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May 1981

Spuriously Elevated Serum Chloride Values Caused by Pyridostigmine Bromide

Author Affiliations

From the Department of Neurology, The New York Hospital-Cornell Medical Center. Dr Ruff is now at the University of Washington, Seattle.

Arch Neurol. 1981;38(5):321. doi:10.1001/archneur.1981.00510050087020

The unusual complication of a spurious elevation of the serum chloride value developed during pyridostigmine bromide (Mestinon) treatment.

REPORT OF A CASE  A 77-year-old man with myasthenia gravis was admitted to The New York Hospital-Cornell Medical Center because of respiratory difficulty. He had been taking 1,260 mg of pyridostigmine bromide daily for six months. He did not take any other medication containing bromide. Multiple determinations of his serum electrolyte values with the use of a standard ion-selective electrode technique (Stat/Ion) indicated chloride values of 119 to 157 mEq/L with corresponding anion gaps of —8 to —47. The ion-selective electrode was checked and was functioning properly. An electrolyte determination using the same technique before the patient received pyridostigmine bromide had given normal values. His serum was analyzed for halides with specific colorimetric techniques. The actual chloride level was 109 mEq/L and the bromide value was 2.1 mEq/L. The ion-selective electrode indicated

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