Innovative Randomized Phase I Study and Dosing Regimen Selection to Accelerate and Inform Pivotal COVID-19 Trial of Nirmatrelvir

Nirmatrelvir exerts distinct antiviral potency against different human coronaviruses

Nirmatrelvir is the main component of Paxlovid, an oral antiviral drug approved for the treatment of COVID-19 caused by SARS-COV-2 infection. Nirmatrelvir targets the main protease (M^pro), which is substantially conserved among different coronaviruses. Here, our molecular docking analysis indicates comparable affinity of nirmatrelvir binding to the M^pro enzymes of SARS-CoV-2 and three seasonal coronaviruses (OC43, 229E and NL63). However, in cell culture models, we found that nirmatrelvir potently inhibited SARS-CoV-2, OC43 and 229E, but not NL63. The insensitivity of NL63 to nirmatrelvir treatment was demonstrated at both viral replication and infectious titer levels. The antiviral activity of nirmatrelvir against OC43 and 229E was further confirmed in human airway organoids. The combination of nirmatrelvir and molnupiravir exerted differential patterns of antiviral response against OC43 and 229E. These results revealed disparities in the ability of nirmatrelvir to inhibit different coronaviruses, and caution against repurposing of nirmatrelvir as a pan-coronavirus treatment.

An update on COVID-19: SARS-CoV-2 variants, antiviral drugs, and vaccines

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly contagious and pathogenic virus that first appeared in late December 2019. This SARS-CoV-2 causes an infection of an acute respiratory disease called "coronavirus infectious disease-2019 (COVID-19). The World Health Organization (WHO) declared this SARS-CoV-2 outbreak a great pandemic on March 11, 2020. As of January 31, 2023, SARS-CoV-2 recorded more than 67 million cases and over 6 million deaths. Recently, novel mutated variants of SARS-CoV are also creating a serious health concern worldwide, and the future novel variant is still mysterious. As infection cases of SARS-CoV-2 are increasing daily, scientists are trying to combat the disease using numerous antiviral drugs and vaccines against SARS-CoV-2. To our knowledge, this is the first comprehensive review that summarized the dynamic nature of SARS-CoV-2 transmission, SARS-CoV-2 variants (a variant of concern and variant of interest), antiviral drugs and vaccines utilized against SARS-CoV-2 at a glance. Hopefully, this review will enable the researcher to gain knowledge on SARS-CoV-2 variants and vaccines, which will also pave the way to identify efficient novel vaccines against forthcoming SARS-CoV-2 strains.

Species differences in plasma protein binding of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease inhibitor nirmatrelvir

Plasma protein binding (PPB) studies on the SARS-CoV-2 main protease inhibitor nirmatrelvir revealed considerable species differences primarily in dog and rabbit, which prompted further investigations into the biochemical basis for these differences.The unbound fraction (f_u) of nirmatrelvir in dog and rabbit plasma was concentration (2-200 µM)-dependent (dog f_u,p 0.024-0.69, rabbit f_u,p 0.010-0.82). Concentration (0.1-100 µM)-dependent binding in serum albumin (SA) (f_u,SA 0.040-0.82) and alpha-1-acid glycoprotein (AAG) (f_u,AAG 0.050-0.64) was observed in dogs. Nirmatrelvir showed minimal binding to rabbit SA (1-100 µM: f_u,SA 0.70-0.79), while binding to rabbit AAG was concentration-dependent (0.1-100 µM: f_u,AAG 0.024-0.66). In contrast, nirmatrelvir (2 µM) revealed minimal binding (f_u,AAG 0.79-0.88) to AAG from rat and monkeys. Nirmatrelvir showed minimal-to-moderate binding to SA (1-100 µM; f_u,SA 0.70-1.0) and AAG (0.1-100 µM; f_u,AAG 0.48-0.58) from humans across tested concentrations.Nirmatrelvir molecular docking studies using published crystal structures and homology models of human and preclinical species SA and AAG were used to rationalise the species differences to plasma proteins. This suggested that species differences in PPB are primarily driven by molecular differences in albumin and AAG resulting in differences in binding affinity.

