Pharmacokinetics and ADME Characterization of Intravenous and Oral [14C]-Linerixibat in Healthy Male Volunteers

Linerixibat, an oral small-molecule ileal bile acid transporter inhibitor under development for cholestatic pruritus in primary biliary cholangitis, was designed for minimal absorption from the intestine (site of pharmacological action). This study characterized the pharmacokinetics, absorption, metabolism, and excretion of [¹⁴C]-linerixibat in humans after an intravenous microtracer concomitant with unlabeled oral tablets and [¹⁴C]-linerixibat oral solution. Linerixibat exhibited absorption-limited flip-flop kinetics: longer oral versus intravenous half-life (6-7 hours vs. 0.8 hours). The short intravenous half-life was consistent with high systemic clearance (61.9 l/h) and low volume of distribution (16.3 l). In vitro studies predicted rapid hepatic clearance via cytochrome P450 3A4 metabolism, which predicted human hepatic clearance within 1.5-fold. However, linerixibat was minimally metabolized in humans after intravenous administration: ∼80% elimination via biliary/fecal excretion (>90%-97% as unchanged parent) and ∼20% renal elimination by glomerular filtration (>97% as unchanged parent). Absolute oral bioavailability of linerixibat was exceedingly low (0.05%), primarily because of a very low fraction absorbed (0.167%; fraction escaping first-pass gut metabolism (fg) ∼100%), with high hepatic extraction ratio (77.0%) acting as a secondary barrier to systemic exposure. Oral linerixibat was almost entirely excreted (>99% recovered radioactivity) in feces as unchanged and unabsorbed linerixibat. Consistent with the low oral fraction absorbed and ∼20% renal recovery of intravenous [¹⁴C]-linerixibat, urinary elimination of orally administered radioactivity was negligible (<0.04% of dose). Linerixibat unequivocally exhibited minimal gastrointestinal absorption and oral systemic exposure. Linerixibat represents a unique example of high CYP3A4 clearance in vitro but nearly complete excretion as unchanged parent drug via the biliary/fecal route. SIGNIFICANCE STATEMENT: This study conclusively established minimal absorption and systemic exposure to orally administered linerixibat in humans. The small amount of linerixibat absorbed was eliminated efficiently as unchanged parent drug via the biliary/fecal route. The hepatic clearance mechanism was mispredicted to be mediated via cytochrome P450 3A4 metabolism in vitro rather than biliary excretion of unchanged linerixibat in vivo.

Mobile chest imaging of neonates in incubators: Optimising DR and CR acquisitions

INTRODUCTION

Neonates are a particularly vulnerable patient group with complex medical needs requiring frequent radiographic examinations. This study aims to compare computed radiography (CR) and direct digital radiography (DDR) portable imaging systems used to acquire chest x-rays for neonates within incubators.

METHODS

An anthropomorphic neonatal chest phantom was imaged under controlled conditions using one portable machine but captured using both CR and DDR technology. Other variables explored were: image receptor position (direct and incubator tray), tube current and kV. All other parameters were kept consistent. Contrast-to-noise ratio (CNR) was measured using ImageJ software and dose-area-product (DAP) was recorded. Optimisation score was calculated by dividing CNR with the DAP for each image acquisition.

RESULTS

The images with the highest CNR were those acquired using DDR direct exposures and the images with lowest CNR were those acquired using CR with the image receptor placed within the incubator tray. This is also supported by the optimisation scores which demonstrated DDR direct produced the optimal combination with regards to CNR and radiation dose. The CNR had a mean increase of 50.3% when comparing DDR direct with CR direct respectively. This was also evident when comparing DDR and CR for in-tray acquisitions, with CNR increasing by a mean of 43.5%. A mean increase of 20.4% was seen in CNR when comparing DDR tray exposures to CR direct.

CONCLUSION

DDR direct produced images of highest CNR, with incubator tray reducing CNR for both CR and DDR. However, DDR tray still had better image quality compared to CR direct.

IMPLICATIONS FOR PRACTICE

Where possible, DDR should be the imaging system of choice for portable examinations on neonates owing to its superior image quality at lower radiation dose.

