Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1   Pharmacodynamic properties

Pharmacotherapeutic group: antivirals for systemic use, protease inhibitors, ATC code: J05AE30 
Mechanism of action

Nirmatrelvir is a peptidomimetic inhibitor of the SARS-CoV-2 main protease (Mpro), also referred to as 3C-like protease (3CLpro) or nsp5 protease. Inhibition of the SARS-CoV-2 Mpro renders the protein incapable of processing polyprotein precursors which leads to the prevention of viral replication.

Ritonavir inhibits the CYP3A-mediated metabolism of nirmatrelvir, thereby providing increased plasma concentrations of nirmatrelvir.

Antiviral activity

Nirmatrelvir exhibited antiviral activity against SARS-CoV-2 infection of differentiated normal human bronchial epithelial (dNHBE) cells, a primary human lung alveolar epithelial cell line (EC50 value of 61.8 nM and EC90 value of 181 nM) after 3 days of drug exposure.



The antiviral activity of nirmatrelvir against the Omicron sub-variants BA.2, BA.2.12.1, BA.4, BA.4.6, BA.5, BF.7 (P252L+F294L), BF.7 (T243I), BQ.1.11, BQ.1, and XBB.1.5 was assessed in Vero E6-TMPRSS2 cells in the presence of a P-gp inhibitor. Nirmatrelvir had a median EC50 value of 83 nM (range: 39-146 nM) against the Omicron sub-variants, reflecting EC50 value fold-changes ≤ 1.5 relative to the USA-WA1/2020 isolate.

In addition, the antiviral activity of nirmatrelvir against the SARS-CoV-2 Alpha, Beta, Gamma, Delta, Lambda, Mu, and Omicron BA.1 variants was assessed in Vero E6 P-gp knockout cells. Nirmatrelvir had a median EC50 value of 25 nM (range: 16-141 nM). The Beta variant was the least susceptible variant tested, with an EC50 value fold-change of 3.7 relative to USA-WA1/2020. The other variants had EC50 value fold-changes ≤ 1.1 relative to USA-WA1/2020.

Antiviral resistance in cell cultures and biochemical assays
SARS-CoV-2 Mpro residues potentially associated with nirmatrelvir resistance have been identified using a variety of methods, including SARS-CoV-2 resistance selection, testing of recombinant SARS-CoV-2 viruses with Mpro substitutions, and biochemical assays with recombinant SARS-CoV-2 Mpro containing amino acid substitutions. Table 3 indicates Mpro substitutions and combinations of Mpro substitutions that have been observed in nirmatrelvir-selected SARS-CoV-2 in cell culture. Individual Mpro substitutions are listed regardless of whether they occurred alone or in combination with other Mpro substitutions. Note that the Mpro S301P and T304I substitutions overlap the P6 and P3 positions of the nsp5/nsp6 cleavage site located at the C-terminus of Mpro. Substitutions at other Mpro cleavage sites have not been associated with nirmatrelvir resistance in cell culture. The clinical significance of these substitutions is unknown.

Table 3:   SARS-CoV-2 Mpro amino acid substitutions selected by nirmatrelvir in cell culture (with EC50 fold change >5)
S144A (2.2-5.3), E166V (25-288), P252L (5.9), T304I (1.4-5.5), T21I+S144A (9.4), T21I+E166V (83), T21I+T304I (3.0-7.9), L50F+E166V (34-175), L50F+T304I (5.9), F140L+A173V (10.1), A173V+T304I (20.2), T21+L50F+A193P+S301P (28.8), T21I+S144A+T304I (27.8), T21I+C160F+A173V+V186A+T304I (28.5), T21I+A173V+T304I (15),
L50F+F140L+L167F+T304I (54.7)

Most single and some double Mpro amino acid substitutions identified which reduced the susceptibility of SARS-CoV-2 to nirmatrelvir resulted in an EC50 shift of < 5-fold compared to wild type SARS-CoV-2. In general, triple and some double Mpro amino acid substitutions led to EC50 changes of > 5-fold to that of wild type. The clinical significance of these substitutions needs to be further understood.

Viral load rebound

Post-treatment viral nasal RNA rebounds were observed on Day 10 and/or Day 14 in a subset of Paxlovid and placebo recipients in EPIC-HR, irrespective of COVID-19 symptoms. The incidence of viral rebound in EPIC-HR occurred in both the Paxlovid treated participants and the untreated (placebo) participants, but at a numerically higher incidence in the Paxlovid arm (6.3% vs. 4.2%).
Viral rebound and recurrence of COVID-19 symptoms were not associated with progression to severe disease including hospitalisation, death or emergence of resistance.

