Pharmacokinetics, absorption, and excretion of radiolabeled revexepride: a Phase I clinical trial using a microtracer and accelerator mass spectrometry-based approach

Purpose

Gastroesophageal reflux disease involves the reflux of gastric and/or duodenal content into the esophagus. Prokinetic therapies, such as the selective 5-hydroxytryptamine receptor 4 agonist revexepride, may aid gastric emptying. This Phase I study evaluated the pharmacokinetics and excretion pathways of [¹⁴C]revexepride in healthy individuals using a microtracer approach with accelerator mass spectrometry.

Participants and methods

Six healthy men received a single oral dose of 2 mg [¹⁴C]revexepride containing ~200 nCi of radioactivity; blood, urine, and fecal samples were collected over a 10-day period.

Results

Almost 100% of ¹⁴C was recovered: 38.2%±10.3% (mean ± standard deviation) was recovered in urine, and 57.3%±0.4% was recovered in feces. Blood cell uptake was low, based on the blood plasma total radioactivity ratio of 0.8. The mean revexepride renal clearance was 8.6 L/h, which was slightly higher than the typical glomerular filtration rate in healthy individuals. Time to reach maximal concentration was 1.75±1.17 hours (mean ± standard deviation). No safety signals were identified.

Conclusion

This study demonstrated that revexepride had rapid and moderate-to-good oral absorption. Excretion of radioactivity was completed with significant amounts in feces and urine. Renal clearance slightly exceeded the typical glomerular filtration rate, suggesting the involvement of active transportation in the renal tubules.

A Phase I Study to Investigate the Absorption, Pharmacokinetics, and Excretion of [(14)C]Prucalopride After a Single Oral Dose in Healthy Volunteers

PURPOSE

Chronic constipation is a prevalent gastrointestinal disorder globally. It is often treated with medications such as laxatives. Newer therapies to improve gastric motility include the selective 5-hydroxytryptamine receptor-4 agonist prucalopride, which is licensed for the treatment of chronic constipation in adults. The aim of this study was to investigate the pharmacokinetic properties and excretion of prucalopride in healthy individuals, using a microtracer approach with (14)C radioactivity detection using liquid scintillation counting and accelerator mass spectrometry.

METHODS

This was a single-period, open-label, nonrandomized absorption, metabolism, and excretion study of [(14)C]prucalopride. Participants were 6 healthy men aged 18 to 50 years. After screening, participants were administered a single dose of [(14)C]prucalopride succinate 2 mg (~200 nCi). Postadministration, urine, feces, and blood samples were collected over a 10-day period. Safety and adverse event data were also collected.

FINDINGS

Almost 100% of the administered dose of radioactivity was recovered, with a mean (SD) of 84.2% (8.88%) recovered in urine and 13.3% (1.73%) recovered in feces. The mean blood-to-plasma concentration ratio of 1.9 indicated uptake of prucalopride into blood cells. The renal clearance of prucalopride was 17.0 (2.5) L/h, which is higher than the glomerular filtration rate in healthy individuals, suggesting active renal transport of prucalopride. Prucalopride was well tolerated, with no serious adverse events reported.

IMPLICATIONS

Prucalopride was well absorbed and excreted mainly by the kidneys, including both passive and active transporter mechanisms. Quantitative recovery of the radioactive dose was achieved. Consistent with previous studies, prucalopride was generally well tolerated. ClinicalTrials.gov identifier: NCT01807000.

Molecular, Biologic, and Pharmacokinetic Properties of Monoclonal Antibodies: Impact of These Parameters on Early Clinical Development

