Source: European Medicines Agency (EU) Revision Year: 2022 Publisher: Roche Registration GmbH, Emil-Barell-Strasse 1, 79639 Grenzach-Wyhlen, Germany
Pharmacotherapeutic group: Antivirals for systemic use, other anti-virals
ATC code: J05AX25
Baloxavir marboxil is a prodrug that is converted by hydrolysis to baloxavir, the active form that exerts anti-influenza activity. Baloxavir acts on the cap-dependent endonuclease (CEN), an influenza virus-specific enzyme in the polymerase acidic (PA) subunit of the viral RNA polymerase complex and thereby inhibits the transcription of influenza virus genomes resulting in inhibition of influenza virus replication.
The 50% inhibition concentration (IC50) of baloxavir was 1.4 to 3.1 nmol/L for influenza A viruses and 4.5 to 8.9 nmol/L for influenza B viruses in an enzyme inhibition assay.
In a MDCK cell culture assay, the median 50% effective concentration (EC50) values of baloxavir were 0.73 nmol/L (n=31; range: 0.20-1.85 nmol/L) for subtype A/H1N1 strains, 0.83 nmol/L (n=33; range: 0.35-2.63 nmol/L) for subtype A/H3N2 strains, and 5.97 nmol/L (n=30; range: 2.67-14.23 nmol/L) for type B strains.
In an MDCK cell-based virus titre reduction assay, the 90% effective concentration (EC90) values of baloxavir were in the range of 0.46 to 0.98 nmol/L for subtype A/H1N1 and A/H3N2 viruses, 0.80 to 3.16 nmol/L for avian subtype A/H5N1 and A/H7N9 viruses, and 2.21 to 6.48 nmol/L for type B viruses.
Viruses bearing the PA/I38T/F/M/N mutation selected in vitro or in clinical studies show reduced susceptibility to baloxavir with changes in EC50 values ranging from 11 to 57-fold for influenza A viruses and 2 to 8-fold for influenza B viruses.
In the two Phase 3 studies of treatment of uncomplicated influenza (see below) no resistance to baloxavir was detected in baseline isolates. Treatment-emergent mutations PA/I38T/M/N were detected in 36/370 (9.7%) and in 15/290 (5.2%) patients treated with baloxavir marboxil but were not detected in any patients treated with placebo.
In the Phase 3 study of post-exposure prophylaxis (see below), treatment-emergent mutations PA/I38T/M were found in 10 of 374 (2.7%) baloxavir marboxil-treated subjects. PA/I38 substitutions were not detected in placebo-treated subjects, with the exception of 2 subjects who received baloxavir marboxil as rescue medication.
Baloxavir is active in vitro against influenza viruses that are considered resistant to neuraminidase inhibitors, including strains with the following mutations: H274Y in A/H1N1, E119V and R292K in A/H3N2, R152K and D198E in type B virus, H274Y in A/H5N1, R292K in A/H7N9.
Capstone 1 (1601T0831), was a Phase 3 randomised, double-blind, multicentre study conducted in Japan and the US to evaluate the efficacy and safety of a single oral dose of baloxavir marboxil compared with placebo and with oseltamivir in healthy adult and adolescent patients (aged ≥12 years to ≤64 years) with uncomplicated influenza. Patients were randomised to receive baloxavir marboxil (patients who weighed 40 to <80 kg received 40 mg and patients who weighed ≥80 kg received 80 mg), oseltamivir 75 mg twice daily for 5 days (only if aged ≥20 years) or placebo. Dosing occurred within 48 hours of first onset of symptoms.
A total of 1436 patients (of which 118 were aged ≥12 years to ≤17 years) were enrolled in the 2016- 2017 Northern Hemisphere influenza season. The predominant influenza virus strain in this study was the A/H3 subtype (84.8% to 88.1%) followed by the B type (8.3% to 9.0%) and the A/H1N1pdm subtype (0.5% to 3.0%). The primary efficacy endpoint was time to alleviation of symptoms (cough, sore throat, headache, nasal congestion, feverishness or chills, muscle or joint pain, and fatigue) (TTAS). Baloxavir marboxil elicited a statistically significant reduction in TTAS when compared with placebo (Table 3).
