Dosing regimen optimisation for oseltamivir in immunocompromised paediatric patients with influenza: Extrapolation of efficacy

AIMS

To optimise the dosing regimen of oseltamivir for immunocompromised (IC) paediatric patients (<18 years) with influenza, we used an extrapolation approach alongside clinical data.

METHODS

Efficacy was extrapolated from adult IC patients to paediatric IC patients by leveraging existing efficacy, safety, pharmacokinetic (PK)/pharmacodynamic (PD), and disease-progression models of oseltamivir and oseltamivir carboxylate (OC). Data of IC paediatric patients from two studies (NV25719 and NV20234) were included in the population PK (n = 30), PK/PD analysis (n = 22) and disease modelling approach (n = 36). Simulations were performed to identify the optimal dosing regimen.

RESULTS

Clearance of oseltamivir (CL) and OC (CL_M ) were similar in IC and otherwise-healthy (OwH) patients <10 years, but decreased by 44.4% (95% CI: 26.8-62.0) and 49.1% (95% CI: 34.5-63.8), respectively, in IC patients aged 10-17 years versus OwH patients. There were no notable exposure-response relationships for any of the virologic PD analyses. Thus, no additional benefit was seen with oseltamivir carboxylate exposures higher than achieved with the conventional dose (75 mg twice daily, age- and weight-adjusted for children <13 years). The disease model illustrated that doses above the conventional oseltamivir dose had limited impact on viral kinetics in IC paediatric patients and a prolonged treatment duration of 10 days was favoured to limit potential viral rebound.

CONCLUSION

An oseltamivir dosage recommendation (conventional dose, twice daily for 10 days) was established in IC paediatric patients with influenza, based on extrapolation of efficacy from IC adults, leveraging population PK, PK/PD, and disease modelling, whilst taking resistance and safety data into account.

In vitro and clinical investigations to determine the drug-drug interaction potential of entrectinib, a small molecule inhibitor of neurotrophic tyrosine receptor kinase (NTRK)

Background Entrectinib is a CNS-active, potent inhibitor of tyrosine receptor kinases A/B/C, ROS1 and anaplastic lymphoma kinase approved for use in patients with solid tumors. We describe the in vitro and clinical studies investigating potential entrectinib drug-drug interactions. Methods In vitro studies with human biomaterials assessed the enzymes involved in entrectinib metabolism, and whether entrectinib modulates the activity of the major cytochrome P450 (CYP) enzymes or drug transporter P-glycoprotein. Clinical studies investigated the effect of a strong CYP3A4 inhibitor (itraconazole) and inducer (rifampin) on single-dose entrectinib pharmacokinetics. The effect of entrectinib on sensitive probe substrates for CYP3A4 (midazolam) and P-glycoprotein (digoxin) were also investigated. Results Entrectinib is primarily metabolized by CYP3A4. In vitro, entrectinib is a CYP3A4/5 inhibitor (IC₅₀ 2 μM) and a weak CYP3A4 inducer. Entrectinib inhibited P-glycoprotein (IC₅₀ 1.33 μM) but is a poor substrate. In healthy subjects, itraconazole increased entrectinib C_max and AUC by 73% and 504%, respectively, and rifampin decreased entrectinib C_max and AUC by 56% and 77%, respectively. Single dose entrectinib did not affect midazolam AUC, although C_max decreased by 34%. Multiple dose entrectinib increased midazolam AUC by 50% and decreased C_max by 21%. Single dose entrectinib increased digoxin AUC and C_max by 18% and 28%, respectively, but did not affect digoxin renal clearance. Conclusions Entrectinib is a CYP3A4 substrate and is sensitive to the effects of coadministered moderate/strong CYP3A4 inhibitors and strong inducers, and requires dose adjustment. Entrectinib is a weak inhibitor of CYP3A4 and P-glycoprotein and no dose adjustments are required with CYP3A4/P- glycoprotein substrates.

Registration Number (Study 2) NCT03330990 (first posted online November 6, 2017) As studies 1 and 3 are phase 1 trials in healthy subjects, they are not required to be registered.

Pharmacologic effects of oseltamivir in immunocompromised adult patients as assessed by population PK/PD analysis and drug-disease modelling for dosing regimen optimization

Aim

Pharmacologic effects were analysed to determine a dose recommendation for oseltamivir in immunocompromised (IC) adults with influenza.

