Protocol for the Vitamin D Oral Replacement in Asthma (VDORA) study

Abstract

Obesity and asthma are epidemic in the United States and obesity is an independent risk factor for asthma. Low vitamin D levels (i.e. serum 25-hydroxyvitamin D) have been reported in patients with reduced lung function, more frequent respiratory infections, and asthma exacerbations. Experts have proposed that serum levels > 40 ng/mL are required to offer the immunomodulatory benefits of vitamin D. Low vitamin D levels are common in both obesity and asthma, but it is not known whether supplementation with vitamin D improves asthma symptoms. Guidance for drug development stresses the importance of early phase studies to establish accurate population pharmacokinetics (PK) and drug dosing prior to larger phase 3 trials. The PK of this fat-soluble vitamin in children with increased adiposity are unknown; as are the doses need to reach proposed immunomodulatory levels. The objective of this study is to characterize the PK of vitamin D in children with obesity. Children ages 6-–18 years who had physician diagnosed asthma and a body mass index (BMI) >85th percentile will be randomized to receive either standard daily dosing or loading doses followed by standard daily dosing. Blood samples will be obtained to characterize the PK of vitamin D. The results of this study will be used to identify a sufficient dose of vitamin D supplement to raise serum levels above a pre-specified value that may result in anti-inflammatory actions that could improve asthma symptoms.

1. Background

Asthma and obesity are among the most common chronic conditions in children. Numerous observational studies have noted a relationship between each of these conditions and low serum 25(OH)D3 levels [1–6]. Using data from the National Health And Nutrition Examination Survey, Han et al., reported a positive correlation between vitamin D insufficiency and current asthma or current wheeze in children [7]. In addition, a meta-analysis of observational studies in both children and adults reported positive correlations between vitamin D levels and specific measures of lung function [8]. Reinehr et al. examined vitamin D levels in children with asthma and found the mean serum 25(OH)D level to hover around the insufficiency cut off of 20 ng/ml (20.6 ng/ml, interquartile range, 13.5-–26.0) [9]. In the Childhood Asthma Management Program (CAMP), the largest prospective clinical trial in pediatric asthma, 35% of children ages 5-–12 years with mild or moderate asthma had vitamin D levels < 30 ng/ml [10]. A community-based study conducted in Australia found that vitamin D levels at age 6 years (n= 689) were significant predictors of subsequent atopy / asthma-associated phenotypes at age 14 years [11]. Thus, there is a strong epidemiologic basis to suspect that low vitamin D levels are associated with asthma in children.

Other research has identified an association between obese children and low vitamin D levels. Malden et al. evaluated nine studies and reported that children with obesity had 1.9 times the odds (CI 1.4-–2.5) of vitamin D deficiency [4]. Similarly, Turer et al. found that 79% of children who were overweight (body mass index [BMI] >≥ 85th-–95th percentile for age and gender) and 86% of children with obesity (BMI ≥ 95th percentile) met the criteria for vitamin D insufficiency (serum vitamin D measured as 25(OH)D < 30 ng/ml) [12].

The etiology of low vitamin D levels in obesity is not fully under-stood. It is likely secondary to a number of factors, which may include altered deposition (or sequestration) of vitamin D in adipose tissue (resulting in reduced bioavailability and lower serum levels), as well as “volumetric dilution”, or an increased volume of distribution of both vitamin D and 25(OH)D in tissue mass [13]. In addition, sequestration of the prohormones ergocalciferol and cholecalciferol in adipose tissue limits their availability to liver 25-hydroxylase, the enzyme that converts these prohormones to 25(OH)D (reviewed in) [14]. Hepatic 25-hydrozylation is impaired in non-alcoholic fatty liver disease [14], which is common in children with obesity. Obese individuals may also be less physically active and spend less time outside, and thus may have reduced endogenous synthesis of vitamin D from exposure to sunlight [15]. Finally, the decreased consumption of fruits and vegetables contributes to declining vitamin D levels in children [16].

