Asthma
Conditions
Keywords
asthma, pharmacogenetics, adult, vilanterol, adolescents, fluticasone furoate
Brief summary
This is a Phase III, multicenter, randomized, double-blind, stratified, parallel-group study with three active comparators in subjects with moderate to severe persistent asthma. The study consists of a run-in period of 4 weeks, followed by a treatment period of 12 weeks, and a follow up contact period of one week. The total duration of the study is 17 weeks. 990 subjects will be randomized to one of three treatments (FF/VI Inhalation Powder 200/25 mcg once daily in the evening; FF/VI Inhalation Powder 100/25 mcg once daily in the evening; FF 100 Inhalation Powder once daily in the evening) for 12 weeks. In addition, all subjects will be supplied albuterol/salbutamol inhalation aerosol at Visit 1 to use as needed for acute asthma symptoms throughout the entire study. Subjects will attend four on-treatment visits at Weeks 2, 4, 8, and 12 (Visits 4 through 7).
Interventions
DRUGFluticasone Furoate/ Vilanterol 200/25 mcg
Fluticasone furoate/ vilanterol will be available as 200/25 mcg Novel dry powder inhaler (NDPI) with 30 doses per device and 200/25 mcg per actuation
DRUGFluticasone Furoate/ Vilanterol 100/25 mcg
Fluticasone furoate/ vilanterol will be available as 100/25 mcg NDPI with 30 doses per device and 100/25 mcg per actuation
Fluticasone furoate will be available as 100 mcg NDPI with 30 doses per device and 100/25 mcg per actuation
Sponsors
GlaxoSmithKline
Study design
Allocation
RANDOMIZED
Intervention model
SINGLE_GROUP
Primary purpose
TREATMENT
Masking
DOUBLE (Subject, Investigator)
Eligibility
Sex/Gender
ALL
Age
12 Years to No maximum
Healthy volunteers
No
Inclusion criteria
* Subjects must give their signed and dated (written) informed consent to participate. Written informed consent must be obtained if a subject's current medication is changed as a result of study participation * Outpatient \>=12 years of age at Visit 1 who have had a diagnosis of asthma, as defined by the National Institutes of Health. Countries with local restrictions prohibiting enrolment of adolescents will only enroll subjects \>=18 years of age * Male or an eligible female. Eligible female is defined as having non-childbearing potential or having childbearing potential and using an acceptable method of birth control consistently and correctly. * Best pre-bronchodilator FEV1 of 40% to 80% of their predicted normal value. * Demonstrate \>=12% and \>=200 mL reversibility of FEV1 within 10 to 40 minutes following 4 inhalations of albuterol/salbutamol inhalation aerosol (or an equivalent nebulized treatment with albuterol/salbutamol solution) or have documented reversibility testing within the 6 months prior to Visit 1 meeting this measure of reversibility. A spacer device may be used for testing, if required. * If subject have received ICS for at least 12 weeks prior to Visit 1 and their treatment during the 4 weeks immediately prior to Visit 1 consisted of either of the two regimens (a or b).a.) A stable mid-dose or high-dose of ICS alone (e.g., \>=FP 250 mcg twice daily) or b.) A stable dose of a mid-dose ICS/LABA combination (e.g., FP/Salmeterol \[SALM\] 250/50 mcg twice daily) or an equivalent combination via separate inhalers. * Use of ICS/LABA are not permitted with LABA on the day of Visit 1. * Must be able to replace current SABA treatment with albuterol/salbutamol aerosol inhaler at Visit 1 for use as needed, during the study. Subjects must be able to withhold albuterol/salbutamol for at least 6 hours prior to study visits
Exclusion criteria