Methods

Quantitative clinical pharmacology methods were applied to data from 160 adult IC patients (aged 18‐78 years) from two studies (NV20234, 150 patients; NV25118, 10 patients) who received oseltamivir 75‐200 mg twice daily for up to 10 days. An established population‐pharmacokinetic (PK) model with additional effects on oseltamivir and oseltamivir carboxylate (OC) clearance described the PK characteristics of oseltamivir in IC patients versus otherwise healthy (OwH) patients from previous clinical trials. Estimated PK parameters were used to evaluate exposure‐response relationships for virologic endpoints (time to cessation of viral shedding, viral load measures and treatment‐emergent resistance). A drug‐disease model characterized the viral kinetics of influenza accounting for the effect of OC on viral production.

Results

Oseltamivir clearance was 32.5% lower (95% confidence interval [CI], 26.1‐38.8) and OC clearance was 33.7% lower (95% CI, 23.2‐44.1) in IC versus OwH patients. No notable exposure‐response relationships were identified for exposures higher than those achieved after conventional dose oseltamivir 75 mg, which appeared to be close to the maximum effect of oseltamivir. Simulations of the drug‐disease model predicted that initiating treatment within 48 hours of symptom onset had maximum impact, and a treatment duration of 10 days was favourable over 3‐5 days to limit viral rebound.

Conclusions

Our findings support the use of conventional‐dose oseltamivir 75 mg twice daily for 10 days in the treatment of IC adult patients with influenza.

Baloxavir treatment of ferrets infected with influenza A(H1N1)pdm09 virus reduces onward transmission

Influenza viruses cause seasonal outbreaks and pose a continuous pandemic threat. Although vaccines are available for influenza control, their efficacy varies each season and a vaccine for a novel pandemic virus manufactured using current technology will not be available fast enough to mitigate the effect of the first pandemic wave. Antivirals can be effective against many different influenza viruses but have not thus far been used extensively for outbreak control. Baloxavir, a recently licensed antiviral drug that targets the influenza virus endonuclease, has been shown to reduce virus shedding more effectively than oseltamivir, a widely used neuraminidase inhibitor drug. Thus it is possible that treatment with baloxavir might also interrupt onward virus transmission. To test this, we utilized the ferret model, which is the most commonly used animal model to study influenza virus transmission. We established a subcutaneous baloxavir administration method in ferrets which achieved similar pharmacokinetics to the approved human oral dose. Transmission studies were then conducted in two different locations with different experimental setups to compare the onward transmission of A(H1N1)pdm09 virus from infected ferrets treated with baloxavir, oseltamivir or placebo to naïve sentinel ferrets exposed either indirectly in adjacent cages or directly by co-housing. We found that baloxavir treatment reduced infectious viral shedding in the upper respiratory tract of ferrets compared to placebo, and reduced the frequency of transmission amongst sentinels in both experimental setups, even when treatment was delayed until 2 days post-infection. In contrast, oseltamivir treatment did not substantially affect viral shedding or transmission compared to placebo. We did not detect the emergence of baloxavir-resistant variants in treated animals or in untreated sentinels. Our results support the concept that antivirals which decrease viral shedding could also reduce influenza transmission in the community.

Mechanistic Population Pharmacokinetic Model of Oseltamivir and Oseltamivir Carboxylate Accounting for Physiological Changes to Predict Exposures in Neonates and Infants

A mechanistic population‐pharmacokinetic model was developed to predict oseltamivir exposures in neonates and infants accounting for physiological changes during the first 2 years of life. The model included data from 13 studies, comprising 436 subjects with normal renal function (317 pediatric subjects (≥ 38 weeks postmenstrual age (PMA), ≥ 13 days old) and 119 adult subjects < 40 years). Concentration–time profiles of oseltamivir and its active metabolite, oseltamivir carboxylate (OC), were characterized by a four‐compartment model, with absorption described by three additional compartments. Renal maturational changes were implemented by description of OC clearance with allometric function of weight and Hill function of PMA. Clearance of OC increased with weight up to 43 kg (allometric coefficient 0.75). Half the adult OC clearance was reached at a PMA of 45.6 weeks (95% confidence interval (CI) 41.6–49.6) with a Hill coefficient of 2.35 (95% CI 1.67–3.04). The model supports the European Union/United States‐approved 3 mg/kg twice‐daily oseltamivir dose for infants < 1 year (PMA ≥ 38 weeks) and allows prediction of exposures in preterm neonates.

