Pharmacokinetic Enhancer Research Articles

Elucidation of the Pharmacological Development and Action Mechanism of Remdesivir and Paxlovid in Combatting COVID-19

COVID-19, the disease identified in 2019 as coronavirus disease, stems from an infection by severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2, which possesses a single-stranded RNA genome. Since the onset of the pandemic attributed to COVID-19, a variety of vaccines and antiviral medications have received approval from international regulatory bodies. Two notable antiviral agents, remdesivir and paxlovid, serve as treatments for viral infections. Initially developed to combat Ebola, remdesivir has also demonstrated efficacy against a broad spectrum of coronaviruses (CoV). It is a nucleoside analogue and functions by being incorporated into the RNA chain of the virus and thus induce the early termination of RNA synthesis. Paxlovid comprises two pharmacological agents, nirmatrelvir and ritonavir. The mechanism of nirmatrelvir involves the specific targeting and inhibition of the viral protease’s active site, thereby impeding the viral replication process. By inhibiting the cytochrome CYP3A4 enzyme which metabolites nirmatrelvir, ritonavir acts as a pharmacokinetic enhancer in this combination. The initial section of this review provides a comprehensive analysis of SARS-CoV-2, detailing the mechanisms of its pathogenesis and the subsequent immune responses elicited by the body. Then this article generalizes the history of development, the structure, and the mode of action of remdesivir and paxlovid.

Modulation of tenofovir by probenecid: Impact on drug, interleukin-1β, and dopamine concentration in the prefrontal cortex and cerebellum

The blood–brain barrier’s limited permeability to tenofovir restricts its ability to clear HIV from the brain. Probenecid acting as an adjuvant increases tenofovir concentrations in plasma and the kidneys thereby enhancing its therapeutic effect. However, the probenecid effect on brain tenofovir concentration and possible adverse effects remains poorly understood. We investigated the effect of probenecid co-administered tenofovir on tenofovir brain concentration, interleukin-1β (IL-1β) and dopamine concentration in the prefrontal cortex (PFC) and the cerebellum. Ninety-six male BALB/c mice were divided into four groups viz: a control group, Tenofovir disoproxil fumarate (TDF) treated, probenecid treated, and TDF + probenecid treated. We orally administered a single dose of TDF (5 mg/kg), and probenecid (8.3 mg/kg), and sacrificed six mice per group after 1 h, 4 h, and 6 h post-treatment to collect plasma, PFC, and cerebellar tissue. Co-administered tenofovir increased tenofovir concentration, peaking at 6 h with the cerebellum having the highest concentration. This suggests that probenecid enhanced the entry of tenofovir into the brain. Tenofovir alone increased IL-1β concentration at all intervals post-administration, while probenecid alone had no impact on IL-1β concentration. Co-administered tenofovir also increased IL-1β concentration. Probenecid’s limited impact on IL-1β concentration following co-administration suggests that its anti-inflammatory properties may require more than 6 h to have an effect. Furthermore, neither tenofovir nor probenecid affected dopamine concentration. In conclusion, probenecid enhances the concentration and retention of tenofovir in the brain, making it a possible pharmacokinetic enhancer. However, its anti-inflammatory effects may require a longer duration to fully manifest.

Model informed dose regimen optimizing in development of leritrelvir for the treatment of mild or moderate COVID-19.

Leritrelvir (RAY1216) acts as a main protease inhibitor that hinders the cleavage of viral precursor proteins, thereby inhibiting virus replication of SARS-CoV-2). This antiviral mechanism has shown significant efficacy against the novel coronavirus. Preclinical studies have demonstrated the potent antiviral activity and favorable safety profile of this compound. This study aims to develop a pharmacokinetic model for leritrelvir, with and without ritonavir as a pharmacokinetic enhancer and to evaluate the necessity of co-administration with ritonavir and to investigate different dosage regimens. The model establishment was based on plasma concentration data from a phase I trial involving 72 subjects in single-ascending dose (SAD), multiple-ascending dose (MAD), and a food effect cohort. Analysis was conducted using a nonlinear mixed-effects model, and clinical trial simulations were carried out. The findings of this study demonstrate a favorable safety profile for leritrelvir. With simulation suggests that a 400mg thrice-daily (TID) regimen may be optimal to maintain the trough concentrations (Ctrough) above levels required for inhibiiting viral replication. While ritonavir was found to enhance exposure, it was deemed unnecessary. Gender and food consumption were identified as significant covariates affecting pharmacokinetic parameters, however, no dose adjustments were deemed necessary. This findings supported by subsequent phase II and phase III trials validated the appropriateness of a 400mg TID regimen for the administration of leritrelvir.