An Innovative Approach to Characterize Clinical ADME and Pharmacokinetics of the Inhaled Drug Nemiralisib Using an Intravenous Microtracer Combined with an Inhaled Dose and an Oral Radiolabel Dose in Healthy Male Subjects

An innovative open-label, crossover clinical study was used to investigate the excretion balance, pharmacokinetics, and metabolism of nemiralisib-an inhaled phosphoinositide 3-kinase delta inhibitor being developed for respiratory diseases. Six healthy men received a single intravenous microtracer of 10 µg [¹⁴C]nemiralisib with a concomitant inhaled nonradiolabeled 1000 µg dose followed by an oral 800 µg dose of [¹⁴C]nemiralisib 14 days later. Complementary methods including accelerator mass spectrometry allowed characterization of a range of parameters including oral absorption (F_abs), proportion of nemiralisib escaping gut wall metabolism (F_g), hepatic extraction (E_h), fraction of dose absorbed from inhaled dose (F_lung), and renal clearance. Intravenous pharmacokinetics of nemiralisib were characterized by low blood clearance (10.0 l/h), long terminal half-life (55 hours), and high volume of distribution at steady state (728 l). Nemiralisib exhibited moderate inhaled and oral bioavailability (38% and 35%) while F_lung was 29%. Absorption and first-pass parameters were corrected for blood renal clearance and compared with values without correction. Any swallowed nemiralisib was relatively well absorbed (F_abs, 0.48) with a high fraction escaping gut wall metabolism and low extraction by the liver (F_g and E_h being 0.83 and 0.10, respectively). There were no major human plasma metabolites requiring further qualification in animal studies. Both unchanged nemiralisib and its oxidative/conjugative metabolites were secreted in bile, with nemiralisib likely subject to further metabolism through enterohepatic recirculation. Direct renal clearance and metabolism followed by renal clearance were lesser routes of elimination. SIGNIFICANCE STATEMENT: A number of innovative features have been combined into one small clinical study enabling a comprehensive description of the human pharmacokinetics and metabolism of an inhaled molecule. Design elements included an intravenous ¹⁴C tracer administration concomitant with an inhalation dose that enabled derivation of parameters such as fraction absorbed (F_abs), the proportion of drug escaping first-pass extraction through the gut wall and liver (F_g and F_h) and hepatic extraction (E_h). Entero-test bile sampling enabled characterization of biliary elimination pathways.

Radical curative efficacy of tafenoquine combination regimens in Plasmodium cynomolgi-infected Rhesus monkeys (Macaca mulatta)

BACKGROUND

Tafenoquine is an 8-aminoquinoline being developed for radical cure (blood and liver stage elimination) of Plasmodium vivax. During monotherapy treatment, the compound exhibits slow parasite and fever clearance times, and toxicity in glucose-6-phosphate dehydrogenase (G6PD) deficiency is a concern. Combination with other antimalarials may mitigate these concerns.

METHODS

In 2005, the radical curative efficacy of tafenoquine combinations was investigated in Plasmodium cynomolgi-infected naïve Indian-origin Rhesus monkeys. In the first cohort, groups of two monkeys were treated with a three-day regimen of tafenoquine at different doses alone and in combination with a three-day chloroquine regimen to determine the minimum curative dose (MCD). In the second cohort, the radical curative efficacy of a single-day regimen of tafenoquine-mefloquine was compared to that of two three-day regimens comprising tafenoquine at its MCD with chloroquine or artemether-lumefantrine in groups of six monkeys. In a final cohort, the efficacy of the MCD of tafenoquine against hypnozoites alone and in combination with chloroquine was investigated in groups of six monkeys after quinine pre-treatment to eliminate asexual parasites. Plasma tafenoquine, chloroquine and desethylchloroquine concentrations were determined by LC-MS in order to compare doses of the drugs to those used clinically in humans.

RESULTS

The total MCD of tafenoquine required in combination regimens for radical cure was ten-fold lower (1.8 mg/kg versus 18 mg/kg) than for monotherapy. This regimen (1.8 mg/kg) was equally efficacious as monotherapy or in combination with chloroquine after quinine pre-treatment to eliminate asexual stages. The same dose of (1.8 mg/kg) was radically curative in combination with artemether-lumefantrine. Tafenoquine was also radically curative when combined with mefloquine. The MCD of tafenoquine monotherapy for radical cure (18 mg/kg) appears to be biologically equivalent to a 600-1200 mg dose in humans. At its MCD in combination with blood schizonticidal drugs (1.8 mg/kg), the maximum observed plasma concentrations were substantially lower than (20-84 versus 550-1,100 ng/ml) after administration of 1, 200 mg in clinical studies.

CONCLUSIONS

Ten-fold lower clinical doses of tafenoquine than used in prior studies may be effective against P. vivax hypnozoites if the drug is deployed in combination with effective blood-schizonticidal drugs.

Achieving lifelong learning in nursing

In an attempt to increase the quality of care provision, nurse education has undergone radical change. The number of women returning to nursing after a break and mature nurses requiring post-registration education has led to more flexible educational options. Open and distance learning can provide this flexibility and encourages confidence among students.