Use of Titration as a Therapeutic Individualization Strategy: An Analysis of Food and Drug Administration-Approved Drugs

Population Pharmacokinetic and Exposure-Response Analyses for Ponatinib in the Phase 3 PhALLCON Study

In March 2024, ponatinib received accelerated FDA approval for the treatment of newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph + ALL) in combination with chemotherapy based on the Phase 3 PhALLCON study (NCT03589326), which demonstrated a higher rate of minimal residual disease (MRD)-negative complete remission (CR) at the end of induction (EOI) with ponatinib (34.4%) versus imatinib (16.7%; p = 0.002). Patients received ponatinib (30 mg QD with reduction to 15 mg QD upon achievement of MRD-negative CR at EOI) or imatinib (600 mg QD) combined with 20 cycles of reduced-intensity chemotherapy (induction: 3 cycles; consolidation: 6 cycles; and maintenance: 11 cycles). Ponatinib pharmacokinetics (PK) were similar in patients in PhALLCON and patients in a previous population PK analysis. Bayesian re-estimation of the previously developed population PK model adequately described PhALLCON PK data. Exposure-efficacy analyses did not identify a significant relationship between ponatinib exposure and the probability of MRD-negative CR at EOI (p = 0.619), suggesting a consistent efficacy benefit across exposures. Ponatinib exposure was not a significant predictor of arterial occlusive events, venous thromboembolic events, thrombocytopenia, or lipase increase (p > 0.05). However, higher exposures were associated with a higher probability of hypertension (p = 0.0340) and alanine aminotransferase (ALT) increase (p = 0.0034). Dose reduction from 30 to 15 mg was predicted to decrease the odds of experiencing hypertension by 37.7% and ALT increase by 44.2%. Collectively, exposure-response analyses support a favorable benefit-risk profile of the approved ponatinib dosage (30 mg QD reduced to 15 mg QD upon achievement of MRD-negative CR at EOI), combined with chemotherapy, for frontline treatment of Ph + ALL.

Recommendation of mavacamten posology by model-based analyses in adults with obstructive hypertrophic cardiomyopathy

Mavacamten is the first cardiac myosin inhibitor approved by the US Food and Drug Administration for the treatment of adults with symptomatic obstructive hypertrophic cardiomyopathy (HCM). The phase III EXPLORER-HCM (NCT03470545) study used a dose-titration scheme based on mavacamten exposure and echocardiographic assessment of Valsalva left ventricular outflow tract gradient (VLVOTg) and left ventricular ejection fraction (LVEF). Using population pharmacokinetic/exposure-response modeling and simulations of virtual patients, this in silico study evaluated alternative dose-titration regimens for mavacamten, including regimens that were guided by echocardiographic measures only. Mavacamten exposure-response models for VLVOTg (efficacy) and LVEF (safety) were developed using patient data from five clinical studies and characterized using nonlinear mixed-effects models. Simulations of five echocardiography-guided regimens were performed in virtual cohorts constructed based on either expected or equal population distributions of cytochrome P450 2C19 (CYP2C19) metabolizer phenotypes. Each regimen aimed to maximize the proportions of patients who achieved a VLVOTg below 30 mm Hg while maintaining LVEF above 50% over 40 weeks and 104 weeks, respectively. The exposure-response models successfully characterized mavacamten efficacy and safety parameters. Overall, the simulated regimen with the optimal benefit-risk profile across CYP2C19 phenotypes had steps for down-titration at weeks 4 and 8 (for VLVOTg <20 mm Hg), and up-titration at week 12 (for VLVOTg ≥30 mm Hg and LVEF ≥55%), and every 12 weeks thereafter. This simulation-optimized regimen is recommended in the mavacamten US prescribing information.

Assessment of Dosing Strategies for Pediatric Drug Products

Pediatric drug dosing is challenged by the heterogeneity of developing physiology and ethical considerations surrounding a vulnerable population. Often, pediatric drug dosing leverages findings from the adult population; however, recent regulatory efforts have motivated drug sponsors to pursue pediatric-specific programs to meet an unmet medical need and improve pediatric drug labeling. This paradigm is further complicated by the pathophysiological implications of obesity on drug distribution and metabolism and the roles that body composition and body size play in drug dosing. Therefore, we sought to understand the landscape of pediatric drug dosing by characterizing the dosing strategies from drug products recently approved for pediatric indications identified using FDA Drug Databases and analyze the impact of body size descriptors (age, body surface area, weight) on drug pharmacokinetics for several selected antipsychotics approved in pediatric patients. Our review of these pediatric databases revealed a dependence on body size-guided dosing, with 68% of dosing in pediatric drug labelings being dependent on knowing either the age, body surface area, or weight of the patient to guide dosing for pediatric patients. This dependence on body size-guided dosing drives the need for special consideration when dosing a drug in overweight and obese patients. Exploratory pharmacokinetic analyses in antipsychotics illustrate possible effects of drug exposure when applying different dosing strategies for this class of drugs. Future efforts should aim to further understand the pediatric drug dosing and obesity paradigm across pediatric age ranges and drug classes to optimize drug development and clinical care for this patient population.

