Population Pharmacokinetic Approach Research Articles

Clofazimine pharmacokinetics in HIV-infected adults with diarrhea: Implications of diarrheal disease on absorption of orally administered therapeutics.

Oral drug absorption kinetics are usually established in populations with a properly functioning gastrointestinal tract. However, many diseases and therapeutics can alter gastrointestinal physiology and cause diarrhea. The extent of diarrhea-associated impact on drug pharmacokinetics has not been quantitatively described. To address this knowledge gap, we used a population pharmacokinetic modeling approach with data collected in a phase IIa study of matched human immunodeficiency virus (HIV)-infected adults with/without cryptosporidiosis and diarrhea to examine diarrhea-associated impact on oral clofazimine pharmacokinetics. A population pharmacokinetic model was developed with 428 plasma samples from 23 HIV-infected adults with/without Cryptosporidium infection using nonlinear mixed-effects modeling. Covariates describing cryptosporidiosis-associated diarrhea severity (e.g., number of diarrhea episodes, diarrhea grade) or HIV infection (e.g., viral load, CD4+ T cell count) were evaluated. A two-compartment model with lag time and first-order absorption and elimination best fit the data. Maximum diarrhea grade over the study duration was found to be associated with a more than sixfold reduction in clofazimine bioavailability. Apparent clofazimine clearance, intercompartmental clearance, central volume of distribution, and peripheral volume of distribution were 3.71 L/h, 18.2 L/h (interindividual variability [IIV] 45.0%), 473 L (IIV 3.46%), and 3434 L, respectively. The absorption rate constant was 0.625 h-1 (IIV 149%) and absorption lag time was 1.83 h. In conclusion, the maximum diarrhea grade observed for the duration of oral clofazimine administration was associated with a significant reduction in clofazimine bioavailability. Our results highlight the importance of studying disease impacts on oral therapeutic pharmacokinetics to inform dose optimization and maximize the chance of treatment success.

Scaling approaches for the prediction of human clearance of LNA-i-mir-221: A retrospective validation

LNA-i-miR-221 is a novel microRNA(miRNA)-221 inhibitor designed for the treatment of human malignancies. It has recently undergone phase 1 clinical trial (P1CT) and early pharmacokinetics (PKs) data in cancer patients are now available. We previously used multiple allometric interspecies scaling methods to draw inferences about LNA-i-miR-221 PKs in humans and estimated the patient dose based on the safe and pharmacodynamic (PD) active dose observed in mice, therefore providing a framework for the definition of safe starting and escalation doses for the P1CT. The preliminary data collected during the P1CT showed that the LNA-i-miR-221 anticipated doses, according to our human PK estimation approach, were indeed well tolerated and effective. PD data demonstrated concentration-dependent downregulation of miR-221 and upregulation of its CDKN1B/p27 and PTEN canonical targets as well as stable disease in 8 (50.0%) patients and partial response in 1 (6.3%) colorectal cancer case. Here, we detail the experimentally evaluated PK parameters of LNA-i-miR-221 in human, using both a non-compartmental and a population PKs approach. The population approach was adequately described by a three-compartments model with first-order elimination. The recorded age, sex and body weight of patients were evaluated as potential covariates. The estimated typical population parameter values were clearance (CL = 200 mL/h/kg), central volume of distribution (V1 = 45 mL/kg), peripheral volume of distribution (V2 = 200 mL/kg, volume of the second peripheral compartment V3 = 930 mL/h/kg) and inter-compartmental clearance (Q2 = 480 mL/h/kg and Q3 = 68 mL/h/kg). Age was found to be a predictor of Q3, with a statistically significant correlation. This work aimed also at retrospectively comparing the measured plasmatic clearance values with those predicted by different allometric scaling approaches. Our comparative analysis showed that the most accurate prediction was achieved by applying the single species allometric scaling approach and that the use of more than one species in allometric scaling to predict therapeutic oligonucleotides PKs would not necessarily generate the best prediction. Finally, our predictive approach was found accurate not only in predicting the main PK parameters in human but suggesting the range of effective and safe dose to be applied in the next clinic phase 2.

Population pharmacokinetics and target attainment analysis of vancomycin after intermittent dosing in adults with cystic fibrosis.

