Molnupiravir: Mechanism of action, clinical, and translational science

Molnupiravir is an oral prodrug of the broadly active, antiviral ribonucleoside analog N-hydroxycytidine (NHC). The primary circulating metabolite NHC is taken up into cells and phosphorylated to NHC-triphosphate (NHC-TP). NHC-TP serves as a competitive substrate for viral RNA-dependent RNA polymerase (RdRp), which results in an accumulation of errors in the viral genome, rendering virus replication incompetent. Molnupiravir has demonstrated activity against SARS-CoV-2 both clinically and preclinically and has a high barrier to development of viral resistance. Little to no molnupiravir is observed in plasma due to rapid hydrolysis to NHC. Maximum concentrations of NHC are reached at 1.5 h following administration in a fasted state. The effective half-life of NHC is 3.3 h, reflecting minimal accumulation in the plasma following twice-daily (Q12H) dosing. The terminal half-life of NHC is 20.6 h. NHC-TP exhibits a flatter profile with a lower peak-to-trough ratio compared with NHC, which supports Q12H dosing. Renal and hepatic pathways are not major routes of elimination, as NHC is primarily cleared by metabolism to uridine and cytidine, which then mix with the endogenous nucleotide pools. In a phase III study of nonhospitalized patients with COVID-19 (MOVe-OUT), 5 days of treatment with 800 mg molnupiravir Q12H significantly reduced the incidence of hospitalization or death compared with placebo. Patients treated with molnupiravir also had a greater reduction in SARS-CoV-2 viral load and improved clinical outcomes, compared with those receiving placebo. The clinical effectiveness of molnupiravir has been further demonstrated in several real-world evidence studies. Molnupiravir is currently authorized or approved in more than 25 countries.

Population pharmacokinetics of molnupiravir in adults with COVID-19: Lack of clinically important exposure variation across individuals

Effective antiviral treatments for coronavirus disease 2019 (COVID-19) are needed to reduce the morbidity and mortality associated with severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection, particularly in patients with risk factors for severe disease. Molnupiravir (MK-4482, EIDD-2801) is an orally administered, ribonucleoside prodrug of β-D-N4-hydroxycytidine (NHC) with submicromolar potency against SARS-CoV-2. A population pharmacokinetic (PopPK) analysis for molnupiravir exposure was conducted using 4202 NHC plasma concentrations collected in 1207 individuals from a phase I trial in healthy participants, a phase IIa trial in non-hospitalized participants with COVID-19, a phase II trial in hospitalized participants with COVID-19, and a phase II/III trial in non-hospitalized participants with COVID-19. Molnupiravir pharmacokinetics (PK) was best described by a two-compartment model with a transit-compartment absorption model and linear elimination. Molnupiravir apparent elimination clearance increased with body weight less-than-proportionally (power 0.412) and was estimated as 70.6 L/h in 80-kg individuals with a moderate interindividual variability (43.4% coefficient of variation). Additionally, effects of sex and body mass index on apparent central volume and food status and formulation on the absorption mean transit time were identified as statistically significant descriptors of variability in these PK parameters. However, none of the identified covariate effects caused clinically relevant changes in the area under the NHC concentration versus time curve between doses, the exposure metric most closely related to clinical response. Overall, the PopPK model indicates that molnupiravir can be administered in adults without dose adjustment based on age, sex, body size, food, and mild-to-moderate renal or mild hepatic impairment.

Factors Influencing COVID-19 Risk: Insights from Molnupiravir Exposure-Response Modeling of Clinical Outcomes

Molnupiravir (MOV) is an oral antiviral for the treatment of COVID-19 in outpatient settings. This analysis investigated the relationship between β-D-N4-hydroxycytidine (NHC) pharmacokinetics (PK) and clinical outcomes in patients with mild to moderate COVID-19 in the Phase 3 part of the randomized, double-blind, placebo-controlled MOVe-OUT trial. Logistic regression models of the dependency of outcomes on exposures and covariates were constructed using a multi-step process. Influential covariates were identified first using placebo arm data, followed by assessment of exposure-dependency in drug effect using data from both the placebo and MOV arms. The exposure-response (E-R) analysis included 1,313 participants; 630 received MOV and 683 received placebo. Baseline viral load, baseline disease severity, age, weight, viral clade, active cancer, and diabetes were identified as significant determinants of response using placebo data. Absolute measures of viral load on days 5 and 10 were strong on-treatment predictors of hospitalization. An additive area under the curve (AUC)-based E_max model with a fixed Hill coefficient of 1 best represented the exposure-dependency in drug effect and the AUC50 was estimated to be 19,900 nM*hr. Patients at 800 mg achieved near maximal response which was larger than for 200 or 400 mg. The final E-R model was externally validated and predicted that the relative reduction in hospitalization with MOV treatment would vary with patient characteristics and factors in the population. In conclusion, the E-R results support the MOV dose of 800 mg twice daily to treat COVID-19. Many patient characteristics and factors impacted outcomes beyond drug exposures.

Imipenem/cilastatin/relebactam efficacy, safety and probability of target attainment in adults with hospital-acquired or ventilator-associated bacterial pneumonia among patients with baseline renal impairment, normal renal function, and augmented renal clearance

Objectives

To assess the relationship between renal function and efficacy/safety of imipenem/cilastatin/relebactam for the treatment of hospital-acquired/ventilator-associated pneumonia (HABP/VABP) from RESTORE-IMI 2 and determine the PTA.