Vitamin D supplementation, if efficacious, would be a safe, simple, and inexpensive way to augment asthma control in pediatric obesity-related asthma patients. A 2019 meta-analysis of randomized trials of Vitamin D supplementation for asthma control supports the potential therapeutic role for Vitamin D supplementation in some patients with asthma [17]. A pediatric-specific meta-analysis published in 2015 also supported the potential role of Vitamin D supplementation in children with asthma, but acknowledged that future studies were needed to evaluate patient-relevant outcomes [18].

A body of literature supports the concept that the anti-inflammatory effects of vitamin D are associated with higher serum levels of 25(OH)D3 and levels of >40 ng/ml have been recommended to achieve the immune modulatory properties of vitamin D [19,20]. Epidemiologic data from the cancer literature supports the idea that vitamin D’s cancer protective role is concentration dependent [19]. A large, five-year, randomized, placebo-controlled trial of high dose vitamin D (2000 IU/ L daily) with one gram of omega-3 fatty acids involving more than >28,000 individuals found that individuals with BMIs <25 had a greater cancer protective effect, than individuals with a BMI > 25 [21]. This finding supports the concept that vitamin D’s effects may be concentration-dependent, particularly in the setting of obesity.

To fully evaluate its therapeutic potential, several questions regarding vitamin D supplementation must be answered. Ideal serum vitamin D levels and the benefits of supplementation are still debated [22], even for areas with a greater body of research such as bone health. A recent large trial showed no benefit in bone mineral density across three groups of adults supplemented with three different doses of vitamin D [23]. Similarly, studies of vitamin D supplementation in adults with either cardiovascular disease or diabetes have shown no benefit [21]. For children with asthma, this relationship is even less well understood and a recent pediatric trial showed no impact of supplemental vitamin D on asthma symptoms [24]. Notably, none of these studies picked a target serum level for vitamin D a priori.

Prior to developing an efficacy trial of vitamin D supplementation in obesity-related asthma with a target serum level, a better understanding of the metabolism of vitamin D in children with obesity is needed. Guidance for drug development stresses the importance of early phase studies to establish accurate population-specific PK and drug dosing prior to larger phase 3 trials [25–27]. The paucity of PK data for this fat-soluble vitamin, a possible therapeutic strategy for pediatric asthma and other pediatric immune-related diseases, was recently noted by Rosen et al [28].

In the following work, we report the detailed clinical protocol for a PK study of vitamin D recently to be conducted by the IDeA States Pediatric Clinical Trials Network (ISPCTN; Clinicaltrials.gov # NCT03686150). This study is novel in that few studies have evaluated the PKs of fat-soluble vitamins in children. Further, we will use a unique two-part design conducted under a single protocol, with two sequential dosing components. A planned interim analysis of the PK of vitamin D obtained in part 1 will be used to refine the dosing strategy for part 2 of the study. This approach can serve as a model for other pediatric researchers seeking to examine the potential therapeutic efficacy of this fat-soluble supplement in obesity-related asthma, as well as other obesity and inflammation associated diseases of childhood.

2. Methods and analysis

2.1. Primary objective and endpoint

The primary objective is to determine the appropriate vitamin D dosing regimen to achieve serum levels of ≥40 ng/ml in overweight/ obese children with asthma. The primary endpoint will be vitamin D levels, measured as serum 25(OH)D3 with a study goal to achieve 75% of participants with a serum 25(OH)D level ≥ 40 ng/ml. If neither dosing cohort achieves this goal, the observed dose-exposure relationships in children participating in the pilot study, as well as published adult data, will be used to model an appropriate dose to obtain this level if a larger intervention trial were to be considered.

2.2. Secondary objectives and endpoints

The secondary objectives will be examined the effect of vitamin D supplementation on asthma control and inflammatory biomarkers in overweight/obese participants. Endpoints for these exploratory endpoints will be (1) the number of severe asthma exacerbations as defined by unscheduled physician visits, emergency department visits, use of oral or parenteral corticosteroids, or hospitalization; (2) the Asthma Control Test (ACT); (3) and a panel of serum inflammatory biomarkers including platelet count, leptin, tumor necrosis factor alpha (TNFα) and multiple interleukin (IL) levels.