Vancomycin is the first-line agent to treat pulmonary infections caused by methicillin-resistant Staphylococcus aureus (MRSA) in people with cystic fibrosis (PwCF). However, there is no consensus on vancomycin initial dosing in this population among health institutions, and there is a large variability in initial dosing across the United States. In this study, we characterized the pharmacokinetics (PK) of vancomycin in PwCF using a population PK approach. The clinical PK data to develop the population PK model were obtained from vancomycin therapeutic monitoring data from PwCF undergoing treatment for infections due to MRSA. The population PK model was then used to perform comprehensive Monte Carlo simulations to evaluate the probability of target attainment (PTA) of 12 different initial dosing scenarios. The area under the curve to minimum inhibitory concentration (MIC) ratio ≥400 mg*h/L and <650 mg*h/L were used as efficacy and toxicity targets for PTA analysis. A total of 181 vancomycin plasma concentrations were included in the analysis. A one-compartment model with first-order elimination best described the data. Weight significantly influenced the vancomycin PK (P < 0.05). In the final model, clearance was estimated as 5.52 L/h/70 kg, and the volume of distribution was 31.5 L/70 kg. The PTA analysis showed that at MIC = 1 µg/mL, doses 1,500 q8h and 2,000 q12h showed the highest %PTA in achieving both efficacy and toxicity targets. The PTA results from this study may potentially inform the initial dosing regimens of vancomycin to treat pulmonary infections due to MRSA in PwCF.

Fludarabine Lymphodepletion Exposure Is Associated with Idecabtagene Vicleucel Toxicity in Relapsed and Refractory Multiple Myeloma Patients: Real-World Experience from the US Myeloma Immunotherapy Consortium

Background. Idecabtagene vicleucel (ide-cel) is an anti-B-cell maturation antigen (BCMA) CAR-T associated with durable responses in relapsed/refractory multiple myeloma (RRMM) patients. Fludarabine (Flu), part of standard lymphodepleting chemotherapy (LDC), improves T-cell expansion and persistence, but BSA dosing results in significant pharmacokinetic (PK) variability. Flu exposure, defined by the area under the curve (AUC), has been shown to predict rates of relapse after anti-CD19 CAR-T in B-cell acute lymphoblastic leukemia (Fabrizio et al, Blood Advances 2022). We hypothesized Flu AUC may predict outcomes after ide-cel and, using a published population model (Langenhorst et al, Clin Pharmacokinet 2019 ) we assessed the impact of Flu AUC on standard-of-care (SOC) ide-cel outcomes. Methods. RRMM patients receiving SOC ide-cel from 11 of the US Myeloma Immunotherapy Consortium centers were retrospectively analyzed. FluCy was given on days -5 to -3 before CAR-T infusion. Patients were excluded if they did not receive FluCy LDC or ide-cel infusion, had ESRD on hemodialysis, or did not have creatinine values on LDC days. A population PK approach using cumulative Flu dose and PK covariates, eGFR and body weight (BW), was used to calculate C max and AUC 0-72h. PK parameters were first tested as continuous variables in univariable and multivariable (MV) analysis. ORs are expressed per 1 mg * hr/L in the model. Results. 285 patients were included with a median follow-up of 8.7 (4.3-14.2) months. eGFR distribution indicated large variability (mean=86.5 ml/min, CV 38.4%), with 151 (53%) having renal dysfunction (eGFR &amp;lt;90 ml/min/1.73). BW ranged from 42 to 147.2 kg. Wide PK variability was observed with a median Flu AUC of 19.01 (11.23-41.47) mg * h/L (Fig 1). When adjusted for high-risk features including high risk cytogenetics, extramedullary disease, exposure to BCMA agents, and receipt of bridging therapy in a MV model, Flu AUC was not found to be associated with efficacy, including overall response and progression free survival. However, when adjusted for bridging therapy response and prior lines of therapy as an indicator of disease status/burden pre-CAR-T, each 1 mg * h/L increment in Flu AUC was found to be associated with maximum grade &amp;gt;/= 2 cytokine release syndrome (CRS) (OR 1.083; 95% CI 1.013-1.160; p=0.020). While there was no difference in the occurrence of Grade 3/4 cytopenias, each 1 mg * h/L increment in Flu AUC was significantly associated with use of stem cell boost (OR 1.130; 95% CI 1.038-1.235; p=0.005). Discussion. In this real-world dataset of ide-cel treated RRMM patients, Flu exposure was found to have a significant association with severe CRS and need for stem cell boost. This is consistent with prior studies (Hirayama et al, Blood, 2019) where a greater increase in cytokine levels and risk for CRS is seen with high intensity LDC. These data highlight how standard BSA-based Flu dosing results in significant PK variability and overestimates Flu AUC, increasing the risk of CAR-T toxicities. Prospective validation of our model-based findings through measurement of Flu blood levels, CAR-T PK, and clinical outcomes is warranted.

The cycle effect quantified: reduced tumour uptake in subsequent cycles of [177Lu]Lu-HA-DOTATATE during peptide receptor radionuclide therapy.