Paxlovid (Nirmatrelvir/Ritonavir): A new approach to Covid-19 therapy?

Despite the need for novel, effective therapeutics for the COVID-19 pandemic, no curative regimen is yet available, therefore patients are forced to rely on supportive and nonspecific therapies. Some SARS-CoV-2 proteins, like the 3C-like protease (3CLpro) or the major protease (Mpro), have been identified as promising targets for antiviral drugs. The Mpro has major a role in protein processing as well as pathogenesis of the virus, and could be a useful therapeutic target. The antiviral drug nirmatrelvir can keep SARS-CoV-2 from replicating through inhibiting Mpro. Nirmatrelvir was combined with another HIV protease inhibitor, ritonavir, to create Paxlovid (Nirmatrelvir/Ritonavir). The metabolizing enzyme cytochrome P450 3 A is inhibited by ritonavir to lengthen the half-life of nirmatrelvir, so rintonavir acts as a pharmacological enhancer. Nirmatrelvir exhibits potent antiviral activity against current coronavirus variants, despite significant alterations in the SARS-CoV-2 viral genome. Nevertheless, there are still several unanswered questions. This review summarizes the current literature on nirmatrelvir and ritonavir efficacy in treating SARS-CoV-2 infection, and also their safety and possible side effects.

Early Clinical Development of Lufotrelvir as a Potential Therapy for COVID-19

Lufotrelvir was designed as a first in class 3CL protease inhibitor to treat COVID-19. Development of lufotrelvir was challenged by its relatively poor stability due to its propensity to epimerize and degrade. Key elements of process development included improvement of the supply routes to the indole and lactam fragments, a Claisen addition to homologate the lactam, and a subsequent phosphorylation reaction to prepare the prodrug as well as identification of a DMSO solvated form of lufotrelvir to enable long-term storage. As a new approach to preparing the indole fragment, a Cu-catalyzed C-O coupling using oxalamide ligands was demonstrated. The control of process-related impurities was essential to accommodate the parenteral formulation. Isolation of an MEK solvate followed by the DMSO solvate ensured that all impurities were controlled appropriately.

Nirmatrelvir plus ritonavir in COVID-19: a profile of its use

Oral nirmatrelvir plus ritonavir (Paxlovid^™) is an effective treatment option for coronavirus disease 2019 (COVID-19), the illness caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Nirmatrelvir inhibits the main protease of SARS-CoV-2, with ritonavir acting as a pharmacokinetic booster. In the phase II/III EPIC-HR trial, nirmatrelvir plus ritonavir reduced the risk of progression to severe COVID-19 in symptomatic, unvaccinated, non-hospitalized adults with mild-to-moderate COVID-19 at high risk for progression to severe disease. The incidence of COVID-19-related hospitalization or death through day 28 was significantly lower with nirmatrelvir plus ritonavir than with placebo. The efficacy of nirmatrelvir plus ritonavir has also been demonstrated in the real-world setting. Nirmatrelvir plus ritonavir is generally well tolerated, with most adverse events being of mild or moderate severity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40267-022-00971-1.

Theranostics for COVID-19 Antiviral Drugs: Prospects and Challenges for Worldwide Precision/Personalized Medicine

Coronavirus disease 2019 (COVID-19) is a systemic disease that impacts multiple organ systems with a complex clinical presentation and outcomes that can vary from person to person and between populations. To optimize COVID-19 treatment outcomes, and in light of the availability of antiviral drugs, there is a need for greater attention to the field of theranostics, the fusion of therapeutics and diagnostics. Theranostics tests would be invaluable, we suggest in this expert review, so as to optimize the efficacy and safety of current and future antiviral drugs against COVID-19. Theranostics would also assist in the design and implementation of clinical trials with antiviral drug candidates. We discuss here theranostics considering drugs such as remdesivir, Paxlovid™, and molnupiravir. All in all, we underscore that theranostics as a concept and practice is essential for efficient and safe health interventions against COVID-19 and other ecological crises in the 21st century.

