Urinary loss of thiamine is increased by low doses of furosemide in healthy volunteers,☆☆,

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Abstract

Prolonged furosemide treatment is associated with urinary loss of thiamine and thiamine deficiency in some patients with congestive heart failure and low dietary thiamine intake. In the rat, diuretic-induced thiamine urinary loss is solely dependent on increased diuresis and is unrelated to the type of diuretic used. We studied the effects of single intravenous doses of furosemide (1, 3, and 10 mg) and of normal saline infusion (750 mL) on urinary thiamine excretion in 6 volunteers. Over a 6-hour period, furosemide induced dose-dependent increases in urine flow and sodium excretion rates (mean ± SD), from 51 ± 17 mL/h at baseline to 89 ± 29 mL/h, 110 ± 38 mL/h, and 183 ± 58 mL/h (F = 10.4, P <.002) and from 5.1 ± 2.3 mmol/h to 9.4 ± 6.8 mmol/h, 12.1 ± 2.6 mmol/h, and 20.9 ± 10.6 mmol/h (F = 6.3, P <.005) for the three doses, respectively (104 ± 35 mL/h and 13.0 ± 6.2 mmol/h for the saline infusion). During this period the thiamine excretion rate doubled from baseline levels (mean of four 24-hour periods before the diuretic interventions) of 6.4 ± 5.1 nmol/h to 11.6 ± 8.2 nmol/h (F = 5.03, P <.01, for all four interventions, no difference being found between them), then returning over the following 18 hours to 6.1 ± 3.9 nmol/h. The thiamine excretion rate was correlated with the urine flow rate (r = 0.54, P <.001), with no further effect of the type of intervention or sodium excretion rate. These findings complement our previous results in animals and indicate that sustained diuresis of >100 mL/h induces a nonspecific but significant increase in urinary loss of thiamine in human subjects. Thiamine supplements should be considered in patients undergoing sustained diuresis, when dietary deficiency may be present. (J Lab Clin Med 1999;134:238-43)

Section snippets

Volunteers

The study was approved by the institutional review board. Six consenting healthy adults (ages 21 to 27 years, 5 men, 1 woman) were recruited after screening by medical history, physical examination, routine laboratory tests, and an electrocardiogram. No volunteer was a smoker or drank alcoholic beverages. All were consuming unrestricted diets and none was using any medications or vitamin supplements of any kind.

Procedures

Volunteers were tested on 4 study days, 1 for each of the four diuretic

Results

There were no significant individual differences in urine variables between the 6 volunteers on the 4 pre-intervention days (data not shown). Baseline values for the urine variables on the pre-intervention days are presented in Table I.

. Urine variables 24 hours before diuretic interventions

Empty CellBefore 1 mgBefore 3 mgBefore 10 mgBefore salineMean
Volume (mL/d)1224 ± 4541218 ± 4131225 ± 3691232 ± 5041223 ± 408
Creatinine (mg/d)943 ± 4361271 ± 3181200 ± 3451224 ± 2911169 ± 345
Flow (mL/h)50 ± 1751 ± 1951 ±

Discussion

Thiamine is eliminated from the body by renal excretion that is dependent on glomerular filtration rate and on thiamine plasma concentrations.11 Under normal conditions free thiamine constitutes only a small fraction of total blood concentration, because it is rapidly taken up by blood cells and phosphorylated to thiamine pyrophosphate, which cannot diffuse out of the cell.12 The vitamin undergoes glomerular filtration as well as active tubular reabsorption and secretion,11 with the latter

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From the Division of Clinical Pharmacology and Toxicology, Department of Medicine, Sheba Medical Center and Tel Aviv University, Sackler School of Medicine.

☆☆

Reprint requests: Hillel Halkin, MD, Department of Medicine, Sheba Medical Center, Tel Hashomer 52621, Israel.

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