Methods

Adults with HABP/VABP were randomized 1:1 to IV imipenem/cilastatin/relebactam 1.25 g or piperacillin/tazobactam 4.5 g every 6 h for 7-14 days. Initial doses were selected by CL_CR and adjusted thereafter, as appropriate. Outcomes included Day 28 all-cause mortality (ACM), clinical response, microbiological response and adverse events. Population pharmacokinetic modelling and Monte Carlo simulations assessed PTA.

Results

The modified ITT population comprised those with normal renal function (n = 188), augmented renal clearance (ARC; n = 88), mild renal impairment (RI; n = 124), moderate RI (n = 109) and severe RI (n = 22). ACM rates were comparable between treatment arms among all baseline renal function categories. Clinical response rates were comparable between treatment arms for participants with RI and normal renal function but were higher (91.7% versus 44.4%) for imipenem/cilastatin/relebactam-treated versus piperacillin/tazobactam-treated participants with CL_CR ≥250 mL/min (n = 21). Microbiologic response rates were comparable between treatment arms for participants with RI but higher among those treated with imipenem/cilastatin/relebactam in participants with CL_CR ≥90 mL/min (86.6% versus 67.2%). Adverse events were comparable between treatment arms across renal function categories. Joint PTA was >98% for key pathogen MICs for susceptible pathogens (MIC ≤2 mg/L).

Conclusions

Prescribing information-defined dose adjustments in participants with baseline RI and full dosing of imipenem/cilastatin/relebactam 1.25 g every 6 h for participants with normal renal function or augmented renal clearance achieved sufficiently high drug exposures and favourable safety and efficacy profiles.

Population pharmacokinetic/pharmacodynamic assessment of imipenem/cilastatin/relebactam in patients with hospital-acquired/ventilator-associated bacterial pneumonia

In the phase III RESTORE-IMI 2 study (ClinicalTrials.gov: NCT02493764), the combination antibacterial agent imipenem/cilastatin/relebactam (IMI/REL) demonstrated noninferiority to piperacillin/tazobactam for the end points of all-cause mortality at day 28 and favorable clinical response at the early follow-up visit in adult participants with gram-negative hospital-acquired bacterial pneumonia/ventilator-associated bacterial pneumonia (HABP/VABP). Existing population pharmacokinetic models for imipenem (IPM) and REL were updated using data from patients with HABP/VABP from RESTORE-IMI 2. Creatinine clearance (CrCl), body weight, infection type, and ventilation status were significant covariates in the updated model. The following simulations were performed to calculate the pharmacokinetic/pharmacodynamic joint probability of target attainment among patients with HABP/VABP and varying degrees of renal function: augmented renal clearance (CrCl ≥150 ml/min), normal renal function (CrCl ≥90 to <150 ml/min), renal impairment (mild, CrCl ≥60 to <90 ml/min; moderate, CrCl ≥30 to <60 ml/min; or severe, CrCl ≥15 to <30 ml/min), and end-stage renal disease (CrCl <15 ml/min). At the recommended IMI/REL dosing regimens across renal categories, greater than 90% of patients in all renal function groups were predicted to achieve joint pharmacokinetic/pharmacodynamic targets at a minimum inhibitory concentration breakpoint of ≤2 μg/ml, regardless of ventilation status. This modeling and simulation analysis supports use of the recommended IMI/REL dosing regimens, adjusted based on renal function, in patients with HABP/VABP.

Ceftolozane/Tazobactam in Neonates and Young Infants: The Challenges of Collecting Pharmacokinetics and Safety Data in This Vulnerable Patient Population

OBJECTIVE

New treatments are needed for multidrug-resistant (MDR) gram-negative infections in neonates. Ceftolozane/tazobactam is a β-lactam/β-lactamase inhibitor combination that has broad-spectrum activity against most common gram-negative bacteria, including MDR strains. We evaluated pharmacokinetics (PK) and safety of ceftolozane/tazobactam in term and premature neonates and young infants.

STUDY DESIGN

This is a subgroup analysis of a phase 1, noncomparative, open-label, multicenter study that characterized the PK, safety, and tolerability of a single intravenous (IV) dose of ceftolozane/tazobactam in pediatric patients with proven/suspected gram-negative infection or receiving perioperative prophylaxis.

RESULTS

Seven patients were enrolled in Group A (birth [7 days postnatal] to < 3 months, > 32 weeks gestation) and six patients were enrolled in Group B (birth [7 days postnatal] to < 3 months, ≤ 32 weeks gestation). PK profiles in neonates and young infants were generally comparable to those of older children receiving a single IV dose of ceftolozane/tazobactam. No serious adverse events (AEs), treatment-related AEs, severe AEs, or clinically significant laboratory abnormalities were reported.

CONCLUSION

Among term and premature neonates and young infants, PK was comparable to older children and ceftolozane/tazobactam was generally well tolerated. An adaptable and flexible study design is necessary for enrollment in neonatal PK trials.

Understanding effect site pharmacology of uprifosbuvir, a hepatitis C virus nucleoside inhibitor: Case study of a multidisciplinary modeling approach in drug development

Uprifosbuvir is a uridine nucleoside monophosphate prodrug inhibitor of the hepatitis C virus NS5B RNA polymerase. To quantitatively elucidate key metabolic pathways, assess the link between unmeasurable effect site concentrations and viral load reduction, and evaluate the influence of intrinsic and extrinsic factors on pharmacokinetics and pharmacodynamics, a model‐informed drug development (MIDD) framework was initiated at an early stage. Originally scoped as a modeling effort focused on minimal physiologically based pharmacokinetic and covariate analyses, this project turned into a collaborative effort focused on gaining a deeper understanding of the data from drug metabolism, biopharmaceutics, pharmacometrics, and clinical pharmacology perspectives. This article presents an example of the practical execution of a MIDD‐based, cooperative multidisciplinary modeling approach, creating a model that grows along with the team's integrated knowledge. Insights gained from this process could be used in forming optimal collaborations between disciplines in drug development for other investigative compounds.

