Thanks to Dr. Janet Olson, DACVIM (Cardiology) of Veterinary Cardiology Specialists in Minneapolis, MN for this great VETgirl guest blog! Here, she discusses the appropriate and inappropriate uses of furosemide, the diuretic (commonly called Lasix in North America).
Furosemide is the most common medication used in dogs with confirmed heart failure. It is also, unfortunately commonly misused. Here are some general “DOs and DONʼTs” for Furosemide use.
1) Prior to prescribing furosemide, a renal panel with electrolytes and a urine specific gravity should always be performed. This is necessary to establish a baseline for which to assess renal function and tolerance and response to therapy.
2) Any time the furosemide dose is increased, a renal panel with electrolytes should be performed. This is indicated to ensure continued tolerance to the medication.
3) When performing a furosemide trial, a dose of 2 mg/kg of furosemide PO BID is recommended. If you use too low of a dose and they donʼt respond, you wonʼt know if they didnʼt respond because they werenʼt actually in heart failure, or if your dose was just too low.
1) Donʼt start a dog on furosemide just because the NTproBNP level is elevated, even if they are coughing or having respiratory distress. Causes other than left sided heart failure can cause elevated NTproBNP levels such as pulmonary hypertension. Moreover, false positives can occur. For example, I have also seen dogs with laryngeal paralysis have elevated NTproBNP levels. Therefore, it is necessary to take thoracic radiographs to confirm the presence of pulmonary edema prior to starting furosemide. If left sided heart failure is equivocal based on the radiographs, a furosemide trial is indicated.
2) Donʼt start a dog on furosemide just because it has a heart murmur and respiratory signs such as coughing or labored breathing. Many dogs have heart murmurs (particularly middle aged to older small breed dogs with chronic degenerative valve disease), but a heart murmur and cough or labored breathing does not equal heart failure. Dogs with CDVD can have concurrent pulmonary disease which may be the cause of their clinical signs, rather than heart failure. Thoracic radiographs are a must as you donʼt want to use furosemide if it is not indicated. Plus, you want to give the owner an accurate diagnosis so appropriate decisions can be made.
3) Donʼt base your furosemide trial on improvement of clinical signs alone. Turns out furosemide also has some bronchodilator effects. Thus, a dogʼs respiratory signs may improve with the use of furosemide, even if they are not in heart failure. In addition, there is the owner placebo effect. You donʼt want to put your patient on life long furosemide if it is not (or not yet) indicated. So, follow-up radiographs 5 to 7 days after starting the therapy is necessary to look for an objective radiographic improvement.
4) Donʼt taper down and then discontinue the use of furosemide once your patient starts breathing comfortably. Once a dog is in heart failure, he/she will always need furosemide therapy. 2 mg/kg PO BID is generally a good maintenance dose. If you taper the dose down below this dose he/she will most likely go back into heart failure. This adds additional stress to the patient and owner, added visits to the hospital, and may even result in a choice for euthanasia. So as long his/her kidneys are tolerating this baseline dose, dropping below that is not necessary.
5) Donʼt prescribe furosemide and then tell the owner to give a particular dose two to three times daily as needed. Consistent dosing is important for management of heart failure and the comfort of the patient. Donʼt rely on your clients to know how and when to give their dog furosemide. Be specific in your instructions. If you want to give them the ability to make some judgement calls at home, do so in a very specific manner. For example, “Give X mgs orally three times daily. If after 3 days, the resting respiratory rate (RRR) is consistently < 30 breaths per minute, decrease to twice daily dosing. Continue to monitor RRR carefully. If values begin to exceed 30 breaths per minute, increase back to every 8 hour dosing and inform us so we can adjust the record accordingly” OR “Give X mgs orally twice daily and if he/she is having a particularly bad day in regards to elevated resting respiratory rates, add a mid day dose. However, if you frequently need to give the medication three times daily, contact our clinic so we can reassess
6) Donʼt keep increasing the dose of furosemide in a patient that is not responding. If a patient is not responding to your furosemide dose, consider why not. Doses as high as 4 mg/kg PO TID can be appropriate if the kidneys are tolerating the furosemide well, but going above this dose can be futile. If they are not responding, consider the following:
- a) They may have become refractory to furosemide and addition of another diuretic may need to be considered
- b) Switching from furosemide to another loop diuretic such as torsemide may need to be considered
- c) They may not be absorbing / metabolizing the oral form of furosemide and injectable furosemide may need to be considered
- d) They may not actually be getting their medication. A renal panel is typically telling as dogs on high doses of furosemide should have at least some degree of azotemia. If they do not, they either arenʼt getting it, or they arenʼt metabolizing it.
Copyright, Dr. Janet Olson, Veterinary Cardiology Specialists, 2017.