* History of life-threatening asthma, defined as an asthma episode that required intubation and/or was associated with hypercapnia, respiratory arrest or hypoxic seizures within the last 5 years. * Upper or lower respiratory tract, sinus, or middle ear that is: not resolved within 4 weeks of Visit 1 and led to a change in asthma management or, in the opinion of the investigator, expected to affect the subject's asthma status or the subject's ability to participate in the study. * Any asthma exacerbation that required oral corticosteroids within the 12 weeks prior to Visit 1 or, resulted in an overnight hospitalization requiring additional treatment for asthma within 6 months prior to Visit 1. * A subject must not have current evidence of atelectasis (segmental or larger), bronchopulmonary dysplasia, chronic obstructive pulmonary disease, Or any evidence of concurrent respiratory disease other than asthma * A subject must not have any clinically significant, uncontrolled condition or disease state that, in the opinion of the investigator, would put the safety of the subject at risk through study participation or would confound the interpretation of the efficacy results if the condition/disease exacerbated during the study * Chronic stable hepatitis B or C are acceptable provided their screening alanine transaminase (ALT) is \<2x upper limit of normal (ULN) and the y otherwise meet the entry criteria. Chronic co-infection with both hepatitis B and hepatitis C are not eligible * Clinical visual evidence of candidiasis at Visit 1 * Use of any investigational drug within 30 days prior to Visit 1 or within five half-lives (t½), whichever is longer of the two. * Allergies to drug or milk protein: any adverse reaction, to any beta2-agonist, sympathomimetic drug, or any intranasal, inhaled, or systemic corticosteroid therapy or known or suspected sensitivity to the constituents of the NDPI, or history of severe milk protein allergy * Administration of medication that would significantly affect the course of asthma, or interact with study drug * Use of immunosuppressive medications during the study. * Use of potent CYP3A4 inhibitor within 4 weeks of Visit 1. * A subject or his/her parent or legal guardian has any infirmity, disability, disease, or resides in a geographical location which seems likely, in the opinion of the Investigator, to impair compliance with any aspect of this study protocol, including visit schedule, and completion of the daily diaries. * Current smoker or has a smoking history of 10 pack-years (20 cigarettes/day for 10 years). A subject may not have used inhaled tobacco products within the past 3 months (i.e., cigarettes, cigars, or pipe tobacco). * If subject is an immediate family member of the participating investigator, sub-investigator, study coordinator, or employee of the participating investigator. * Subject previously randomized to treatment with FF/VI or FF in another Phase III study * Subjects working on night shift a week prior to Visit 1 or during the study period. * Adolescents who are wards of the state or government
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Change From Baseline in Weighted Mean Forced Expiratory Volume in One Second (FEV1) Over 0 to 24 Hours Post-dose at the End of the 12-week Treatment Period | Baseline and Week 12 | Pulmonary function was measured by FEV1, defined as the maximal amount of air that can be forcefully exhaled in one second. The weighted mean was calculated from the pre-dose FEV1 (within 30 minutes prior to dosing) and post-dose FEV1 measurements at 5, 15, and 30 minutes and at 1, 2, 3, 4, 5, 12, 16, 20, 23, and 24 hours on Day 84/Week 12. At each time point, the highest of three technically acceptable measurements was recorded. Change from Baseline was calculated as the weighted mean of the 24-hour serial FEV1 measures on Day 84/Week 12 minus the Baseline value. Baseline was the pre-dose FEV1 measurement value obtained at Visit 3. The analysis was performed using an Analysis of Covariance (ANCOVA) model with covariates of Baseline FEV1, region, sex, age, and treatment. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Change From Baseline in Clinic Visit Trough FEV1 at the End of the 12-week Treatment Period | Baseline and Week 12 | Pulmonary function was measured by FEV1, defined as the maximal amount of air that can be forcefully exhaled in one second. Trough FEV1 is defined as a pre-dose FEV1 measurement taken at a clinic visit while still on-treatment. Change from Baseline in trough FEV1 at the end of the 12-week treatment period was defined using the 24-hour post-dose serial FEV1 measurement taken at the Week 12 clinic visit. Change from Baseline was calculated as the Week 12 trough FEV1 value minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline trough FEV1, region, sex, age, and treatment. The last observation carried forward (LOCF) method was used to impute missing data, in which the last non-missing post-Baseline on-treatment measurement at scheduled clinic visits was used to impute the missing measurements. |