Ritonavir: 25 Years' Experience of Concomitant Medication Management. A Narrative Review.

Ritonavir is a potent inhibitor of the cytochrome P450 3A4 enzyme and is commonly used as a pharmacokinetic (PK) enhancer in antiviral therapies because it increases bioavailability of concomitantly administered antivirals. Decades of experience with ritonavir-enhanced HIV therapies and, more recently, COVID-19 therapies demonstrate that boosting doses of ritonavir are well tolerated, with an established safety profile. The mechanisms of PK enhancement by ritonavir result in the potential for drug-drug interactions (DDIs) with several classes of drugs, thus making co-medication management an important consideration with enhanced antiviral therapies. However, rates of DDIs with contraindicated medications are low, suggesting these risks are manageable by infectious disease specialists who have experience with the use of PK enhancers. In this review, we provide an overview of ritonavir's mechanisms of action and describe approaches and resources available to mitigate adverse events and manage concomitant medication in both chronic and short-term settings.

Pharmacokinetic enhancement of oncolytic virus M1 by inhibiting JAK‒STAT pathway

Oncolytic viruses (OVs), a group of replication-competent viruses that can selectively infect and kill cancer cells while leaving healthy cells intact, are emerging as promising living anticancer agents. Unlike traditional drugs composed of non-replicating compounds or biomolecules, the replicative nature of viruses confer unique pharmacokinetic properties that require further studies. Despite some pharmacokinetics studies of OVs, mechanistic insights into the connection between OV pharmacokinetics and antitumor efficacy remain vague. Here, we characterized the pharmacokinetic profile of oncolytic virus M1 (OVM) in immunocompetent mouse tumor models and identified the JAK‒STAT pathway as a key modulator of OVM pharmacokinetics. By suppressing the JAK‒STAT pathway, early OVM pharmacokinetics are ameliorated, leading to enhanced tumor-specific viral accumulation, increased AUC and Cmax, and improved antitumor efficacy. Rather than compromising antitumor immunity after JAK‒STAT inhibition, the improved pharmacokinetics of OVM promotes T cell recruitment and activation in the tumor microenvironment, providing an optimal opportunity for the therapeutic outcome of immune checkpoint blockade, such as anti-PD-L1. Taken together, this study advances our understanding of the pharmacokinetic-pharmacodynamic relationship in OV therapy.

Pharmacokinetic Enhancement of Elexacaftor/Tezacaftor/Ivacaftor for Cystic Fibrosis: A Cost Reduction Strategy to Address Global Disparities in Access.

Pharmacokinetic Enhancement of Elexacaftor/Tezacaftor/Ivacaftor for Cystic Fibrosis: A Cost Reduction Strategy to Address Global Disparities in Access.

The Design, Synthesis and Mechanism of Action of Paxlovid, a Protease Inhibitor Drug Combination for the Treatment of COVID-19.

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has presented an enormous challenge to health care systems and medicine. As a result of global research efforts aimed at preventing and effectively treating SARS-CoV-2 infection, vaccines with fundamentally new mechanisms of action and some small-molecule antiviral drugs targeting key proteins in the viral cycle have been developed. The most effective small-molecule drug approved to date for the treatment of COVID-19 is PaxlovidTM, which is a combination of two protease inhibitors, nirmatrelvir and ritonavir. Nirmatrelvir is a reversible covalent peptidomimetic inhibitor of the main protease (Mpro) of SARS-CoV-2, which enzyme plays a crucial role in viral reproduction. In this combination, ritonavir serves as a pharmacokinetic enhancer, it irreversibly inhibits the cytochrome CYP3A4 enzyme responsible for the rapid metabolism of nirmatrelvir, thereby increasing the half-life and bioavailability of nirmatrelvir. In this tutorial review, we summarize the development and pharmaceutical chemistry aspects of Paxlovid, covering the evolution of protease inhibitors, the warhead design, synthesis and the mechanism of action of nirmatrelvir, as well as the synthesis of ritonavir and its CYP3A4 inhibition mechanism. The efficacy of Paxlovid to novel virus mutants is also overviewed.

A Comprehensive Review of the Clinical Pharmacokinetics, Pharmacodynamics, and Drug Interactions of Nirmatrelvir/Ritonavir.