Clear evidence regarding the effect of reduced tumour accumulation in later peptide receptor radionuclide therapy (PRRT) cycles is lacking. Therefore, we aimed to quantify potential cycle effects for patients treated with [177Lu]Lu-HA-DOTATATE using a population pharmacokinetic (PK) modelling approach. A population PK model was developed using imaging data from 48 patients who received multiple cycles of [177Lu]Lu-HA-DOTATATE. The five-compartment model included a central, kidney, spleen, tumour and lumped rest compartment. Tumour volume and continued use of long-acting somatostatin analogues (SSAs) were tested as covariates in the model. In addition, the presence of a cycle effect was evaluated by relating the uptake rate in a specific cycle as a fraction of the (tumour or organ) uptake rate in the first cycle. The final PK model adequately captured observed radioactivity accumulation in kidney, spleen and tumour. A higher tumour volume was identified to increase the tumour uptake rate, where a twofold increase in tumour volume resulted in a 2.3-fold higher uptake rate. Also, continued use of long-acting SSAs significantly reduced the spleen uptake rate (68.4% uptake compared to SSA withdrawal (10.5% RSE)). Lastly, a cycle effect was significantly identified, where tumour uptake rate decreased to 86.9% (5.3% RSE) in the second cycle and even further to 79.7% (5.6% RSE) and 77.6% (6.2% RSE) in the third and fourth cycle, respectively, compared to cycle one. Using a population PK modelling approach, the cycle effect of reduced tumour uptake in subsequent PRRT cycles was quantified. Our findings implied that downregulation of target receptors is probably not the major cause of the cycle effect, due to a plateau in the decrease of tumour uptake in the fourth cycle.

Population pharmacokinetics of apixaban in a real-life hospitalized population from the OptimAT study.

This study aimed to characterize apixaban pharmacokinetics (PKs) and its variability in a real-world clinical setting of hospitalized patients using a population PK (PopPK) approach. Model-based simulations helped to identify factors that affect apixaban exposure and their clinical significance. A classic stepwise strategy was applied to determine the best PopPK model for describing typical apixaban PKs in hospitalized patients from the OptimAT study (n = 100) and evaluating the associated variability and influencing factors. Apixaban exposure under specific conditions was assessed using the final model. A two-compartment model with first-order absorption and elimination best described the data. The developed PopPK model revealed a major role of renal function and a minor role of P-glycoprotein phenotypic (P-gp) activity in explaining apixaban variability. The final model indicated that a patient with stage 4 chronic kidney disease (creatinine clearance [CLcr] = 15-29 mL/min) would have a 45% higher drug exposure than a patient with normal renal function (CLcr >90 mL/min), with a further 12% increase if the patient was also a poor metabolizer of P-gp. A high interindividual variability in apixaban PKs was observed in a real-life setting, which was partially explained by renal function and by P-gp phenotypic activity. Target apixaban concentrations are reached under standard dosage regimens, but overexposure can rapidly occur in the presence of cumulative factors warranting the development of a predictive tool for tailoring apixaban exposure and its clinical utility in at-risk patients.

­Pharmacokinetics of antimalarial drugs used to treat uncomplicated malaria in breastfeeding mother-infant pairs: An observational pharmacokinetic study

Background: Data surrounding the exposure of the breastfed infant to drugs and any associated risks are sparse. Drugs usually are transferred to milk in small quantities, and many have been used without obviously noticeable infant toxicity for many years – this lack of a ‘safety signal’ has further reduced the interest in studying mother-to-infant transfer of the drugs. In sub-Saharan Africa, pregnant women are at risk of Plasmodium falciparum infection, and one in four women have evidence of placental infection at the time of delivery. Artemisinin-based combination therapies (ACTs), primarily artemether-lumefantrine (AL), are the current first-line treatment for uncomplicated Plasmodium falciparum malaria, with the same dosing recommendations in breastfeeding women as those in the adult population. Dihydroartemisinin-piperaquine (DP) is routinely used as an alternative to AL in Uganda. However, lactation pharmacokinetics (PK) of ACTs are unknown. Pharmacokinetic characterization of anti-malarial transfer to breast milk and breastfed infants is crucial in understanding the potential consequences to the infant, in terms of therapeutic- and prophylactic effects as well as potential toxicity. Methods: This observational study will enroll 30 mother-infant pairs, and aims to characterize the breastmilk transfer of antimalarial medications (AL and DP) to infants when these ACTs are administered to mothers as part of treatment for uncomplicated malaria. In addition, we will assess the mental health of the breastfeeding mothers enrolled as well as the well-being of their children. PK samples of maternal blood, breastmilk and breastfeeding infant’s blood will be obtained at specific times points. Pharmacokinetic data will be analyzed using a population pharmacokinetic approach. Conclusions: We anticipate that findings from this research will guide to develop a PK model describing lumefantrine and piperaquine disposition and will provide a framework to foster other lactation pharmacokinetic studies in different disease areas.

Population Pharmacokinetic Modeling and Determination of Individual Exposure to Avalglucosidase Alfa in Adolescent and Adult Patients With Late-Onset Pompe Disease: Analysis of Pooled Data From Phase I to III Clinical Trials.

