Tolerability to high doses of formoterol and terbutaline via Turbuhaler for 3 days in stable asthmatic patients.
This randomized, double-blind, crossover study in two parts compared tolerability to high doses of formoterol (Oxis Turbuhaler) with that of high doses of terbutaline (Bricanyl Turbuhaler). After Holter monitoring at home, 12 patients were treated with 4+4+4 doses of formoterol Turbuhaler, 6 microg x dose(-1), (total daily metered dose 72 microg) or 4+4+4 doses of terbutaline Turbuhaler, 0.5 mg x dose(-1) (daily dose 6 mg) given in the morning, after lunch and in the evening, for 3 consecutive days. After a one week washout period at home, patients received the alternative treatment. Thereafter, 15 other patients received 8+6+6 doses of formoterol Turbuhaler (total daily metered dose 120 microg) or 8+6+6 doses of terbutaline Turbuhaler (daily dose 10 mg). Pulse, cardiac frequency, blood pressure, serum potassium, electrocardiogram and forced expiratory volume in one second (FEV1) were registered at regular intervals and Holter monitoring was applied during all 4 treatment days. Terbutaline 6 mg showed significantly greater systemic effects than formoterol 72 microg on pulse, blood pressure, cardiac frequency and QTc (QT interval corrected for heart rate). Terbutaline 10 mg had significantly greater effects than formoterol 120 microg on serum potassium levels, pulse, cardiac frequency and QTc. No differences in FEV1 levels were found. Both drugs were safe and generally well tolerated on both dose levels. In conclusion, high doses of formoterol Turbuhaler over 3 days were generally safe and well tolerated. Daily doses of 6 mg and 10 mg terbutaline Turbuhaler were systemically more potent than 72 microg and 120 microg formoterol, respectively. The safety margin thus appears to be wide if patients happen to use extra doses of formoterol in addition to those prescribed for regular use.