A proof-of-concept study on the genomic evolution of Sars-Cov-2 in molnupiravir-treated, paxlovid-treated and drug-naïve patients

Little is known about SARS-CoV-2 evolution under Molnupiravir and Paxlovid, the only antivirals approved for COVID-19 treatment. By investigating SARS-CoV-2 variability in 8 Molnupiravir-treated, 7 Paxlovid-treated and 5 drug-naïve individuals at 4 time-points (Days 0-2-5-7), a higher genetic distance is found under Molnupiravir pressure compared to Paxlovid and no-drug pressure (nucleotide-substitutions/site mean±Standard error: 18.7 × 10^-4 ± 2.1 × 10^-4 vs. 3.3 × 10^-4 ± 0.8 × 10^-4 vs. 3.1 × 10^-4 ± 0.8 × 10^-4, P = 0.0003), peaking between Day 2 and 5. Molnupiravir drives the emergence of more G-A and C-T transitions than other mutations (P = 0.031). SARS-CoV-2 selective evolution under Molnupiravir pressure does not differ from that under Paxlovid or no-drug pressure, except for orf8 (dN > dS, P = 0.001); few amino acid mutations are enriched at specific sites. No RNA-dependent RNA polymerase (RdRp) or main proteases (Mpro) mutations conferring resistance to Molnupiravir or Paxlovid are found. This proof-of-concept study defines the SARS-CoV-2 within-host evolution during antiviral treatment, confirming higher in vivo variability induced by Molnupiravir compared to Paxlovid and drug-naive, albeit not resulting in apparent mutation selection.

Small molecules in the treatment of COVID-19

The outbreak of COVID-19 has become a global crisis, and brought severe disruptions to societies and economies. Until now, effective therapeutics against COVID-19 are in high demand. Along with our improved understanding of the structure, function, and pathogenic process of SARS-CoV-2, many small molecules with potential anti-COVID-19 effects have been developed. So far, several antiviral strategies were explored. Besides directly inhibition of viral proteins such as RdRp and M^pro, interference of host enzymes including ACE2 and proteases, and blocking relevant immunoregulatory pathways represented by JAK/STAT, BTK, NF-κB, and NLRP3 pathways, are regarded feasible in drug development. The development of small molecules to treat COVID-19 has been achieved by several strategies, including computer-aided lead compound design and screening, natural product discovery, drug repurposing, and combination therapy. Several small molecules representative by remdesivir and paxlovid have been proved or authorized emergency use in many countries. And many candidates have entered clinical-trial stage. Nevertheless, due to the epidemiological features and variability issues of SARS-CoV-2, it is necessary to continue exploring novel strategies against COVID-19. This review discusses the current findings in the development of small molecules for COVID-19 treatment. Moreover, their detailed mechanism of action, chemical structures, and preclinical and clinical efficacies are discussed.

Liver tests abnormalities with licensed antiviral drugs for COVID-19: a narrative review

INTRODUCTION

Liver involvement in COVID-19 is multifactorial, and the three potential mechanisms are direct hepatocyte viral damage, vascular or cellular damage during the cytokine storm of severe COVID-19 and drug-induced liver injury. To date, three antivirals are licensed for the treatment of COVID-19 by most guidelines: remdesivir, molnupiravir, and ritonavir-boosted nirmatrelvir.

AREAS COVERED

We performed a narrative review about the hepatic safety profile of the three antivirals licensed for COVID-19 treatment. We used data about hepatobiliary adverse events from English-language randomized clinical trials (RCTs).

EXPERT OPINION

Remdesivir was found to be potentially hepatotoxic, and liver biochemistry abnormalities were common (2-34%) but mild and reversible. Molnupiravir exhibits a favorable safety profile and the increase in aminotransferases was usually mild and reversible (up to 11% of patients in one study). Ritonavir-boosted nirmatrelvir is potentially hepatotoxic, but in the only phase 3 RCT there were no safety issues and aspartate aminotransferase/alanine aminotransferase levels increase did not exceed 2.4% of patients. All antivirals have a favorable safety profile, but they are not sufficiently studied in patients with underlying chronic kidney or liver disease. In this special populations, antivirals should be used with caution and careful monitoring during treatment should be pursued on a case-by-case basis.

