Pharmacokinetics and safety of cavosonstat (N91115) in healthy and cystic fibrosis adults homozygous for F508DEL-CFTR.

BACKGROUND: Cavosonstat (N91115), an orally bioavailable inhibitor of S-nitrosoglutathione reductase, promotes cystic fibrosis transmembrane conductance regulator (CFTR) maturation and plasma membrane stability, with a mechanism of action complementary to CFTR correctors and potentiators. METHODS: A Phase I program evaluated pharmacokinetics, drug-drug interactions and safety of cavosonstat in healthy and cystic fibrosis (CF) subjects homozygous for F508del-CFTR. Exploratory outcomes included changes in sweat chloride in CF subjects. RESULTS: Cavosonstat was rapidly absorbed and demonstrated linear and predictable pharmacokinetics. Exposure was unaffected by a high-fat meal or rifampin-mediated effects on drug metabolism and transport. Cavosonstat was well tolerated, with no dose-limiting toxicities or significant safety findings. At the highest dose, significant reductions from baseline in sweat chloride were observed (-4.1mmol/L; P=0.032) at day 28. CONCLUSIONS: The favorable safety and clinical profile warrant further study of cavosonstat in CF. ClinicalTrials.gov Numbers: NCT02275936, NCT02013388, NCT02500667.

Effects of rifampicin (rifampin) on the pharmacokinetics and safety of ambrisentan in healthy subjects: a single-sequence, open-label study.

BACKGROUND: Ambrisentan is a once-daily, endothelin (ET) type A receptor-selective antagonist approved for the treatment of pulmonary arterial hypertension. Ambrisentan is primarily metabolized by glucuronidation and undergoes cytochrome P450 (CYP)-mediated oxidation to a lesser extent. OBJECTIVE: To assess the effects of rifampicin (rifampin), a potent inducer of CYP3A4 and inhibitor of organic anion transporter polypeptides (OATPs), on the steady-state pharmacokinetics, safety and tolerability of ambrisentan. METHODS: This was a 14-day, single-sequence, open-label study that was conducted in 24 healthy adults. Subjects were administered oral doses of ambrisentan (10 mg) once daily on days 1 through 5 and were then co-administered ambrisentan (10 mg) plus rifampicin (600 mg) once daily on days 6 through 13. The steady-state pharmacokinetics of ambrisentan and its oxidative metabolite 4-hydroxymethyl ambrisentan were determined in the absence and presence of repeated administration of rifampicin. The main outcome measure was the analysis of ambrisentan pharmacokinetics (area under the plasma concentration-time curve during a dosage interval [AUC(τ)], maximum plasma drug concentration [C(max)] and minimum plasma drug concentration [C(min)]) for steady-state ambrisentan alone (day 5) as compared with steady-state ambrisentan plus steady-state rifampicin (day 13). Adverse events (AEs), ECG recordings, vital signs and clinical laboratory parameters were monitored throughout the study and at follow-up. RESULTS: A transient increase (+87% [95% CI 79, 95]) in ambrisentan steady-state systemic exposure (AUC(τ)) was observed during the first 2 days of rifampicin co-administration. However, in the presence of steady-state rifampicin, ambrisentan C(max) and AUC(τ) values were similar (+2% [95% CI -7, 12] and -4% [-9, 2], respectively) to those observed for ambrisentan alone. Relative systemic exposure of 4-hydroxymethyl ambrisentan was unaffected by either acute or steady-state rifampicin. No serious AEs or AEs leading to withdrawal were reported and there were no clinically significant changes in vital signs, ECG recordings or clinical laboratory parameters with co-administration of ambrisentan and rifampicin. CONCLUSION: Steady-state rifampicin had no clinically relevant effects on the steady-state pharmacokinetics of ambrisentan. The overall safety profile of ambrisentan was similar in the presence and absence of rifampicin. No dose adjustment of ambrisentan should be required when it is co-administered with rifampicin, a strong inducer of CYP3A4 activity and inhibitor of OATPs.

Evaluation of the endothelin receptor antagonists ambrisentan, darusentan, bosentan, and sitaxsentan as substrates and inhibitors of hepatobiliary transporters in sandwich-cultured human hepatocytes.

