Statin Drug-Drug Interactions: Pharmacokinetic Basis of FDA Labeling Recommendations and Comparison Across Common Tertiary Clinical Resources.

Statins are widely prescribed and highly susceptible to pharmacokinetic (PK)-based drug-drug interactions (DDIs). To date, there has not been a comprehensive analysis of the basis upon which statin DDI recommendations in US Food and Drug Administration (FDA) prescribing information (PI) are derived. We have conducted such an analysis. We also assessed the degree of concordance of statin DDI recommendations in FDA PI and those provided in common tertiary clinical resources. We catalogued statin DDI information, including PK data and management recommendations, for statin precipitant drugs approved from 2010 to 2021, available from FDA PI and tertiary clinical resource databases. Recommendations were categorized and mapped with associated PK data to assess consistency in the PK basis for labeling recommendations. From the 80 precipitant drugs evaluated, 180 statin DDIs were identified in FDA PI. Dedicated clinical DDI studies were conducted for 54% (n = 97) of these DDIs and 34% (n = 61) of DDI recommendations were extrapolated from clinical data with other statins. Overall, we found that PK-based statin recommendations were consistent across PI. These findings highlight regulatory precedence for translating information across statins without conducting dedicated clinical DDI studies, which may support future efforts toward streamlining the approach to investigation and labeling of statin DDIs. In addition, with the exception of some notable discrepancies, general concordance was observed between FDA and tertiary resources regarding "Dose Adjustment" and "Avoid Coadministration" recommendations. However, further analyses are warranted across other DDI pairs to determine whether discordance can routinely lead to different clinical recommendations depending on the drug information resource.

Phenibut: Review and Pharmacologic Approaches to Treating Withdrawal.

ß-Phenyl-γ-aminobutyric acid (phenibut) is an analog of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) that was first synthesized in Russia in the early 1960s. It is marketed as a nootropic (smart drug) to improve cognitive performance, and to treat generalized and social anxiety, insomnia, and alcohol withdrawal. The use of phenibut is legal in the USA and it is widely available online without a prescription. Increased public awareness of phenibut has led to a growing number of reports of acute intoxication and withdrawal. In this review, we describe the pharmacology of phenibut, the presentation and management of acute intoxication, and regulatory issues, placing particular emphasis on the treatment of acute withdrawal, for which there are no comparative studies. Among 29 cases of phenibut withdrawal, patients were successfully treated with baclofen, benzodiazepines, and phenobarbital, as individual agents or in various combinations. Ancillary medications included antipsychotics, dexmedetomidine, gabapentin, and pregabalin. After stabilization, a number of patients did well on baclofen tapers, whereas others were weaned off benzodiazepines or phenobarbital. Phenobarbital may be preferred over baclofen, or used as an added agent, in patients at risk for seizures. As long as phenibut remains legal, cases of phenibut intoxication and withdrawal are likely to increase. As urine or plasma drug screening for phenibut is not widely available, it is vital that clinicians obtain a detailed medication history in patients presenting to the emergency department with nonspecific symptoms that may represent phenibut intoxication or withdrawal. Further, clinicians may wish to consult an addiction specialist or toxicologist in these situations.

Population Pharmacokinetics of Monalizumab in Patients With Advanced Solid Tumors.

Monalizumab is a novel, first-in-class humanized immunoglobulin G4 monoclonal antibody immune checkpoint inhibitor that targets the inhibitory CD94/NKG2A receptors. The objectives of this analysis were to develop a population pharmacokinetic (PK) model of monalizumab, evaluate the impact of clinically relevant covariates on monalizumab PK, and provide dose justification for clinical trials. We developed a monalizumab population PK model to characterize the PK properties of monalizumab in patients with advanced solid tumors or head and neck squamous cell carcinoma. Data from clinical studies D419NC00001 (NCT02671435) and IPH2201-203 (NCT02643550) were pooled for the analysis, resulting in a data set of 3066 PK samples derived from 507 subjects. The PK of monalizumab were reasonably described by a 2-compartment model with first-order elimination. Monalizumab generally exhibited linear PK over a dose range of 22.5-750 mg or 10 mg/kg every 2 weeks. The estimate of clearance was ≈0.255 L/day, and apparent volume of distribution was 6.36 L for a typical individual, consistent with previous findings for endogenous immunoglobulin Gs and other therapeutic monoclonal antibodies. Baseline albumin and body weight were identified as significant covariates of clearance; body weight, sex, and smoking status had a significant impact on volume of distribution; and none of these covariates had impact on peripheral volume of distribution. Although these covariates were identified as statistically significant, they are considered to be not clinically meaningful, as changes in monalizumab exposure were <30%. Therefore, no dose adjustments of monalizumab based on patient or disease characteristics are recommended.