Clinical efficacy

The efficacy of Paxlovid is based on the interim analysis and the supporting final analysis of EPIC-HR, a phase 2/3, randomised, double-blind, placebo-controlled study in non-hospitalised, symptomatic adult participants with a laboratory confirmed diagnosis of SARS-CoV-2 infection.
Eligible participants were 18 years of age and older with at least 1 of the following risk factors for 

progression to severe disease: diabetes, overweight (BMI > 25 kg/m2), chronic lung disease (including asthma), chronic kidney disease, current smoker, immunosuppressive disease or immunosuppressive treatment, cardiovascular disease, hypertension, sickle cell disease, neurodevelopmental disorders, active cancer, medically-related technological dependence, or were 60 years of age and older regardless of comorbidities. Participants with COVID-19 symptom onset of ≤ 5 days were included in the study. The study excluded individuals with a history of prior COVID-19 infection or vaccination.

Participants were randomised (1:1) to receive Paxlovid (nirmatrelvir/ritonavir 300 mg/100 mg) or placebo orally every 12 hours for 5 days. The primary efficacy endpoint was the proportion of participants with COVID-19 related hospitalisation or death from any cause through Day 28. The analysis was conducted in the modified intent-to-treat (mITT) analysis set (all treated participants with onset of symptoms ≤ 3 days who at baseline did not receive nor were expected to receive COVID-19 therapeutic mAb treatment), the mITT1 analysis set (all treated participants with onset of symptoms ≤ 5 days who at baseline did not receive nor were expected to receive COVID-19 therapeutic mAb treatment), and the mITT2 analysis set (all treated participants with onset of symptoms ≤ 5 days).

A total of 2113 participants were randomised to receive either Paxlovid or placebo. At baseline, mean age was 45 years with 12% of participants 65 years of age and older (3% were 75 years of age and older); 51% were male; 71% were White, 4% were Black or African American, and 15% were Asian; 41% were Hispanic or Latino; 67% of participants had onset of symptoms ≤ 3 days before initiation of study treatment; 80% had a BMI > 25 kg/m2 (36% a BMI > 30 kg/m2); 11% had diabetes mellitus; less than 1% of the study population had immune deficiency, 49% of participants were serological negative at baseline and 49% were serological positive. The mean (SD) baseline viral load was 4.71 log10 copies/mL (2.89); 27% of participants had a baseline viral load of > 10^7 (copies/mL);
6.0% of participants either received or were expected to receive COVID-19 therapeutic mAb treatment at the time of randomisation and were excluded from the mITT and mITT1 analyses. The primary SARS-CoV-2 variant across both treatment arms was Delta (99%), mostly clade 21J.

The baseline demographic and disease characteristics were balanced between the Paxlovid and placebo groups.

The determination of primary efficacy was based on a planned interim analysis of 754 participants in mITT population. The estimated risk reduction was -6.5% with unadjusted 95% CI of (-9.3%, -3.7%) and a 95% CI of (-10.92%, -2.09%) when adjusting for multiplicity. The 2-sided p-value was < 0.0001 with 2-sided significance level of 0.002.

Table 4 provides results of the primary endpoint in the mITT1 analysis population for the full data set at final study completion.




Table 4:    Efficacy results in non-hospitalised adults with COVID-19 dosed within 5 days of symptom onset who did not receive COVID-19 mAb treatment at baseline (mITT1 analysis setb)
Paxlovid                      Placebo
(N=977)                       (N=989)
COVID-19 related hospitalisation or death from any cause through Day 28 n (%)                                                   9 (0.9%)                     64 (6.5%) Reduction relative to placeboa (95% CI), %         -5.64 (-7.31, -3.97) p-value                                                 < 0.0001
All-cause mortality through Day 28, %                       0                        12 (1.2%) Abbreviations: CI=confidence interval; COVID-19=Coronavirus Disease 2019; mAb=monoclonal antibody; mITT1=modified intent-to-treat 1 (all participants randomly assigned to study intervention, who took at least 1 dose of study intervention, with at least 1 post-baseline visit through Day 28, who at baseline did not receive nor were expected to receive COVID-19 therapeutic mAb treatment and were treated ≤ 5 days after COVID-19 symptom onset).
a. The estimated cumulative proportion of participants hospitalised or death by Day 28 was calculated for each treatment group using the Kaplan-Meier method, where participants without hospitalisation and death status through Day 28 were censored at the time of study discontinuation.
b. Data analysis set was updated after post-hoc removal of data for 133 participants due to GCP quality issues

The estimated risk reduction was -6.1% with 95% CI of (-8.2%, -4.1%) in participants dosed within 3 days of symptom onset, and -4.6% with 95% CI of (-7.4%, -1.8%) in the mITT1 subset of participants dosed > 3 days from symptom onset.