Pharmacokinetics and Pharmacodynamics of Ceftolozane/Tazobactam in Critically Ill Patients With Augmented Renal Clearance

OBJECTIVE

To determine whether established ceftolozane/tazobactam (C/T) dosing is adequate for patients with augmented renal clearance (ARC) and bacterial infection.

METHODS

ARC (creatinine clearance [CrCl] ≥ 130 mL/min) was confirmed by directly measured CrCl in 11 critically ill patients in a phase 1 pharmacokinetics study. Patients received 3 g C/T (ceftolozane 2 g/tazobactam 1 g) as a 60-minute intravenous infusion. Pharmacokinetic sampling occurred at 0 (predose), 1, 2, 4, 6, and 8 hours after the start of the infusion. Noncompartmental analyses were conducted on concentration data. The following pharmacodynamic targets were evaluated: time that free (unbound) drug concentrations exceeded the minimum inhibitory concentration (fT>MIC) of 4 μg/mL for ceftolozane and time that the unbound concentration exceeded the 1 μg/mL target threshold (fT>threshold = 1 µg/mL) for > 20% of the dosing interval for tazobactam. Safety was evaluated.

RESULTS

Mean (SD) area under the plasma concentration-time curve from 0 to infinity, clearance and volume of distribution at steady state (V_ss) were 236 (118) h*µg/mL, 10.4 (4.5) L/h and 30.8 (10.8) L, respectively, for ceftolozane; and 35.5 (18.5) h*µg/mL, 35.3 (16.5) L/h and 54.8 (20.1) L, respectively, for tazobactam. Clearance and V_ss were higher for both ceftolozane and tazobactam in patients with ARC compared with healthy individuals. The mean estimated ceftolozane fT>MIC at 4 µg/mL was 86.4%; the mean estimated tazobactam fT>threshold = 1 µg/mL was 54.9%. Treatment-emergent adverse events were mild to moderate.

CONCLUSIONS

In patients with ARC, a 3 g C/T dose met respective pharmacodynamic targets for ceftolozane and tazobactam. CLINICALTRIALS.

GOV IDENTIFIER

NCT02387372.

In Vitro Hollow-Fiber Studies Assessing Antibacterial Activity of Ceftolozane/Tazobactam Against Multidrug-Resistant Pseudomonas Aeruginosa

Our hollow-fiber infection model simulated the projected steady-state pharmacokinetics of ceftolozane and tazobactam in lung epithelial lining fluid of patients with pneumonia receiving 3 g of ceftolozane/tazobactam every 8 hours. Results confirmed the previously established in vitro activity of ceftolozane/tazobactam at and above approved breakpoints against multidrug-resistant Pseudomonas aeruginosa, regardless of Pseudomonas-derived cephalosporinase allele.

Pharmacokinetics and Pharmacological Properties of Chloroquine and Hydroxychloroquine in the Context of COVID-19 Infection

Chloroquine and hydroxychloroquine are quinoline derivatives used to treat malaria. To date, these medications are not approved for the treatment of viral infections, and there are no well‐controlled, prospective, randomized clinical studies or evidence to support their use in patients with coronavirus disease 2019 (COVID‐19). Nevertheless, chloroquine and hydroxychloroquine are being studied alone or in combination with other agents to assess their effectiveness in the treatment or prophylaxis for COVID‐19. The effective use of any medication involves an understanding of its pharmacokinetics, safety, and mechanism of action. This work provides basic clinical pharmacology information relevant for planning and initiating COVID‐19 clinical studies with chloroquine or hydroxychloroquine, summarizes safety data from healthy volunteer studies, and summarizes safety data from phase II and phase II/III clinical studies in patients with uncomplicated malaria, including a phase II/III study in pediatric patients following administration of azithromycin and chloroquine in combination. In addition, this work presents data describing the proposed mechanisms of action against the severe acute respiratory distress syndrome coronavirus–2 and summarizes clinical efficacy to date.

A Randomized, Double-blind, Multicenter Trial Comparing Efficacy and Safety of Imipenem/Cilastatin/Relebactam Versus Piperacillin/Tazobactam in Adults With Hospital-acquired or Ventilator-associated Bacterial Pneumonia (RESTORE-IMI 2 Study)

Background

Imipenem combined with the β-lactamase inhibitor relebactam has broad antibacterial activity, including against carbapenem-resistant gram-negative pathogens. We evaluated efficacy and safety of imipenem/cilastatin/relebactam in treating hospital-acquired/ventilator-associated bacterial pneumonia (HABP/VABP).

Methods

This was a randomized, controlled, double-blind phase 3 trial. Adults with HABP/VABP were randomized 1:1 to imipenem/cilastatin/relebactam 500 mg/500 mg/250 mg or piperacillin/tazobactam 4 g/500 mg, intravenously every 6 hours for 7–14 days. The primary endpoint was day 28 all-cause mortality in the modified intent-to-treat (MITT) population (patients who received study therapy, excluding those with only gram-positive cocci at baseline). The key secondary endpoint was clinical response 7–14 days after completing therapy in the MITT population.