Metabolism and Excretion of Nirmatrelvir in Humans Using Quantitative Fluorine Nuclear Magnetic Resonance Spectroscopy: A Novel Approach for Accelerating Drug Development

Typically human absorption, distribution, metabolism, and excretion (ADME) studies are executed using radiolabeled (e.g., carbon-14) material, the synthesis of which is a time-consuming activity. In this study, we were able to assess the metabolism and excretion of unlabeled nirmatrelvir (PF-07321332) within the first-in-human study via a novel application of quantitative fluorine (¹⁹ F) nuclear magnetic resonance (NMR) spectroscopy in place of a standard radiolabel ADME study. Six healthy participants received a single 300-mg oral dose of nirmatrelvir (in combination with ritonavir), and excreta were collected up to 10 days. Virtually all drug-related material was recovered within 5 days, and mass balance was achieved with 84.9 ± 8.9% (range = 70.7-95.5%) of the administered dose recovered in urine and feces. The excretion of fluorine-containing material in urine and feces was 47.0% and 33.7%, respectively. Unchanged nirmatrelvir represented 82.5% of the normalized drug-related material with a carboxylic acid metabolite M5, derived from hydrolysis of the P2 amide bond, present at 12.1% of dose. Nirmatrelvir was the only drug-related entity observed in plasma. Approximately 4.2% of the dose was excreted as metabolite M8 (measured by liquid chromatography-mass spectrometry), which was ¹⁹ F NMR silent due to hydrolysis of the trifluoroacetamide moiety. Hydrolysis of nirmatrelvir to M5 and M8 was shown to occur in cultures of human gut microflora. This successful demonstration of quantitative ¹⁹ F NMR spectroscopy to establish the mass-balance, excretion, and metabolic profile of nirmatrelvir offers an advantageous means to execute human ADME studies for fluorine-containing compounds early in drug development.

Progress on COVID-19 Chemotherapeutics Discovery and Novel Technology

COVID-19 is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel highly contagious and pathogenic coronavirus that emerged in late 2019. SARS-CoV-2 spreads primarily through virus-containing droplets and small particles of air pollution, which greatly increases the risk of inhaling these virus particles when people are in close proximity. COVID-19 is spreading across the world, and the COVID-19 pandemic poses a threat to human health and public safety. To date, there are no specific vaccines or effective drugs against SARS-CoV-2. In this review, we focus on the enzyme targets of the virus and host that may be critical for the discovery of chemical compounds and natural products as antiviral drugs, and describe the development of potential antiviral drugs in the preclinical and clinical stages. At the same time, we summarize novel emerging technologies applied to the research on new drug development and the pathological mechanisms of COVID-19.

Paxlovid-like nirmatrelvir/ritonavir fails to block SARS-CoV-2 transmission in ferrets

Despite the continued spread of SARS-CoV-2 and emergence of variants of concern (VOC) that are capable of escaping preexisting immunity, therapeutic options are underutilized. In addition to preventing severe disease in high-risk patients, antivirals may contribute to interrupting transmission chains. The FDA has granted emergency use authorizations for two oral drugs, molnupiravir and paxlovid. Initial clinical trials suggested an efficacy advantage of paxlovid, giving it a standard-of-care-like status in the United States. However, recent retrospective clinical studies suggested a more comparable efficacy of both drugs in preventing complicated disease and case-fatalities in older adults. For a direct efficacy comparison under controlled conditions, we assessed potency of both drugs against SARS-CoV-2 in two relevant animal models; the Roborovski dwarf hamster model for severe COVID-19 in high-risk patients and the ferret model of upper respiratory tract disease and transmission. After infection of dwarf hamsters with VOC omicron, paxlovid and molnupiravir were efficacious in mitigating severe disease and preventing death. However, a pharmacokinetics-confirmed human equivalent dose of paxlovid did not significantly reduce shed SARS-CoV-2 titers in ferrets and failed to block virus transmission to untreated direct-contact ferrets, whereas transmission was fully suppressed in a group of animals treated with a human-equivalent dose of molnupiravir. Prophylactic administration of molnupiravir to uninfected ferrets in direct contact with infected animals blocked productive SARS-CoV-2 transmission, whereas all contacts treated with prophylactic paxlovid became infected. These data confirm retrospective reports of similar therapeutic benefit of both drugs for older adults, and reveal that treatment with molnupiravir, but not paxlovid, may be suitable to reduce the risk of SARS-CoV-2 transmission.