2.3. Study design

The Vitamin D Oral Replacement in Asthma (VDORA) study will be a multi-center, open label, randomized study to determine PKs of vitamin D in children with overweight or obesity and physician diagnosed asthma. The study will be conducted in two parts (Fig. 1) and will include institutions participating in the ISPCTN [29–31]. The two-part design will allow for preliminary analysis of the PK data from four dose groups in part 1, which will then be used to inform and expand upon the PK design for part 2. This approach increases clinical trial efficiency for multi-site studies in that a single protocol with planned modifications can be utilized over the course of the study. The Data Coordinating and Operations Center (DCOC) for the study will be the University of Arkansas for Medical Sciences (UAMS).

Fig. 1.

Study Design

The inclusion and exclusion criteria for the study are described in Table 1. Children ages 6 to ≤18 years of age with a BMI percentile for age and gender greater than or equal to the 85th percentile will be recruited from participating centers. Serum 25(OH)D3 levels will be obtained at screening and must be ≥10 ng/ml and < 30 ng/ml to qualify for the study. Children with serum 25(OH)D levels <10 ng/ml will be referred to their primary care provider for further management. Children who meet the BMI and serum 25(OH)D level inclusion criteria will complete a daily symptom and medication adherence diary for two weeks to demonstrate compliance with symptom and treatment self-reporting. Only those children demonstrating diary completion compliance >75th percentile will be randomized for study drug.

Table 1.

Inclusion and Exclusion criteria.

Inclusion criteria

Exclusion criteria

Age > 6 and < 18 years BMI ≥ 85th percentile for age and sex Physician-diagnosed asthma Ongoing relationship with an asthma provider Serum 25(OH)D level ≥ 10 and ≤ 30 ng/ml at screening (Visit 1) Ability to swallow pills Signed consent and assent as Females not pregnant, lactating and willing to practice birth control method Child and parent, legal guardian, or caregiver must speak English or Spanis

Known diseases of calcium metabolism or the parathyroid History of renal insufficiency or kidney stones Known liver failure or abnormal liver function of clinical significance History of Williams syndrome, sarcoidosis, or granulomatous disease Active tuberculosis Spot urine calcium/creatinine ratio > 0.37 on 2 consecutive visits. Clinical evidence of rickets Taking supplemental vitamin D > 1000 IU/day Administration of systemic glucocorticoids, drugs affecting calcium metabolism or fat absorption within 30 days prior to enrollment Known fat malabsorption, cystic fibrosis, chronic lung disease of prematurity, congenital heart disease. Type 2 diabetes is not an exclusion criterion. Anticipated move from study area in the next 9 months Another child in the household enrolled in the study Plans for significant lifestyle, including dietary, changes in the next 9 months Non-adherence during run-in procedures (diary card completion ≥75%)

Children meeting all eligibility criteria and having no exclusion criteria will be supplemented with vitamin D3 (cholecaldiferol, Bio-Tech Pharmacal, Fayetteville, Arkansas) provided as gelatin capsules containing vitamin D3 powder and microcrystalline cellulose. All supplements will be given orally. A placebo control group will not be used due to ethical concerns related to denying treatment to vitamin D insufficient or deficient children [32]. Instead, standard of care dosing (600 IU per day) will be used in a “control” group [33].

2.4. Dose groups and randomization

Part 1 of this study will include 4 dose groups with 4–8 children per group (Fig. 1). Doses were derived from previous studies of vitamin D dosing in obesity [34–36]. Randomization will be competitive across participating sites with a total randomization goal of 16 children for Part 1 and 64 children for Part 2.

1. 50,000 International Units (IU) loading dose followed by 6000 IU per day

2. 50,000 IU loading dose followed by 10,000 IU per day

3. No loading dose; 6000 IU per day

4. No loading dose; 600 IU per day (standard of care)

Part 2 will include 2 dose groups:

1. dose derived from the PK analysis of Part 1, which may be one of the existing doses or a new dose.