Results

Of 537 randomized patients (from 113 hospitals in 27 countries), the MITT population comprised 264 imipenem/cilastatin/relebactam and 267 piperacillin/tazobactam patients; 48.6% had ventilated HABP/VABP, 47.5% APACHE II score ≥15, 24.7% moderate/severe renal impairment, 42.9% were ≥65 years old, and 66.1% were in the intensive care unit. The most common baseline pathogens were Klebsiella pneumoniae (25.6%) and Pseudomonas aeruginosa (18.9%). Imipenem/cilastatin/relebactam was noninferior (P < .001) to piperacillin/tazobactam for both endpoints: day 28 all-cause mortality was 15.9% with imipenem/cilastatin/relebactam and 21.3% with piperacillin/tazobactam (difference, −5.3% [95% confidence interval {CI}, −11.9% to 1.2%]), and favorable clinical response at early follow-up was 61.0% and 55.8%, respectively (difference, 5.0% [95% CI, −3.2% to 13.2%]). Serious adverse events (AEs) occurred in 26.7% of imipenem/cilastatin/relebactam and 32.0% of piperacillin/tazobactam patients; AEs leading to treatment discontinuation in 5.6% and 8.2%, respectively; and drug-related AEs (none fatal) in 11.7% and 9.7%, respectively.

Conclusions

Imipenem/cilastatin/relebactam is an appropriate treatment option for gram-negative HABP/VABP, including in critically ill, high-risk patients.

Clinical Trials Registration

NCT02493764.

Plasma pharmacokinetics of ceftolozane/tazobactam in pediatric patients with cystic fibrosis

BACKGROUND

The antipseudomonal cephalosporin/β-lactamase inhibitor combination ceftolozane/tazobactam could be a potential treatment option for cystic fibrosis (CF) pulmonary exacerbations. The pharmacokinetics (PK) of ceftolozane/tazobactam in children with CF merits further evaluation.

METHODS

This is a retrospective subgroup analysis of a phase 1, noncomparative trial that characterized PK, safety, and tolerability of single intravenous doses of ceftolozane/tazobactam in pediatric patients. This analysis compares ceftolozane and tazobactam plasma PK parameters, estimated from a population PK model, between patients with and without CF enrolled in that trial. Individual attainment of PK/pharmacodynamic (PD) targets of ceftolozane and tazobactam (free ceftolozane concentration >4 µg/mL for >30% and free tazobactam concentration >1 µg/mL for 20% of the dosing interval) in patients with and without CF were evaluated.

RESULTS

The study enrolled 18 patients aged greater than or equal to 2 to less than 18 years old, which included 9 with CF. Weight-normalized ceftolozane PK parameters were similar between patients with CF (clearance: 0.16 L/h/kg, half-life: 1.54 hours, volume of distribution: 0.26 L/kg) and without CF (clearance: 0.15 L/h/kg, half-life: 1.62 hours, volume of distribution: 0.26 L/kg), as were most weight-normalized tazobactam PK parameters. Weight-normalized tazobactam clearance was higher in patients with CF (0.73 L/h/kg) than patients without CF (0.42 L/h/kg). All patients achieved the prespecified PK/PD targets for ceftolozane and tazobactam.

CONCLUSIONS

This retrospective analysis demonstrated generally similar weight-normalized plasma PK parameters for ceftolozane and tazobactam among children with and without CF; thus, projected doses for treatment of pediatric hospital-acquired/ventilator-associated pneumonia, which are higher than the pediatric complicated urinary tract infection/intra-abdominal infection doses, may be appropriate for treatment of CF pulmonary exacerbation.

Thorough QTc Study of a Single Supratherapeutic Dose of Relebactam in Healthy Participants

The effects of supratherapeutic doses of intravenous (IV) relebactam on duration of ventricular depolarization and subsequent repolarization were assessed in a thorough QT/corrected QT study. This was a single-dose, double-blind (relebactam only), randomized, placebo- and positive-controlled, 3-period, balanced crossover study in healthy participants. Participants received in randomized order, and separated by a washout (≥4 days), a single dose of IV relebactam 1150 mg, oral moxifloxacin 400 mg (open-label positive control), and IV placebo. Least squares mean and 2-sided 90% confidence interval for change from baseline in population-derived corrected QT intervals for relebactam, moxifloxacin, and placebo were estimated for 24 hours. The upper limit of the 90% confidence interval of all least squares mean population-derived corrected QT treatment differences from placebo was not >10 milliseconds at any time point for 24 hours. Corrected QT assay sensitivity was confirmed with moxifloxacin treatment. Analysis of electrocardiogram parameters resulted in no additional cardiac safety concerns. Overall, a supratherapeutic dose of relebactam yielded no cardiac safety events; the 1150-mg supratherapeutic dose (4.6-fold above the 250-mg therapeutic dose) was not associated with QT prolongation or other abnormal cardiodynamic parameters. This study lends additional support to relebactam's use as a β-lactamase inhibitor in antimicrobial therapy.

Impact of renal impairment and human organic anion transporter inhibition on pharmacokinetics, safety and tolerability of relebactam combined with imipenem and cilastatin

AIMS

Two phase 1, open-label studies were conducted to investigate the effect of renal impairment (RI) and organic anion transporter (OAT) inhibition on pharmacokinetics (PK) and safety of relebactam (REL) plus imipenem/cilastatin (IMI).

METHODS

Study PN005 evaluated the PK of REL (125 mg) plus IMI (250 mg) in participants with RI vs healthy controls. Study PN019 evaluated the PK of REL (250 mg) and imipenem (500 mg; dosed as IMI) with/without probenecid (1 g; OAT inhibitor) in healthy adults.

