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Routes of furosemide administration in dogs | VETgirl Veterinary CE Podcasts

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What’s your favorite way of giving furosemide to the critically ill, fragile, dyspneic congestive heart failure patient? Is it worth putting in an IV catheter just to give furosemide IV? (No). Does it matter what route you give it?

In today’s VETgirl online veterinary CE podcast, we review different routes of administration of the commonly used diuretic, furosemide. To review, furosemide is a potent loop diuretic used for treatment of congestive heart failure that causes increased urine production via inhibition of sodium, potassium, chloride, and water reabsorption in the thick ascending loop of Henle within the kidney. The diuretic effect is determined by the amount of drug that reaches the renal tubules more so than the plasma concentration. Furosemide is also highly protein bound (>95%) which affects the amount of free drug available in plasma for delivery to the renal tubules.

In veterinary medicine, furosemide is most commonly administered via orally (PO), intravenously (IV), intramuscularly (IM), and by constant-rate infusion (CRI). The oral route carries the slowest onset of action (albeit of longer duration) and weakest overall action, due to low bioavailability via this method. The intravenous route is rapid in onset but has a short duration (which can be overcome/sustained via CRI) due to rapid metabolism and excretion. So, can we use it subcutaneously (SC) also for ease of administration? Will it still be effective? Harada et al out of Japan wanted to evaluate the safety and diuretic effect of SC furosemide administration in the study “Comparison of the diuretic effect of furosemide by different methods of administration in healthy dogs.” They wanted to compare SQ administration versus the more common methods of administration in healthy dogs to see if it was effective.

In this prospective, randomized, cross-over design study, they enrolled 7 healthy dogs. All dogs received SC, IV, PO, and a CRI of furosemide, with a 2-week washout period between each method of administration. When dosing, the SC injections were performed over the dorsum of the patient. The oral dose was a single dose, while the CRI dosing was 2 mg/kg/8h. Each patient had a CBC, total protein, BUN, creatinine, and renin level measured at time o, 1, 2, 4, 6, and 8 hours. Hourly urine output (UOP/h) was also measured during this study.

Overall, the authors found that the onset of action and UOP/h for SC furosemide administration was similar to IV administration over the initial 2 hours. The duration of furosemide’s action was slightly longer (2 hours) with SC injection versus the intravenous route. The oral route (4 hours) and CRI route (8 hours) indicated longer duration of increased UOP/h. Overall, the total UOP of the CRI group was greater as compared to other methods. The plasma renin activity was increased in all groups.

This study aimed to investigate the benefits or effect of SC furosemide administration in dogs, which has not specifically been investigated to the author’s knowledge. The use of SC furosemide administration has resurfaced in humans due to settings where IV use is not practical or feasible (lack of IV access) and IM use is challenging due to lack of muscle mass or discomfort with administration. So what did this study find? This study confirmed previous data on the rapid onset but short duration of action of IV furosemide in dogs (which has a peak UOP/h increase within 1 hour with rapid return to baseline), as well as the sustained duration of action with a CRI. Plasma renin activity (which increases in response to diuresis and blood volume reduction) increased in all groups, with greatest increase in the CRI group. SC administration depends on absorption from adipose tissue into local capillary beds. The slower absorption through adipose tissue (as compared to IV) likely accounts for the more sustained effect. However, onset of action and UOP/h for SC were similar to that of the IV method of administration for a single dose.

So what can we take from this VETgirl podcast?

Administration of subcutaneous furosemide provided similar onset of action and urine output to the intravenous route, but with a slightly longer duration of action. Subcutaneous injection provides a safe and effective alternative method of administration of furosemide vs intramuscular injection that may reduce patient pain/morbidity or be more feasible in cachectic patients when intravenous access is not possible/present. Important to note that this study was performed in healthy dogs thus whether the findings would be equivalent in patients suffering from congestive heart failure, renal disease, dehydration, hypotension, or severe cachexia remains to be seen.

References:
1. Harada K, Ukai Y, Kanakubo K et al. Comparison of the diuretic effect of furosemide by different methods of administration in healthy dogs. J Vet Emerg Crit Care 2015; 25(3): 364-371.

Abbreviations:

PO: Oral administration

IV: Intravenous

IM: Intramuscular

CRI: Constant rate infusion

CBC: Complete blood count

TP: Total protein

BUN: Blood urea nitrogen

Cr: Creatinine

UOP/h: Urine output per hour

 

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