Landscape and Regulatory Perspective on Oncology Drugs in Pregnancy.

Cancers affecting pregnant women include breast cancer, melanoma, thyroid cancer, cervical cancer, lymphomas, and leukemias. The medical management of cancer during pregnancy with molecularly targeted oncology drugs remains quite challenging, with knowledge gaps about the drugs' safety and efficacy due to exclusion of pregnant women from cancer clinical trials, discontinuation of individuals who become pregnant during clinical trials, and limited information on appropriate dosing of molecularly targeted oncology drugs during pregnancy. Physiological changes occur during pregnancy and may result in alterations in the absorption, distribution, metabolism, and excretion of drugs used in pregnant women. Physiologically based pharmacokinetic modeling that incorporates physiological changes induced by both the cancer disease state and pregnancy has the potential to inform dosing of molecularly targeted oncology drugs for pregnant women, improve our understanding of the pharmacokinetic changes associated with pregnancy in patients with cancer, facilitate the design of potential studies of molecularly targeted oncology drugs in pregnant women to support dosing recommendations, and provide model-informed pharmacokinetic data to support regulatory decision making.

Effect of Obesity on the Pharmacokinetics and Pharmacodynamics of Anticancer Agents.

An objective of the Precision Medicine Initiative, launched in 2015 by the US Food and Drug Administration and National Institutes of Health, is to optimize and individualize dosing of drugs, especially anticancer agents, with high pharmacokinetic and pharmacodynamic variability. The American Society of Clinical Oncology recently reported that 40% of obese patients receive insufficient chemotherapy doses and exposures, which may lead to reduced efficacy, and recommended pharmacokinetic studies to guide appropriate dosing in these patients. These issues will only increase in importance as the incidence of obesity in the population increases. This publication reviews the effects of obesity on (1) tumor biology, development of cancer, and antitumor response; (2) pharmacokinetics and pharmacodynamics of small-molecule anticancer drugs; and (3) pharmacokinetics and pharmacodynamics of complex anticancer drugs, such as carrier-mediated agents and biologics. These topics are not only important from a scientific research perspective but also from a drug development and regulator perspective. Thus, it is important to evaluate the effects of obesity on the pharmacokinetics and pharmacodynamics of anticancer agents in all categories of body habitus and especially in patients who are obese and morbidly obese. As the effects of obesity on the pharmacokinetics and pharmacodynamics of anticancer agents may be highly variable across drug types, the optimal dosing metric and algorithm for difference classes of drugs may be widely different. Thus, studies are needed to evaluate current and novel metrics and methods for measuring body habitus as related to optimizing the dose and reducing pharmacokinetic and pharmacodynamic variability of anticancer agents in patients who are obese and morbidly obese.

Child and Adolescent Bariatric Surgery in an Urban Tertiary Center: Special Anesthetic Considerations for Obesity.

Children and adolescents with obesity who present for weight loss surgery are a unique subset of patients. A thorough understanding of the perioperative needs of these individuals is essential to avoid deleterious complications. This review illustrates the necessity for specialized care, including the continued need of specified drug dosing and a systematic approach in the management of the pediatric bariatric patient.

Is There a Need for a Dedicated Pharmacokinetic Trial for a Drug in Obese Populations? A Drug Prioritization Decision Tree Framework.

Obesity is a growing global health concern associated with high comorbidity rates, leading to an increasing number of patients who are obese requiring medication. However, clinical trials often exclude or under-represent individuals who are obese, creating the need for a methodology to adjust labeling to ensure safe and effective dosing for all patients. To address this, we developed a 2-part decision tree framework to prioritize drugs for dedicated pharmacokinetic studies in obese subjects. Leveraging current drug knowledge and modeling techniques, the decision tree system predicts expected exposure changes and recommends labeling strategies, allowing stakeholders to prioritize resources toward the drugs most in need. In a case study evaluating 30 drugs from literature across different therapeutic areas, our first decision tree predicted the expected direction of exposure change accurately in 73% of cases. We conclude that this decision tree system offers a valuable tool to advance research in obesity pharmacology and personalize drug development for patients who are obese, ensuring safe and effective medication.

Medication Optimization Using Pharmacogenomic Testing in a Complex Mental Health Population Prescribed Psychiatric Polypharmacy.

