Today's Veterinary Practice

JAN-FEB 2016

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Today's VeTerinary PracTice | January/February 2016 | tvpjournal.com PracTicaL TecHniQUes FroM THe naVc insTiTUTe Peer reviewed 104 torsemide is actually less "wasteful" of potassium and magnesium than furosemide. Monitoring of serum electrolytes is still advisable (Table 3, page 102). Indications & Dosage Torsemide is available for both intravenous and oral use, with tablet sizes of 5, 10, 20, and 100 mg. The accepted oral torsemide dosage is one tenth that of the expected, or current, furosemide dosage, which works out to 0.2 mg/kg Q 12 H if a patient is started on torsemide initially (ie, 10% of the 2 mg/kg furosemide dosage). To our knowledge, intravenous administration of torsemide has not been studied in veterinary medicine. We are reluctant to speculate from the human dosage because of the apparent differences between species with regard to administration of oral torsemide. currently, torsemide is used most often as a rescue agent when furosemide (usually with stan - dard cHF drugs, including hydrochlorothiazide and spironolactone) no longer adequately controls signs of congestion (Table 4, page 106). one author considers using torsemide when the furosemide response is inadequate at a furosemide dosage of 4 mg/kg Q 24 H or greater. 12 in our practices, the set point for change is somewhat higher, at a furosemide dosage greater than 6 to 8 mg/kg Q 24 H. Torsemide can be initiated in this circumstance as one dose per day, replacing one dose of furosemide (at one tenth the mg dosage) and leaving other treatments (including later daily doses of furosemide) intact. alternatively, with twice daily furosemide therapy, torsemide could be added as the third diuretic dose of the day. Lastly, it might be used to replace all diuretic therapy, given orally Q 12 H at one tenth the furosemide dosage, and titrated upward as needed. renal function should be carefully monitored during the addition of, or transition to, torsemide, and use of additional diuretics, such as hydrochlo - rothiazide, should be limited. Table 3 suggests monitoring practices for patients receiving potent loop diuretics. IN SUMMARY Unfortunately, the data available on diuretics in veterinary patients are still limited. More studies are needed to establish comparative aspects of the undesirable adverse effects and the effcacy of various loop diuretics. read Part 2 of this article series—a discussion on spironolactone—in an upcoming issue of Today's Veterinary Practice. Furosemide & Torsemide: effects on renal Function All diuretics can have a negative effect on renal perfusion if they produce excessive diuresis, resulting in prerenal azotemia and contributing to renal failure in: • Older dogs • Dogs with underlying kidney disease • Dogs with multipronged off-loading therapy (amlodipine, sildenafil, nitroglycerin, and ACE inhibitors) in the treatment of CHF. Serum creatinine, phosphorus, and blood urea nitrogen (bUN) concentra- tions all rise with the use of furosemide or torsemide, in both normal dogs and those with heart disease, and in those with and without CHF. 11-13,15 In a study by Peddle and colleagues, b UN, serum creatinine, and phosphorus were increased to a signifcantly greater degree with torsemide than with furosemide in dogs with heart failure, although the values remained within the normal reference range. 11 For these reasons, the lowest effective dosage of furosemide and/ or torsemide should be sought and use of these drugs should be coupled with careful monitoring of renal function. However, we believe that changes in drugs or dosages based simply on serum creatinine concentration should not be made unless levels increase at least 35%. Most often, the loop diuretic will be temporarily discontinued or have its dosage reduced frst, with the ACE inhibitor being manipulated last. F u r o s FIGURE 7. Serum aldosterone concentrations in normal dogs receiving placebo, furosemide, or torsemide on days 1 ( white bar) and 14 (green bar ). Note the 6-fold increase with torsemide. This fnding is potentially related to RAAS activation or blockade of MR. If the former, this effect would be a disadvantage of using torsemide as opposed to furosemide. * = value signifcantly (P < 0.05) different from short-term administration value; † = value signifcantly (P = 0.01) different from placebo treatment value; ‡ = value signifcantly (P = 0.01) different from value of the corresponding furosemide administration

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