Pompe disease is a rare genetic disorder caused by a deficiency of a lysosomal enzyme called acid alpha-glucosidase and is classified into infantile and late-onset forms. Since 2006, an enzyme replacement therapy involving alglucosidase alfa has been available. In 2021, a new enzyme replacement therapy involving avalglucosidase alfa demonstrated improved clinical benefits. In this article, the authors describe the pharmacokinetics of avalglucosidase alfa using a population pharmacokinetic approach. The population pharmacokinetic model was developed using a data set that included 75 patients and 2042 plasma drug concentrations determined through enzymatic activity assay from 3 studies (phases I/II and III) and involved 3 dose levels (5, 10, and 20 mg/kg). The analysis was performed using NONMEM software. Two sequences were observed in the plasma drug concentration profile: the first kinetic driving exposure, and after 12 hours postdose, a slight rebound addressing very low concentrations that lasted up to 2 weeks. Following model screening, a model with a central compartment with parallel linear and nonlinear elimination and 2 concatenated peripheral compartments was proposed. A putative back-redistribution of a marginal fraction of the drug from the second peripheral compartment to the central compartment may explain the slight rebound in concentration. The final model's mean bias and precision for individual predictions were -2.66% and 30.7%, respectively, and -0.433% and 38.9%, respectively, for population predictions. A concatenated 3-compartment model was developed to describe the avalglucosidase alfa concentrations in patients with late-onset Pompe disease. None of the covariates tested could explain the interindividual variability.

Extended Use of Levonorgestrel-Releasing Intrauterine System (LNG-IUS) 52 mg: A Population Pharmacokinetic Approach to Estimate In Vivo Levonorgestrel Release Rates and Systemic Exposure Including Comparison With Two Other LNG-IUSs

ABSTRACT With over 30 years of use, levonorgestrel-releasing intrauterine systems (LNG-IUSs) have proven to be highly effective methods of contraceptives. The active ingredient in LNG-IUS, levonorgestrel (LNG), is released directly into the uterine cavity, which causes suppression of endometrial maturation and thickened cervical mucus. A variety of LNG-IUS options exhibit well-established safety profiles and efficacy, providing anywhere between 2 and 18 times lower systemic exposure when compared with LNG-containing pills or implants. Patient-centered decision-making regarding product choice may be encouraged through standardized comparisons of LNG release and exposure during the time of their respective usage periods. Evaluation of the efficacy, safety, and PK of extended Mirena use from beyond 5 years to the conclusion of 8 years was designed in the Mirena Extension Trial (MET), thereby facilitating comparisons with LNG-IUS 19.5 mg and LNG-IUS 13.5 mg. Using validated liquid chromatography-tandem mass spectrometry methods and SHBG concentrations, the authors determined concentrations of plasma LNG levels. Dichloromethane was used for extracting residual LNG from the elastomer material from removed IUS devices, which was then quantified via liquid chromatography and external calibration on a reversed-phase column. Although previous models used measured LNG and SHBG (serum) concentrations, the population pharmacokinetics (popPK) allows for a uniform method of comparison among different pharmacologic studies. The popPK approach allows for a reliable estimates of in vivo LNG exposure and release during the entirety of the 8-year use period. The MET enrolled premenopausal women aged 18–35 years for a multicenter, single-arm study regarding patients who had used LNG-IUS 52 mg for the last 4.5–5 years for up to 8 years. The study took place from December 22, 2016 to May 28, 2021 throughout 54 US centers, with the primary outcome of contraceptive efficacy and failure rate. Participants each provided written, informed consent. Study strengths of the popPK approach included its robust methodology, its ability to provide in vivo release rate estimates, a stepwise demo of model suitability from use years 6 to 8, model-based estimation of unbound LNG, and the ability to provide estimates for both population and individual PK profiles from sparse available sampling. Limitations include the possibility of findings being group effects possibly inapplicable to all LNG-IUS users. In addition, the data fail to provide local endometrial and cervical LNG concentrations due to the systemic nature of the LNG exposure. Finally, the popPK Mondale should not be used for theoretical question addressing (such as creating rate release estimates outside of available data sets). In conclusion, a broad data set indicates that reliable LNG exposure is delivered by 8-year popPK and release models for up to 7 years of LNG-IUs 52 mg use. Efficacy is data-supported for 6–8 years of use, with constant LNG release throughout this time frame. Systemic LNG exposure from LNG-IUD 52 mg proved both comparable to other LNG-IUS devices and significantly lower than oral and implanted LNG-containing contraceptives.

Population Pharmacokinetic Analysis of Perampanel in Portuguese Patients Diagnosed with Refractory Epilepsy.

