Formoterol thrice weekly does not result in the development of tolerance to bronchoprotection

Division of Respiratory Medicine, Department of Medicine, Royal University Hospital, Saskatoon, Saskatchewan Correspondence and reprints: Dr Donald W Cockcroft, Division of Respiratory Medicine, Royal University Hospital, 103 Hospital Drive, Saskatoon, Saskatchewan S7N 0W8. Telephone 306-966-8294, fax 306-966-8694, e-mail cockcroft@sask.usask.ca BE Davis, JK Reid, DW Cockcroft. Formoterol thrice weekly does not result in the development of tolerance to bronchoprotection. Can Respir J 2003;10(1):23-26.

T olerance to the bronchoprotective effect of both long and short acting beta 2 -agonists has been well documented (1).Researchers have shown that protection is lost rapidly at standard doses and has a greater effect against indirect than against direct stimuli.
Formoterol, an immediate and long lasting beta 2 -agonist, initially indicated as add-on therapy for patients whose lung function and symptoms are not adequately maintained with inhaled corticosteroid, has recently been approved as rescue therapy for acute bronchoconstriction.Like salbutamol, rescue use of formoterol is 'as needed' but should not exceed three times a week (2).At least one study has shown the development of tolerance with daily administration of 12 µg of formoterol over a 14-day period (3).There are, however, no data determining the effects of thrice weekly administration.We therefore investigated thrice weekly administration of 12 µg of formoterol versus placebo and included a daily 12 µg treatment arm as an anticipated positive 'control' for the development of tolerance.

Subjects
The study protocol was approved by the University of Saskatchewan BioMedical Ethics Committee, and 13 patients with mild to moderate asthma were enrolled into the study after providing consent and meeting eligibility criteria.Patients with a forced expiratory volume in 1 s (FEV 1 ) of less than 65% of the predicted volume or a concentration of methacholine that causes a 20% fall in FEV 1 (PC 20 ) of more than 8 mg/mL were not eligible.In addition, subjects had to be free of an upper respiratory infection for more than six weeks.Short acting beta-agonists were withheld for more than one week before enrolment, and no subjects had been using long acting beta-agonists.Atopic subjects avoided known allergen exposure for more than four weeks before and throughout the trial.Two participants were using a stable dose of inhaled corticosteroid, which they were allowed to continue using at the same dose for the duration of the study.
©2003 Pulsus Group Inc.All rights reserved

Methacholine bronchoprovocation challenge
Subjects underwent the tidal breathing method of Juniper et al (4).Briefly, subjects presented to the laboratory daily and were required to rest to ensure stable lung function.Three reproducible flow volume loops were then obtained according to the guidelines of the American Thoracic Society (5).Following diluent inhalation, doubling doses of methacholine were administered at 5 min intervals until FEV 1 manoeuvres, obtained at 30 and 90 s after 2 min inhalations, fell by 17% or greater.The decrease from the lowest FEV 1 after diluent inhalation to the lowest FEV 1 after methacholine inhalation was calculated.If the fall was 17%, 18% or 19%, then the PC 20 was obtained by extrapolation using a single-point algebraic formula (6).If the fall was greater than 20%, the PC 20 was interpolated using the standard algebraic formula (7).Starting concentrations were identical within a given subject and were at least two concentrations below the known PC 20 for a given subject.Bronchoconstriction was reversed with 20 to 40 µg of ipratropium bromide; in some cases spontaneous reversal was preferred.

Study design
This was a double-blind, placebo controlled, randomized crossover trial.Three kits containing six blinded Turbuhalers (Astra Pharma, Mississauga), three for days 1, 3 and 5, and three for days 2, 4, 6 and 7 were prepared.Each kit contained three treatment regimens: formoterol plus formoterol; placebo plus placebo and formoterol (days 1, 3, 5); and placebo (days 2, 4, 6 and 7).Each treatment arm required visits to the laboratory at the same time of day (±1 h) on days 1 through 5 and again on day 8.Consistent with the authors' previous investigations of beta-agonist tolerance (1), the washout duration between treatment periods was a minimum of seven days.Each visit consisted of baseline FEV 1 determination followed by administration of blinded study medication, with the exception of day 8, on which 12 µg of openlabel formoterol was administered.FEV 1 was measured again 10 min after inhalation of blinded or unblinded (day 8) medication just before methacholine bronchoprovocation challenge.Subjects administered doses on their own on days 6 and 7 with a blinded inhaler provided to them on leaving the laboratory on day 5.

Statistical analysis
The primary end point, day 8 methacholine PC 20 , was analyzed using a two-way (subject versus treatment) analysis of variance (ANOVA) (STATISTIX for Windows, Analytical Software, USA).Least significant difference comparison of means was used when the ANOVA generated a P<0.05.Secondary end points, baseline FEV 1 and delta FEV 1 after treatment, were analyzed in the same manner.A paired t test was used for within-group post hoc analyses.This study had a greater than 90% power to detect a 0.5 concentration change in methacholine PC 20 .

Davis et al
Can Respir J Vol 10 No 1 January/February 2003 24

Safety
Thirteen subjects were enrolled (Table 1), 10 of whom completed the trial.One subject voluntarily withdrew before completing the second treatment arm because of the required time commitment, and two subjects were withdrawn because of worsening asthma.There were no other adverse events.
Results are presented on 10 subjects with complete data.

