Fall in peak expiratory flow during haemodialysis in patients with chronic renal failure.

Role of histamine release in hypertonic saline induced bronchoconstrictionIn a recent study Dr O'Hickey and his colleagues (August 1989;44:650-3) inves- tigated the inhibitory effect of terfenadine on hypertonic saline induced bronchoconstric- tion in asthmatic subjects.Terfenadine was administered in two doses of 120 mg 12 hours and two hours before challenge with hyper- tonic saline, and gave significant protection against this stimulus, displacing the geometric mean PD20 FEV, from 22 to 56 1 drawn from the ultrasonic nebuliser.The authors concluded that airway his- tamine release was only one of several mechanisms mediating the bronchoconstrictor response to hypertonic saline, because of the substantial intersubject variation in the inhibitory effect of terfenadine in their study.This apparent heterogeneity may be due, among other factors, to an inadequate dose of terfenadine.Previous work, by Hopp et al, showed that when terfenadine was administered four hours before bronchial challenge with ultrasonically nebulised distilled water a drug dose of 240 mg gave better protection than that afforded by 120 mg.' A recent study using a dose of 180 mg terfenadine adminis- tered three hours before hypertonic saline challenge showed a geometric mean increase of PD25 by a factor of 7 2,' somewhat greater than the 2-5 fold shift reported by Dr O'Hickey and colleagues.It may be supposed that after airway mast cell degranulation a histamine concentration gradient exists,