Melissa O'Gorman

Lack of Pharmacokinetic and Pharmacodynamic Interactions Between a Smoking Cessation Therapy, Varenicline, and Warfarin: An In Vivo and In Vitro Study1

This study investigated the effect of varenicline on the pharmacokinetics and pharmacodynamics of a single dose of warfarin in 24 adult smokers and compared these findings with data generated using human in vitro systems. Subjects were randomized to receive varenicline 1 mg twice a day or placebo for 13 days and then switched to the alternative treatment after a 1‐week washout period. A single dose of warfarin 25 mg was given on day 8 of each treatment period, and serial blood samples were collected over 144 hours postdose. Pharmacokinetic parameters for both (R)‐ and (S)‐warfarin and international normalized ratio (INR) values were determined. Varenicline was assessed as an inhibitor and inducer of human cytochrome P450 activities using liver microsomes and hepatocytes, respectively. Consistent with the in vitro data, no alteration in human pharmacokinetics of warfarin enantiomers was observed with varenicline treatment. The 90% confidence intervals for the ratios of area under the concentration–time curve from zero hours to infinity and peak plasma concentrations were completely contained within 80% to 125%. Warfarin pharmacodynamic parameters, maximum INR, and the area under the prothrombin (INR)–time curve, were also unaffected by steady‐state varenicline. Concomitant administration of varenicline and warfarin was well tolerated. Consequently, warfarin can be safely administered with varenicline without the need for dose adjustment.

The Effect of Renal Impairment on the Pharmacokinetics and Pharmacodynamics of Ertugliflozin in Subjects With Type 2 Diabetes Mellitus.

Ertugliflozin is a highly selective and potent inhibitor of the sodium‐glucose cotransporter 2 in development for the treatment of type 2 diabetes mellitus. The glycemic efficacy of sodium‐glucose cotransporter 2 inhibitors such as ertugliflozin depends on glucose filtration through the kidney. This phase 1, open‐label study evaluated the effect of renal impairment on the pharmacokinetics, pharmacodynamics, and tolerability of ertugliflozin (15 mg) in type 2 diabetes mellitus and healthy subjects with normal renal function (estimated glomerular filtration rate not normalized for body surface area ≥90 mL/min) and type 2 diabetes mellitus subjects with mild (60‐89 mL/min), moderate (30‐59 mL/min), or severe (<30 mL/min) renal impairment (n = 36). Blood and urine samples were collected predose and over 96 hours postdose for pharmacokinetic evaluation and measurement of urinary glucose excretion over 24 hours. Log‐linear regression analyses indicated predicted mean area under the concentration‐time curve values for mild, moderate, and severe renal function groups that were ≤70% higher relative to subjects with normal renal function. Generally consistent results were obtained with categorical analysis based on analysis of variance. The increase in ertugliflozin exposure in subjects with renal impairment is not expected to be clinically meaningful. Regression analysis of change from baseline in urinary glucose excretion over 24 hours vs estimated glomerular filtration rate showed a decrease in urinary glucose excretion with declining renal function. A single 15‐mg dose of ertugliflozin was well tolerated in all groups.

Pharmacokinetics, Safety, and Tolerability Following Multiple Oral Doses of Varenicline Under Various Titration Schedules in Elderly Nonsmokers

This study was designed to investigate the multiple‐dose pharmacokinetics, safety, and tolerability of the selective α4β2 nicotinic acetylcholine partial agonist, varenicline, in elderly (65–85 years old) nonsmokers. Fifty male and female subjects with normal renal function for their age were randomized to receive varenicline or placebo once or twice daily for 3 weeks in an investigator‐ and subject‐blinded parallel‐group design. Treatment regimens included weekly titration (n = 14; days 1–7, 0.5 mg once daily; days 8–14, 0.5 mg twice daily; days 15–21, 1 mg twice daily); 2‐week twice‐daily titration (n = 13; days 1–14, 0.5 mg once daily; days 15–21, 0.5 mg twice daily); 2‐week once‐daily titration (n = 13; days 1–14, 0.5 mg once daily; days 15–21, 1 mg once daily); and placebo (n = 10). Approximate dose‐proportional increases in systemic exposure of varenicline at steady state, based on maximum concentration and area under the plasma concentration‐time curve over the 24‐hour period at steady state, were observed across the dose range of 0.5 to 2 mg/d. Median time to maximum concentration was 3 hours. Mean elimination half‐life was estimated to be approximately 24 to 32 hours and independent of dose. Varenicline was considered to be safe and well tolerated in this elderly nonsmoking population.