| Change From Baseline in the Percentage of Rescue-free 24-hour (hr) Periods During the 12-week Treatment Period | Baseline and Weeks 1-12 | The number of inhalations of rescue albuterol/salbutamol inhalation aerosol used during the day and night was recorded by the participants in a daily electronic diary (eDiary). A 24-hour (hr) period in which a participant's responses to both the morning and evening assessments indicated no use of rescue medication was considered to be rescue free. The Baseline value was derived from the last 7 days of the daily eDiary prior to the randomization of the participant. Change from Baseline was calculated as the averaged value during the 12-week treatment period minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline, region, sex, age, and treatment. |
| Change From Baseline in the Percentage of Symptom-free 24-hour (hr) Periods During the 12-week Treatment Period | Baseline and Weeks 1-12 | Asthma symptoms were recorded in a daily eDairy by the participants every day in the morning and evening before taking any rescue or study medication and before the peak expiratory flow measurement. A 24-hour (hr) period in which a participant's responses to both the morning and evening assessments indicated no symptoms was considered to be symptom free. The Baseline value was derived from the last 7 days of the daily eDiary prior to the randomization of the participant. Change from Baseline was calculated as the averaged value during the 12-week treatment period minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline, region, sex, age, and treatment. |
| Change From Baseline in Daily Morning (AM) Peak Expiratory Flow (PEF) Averaged Over the 12-week Treatment Period | Baseline and Weeks 1-12 | Peak Expiratory Flow (PEF) is defined as the maximum airflow during a forced expiration beginning with the lungs fully inflated. PEF was measured by the participants using a hand-held electronic peak flow meter each evening prior to the dose of study medication and any rescue albuterol/salbutamol inhalation aerosol use and each morning. The best of three measurements was recorded. Change from Baseline (defined as the last 7 days prior to randomization of the participants) was calculated as the value of the averaged daily AM PEF over the 12-week treatment period minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline, region, sex, age, and treatment. |
| Change From Baseline in Daily Evening (PM) PEF Averaged Over the 12-week Treatment Period | Baseline and Weeks 1-12 | PEF is defined as the maximum airflow during a forced expiration beginning with the lungs fully inflated. PEF was measured by the participants using a hand-held electronic peak flow meter each evening prior to the dose of study medication and any rescue albuterol/salbutamol inhalation aerosol use and each morning. The best of three measurements was recorded. Change from Baseline (defined as the last 7 days prior to randomization of the participants) was calculated as the value of the averaged daily PM PEF over the 12-week treatment period minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline, region, sex, age, and treatment. |
Countries
Argentina, Chile, Germany, Mexico, Netherlands, Poland, Romania, Russia, Sweden, Ukraine, United States
Participant flow
Recruitment details
Participants meeting eligibility criteria at the Screening visit entered a 4-week Run-in Period for Baseline safety evaluations and measures of asthma status. Participants were then randomized to a 12-week Treatment Period. A total of 2019 participants were screened; 1039 were randomized and received \>=1 dose of study treatment.
Pre-assignment details
One participant was determined to have been randomized at each of two United States sites. Upon discovery of the duplicate enrollment, the participant was withdrawn. To account for only one randomization by this participant, a total randomized population of 1039 was used as the basis for the study analysis.