Advances And Challenges In Using Nirmatrelvir And Its Derivatives Against Sars-Cov-2 Infection

On 22 December 2021, the United States Food and Drug Administration (FDA) approved the first M^pro inhibitor, i.e., oral antiviral nirmatrelvir (PF-07321332)/ritonavir (Paxlovid), for the treatment of early severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Nirmatrelvir inhibits SARS-CoV-2 infection, but high doses or long-term treatment may cause embryonic developmental toxicity and changes in host gene expression. The chiral structure of nirmatrelvir plays a key role in its antiviral activity. Ritonavir boosts the efficacy of nirmatrelvir by inactivating cytochrome P450 3A4 (CYP3A4) expression and occupying the plasma protein binding sites. Multidrug resistance protein 1 (MDR1) inhibitors may increase the efficacy of nirmatrelvir. However, paxlovid has many contraindications. Some patients treated with paxlovid experience a second round of coronavirus disease 2019 (COVID-19) symptoms soon after recovery. Interestingly, the antiviral activity of nirmatrelvir metabolites, such as compounds 12−18, is similar to or higher than that of nirmatrelvir. Herein, we review the advances and challenges in using nirmatrelvir and its derivatives with the aim of providing knowledge to drug developers and physicians in the fight against COVID-19.

A UPLC-MS/MS Method for Plasma Biological Monitoring of Nirmatrelvir and Ritonavir in the Context of SARS-CoV-2 Infection and Application to a Case

Nirmatrelvir/ritonavir association has been authorized for conditional use in the treatment of COVID-19, especially in solid-organ transplant recipients who did not respond to vaccine and are still at high risk of severe disease. This combination remains at risk of drug interactions with immunosuppressants, so monitoring drug levels seems necessary. After a simple protein precipitation of plasma sample, analytes were analyzed using an ultrahigh performance liquid chromatography system coupled with tandem mass spectrometry in a positive ionization mode. Validation procedures were based on the guidelines on bioanalytical methods issued by the European Medicine Agency. The analysis time was 4 min per run. The calibration curves were linear over the range from 10 to 1000 ng/mL for ritonavir and 40 to 4000 ng/mL for nirmatrelvir, with coefficients of correlation above 0.99 for all analytes. Intra-/interday imprecisions were below 10%. The analytical method also meets criteria of matrix effect, carryover, dilution integrity, and stability. In the context of a SARS-CoV-2 infection in a renal transplant recipient, we present a case of tacrolimus overdose with serious adverse events despite discontinuation of nirmatrelvir and ritonavir. The patient had still effective concentrations of nirmatrelvir and tacrolimus 4 days after drug discontinuation. This method was successfully applied for therapeutic drug monitoring in clinical practice.

SARS-CoV-2 Variants, Current Vaccines and Therapeutic Implications for COVID-19

Over the past two years, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused hundreds of millions of infections, resulting in an unprecedented pandemic of coronavirus disease 2019 (COVID-19). As the virus spreads through the population, ongoing mutations and adaptations are being discovered. There is now substantial clinical evidence that demonstrates the SARS-CoV-2 variants have stronger transmissibility and higher virulence compared to the wild-type strain of SARS-CoV-2. Hence, development of vaccines against SARS-CoV-2 variants to boost individual immunity has become essential. However, current treatment options are limited for COVID-19 caused by the SARS-CoV-2 variants. In this review, we describe current distribution, variation, biology, and clinical features of COVID-19 caused by SARS-CoV-2 variants (including Alpha (B.1.1.7 Lineage) variant, Beta (B.1.351 Lineage) variant, Gamma (P.1 Lineage) variant, Delta (B.1.617.2 Lineage) variant, and Omicron (B.1.1.529 Lineage) variant and others. In addition, we review currently employed vaccines in clinical or preclinical phases as well as potential targeted therapies in an attempt to provide better preventive and treatment strategies for COVID-19 caused by different SARS-CoV-2 variants.