The use of polypharmacy has become significantly more common over the past two decades, increasing the risk of drug-drug interactions and adverse drug reactions. Pharmacogenomic (PGx) assays have the purported benefit of being able to predict an individual's response to a specific medication based on genetic markers, which may facilitate the development of optimized medication regimens for patients prescribed polypharmacy. This 12-week pilot study examined the impact of the PGx results on the clinical management of Veterans who were prescribed psychiatric polypharmacy. Psychiatric medication providers were given access to the PGx assay results, including notification of drug-drug-gene interactions computed from an algorithm decision tool, to assist with medication management decisions. Veteran outpatients (N = 53) prescribed polypharmacy (mean = 13.15 medications) were enrolled into the study. In 92.4% of cases, providers changed medications at baseline, with 83% of providers indicating that they changed their original medication plan based on the PGx results. Clinical improvement over the 12-week treatment phase was seen in depression (F(1.63, 45) = 5.45, P = .01, η2  = .11) and mental health quality of life (F(2.00, 45) = 4.16, P < .05, η2  = .16). Adverse drug effects were unchanged or improved over time. Rates of polypharmacy remained unchanged. The results suggest that medication changes based on the PGx assay may be beneficial in a complex patient population prescribed polypharmacy.

Parametric Approaches in Population Pharmacokinetics.

Population pharmacokinetic (popPK) approaches have spread widely throughout clinical pharmacology research, and every clinician should have some understanding of them. After a general introduction on the fundamentals and fields of application of these approaches, this review focuses on parametric popPK methods to provide the clinicians with the conceptual tools to interpret appropriately the results of parametric popPK analyses and to understand their clinical utility. The emphasis is put on the clinical questions that popPK methods are best suited to address. The basic principles of the methodology are introduced first, and then the main algorithms and reference software programs used in such analyses are presented. The description of data analysis and clinical applications of the parametric popPK approach (ie, use in simulations and therapeutic drug monitoring) are illustrated with the example of the antiretroviral drug efavirenz.

Continued Risk of Dietary Supplements Adulterated With Approved and Unapproved Drugs: Assessment of the US Food and Drug Administration's Tainted Supplements Database 2007 Through 2021.

The US Food and Drug Administration created the Tainted Dietary Supplement Database in 2007 to identify dietary supplements adulterated with active pharmaceutical ingredients (APIs). This article compares the determination of API adulteration in dietary supplements from the 10-year time period of 2007 through 2016 to the most recent 5-year period of 2017 through 2021. From 2007 through 2021, 1068 unique products were found to be adulterated with APIs. Sexual enhancement and weight loss dietary supplements are the most common products adulterated with APIs. Phosphodiesterase-5 inhibitors are commonly included in sexual enhancement dietary supplements and a single product can include up to 5 APIs. Sibutramine, a drug removed from the market due to cardiovascular adverse events, is the most included adulterant API in weight loss products, although sibutramine analogues, phenolphthalein (which was removed from the US market because of cancer risk), and fluoxetine were also included. While muscle-building dietary supplements were commonly adulterated before 2016, since 2017 no additional adulterated products have been identified. The lack of disclosure of APIs in dietary supplements, circumventing the normal procedure with clinician oversight of prescription drug use, and the use of APIs that are banned by the Food and Drug Administration or used in combinations that were never studied are important health risks for consumers.

Early Exposure of Fosphenytoin, Levetiracetam, and Valproic Acid After High-Dose Intravenous Administration in Young Children With Benzodiazepine-Refractory Status Epilepticus.

Fosphenytoin (FOS) and its active form, phenytoin (PHT), levetiracetam (LEV), and valproic acid (VPA) are commonly used second-line treatments of status epilepticus. However, limited information is available regarding LEV and VPA concentrations following high intravenous doses, particularly in young children. The Established Status Epilepticus Treatment Trial, a blinded, comparative effectiveness study of FOS, LEV, and VPA for benzodiazepine-refractory status epilepticus provided an opportunity to investigate early drug concentrations. Patients aged ≥2 years who continued to seizure despite receiving adequate doses of benzodiazepines were randomly assigned to FOS, LEV, or VPA infused over 10 minutes. A sparse blood-sampling approach was used, with up to 2 samples collected per patient within 2 hours following drug administration. The objective of this work was to report early drug exposure of PHT, LEV, and VPA and plasma protein binding of PHT and VPA. Twenty-seven children with median (interquartile range) age of 4 (2.5-6.5) years were enrolled. The total plasma concentrations ranged from 69 to 151.3 µg/mL for LEV, 11.3 to 26.7 µg/mL for PHT and 126 to 223 µg/mL for VPA. Free fraction ranged from 4% to 19% for PHT and 17% to 51% for VPA. This is the first report in young children of LEV concentrations with convulsive status epilepticus as well as VPA concentrations after a 40 mg/kg dose. Several challenges limited patient enrollment and blood sampling. Additional studies with a larger sample size are required to evaluate the exposure-response relationships in this emergent condition.