RESULTS

Geometric mean ratios (RI/healthy matched controls) of area under the concentration-time curve from time 0 to infinity (AUC_0-∞ ; 90% confidence interval) for REL, imipenem and cilastatin increased as RI increased from mild (1.6 [1.1, 2.4], 1.4 [1.1, 1.8] and 1.6 [1.0, 2.5], respectively) to severe (4.9 [3.4, 7.0], 2.5 [1.9, 3.3] and 5.6 [3.6, 8.6], respectively). For all 3 analytes, plasma and renal clearance decreased and corresponding plasma apparent terminal half-life increased with increasing RI. Geometric mean ratios ([probenecid+IMI/REL]/[IMI/REL]) of plasma exposure for REL and imipenem were 1.24 (1.19, 1.28) and 1.16 (1.13, 1.20), respectively. The dose fraction excreted (fe) in the urine decreased progressively from mild to severe RI. Probenecid reduced renal clearance of REL and imipenem by 25 and 31%, respectively. Compared with IMI/REL, coadministration of IMI/REL with probenecid yielded lower fe for REL and imipenem. In both studies, treatment was well tolerated; there were no serious adverse events or discontinuations due to adverse events.

CONCLUSION

RI increased plasma exposure and similarly decreased clearance of REL, imipenem and cilastatin; IMI/REL dose adjustment (fixed-ratio) will be required for patients with RI. Probenecid had no clinically meaningful impact on the PK of REL or imipenem.

Population Pharmacokinetic Analysis for Imipenem-Relebactam in Healthy Volunteers and Patients With Bacterial Infections

Relebactam is a small‐molecule β‐lactamase inhibitor developed as a fixed‐dose combination with imipenem/cilastatin. The pharmacokinetics of relebactam and imipenem across 10 clinical studies were analyzed using data from adult healthy volunteers and patients with bacterial infections. Renal function estimated by creatinine clearance significantly affected the clearance of both compounds, whereas weight and health status were of less clinical significance. Simulations were used to calculate probability of joint target attainment (ratio of free drug area under the curve from 0 to 24 hours to minimum inhibitory concentration (MIC) for relebactam and percentage of time the free drug concentration exceeded the MIC for imipenem) for the proposed imipenem/relebactam dose of 500/250 mg, with adjustments for patients with renal impairment, administered as a 30‐minute intravenous infusion four times daily. These dosing regimens provide sufficient antibacterial coverage (MIC ≤ 4 μg/mL) for all renal groups.

A translational pharmacokinetic/pharmacodynamic model to characterize bacterial kill in the presence of imipenem-relebactam

OBJECTIVES

Relebactam is a small molecule β-lactamase inhibitor under clinical investigation for use as a fixed-dose combination with imipenem/cilastatin. Here we present a translational pharmacokinetic/pharmacodynamic mathematical model to support optimal dose selection of relebactam.

METHODS

Data derived from in vitro checkerboard and hollow fiber infection studies of imipenem-resistant strains of Pseudomonas aeruginosa were incorporated into the model. The model integrates the effect of relebactam concentration on imipenem susceptibility in a semi-mechanistic manner using the checkerboard data and characterizes the bacterial time-kill profiles from the hollow fiber infection model data.

RESULTS

Simulations demonstrated that the ratio of the area under the concentration-time curve for free drug to the minimum inhibitory concentration (fAUC/MIC) was the pharmacokinetic driver for relebactam, with a target fAUC/MIC=7.5 associated with 2-log kill. At a clinical dose of 250mg relebactam, greater than 2-log reductions in bacterial load are projected for imipenem-resistant strains with an imipenem/relebactam MIC≤4μg/mL.

CONCLUSIONS

The study confirms that the pharmacokinetic/pharmacodynamic driver for relebactam is fAUC/MIC, that an fAUC/MIC ratio of 7.5 is associated with 2-log kill in vitro, and that a 250mg clinical dose of relebactam achieves this target value when delivered in combination with imipenem/cilastatin.

Pharmacokinetic Interactions Between the Fixed-Dose Combinations of Elvitegravir/Cobicistat/Tenofovir Disoproxil Fumarate/Emtricitabine and Elbasvir/Grazoprevir in Healthy Adult Participants

Treatment of individuals coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV) requires careful consideration of potential drug-drug interactions. The pharmacokinetic interaction of the HCV fixed-dose combination treatment of elbasvir/grazoprevir (EBR/GZR) when coadministered with the fixed-dose combination HIV treatment of elvitegravir/cobicistat/tenofovir disoproxil fumarate/emtricitabine (EVG/COB/TDF/FTC) was evaluated in 22 healthy adults. In period 1, oral doses of EVG/COB/TDF/FTC (150 mg/150 mg/300 mg/200 mg) were administered once daily for 7 days. In period 2, oral doses of EBR/GZR (50 mg/100 mg) were administered once daily for 10 days. In period 3, oral doses of EVG/COB/TDF/FTC were coadministered with EBR/GZR once daily for 10 days. The pharmacokinetics of EVG/COB/TDF/FTC were not clinically meaningfully altered by concomitant EBR/GZR administration. Geometric mean ratios (90%CIs) for area under the plasma concentration-time curve from time 0 to 24 hours (AUC_0-24 ) in the presence/absence of EBR/GZR were 1.1 (1.0, 1.2) for elvitegravir; 1.1 (1.0, 1.1) for emtricitabine; 1.2 (1.1, 1.2) for tenofovir; and 1.5 (1.4, 1.6) for cobicistat. In comparison, the AUC_0-24 of elbasvir was ∼2 times higher and the AUC_0-24 of grazoprevir was ∼5 times higher following concomitant administration of EVG/COB/TDF/FTC and EBR/GZR. Geometric mean ratios (90%CI) for AUC_0-24 in the presence/absence of EVG/COB/TDF/FTC were 2.2 (2.0, 2.4) for elbasvir and 5.4 (4.5, 6.4) for grazoprevir. Coadministration of EVG/COB/TDF/FTC and EBR/GZR was generally well tolerated in healthy adults in this study. Nevertheless, because of the increased GZR exposure that occurs with coadministration of EVG/COB/TDF/FTC and EBR/GZR, coadministration of this combination is not recommended in those coinfected with HIV and HCV.