2. No loading dose, 600 IU per day (standard of care)

Randomization for Part 1 will use a 1:1:1:1 scheme, while randomization for Part 2 will use a 2:1 schedule (2 participants receiving the newly determined dose, 1 participant receiving the standard of care dose). As shown in Table 2, children will receive vitamin D supplementation for 16 weeks with monthly vitamin D level determinations and return to the study center for PK blood draws at 20, 24, and 28 weeks to assess post-dose clearance. Participants (stratified by BMI and gender) will be randomized in blocks to 2 age groups: 6–11 years and 12–18 years.

Table 2.

Schedule of assessments and procedures.

Activities	Screening		Dosing phase					Follow-up
Empty Cell	Screening (Visit 1)	Baseline (Visit 2)	Optional blood draw	Visit 3	Visit 4	Visit 5	Visit 6	Visits 7–9
Empty Cell	Day −14a,b	Day 0	Day 7–21	Day 28a	Day 56a	Day 84a	Day 112a	Empty Cell
Empty Cell	Empty Cell	Week 1	Week 1 - Week 3	Week 4	Week 8	Week 12	Week 16	Weeks 20, 24, 28a
Informed consent/assent	X
Demographics	X
Inclusion/exclusion criteria	X	X
Medical history	X
Collection of height/weight	X	X		X	X	X	X
Urine pregnancy testc	X				X		X
Begin run-in periodd	X
Dispense/review diary cards	X	X		X	X	X	X	X
Randomize to dose group		X
Dispense study drug		X		X	X	X
Collect unused study drug				X	X	X	X
Assess adherencee		X		X	X	X	X
Adherence communicationf		X		X	X	X	X	X
Urine calcium/creatinine ratiog	X			X	X	X	X
Inflammatory biomarkersh		X		Xi	Xi	Xi	X	Xi
Serum 25(OH) vitamin D (local laboratory)	X							Xj
Serum 25(OH) vitamin D (central laboratory)k		X	Xl	X	X	X	X	X
Asthma assessments (ACT, c-ACT)	X	X		X	X	X	X
Concomitant medications review	X	X		X	X	X	X	X
Adverse event assessment	X	X		X	X	X	X	X

^aScreening is 14 (±7) days prior to baseline. Except for the optional blood draw and basely, days are ±7.

^bA focused physical examination will only be required if an unplanned study termination visit occurs.

^cFor females of child-bearing potential only; a pregnancy test will also be done if a female participant does not remain in the study through Visit 6.

^dStart of daily diary cards.

^eWeekly adherence will be assessed by diary cards and pill count at visits.

^fPeriodic communication may be via phone, text, or email as participant prefers. Communication will occur at least every other week in weeks without a study visit between Visits 2 and 6, and then contact will be made, minimally, during the week prior to each Follow-up Visit (visits 7, 8 and 9).

^gPerformed locally; if urine Ca++/Cr ratio is >0.37 on repeat testing [after adequate hydration and within 2 business days of initial test], the patient will return for a local serum calcium and 25(OH)D. If urine Ca++/Cr sample is not obtained at the scheduled visit, the sample must be obtained within 2 business days.

^hTNFα, IL-2, IL-6, IL-10, IL-17 and leptin will be obtained by venipuncture at baseline and Visit 6. If blood for vitamin D level is drawn by venipuncture (vs fingerstick) at other times, sufficient blood will be collected for inflammatory marker determination.

ⁱFor participants having venipuncture (vs fingerstick) blood draw.

^jLocal laboratory determination of serum 25(OH)D will be performed at week 28 (Visit 9).

^kBlood for central laboratory vitamin D determination can be collected by venipuncture or by fingerstick using a microtainer collection tube.

^lAn optional blood draw (fingerstick or venipuncture) can occur any time between week 1 and 3 (from day 7 to day 21, inclusive).

Vitamin D will be packaged and distributed by the manufacturer to study sites for dispensing to the participant’s caregiver (parent or guardian). Loading doses will be administered under the supervision of site research personnel. Participants will receive dosing diaries for recording all doses of vitamin D taken through the 16-week dosing phase. Missed doses will also be noted in the daily diary cards for dosing visits.