Application of PBPK Modeling and Simulation for Regulatory Decision Making and Its Impact on US Prescribing Information: An Update on the 2018-2019 Submissions to the US FDA's Office of Clinical Pharmacology.

Since 2016, results from physiologically based pharmacokinetic (PBPK) analyses have been routinely found in the clinical pharmacology section of regulatory applications submitted to the US Food and Drug Administration (FDA). In 2018, the Food and Drug Administration's Office of Clinical Pharmacology published a commentary summarizing the application of PBPK modeling in the submissions it received between 2008 and 2017 and its impact on prescribing information. In this commentary, we provide an update on the application of PBPK modeling in submissions received between 2018 and 2019 and highlight a few notable examples.

Integrated Model to Describe Morphine Pharmacokinetics in Humans.

The pharmacokinetics (PK) of morphine has been extensively investigated. Though different publications have focused on the various aspects of morphine PK, none have quantitatively interpreted morphine PK across different publications. The objective of this research is to summarize the current understanding of morphine PK in humans quantitatively. In this research, a parent-metabolite compartmental PK modeling approach was used to summarize the current understanding of morphine PK in humans. Plasma concentration-time profiles and cumulative urine recovery time profiles of morphine, morphine-3-glucuronide, and morphine-6-glucuronide were digitized from the previous publications to develop the parent-metabolite PK model. The parent-metabolite PK model successfully described the plasma concentration-time profiles and cumulative urine recovery of morphine as well as its two major metabolites, morphine-3-glucuronide and morphine-6-glucuronide, after intravenous and oral administration of morphine. This research separated out the first-pass effect on morphine metabolism after oral administration. By integrating these results with two mass balance studies of morphine, a clear picture of morphine absorption and disposition is given. Though the results are mainly based on data collected from healthy volunteers or patients whose disease is not expected to impact morphine PK, the parent-metabolite model sets a framework to further evaluate morphine PK in special populations, such as pediatrics and patients with renal impairment.

Comparing Various In Vitro Prediction Methods to Assess the Potential of a Drug to Inhibit P-glycoprotein (P-gp) Transporter In Vivo.

The evaluation of potential of a new molecular entity (NME) to inhibit P-glycoprotein (P-gp) in vivo is an integral part of drug development and is recommended by regulatory agencies. In this study, we compared the performance of 5 prediction methods and their associated criteria (including those from the European Medicines Agency, the US Food and Drug Administration, and the Pharmaceuticals and Medical Devices Agency of Japan) for assessing the potential of an NME to inhibit P-gp in vivo based on in vitro assessment. We collected in vitro (eg, half-maximal inhibitory concentration [IC50 ], fraction unbound to plasma protein) and in vivo (eg, dose, maximum concentration, change in maximum concentration or area under the plasma concentration-time curve of the substrate digoxin) data for 50 Food and Drug Administration-approved, orally administered drug products containing 53 NMEs, from the University of Washington Metabolism and Transport Drug Interaction Database, Drugs@FDA, and PubMed. All methods yielded similar accuracy with small differences in false-negative (FN) and false-positive (FP) predictions. In addition, use of ratio of the theoretical maximum gastrointestinal concentration to IC50 is sufficient for a reasonable prediction for these orally administered drugs as potential P-gp inhibitors based on our dataset. The FN and FP rates varied depending on the cut-off value for the ratio of the theoretical maximum gastrointestinal concentration/IC50 . Possible reasons underlying FP and FN results from different methods should be taken into consideration to predict in vivo P-gp inhibition.

A Phase 1 Mass Balance Study of 14 C-Labeled Talazoparib in Patients With Advanced Solid Tumors.

This paper describes the pharmacokinetics (PK), mass balance, metabolic profiling, and safety of talazoparib after a single oral dose of 14 C-talazoparib in 6 patients with advanced solid tumors. Patients were aged ≥18 years, with a histologically confirmed advanced solid tumor at screening. A single 1-mg dose of talazoparib oral solution supplemented with 100 µCi of 14 C-labeled talazoparib was administered. Blood, urine, and feces samples were collected at various time points and analyzed for talazoparib and 14 C radioactivity. Metabolic profiling and identification were also carried out. Mean recovery of 14 C radioactivity was 68.7% in urine and 19.7% in feces. Talazoparib was minimally metabolized. Renal excretion of unchanged talazoparib was a major route of elimination, with mean recovery of 54.6% of the administered dose, whereas fecal excretion of talazoparib was limited, with mean recovery of 13.6% of the administered dose. No major metabolites of talazoparib were identified in plasma, and no metabolites that individually represented more than 10% of the administered dose were recovered in urine or feces. The concentration-time profiles of unchanged talazoparib, total 14 C radioactivity in plasma, and total 14 C radioactivity in whole blood were similar, with a median time at peak concentrations of 30 minutes and mean half-life of 89.8, 96.2, and 77.6 hours, respectively. Talazoparib was minimally metabolized, and renal excretion of unchanged talazoparib was the major route of elimination.