A Randomized, Open‐Label, 3‐Way Crossover Study to Demonstrate Bioequivalence of Sildenafil Powder for Oral Suspension With Tablets Used Commercially and in Clinical Studies for the Treatment of Pulmonary Arterial Hypertension

Sildenafil citrate (Revatio) is approved for pediatric pulmonary arterial hypertension (PAH) in the European Union. A new pediatric formulation, 10 mg/mL sildenafil citrate powder for oral suspension (POS), was developed for pediatric PAH patients. Bioequivalence among the POS suspension (20 mg), the Revatio 20‐mg commercial tablet, and the sildenafil citrate 2 × 10‐mg clinical trial tablets was assessed. In this randomized, open‐label study, 42 healthy adult volunteers received the 3 different sildenafil treatments, each in a single 20‐mg oral dose, using a 3‐way crossover design. Blood samples were collected at predefined times and analyzed for sildenafil plasma concentrations. Natural log‐transformed sildenafil pharmacokinetic parameters (Cmax, AUClast, and AUC∞) were evaluated for bioequivalence using a mixed‐effects model. Results were used to estimate relative bioavailability and construct 90% confidence intervals (CIs). Bioequivalence was concluded if the 90% CIs for Cmax, AUClast, and AUC∞ were wholly contained within 80% to 125%. All 90% CIs for the ratios of adjusted geometric means of Cmax, AUClast, and AUC∞ were within 80% to 125%, the prespecified bioequivalence criteria. All 3 formulations were well tolerated. In conclusion, the POS suspension, the commercial 20‐mg Revatio tablet, and the 10‐mg sildenafil tablets were all bioequivalent to one another when given at the equal doses.

Palbociclib plus letrozole as first-line treatment for ER-positive and HER2-negative advanced breast cancer in Chinese women: a phase 1 study

Abstract Background Palbociclib, a cyclin-dependent kinase 4 and 6 inhibitor, is approved in many countries for the treatment of ER-positive and HER2-negative advanced breast cancer in combination with endocrine therapy. We aimed to evaluate the pharmacokinetics, safety, and efficacy of palbociclib combined with letrozole as first-line treatment for ER-positive and HER2-negative advanced breast cancer. Methods This is a phase 1, open-label, single-arm study in Chinese women with ER-positive and HER2-negative advanced breast cancer. From cycle 1 day 1, patients received letrozole 2·5 mg orally once daily continuously plus palbociclib 125 mg orally once daily for 3 weeks followed by 1 week off treatment. Blood samples for pharmacokinetic evaluation of palbociclib were collected up to 120 h after a single dose of palbociclib in a lead-in phase and after palbociclib dose on cycle 1 day 21 for multiple dose pharmacokinetic evaluation. Predose blood samples for pharmacokinetic evaluation of palbociclib and letrozole were collected on days 19–21 of cycle 1 and cycle 2 day 1 (letrozole only). Disease assessments were done every 12 weeks from cycle 1 day 1. Safety was assessed per Common Terminology Criteria for Adverse Events, version 4.0. This study is registered with ClinicalTrials, number NCT02499146, and is ongoing but not recruiting. Findings As of March 16, 2016, the cutoff date, the study completed enrolment with 26 patients. All patients completed single dose pharmacokinetic evaluation and 13 completed multiple dose pharmacokinetic evaluation. After multiple doses, the steady-state palbociclib geometric mean area under the concentration–time curve from 0 to 24 h was 2005 ng × h/mL and maximum observed concentration was 112·3 ng/mL, similar to those obtained in Caucasian patients following the same dosing regimen. Comparisons of single dose and multiple dose pharmacokinetic data indicated linear pharmacokinetics of palbociclib. The geometric mean accumulation ratio of palbociclib exposure after multiple dose compared with single dose was 2·1, consistent with a terminal half-life of 23·4–27·5 h. Trough concentrations of letrozole were similar to concentrations obtained in Caucasian patients. No deaths or permanent discontinuations due to adverse events were reported. One serious adverse event occurred but was not considered to be treatment-related. The most common clustered adverse events were neutropaenia (n=20, 77%), leukopaenia (n=19, 73%), and anemia (n=11, 42%), with neutropaenia (n=15, 58%) and leukopaenia (n=8, 31%) the most common grade 3–4 adverse events. Interpretation No dose adjustment for palbociclib is needed based on the Chinese population. The toxicity of palbociclib in combination with letrozole treatment was tolerable and manageable. Funding Pfizer Inc.