To evaluate potential mechanisms of clinical hepatotoxicity, 4 endothelin receptor antagonists (ERAs) were examined for substrate activity and inhibition of hepatic uptake and efflux transporters in sandwich-cultured human hepatocytes. The 4 transporters studied were sodium-dependent taurocholate cotransporter (NTCP), organic anion transporter (OATP), bile salt export pump (BSEP), and multidrug resistance-associated protein 2 (MRP2). ERA transporter inhibition was examined using the substrates taurocholate (for NTCP and BSEP), [(3)H]estradiol-17beta-D-glucuronide (for OATP), and [2-D-penicillamine, 5-D-penicillamine]enkephalin (for MRP2). ERA substrate activity was evaluated using probe inhibitors ritonavir (OATP and BSEP), bromosulfalein (OATP), erythromycin (P-glycoprotein), probenecid (MRP2 and OATP), and cyclosporin (NTCP). ERAs were tested at 2, 20, and 100 micromol*L-1 for inhibition and at 2 micromol*L-1 as substrates. OATP, NTCP, or BSEP transport activity was not reduced by ambrisentan or darusentan. Bosentan and sitaxsentan attenuated NTCP transport at higher concentrations. Only sitaxsentan decreased OATP transport (52%), and only bosentan reduced BSEP transport (78%). MRP2 transport activity was unaltered. OATP inhibitors decreased influx of all ERAs. Darusentan influx was least affected (84%-100% of control), whereas bosentan was most affected (32%-58% of control). NTCP did not contribute to influx of ERAs. Only bosentan and darusentan were shown as substrates for both BSEP and P-glycoprotein efflux. All ERAs tested were substrates for at least one hepatic transporter. Bosentan and sitaxsentan, but not ambrisentan and darusentan, inhibited human hepatic transporters, which provides a potential mechanism for the increased hepatotoxicity observed for these agents in the clinical setting.

Effect of steady-state ambrisentan on the pharmacokinetics of a single dose of the oral contraceptive norethindrone (norethisterone) 1 mg/ethinylestradiol 35 microg in healthy subjects: an open-label, single-sequence, single-centre study.

BACKGROUND: Ambrisentan is an oral, once-daily endothelin receptor antagonist (ERA) that is approved for the treatment of pulmonary arterial hypertension (PAH). Pregnancy is not recommended for women of childbearing potential with PAH, due to an increased risk of mortality. Additionally, the ERA class is teratogenic in animal studies. A highly effective method of contraception is therefore strongly recommended for women of childbearing potential who are treated with an ERA for PAH. OBJECTIVE: This study investigated the effect of ambrisentan on the pharmacokinetics (PK) of the oral contraceptive norethindrone (norethisterone) 1 mg/ethinylestradiol 35 microg (NT 1 mg/EE 35 microg). METHODS: The study was an open-label, single-sequence, PK study designed to assess the effect of multiple doses of ambrisentan (Letairis; Volibris) on the PK of a single oral dose of NT 1 mg/EE 35 microg (Ortho-Novum 1/35) in a single clinical research centre in the US. The study included 28 healthy female subjects in general good health, aged 18-45 years, and who had a body mass index of 18.5-29.9 kg/m2. A single oral dose of NT 1 mg/EE 35 microg was administered on day 1. On day 10, following a wash-out period, fasted subjects received once-daily 10 mg doses of ambrisentan for 12 days. On day 22, a single oral dose of NT 1 mg/EE 35 microg and a single 10 mg oral dose of ambrisentan were coadministered; thereafter, subjects continued to receive once-daily oral doses of ambrisentan 10 mg on days 23 through 26. The primary PK endpoints included maximum observed plasma drug concentration (C(max)), time to reach C(max) (t(max)), and the area under the plasma concentration-time curve from time zero to the time of last measurable concentration (AUC(last)). RESULTS: Ethinylestradiol C(max) was slightly decreased (geometric mean ratio [GMR] 91.7%; 90% CI 86.1, 97.8) and AUC(last) was similar (GMR 99.1%; 90% CI 91.0, 107.9) in the presence of ambrisentan compared with NT 1 mg/EE 35 microg. Norethindrone C(max) (GMR 113.2%; 90% CI 102.4, 125.1) and AUC(last) (GMR 112.9%; 90% CI 104.9, 121.6) were slightly increased in the presence of ambrisentan. The 90% CIs were within the pre-defined no-effect boundaries for all PK parameters, except for the C(max) of norethindrone, which was slightly above the upper limit of 125%. No safety concerns were apparent with the coadministration of NT 1 mg/EE 35 microg and ambrisentan. CONCLUSION: No dose adjustment of the oral contraceptive NT 1 mg/EE 35 microg is warranted with the coadministration of ambrisentan.

The pharmacokinetics and pharmacodynamics of warfarin in combination with ambrisentan in healthy volunteers.