Dose/exposure-response modeling in dose titration trials: Overcoming the titration paradox

Response-based dose individualization or dose titration is a powerful approach to achieve precision dosing. Yet, titration as an individualization strategy is underused in drug development and therefore not reflected in labeling, possibly partly because of the data analysis challenges associated with assessing dose/exposure-response under dose titration, where there is an inherent risk of selection bias because poor responders would get high doses, whereas good responders would get low doses. In a recent article, this issue of selection bias was termed the "titration paradox." In this study, we demonstrate by means of simulation that the titration paradox may be overcome if longitudinal data from dose titration trials is analyzed using a population approach that accounts for the fact that dose/exposure-response relationships differ between individuals. We show that with an appropriate sample size and missing data missing at random, stepwise dose/exposure-response modeling based on data obtained under dose titration is not by definition subject to model selection bias or bias in parameter estimates. We also illustrate the challenges of graphical exploration of data obtained under dose titration and discuss the use of model diagnostic tools with such data. Our study shows that if, at every timepoint in the course of a trial, there is a clear causal relationship between the response and the dose/exposure level, and a population approach is used, it will in many cases be possible to develop, estimate, and appropriately qualify a dose/exposure-response model also for data obtained under dose titration, thus overcoming the titration paradox.

Model enhanced reinforcement learning to enable precision dosing: A theoretical case study with dosing of propofol

Extending the potential of precision dosing requires evaluating methodologies offering more flexibility and higher degree of personalization. Reinforcement learning (RL) holds promise in its ability to integrate multidimensional data in an adaptive process built toward efficient decision making centered on sustainable value creation. For general anesthesia in intensive care units, RL is applied and automatically adjusts dosing through monitoring of patient's consciousness. We further explore the problem of optimal control of anesthesia with propofol by combining RL with state-of-the-art tools used to inform dosing in drug development. In particular, we used pharmacokinetic-pharmacodynamic (PK-PD) modeling as a simulation engine to generate experience from dosing scenarios, which cannot be tested experimentally. Through simulations, we show that, when learning from retrospective trial data, more than 100 patients are needed to reach an accuracy within the range of what is achieved with a standard dosing solution. However, embedding a model of drug effect within the RL algorithm improves accuracy by reducing errors to target by 90% through learning to take dosing actions maximizing long-term benefit. Data residual variability impacts accuracy while the algorithm efficiently coped with up to 50% interindividual variability in the PK and 25% in the PD model's parameters. We illustrate how extending the state definition of the RL agent with meaningful variables is key to achieve high accuracy of optimal dosing policy. These results suggest that RL constitutes an attractive approach for precision dosing when rich data are available or when complemented with synthetic data from model-based tools used in model-informed drug development.

Solriamfetol Titration and AdministRaTion (START) in Patients with Obstructive Sleep Apnea: A Retrospective Chart Review and Hypothetical Patient Scenario

Introduction

Solriamfetol (Sunosi™), a dopamine/norepinephrine reuptake inhibitor, is approved (USA and EU) to treat excessive daytime sleepiness (EDS) in adults with obstructive sleep apnea (OSA) (37.5–150 mg/day). Real-world research on solriamfetol initiation is limited. The objective of this study was to describe dosing and titration strategies used when initiating solriamfetol and to assess whether and how patient factors affected these strategies.

Methods

This descriptive study, featuring a quantitative retrospective patient chart review and hypothetical patient scenario, enrolled US-based physicians prescribing solriamfetol for EDS associated with OSA and/or narcolepsy. Initiation of solriamfetol was classified as: (1) de novo (EDS medication-naive); (2) transition (switched/switching from existing EDS medication[s] to solriamfetol), or (3) add-on (adding solriamfetol to current EDS medication[s]). Study fielding occurred 3–19 June 2020. Data were summarized descriptively.