A critical overview of current progress for COVID-19: development of vaccines, antiviral drugs, and therapeutic antibodies

The novel coronavirus disease (COVID-19) pandemic remains a global public health crisis, presenting a broad range of challenges. To help address some of the main problems, the scientific community has designed vaccines, diagnostic tools and therapeutics for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The rapid pace of technology development, especially with regard to vaccines, represents a stunning and historic scientific achievement. Nevertheless, many challenges remain to be overcome, such as improving vaccine and drug treatment efficacies for emergent mutant strains of SARS-CoV-2. Outbreaks of more infectious variants continue to diminish the utility of available vaccines and drugs. Thus, the effectiveness of vaccines and drugs against the most current variants is a primary consideration in the continual analyses of clinical data that supports updated regulatory decisions. The first two vaccines granted Emergency Use Authorizations (EUAs), BNT162b2 and mRNA-1273, still show more than 60% protection efficacy against the most widespread current SARS-CoV-2 variant, Omicron. This variant carries more than 30 mutations in the spike protein, which has largely abrogated the neutralizing effects of therapeutic antibodies. Fortunately, some neutralizing antibodies and antiviral COVID-19 drugs treatments have shown continued clinical benefits. In this review, we provide a framework for understanding the ongoing development efforts for different types of vaccines and therapeutics, including small molecule and antibody drugs. The ripple effects of newly emergent variants, including updates to vaccines and drug repurposing efforts, are summarized. In addition, we summarize the clinical trials supporting the development and distribution of vaccines, small molecule drugs, and therapeutic antibodies with broad-spectrum activity against SARS-CoV-2 strains.

A novel cyclic γ-AApeptide-based long-acting pan-coronavirus fusion inhibitor with potential oral bioavailability by targeting two sites in spike protein

The receptor-binding domain (RBD) in S1 subunit and heptad repeat 1 (HR1) domain in S2 subunit of SARS-CoV-2 spike (S) protein are the targets of neutralizing antibodies (nAbs) and pan-coronavirus (CoV) fusion inhibitory peptides, respectively. However, neither nAb- nor peptide-based drugs can be used orally. In this study, we screened a one-bead-two-compound (OBTC) cyclic γ-AApeptide library against SARS-CoV-2 S protein and identified a hit: S-20 with potent membrane fusion inhibitory activity, but moderate selectivity index (SI). After modification, one derivative, S-20-1, exhibited improved fusion inhibitory activity and SI (>1000). S-20-1 could effectively inhibit infection by pseudotyped and authentic SARS-CoV-2 and pseudotyped variants of concern (VOCs), including B.1.617.2 (Delta) and B.1.1.529 (Omicron), as well as MERS-CoV, SARS-CoV, HCoV-OC43, HCoV-229E, and HCoV-NL63. It could also inhibit infection of a pseudotyped SARS-related coronavirus WIV1 (SARSr-CoV-WIV1) from bats. Intranasal application of S-20-1 to mice before or after challenge with HCoV-OC43 or SARS-CoV-2 provided significant protection from infection. Importantly, S-20-1 was highly resistant to proteolytic degradation, had long half-life, and possessed favorable oral bioavailability. Mechanistic studies suggest that S-20-1 binds with high affinity to RBD in S1 and HR1 domain in S2 of SARS-CoV-2 S protein. Thus, with its pan-CoV fusion and entry inhibitory activity by targeting two sites in S protein, desirable half-life, and promising oral bioavailability, S-20-1 is a potential candidate for further development as a novel therapeutic and prophylactic drug against infection by SARS-CoV-2 and its variants, as well as future emerging and reemerging CoVs.