Impact of Acid-Reducing Agents on the Pharmacokinetics of Palbociclib, a Weak Base With pH-Dependent Solubility, With Different Food Intake Conditions

Palbociclib free base capsule is a weak base drug with highly pH‐dependent solubility. In vitro and in vivo studies evaluated the impact of acid‐reducing agents on exposure of palbociclib and determined whether the impact, if any, can be mitigated by food. A drug‐drug interaction study (study 1) was conducted first under fasted conditions and showed that coadministration of multiple doses of the proton‐pump inhibitor rabeprazole substantially reduced palbociclib mean area under the concentration‐time curve from time 0 to infinity and maximum observed plasma concentration by 62% and 80%, respectively. In vitro assessment suggested that the presence of bile salt mixed micelles to mimic the fed state can significantly enhance the solubility of palbociclib. Subsequently, study 2 was conducted under fed conditions and demonstrated that coadministration of rabeprazole decreased palbociclib maximum observed plasma concentration by 41% but had limited impact on area under the concentration‐time curve from 0 to infinity (13% decrease). This study also showed that the histamine‐2 receptor antagonist famotidine and local antacid with staggered dosing had no impact on palbociclib exposure under fed conditions. Food intake effectively mitigated the impact of acid‐reducing agents on palbociclib exposure. Palbociclib free base capsule should be taken with food, and acid‐reducing agent use does not need to be avoided.

Abstract LB-229: A phase 1 open-label fixed-sequence two-period crossover study of the effect of multiple doses of tamoxifen on palbociclib (PD-0332991) pharmacokinetics in healthy male volunteers