Results

Twenty-six physicians participated in the study, of whom 24 provided data from 50 patients with OSA (mean ± standard deviation [SD] age, 51.9 ± 9.1 years; 62% male). Mean apnea–hypopnea index at diagnosis indicated that most patients had severe OSA and 92% were adherent to positive airway pressure therapy. EDS was primarily moderate (56%) or severe (36%). Solriamfetol initiation was de novo for 44% of patients, transition for 52%, and add-on for 4%. Efficacy (including the need for better efficacy) was the primary reason for the initiation of solriamfetol as de novo (82%), transition (58%), and add-on (100%) therapy. Starting doses were predominantly 37.5 mg/day (48%) or 75 mg/day (48%); stable doses were typically 75 mg/day (56%) or 150 mg/day (40%). Most patients (64%) adjusted dosages once, reaching stable doses over a median (range) of 14 (1–74) days. Physicians considered EDS severity (32% of patients) when titrating, but more commonly no specific patient factors caused them to alter their titration (44% of patients). Physicians abruptly discontinued wake-promoting agents (WPAs; 17/18, 94%) and stimulants (6/9, 67%) for transitioning patients. The hypothetical patient scenario showed that physicians discontinuing prior WPAs commonly considered the current dose (23%) and potential adverse events (15%). Most patients (96%) were stable on solriamfetol at data collection.

Conclusions

In a real-world study, most physicians initiated solriamfetol at 37.5 or 75 mg/day and titrated to 75 or 150 mg/day for patients with EDS associated with OSA, adjusted dosages once, and abruptly discontinued prior WPAs. At data collection, most patients remained on solriamfetol.

Graphical abstract

Towards next-generation personalization of tacrolimus treatment: a review on advanced diagnostic and therapeutic approaches

The benefit of personalized medicine is that it allows the customization of drug therapy - maximizing efficacy while avoiding side effects. Genetic polymorphisms are one of the major contributors to interindividual variability. Currently, the only gold standard for applying personalized medicine is dose titration. Because of technological advancements, converting genotypic data into an optimum dose has become easier than in earlier years. However, for many medications, determining a personalized dose may be difficult, leading to a trial-and-error method. On the other hand, the technologically oriented pharmaceutical industry has a plethora of smart drug delivery methods that are underutilized in customized medicine. This article elaborates the genetic polymorphisms of tacrolimus as case study, and extensively covers the diagnostic and therapeutic technologies which aid in the delivery of personalized tacrolimus treatment for better clinical outcomes, thereby providing a new strategy for implementing personalized medicine.

What I have learnt from helping thousands of people taper off antidepressants and other psychotropic medications

Although psychiatric drug withdrawal syndromes have been recognized since the 1950s - recent studies confirm antidepressant withdrawal syndrome incidence upwards of 40% - medical information about how to safely go off the drugs has been lacking. To fill this gap, over the last 25 years, patients have developed a robust Internet-based subculture of peer support for tapering off psychiatric drugs and recovering from withdrawal syndrome. This account from the founder of such an online community covers lessons learned from thousands of patients regarding common experiences with medical providers, identification of adverse drug reactions, risk factors for withdrawal, tapering techniques, withdrawal symptoms, protracted withdrawal syndrome, and strategies to cope with symptoms, in the context of the existing scientific literature.

Idiosyncratic Drug-Induced Liver Injury: Mechanistic and Clinical Challenges

Idiosyncratic drug-induced liver injury (IDILI) remains a significant problem for patients and drug development. The idiosyncratic nature of IDILI makes mechanistic studies difficult, and little is known of its pathogenesis for certain. Circumstantial evidence suggests that most, but not all, IDILI is caused by reactive metabolites of drugs that are bioactivated by cytochromes P450 and other enzymes in the liver. Additionally, there is overwhelming evidence that most IDILI is mediated by the adaptive immune system; one example being the association of IDILI caused by specific drugs with specific human leukocyte antigen (HLA) haplotypes, and this may in part explain the idiosyncratic nature of these reactions. The T cell receptor repertoire likely also contributes to the idiosyncratic nature. Although most of the liver injury is likely mediated by the adaptive immune system, specifically cytotoxic CD8+ T cells, adaptive immune activation first requires an innate immune response to activate antigen presenting cells and produce cytokines required for T cell proliferation. This innate response is likely caused by either a reactive metabolite or some form of cell stress that is clinically silent but not idiosyncratic. If this is true it would make it possible to study the early steps in the immune response that in some patients can lead to IDILI. Other hypotheses have been proposed, such as mitochondrial injury, inhibition of the bile salt export pump, unfolded protein response, and oxidative stress although, in most cases, it is likely that they are also involved in the initiation of an immune response rather than representing a completely separate mechanism. Using the clinical manifestations of liver injury from a number of examples of IDILI-associated drugs, this review aims to summarize and illustrate these mechanistic hypotheses.