Association of Nirmatrelvir/Ritonavir Treatment on Upper Respiratory Severe Acute Respiratory Syndrome Coronavirus 2 Reverse Transcription-Polymerase Chain Reaction (SARS-Cov-2 RT-PCR) Negative Conversion Rates Among High-Risk Patients With Coronavirus Disease 2019 (COVID-19)

BACKGROUND

Acceleration of negative respiratory conversion of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in patients with coronavirus disease 2019 (COVID-19) might reduce viral transmission. Nirmatrelvir/ritonavir is a new antiviral agent recently approved for treatment of COVID-19 that has the potential to facilitate negative conversion.

METHODS

A cohort of hospitalized adult patients with mild-to-moderate COVID-19 who had a high risk for progression to severe disease were studied. These patients presented with COVID-19 symptoms between 5 March and 5 April 2022. The time from positive to negative upper respiratory reverse transcription-polymerase chain reaction (RT-PCR) conversion was assessed by Kaplan-Meier plots and Cox proportional hazards regression with the adjustment for patients' baseline demographic and clinical characteristics.

RESULTS

There were 258 patients treated with nirmatrelvir/ritonavir and 224 nontreated patients who had mild-to-moderate COVID-19. The median (interquartile range) time for patients who converted from positive to negative RT-PCR was 10 days (7-12 days) in patients treated ≤5 days after symptom onset and 17 days (12-21 days) in nontreated patients. The proportions of patients with a negative conversion at day 15 were 89.7% and 42.0% in treated patients and nontreated patients, corresponding to a hazard ratio of 4.33 (95% confidence interval, 3.31-5.65). Adjustment for baseline differences between the groups had little effect on the association. Subgroup analysis on treated patients suggests that time to negative conversion did not vary with the patients' baseline characteristics.

CONCLUSIONS

This cohort study of high-risk patients with mild-to-moderate COVID-19 found an association between nirmatrelvir/ritonavir treatment and accelerated negative RT-PCR respiratory SARS-CoV-2 conversion that might reduce the risk of viral shedding and disease transmission.

A commentary on the use of pharmacoenhancers in the pharmaceutical industry and the implication for DMPK drug discovery strategies

Paxlovid, a drug combining nirmatrelvir and ritonavir, was designed for the treatment of COVID-19 and its rapid development has led to emergency use approval by the FDA to reduce the impact of COVID-19 infection on patients.In order to overcome potentially suboptimal therapeutic exposures, nirmatrelvir is dosed in combination with ritonavir to boost the pharmacokinetics of the active product.Here we consider examples of drugs co-administered with pharmacoenhancers.Pharmacoenhancers have been adopted for multiple purposes such as ensuring therapeutic exposure of the active product, reducing formation of toxic metabolites, changing the route of administration, and increasing the cost-effectiveness of a therapy.We weigh the benefits and risks of this approach, examining the impact of technology developments on drug design and how enhanced integration between cross-discipline teams can improve the outcome of drug discovery.

Comprehensive Nonclinical Safety Assessment of Nirmatrelvir Supporting Timely Development of the SARS-COV-2 Antiviral Therapeutic, Paxlovid™

COVID-19 is a potentially fatal infection caused by the SARS-CoV-2 virus. The SARS-CoV-2 3CL protease (Mpro) is a viral enzyme essential for replication and is the target for nirmatrelvir. Paxlovid (nirmatrelvir co-administered with the pharmacokinetic enhancer ritonavir) showed efficacy in COVID-19 patients at high risk of progressing to hospitalization and/or death. Nonclinical safety studies with nirmatrelvir are essential in informing benefit-risk of Paxlovid and were conducted to support clinical development. In vivo safety pharmacology assessments included a nervous system/pulmonary study in rats and a cardiovascular study in telemetered monkeys. Potential toxicities were assessed in repeat dose studies of up to 1 month in rats and monkeys. Nirmatrelvir administration (1,000 mg/kg, p.o.) to male rats produced transient increases in locomotor activity and respiratory rate but did not affect behavioral endpoints in the functional observational battery. Cardiovascular effects in monkeys were limited to transient increases in blood pressure and decreases in heart rate, observed only at the highest dose tested (75 mg/kg per dose b.i.d; p.o.). Nirmatrelvir did not prolong QTc-interval or induce arrhythmias. There were no adverse findings in repeat dose toxicity studies up to 1 month in rats (up to 1,000 mg/kg daily, p.o.) or monkeys (up to 600 mg/kg daily, p.o.). Nonadverse, reversible clinical pathology findings without clinical or microscopic correlates included prolonged coagulation times at ≥60 mg/kg in rats and increases in transaminases at 600 mg/kg in monkeys. The safety pharmacology and nonclinical toxicity profiles of nirmatrelvir support clinical development and use of Paxlovid for treatment of COVID-19.