Nirmatrelvir is a potent and selective inhibitor of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease that is used as an oral antiviral coronavirus disease 2019 (COVID-19) treatment. To sustain unbound systemic trough concentrations above the antiviral in vitro 90% effective concentration value (EC90), nirmatrelvir is coadministered with 100 mg of ritonavir, a pharmacokinetic enhancer. Ritonavir inhibits nirmatrelvir's cytochrome P450 (CYP) 3A4-mediated metabolism which results in renal elimination becoming the primary route of nirmatrelvir elimination when dosed concomitantly. Nirmatrelvir exhibits absorption-limited nonlinear pharmacokinetics. When coadministered with ritonavir in patients with mild-to-moderate COVID-19, nirmatrelvir reaches a maximum concentration of 3.43 µg/mL (11.7× EC90) in approximately 3 h on day 5 of dosing, with a geometric mean day 5 trough concentration of 1.57 µg/mL (5.4× EC90). Drug interactions with nirmatrelvir/ritonavir (PAXLOVIDTM) are primarily attributed to ritonavir-mediated CYP3A4 inhibition, and to a lesser extent CYP2D6 and P-glycoprotein inhibition. Population pharmacokinetics and quantitative systems pharmacology modeling support twice daily dosing of 300 mg/100 mg nirmatrelvir/ritonavir for 5 days, with a reduced 150 mg/100 mg dose for patients with moderate renal impairment. Rapid clinical development of nirmatrelvir/ritonavir in response to the emerging COVID-19 pandemic was enabled by innovations in clinical pharmacology research, including an adaptive phase 1 trial design allowing direct to pivotal phase 3 development, fluorine nuclear magnetic resonance spectroscopy to delineate absorption, distribution, metabolism, and excretion profiles, and innovative applications of model-informed drug development to accelerate development.

Pharmacokinetic enhancement of marbofloxacin by alpha-1-monolaurin pre-treatment in broiler chickens.

The present study investigated the prospect of improvement in pharmacokinetic (PK) parameters of marbofloxacin due to alpha-1-monolaurin pre-treatment in broiler chickens. Two groups of broilers were administered a single oral dose of marbofloxacin (5.00 mg kg-1 body weight): Group-I without pre-treatment and Group-II with alpha-1-monolaurin pre-treatment (4.00 g kg-1 feed for 10 days). Blood sampling was done periodically for both groups and plasma marbofloxacin concentrations were determined using ultra-high performance liquid chromatography. Pharmacokinetic parameters using non-compartmental modelling approach were calculated with the PKSolver software. Statistical analysis revealed significant differences in plasma marbofloxacin concentrations between the two groups at 1, 2, and 24 hr. Group-II birds exhibited a higher mean maximum plasma concentration (2.43 µg mL-1) at an earlier time (Tmax: 1.38 hr) compared to Group-I. The plasma concentrations of marbofloxacin were maintained above 0.10 and 0.18 µg mL-1 up to 24 hr in Group-I and Group-II broilers, respectively. Significant differences were observed in PK parameters such as the area under the curve and total body clearance. The mean relative oral bioavailability of Group-II birds compared to Group-I was 119.61%. The findings of the study provided evidence of PK parameters enhancement of marbofloxacin in the alpha-1-monolaurin pre-treated group. The calculated PK-pharmacodynamic indices for marbofloxacin predicted clinical efficaciousness in the broiler chickens.

A Short Appraisal of Biological Macromolecules as Tethering Excipients for Improved Drug Delivery: Current Advances

Biological macromolecules, encompassing proteins, nucleic acids, lipids, and carbohydrates, have garnered increasing attention as tethering excipients within the realms of pharmaceuticals and biotechnology. This concise appraisal offers a comprehensive overview of their multifaceted role, highlighting the latest advancements in their applications. Biological macromolecules, long regarded as fundamental components of life, have transitioned into pivotal agents that contribute significantly to drug development, drug formulation stability and the optimization of pharmacokinetic profiles. This review delineates how these macromolecules serve as integral players in the enhancement of drug delivery systems, enabling controlled release, targeted delivery, and improved bioavailability. Furthermore, they play a critical role in the stabilization of sensitive compounds, preserving their efficacy and extending their shelf life. Additionally, the interactions between macromolecules and therapeutic agents are pivotal in mitigating issues of solubility and bioavailability, further propelling their utility as excipients. Despite these promising attributes, challenges such as immunogenicity, scalability, and regulatory compliance persist. Navigating these hurdles necessitates a concerted effort from researchers, engineers, and regulatory bodies alike. In conclusion, biological macromolecules stand as formidable contenders in the field of tethering excipients. Their versatile applications in drug delivery, formulation stability, and pharmacokinetic enhancement hold the promise of revolutionizing the pharmaceutical and biotechnological landscapes. To realize this potential fully, the scientific community must continue to probe their intricacies, address challenges proactively, and foster collaborative efforts to ensure their seamless integration into the future of healthcare and therapeutics. Ultimately, the enduring impact of biological macromolecules on patient care is poised to be transformative and far-reaching.