Currently, 14 intact, unconjugated, monoclonal antibodies (Mabs) are approved for therapeutic use in the United States, and more than 100 Mabs are presently undergoing clinical development or regulatory review. Mabs are large molecular weight glycoproteins that embody structural, biochemical, and pharmacologic properties distinct from other biologics or chemically synthesized compounds. Early therapeutic Mabs were murine proteins, and clinical testing of these agents revealed serious immune-mediated toxicities. The side effect profile of murine Mab therapeutic agents restricted the clinical development of these agents to indications with high morbidity and/or mortality (ie, oncology, graft vs host rejection). Advances in genetic engineering and protein expression technologies resulted in the development of Mabs composed either predominately (ie, mouse/human chimeric, "humanized") or completely (ie, "fully human" Mabs) of the human amino acid sequence. The production of chimeric, humanized, and fully human Mabs significantly reduced the immune-mediated toxicities and expanded the utility for these agents in numerous therapeutic areas, particularly in chronic disorders requiring either long-term administration (ie, rheumatoid arthritis) or treatment upon the flare up of disease (Crohn's disease, psoriasis). This review provides an overview of the molecular, biochemical, and pharmacokinetic properties and clinical development history of Mabs and details how these factors currently affect the scope and design of early clinical development strategies for these drug candidates. Emphasis is placed on the criteria for selecting appropriate subject populations for phase I testing of Mabs.

Pharmacokinetic interactions between sirolimus and microemulsion cyclosporine when orally administered jointly and 4 hours apart in healthy volunteers

Sirolimus (RAPA) and cyclosporine (CsA) are immunosuppressive compounds that are being used concomitantly in renal transplant patients. Both drugs are dosed orally, have common intestinal and hepatic metabolism and intestinal transport mechanisms, and thus offer potential for pharmacokinetic drug interactions. A single-dose, open-label, four-period, four-treatment, randomized crossover study was completed in 15 male and 6 female volunteers. Each subject received a 10-mg oral dose of RAPA alone (Rapamune Oral Solution), a 300-mg oral dose of CsA alone (3 x 100-mg Neoral Soft Gelatin Capsules), RAPA and CsA jointly, and CsA followed by RAPA delayed by 4 hours. Blood samples were collected for either 144 hours (RAPA) or 48 hours (CsA) and analyzed by either liquid chromatography/tandem mass spectrometry (RAPA) or radioimmunoassay (CsA). RAPA bioavailability was markedly increased by CsA when given jointly, with Cmax,tmax, and AUC being increased 116%, 92%, and 230%, respectively. However, when RAPA was administered 4 hours after CsA, increases in RAPA Cmax, tmax, and AUC were only 37%, 58%, and 80%, respectively. CsA did not affect t1/2 or mean residence time (MRT) by either mode of combined administration. RAPA did not significantly affect CsA bioavailability after either joint or delayed combined administrations. It was concluded that CsA markedly increases the bioavailability of RAPA, which may be attributed to a large intestinal and hepatic first-pass effect, rather than altered elimination. RAPA did not affect the bioavailability of CsA.

Underappreciation of sleep disorders as a cause of motor vehicle crashes

Despite an increased risk of motor vehicle crashes (MVC) in patients with obstructive sleep apnea (OSA), we hypothesized that OSA was not considered in drivers admitted to trauma centers after an injury-producing MVC. A retrospective study on drivers involved in MVCs admitted to a level 1 trauma center was performed, with crash cause determined and the frequency of sleep studies recorded. A questionnaire was also mailed to 240 trauma centers seeking information on evaluation of patients with unexplained causes for MVCs, including screening for OSA. There were 122 drivers of MVCs admitted to our hospital, 60/122 (49%) had unexplained crashes and no sleep studies were performed. There were 70 survey respondents (30% return rate), 35/70 (50%) centers routinely screened for syncope after unexplained MVC, however, no center screened for OSA. US trauma centers do not screen for sleep disorders despite the associated increased crash risk and the high prevalence of crashes that can not be explained by other causes. We believe this reflects a lack of awareness of sleep disorders by health care professionals caring for trauma victims and education is of utmost importance.

Pharmacokinetics of pantoprazole in patients with moderate and severe hepatic dysfunction

BACKGROUND

Patients with impaired hepatic function usually require gastric acid-suppressant therapy but are at increased risk for drug interactions and may require dosage adjustments. The proton pump inhibitor pantoprazole is rapidly absorbed and eliminated, primarily by cytochrome P450 (CYP) 2C19 isozymes.