Perampanel is a promising antiepileptic drug (AED) for refractory epilepsy treatment due to its innovative mechanism of action. This study aimed to develop a population pharmacokinetic (PopPK) model to be further used in initial dose optimization of perampanel in patients diagnosed with refractory epilepsy. A total of seventy-two plasma concentrations of perampanel obtained from forty-four patients were analyzed through a population pharmacokinetic approach by means of nonlinear mixed effects modeling (NONMEM). A one-compartment model with first-order elimination best described the pharmacokinetic profiles of perampanel. Interpatient variability (IPV) was entered on clearance (CL), while the residual error (RE) was modeled as proportional. The presence of enzyme-inducing AEDs (EIAEDs) and body mass index (BMI) were found as significant covariates for CL and volume of distribution (V), respectively. The mean (relative standard error) estimates for CL and V of the final model were 0.419 L/h (5.56%) and 29.50 (6.41%), respectively. IPV was 30.84% and the proportional RE was 6.44%. Internal validation demonstrated an acceptable predictive performance of the final model. A reliable population pharmacokinetic model was successfully developed, and it is the first enrolling real-life adults diagnosed with refractory epilepsy.

Pharmacokinetics of drugs used to treat drug sensitive-tuberculosis in breastfeeding mother-infant pairs: An observational pharmacokinetic study

Background Globally, more than half of women take medicines whilst breastfeeding. Data concerning the exposure of the breastfed infant to drugs and any related risks are sparce. Lactation studies are only rarely performed close to licensing for medicines anticipated to be widely used in women of childbearing age. Medicines taken by breastfeeding mothers on tuberculosis (TB) treatment can be transferred to the breastfed infant. Potential effects of anti-tuberculosis medicines on nursing infants are not well understood. Potential risks are the development of adverse drug effects in the breastfed infant and selection for resistance, whereas potential benefits might include exposure to potentially prophylactic concentrations of the drug. Pharmacokinetic studies are therefore necessary to understand this situation fully. Methods This study will enroll 20 mothers receiving first-line anti-tuberculosis medicines, together with their breastfed infants, with the aim of characterizing the breastmilk transfer of the medicines from the mother to the infants. Samples of maternal blood, breastmilk and breastfeeding infant’s blood will be obtained at specific time points for bioanalysis of drug concentrations. Pharmacokinetic data will be analyzed using a population pharmacokinetic approach. Additionally, the study will assess the psychological status of breastfeeding women and the well-being of their infants. Maternal depression is linked to long-term negative consequences for the infant’s physiological regulation, poor growth-promoting setting for the infants, and inappropriate interactive conduct, characterized by low compassion, constrained range of emotional expression, and varying provision of the infant’s budding engagement. Conclusions This study will provide the first systematic characterization of mother-to-infant transfer of first-line anti-tuberculosis medicines through breast milk. A mathematical pharmacokinetics model characterizing plasma-to-breastmilk transfer of rifampicin, isoniazid, ethambutol, and pyrazinamide will be developed and used to characterize infant exposure through breast milk. Our findings will contribute towards treatment optimization in breastfeeding and provide a framework to foster other lactation pharmacokinetic studies.

Predicting Chemotherapy Distribution into Breast Milk for Breastfeeding Women Using a Population Pharmacokinetic Approach.

Information on the distribution of chemotherapeutic drugs to breast milk is scarce, and reports are limited to small sample sizes. Anecdotal pharmacokinetic data have typically been acquired from lactating but non-breastfeeding patients who collect breast milk by means of an expression pump, which might not necessarily be representative for a breastfeeding population due to differences in milk production. Consequently, little is known about the variability of chemotherapy distribution to breast milk and the effect of milk production on the distribution of chemotherapy to breast milk. Our aim was to predict chemotherapy distribution to breast milk in a more realistic breastfeeding population and evaluate the effect of discarding breast milk on the potential chemotherapy exposure in infants. We developed a population pharmacokinetic model that described the breast milk production and the chemotherapy distribution to breast milk of a non-breastfeeding population, linked it to plasma pharmacokinetics, and extrapolated this to a breastfeeding population. We found that cumulative relative infant doses (RID) were higher than 10% for cyclophosphamide and doxorubicin and approximately 1% for paclitaxel. Simulations allowed us to predict the cumulative RID and its variability in the population for patients with different milk productions and the amount of breast milk that has to be discarded to reach cumulative RIDs below 1%, 0.1%, and 0.01%. Discarding 1-2, 3-6, and 0-1 days of breast milk (depending on the milk production of the patient) resulted in cumulative RID below 1% for cyclophosphamide, doxorubicin, and paclitaxel, respectively. Our results may help clinicians to derive the optimal breast milk discarding strategy for an individual patient that wants to breastfeed during chemotherapy and minimize chemotherapy exposure in their infants.

Evaluation of vancomycin individualized model-based dosing approach in neonates.