Prediction of Vancomycin Dose for Recommended Trough Concentrations in Pediatric Patients With Cystic Fibrosis.

Vancomycin is a key antibiotic used in the treatment of multiple conditions including infections associated with cystic fibrosis and methicillin-resistant Staphylococcus aureus. The present study sought to develop a model based on empirical evidence of optimal vancomycin dose as judged by clinical observations that could accelerate the achievement of desired trough level in children with cystic fibrosis. Transformations of dose and trough were used to arrive at regression models with excellent fit for dose based on weight or age for a target trough. Results of this study indicate that the 2 proposed regression models are robust to changes in age or weight, suggesting that the daily dose on a per-kilogram basis is determined primarily by the desired trough level. The results show that to obtain a vancomycin trough level of 20 µg/mL, a dose of 80 mg/kg/day is needed. This analysis should improve the efficiency of vancomycin usage by reducing the number of titration steps, resulting in improved patient outcome and experience.

Usability of Functional MRI in Clinical Studies for Fast and Reliable Assessment of Renal Perfusion and Quantification of Hemodynamic Effects on the Kidney.

The purpose of this study was to evaluate contrast-media-free arterial spin labeling, a technique of functional magnetic resonance imaging (MRI), for assessment of kidney perfusion in a clinical study. We examined renal perfusion by arterial spin labeling in 15 healthy adults using a clinical 1.5-T MRI system, twice under baseline conditions and 60 minutes after a single oral dose of 50 mg captopril. Data evaluation included assessment of interstudy and interrater reproducibility in addition to the pharmacological effect of captopril on kidney perfusion and a sample size calculation for potential application of the technique in pharmacological intervention studies. Interstudy reproducibility of cortical and medullary kidney perfusion was excellent (intraclass correlation coefficients 0.77 and 0.83, respectively). Interrater reproducibility was excellent in the cortex and good in the medulla (intraclass correlation coefficients 0.97 and 0.66, respectively). Ingestion of 50 mg captopril was associated with an 11% drop of systolic blood pressure and a rise in kidney perfusion by 22% in the cortex (369 ± 48 vs 452 ± 56 mL/[min·100 g], P < .001) and 26% in the medulla (157 ± 39 to 198 ± 45 ml/[min·100 g]; P < .01). Statistical power analysis revealed that a small sample size of only 6 participants is needed in a clinical trial to capture an equal change in kidney perfusion to the one induced by 50 mg captopril with a statistical power of 82% and an α error of 0.05. In conclusion, funtional MRI with arterial spin labeling is a reliable method for quantification of kidney perfusion and for fast assessment of pharmacologically induced renal perfusion changes, allowing low case numbers.

Prediction of Clearance in Neonates and Infants (≤ 3 Months of Age) for Drugs That Are Glucuronidated: A Comparative Study Between Allometric Scaling and Physiologically Based Pharmacokinetic Modeling.

The objective of this study was to evaluate the predictive performances of allometric models and a physiologically based pharmacokinetic model (PBPK) to predict clearance of glucuronidated drugs in neonates (≤ 3 months of age). From the literature, clearance values for 9 drugs (glucuronidated) for neonates and adults were obtained. Three allometric models were used to predict clearances of these glucuronidated drugs. A PBPK model was developed using the physicochemical, biopharmaceutical, and metabolic properties together with known pediatric physiology and enzymatic ontogeny. The model was first developed for adult subjects and then verified using external data and then applied to simulations in neonates. The predictive performances of allometric and PBPK models were evaluated by comparing the predicted values of clearance with the observed clearance values in the neonates. For 9 drugs, there were 13 age groups (preterm and term neonates) for which prediction error in mean clearance values within 0.5- to 1.5-fold was observed in 10 and 11 age groups by 2 allometric models and a PBPK model, respectively. The proposed allometric methods can predict mean clearances of glucuronidated drugs in preterm and term neonates (≤ 3 months of age) with reasonable accuracy (within 0.5- to 1.5-fold or 50% error) and are of practical value during neonatal drug development. The predicted mean clearance values of glucuronidated drugs in neonates ≤ 3 months of age by 2 allometric methods were comparable with the PBPK model.