OBJECTIVE

This study sought to determine whether dosage adjustment of pantoprazole is required in patients with moderate or severe hepatic impairment by comparing the pharmacokinetic profile of pantoprazole in such patients with that in healthy slow metabolizers of pantoprazole, in whom no dosage adjustment is required.

METHODS

Patients with moderate (Child-Pugh class B) and severe (Child-Pugh class C) hepatic impairment received oral pantoprazole 40 mg once daily on days 1 through 4 and then on alternate days (days 6 and 8). Serial blood samples were collected on days 4 and 8 for analyses of plasma pantoprazole concentrations. Pharmacokinetic data were compared between the 2 groups with hepatic impairment and against historical data from 17 healthy subjects who were genetically slow CYP2C19 metabolizers of pantoprazole.

RESULTS

Twenty-two patients participated in the study, 13 in the Child-Pugh class B group and 9 in the Child-Pugh class C group. No clinically significant differences in pantoprazole pharmacokinetics were noted between the patients with hepatic impairment and the healthy slow metabolizers of pantoprazole on days 4 and 8. Pantoprazole was well tolerated. Four Child-Pugh class B patients and 3 Child-Pugh class C patients reported > or = 1 adverse event. Adverse events were generally mild or moderate, and were similar to those reported in healthy subjects. Two patients discontinued the study because of severe events related to their underlying disease.

CONCLUSIONS

The pharmacokinetics and tolerability of pantoprazole were similar in patients with moderate hepatic impairment, patients with severe hepatic impairment, and healthy slow metabolizers of pantoprazole, in whom no dosage adjustment is required. Thus, no dosage adjustment of pantoprazole is required in patients with hepatic impairment, regardless of its severity. However, caution should be exercised when giving pantoprazole to patients with severe hepatic impairment.

Nasal airway changes assessed by acoustic rhinometry and mediator release during immediate and late reactions to allergen challenge

BACKGROUND

We have found that acoustic rhinometry is a reliable means of assessing nasal airway caliber changes during the immediate reaction to nasal allergen challenge of sensitive subjects. Comparison of such changes with symptoms and patterns of mediator release could help in the understanding of mechanisms of immediate and late-phase reactions after allergen challenge and their clinical relevance.

METHODS

Nasal minimal cross-sectional area (MCA) was assessed sequentially for 6 hours after two blinded challenges in random order with pollen antigens and buffer diluent in five sensitive human subjects. Comparisons were made with: (1) symptom scores; (2) olfaction changes; and (3) nasal secretion levels of histamine, tryptase, leukotriene C4, serum albumin (a marker of vascular permeability), lactoferrin (a marker of local glandular secretion), and inflammatory cells in nasal scrapings.

RESULTS

In four of five subjects there was a significantly greater decrease in MCA after antigen challenge than after diluent challenge, correlating with the degree of subjective nasal congestion. In two of these four subjects there was a prominent second late-phase decrease in MCA at 3 to 5 hours, whereas the MCA was persistently decreased in an additional subject with accompanying subjective congestion. No significant decrease in olfactory acuity occurred. Levels were significantly higher in nasal secretions obtained after antigen challenge than in those obtained after buffer challenge with histamine (9 +/- 2.7 ng/ml vs 1.2 +/- 0.5 ng/ml; p = 0.04); tryptase (95 +/- 83 ng/ml vs 3 +/- 0.9 ng/ml; p = 0.02), leukotriene C4 (5293 +/- 1385 ng/ml vs 578 +/- 183 ng/ml; p = 0.02), and albumin (123 +/- 9 ng/ml vs 19 +/- 1.6 ng/ml; p = 0.005) but not with lactoferrin (4.6 +/- 1.2 ng/ml vs 4.1 +/- 28 ng/ml; p = not significant). Granulocyte exudation was seen after antigen challenge but not after buffer diluent challenge. However, there was not a precise correlation between decreases in MCA with changes in levels of these mediators in individual subjects.

CONCLUSIONS

Acoustic rhinometry can quantitatively assess congestion during immediate and late-phase reactions after nasal challenge without significant correlation to the degree of individual inflammatory events assessed.