Vancomycin is commonly used to treat methicillin-resistant staphylococcal infections in neonates. Consensus on its ideal dosing in neonates has not been achieved. Model-based dosing recently has evolved as an important tool to optimize vancomycin initial dosing. The aim of this is to evaluate a population pharmacokinetic model-based approach in achieving the vancomycin therapeutic target of an AUC0-24 400 as recommended by the recent IDSA treatment guidelines. This model was implemented as a simple Excel calculator to individualize and optimize vancomycin initial dosing in neonates. An Excel calculator was developed using a previously published population pharmacokinetic model in neonates. It was evaluated using retrospectively retrieved data. For each patient, the initial empiric dose was calculated using the proposed Excel model and the most widely used neonatal dosing references. The probability of achieving the target AUC0-24 of >400mgh/L using the model-based method was calculated and compared with that of the empiric doses using other references. This analysis included 225 neonates. The probability of achieving the target AUC0-24 >400 was 89% using our model-based approach compared with 11%-59% using tertiary neonatal dosing references (p<0.01 for all comparisons). These innovative personalized dosing calculators are promising to improve vancomycin initial dosing in neonates and are easily applicable in routine practices.

Predictive Performance of Population Pharmacokinetic Models for Amikacin in Term Neonates.

Amikacin is preferred in treating Gram-negative infections in neonates and it has a narrow therapeutic window. The population pharmacokinetic modeling approach can aid in designing optimal dosage regimens for amikacin in neonates. In this study, we attempted to identify the suitable population pharmacokinetic model from the published reports for the study population from an Indian setting. Published population pharmacokinetic studies for amikacin in neonates were identified. Data on structural models and typical pharmacokinetic parameters were extracted from the studies. For the clinical study, neonates who met the inclusion criteria were enrolled in the study from the NICU, Kasturba Medical College, Manipal, during Jan 2020 to March 2022. Drug concentrations were estimated, and demographic and clinical data were collected. Identified population pharmacokinetic models were used to predict the amikacin concentrations in neonates. Predicted concentrations were compared against the observed concentrations. Differences between predicted and observed concentrations were quantified using statistical measures. The population pharmacokinetic model, which was able to predict the data well, is considered a suitable model for the study population. Dosing regimens were suggested for neonates using the pharmacometric simulation approach generated by the selected model. A total of 43 plasma samples were collected from 31 neonates. Twelve population pharmacokinetic models were found for amikacin in neonates. The predictive performance of the 12 studies was performed using clinical data. A two-compartment model reported by Illamola et al. predicted the amikacin concentrations better than other models. Illamola et al. reported creatinine clearance and body weight as the significant covariates impacting the pharmacokinetic parameters of amikacin. This model was able to predict the clinical data with 29.97% and 0.686 of relative median absolute prediction error and relative root mean square error, respectively, which is the best among the published models. The Illamola et al. model was selected as the final model to perform pharmacometric simulations for the subjects with different combinations of creatinine clearance and body weight. Dosage regimens were designed to attain target therapeutic concentrations for the virtual subjects and a nomogram was developed. The population pharmacokinetic model reported by the Illamola et al. model was selected as the final model to explain the clinical data with the lowest relative median absolute prediction error and relative root mean square error when compared with other models. An amikacin nomogram was developed for the neonates whose creatinine clearance and body weight ranged between 10 and 90 mL/min and between 2 and 4 kg, respectively. A developed nomogram can assist clinicians to design an optimal dosage regimen of amikacin for term neonates.

Population pharmacokinetic analysis reveals no impact of aprepitant on the pharmacokinetics of ifosfamide, 2-dechloroifosfamide, and 3-dechloroifosfamide

PurposeSeveral case reports and retrospective series have clearly pointed to the role of aprepitant, an antiemetic drug, in the development of encephalopathy when used with ifosfamide. Described as an inhibitor of several CYP metabolic pathways, aprepitant is suspected of drug-drug-interaction on ifosfamide pharmacokinetics. The pharmacokinetics of ifosfamide and two of its metabolites (2-dechloroifosfamide and 3-dechloroifosfamide) was studied in patients with soft tissue sarcomas to evaluate the impact of aprepitant administration. MethodsA population pharmacokinetic approach was applied to analyze data obtained in 42 patients at cycle 1 (without aprepitant) and cycle 2 (with aprepitant for 34 of them). ResultsA previously published pharmacokinetic model including a time-dependency process well fit the data. Aprepitant had no impact on ifosfamide or its two metabolite pharmacokinetic parameters. ConclusionThis study suggests that aprepitant does not lead to a significant modification of ifosfamide metabolization, even though other metabolites such as 4 hydroxyifosfamide and chloroacetaldehyde were not monitored in this study.

Population pharmacokinetics and exposure-clinical outcome relationship of remdesivir major metabolite GS-441524 in patients with moderate and severe COVID-19.