Participants by arm
| Arm | Count |
|---|---|
| FF 100 µg OD Participants received FF 100 µg inhalation powder OD in the evening from a DPI for 12 weeks. Participants were provided albuterol/salbutamol inhalation aerosol to be used as rescue medication during the Treatment Period. | 347 |
| FF/VI 100/25 µg OD Participants received FF/VI 100/25 µg inhalation powder OD in the evening from a DPI for 12 weeks. Participants were provided albuterol/salbutamol inhalation aerosol to be used as rescue medication during the Treatment Period. | 346 |
| FF/VI 200/25 µg OD Participants received FF/VI 200/25 µg inhalation powder OD in the evening from a DPI for 12 weeks. Participants were provided albuterol/salbutamol inhalation aerosol to be used as rescue medication during the Treatment Period. | 346 |
| Total | 1,039 |
Withdrawals & dropouts
| Period | Reason | FG000 | FG001 | FG002 |
|---|---|---|---|---|
| Overall Study | Adverse Event | 4 | 3 | 3 |
| Overall Study | Lack of Efficacy | 33 | 13 | 11 |
| Overall Study | Lost to Follow-up | 0 | 1 | 1 |
| Overall Study | Physician Decision | 3 | 4 | 4 |
| Overall Study | Protocol-defined Stopping Criteria | 1 | 0 | 1 |
| Overall Study | Protocol Violation | 2 | 3 | 0 |
| Overall Study | Withdrawal by Subject | 8 | 8 | 5 |
Baseline characteristics
| Characteristic | FF 100 µg OD | Total | FF/VI 200/25 µg OD | FF/VI 100/25 µg OD |
|---|---|---|---|---|
| Age, Continuous | 44.7 Years STANDARD_DEVIATION 15.89 | 45.7 Years STANDARD_DEVIATION 15.6 | 46.6 Years STANDARD_DEVIATION 14.72 | 45.9 Years STANDARD_DEVIATION 16.14 |
| Race/Ethnicity, Customized African American/African Heritage | 26 participants | 74 participants | 28 participants | 20 participants |
| Race/Ethnicity, Customized American Indian or Alaska Native | 0 participants | 2 participants | 2 participants | 0 participants |
| Race/Ethnicity, Customized Asian - East Asian Heritage | 0 participants | 1 participants | 0 participants | 1 participants |
| Race/Ethnicity, Customized Asian - Japanese Heritage | 1 participants | 1 participants | 0 participants | 0 participants |
| Race/Ethnicity, Customized Asian - South East Asian Heritage | 3 participants | 6 participants | 2 participants | 1 participants |
| Race/Ethnicity, Customized Missing | 0 participants | 1 participants | 1 participants | 0 participants |
| Race/Ethnicity, Customized Mixed Race | 12 participants | 41 participants | 13 participants | 16 participants |
| Race/Ethnicity, Customized Native Hawaiian or other Pacific Islander | 0 participants | 1 participants | 0 participants | 1 participants |
| Race/Ethnicity, Customized White - White/Caucasian/European Heritage | 305 participants | 912 participants | 300 participants | 307 participants |
| Sex: Female, Male Female | 199 Participants | 628 Participants | 224 Participants | 205 Participants |
| Sex: Female, Male Male | 148 Participants | 411 Participants | 122 Participants | 141 Participants |
Adverse events
| Event type | EG000 affected / at risk | EG001 affected / at risk | EG002 affected / at risk |
|---|---|---|---|
| deaths Total, all-cause mortality | — / — | — / — | — / — |
| other Total, other adverse events | 67 / 347 | 54 / 346 | 52 / 346 |
| serious Total, serious adverse events | 3 / 347 | 4 / 346 | 1 / 346 |
Outcome results
Primary
Change From Baseline in Weighted Mean Forced Expiratory Volume in One Second (FEV1) Over 0 to 24 Hours Post-dose at the End of the 12-week Treatment Period
Pulmonary function was measured by FEV1, defined as the maximal amount of air that can be forcefully exhaled in one second. The weighted mean was calculated from the pre-dose FEV1 (within 30 minutes prior to dosing) and post-dose FEV1 measurements at 5, 15, and 30 minutes and at 1, 2, 3, 4, 5, 12, 16, 20, 23, and 24 hours on Day 84/Week 12. At each time point, the highest of three technically acceptable measurements was recorded. Change from Baseline was calculated as the weighted mean of the 24-hour serial FEV1 measures on Day 84/Week 12 minus the Baseline value. Baseline was the pre-dose FEV1 measurement value obtained at Visit 3. The analysis was performed using an Analysis of Covariance (ANCOVA) model with covariates of Baseline FEV1, region, sex, age, and treatment.
Time frame: Baseline and Week 12
Population: Intent-to-Treat (ITT) Population: all participants randomized to treatment, who received at least one dose of the study medication. Only those participants with non-missing covariates and Week 12 weighted mean data were analyzed.