Table 3. Capstone 1: Time to alleviation of symptoms (baloxavir marboxil vs placebo):
| Time to Alleviation of Symptoms (Median [hours]) | |||
|---|---|---|---|
| Baloxavir marboxil 40/80 mg (95% CI) N=455 | Placebo (95% CI) N=230 | Difference between Baloxavir marboxil and placebo (95% CI for difference) | P-value |
| 53.7 (49.5, 58.5) | 80.2 (72.6, 87.1) | -26.5 (−35.8, −17.8) | <0.0001 |
CI: Confidence interval
When the baloxavir marboxil group was compared to the oseltamivir group, there was no statistically significant difference in TTAS (53.5 h vs 53.8 h respectively).
The median (95% CI) TTAS was 49.3 (44.0, 53.1) and 82.1 (69.5, 92.9) hours for patients who were symptomatic for >0 to ≤24 hours, and 66.2 (54.4, 74.7) and 79.4 (69.0, 91.1) hours for patients who were symptomatic for >24 to ≤48 hours for baloxavir marboxil and placebo, respectively.
The median time to resolution of fever in patients treated with baloxavir marboxil was 24.5 hours (95% CI: 22.6, 26.6) compared with 42.0 hours (95% CI: 37.4, 44.6) in those receiving placebo. No difference was noted in duration of fever in the baloxavir marboxil group compared with the oseltamivir group.
Capstone 2 (1602T0832) was a Phase 3 randomised, double-blind, multicentre study to evaluate the efficacy and safety of a single oral dose of baloxavir marboxil compared with placebo and with oseltamivir in adult and adolescent patients (aged ≥ 12 years) with uncomplicated influenza who had at least one host factor predisposing to the development of complications. Patients were randomised to receive a single oral dose of baloxavir marboxil (according to weight as in Capstone 1), oseltamivir 75 mg twice daily for 5 days, or placebo. Dosing occurred within 48 hours of first onset of symptoms.
Of the total 2184 patients 59 were aged ≥12 to ≤17 years, 446 were aged ≥ 65 to ≤ 74 years, 142 were aged ≥75 to ≤84 years and 14 were aged ≥85 years. The predominant influenza viruses in this study were the A/H3 subtype (46.9% to 48.8%) and influenza B (38.3% to 43.5%). The primary efficacy endpoint was time to improvement of influenza symptoms (cough, sore throat, headache, nasal congestion, feverishness or chills, muscle or joint pain, and fatigue) (TTIS). Baloxavir marboxil elicited a statistically significant reduction in TTIS when compared with placebo (Table 4).
Table 4. Capstone 2: Time to improvement of influenza symptoms (baloxavir marboxil vs placebo):
| Time to Improvement of Influenza Symptoms (Median [hours]) | |||
|---|---|---|---|
| Baloxavir marboxil 40/80 mg (95% CI) N=385 | Placebo (95% CI) N=385 | Difference between Baloxavir marboxil and placebo (95% CI for difference) | P-value |
| 73.2 (67.5, 85.1) | 102.3 (92.7, 113.1) | -29.1 (−42.8, −14.6) | <0.0001 |
When the baloxavir marboxil group was compared to the oseltamivir group, there was no statistically significant difference in TTIS (73.2 h vs 81.0 h respectively).
The median (95% CI) TTIS was 68.6 (62.4, 78.8) and 99.1 (79.1, 112.6) hours for patients who were symptomatic for >0 to ≤24 hours and 79.4 (67.9, 96.3) and 106.7 (92.7, 125.4) hours for patients who were symptomatic for >24 to ≤48 hours for baloxavir marboxil and placebo, respectively.
For patients infected with type A/H3 virus, the median TTIS was shorter in the baloxavir marboxil group compared with the placebo group but not compared with the oseltamivir group (see Table 5). In the subgroup of patients infected with type B virus, the median TTIS was shorter in the baloxavir marboxil group compared with both the placebo and oseltamivir group (see Table 5).
Table 5. Time to improvement of symptoms by influenza virus subtype:
| Time to Improvement of Symptoms (Hours) Median [95% CI] | |||
|---|---|---|---|
| Virus | Baloxavir marboxil | Placebo | Oseltamivir |
| A/H3 | 75.4 [62.4, 91.6] N=180 | 100.4 [88.4, 113.4] N=185 | 68.2 [53.9, 81.0] N=190 |
| B | 74.6 [67.4, 90.2) N=166 | 100.6 [82.8, 115.8] N=167 | 101.6 [90.5, 114.9] N=148 |
The median time to resolution of fever was 30.8 hours (95% CI: 28.2, 35.4) in the baloxavir marboxil group compared with 50.7 hours (95% CI: 44.6, 58.8) in the placebo group. No clear differences between the baloxavir marboxil group and the oseltamivir group were observed.