Additional optional blood samples will be obtained at baseline and monthly during treatment for determination of inflammatory biomarkers to assess secondary points of interest including baseline inflammation and any changes seen with vitamin D supplementation. These markers will include IL-2, IL-6, IL-10, IL-17, TNF-α, platelet counts, and serum leptin.

Safety labs will include the urine calcium/creatinine ratio. For ratio values >0.37, the test will be repeated. If the ratio value remains >0.37, the family will be notified and asked to have the child increase fluid intake and return to the study site within two business days for a repeat urine collection and a serum 25(OH)D level to be run at the local laboratory. If the third value for urine calcium/creatinine ratio is >0.37, the child will be withdrawn from the study and referred to their primary care physician for further medical evaluation.

2.5. Blood sampling and laboratory analysis

As noted in Table 2, research participants will return to the clinical study sites for determination of vitamin D levels at pre-defined time points, selected to characterize the long elimination half-life of vitamin D. Blood samples for determination of the PK of vitamin D will be analyzed by Quest Labs using a validated immunoassay. Other blood samples will be analyzed at the local participating hospital laboratories. Blood samples for inflammatory markers will be analyzed by a central laboratory through a quantitative multiplex bead assay. Batched results will be transferred to the DCOC monthly, in accordance with the predetermined data transfer agreement. The DCOC will perform quality checks and report any discrepancies to Quest Labs, who will be responsible for adjudication and reconciliation. Results will be submitted by the site to the DCOC via the study electronic data capture system (EDC).

2.6. Study adherence

Research assistants will call, email, or text families weekly to provide encouragement regarding adherence to taking the study supplement. Several methods previously used in large asthma studies will be used to optimize intervention and documentation compliance [19,20,25]. Diary cards for dosing will be used to document adherence to daily Vitamin D dosing, asthma medication use and asthma symptoms. At visit 1, participants will be given diary cards and taught to use them to document asthma medication use and asthma symptoms [37,38]. Participants will be randomized to treatment after they demonstrate daily diary card adherence (defined as ≥75th percentile) during a two-week run-in period. As shown in Table 2, the first vitamin D dose will be witnessed by study staff at visit 2. Pharmacists/designees will perform pill count from sealed bottles prior to dispensing to participants.

Study staff will be trained to review the diary cards at the visit with the participant to clarify any issues or questions, and to provide positive feedback to participants who demonstrate good adherence and ongoing encouragement when warranted at each visit. Sites will make every effort to schedule participant clinic visits ±7 days of the scheduled visit, per the schedule of activities. Enrolling sites will receive a minimum of 1 on-site monitoring visit by a study monitor, as described in the Clinical Monitoring Plan. During the monitoring visit, drug accountability will be performed. Sites are to maintain all shipment records and non-dispensed product received from Bio-Tech Pharmacal, Inc.

2.7. Data handling and management

Data management for the study will be conducted by in accordance with the Society for Clinical Data Management’s (SCDM) Good Clinical Data Management Practices (GCDMP) [39] standard guidelines and the DCOC’s Standard Operating Procedures (SOPs). A study-specific data management plan (DMP) maintained by the DCOC will outline all data-related activities, including a listing of all data sources and responsible parties, case report form development and change control procedures, quality control procedures, and data acquisition and processing guidelines.

All trial data (demographics, medical history, body mass index measurements, and intervention-specific questionnaires) and laboratory test results will be captured using the community version of the OpenClinica v3.14 EDC system, which is installed, validated, and privately hosted by the UAMS Department of Biomedical Informatics. Trial data will be securely backed up to a protected server at UAMS on a regular basis for disaster recovery and to permit the generation of needed statistical reports. Full provenance tracking will be used throughout. The study EDC includes password protection and internal quality checks, such as automatic range checks, to identify data that appear inconsistent, incomplete, or inaccurate. OpenClinica Randomize, an additional EDC module [Sealed Envelope Ltd., London, UK], will be used for participant randomization.