Simultaneous determination of nirmatrelvir and ritonavir in human plasma by LC-MS/MS and its pharmacokinetic application in healthy Chinese subjects

Paxlovid, a co-packaged medication of nirmatrelvir tablets (150 mg) and ritonavir tablets (100 mg) developed by Pfizer, is one of the first orally accessible COVID-19 antiviral medicines to be approved for the emergency usage. In this research, an efficient LC-MS/MS method for simultaneous determining nirmatrelvir and ritonavir in human plasma was established and validated with remdesivir as an internal standard. Chromatographic separations were carried out on a Thermo BDS Hypersil C18 (4.6mm×100, 2.4μm) column using deionized water and methanol as mobile phase, both added with 0.1% (v/v) formic acid. Based on the positive electrospray ionization mode, nirmatrelvir and ritonavir were analyzed by selective reaction monitoring. Excellent precision, accuracy, recovery, and linearity were demonstrated covering the range of 50-5000 ng/mL for nirmatrelvir and 10-1000 ng/mL for ritonavir. Then, the established method was utilized to the pharmacokinetic profile of Paxlovid in healthy Chinese subjects. The Pharmacokinetic parameters, including C_max , T_max , t_1/2 and AUC_0-∞ of western subjects correspond well with the results of this pharmacokinetic investigation.

Paxlovid: Mechanism of Action, Synthesis, and In Silico Study

In this work, the discovery and description of PF-07321332, a major bioavailable oral SARS-CoV-2 protease inhibitor with in vitro human coronavirus antiviral activity, and excellent selection of off-target and in vivo immune profiles are reported. Various drugs and novel compound candidates for the treatment of the COVID-19 pandemic have been developed. PF-07321332 (or nirmatrelvir) is a new oral antiviral drug developed by Pfizer. In response to the pandemic, Pfizer has developed the COVID vaccine and in 2022 will launch its new major anti-SARS-Cov-2 protease inhibitor (PI). The combination of ritonavir and nirmatrelvir is under study in phase III of the clinical trial with a brand name Paxlovid. Paxlovid is an active 3Cl protease inhibitor. Paxlovid exerts its antiviral efficacy by inhibiting a necessary protease in the viral replication procedure. Proteases of coronavirus cleave several sites in the viral polyprotein where pyrrolidone was replaced by flexible glutamine. Due to the coronavirus pandemic, there is high demand for synthesis and development of this novel drug. Herein, we report the synthetic route and the mechanism of action was recently published on nirmatrelvir. Also, a comparison of the performance of two new oral antiviruses (molnupiravir and nirmatrelvir) for the treatment of COVID-19 is described. This review will be helpful for different disciplines such as biochemistry, organic chemistry, medicinal chemistry, and pharmacology.

In Silico Evaluation of Paxlovid's Pharmacometrics for SARS-CoV-2: A Multiscale Approach

Paxlovid is a promising, orally bioavailable novel drug for SARS-CoV-2 with excellent safety profiles. Our main goal here is to explore the pharmacometric features of this new antiviral. To provide a detailed assessment of Paxlovid, we propose a hybrid multiscale mathematical approach. We demonstrate that the results of the present in silico evaluation match the clinical expectations remarkably well: on the one hand, our computations successfully replicate the outcome of an actual in vitro experiment; on the other hand, we verify both the sufficiency and the necessity of Paxlovid's two main components (nirmatrelvir and ritonavir) for a simplified in vivo case. Moreover, in the simulated context of our computational framework, we visualize the importance of early interventions and identify the time window where a unit-length delay causes the highest level of tissue damage. Finally, the results' sensitivity to the diffusion coefficient of the virus is explored in detail.