Reduced renal fractional excretion of lithium in cystic fibrosis

We hypothesized that patients with cystic fibrosis would have abnormal lithium handling because the genetic defect in cystic fibrosis encodes an ion channel which causes a generalized electrolyte transport disorder in epithelial membranes. Eight patients with cystic fibrosis and eight age-sex matched healthy subjects ingested 600 mg lithium carbonate and had urine and serum lithium levels assessed 24 h later. Compared with healthy subjects, the patients with cystic fibrosis had higher serum lithium levels (0.071 +/- 0.038 vs 0.113 +/- 0.055 mmol l-1, P = 0.03) and had lower fractional renal excretion of lithium (27.5 +/- 14.8 vs 18.8 +/- 9.3%, P = 0.03). Caution should be used in prescribing standard doses of lithium to patients with cystic fibrosis until more definitive data are available.