Safety-related data will be reported to the DCOC in accordance with the DCOC Data Safety Monitoring Plan. Sites will collect and submit all safety-related to the DCOC via the study EDC. Adverse and Serious Adverse Event coding will be performed using the MedDRA (https://www.meddra.org/) standard coding dictionary and documented within the study EDC.

Study participant data will be collected and transmitted to the DCOC only for consented participants. Once consent has been obtained, participant information will be entered into the study EDC under an assigned, unique, study-specific identifier and the sites will store the mapping between site specific patient identifiers and the study-specific identifier securely. Protected health information associated with trial data, including biological samples, will be managed using the Safe Harbor Method outlined in the Health Insurance and Portability and Accountability (HIPAA) Privacy Rule (45 CFR Part 160 and Part 164) [40]. Minimal protected health information and personal identifiable information will be collected in the study EDC and study-specific reports that include identifying data will be stored electronically in IRB-approved, limited access folders. Access to data in the study EDC will be limited to only protocol identified roles. Individuals in those roles will be required to complete appropriate documentation and training prior to being granted access. The DCOC will periodically check the list of system users and review audit trail reports to ensure study EDC use only by authorized individuals in roles for which they were trained.

Data recorded in the EDC derived from source documents must be consistent with the data recorded on the source documents. Instructions on using the study EDC and completing the data capture forms will be communicated via training sessions and documented in the study-specific Manual of Procedures (MOP). All source documents will be maintained by the sites in accordance with local and federal regulations. The DCOC will consistently monitor EDC data entry, using both automated and manual methods, for data quality. Data anomalies will be conveyed to the sites for investigation and resolution. Investigators will also be asked to review and electronically sign off their site’s data in the study EDC.

2.8. Statistical analysis

Unless otherwise specified, statistical tests will be 2-sided for all analyses and the null hypothesis will be rejected at the significance level of α = 0.05. In this PK study, no adjustments for multiple comparisons for exploratory analyses will be made. Descriptive statistics for continuous data will be summarized using mean and standard deviation or median and interquartile range, as appropriate. Categorical data will be summarized using frequency and percent. Any outliers detected during data review will be investigated and methods for handling outliers or data transformation will be defined in the Statistical Analysis Plan (SAP).

2.8.1. Analysis of part 1 endpoints/outcomes

This study does not include an efficacy endpoint. The primary objective is to conduct a population PK analysis. The proportion of participants who achieve a vitamin D level ≥ 40 ng/ml will be estimated along with the corresponding 95th percentile confidence interval (CI) for each dose regimen in Part 1.

2.8.2. Analysis of part 2 endpoints/outcomes

Participants who achieve a vitamin D level ≥ 40 ng/ml at 16 weeks will be estimated along with the corresponding 95th percentile CI for each dose regimen in Part 2. Initially, a one-group test of proportion will be used to analyze the overall proportion, p, of participants with 25(OH) D ≥ 40 ng/ml at 16 weeks for each group separately.

2.8.2.1. Hypothesis test. Null hypothesis H₀: p ≤ 0.5

Alternative hypothesis H₁: p > 0.5

The test statistic will be a one-sided z-test with a significance level (alpha) of 0.05.

Next, the difference between two population proportions, P₁ (proportion of participants who achieve a vitamin D level ≥ 40 ng/ml at 16 weeks randomized to the PK optimal dose) and P₂ (proportion of participants who achieve a vitamin D level ≥ 40 ng/ml at 16 weeks randomized to the standard of care dose), will be evaluated with the following hypothesis:

2.8.2.2. Hypothesis test. Null hypothesis H₀: P₁ – P₂ = 0

Alternative hypothesis H₁: P₁ ∕= P₂

The test statistic will be a two-sided z-test with a significance level (alpha) of 0.05.