Introduction: Tamoxifen and one of its primary active metabolites, 4‑hydroxy‑tamoxifen, are known to induce CYP3A4 in vitro, and in vivo coadministration of tamoxifen with letrozole and anastrozole (both CYP3A4 substrates) has resulted in decreased exposures (AUC) of each by 37% and 27%, respectively. The primary route of oxidative metabolism of palbociclib (PD‑0332991) is through CYP3A4, thus coadministration of tamoxifen and palbociclib could result in decreased exposure of palbociclib. The primary objective of this study is to estimate the relative exposure of single 125 mg palbociclib oral doses alone and in the presence of steady‑state concentrations of tamoxifen and its active metabolites (4‑hydroxy‑tamoxifen, N‑desmethyl‑tamoxifen, and endoxifen (N‑desmethyl‑4-hydroxytamoxifen)) in healthy male subjects in order to inform appropriate palbociclib dosing when administered in combination with tamoxifen in the upcoming Phase 3 PENELOPEB study. Methods: This was an open label, 2‑period fixed‑sequence study of the effect of multiple oral doses of tamoxifen on palbociclib pharmacokinetics in 25 healthy male volunteers. Each subject received a single 125 mg oral dose of palbociclib alone, followed by a single 125 mg dose of palbociclib on Day 22 of a 27-day tamoxifen loading dose regimen (60mg QD for 4 days, followed by 20mg QD for 23 days). Serial blood sampling for palbociclib pharmacokinetics was performed up to 144 hours post-palbociclib dose in both periods. Tamoxifen pre-dose blood sampling was performed on specified visits to document achievement of steady-state tamoxifen and metabolite concentrations. Plasma concentrations of palbociclib, tamoxifen, 4‑hydroxy‑tamoxifen, N‑desmethyl‑tamoxifen, and endoxifen were each measured using validated LC/MS/MS (liquid chromatography coupled with mass spectrometry) methods. Palbociclib plasma pharmacokinetic (PK) parameters were estimated using standard non-compartmental methods. Discussion: There were no significant changes in the palbociclib plasma PK parameters AUCinf (area under the curve from time zero to infinity) and Cmax (maximal plasma concentration) in the presence of steady-state tamoxifen when compared to palbociclib alone. Tamoxifen, 4‑hydroxy‑tamoxifen, N‑desmethyl‑tamoxifen, and endoxifen all achieved steady-state prior to administration of palbociclib in period 2. In general, palbociclib and the combination of palbociclib and tamoxifen were well tolerated with no reported serious adverse events; 1 subject discontinued due to generalized itchiness which resolved with a single dose of fexofenadine. Citation Format: Justin T. Hoffman, Melissa O9Gorman, Cho-Ming Loi, Anna Plotka, Tanya Boutros, Leonid Kirkovsky, Corrado Gallo Stampino, Diane Wang. A phase 1 open-label fixed-sequence two-period crossover study of the effect of multiple doses of tamoxifen on palbociclib (PD-0332991) pharmacokinetics in healthy male volunteers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-229. doi:10.1158/1538-7445.AM2014-LB-229

Abstract 4515: A phase 1 randomized, open-label, fixed-sequence, 2-period study of the effect of multiple doses of rifampin on palbociclib (PD-0332991) pharmacokinetics in healthy volunteers

Background Rifampin is a strong inducer of multiple Phase 1 and Phase 2 metabolic enzymes including cytochrome (CYP) P450 3A4 and sulfotransferases (SULT). In vitro, the metabolism of palbociclib occurs primarily through CYP3A4 and SULT2A1; thus, coadministration of rifampin and palbociclib could result in decreased exposure of palbociclib. Methods This open-label, 2-period, fixed-sequence study assessed the effect of multiple oral doses of rifampin on single-dose palbociclib pharmacokinetics (PK) in 15 healthy volunteers (ClinicalTrials.gov; NCT01953731). Each subject received the following treatments: Period 1, oral palbociclib 125 mg on day 1; Period 2, oral rifampin 600 mg for 12 days and oral palbociclib 125 mg on day 8 (washout of ≥12 days between the 2 palbociclib doses). Serial blood sampling for palbociclib PK was performed predose and up to 120 hours post-palbociclib dose in both periods. Plasma concentrations of palbociclib were measured using validated high-performance liquid chromatography tandem mass spectrometry methods. Palbociclib plasma PK parameters were estimated using standard non-compartmental methods. Results Median time to maximum plasma concentration (Tmax) and mean half-life (t1/2) were shorter with palbociclib plus rifampin relative to palbociclib alone. Adjusted geometric mean palbociclib AUCinf (area under the curve from time zero to infinity) and Cmax (maximal plasma concentration) following treatment with rifampin (242.5 ng•h/mL and 15.52 ng/mL, respectively) were considerably lower relative to palbociclib administered alone (1568 ng•h/mL and 51.42 ng/mL). Generally, study treatments were well tolerated with no reported serious adverse events; 1 subject discontinued due to liver function test abnormalities after receiving rifampin alone for 7 days in Period 2. Conclusions Treatment with multiple doses of rifampin with palbociclib decreased total (AUCinf) and peak (Cmax) palbociclib exposure by approximately 85% and 70%, respectively, versus palbociclib alone. Palbociclib was well tolerated when administered alone or in combination with rifampin. Based on these results, concurrent administration of palbociclib with strong CYP3A inducers should be avoided. Citation Format: Justin T. Hoffman, Anna Plotka, Melissa O9Gorman, Andrew Chang, Maha Kosa, Cho-Ming Loi, Corrado Gallo-Stampino, Diane D. Wang. A phase 1 randomized, open-label, fixed-sequence, 2-period study of the effect of multiple doses of rifampin on palbociclib (PD-0332991) pharmacokinetics in healthy volunteers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4515. doi:10.1158/1538-7445.AM2015-4515