Effect of Hepatic Impairment on the Pharmacokinetics of Nirmatrelvir/Ritonavir, the First Oral Protease Inhibitor for the Treatment of COVID-19.

Nirmatrelvir, a novel, potent, orally bioavailable severe acute respiratory syndrome coronavirus 2 main protease inhibitor, coadministered with ritonavir for pharmacokinetic (PK) enhancement is licensed for the treatment of mild to moderate COVID-19 in individuals at increased risk of progression to severe disease. Cytochrome P450 3A4 is the primary metabolic enzyme responsible for nirmatrelvir metabolism; however, when cytochrome P450 3A4 is inhibited by ritonavir, nirmatrelvir is primarily excreted, unchanged, in urine. Because of intended use of nirmatrelvir among individuals with hepatic impairment, this Phase 1 study (NCT05005312) evaluated the effects of hepatic impairment on nirmatrelvir PK parameters to assess the potential need for any dose adjustments in this population. Participants with normal hepatic function or moderate hepatic impairment (n=8 each) were administered a single 100-mg nirmatrelvir dose, with 100mg of ritonavir administered 12hours before, together with, and 12 and 24hours after nirmatrelvir. Nirmatrelvir median plasma concentrations and systemic exposure measured by area under the plasma concentration-time curve from time zero extrapolated to infinite time and maximum observed plasma concentration values were comparable in both groups. Nirmatrelvir/ritonavir had an acceptable safety profile in both groups, and no clinically significant changes in laboratory measurements, vital signs, or electrocardiogram assessments were observed. Based on these results, no dose adjustment is deemed necessary in patients with moderate hepatic impairment and, by extension, in patients with mild hepatic impairment.

Dosing recommendation of nirmatrelvir/ritonavir using an integrated population pharmacokinetic analysis.

Protease inhibitor nirmatrelvir coadministered with ritonavir as a pharmacokinetic enhancer (PAXLOVID™; Pfizer Inc) became the first orally bioavailable antiviral agent granted Emergency Use Authorization in the United States in patients ≥12 years old with mild to moderate coronavirus disease 2019 (COVID-19). This population pharmacokinetic analysis used pooled plasma nirmatrelvir concentrations from eight completed phase I and II/III studies to characterize nirmatrelvir pharmacokinetics when coadministered with ritonavir in adults with/without COVID-19. Influence of covariates (e.g., formulation, dose, COVID-19) was examined using a stepwise forward selection (α = 0.05) and backward elimination (α = 0.001) approach. Simulations with 5000 subjects for each age and weight group and renal function category were performed to support dosing recommendations of nirmatrelvir/ritonavir for adults with COVID-19 and guide dose adjustments for specific patient populations (e.g., renal insufficiency, pediatrics). The final model was a two-compartment model with first-order absorption, including allometric scaling of body weight and dose-dependent absorption (power function on relative bioavailability). Nirmatrelvir clearance (CL) increased proportionally to body surface area-normalized creatinine CL (nCLCR) up to 70 ml/min/1.73 m2 and was independent of nCLCR above the breakpoint. Significant covariates included carbamazepine or itraconazole coadministration as markers for drug interactions, COVID-19 on CL, formulation on relative bioavailability, and age on central volume of distribution. Simulation results support current dosing recommendations of nirmatrelvir/ritonavir 300/100 mg twice daily (b.i.d.) in adults with normal renal function or mild impairment and pediatrics (12 to <18 years) weighing ≥40 kg and nirmatrelvir/ritonavir 150/100 mg b.i.d. in adults with moderate renal impairment.

Saquinavir potentiates itraconazole's antifungal activity against multidrug-resistant Candida auris in vitro and in vivo.