| Arm | Measure | Value (LEAST_SQUARES_MEAN) | Dispersion |
|---|---|---|---|
| FF 100 µg OD | Change From Baseline in Weighted Mean Forced Expiratory Volume in One Second (FEV1) Over 0 to 24 Hours Post-dose at the End of the 12-week Treatment Period | 0.366 Liters | Standard Error 0.0231 |
| FF/VI 100/25 µg OD | Change From Baseline in Weighted Mean Forced Expiratory Volume in One Second (FEV1) Over 0 to 24 Hours Post-dose at the End of the 12-week Treatment Period | 0.474 Liters | Standard Error 0.0221 |
| FF/VI 200/25 µg OD | Change From Baseline in Weighted Mean Forced Expiratory Volume in One Second (FEV1) Over 0 to 24 Hours Post-dose at the End of the 12-week Treatment Period | 0.499 Liters | Standard Error 0.0222 |
p-value: <0.00195% CI: [0.045, 0.171]ANCOVA
95% CI: [-0.037, 0.086]
Secondary
Change From Baseline in Clinic Visit Trough FEV1 at the End of the 12-week Treatment Period
Pulmonary function was measured by FEV1, defined as the maximal amount of air that can be forcefully exhaled in one second. Trough FEV1 is defined as a pre-dose FEV1 measurement taken at a clinic visit while still on-treatment. Change from Baseline in trough FEV1 at the end of the 12-week treatment period was defined using the 24-hour post-dose serial FEV1 measurement taken at the Week 12 clinic visit. Change from Baseline was calculated as the Week 12 trough FEV1 value minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline trough FEV1, region, sex, age, and treatment. The last observation carried forward (LOCF) method was used to impute missing data, in which the last non-missing post-Baseline on-treatment measurement at scheduled clinic visits was used to impute the missing measurements.
Time frame: Baseline and Week 12
Population: ITT Population. Only those participants with non-missing covariates and post-Baseline FEV1 data were analyzed.
| Arm | Measure | Value (LEAST_SQUARES_MEAN) | Dispersion |
|---|---|---|---|
| FF 100 µg OD | Change From Baseline in Clinic Visit Trough FEV1 at the End of the 12-week Treatment Period | 0.365 Liters | Standard Error 0.022 |
| FF/VI 100/25 µg OD | Change From Baseline in Clinic Visit Trough FEV1 at the End of the 12-week Treatment Period | 0.441 Liters | Standard Error 0.0221 |
| FF/VI 200/25 µg OD | Change From Baseline in Clinic Visit Trough FEV1 at the End of the 12-week Treatment Period | 0.457 Liters | Standard Error 0.022 |
Secondary
Change From Baseline in Daily Evening (PM) PEF Averaged Over the 12-week Treatment Period
PEF is defined as the maximum airflow during a forced expiration beginning with the lungs fully inflated. PEF was measured by the participants using a hand-held electronic peak flow meter each evening prior to the dose of study medication and any rescue albuterol/salbutamol inhalation aerosol use and each morning. The best of three measurements was recorded. Change from Baseline (defined as the last 7 days prior to randomization of the participants) was calculated as the value of the averaged daily PM PEF over the 12-week treatment period minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline, region, sex, age, and treatment.
Time frame: Baseline and Weeks 1-12
Population: ITT Population. Only those participants available at the specified time points were analyzed.
| Arm | Measure | Value (LEAST_SQUARES_MEAN) | Dispersion |
|---|---|---|---|
| FF 100 µg OD | Change From Baseline in Daily Evening (PM) PEF Averaged Over the 12-week Treatment Period | 15.5 Liters per minute | Standard Error 2.24 |
| FF/VI 100/25 µg OD | Change From Baseline in Daily Evening (PM) PEF Averaged Over the 12-week Treatment Period | 39.7 Liters per minute | Standard Error 2.24 |
| FF/VI 200/25 µg OD | Change From Baseline in Daily Evening (PM) PEF Averaged Over the 12-week Treatment Period | 41.7 Liters per minute | Standard Error 2.24 |
Secondary
Change From Baseline in Daily Morning (AM) Peak Expiratory Flow (PEF) Averaged Over the 12-week Treatment Period
Peak Expiratory Flow (PEF) is defined as the maximum airflow during a forced expiration beginning with the lungs fully inflated. PEF was measured by the participants using a hand-held electronic peak flow meter each evening prior to the dose of study medication and any rescue albuterol/salbutamol inhalation aerosol use and each morning. The best of three measurements was recorded. Change from Baseline (defined as the last 7 days prior to randomization of the participants) was calculated as the value of the averaged daily AM PEF over the 12-week treatment period minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline, region, sex, age, and treatment.