The Drug Titration Paradox: Correlation of More Drug With Less Effect in Clinical Data

While analyzing clinical data where an anesthetic was titrated based on an objective measure of drug effect, we observed paradoxically that greater effect was associated with lesser dose. With this study we sought to find a mathematical explanation for this negative correlation between dose and effect, to confirm its existence with additional clinical data, and to explore it further with Monte Carlo simulations. Automatically recorded dosing and effect data from more than 9,000 patients was available for the analysis. The anesthetics propofol and sevoflurane and the catecholamine norepinephrine were titrated to defined effect targets, i.e., the processed electroencephalogram (Bispectral Index, BIS) and the blood pressure. A proportional control titration algorithm was developed for the simulations. We prove by deduction that the average dose–effect relationship during titration to the targeted effect will associate lower doses with greater effects. The finding of negative correlations between propofol and BIS, sevoflurane and BIS, and norepinephrine and mean arterial pressure confirmed the titration paradox. Monte Carlo simulations revealed two additional factors that contribute to the paradox. During stepwise titration toward a target effect, the slope of the dose–effect data for the population will be “reversed,” i.e., the correlation between dose and effect will not be positive, but will be negative, and will be “horizontal” when the titration is “perfect.” The titration paradox must be considered whenever data from clinical titration (flexible dose) studies are interpreted. Such data should not be used naively for the development of dosing guidelines.

The art and science of drug titration

A “one-size-fits-all” approach has been the standard for drug dosing, in particular for agents with a wide therapeutic index. The scientific principles of drug titration, most commonly used for medications with a narrow therapeutic index, are to give the patient adequate and effective treatment, at the lowest dose possible, with the aim of minimizing unnecessary medication use and side effects. The art of drug titration involves the interplay of scientific drug titration principles with the clinical expertise of the healthcare provider, and an individualized, patient-centered partnership between the provider and the patient to review the delicate balance of perceived benefits and risks from both perspectives. Drug titration may occur as up-, down-, or cross-titration depending on whether the goal is to reach or maintain a therapeutic outcome, decrease the risk of adverse effects, or prevent withdrawal/discontinuation syndromes or recurrence of disease. Drug titration introduces additional complexities surrounding the conduct of clinical trials and real-world studies, confounding our understanding of the true effect of medications. In clinical practice, wide variations in titration schedules may exist due to a lack of evidence and consensus on titration approaches that achieve an optimal benefit-harm profile. Further, drug titration may be challenging for patients to follow, resulting in suboptimal adherence and may require increased healthcare-related visits and coordination of care amongst providers. Despite the challenges associated with drug titration, it is a personalized approach to drug dosing that blends science with art, and with supportive real-world outcomes-based evidence, can be effective for optimizing pharmacotherapeutic outcomes and improving drug safety.

A Systematic Assessment of US Food and Drug Administration Dosing Recommendations For Drug Development Programs Amenable to Response-Guided Titration

A key goal in drug development is optimized dosing for patients. Interactions between drug developers and regulatory scientists throughout development are important for the optimization of dosing and serve as a forum to discuss approaches for optimal dosing, such as precision or individualized dosing. To date, there has not been a systematic assessment of the advice provided by the US Food and Drug Administration (FDA) to drug developers from an individualized dosing perspective. Here, we reviewed FDA recommendations on dose selection for efficacy trials at end-of-phase meetings between the FDA and drug developers for 76 new molecular entities approved between 2013 and 2017 that are considered amenable for an individualized dosing method, response-guided titration. Forty FDA dosing recommendations were identified as specific to dose selection and design of the respective efficacy trials and subsequently: (i) characterized based on if they were supportive of individualized dosing and (ii) compared with dosing regimens used in efficacy trials and labeling at approval to evaluate if FDA recommendations were implemented. Of these 40 recommendations for efficacy trials, 35 (88%) were considered supportive of individualized dosing. Eighteen of these 40 recommendations (45%) were incorporated into efficacy trials and 11 (28%) were incorporated into labeling. This research suggests that early FDA-sponsor interactions can support the study of doses in efficacy trials that may lead to individualized dosing strategies in labeling.