Candida species are highly opportunistic yeasts that are responsible for serious invasive fungal infections among immunocompromised patients worldwide. Due to the increase of drug resistance and incidence of infections, there is an urgent need to develop new antifungals and to identify co-drugs that can sensitize drug-resistant Candida to antifungals. The objective of this study was to assess the effect of saquinavir on the activity of azole antifungals against Candida auris. The in vitro interaction of saquinavir and three azole antifungals (itraconazole, voriconazole and fluconazole) was evaluated against a panel of C. auris isolates. The itraconazole/saquinavir combination exhibited a synergistic relationship against all C. auris isolates tested with the fractional inhibitory concentration index (FICI) ranging from 0.03 to 0.27. Moreover, a time-kill kinetics assay revealed that saquinavir restored the itraconazole's fungistatic activity against C. auris. Furthermore, saquinavir restored itraconazole's antifungal activity against other clinically important Candida species. The mechanistic investigation indicated that saquinavir significantly inhibited efflux pumps, glucose utilization and ATP synthesis in Candida. Finally, a murine model of C. auris infection was used to evaluate the efficacy of the itraconazole/saquinavir combination in the presence of ritonavir (as a pharmacokinetic enhancer). The combination significantly reduced the fungal burden in the kidneys by 0.93-log10 colony forming units (88%) compared to itraconazole alone. This study identified that saquinavir exhibits a potent synergistic relationship in combination with itraconazole against Candida species, which warrants further consideration.

Real-World Evidence of the Top 100 Prescribed Drugs in the USA and Their Potential for Drug Interactions with Nirmatrelvir; Ritonavir

Nirmatrelvir (coadministered with ritonavir as PAXLOVIDTM) reduces the risk of COVID-19-related hospitalizations and all-cause death in individuals with mild-to-moderate COVID-19 at high risk of progression to severe disease. Ritonavir is coadministered as a pharmacokinetic enhancer. However, ritonavir may cause drug-drug interactions (DDIs) due to its interactions with various drug-metabolizing enzymes and transporters, including cytochrome P450 (CYP) 3A, CYP2D6, and P-glycoprotein transporters. To better understand the extent of DDIs (or lack thereof) of nirmatrelvir; ritonavir in a clinical setting, this study used real-world evidence (RWE) from the Optum Clinformatics Data Mart database to identify the top 100 drugs most commonly prescribed to US patients at high risk of progression to severe COVID-19 disease. The top 100 drugs were identified based on total counts associated with drugs prescribed to high-risk patients (i.e., ≥ 1 medical condition associated with an increased risk of severe COVID-19) who were continuously enrolled in the database throughout 2019 and had ≥ 1 prescription claim. Each of the 100 drugs was then assessed for DDI risk based on their metabolism, excretion, and transport pathways identified from available US prescribing and medical literature sources. Seventy drugs identified were not expected to have DDIs with nirmatrelvir; ritonavir, including many cardiovascular agents, anti-infectives, antidiabetic agents, and antidepressants. Conversely, 30 drugs, including corticosteroids, narcotic analgesics, anticoagulants, statins, and sedatives/hypnotics, were expected to cause DDIs with nirmatrelvir; ritonavir. This RWE analysis is complementary to the prescribing information and other DDI management tools for guiding healthcare providers in managing DDIs.Graphical

Efficacy and safety of SIM0417 (SSD8432) plus ritonavir for COVID-19 treatment: a randomised, double-blind, placebo-controlled, phase 1b trial

SIM0417 (SSD8432) is an orally administered coronavirus main proteinase (3CLpro) inhibitor with potential anti-SARS-CoV-2 activity. This study aimed to evaluate the efficacy and safety of SIM0417 plus ritonavir (a pharmacokinetic enhancer) in adults with COVID-19. This was a randomised, double-blind, placebo-controlled, phase 1b study in China. Adults with asymptomatic infection, mild or moderate COVID-19 were randomly assigned (3:3:2) to receive either 750mg SIM0417 plus 100mg ritonavir, 300mg SIM0417 plus 100mg ritonavir or placebo every 12h for 10 doses. The main efficacy endpoints included SARS-CoV-2 viral load, proportion of participants with positive SARS-CoV-2 nucleic acid test and time to alleviation of COVID-19 symptoms. This trial is registered with ClinicalTrials.gov, NCT05369676. Between May 12 and August 29, 2022, 32 participants were enrolled and randomised to high dose group (n=12), low dose group (n=12) or placebo (n=8). The viral load change from baseline in high dose group was statistically lower compared with placebo, with a maximum mean difference of-2.16±0.761 log10 copies/mL (p=0.0124) on Day 4. The proportion of positive SARS-CoV-2 in both active groups were lower than the placebo. The median time to sustained alleviation of COVID-19 symptoms was 2.0 days in high dose group versus 6.0 days in the placebo group (HR=3.08, 95% CI 0.968-9.818). SIM0417 plus ritonavir were well tolerated with all adverse events in grade1. SIM0417 plus ritonavir was generally well tolerated. The efficacy of SIM0417 showed a monotonic dose-response relationship, and the 750mg SIM0417 plus 100mg ritonavir was selected as the recommended clinical dose. The study was funded by Jiangsu Simcere Pharmaceutical Co., Ltd.