Time frame: Baseline and Weeks 1-12
Population: ITT Population. Only those participants available at the specified time points were analyzed.
| Arm | Measure | Value (LEAST_SQUARES_MEAN) | Dispersion |
|---|---|---|---|
| FF 100 µg OD | Change From Baseline in Daily Morning (AM) Peak Expiratory Flow (PEF) Averaged Over the 12-week Treatment Period | 19.1 Liters per minute | Standard Error 2.25 |
| FF/VI 100/25 µg OD | Change From Baseline in Daily Morning (AM) Peak Expiratory Flow (PEF) Averaged Over the 12-week Treatment Period | 44.3 Liters per minute | Standard Error 2.25 |
| FF/VI 200/25 µg OD | Change From Baseline in Daily Morning (AM) Peak Expiratory Flow (PEF) Averaged Over the 12-week Treatment Period | 47.7 Liters per minute | Standard Error 2.25 |
Secondary
Change From Baseline in the Percentage of Rescue-free 24-hour (hr) Periods During the 12-week Treatment Period
The number of inhalations of rescue albuterol/salbutamol inhalation aerosol used during the day and night was recorded by the participants in a daily electronic diary (eDiary). A 24-hour (hr) period in which a participant's responses to both the morning and evening assessments indicated no use of rescue medication was considered to be rescue free. The Baseline value was derived from the last 7 days of the daily eDiary prior to the randomization of the participant. Change from Baseline was calculated as the averaged value during the 12-week treatment period minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline, region, sex, age, and treatment.
Time frame: Baseline and Weeks 1-12
Population: ITT Population. Only those participants available at the specified time points were analyzed.
| Arm | Measure | Value (LEAST_SQUARES_MEAN) | Dispersion |
|---|---|---|---|
| FF 100 µg OD | Change From Baseline in the Percentage of Rescue-free 24-hour (hr) Periods During the 12-week Treatment Period | 22.6 Percentage of rescue-free 24-hr periods | Standard Error 1.84 |
| FF/VI 100/25 µg OD | Change From Baseline in the Percentage of Rescue-free 24-hour (hr) Periods During the 12-week Treatment Period | 34.8 Percentage of rescue-free 24-hr periods | Standard Error 1.85 |
| FF/VI 200/25 µg OD | Change From Baseline in the Percentage of Rescue-free 24-hour (hr) Periods During the 12-week Treatment Period | 35.8 Percentage of rescue-free 24-hr periods | Standard Error 1.85 |
Secondary
Change From Baseline in the Percentage of Symptom-free 24-hour (hr) Periods During the 12-week Treatment Period
Asthma symptoms were recorded in a daily eDairy by the participants every day in the morning and evening before taking any rescue or study medication and before the peak expiratory flow measurement. A 24-hour (hr) period in which a participant's responses to both the morning and evening assessments indicated no symptoms was considered to be symptom free. The Baseline value was derived from the last 7 days of the daily eDiary prior to the randomization of the participant. Change from Baseline was calculated as the averaged value during the 12-week treatment period minus the Baseline value. The analysis was performed using an ANCOVA model with covariates of Baseline, region, sex, age, and treatment.
Time frame: Baseline and Weeks 1-12
Population: ITT Population. Only those participants available at the specified time points were analyzed.
| Arm | Measure | Value (LEAST_SQUARES_MEAN) | Dispersion |
|---|---|---|---|
| FF 100 µg OD | Change From Baseline in the Percentage of Symptom-free 24-hour (hr) Periods During the 12-week Treatment Period | 19.4 Percentage of symptom-free 24-hr periods | Standard Error 1.74 |
| FF/VI 100/25 µg OD | Change From Baseline in the Percentage of Symptom-free 24-hour (hr) Periods During the 12-week Treatment Period | 27.2 Percentage of symptom-free 24-hr periods | Standard Error 1.74 |
| FF/VI 200/25 µg OD | Change From Baseline in the Percentage of Symptom-free 24-hour (hr) Periods During the 12-week Treatment Period | 29.0 Percentage of symptom-free 24-hr periods | Standard Error 1.74 |