Although remdesivir, a prodrug of nucleoside analog (GS-441524), has demonstrated clinical benefits in coronavirus disease 2019 (COVID-19) treatment, its pharmacokinetics (PKs) in patients with COVID-19 remain poorly understood. Therefore, in this study, the PKs of remdesivir and its major metabolite, GS-441524, were evaluated using a population PK (PopPK) approach to understand the PK aspect and exposure-clinical outcome relationship. The serum concentrations of remdesivir and GS-441524 (102 points in 39 patients) were measured using liquid chromatography-tandem mass spectrometry. All patients received 200 mg remdesivir on the first day, followed by 100 mg on 2-5 days, except for one patient who discontinued remdesivir on day 4. The median (range) age, body surface area, and estimated glomerular filtration rate (eGFR) were 70 (42-85), 1.74 m2 (1.36-2.03), and 68 mL/min/1.73 m2 (33-113), respectively. A compartment model with first-order elimination combined with remdesivir and GS-441524 was used for nonlinear mixed-effects model analysis. Remdesivir was rapidly eliminated after infusion, whereas GS-441524 was eliminated relatively slowly (half-time=17.1h). The estimated apparent clearance (CL) and distribution volume of GS-441524 were 11.0L/h (intersubject variability [ISV]%=43.0%) and 271 L (ISV%=58.1%), respectively. The CL of GS-441524 was significantly related to the eGFR (CL × [eGFR/68]0.745 ). The post hoc area under the curve of GS-441524 was unrelated to the recovery rate or aspartate aminotransferase/alanine aminotransferase elevation. Overall, PopPK analysis showed the rapid elimination of remdesivir in the blood, and GS-441524 accumulation depended on eGFR in patients with COVID-19. However, no relevance of exposure-clinical outcome was not suggestive of the dose adjustment of remdesivir.

Individual dose recommendations for drug interaction between tacrolimus and voriconazole in adult liver transplant recipients: A semiphysiologically based population pharmacokinetic modeling approach

The magnitude of drug-drug interaction between tacrolimus and voriconazole is highly variable, and individually tailoring the tacrolimus dose when concomitantly administered with voriconazole remains difficult. This study aimed to develop a semiphysiologically based population pharmacokinetic (semi-PBPK) model and a web-based dashboard to identify the dynamic inhibition of tacrolimus metabolism caused by voriconazole and provide individual tacrolimus regimens for Chinese adult liver transplant recipients. A total of 264 tacrolimus concentrations and 146 voriconazole concentrations were prospectively collected from 32 transplant recipients. A semi-PBPK model with physiological compartments including the gut wall, portal vein, and liver was developed using the nonlinear mixed-effects modeling software NONMEM (version 7.4). A web-based dashboard was established in R software (version 3.6.1) to recommend the individual tacrolimus regimens when concomitantly administered with voriconazole. The reversible inhibition of tacrolimus metabolism caused by voriconazole was investigated in both the liver and the gut wall. Moreover, voriconazole could highly inhibit the CYP3A activity in the gut wall more than in the liver. BMI and postoperative days were identified as significant covariates on intrinsic intestinal and hepatic clearance of tacrolimus, respectively. Age and postoperative days were identified as significant covariates on the volume of distribution of voriconazole. The individual tacrolimus regimens when concomitantly administered with voriconazole could be recommended in the dashboard (https://tac-vor-ddi.shinyapps.io/shinyapp3/). In conclusion, the semi-PBPK model successfully described the dynamic inhibition process between tacrolimus and voriconazole, and the web-based dashboard could provide individual tacrolimus regimens when concomitantly administered with voriconazole.

Fexofenadine Plasma Concentrations to Estimate Systemic Exposure in Healthy Adults Using a Limited Sampling Strategy with a Population Pharmacokinetic Approach.

Fexofenadine is a recommended in vivo probe drug for phenotyping P-glycoprotein (P-gp) and organic anion transporting polypeptide (OATP) 1B1/3 transporter activities. This study evaluated a limited sampling strategy using a population pharmacokinetic approach to estimate plasma fexofenadine exposure as an index of P-gp and OATP activities. In a previous study, a single oral dose of fexofenadine (120 mg) was administered alone or in combination with grapefruit juice, Panax ginseng , or Echinacea purpurea to healthy adult participants. Serial plasma samples were collected up to 72 hours after administration and fexofenadine concentrations were measured. A population pharmacokinetic model was developed using nonlinear mixed-effects modeling. Limited sampling models (LSMs) using single and 2-timepoint fexofenadine concentrations were compared with full profiles from intense sampling using empirical Bayesian post hoc estimations of systemic exposure derived from the population pharmacokinetic model. Predefined criteria for LSM selection and validation included a coefficient of determination (R 2 ) ≥ 0.90, relative percent mean prediction error ≥ -5 to ≤5%, relative percent mean absolute error ≤ 10%, and relative percent root mean square error ≤ 15%. Fexofenadine concentrations (n = 1520) were well described using a 2-compartment model. Grapefruit juice decreased the relative oral bioavailability of fexofenadine by 25%, whereas P. ginseng and E. purpurea had no effect. All the evaluated single timepoint fexofenadine LSMs showed unacceptable percent mean prediction error, percent mean absolute error, and/or percent root mean square error. Although adding a second time point improved precision, the predefined criteria were not met. Identifying novel fexofenadine LSMs to estimate P-gp and OATP1B1/3 activities in healthy adults for future transporter-mediated drug-drug interaction studies remains elusive.