The overall incidence of influenza-related complications (death, hospitalisation, sinusitis, otitis media, bronchitis, and/or pneumonia) was 2.8% (11/388 patients) in the baloxavir marboxil group compared with 10.4% (40/386 patients) in the placebo group. The lower overall incidence of influenza-related complications in the baloxavir marboxil group compared with the placebo group was mainly driven by lower incidences of bronchitis (1.8% vs. 6.0%, respectively) and sinusitis (0.3% vs. 2.1%, respectively).
Flagstone (CP40617) was a randomised double blind Phase 3 study of baloxavir marboxil versus placebo in combination with a standard of care neuraminidase inhibitor in hospitalized patients ≥ 12 years with severe influenza. There was no statistically significant difference in the primary endpoint of time to clinical improvement vs a standard of care neuraminidase inhibitor alone (N=322 patients were eligible for the primary endpoint analysis, of which 7 were aged ≥12 years to ≤17 years). Baloxavir marboxil was well tolerated (N=363, safety population, of which 11 were ≥12 years to ≤17 years) and no new adverse drug reactions were identified.
Study 1719T0834 was a Phase 3, randomised, double-blind, multicentre study conducted in 749 subjects in Japan to evaluate the efficacy and safety of a single oral dose of baloxavir marboxil compared with placebo for post-exposure prophylaxis of influenza. Subjects were household contacts of influenza-infected index patients.
A total of 607 subjects 12 years of age and over received either baloxavir marboxil dosed according to weight, as in the treatment studies, or placebo. The majority (74%) was enrolled within 24 hours of symptom onset in the index patient group. The predominant influenza virus strains in the index patients were the A/H3 subtype (49.1%) and the A/H1N1pdm subtype (46.2%) followed by influenza B (0.9%).
The primary efficacy endpoint was the proportion of household subjects who were infected with influenza virus and presented with fever and at least one respiratory symptom in the period from Day 1 to Day 10.
There was a statistically significant reduction in the proportion of subjects with laboratory-confirmed clinical influenza from 13.6% in the placebo group to 1.9% in the baloxavir marboxil group (see Table 6).
Table 6. Proportion of subjects with influenza virus, fever, and at least one respiratory symptom (baloxavir vs placebo):
| Proportion of Subjects with Influenza Virus, Fever, and at least one Respiratory Symptom (%) mITT population | |||
| Baloxavir marboxil (95% CI) | Placebo (95% CI) | Risk Ratio (95% CI for risk ratio) | P-value |
| N=374 1.9 (0.8, 3.8) | N=375 13.6 (10.3, 17.5) | 0.14 (0.06, 0.30) | <0.0001 |
| Proportion of Subjects ≥12 years with Influenza Virus, Fever, and at least one Respiratory Symptom (%) | |||
| N=303 1.3 (0.4, 3.3) | N=304 13.2 (9.6, 17.5) | 0.10 (0.04, 0.28) | <0.0001 |
The European Medicines Agency has deferred the obligation to submit the results of studies with Xofluza in one or more subsets of the paediatric population for the treatment of influenza and prevention of influenza (see section 4.2 for information on paediatric use).
After oral administration, baloxavir marboxil is extensively converted to its active metabolite, baloxavir. The plasma concentration of baloxavir marboxil is very low or below the limit of quantitation (<0.100 ng/mL).
Following a single oral administration of 80 mg of baloxavir marboxil, the time to achieve peak plasma concentration (Tmax) is approximately 4 hours in the fasted state. The absolute bioavailability of baloxavir after oral dosing with baloxavir marboxil has not been established.
A food-effect study involving administration of baloxavir marboxil to healthy volunteers under fasting conditions and with a meal (approximately 400 to 500 kcal including 150 kcal from fat) indicated that the Cmax and AUC of baloxavir were decreased by 48% and 36%, respectively, under fed conditions. Tmax was unchanged in the presence of food. In clinical studies there were no clinically relevant differences in efficacy when baloxavir was taken with vs. without food.
In an in-vitro study, the binding of baloxavir to human serum proteins, primarily albumin, is 92.9% to 93.9%. The apparent volume of distribution of baloxavir during the terminal elimination phase (Vz/F) following a single oral administration of baloxavir marboxil is approximately 1180 litres in Caucasian subjects and 647 litres in Japanese subjects.
Baloxavir is primarily metabolised by UGT1A3 to form a glucuronide with a minor contribution from CYP3A4 to form a sulfoxide.