Simplification of Imipenem Dosing by Removal of Weight-Based Adjustments

In patients with renal insufficiency, dose adjustments based on creatinine clearance and body weight have been a component of imipenem dosage instructions. The objective of the current analysis was to provide revised dosing recommendations by evaluating the impact of creatinine clearance and body weight on the pharmacokinetics of imipenem. A population pharmacokinetics model was developed with data from 465 patients and 3300 pharmacokinetic samples. Simulations provided data to support revision of the dosing recommendations to remove body weight-adjusted dosing, and the analysis formed the basis for updates that are reflected on the current imipenem label for both the United States and Europe. The optimized regimen provided an advantage in terms of improved target attainment at breakpoint minimum inhibitory concentration values of 1 and 2 μg/mL, as low-body-weight patients maintained >90% probability of target attainment compared to <90% probability of target attainment achieved with the previously approved regimen. It was concluded that additional dose adjustments for body weight were not necessary and the new scheme would simplify dosing while maintaining patient safety and efficacy.

Population pharmacokinetics of tazobactam/ceftolozane in Japanese patients with complicated urinary tract infection and complicated intra-abdominal infection

Tazobactam/ceftolozane is a combination of a β-lactamase inhibitor and a cephalosporin antibiotic, with recommended dosage for patients with normal renal function of tazobactam 0.5 g/ceftolozane 1 g administered as a 1-h intravenous infusion every 8 h. The doses in patients with moderate and severe renal impairment are recommended to be reduced by half and 1/4th, respectively. The dose in patients undergoing dialysis is a single loading dose of 750 mg followed after 8 h by a 150 mg maintenance dose. In order to evaluate pharmacokinetics (PK) in Japanese patients, individual Bayes PK parameters were derived using the previously developed population PK models. Furthermore, attainment of PK/pharmacodynamic target in Japanese patients was calculated to confirm the recommended dosage. Based on PK data from 200 Japanese patients in the phase 3 studies, including patients with mild and moderate renal impairment, individual tazobactam/ceftolozane PK parameters were derived. No clinically relevant difference was observed in tazobactam/ceftolozane exposures between Japanese and non-Japanese patients. All Japanese patients achieved a target percent of time that free ceftolozane concentrations are above the minimum inhibitory concentration (MIC) of 30% for MICs of up to 8 μg/mL. Also for tazobactam, all Japanese patients achieved a target percent of time that the free tazobactam concentration exceeds a threshold concentration (1 μg/mL) of 20%. The results suggest that the doses will be efficacious in the Japanese population. The results indicate that the recommended dose in patients with normal renal function or renal impairment is appropriate in Japanese patients.

Perspective on the State of Pharmacometrics and Systems Pharmacology Integration

Reliance on modeling and simulation in drug discovery and development has dramatically increased over the past decade. Two disciplines at the forefront of this activity, pharmacometrics and systems pharmacology (SP), emerged independently from different fields; consequently, a perception exists that only few examples integrate these approaches. Herein, we review the state of pharmacometrics and SP integration and describe benefits of combining these approaches in a model-informed drug discovery and development framework.

A Two-Way Steady-State Pharmacokinetic Interaction Study of Doravirine (MK-1439) and Dolutegravir

INTRODUCTION

Doravirine, a non-nucleoside reverse-transcriptase inhibitor in development for the treatment of patients with human immunodeficiency virus-1 infection, has potential to be used concomitantly in antiretroviral therapy with dolutegravir, an integrase strand transfer inhibitor. The pharmacokinetic interactions between these drugs were therefore assessed.

METHODS

Oral formulations of doravirine and dolutegravir were dosed both individually and concomitantly once daily in healthy adults. Twelve subjects (six were male), 23-42 years of age, were enrolled and 11 completed this phase I, open-label, three-period, fixed-sequence study per protocol; one subject was discontinued for a positive cotinine test at admission to period 2. In period 1, dolutegravir 50 mg was administered for 7 days. After a 7-day washout, doravirine 200 mg was dosed for 7 days in period 2, followed (without washout) by both doravirine and dolutegravir simultaneously for 7 days in period 3. Plasma samples were taken to determine dolutegravir and doravirine concentrations.

RESULTS

The steady-state concentration 24 h post-dose (C₂₄) of dolutegravir was not substantially altered by co-administration of doravirine multiple doses; area under the plasma concentration-time curve from dosing to 24 h post-dose (AUC_0-24), maximum concentration (C _max), and C₂₄ geometric mean ratios were 1.36, 1.43, and 1.27, respectively. The pharmacokinetics of doravirine was not affected by multiple doses of dolutegravir (geometric mean ratios: 1.00, 0.98, and 1.06 for AUC_0-24, C₂₄, and C _max, respectively). Both drugs were generally well tolerated.