Abstract CT419: A phase 1 randomized, open-label, 2-sequence, 2-period crossover study of the effect of multiple doses of palbociclib (PD-0332991) on midazolam pharmacokinetics in healthy women of non-childbearing potential

Introduction: Palbociclib (PD‑0332991) is an oral cyclin‑dependent kinase (CDK) 4/6 inhibitor currently in Phase 2 and Phase 3 clinical trials in multiple oncology indications. In vitro, palbociclib and its active lactam metabolite (PF‑05089326) caused time‑dependent inhibition of CYP3A-mediated midazolam 1’‑hydroxylase and testosterone 6β‑hydroxylase activities. The primary objective of this study is to investigate the effect of multiple doses of palbociclib on the pharmacokinetics of a single oral dose of the sensitive CYP3A4/5 probe substrate midazolam in healthy women of non-childbearing potential. Methods: This was an open label, randomized, 2‑period 2‑sequence study of the effect of multiple oral doses of palbociclib on midazolam pharmacokinetics in 26 healthy female volunteers of non-childbearing potential. Simulations were performed with SimCYP, using the in vitro CYP inhibition data and human pharmacokinetic data for palbociclib from Study A5481001 as inputs, to optimize the duration of dosing and washout periods. Each subject received two treatments (Treatment A = 2 mg oral dose of midazolam alone, Treatment B = 2 mg oral dose of midazolam on Day 7 of an 8-day 125 mg QD palbociclib dose regimen) in a crossover scheme. Subjects were randomized to one of two sequences (Sequence 1 = A→B, Sequence 2 = B→A). In Sequence 2 there was a washout period of no less than 14 days after the last administered dose of palbociclib to ensure that there was no carryover effect of CYP3A inhibition into Period 2. Serial blood sampling for midazolam pharmacokinetics was performed up to 36 hours post-midazolam dose in both periods. Palbociclib pre-dose blood sampling was performed on specified visits to document achievement of steady-state concentrations. Plasma concentrations of midazolam and palbociclib were each measured using validated LC/MS/MS (liquid chromatography- tandem mass spectrometry) methods. Midazolam plasma pharmacokinetic (PK) parameters were estimated using standard non-compartmental methods. Discussion:In general, palbociclib reached steady-state levels prior to co-administration of midazolam, allowing for a worst case assessment of the potential palbociclib-mediated time-dependent CYP3A inhibition. Midazolam geometric mean Cmax and AUCinf values increased 37% and 61%, respectively, when midazolam was co-administered with multiple doses of palbociclib as compared to its administration alone. These results indicate that palbociclib is a weak CYP3A inhibitor following daily 125 mg dosing at steady-state according to the FDA classification. In general, the combination of palbociclib and midazolam were well tolerated with no reported serious adverse events or treatment discontinuations. Reversible neutropenia was reported in 15 out of the 26 subjects. Citation Format: Justin T. Hoffman, Anna Plotka, Melissa O9Gorman, Cho-Ming Loi, Leonid Kirkovsky, Corrado Gallo-Stampino, Diane Wang. A phase 1 randomized, open-label, 2-sequence, 2-period crossover study of the effect of multiple doses of palbociclib (PD-0332991) on midazolam pharmacokinetics in healthy women of non-childbearing potential. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr CT419. doi:10.1158/1538-7445.AM2014-CT419