Effects of itraconazole and carbamazepine on the pharmacokinetics of nirmatrelvir/ritonavir in healthy adults.

The objective of this study was to evaluate the effects of a strong cytochrome P450 family (CYP) 3A4 inhibitor (itraconazole) and inducer (carbamazepine) on the pharmacokinetics and safety of nirmatrelvir/ritonavir. Pharmacokinetics were measured in two phase 1, open-label, fixed-sequence studies in healthy adults. During Period 1, oral nirmatrelvir/ritonavir 300 mg/100 mg twice daily was administered alone; during Period 2, it was administered with itraconazole or carbamazepine. Nirmatrelvir/ritonavir was administered as repeated doses or one dose in the itraconazole and carbamazepine studies, respectively. Nirmatrelvir and ritonavir plasma concentrations and adverse event (AE) rates in both periods were analysed. Each study included 12 participants. Following administration of nirmatrelvir/ritonavir with itraconazole (Test) or alone (Reference), test/reference ratios of the adjusted geometric means (90% CIs) for nirmatrelvir AUCtau and Cmax were 138.82% (129.25%, 149.11%) and 118.57% (112.50%, 124.97%), respectively. After administration of nirmatrelvir/ritonavir with carbamazepine (Test) or alone (Reference), test/reference ratios (90% CIs) of the adjusted geometric means for nirmatrelvir AUCinf and Cmax were 44.50% (33.77%, 58.65%) and 56.82% (47.04%, 68.62%), respectively. Nirmatrelvir/ritonavir was generally safe when administered with or without itraconazole or carbamazepine. No serious or severe AEs were reported. Coadministration of a strong CYP3A4 inhibitor with a strong CYP3A inhibitor used for pharmacokinetic enhancement (i.e., ritonavir) resulted in small increases in plasma nirmatrelvir exposure, whereas coadministration of a strong inducer substantially decreased systemic nirmatrelvir and ritonavir exposures suggesting a contraindication in the label with CYP3A4 strong inducers. Administration of nirmatrelvir/ritonavir alone or with itraconazole or carbamazepine was generally safe.

Therapeutic drug monitoring and dosage adjustments of immunosuppressive drugs when combined with nirmatrelvir/ritonavir in patients with COVID-19.

Nirmatrelvir/ritonavir (Paxlovid®) consists of a peptidomimetic inhibitor (Nirmatrelvir) of the SARS-CoV-2 main protease and a pharmacokinetic enhancer (Ritonavir). It is approved for the treatment of mild-to-moderate COVID-19. This combination of nirmatrelvir and ritonavir can mediate significant and complex drug-drug interactions (DDIs), primarily due to the ritonavir component. Indeed, ritonavir inhibits the metabolism of nirmatrelvir through cytochrome P450 3A (CYP3A) leading to higher plasma concentrations and a longer half-life of nirmatrelvir. Co-administration of nirmatrelvir/ritonavir with immunosuppressant drugs (ISDs) is particularly challenging given the major involvement of CYP3A in the metabolism of most of these drugs and their narrow therapeutic ranges. Exposure of ISDs will be drastically increased through the potent ritonavir-mediated inhibition of CYP3A, resulting in an increased risk of adverse drug reactions. While a decrease in the dosage of ISDs can prevent toxicity, an inappropriate dosage regimen may also result in insufficient exposure and a risk of rejection. Here we provide some general recommendations for therapeutic drug monitoring (TDM) of ISDs and dosing recommendations when co-administered with nirmatrelvir/ritonavir. Particularly, tacrolimus should be discontinued, or patients should be given a microdose on day-1, while cyclosporine dosage should be reduced to 20% of the initial dosage during the antiviral treatment. Dosages of mammalian target of rapamycin inhibitors (m-TORis) should also be adjusted while dosages of mycophenolic acid and corticosteroids are expected to be less impacted.