Bronchoprotection
Daily geometric mean log PC 20 values for each treatment arm are shown in Figure 1.ANOVA of the primary end point showed no significant difference between the three treatment arms (P=0.34).Day 8 geometric mean PC 20 concentrations were 6.3 mg/mL, 9.2 mg/mL and 9.6 mg/mL for daily formoterol, thrice weekly formoterol and placebo, respectively.Both formoterol treatment arms were significantly greater than placebo on days 1, 3 and 5, and not significantly different from each other.On days 2 and 4, placebo and placebo days for the thrice weekly formoterol were significantly lower than daily formoterol but not significantly different from each other.

Baseline FEV 1
The only significant difference (ANOVA, P=0.012) was on day 4.The mean baseline FEV 1 (Table 2) of the thrice weekly treatment arm (3.98±1.05L) 24 h after administration of 12 µg formoterol (administered on day 3) was significantly greater than the mean for the placebo group (3.73±0.96L).ANOVA for the analogous day 2 baseline FEV 1 values indicated no significant difference between the three treatments (P=0.23;paired t test for placebo versus thrice weekly formoterol yielded P=0.092).

Bronchodilation
ANOVA of day 8 mean daily absolute delta FEV 1 (FEV 1 10 min after treatment minus baseline FEV 1 ; Table 2) indicated a reduction in bronchodilation in the daily (0.21±0.17L) versus the every other day treatment (0.32±0.27L) at the 0.05 level.Subsequent paired t test for day 1 versus day 8 for delta FEV 1 within the daily treatment arm showed significant reduction in bronchodilation on day 8 (P=0.0035).There was, however, no significant difference in the post-formoterol FEV 1 on day 8 (ANOVA P=0.62, FEV 1 3.97 to 4.05 L).

DISCUSSION
In our study the long acting beta 2 -agonist formoterol taken once daily or once every other day over a seven-day period did not result in a loss of the protection afforded by a single 12 µg dose against methacholine-induced bronchoconstriction.There is little in the literature with which to compare our findings; however, our findings do contradict the work of Lipworth et al (3), who found tolerance at various doses of formoterol, including 12 µg administered once daily.Interestingly, the plot of our data for the daily formoterol group shown in Figure 1 develops a downward trend at day 4 and is lower by day 8, but this was not statistically significant.The conflict between our results and those of Lipworth and colleagues may be explained by differences in the duration of treatment or the method of analysis.We administered a 12 µg dose for seven days, compared with a 12 µg dose for 14 days in the Lipworth et al study.At least one other seven-day investigation has failed to show tolerance despite the population being 'at risk' for its development and despite twice the daily dose of formoterol (8).We also chose between-treatment (formoterol versus placebo) protection afforded by formoterol as our primary end point, compared with a within-treatment first dose versus last dose comparison, as used by Lipworth and colleagues.The development of a downward trend of PC 20 in our daily formoterol data may have significance with longer treatment duration, a larger sample size or both; a trend toward the loss of bronchoprotection following administration of 12 µg formoterol twice a day for seven days has been previously documented (9).We did not consider concomitant administration or inconsistent administration of inhaled corticosteroid to be a contributing factor in the difference between our results and others' because inhaled corticosteroid administration does not prevent the development of tolerance (10), and oral prednisolone does not reverse established tolerance (11).
Our findings with respect to baseline FEV 1 (Table 2) suggest improvements in daily lung function with thrice weekly dosing.Baseline FEV 1 values for the every other day treatment arm deviate to significance from placebo on day 4.However, the same improvement was not evident on day 2.This phenomenon is perhaps the result of prolonged or residual bronchodilator action from the previous day, suggesting that the duration of action of formoterol may extend up to 24 h when administered in a dose of 12 µg every other day.The same effect was not evident with daily treatment.The acute bronchodilator properties of 12 µg formoterol, measured as the absolute delta FEV 1 from baseline to 10 min after treatment, were significantly less pronounced following 12 µg daily formoterol administration, signifying possible loss of bronchodilation, which was not seen with thrice weekly treatment.Of clinical importance is the timeframe in which this loss occurs with daily treatment.The most pronounced loss in the delta FEV 1 over the study period occurred with the second dose (Table 2).This partially recovered at the third dose, but the difference in delta FEV 1 remained significant when compared with the first dose (within-group paired t test).In fact, all measurements of delta FEV 1 were significantly lower than those of the first dose within the daily treatment group; the day 8 delta FEV 1 was significantly lower for daily versus every other day treatments.However, post-formoterol FEV 1 values did not differ significantly (Table 2).
We have shown that the long-acting beta 2 -agonist formoterol administered in a dose of 12 µg thrice weekly for a period of seven days does not result in the development of tolerance to the bronchoprotective effects against the direct-acting stimulus methacholine.Although statistical significance was not reached, there does appear to be a trend toward a loss in bronchoprotection when the same dose is administered daily.ACKNOWLEDGEMENTS: John K Reid is Moorehead Fellow, supported by the Saskatchewan Lung Association; Donald W Cockcroft is Ferguson Professor, supported by the Saskatchewan Lung Association.

Figure 1 )
Figure 1) Geometric mean concentrations of methacholine that caused a 20% fall in forced expiratory volume in 1 s (PC 20 ) for each treatment group (vertical axis) plotted for each day bronchoprovocation challenges were given (horizontal axis).Thrice weekly formoterol (closed triangle) PC 20 values differed significantly from placebo treatment (open circles) on days 1, 3 and 5. Day 8 PC 20 values were not significantly different.Note, however, the trend toward the development of tolerance in the daily formoterol group (closed circles).Error bars represent SEM

TABLE 1 Baseline demographics
BD Budesonide; F Female; FEV 1 Forced expiratory volume in 1s; FP Fluticasone propionate; M Male; PC 20 Concentration of methacholine that causes a 20% fall in FEV 1