Based on in vitro and in vivo drug-drug interaction (DDI) studies, baloxavir marboxil and baloxavir are not expected to inhibit isozymes of the CYP or UGT families or cause relevant induction of CYP enzymes.
Based on in vitro transporter studies and in vivo DDI studies, no relevant pharmacokinetic interaction is anticipated between baloxavir marboxil or baloxavir and medicines which are substrates of the followingtransporters: OATP1B1, OATP1B3, OCT1, OCT2, OAT1, OAT3, MATE1, or MATE2K.
Following a single oral administration of 40 mg of [14C]-labeled baloxavir marboxil, the proportion of total radioactivity excreted in faeces was 80.1% of the administered dose, with the urine accounting for 14.7% (3.3% and 48.7% of the administered dose was excreted as baloxavir in urine and faeces respectively).
The apparent terminal elimination half-life (t1/2,z) of baloxavir after a single oral administration of baloxavir marboxil is 79.1 hours in Caucasian subjects.
Following single oral administration of baloxavir marboxil, baloxavir exhibits linear pharmacokinetics within the dose range of 6 mg to 80 mg.
Body weight is a significant covariate for baloxavir pharmacokinetics based on the population pharmacokinetic analysis. Dosing recommendations for baloxavir marboxil are based on body weight (see section 4.2).
A population pharmacokinetic analysis did not identify a clinically meaningful effect of gender on the pharmacokinetics of baloxavir. No dose adjustment based on gender is required.
Based on a population pharmacokinetic analysis, race is a covariate on oral clearance (CL/F) of baloxavir in addition to body weight; however, no dose adjustment of baloxavir marboxil based on race is required.
A population pharmacokinetic analysis using plasma baloxavir concentrations from clinical studies in subjects aged 12 to 64 years did not identify age as a relevant covariate on the pharmacokinetics of baloxavir.
There are limited data on the pharmacokinetics of baloxavir in paediatric patients (<12 years of age).
Pharmacokinetic data collected in 181 patients aged ≥65 years show that exposure to baloxavir in the plasma was similar to that in patients aged ≥12 to 64 years.
The effects of renal impairment on the pharmacokinetics of baloxavir marboxil or baloxavir have not been evaluated. Renal impairment is not expected to alter the elimination of baloxavir marboxil or baloxavir.
No clinically meaningful differences in the pharmacokinetics of baloxavir were observed in patients with mild or moderate hepatic impairment (Child-Pugh class A and B) compared with healthy controls with normal hepatic function.
The pharmacokinetics in patients with severe hepatic impairment have not been evaluated (see section 4.2).
Nonclinical data reveal no special hazards for humans based on conventional studies of safety pharmacology, acute and repeated dose toxicity.
Prolongation of PT and APTT were observed in rats at exposures at least equal to the human exposure based on AUC0-24hr under specific experimental conditions, i.e. when fasted and when the food was either autoclaved or radiation-treated, resulting in vitamin K limiting/deficient conditions. These effects were not observed in monkey studies up to 4 weeks duration at the highest tested dose equivalent to 8-times the human exposure based on AUC0-24hr. They are considered to be of limited clinical relevance.
Carcinogenicity studies have not been performed with baloxavir marboxil.
The pro-drug baloxavir marboxil, and its active form, baloxavir, were not considered genotoxic as they tested negative in bacterial reverse mutation tests, micronucleus tests with cultured mammalian cells, and as baloxavir marboxil was negative in an in vivo rodent micronucleus test.
Baloxavir marboxil had no effects on fertility when given orally to male and female rats at doses providing exposure equivalent to 5-times the human exposure based on AUC0-24hr.
Baloxavir marboxil did not cause malformations in rats or rabbits.
The oral embryo-foetal development study of baloxavir marboxil in rats with daily doses from gestation day 6 to 17 revealed no signs of maternal or foetal toxicity up to the highest tested dose providing exposure equivalent to 5-times the human exposure based on AUC0-24hr.
In rabbits, a dose providing exposure equivalent to 14-times the human exposure based on AUC0-24hr following the MHRD caused maternal toxicity resulting in miscarriages and significant increase in incidence of foetuses with a skeletal variation (cervical rib). The skeletal variations were reabsorbed during the growing process of adjacent cervical vertebra. A dose providing exposure equivalent to 6- times the human exposure based on AUC0-24hr in rabbits was without adverse effects.
The pre- and postnatal study in rats did not show drug-related adverse findings in dams and pups up to the highest tested dose providing exposure equivalent to 5-times the human exposure based on AUC0-24hr.
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