Prasugrel — gone, but not forgotten

AbstractHuman immunodeficiency virus (HIV) infection and certain retroviral therapies are associated with an increased risk of atherosclerosis with plaque rupture resulting in acute coronary syndromes. Therefore, there is often a need to co‐prescribe antiretroviral and cardiovascular therapies, including antiplatelet agents. Antiplatelet agents, such as the P2Y12 receptor antagonists clopidogrel and prasugrel, require activation by cytochrome P450 3A4 (CYP3A4). The P2Y12 receptor antagonist ticagrelor is also metabolised by CYP3A4. Pharmacokinetic enhancers, such as ritonavir and cobicistat, are utilised to increase the systemic exposure of certain agents within multidrug HIV regimens and are potent CYP3A4 inhibitors. Using these drugs together can result in unintended and undesirable drug–drug interactions. A 55‐year‐old male with a history of HIV presented to the emergency department with central chest pain. He was found to have had a non‐ST‐elevation myocardial infarction and was commenced on dual antiplatelet therapy including ticagrelor, anticoagulation and statin therapy, in addition to his usual HIV therapy, Genvoya (elvitegravir, cobicistat, emtricitabine, tenofovir alafenamide). A drug–drug interaction between Genvoya and ticagrelor was identified by the pharmacist, and the patient was switched to prasugrel on the pharmacist's recommendation. Although prasugrel was delisted from the Pharmaceutical Benefits Scheme (PBS) in July 2020, it remains accessible as a non‐PBS medicine. Prasugrel should be considered the P2Y12 antagonist of choice for patients who are on HIV regimens containing a pharmacokinetic enhancer such as ritonavir or cobicistat.

1259. Bictegravir or Dolutegravir-Containing Antiretroviral Regimens in Solid Organ Transplantation: Single-Center Experience

Abstract Background Solid organ transplantation (SOT) is the definitive treatment for end-organ failure in HIV-positive recipients. Bictegravir (BIC) or dolutegravir (DTG) based antiretroviral therapy (ART) is the preferred ART due to high efficacy, excellent tolerability and minimal drug interactions, yet there is a paucity of data on these second generation integrase inhibitors (INSTIs) in SOT. We report the Memorial Transplant Institute’s experience using second generation INSTI-containing ART with or without emtricitabine/tenofovir alafenamide (FTC/TAF) in persons with HIV. Table 1.Demographics and clinical features of 16 patients with HIV undergoing solid organ transplantation (SOT).3TC: lamivudine; AA: African American; BIC: bictegravir; DTG: dolutegravir; F: female; FTC: emtricitabine; H: Hispanic/Latino/a/x; IN: integrase; M: male; NH: Non-Hispanic/Latino/a/x; PR: protease; RPV: rilpivirine; RT: reverse transcriptase; SOT: solid organ transplantation; TAF: tenofovir alafenamide; W: whiteTable 2.Clinical course of 8 patients with HIV after solid organ transplantation (SOT).3TC: lamivudine; ABC: abacavir; ART: antiretroviral therapy; ATV: atazanavir; BIC: bictegravir; c: cobicistat; DTG: dolutegravir; DRV: darunavir; eFGR: estimated glomerular filtration rate; ETR: etravirine; FTC: emtricitabine; r: ritonavir; RAL: raltegravir; RPV: rilpivirine; RTV: ritonavir; SOT: solid organ transplantation; TAF: tenofovir alafenamide Methods This single-center observational study compiles data from medical records of all persons with HIV undergoing SOT seen by the Division of Infectious Disease from January 2017 through April 2022. We report clinical information and ART management of SOT candidates and recipients in our center. Results Sixteen patients met inclusion criteria: 8 SOT candidates (7 kidney, 1 heart) and 8 SOT recipients (all kidney). Demographics are presented in Table 1. Patients were 63% male with a mean age of 55 years, CD4 323 cells/mm3, and living with HIV for 16 years. ART regimens were BIC/FTC/TAF (50%), DTG/rilpivirine (RPV) (19%), DTG + FTC/TAF (19%) and RPV/FTC/TAF + DTG (6%), and DTG/lamivudine (6%). All pharmacokinetic enhancers were discontinued to avoid drug interactions with anti-rejection medications. Last on-treatment HIV RNA was &amp;lt; 200 copies/mL for 100% of patients. The clinical course of 8 post-renal transplant recipients is presented in Table 2. The most common post-SOT regimen was BIC/FTC/TAF. Post-SOT patients maintained HIV RNA &amp;lt; 200 copies/mL. No ART-related adverse effects were documented. Two allograft- or life-threatening infections and one episode of acute antibody rejection was reported. Expectedly, serum creatinine decreased and estimated glomerular filtration rate increased post-renal transplant. Conclusion We provide additional insight into the use of BIC- and DTG-containing ART with or without FTC/TAF in the peri-SOT period. Our growing experience suggests second generation INSTI-containing ART regimens with or without FTC/TAF are effective and well tolerated following kidney transplantation. Additional research on the use of second generation INSTIs in the SOT patient population is needed. Disclosures All Authors: No reported disclosures.