Safety Considerations in Cannabinoid-Based Medicine

Cannabinoids are a diverse class of chemical compounds that are increasingly recognized as potential therapeutic options for a range of conditions. While many studies and reviews of cannabinoids focus on efficacy, safety is much less well reported. Overall assessment of the safety of cannabinoid-based medicines is confounded by confusion with recreational cannabis use as well as different study designs, indications, dosing, and administration methods. However, clinical studies in registered products are increasingly available, and this article aims to discuss and clarify what is known regarding the safety profiles of cannabinoid-based medicines, focusing on the medical and clinical safety evidence and identifying areas for future research. The two most well-studied cannabinoids are Δ9-tetrahydrocannabinol (THC), or its synthetic variants (dronabinol, nabilone), and cannabidiol (CBD). Across diverse indications, dizziness and fatigue are generally the most common adverse events experienced by patients receiving THC or combined THC and CBD. Patients receiving THC may experience adverse cognitive effects and impairment in psychomotor skills, with implications for driving and some occupations, while CBD may help to lower the psychotropic effects of THC when used in combination. Studies on dependency and addiction in a medical context are limited, but have shown inconsistent findings regarding misuse potential. Generally, the recommended route of administration is oral ingestion, as smoking medicinal cannabinoid products potentially releases mutagenic and carcinogenic by-products. There are several potential drug-drug interactions and contraindications for cannabinoid-based medicines, which physicians should account for when making prescribing decisions. The available evidence shows that, as with any other class of pharmaceuticals, cannabinoid-based medicines are associated with safety risks which should be assessed in the context of potential therapeutic benefits. Each patient should be assessed on an individual basis and physicians must rely on informed, evidence-based decision-making when determining whether a cannabinoid-based medicine could be an appropriate treatment option.

Absorption of the orally active multikinase inhibitor axitinib as a therapeutic index to guide dose titration in metastatic renal cell carcinoma

Purpose Axitinib is an orally active multikinase inhibitor currently used to treat patients with metastatic renal cell carcinoma (RCC). This study examined the pharmacokinetics of axitinib and the relationship between peak drug concentration (C_max) and clinical outcomes in real-world practice. Methods Twenty patients with metastatic RCC treated with axitinib monotherapy were enrolled. Post-dose (1-4 h) blood samples were obtained, and axitinib C_max in plasma was measured by liquid chromatography-tandem mass spectrometry. Efficacy endpoints were best overall response (per RECIST 1.1) and progression-free survival (PFS). The safety endpoint was the cumulative incidence of dose-limiting toxicities (DLTs). Results Large inter- and intra-individual variability in dose-adjusted C_max was observed (0.02-11.2 ng/mL/mg). Axitinib absorption was significantly influenced by glucuronidation activity (P = 0.040). C_max at steady state was significantly higher in responders than in non-responders (P = 0.013). The optimal C_max cutoff to predict a clinical response was 12.4 ng/mL. The median PFS was significantly longer in patients who achieved an average steady state C_max above the threshold than in those who did not (799 vs. 336 days; P = 0.047). The cumulative incidence of DLTs was significantly higher in patients with C_max ≥ 40.2 ng/mL than in other patients (sub-hazard ratio, 4.13; 95% confidence interval, 1.27-13.5; P = 0.019). Conclusions The potential therapeutic window of axitinib C_max in metastatic RCC was estimated at 12.4-40.2 ng/mL. Pharmacokinetically guided dose titration using therapeutic drug monitoring may improve the efficacy and safety of axitinib, warranting further investigation in a larger patient population.

Herbal Preparations of Medical Cannabis: A Vademecum for Prescribing Doctors

Cannabis has been used for centuries for therapeutic purposes. In the last century, the plant was demonized due to its high abuse liability and supposedly insufficient health benefits. However, recent decriminalization policies and new scientific evidence have increased the interest in cannabis therapeutic potential of cannabis and paved the way for the release of marketing authorizations for cannabis-based products. Although several synthetic and standardized products are currently available on the market, patients’ preferences lean towards herbal preparations, because they are easy to handle and self-administer. A literature search was conducted on multidisciplinary research databases and international agencies or institutional websites. Despite the growing popularity of medical cannabis, little data is available on the chemical composition and preparation methods of medical cannabis extracts. The authors hereby report the most common cannabis preparations, presenting their medical indications, routes of administration and recommended dosages. A practical and helpful guide for prescribing doctors is provided, including suggested posology, titration strategies and cannabinoid amounts in herbal preparations obtained from different sources of medical cannabis.