AIMS: Ambrisentan is an oral, propanoic acid-based endothelin receptor antagonist often co-administered with warfarin to patients with pulmonary arterial hypertension. The aim of this study was to evaluate the potential for ambrisentan to affect warfarin pharmacokinetics and pharmacodynamics. METHODS: In this open-label cross-over study, 22 healthy subjects received a single dose of racemic warfarin 25 mg alone and after 8 days of ambrisentan 10 mg once daily. Assessments included exposure (AUC(0-last)) and maximum plasma concentration (C(max)) for R- and S-warfarin, and International Normalized Ratio maximum observed value (INR(max)) and area under the curve (INR(AUC(0-last))). The effects of warfarin on ambrisentan steady-state pharmacokinetics and the safety of ambrisentan/warfarin co-administration were assessed. Data are presented as geometric mean ratios. RESULTS: Ambrisentan had no significant effects on the AUC(0-last) of R-warfarin [104.7; 90% confidence interval (CI) 101.7, 107.7) or S-warfarin (101.6; 90% CI 98.4, 105.0). Similarly, ambrisentan had no significant effects on the C(max) of R-warfarin (91.6; 90% CI 86.2, 97.4) or S-warfarin (89.9; 90% CI 84.8, 95.3). Consistent with these observations, little pharmacodynamic change was observed for INR(max) (85.3; 90% CI 82.4, 88.2) or INR(AUC(0-last)) (93.0; 90% CI 90.8, 95.3). In addition, co-administration of warfarin did not alter ambrisentan steady-state pharmacokinetics. Adverse events were infrequent, and there were no bleeding adverse events. CONCLUSIONS: Multiple doses of ambrisentan had no clinically relevant effects on the pharmacokinetics and pharmacodynamics of a single dose of warfarin. Therefore, significant dose adjustments of either drug are unlikely to be required with co-administration.

No clinically relevant pharmacokinetic and safety interactions of ambrisentan in combination with tadalafil in healthy volunteers.

Ambrisentan is a nonsulfonamide, ET(A)-selective endothelin receptor antagonist (ERA) approved for the treatment of pulmonary arterial hypertension (PAH), and tadalafil is a phosphodiesterase type 5 (PDE-5) inhibitor under investigation for treatment of PAH. Due to the potential combination use, the pharmacokinetic (PK) interactions between these two drugs were assessed in a crossover study in 26 healthy adults. Single-dose PK of ambrisentan (10 mg) and its metabolite, 4-hydroxymethyl ambrisentan, were determined in the absence and presence of multiple doses of tadalafil (40 mg QD). Similarly, single-dose PK of tadalafil (40 mg) were evaluated in the absence and presence of multiple doses of ambrisentan (10 mg QD). In the presence of tadalafil, ambrisentan maximum plasma concentration (C(max)) was similar (105.0% [90% CI: 95.9-115.0%]) and systemic exposure (AUC(0-infinity)) was slightly decreased (87.5% [84.0-91.2%]), compared with ambrisentan alone. Similar changes were observed with 4-hydroxymethyl ambrisentan. Tadalafil C(max) (100.6% [94.4-107.1%]) and AUC(0-infinity) (100.2% [92.6-108.4%]) showed no difference in the absence and presence of ambrisentan. The safety profile of the drugs combined was similar to that of either drug alone. No dose adjustments should be necessary when these drugs are coadministered. These results are in contrast to previous reports that the sulfonamide-based ERA bosentan can cause marked decreases in the exposure of tadalafil.

Effect of ketoconazole on the pharmacokinetic profile of ambrisentan.

Ambrisentan is an endothelin type A (ET(A))-selective receptor antagonist that is metabolized primarily by glucuronidation but also undergoes oxidative metabolism by CYP3A4. The potential for ketoconazole, the archetypal strong inhibitor of CYP3A4, to alter the pharmacokinetic profile of ambrisentan and its oxidative metabolite, 4-hydroxymethyl ambrisentan, was assessed in an open-label, nonrandomized, 2-period, single-sequence study in 16 healthy men. Participants received a single dose of ambrisentan 10 mg alone and after 4 days of ketoconazole 400 mg administered once daily. In the presence of multiple doses of ketoconazole, single-dose ambrisentan AUC(0-infinity) estimate was increased by 35.3%, whereas C(max) was increased by 20.0%. For the 4-hydroxymethyl ambrisentan metabolite, AUC(0-infinity) estimate was decreased by 4.0%, whereas C(max) was decreased by 16.5%. Concomitant administration of ambrisentan and ketoconazole was well tolerated. In summary, ketoconazole had no clinically significant effect on the pharmacokinetics or safety profile of ambrisentan; therefore, no changes in ambrisentan dose should be necessary when the drug is administered concomitantly with known CYP3A4 inhibitors.