ASCENT1: A Phase 2 Trial to Evaluate the Efficacy and Safety of Oral Decitabine-Tetrahydrouridine (NDec) in Patients with Sickle Cell Disease

Background: Sickle cell disease (SCD) is driven by the polymerization of mutated hemoglobin (HbS) in red blood cells (RBCs). Fetal hemoglobin (HbF) mitigates the effects of HbS polymerization, but the HbF gene expression is silenced in infancy by DNA methyltransferase 1 (DNMT1). Decitabine induces HbF expression by direct inhibition of DNMT1. NDec is an innovative combination treatment with decitabine, the active component, and the pharmacokinetic enhancer tetrahydrouridine (THU). Hydroxyurea (HU), the current standard of SCD care, indirectly induces HbF by inducing bone marrow stress. As the indirect effect of HU on HbF is clinically variable, the direct HbF induction of NDec is hypothesized to provide a sustainable treatment option for patients with SCD. In a previous trial in high-risk patients with SCD by Molokie R et al. (2017), oral decitabine (0.16 mg/kg) and THU vs placebo significantly increased total Hb, HbF, proportion of HbF-enriched RBCs (%F-cells) and improved RBC health markers, without triggering grade ≥3 non-hematologic toxicity. NDec formulations were further investigated in 2 phase 1 trials in healthy people. The ASCENT1 trial (NCT05405114) aims to study the efficacy and safety of once- or twice-weekly NDec vs placebo in patients with SCD. This study will provide proof of concept and determine the optimal dose for future trials. Study design: ASCENT1 is a randomized, placebo-controlled phase 2 trial with an additional exploratory open-label HU block (Figure). To ease the operational aspects for patients and sites, trial design, visit schedule and trial materials were developed together with patient groups, study nurses and coordinators. The HU non-eligible block will include those who are HU-naïve or who cannot be treated with HU for any reason. Participants randomized to NDec in the HU active block will discontinue HU during a 4-week washout period. Study population: All SCD genotypes are eligible for inclusion; other criteria are ≥18 years of age, 2-10 documented vaso-occlusive crises (VOCs) ≤12 months before screening, Hb ≥5.0-≤10.5 g/dL and reticulocyte count >1.5x upper limit of normal at screening. HU active participants are eligible only if deemed inadequately controlled by investigators despite being prescribed HU in the preceding 6 months and being on a stable dose >3 months. Exclusion criteria include chronic transfusion therapy or treatment 28 days before screening/during trial with hematopoietic growth factors and treatment with voxelotor, crizanlizumab or L-glutamine 12 weeks before signing informed consent. Study treatment and endpoints: HU non-eligible (n=60) and HU active (n=24) participants will be randomized 1:1:1 to NDec once weekly, NDec twice weekly (2 consecutive days) or placebo/open-label HU. The trial consists of a main and extension phase (24 weeks each). NDec will be administered orally, with a meal, according to body weight intervals to attain a decitabine dose level of 0.16−0.25 mg/kg and THU dose level of 8−12.5 mg/kg. The primary endpoint is change in total Hb (g/dL) from baseline (BL) to Week 24. Secondary efficacy endpoints include change in HbF (g/dL and %HbF of total Hb), change in %F-cells of total RBCs, and change in hemolysis markers from BL to Week 24. Secondary efficacy endpoints also include numbers of VOCs, acute chest syndrome and transfused RBC units from BL to Week 48. The secondary safety endpoint is the number of adverse events (grade ≥3) from BL to Week 52. Changes in patient-reported outcomes from BL to Week 48 will be assessed using 5 validated questionnaires for SCD. Statistical analysis: The primary endpoint will be analyzed using an ANCOVA model with treatment, historical VOC rate and sex as fixed factors, and BL Hb as covariate. Treatment policy estimand will be used to handle intercurrent events. Considerations: In this trial, VOCs are defined as ≥1 predefined clinical events requiring a medical visit, including home and telemedicine visits, for those with limited regular access to medical management at a clinic/hospital. NDec and HU both induce HbF and will not be given together due to a theoretical potentiation of hematologic toxicity. The exploratory HU active block enables preliminary comparisons of the efficacy and safety between NDec and HU. The extension phase allows for analyses that may require longer follow-up to show clinical benefits and sustainability of NDec in SCD. The recruitment to ASCENT1 started in summer 2022. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal