Badrul A. Chowdhury

Change in Sweat Chloride as a Clinical End Point in Cystic Fibrosis Clinical Trials: The Ivacaftor Experience

Cystic fibrosis (CF) is a life-shortening inherited disease caused by mutations in the CF transmembrane conductance regulator gene (CFTR), which encodes for the CF transmembrane conductance regulator (CFTR) ion channel that regulates chloride and water transport across the surface of epithelial cells. Ivacaftor, a drug recently approved by the US Food and Drug Administration, represents the first mutation-specific therapy for CF. It is a CFTR channel modulator and improves CFTR function in patients with CF who have a G551D mutation. A clinical trial performed to support ivacaftor dose selection demonstrated a dose-response relationship between improvement in FEV(1) and decrease in sweat chloride, a measure of CFTR function. Validation of such a relationship between FEV(1) and sweat chloride would facilitate development of new drugs that target the defective CFTR. Subsequently, in phase 3 studies, ivacaftor 150 mg bid resulted in significant improvements in FEV(1) (10%-12%) and reduction in sweat chloride (approximately 50 mmol/L). However, a decrease in sweat chloride did not correlate with improvement in FEV(1), nor did there appear to be a threshold level for change in sweat chloride above which an improvement in FEV(1) was apparent. The lack of correlation of sweat chloride with improvement in FEV(1) speaks to the multiplicity of factors, physiologic, environmental, and genetic, that likely modulate CF disease severity. Future clinical trials of drugs that are directed to the defective CFTR will need take into account the uncertainty of using even established measurements, such as sweat chloride, as clinical end points.

Dosing regimen determination for juvenile idiopathic arthritis: A review of studies during drug development

Juvenile idiopathic arthritis (JIA) is the most common childhood arthritis. In the past 10-15 years, the medical treatment options of JIA have greatly evolved and expanded due to a better understanding of the disease and the application of biologic agents. Regulations pertinent to pediatric clinical research have also helped provide a legal basis for investigating the effects of drugs and biologics in pediatrics and facilitate the pediatric drug development. The evaluation of clinical pharmacology, efficacy, and safety has provided valuable labeling information for pediatric use, including comparing exposure between adult and pediatric patients, bridging different formulations and regimens, providing appropriate dose selection recommendation with the modeling and simulation approach, and assessing the risks and benefits. This review summarizes the drugs and biologics with JIA labeling implications and discusses the application of clinical pharmacology, safety, and efficacy assessment in determining pediatric dosing regimens.

Inhaled Corticosteroids and LABAs — Removal of the FDA’s Boxed Warning

Inhaled Corticosteroids and LABAs In December, the FDA removed the boxed warning on combination products containing an inhaled corticosteroid and a long-acting beta-agonist. The decision was based on results from recently completed large safety trials that the agency required manufacturers to conduct.

Exposure–Response Modeling and Power Analysis of Components of ACR Response Criteria in Rheumatoid Arthritis (Part 2: Continuous Model)

Population pharmacokinetic/pharmacodynamic (PK/PD) models were developed to quantitate the exposure–response relationships using continuous longitudinal data on American College of Rheumatology (ACR) subcomponents, that is, tender‐joint count (TJC), swollen‐joint count (SJC), C‐reactive protein, patients assessment of pain, patients global assessment of disease activity, physicians global assessment of disease activity, and patients assessment of physical function for 5 biologics approved for use in rheumatoid arthritis. The models were then used to simulate the time courses of clinical outcomes following different treatment regimens. The relative sensitivity of the 7 subcomponents was assessed using Monte Carlo simulation–based power analysis. The developed population PK/PD models adequately described the relationship between serum concentrations and changes in ACR subcomponents. The trial simulation and subsequent power analysis showed that SJC and TJC appeared to be more sensitive than the other 5 ACR subcomponents to detect treatment effect over placebo/methotrexate. These 7 ACR subcomponents had similar power in detecting the treatment difference between different doses. In addition, the continuous measures of ACR subcomponents did not appear to be more sensitive than binary measures.

Exposure-Response Modeling and Power Analysis of Components of ACR Response Criteria in Rheumatoid Arthritis (Part 1: Binary Model): Journal of Clinical Pharmacology

American College of Rheumatology (ACR) response criteria is used to assess improvement in tender and swollen joint counts and in 3 of the 5 core measures (acute‐phase reactant, physician global assessment, patient global assessment, pain, and physical function). From the clinical trial data on 5 approved biological products for the treatment of rheumatoid arthritis, population pharmacokinetic/pharmacodynamic models were developed to quantitatively describe the relationship between exposure and response rates of 3 individual components of ACR response criteria. The models were then used to simulate the clinical outcomes at various time points following different treatment regimens. The relative sensitivity of these criteria components was assessed using power analysis. As compared to the composite endpoints (ACR20/ACR50/ACR70), the individual ACR criteria components had adequate power and higher sensitivity in distinguishing treatment effects over placebo/methotrexate control. The 3 individual ACR criteria components appeared to have similar powers at different dose levels after long‐term treatment. This research provides a unique approach to assess the relative sensitivity of the 3 binary components of ACR response criteria which would be useful to support future dose selection and trial design in the treatment of rheumatoid arthritis.

Considerations for Developing Targeted Therapies in Low‐Frequency Molecular Subsets of a Disease

Advances in our understanding of the molecular underpinnings of disease have spurred the development of targeted therapies and the use of precision medicine approaches in patient care. While targeted therapies have improved our capability to provide effective treatments to patients, they also present additional challenges to drug development and benefit–risk assessment such as identifying the subset(s) of patients likely to respond to the drug, assessing heterogeneity in response across molecular subsets of a disease, and developing diagnostic tests to identify patients for treatment. These challenges are particularly difficult to address when targeted therapies are developed to treat diseases with multiple molecular subtypes that occur at low frequencies. To help address these challenges, the US Food and Drug Administration recently published a draft guidance entitled “Developing Targeted Therapies in Low‐Frequency Molecular Subsets of a Disease.” Here we provide additional information on specific aspects of targeted therapy development in diseases with low‐frequency molecular subsets.