CONCLUSION

The results of this study demonstrate that concomitant administration of doravirine and dolutegravir in healthy subjects causes no clinically significant alteration in the pharmacokinetic and safety profiles of the two drugs, thereby supporting further evaluation of co-administration of these agents for human immunodeficiency virus-1 treatment.

Characterizing Class-Specific Exposure-Viral Load Suppression Response of HIV Antiretrovirals Using A Model-Based Meta-Analysis

We applied model‐based meta‐analysis of viral suppression as a function of drug exposure and in vitro potency for short‐term monotherapy in human immunodeficiency virus type 1 (HIV‐1)‐infected treatment‐naïve patients to set pharmacokinetic targets for development of nonnucleoside reverse transcriptase inhibitors (NNRTIs) and integrase strand transfer inhibitors (InSTIs). We developed class‐specific models relating viral load kinetics from monotherapy studies to potency normalized steady‐state trough plasma concentrations. These models were integrated with a literature assessment of doses which demonstrated to have long‐term efficacy in combination therapy, in order to set steady‐state trough concentration targets of 6.17‐ and 2.15‐fold above potency for NNRTIs and InSTIs, respectively. Both the models developed and the pharmacokinetic targets derived can be used to guide compound selection during preclinical development and to predict the dose–response of new antiretrovirals to inform early clinical trial design.

Pooled population pharmacokinetic model of imipenem in plasma and the lung epithelial lining fluid

AIMS

Several clinical trials have confirmed the therapeutic benefit of imipenem for treatment of lung infections. There is however no knowledge of the penetration of imipenem into the lung epithelial lining fluid (ELF), the site of action relevant for lung infections. Furthermore, although the plasma pharmacokinetics (PK) of imipenem has been widely studied, most studies have been based on selected patient groups. The aim of this analysis was to characterize imipenem plasma PK across populations and to quantify imipenem ELF penetration.

METHODS

A population model for imipenem plasma PK was developed using data obtained from healthy volunteers, elderly subjects and subjects with renal impairment, in order to identify predictors for inter-individual variability (IIV) of imipenem PK. Subsequently, a clinical study which measured plasma and ELF concentrations of imipenem was included in order to quantify lung penetration.

RESULTS

A two compartmental model best described the plasma PK of imipenem. Creatinine clearance and body weight were included as subject characteristics predictive for IIV on clearance. Typical estimates for clearance, central and peripheral volume, and inter-compartmental clearance were 11.5 l h(-1) , 9.37 l, 6.41 l, 13.7 l h(-1) , respectively (relative standard error (RSE) <8%). The distribution of imipenem into ELF was described using a time-independent penetration coefficient of 0.44 (RSE 14%).

CONCLUSION

The identified lung penetration coefficient confirms the clinical relevance of imipenem for treatment of lung infections, while the population PK model provided insights into predictors of IIV for imipenem PK and may be of relevance to support dose optimization in various subject groups.

Pharmacokinetics and 48-Week Safety and Efficacy of Raltegravir for Oral Suspension in Human Immunodeficiency Virus Type-1-Infected Children 4 Weeks to 2 Years of Age

BACKGROUND

IMPAACT P1066 is a Phase I/II open-label multicenter trial to evaluate safety, tolerability, pharmacokinetics (PK), and efficacy of multiple raltegravir (RAL) formulations in human immunodeficiency virus (HIV)-infected youth.

METHODS

Dose selection of the oral suspension formulation for each cohort (IV: 6 months to <2 years and V: 4 weeks to <6 months) was based on review of short-term safety (4 weeks) and intensive PK evaluation. Safety data through Weeks 24 and 48 and Grade ≥3 or serious adverse events (AEs) were assessed. The primary virologic endpoint was achieving HIV RNA <400 copies/mL or ≥1 log10 reduction from baseline at Week 24 (Success). For Cohort IV, optimized background therapy (OBT) could have been initiated with RAL either at study entry or after intensive PK sampling was completed at Day 5-12. An OBT was started when RAL was initiated for Cohort V subjects because they were not permitted to have received direct antiretroviral therapy before enrollment.

RESULTS

Total accrual was 27 subjects in these 2 cohorts, including 1 subject who was enrolled but never started study drug (excluded from the analyses). The targeted PK parameters (area under the curve [AUC]0-12hr and C12hr) were achieved for each cohort allowing for dose selection. Through Week 48, there were 10 subjects with Grade 3+ AEs. Two were judged related to study drug. There was 1 discontinuation due to an AE of skin rash, 1 event of immune reconstitution syndrome, and no drug-related deaths. At Week 48, for Cohorts IV and V, 87.5% of subjects achieved virologic success and 45.5% had HIV RNA <50 copies/mL. At Week 48, gains in CD4 cells of 527.6 cells/mm(3) and 7.3% were observed.

CONCLUSIONS

A total of 6 mg/kg per dose twice daily of RAL for oral suspension was well tolerated and showed favorable virologic and immunologic responses.