Consistent results were observed in the final mITT and mITT2 analysis populations. A total of 1318 participants were included in the mITT analysis population. The event rates were 5/671 (0.75%) in the Paxlovid group, and 44/647 (6.80%) in the placebo group.

Table 5:     Progression of COVID-19 (hospitalisation or death) through Day 28 in symptomatic adults at increased risk of progression to severe illness; mITT1 analysis set Paxlovid 300 mg/100 mg                 Placebo
Number of patients                                                   N=977                         N=989 Serology Negative                                                    n=475                         n=497 Patients with hospitalisation or deatha (%)                         8 (1.7%)                     56 (11.3%) Estimated proportion over 28 days [95% CI], %                   1.72 (0.86, 3.40)            11.50 (8.97, 14.68) Estimated reduction relative to placebo (95% CI)             -9.79 (-12.86, -6.72) Serology Positive                                                    n=490                         n=479 a
Patients with hospitalisation or death (%)                          1 (0.2%)                      8 (1.7%) Estimated proportion over 28 days [95% CI], %                   0.20 (0.03, 1.44)             1.68 (0.84, 3.33) Estimated reduction relative to placebo (95% CI)              -1.5 (-2.70, -0.25) Abbreviations: CI=confidence interval; COVID-19=Coronavirus Disease 2019; mITT1=modified intent-to-treat 1 (all participants randomly assigned to study intervention, who took at least 1 dose of study intervention, who at baseline did not receive nor were expected to receive COVID-19 therapeutic monoclonal antibody treatment, and were treated ≤ 5 days after COVID-19 symptom onset).
Seropositivity was defined if results were positive in a serological immunoassay specific for host antibodies to either S or N viral proteins.
The difference between the proportions in the 2 treatment groups and its 95% confidence interval based on normal approximation of the data are presented.
a.     COVID-19 related hospitalisation or death from any cause.

Efficacy results for mITT1 were consistent across subgroups of participants including age (≥ 65 years) and BMI (BMI > 25 and BMI > 30) and diabetes.




Pharmacokinetic Properties

5.2   Pharmacokinetic properties

The pharmacokinetics of nirmatrelvir/ritonavir have been studied in healthy participants and in participants with mild-to-moderate COVID-19.

Ritonavir is administered with nirmatrelvir as a pharmacokinetic enhancer resulting in higher systemic concentrations and longer half-life of nirmatrelvir.

Upon repeat-dose of nirmatrelvir/ritonavir 75 mg/100 mg, 250 mg/100 mg, and 500 mg/100 mg administered twice daily, the increase in systemic exposure at steady-state appears to be less than dose proportional. Multiple dosing over 10 days achieved steady-state on Day 2 with approximately 2-fold accumulation. Systemic exposures on Day 5 were similar to Day 10 across all doses.

Absorption

Following oral administration of nirmatrelvir/ritonavir 300 mg/100 mg after a single dose, the geometric mean nirmatrelvir Cmax and AUCinf at steady-state was 2.21 µg/mL and 23.01 µg*hr/mL, respectively. The median time to Cmax (Tmax) was 3.00 hrs. The arithmetic mean terminal elimination half-life was 6.1 hours.

Following oral administration of nirmatrelvir/ritonavir 300 mg/100 mg after a single dose, the geometric mean ritonavir Cmax and AUCinf was 0.36 µg/mL and 3.60 µg*hr/mL, respectively. The median time to Cmax (Tmax) was 3.98 hrs. The arithmetic mean terminal elimination half-life was 6.1 hours.

Effect of food on oral absorption
Dosing with a high fat meal increased the exposure of nirmatrelvir (approximately 61% increase in mean Cmax and 20% increase in mean AUClast) relative to fasting conditions following administration of 300 mg nirmatrelvir (2 × 150 mg)/100 mg ritonavir tablets.

Distribution

The protein binding of nirmatrelvir in human plasma is approximately 69%.
The protein binding of ritonavir in human plasma is approximately 98-99%.

Biotransformation

In vitro studies assessing nirmatrelvir without concomitant ritonavir suggest that nirmatrelvir is primarily metabolised by cytochrome P450 (CYP) 3A4. However, administration of nirmatrelvir with ritonavir inhibits the metabolism of nirmatrelvir. In plasma, the only medicinal product-related entity observed was unchanged nirmatrelvir. Minor oxidative metabolites were observed in the faeces and urine.

In vitro studies utilising human liver microsomes have demonstrated that CYP3A is the major isoform involved in ritonavir metabolism, although CYP2D6 also contributes to the formation of oxidation metabolite M–2.

Elimination

The primary route of elimination of nirmatrelvir when administered with ritonavir was renal excretion of intact medicinal product. Approximately 49.6% and 35.3% of the administered dose of nirmatrelvir 300 mg was recovered in urine and faeces, respectively. Nirmatrelvir was the predominant 

drug-related entity with small amounts of metabolites arising from hydrolysis reactions in excreta. In plasma, the only drug-related entity quantifiable was unchanged nirmatrelvir.

Human studies with radiolabelled ritonavir demonstrated that the elimination of ritonavir was primarily via the hepatobiliary system; approximately 86% of radiolabel was recovered from stool, part of which is expected to be unabsorbed ritonavir.

Specific populations

Age and gender
The pharmacokinetics of nirmatrelvir/ritonavir based on age and gender have not been evaluated.
Racial or ethnic groups
Systemic exposure in Japanese participants was numerically lower but not clinically meaningfully different than those in Western participants.

Patients with renal impairment
Compared to healthy controls with no renal impairment, the Cmax and AUC of nirmatrelvir in patients with mild renal impairment was 30% and 24% higher, in patients with moderate renal impairment was 38% and 87% higher, and in patients with severe renal impairment was 48% and 204% higher, respectively.

Patients with hepatic impairment
Compared to healthy controls with no hepatic impairment, the pharmacokinetics of nirmatrelvir in participants with moderate hepatic impairment was not significantly different. Adjusted geometric mean ratio (90% CI) of AUCinf and Cmax of nirmatrelvir comparing moderate hepatic impairment (test) to normal hepatic function (reference) was 98.78% (70.65%, 138.12%) and 101.96% (74.20%, 140.11%), respectively.

Nirmatrelvir/ritonavir has not been studied in patients with severe hepatic impairment.

Interaction studies conducted with nirmatrelvir/ritonavir
CYP3A4 was the major contributor to the oxidative metabolism of nirmatrelvir when nirmatrelvir was tested alone in human liver microsomes. Ritonavir is an inhibitor of CYP3A and increases plasma concentrations of nirmatrelvir and other drugs that are primarily metabolised by CYP3A. Despite being coadministered with ritonavir as a pharmacokinetic enhancer, there is potential for strong inhibitors and inducers to alter the pharmacokinetics of nirmatrelvir.

Nirmatrelvir does not reversibly inhibit CYP2B6, CYP2D6, CYP2C9, CYP2C19, CYP2C8, or CYP1A2 in vitro at clinically relevant concentrations. In vitro study results showed nirmatrelvir may be inducer of CYP3A4, CYP2B6, CYP2C8 and CYP2C9. The clinical relevance is unknown. Based on in vitro data, nirmatrelvir has a low potential to inhibit BCRP, MATE1, MATE2K, OAT1, OAT3, OATP1B3, OCT1 and OCT2. There is a potential for nirmatrelvir to inhibit MDR1 and OATP1B1 at clinically relevant concentrations.

The effect on the pharmacokinetics of nirmatrelvir/ritonavir was assessed with itraconazole (CYP3A inhibitor) and carbamazepine (CYP3A inducer). The test/reference ratios of the adjusted geometric means for nirmatrelvir AUCinf and Cmax were 44.50% and 56.82%, respectively, following nirmatrelvir/ritonavir 300 mg/100 mg coadministration with multiple oral doses of carbamazepine.
The test/reference ratios of the adjusted geometric means for nirmatrelvir AUCtau and Cmax were 138.82% and 118.57%, respectively, when nirmatrelvir/ritonavir was coadministered with multiple doses of itraconazole as compared to nirmatrelvir/ritonavir administered alone.




The effect of nirmatrelvir/ritonavir on other drugs was assessed with midazolam (CYP3A substrate) and dabigatran (P-gp substrate). The test/reference ratios of the adjusted geometric means for midazolam AUCinf and Cmax were 1430.02% and 368.33%, respectively, when midazolam was coadministered with multiple doses of nirmatrelvir/ritonavir compared to midazolam administered alone. The test/reference ratios of the adjusted geometric means for dabigatran AUCinf and Cmax were 194.47% and 233.06%, respectively, following dabigatran administration with multiple doses of nirmatrelvir/ritonavir as compared to administration of dabigatran alone.