Determination of dalcetrapib by liquid chromatography-tandem mass spectrometry

The cholesteryl ester transfer protein modulator dalcetrapib is currently under development for the prevention of dyslipidemia and cardiovascular disease. Dalcetrapib, a thioester, is rapidly hydrolyzed in vivo to the corresponding thiophenol which in turn is further oxidized to the dimer and mixed disulfides (where the thiophenol binds to peptides, proteins and other endogenous thiols). These forms co-exist in an oxidation-reduction equilibrium via the thiol and cannot be stabilized without influencing the equilibrium, hence specific determination of individual components, i.e., in order to distinguish between the free thiol, the disulfide dimer and mixed disulfide adducts, was not pursued for routine analysis. The individual forms were quantified collectively as dalcetrapib-thiol (dal-thiol) after reduction under basic conditions with dithiothreitol to break disulfide bonds and derivatization with N-ethylmaleimide to stabilize the free thiol. The S-methyl and S-glucuronide metabolites were determined simultaneously with dal-thiol with no effect from the derivatization procedure. Column-switching liquid chromatography-tandem mass spectrometry provided a simple, fast and robust method for analysis of human and animal plasma and human urine samples. Addition of the surfactant Tween 80 to urine prevented adsorptive compound loss. The lower limits of quantitation (LLOQ) were 5 ng/mL for dal-thiol, and 5 ng/mL for the S-methyl and 50 ng/mL for the S-glucuronide metabolites. Using stable isotope-labeled internal standards, inter- and intra-assay precisions were each <15% (<20% at LLOQ) and accuracy was between 85 and 115%. Recovery was close to 100%, and no significant matrix effect was observed.

A phase I dose escalation pharmacokinetic (PK) and pharmacodynamic (PD) study of weekly and twice weekly erlotinib in advanced stage solid malignancies

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Background: Erlotinib is a potent oral TKI of the epidermal growth factor receptor (EGFR). At the current recommended daily dose of 150 mg/day there is activity in advanced stage NSCLC, but with frequent grade 1/2 rash and diarrhea. We performed a phase I dose escalation study of erlotinib with a once and twice weekly schedule to assess the PKs, PDs, and to determine if toxicities would be less on an intermittent but high dose schedule. Methods: A standard dose escalation schedule starting at 1,400 mg once/week and 600 mg twice/week with increments of 200 mg to 4 dose cohorts/schedule was utilized with three patients per cohort. A cycle consisted of 3 weeks of therapy. PKs were performed on cycle 1 and 2. PDs on normal skin punch biopsies were performed at baseline and after cycle 1. Tumour evaluation was done following every 2nd cycle. Subjects were treated until progression or unacceptable toxicity. Results: 32 patients were enrolled from Oct 2004-April 2006. Median age 58 years (28–74 years); median PS 1 (0–2); and median prior palliative systemic regimens 2 (0–6). In the once weekly schedule the maximum tolerated dose (MTD) was not reached with the top dose of 2,000 mg/week. A median of 2 cycles were delivered (1–14), with 3/13 patients achieving stable disease = 3 months. 4/13 patients had G1 rash and 6/13 patients G1 diarrhea during the first 2 cycles. In the twice weekly schedule the MTD was reached at 1,200 mg twice/week with 2/6 subjects experiencing G3 rash. The recommended dose level is 1,000 mg twice/week. A median of 4 cycles were delivered (1–28) with 2 partial responses, 1 minor response and 6 stable disease = 3 months out of 19 patients in total. G1/2 rash or diarrhea occurred in 13 and 9 patients respectively. No corneal toxicity was seen. The PK data demonstrated a variable but linear pattern. At 1,000 mg twice/week the median Cmax, Tmax and AUC0–24 hr was 6.28 μg/ml, 2 hours and 135 μg.h/ml respectively. PD analysis is ongoing. Conclusions: A once weekly and twice weekly high dose schedule of erlotinib is feasible, with MTD not reached in the once weekly schedule. A recommended dose of 1,000 mg twice/week has clinical activity, is generally well tolerated, and results in significantly higher systemic exposure than the 150 mg once daily dose.

No significant financial relationships to disclose.