Pharmacokinetics and safety of ambrisentan in combination with sildenafil in healthy volunteers.

The pharmacokinetic interaction between sildenafil, a phosphodiesterase type 5 (PDE-5) inhibitor, and ambrisentan, an ET(A)-selective, propanoic acid-based endothelin receptor antagonist (ERA), was studied in a 2-period crossover study in 19 healthy volunteers, with ambrisentan exposure (AUC(0-infinity)) and maximum plasma concentration (C(max)) determined over 24 hours for a 10-mg dose of ambrisentan alone and again after 7 days of sildenafil 20 mg 3 times daily. The AUC(0-infinity) and C(max) for sildenafil and N-desmethyl sildenafil (active metabolite) were determined over 24 hours for a 20-mg dose of sildenafil alone and again after 7 days of dosing with ambrisentan 10 mg once daily. There was no clinically relevant pharmacokinetic interaction between ambrisentan and sildenafil or N-desmethyl sildenafil. Ambrisentan C(max) was unchanged (96.3% [90% confidence interval: 86.0%-107.8%]), with a minor increase in AUC(0-infinity) (108.5% [102.6%-111.7%]) with sildenafil coadministration. Sildenafil C(max) was increased slightly (113.4% [99.6%-129.1%]), and AUC(0-infinity) was unchanged (98.7% [91.2%-110.5%]) with ambrisentan coadministration. N-desmethyl sildenafil was unaltered. Dose adjustment of either drug is not necessary compared with administration alone.

Automated robotic liquid handling/laser-based nephelometry system for high throughput measurement of kinetic aqueous solubility.

The ability to rapidly and consistently measure aqueous solubility in a preclinical environment is critical to the successful identification of promising discovery compounds. The advantage of an early solubility screen is timely attrition of compounds likely to fail due to poor absorption or low bioavailability before more costly screens are performed. However, due to the large number of compounds and limited sample amounts, thermodynamic solubility measurements are not feasible at this stage. A kinetic solubility measurement is an alternative to thermodynamic measurements at the discovery stage that provides a rank listing of solubility values with minimal sample requirements. A kinetic solubility measurement is attractive from an automation vantage because it features rapid data acquisition and is amenable to multi-well formats. We describe the use of a robotic liquid/plate handler coupled to nephelometry detection for the measurement of kinetic solubility. We highlight the liquid handling validation, serial dilution parameters, and a comparison to the previous method. Experiments to further enhance throughput, or increase confidence in the automation steps, are described and the effects of these experiments are presented. In our integrated nephelometry method, we observe rapid liquid handling with an error of less than 10%, after a series of validation studies, and a sample throughput up to 1800 compounds per week. We compare the nephelometry method with our semi-thermodynamic flow-injection analysis (FIA) method, and find a 75% bin agreement between the methods.

Graphical model for estimating oral bioavailability of drugs in humans and other species from their Caco-2 permeability and in vitro liver enzyme metabolic stability rates.

This paper describes a graphical model for simplifying in vitro absorption, metabolism, distribution, and elimination (ADME) data analysis through the estimation of oral bioavailability (%F) of drugs in humans and other species. This model integrates existing in vitro ADME data, such as Caco-2 permeability (P(app)) and metabolic stability (percent remaining - %R) in liver S9 or microsomes, to estimate %F into groups of low, medium, or high regions. To test the predictive accuracy of our model, we examined 21 drugs and drug candidates with a wide range of oral bioavailability values, which represent approximately 10 different therapeutic areas in humans, rats, dogs, and guinea pigs. In vitro data from model compounds were used to define the boundaries of the low, medium, and high regions of the %F estimation plot. On the basis of the in vitro data, warfarin (93%), indomethacin (98%), timolol (50%), and carbamazepine (70%) were assigned to the high %F region; propranolol (26%) and metoprolol (38%) to medium %F region; and verapamil (22%) and mannitol (18%) to the low %F region. Similarly, the %F of 11 drug candidates from Elastase Inhibitor, NK1/NK2 antagonist, and anti-viral projects in rats, guinea pigs, and dogs were correctly estimated. This model estimates the oral bioavailability ranges of neutral, polar, esters, acidic, and basic drugs in all species. For a large number of drug candidates, this graphical model provides a tool to estimate human oral bioavailability from in vitro ADME data. When combined with the high throughput in vitro ADME screening process, it has the potential to significantly accelerate the processes of lead identification and optimization.