Letter: Effect of antibiotics on sweat chloride levels in cystic fibrosis.

We have recently studied an 11-year-old child with proved cystic fibrosis in 
whom raised sweat sodium but normal sweat chloride levels were obtained 
while she was receiving cloxacillin. There was no peripheral edema or 
hypoproteinemia, although at necropsy there was evidence of biliary cirrhosis. Although 
the sweat abnormality might have been due to as yet unknown 
factors, the temporal association with cloxacillin administration suggests a causative relationship, 
and it is tempting to speculate that the anomaly was produced 
in this instance by the substitution of the cloxacillin radical for 
the chloride ion in the sweat during the period of therapy. 
In light of our findings it would be of interest to 
know whether the infant reported by MacLean and Tripp was receiving 
any drugs at the time of the initial sweat chloride estimations 
and whether sodium estimations were also performed. 