Extended use of levonorgestrel-releasing intrauterine system (LNG-IUS) 52 mg: A population pharmacokinetic approach to estimate in vivo levonorgestrel release rates and systemic exposure including comparison with two other LNG-IUSs

ObjectiveTo characterize performance of levonorgestrel-releasing intrauterine system (LNG-IUS) 52mg (Mirena) over 8 years of use and facilitate comparisons with LNG-IUS 19.5mg and LNG-IUS 13.5mg. Study designWe estimated in vivo levonorgestrel (LNG) release rates and LNG plasma/serum concentrations for LNG-IUS 52mg up to 8 years of use with a population pharmacokinetic (popPK) approach using data from the Mirena Extension Trial (MET) and earlier clinical trials. We compared these with previously published release rates and exposure data for LNG-IUS 19.5mg and 13.5mg. Our 8-year popPK and release models were developed based on measured plasma/serum LNG and sex hormone-binding globulin concentrations and residual LNG content from removed LNG-IUS 52mg devices. ResultsModel-based estimated LNG release rates for LNG-IUS 52mg decreased from ∼21 µg/d after insertion to ∼7.0 µg/d after 8 years, similar to LNG-IUS 19.5mg after 5 years (7.6 µg/d) and higher than LNG-IUS 13.5mg after 3 years (5.5 µg/d). Model-based estimated and measured plasma/serum LNG concentrations showed satisfactory agreement. Average model-based estimated LNG concentrations after 8 years of LNG-IUS 52mg use (100 ng/L [coefficient of variance 39.9%]) were similar to LNG-IUS 19.5mg after 5 years (84.8 ng/L [39.9%]) and higher than LNG-IUS 13.5mg after 3 years (58.1 ng/L [40.8%]). ConclusionsThe 8-year release and popPK models provide reliable in vivo LNG release rates and concentration estimates, respectively, facilitating direct comparisons between the 3 studied LNG-IUSs. LNG release rates from LNG-IUS 52mg at 8 years are similar to LNG-IUS 19.5mg at 5 years and higher than LNG-IUS 13.5mg at 3 years. ImplicationsLevonorgestrel release from intrauterine system reservoirs declines with duration of use in a predictable way, and in relation to the initial load. As release rates and plasma concentrations of levonorgestrel may influence endometrial and systemic side effects, these data may assist clinical decision-making.

-Pharmacokinetics of antimalarial drugs used to treat uncomplicated malaria in breastfeeding mother-infant pairs: An observational pharmacokinetic study.

Background: Data surrounding the exposure of the breastfed infant to drugs and any associated risks are sparse. Drugs usually are transferred to milk in small quantities, and many have been used without obviously noticeable infant toxicity for many years - this lack of a 'safety signal' has further reduced the interest in studying mother-to-infant transfer of the drugs. In sub-Saharan Africa, pregnant women are at risk of Plasmodium falciparuminfection, and one in four women have evidence of placental infection at the time of delivery. Artemisinin-based combination therapies (ACTs), primarily artemether-lumefantrine (AL), are the current first-line treatment for uncomplicated Plasmodium falciparum malaria, with the same dosing recommendations in breastfeeding women as those in the adult population. Dihydroartemisinin-piperaquine (DP) is routinely used as an alternative to AL in Uganda. However, lactation pharmacokinetics (PK) of ACTs are unknown. Pharmacokinetic characterization of anti-malarial transfer to breast milk and breastfed infants is crucial in understanding the potential consequences to the infant, in terms of therapeutic- and prophylactic effects as well as potential toxicity. Methods: This observational study will enroll 30 mother-infant pairs, and aims to characterize the breastmilk transfer of antimalarial medications (AL and DP) to infants when these ACTs are administered to mothers as part of treatment for uncomplicated malaria. In addition, we will assess the mental health of the breastfeeding mothers enrolled as well as the well-being of their children. PK samples of maternal blood, breastmilk and breastfeeding infant's blood will be obtained at specific times points. Pharmacokinetic data will be analyzed using a population pharmacokinetic approach. Conclusions: We anticipate that findings from this research will guide to develop a PK model describing lumefantrine and piperaquine disposition and will provide a framework to foster other lactation pharmacokinetic studies in different disease areas.