Population pharmacokinetic analysis of raltegravir pediatric formulations in HIV-infected children 4 weeks to 18 years of age

P1066 is an open-label study of raltegravir in HIV positive youth, ages 4 weeks-18 years. Here we summarize P1066 pharmacokinetic (PK) data and a population PK model for the pediatric chewable tablet and oral granules. Raltegravir PK parameters were calculated using noncompartmental analysis. A 2-compartment model was developed using data from P1066 and an adult study of the pediatric formulations. Interindividual variability was described by an exponential error model, and residual variability was captured by an additive/proportional error model. Twelve-hour concentrations (C12h ) were calculated from the model-derived elimination rate constant and 8-hour observed concentration. Simulated steady-state concentrations were analyzed by noncompartmental analysis. Target area under the curve (AUC0-12h ) and C12h were achieved in each cohort. For the pediatric formulations, geometric mean AUC0-12h values were 18.0-22.6 μM-hr across cohorts, and C12h values were 71-130 nM, with lower coefficients of variation versus the film-coated tablet. A 2-compartment model with first-order absorption adequately described raltegravir plasma PK in pediatric and adult patients. Weight was a covariate on clearance and central volume and was incorporated using allometric scaling. Raltegravir chewable tablets and oral granules exhibited PK parameters consistent with those from prior adult studies and older children in P1066, as well as lower variability than the film-coated tablet.

A pharmacokinetic comparison of adult and paediatric formulations of raltegravir in healthy adults

BACKGROUND

Raltegravir is an HIV-1 integrase inhibitor approved for use in adults, children and infants ≥4 weeks of age. As alternatives to the original film-coated tablet, a chewable ethylcellulose (EC) tablet and oral granules for suspension (GFS) have been developed for use in children. The purpose of this study was to evaluate these formulations in adults prior to use in paediatric studies.

METHODS

This open-label, 4-period, randomized, crossover study investigated the safety, tolerability and pharmacokinetics of raltegravir paediatric formulations and the effect of a high-fat meal on EC tablet pharmacokinetics in healthy adults. In a balanced, crossover design (with a 4-day washout between treatments), 12 subjects received one 400 mg film-coated tablet (fasted), four 100 mg EC tablets (fasted), one 400 mg GFS dose (fasted) and four 100 mg EC tablets (after a high-fat meal).

RESULTS

AUC0-∞ and Cmax were 2.6-fold and 4.6-fold higher for GFS and 1.8-fold and 3.2-fold higher for EC versus film-coated tablets. The geometric mean C12h values for the GFS formulation (162 nM) and the EC tablet (134 nM) were similar to that of the film-coated tablet (149 nM). Administration with a high-fat meal increased C12h, decreased Cmax and delayed Tmax for the EC tablet, but did not affect AUC0-∞. There were no serious adverse events (AEs) and no discontinuations due to drug-related clinical or laboratory AEs.

CONCLUSIONS

Both paediatric formulations demonstrate moderately higher AUC0-∞ and Cmax, and similar C12h compared with the film-coated tablet. These data support the use of raltegravir GFS and EC formulations in paediatric studies.

Ensemble modeling of hepatic fatty acid metabolism with a synthetic glyoxylate shunt

The liver plays a central role in maintaining whole body metabolic and energy homeostasis by consuming and producing glucose and fatty acids. Glucose and fatty acids compete for hepatic substrate oxidation with regulation ensuring glucose is oxidized preferentially. Increasing fatty acid oxidation is expected to decrease lipid storage in the liver and avoid lipid-induced insulin-resistance. To increase hepatic lipid oxidation in the presence of glucose, we previously engineered a synthetic glyoxylate shunt into human hepatocyte cultures and a mouse model and showed that this synthetic pathway increases free fatty acid beta-oxidation and confers resistance to diet-induced obesity in the mouse model. Here we used ensemble modeling to decipher the effects of perturbations to the hepatic metabolic network on fatty acid oxidation and glucose uptake. Despite sampling of kinetic parameters using the most fundamental elementary reaction models, the models based on current metabolic regulation did not readily describe the phenotype generated by glyoxylate shunt expression. Although not conclusive, this initial negative result prompted us to probe unknown regulations, and malate was identified as inhibitor of hexokinase 2 expression either through direct or indirect actions. This regulation allows the explanation of observed phenotypes (increased fatty acid degradation and decreased glucose consumption). Moreover, the result is a function of pyruvate-carboxylase, mitochondrial pyruvate transporter, citrate transporter protein, and citrate synthase activities. Some subsets of these flux ratios predict increases in fatty acid and decreases in glucose uptake after glyoxylate expression, whereas others predict no change. Altogether, this work defines the possible biochemical space where the synthetic shunt will produce the desired phenotype and demonstrates the efficacy of ensemble modeling for synthetic pathway design.

Ensemble modeling for aromatic production in Escherichia coli

Ensemble Modeling (EM) is a recently developed method for metabolic modeling, particularly for utilizing the effect of enzyme tuning data on the production of a specific compound to refine the model. This approach is used here to investigate the production of aromatic products in Escherichia coli. Instead of using dynamic metabolite data to fit a model, the EM approach uses phenotypic data (effects of enzyme overexpression or knockouts on the steady state production rate) to screen possible models. These data are routinely generated during strain design. An ensemble of models is constructed that all reach the same steady state and are based on the same mechanistic framework at the elementary reaction level. The behavior of the models spans the kinetics allowable by thermodynamics. Then by using existing data from the literature for the overexpression of genes coding for transketolase (Tkt), transaldolase (Tal), and phosphoenolpyruvate synthase (Pps) to screen the ensemble, we arrive at a set of models that properly describes the known enzyme overexpression phenotypes. This subset of models becomes more predictive as additional data are used to refine the models. The final ensemble of models demonstrates the characteristic of the cell that Tkt is the first rate controlling step, and correctly predicts that only after Tkt is overexpressed does an increase in Pps increase the production rate of aromatics. This work demonstrates that EM is able to capture the result of enzyme overexpression on aromatic producing bacteria by successfully utilizing routinely generated enzyme tuning data to guide model learning.