12.8 h, respectively.

CONCLUSIONS

Niacin was extensively metabolized following oral administration, and about 70% of the administered dose is recovered in urine in 96 h as niacin, NUA, MNA, NNO, NAM and 2PY. The plasma levels of the parent niacin were higher than its metabolites though only about 3% of the unchanged drug is recovered in urine.

Comparison of ceftibuten transport across Caco-2 cells and rat jejunum mounted on modified Ussing chambers

Ceftibuten uptake into Caco-2 cells and intestinal brush border membrane vesicles is mediated by the dipeptide transport system (PEPT1). The apical to basolateral transport characteristics of ceftibuten across Caco-2 cells and rat jejunum mounted on a modified Ussing chamber was examined. Mannitol was used as a paracellular marker along with trans-epithelial electrical resistance (TEER) for monitoring tight junction permeability. Transport across Caco-2 cells and rat jejunum mounted on a modified Ussing chamber was linear across the concentration range 0.25-10 mM. The net flux of mannitol and ceftibuten was higher across rat jejunum compared with Caco-2 cells. At a donor concentration of 0.25 mM, ceftibuten transport across Caco-2 cells was found to be pH dependent. Glycyl proline, a dipeptide, and 2,4- dinitrophenol, an energy poison, caused a reduction in the permeability of 0.25 mM ceftibuten across Caco-2 cells. Benzoic acid and adipic acid also inhibited transcellular transport of ceftibuten. At a donor concentration of 0.25 mM, passive paracellular transport accounts for about 60% and the active carrier mediated mechanism accounts for about 40% of ceftibuten transport across Caco-2 cells. None of the inhibitors however, had a significant effect on ceftibuten transport across rat jejunum mounted on a modified Ussing chamber at a donor concentration of 0.25 mM. In the concentration range 0.25-10 mM, ceftibuten is predominantly transported by paracellular mechanisms across rat jejunum and a mixture of active and passive transport across Caco-2 cells.