Effects of furosemide and slow-release furosemide on thoracic fluid volumes

Transthoracic electrical impedance (TEI) was used to assess the relative effectiveness of a 60 mg sustained-release furosemide preparation (FR) and a 40 mg standard furosemide tablet (F), in reducing the fluid content in the thoracic cavity. A double-blind crossover study was performed, in which 12 men with a history of one or more myocardial infarctions and mild left heart failure treated with 40 mg furosemide once daily participated. The trial, lasting 28 days, was divided into two 14-day periods. Each participant received one active drug and one placebo preparation daily, the same regimen being maintained for 14 days, when the active substances were switched. TEI, body weight, serum potassium, sodium, creatinine, and urate were measured immediately prior to the start of the study, after 14 days, and at the end of the study. TEI was measured at frequencies of 1 and 100 kHz with a constant current of 100 microA, during a period of one hour following an intravenous injection of 40 mg furosemide, when the urine volumes were measured also. TEI and urine production after the furosemide injections were similar irrespective of the drug preparation. No evidence of treatment period interaction was seen. No significant differences were demonstrated in body weight and blood chemistry during the trial. These results suggest clinical equipotency of the two preparations in mild left heart failure.