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Re: Nebulised Colistin in Cystic Fibrosis

This short report by Cunningham et al [1], describes changes in FEV1 following nebulised Colistin in cystic fibrosis (C.F.). The authors report that out of 58 children studied, 34 showed a greater than 10% reduction in FEV1 and conclude that this is of some significance. The study in its conclusions can be criticised on a number of grounds.

The choice of cut-off value at 10% change from baseline FEV1 is arbitrary and probably derived from normal subjects, whereas it is known that the short term variability of spirometry values in children and adults with cystic fibrosis is much greater than in normal subjects. Nickerson et al [2] investigating within-subject variability and percent change for significance of spirometry found that FEV1 percent change greater than 23% was required for significance in C.F. Thus all but four of the results described by Cunningham et al (Figure 1) can be accounted for by the natural within subject variability of FEV1 in C.F. The study design could also have been improved by comparing serial spirometry measurements on a separate occasion, without nebulised Colistin, to determine whether Colistin imposed any additional variability. Finally, the reported finding that chest discomfort (9 children) was independent of change in FEV1, argues against this as being due to broncho-constriction.

Nebulised Colistin is an important therapy in the pseudomonas colonised/infected C.F. patient. We caution against concluding that changes in FEV1 after nebulised Colistin which fall within the natural within-subject variability of the measurement are due to harmful broncho- constriction.

DR J M BHATT
Specialist Registrar in Paediatrics
Jayesh{at}bhatt13.freeserve.co.uk

DR P I MACFARLANE
Consultant Paediatrician
peter.macfarlane{at}rgh-tr.trent.nhs.uk

References

(1) Cunningham S, Prasad A, Collyer L, Balfour-Lynn I, Wallis C. Bronchoconstriction following nebulised Colistin in cystic fibrosis. Arch.Dis.Child 2001; 84: 432-433.
(2) Nickerson BG, Lemen RJ, Gerdes CB, Wegmann MJ and Robertson G. Within- Subject variability and percent change for significance of spirometry in normal subjects and in patients with cystic fibrosis. Am Rev Respir Dis 1980; 122: 859-866.