2.8.3. PK analysis

In addition to estimating the proportion of participants who achieve a vitamin D level of ≥40 ng/ml for each dose group, we will determine the best dosing strategy to obtain serum vitamin D levels ≥40 ng/ml in a majority of participants. We will employ PK/statistical modeling to determine the dose of vitamin D most likely to achieve the desired serum level. In brief, the dose-exposure profiles will be examined, and the rate of accumulation calculated, for each participant to develop a dose-exposure model across the population. The impact of selected covariates on dose exposure will be examined independently and, where relevant, nested into the final model. This will involve extrapolation from both dose groups involved in this pilot study. It is possible that neither of the doses outlined above will be the dose chosen for a larger placebo-controlled, double-masked, randomized intervention trial.

2.8.4. Analysis of secondary endpoints

We will summarize the data for each inflammatory biomarker (listed in Section 2.2) descriptively based on observed values and changes from baseline and present data overall and by dose regimens. For each inflammatory biomarker, separate repeated measures analysis of variance (ANOVA) will be performed without adjusting for any covariates. The model will include fixed effects: dose group, time, and group-by-time. For each analysis, we will calculate the point estimates and their respective CIs for changes in biomarker for each dose group and the differences in the estimated change between dose regimens.

For asthma exacerbations and asthma symptom days (ASD), we will use a separate generalized linear model with log link assuming a negative binomial distribution to account for potential over-dispersion. We will report the point estimates for the dose group mean difference along with a 95th percentile CI. For the ACT measure, we will use a repeated measures ANOVA to examine the change in ACT scores for each dose group and evaluate the difference in the estimated change between dose regimens.

2.9. Sample size estimation

2.9.1. Sample size estimation (part 1)

A sample size of >50 participants is powered >80th percentile to target a 90th percentile CI with 60th percentile and 140th percentile of the geometric mean estimates of 25(OH)D systemic clearance. The sample size assumes a coefficient of variation of 50th percentile in 25 (OH)D steady-state concentration. Based on prior experience, a sample size of 16 participants in the interim analysis will suffice to determine a recommended dose for Part 2.

2.9.2. Sample size estimation (part 2)

For the optimal dosing regimen defined by the interim PK-analysis, 31 participants will be required to test the null hypothesis that the proportion of children who achieve a vitamin D level ≥ 40 ng/ml is 50th percentile or less at 16 weeks against the alternative hypothesis that the proportion is 75th percentile or more at the one-sided 0.05 significance level with power of 0.90. To allow for a 20th percentile attrition rate, 57 participants will be randomized to (A) the PK-model derived daily dose (with a 50,000 IU loading dose) group or to (B) the standard of care (600 IU/day) dose with an allocation ratio of 2:1, so that 38 participants will be randomized to group A and 19 participants to group B.

Analysis of the primary endpoint will be based on the per-protocol population. This includes participants who were enrolled and compliant with the protocol and did not have a major protocol deviation. Safety analysis and summaries will include all participants who were enrolled and received at least one vitamin D dose.

3. Conclusion

This paper describes an individually randomized trial of vitamin D supplementation in children with obesity-related asthma to define the PK of vitamin D in this population. The current PK trial is designed to fill critical gaps in our understanding of appropriate dosing of this fat-soluble vitamin in children with high levels of adiposity. The two-part approach to PK research in children serves an example of promoting clinical trial efficiency while maintaining scientific rigor. The results of this VDORA ISPCTN PK trial will support the conduct of a future network study which could significantly impact the future medical care for children with obesity-related asthma.

Abbreviations:

ANOVA

Analysis of Variance

ACT

Asthma Control Test

ASD

Asthma Symptom Days

BMI

Body Mass Index

CAMP

Childhood Asthma Management Program

CI

Confidence Interval

DCOC

Data Coordinating and Operations Center

DMP

Data Management Plan

EDC

Electronic Data Capture

GCDMP

Good Clinical Data Management Practices

HIPAA

Health Insurance and Portability and Accountability

IL

Interleukin

MOP

Manual of Procedures

PK

Pharmacokinetics

SCDM

Society for Clinical Data Management

SOP

Standard Operating Procedure

SAP

Statistical Analysis Plan

TNFa

Tumor Necrosis Factor Alpha

UAMS

University of Arkansas for Medical Sciences

Data availability

No data was used for the research described in the article.