Cardiovascular Drugs

Chapter 146 Cardiovascular Drugs

Pharmacologic interventions allow the veterinarian to impact pathophysiologic processes in animals with cardiovascular (CV) diseases. To effectively use drugs affecting the heart and circulation, the clinician must understand the pathophysiology of the disease and appreciate the relevant pharmacology of the drugs prescribed. This chapter reviews aspects of cardiovascular pharmacology that are particularly applicable to clinical small animal veterinary practice. Most drugs used to treat CV diseases in dogs and in cats prescribed in an extra-label manner and dosages are at best approximate for many of these agents. Specific drugs and commonly recommended dosages are listed in Table 146-1. Drugs used in management of cardiopulmonary-cerebral resuscitation are discussed in Chapter 157. Management of shock is discussed in Chapter 156.


Drug Preparation(s) Usual Dosageß
Amlodipine Norvasc, 2.5-mg tablet size DOG: 0.05–0.2 mg/kg q12h–24h
CAT: ¼–½ tablet dose, once or twice daily
Amiodarone Cordarone injection, 50 mg/ml DOG: Loading dose of 10 mg/kg PO q12h for 1 week; thereafter 5 mg/kg PO q12–24h
Cordarone and USP scored tablets, 200 mg For IV use: 3–5 mg/kg over 60 min, followed by 5–10 mcg/kg/min CRI
Amrinone Inocor, 5 mg/ml (20-ml vials) DOG: 1–3 mg/kg IV followed by 30–100 mcg/kg/min constant rate infusion
Atenolol Tenormin and USP tablets, 25 and 50 mg DOG: 0.25–1.5 mg/kg PO q12h
CAT: 6.25–12.5 mg dosage, once or twice daily (up-titrate dosages for both species)
Atropine USP: 0.4 and 0.5 mg/ml for injection 0.01–0.04 mg/kg, IV, IM, SQ
Benazepril hcl Lotensin tablets, 5, 10, 20, 40 mg DOG: 0.25–0.5 mg/kg PO q12–24h (initial daily dose typically 0.5 mg/kg daily)
CAT: 0.25–0.5 mg/kg PO q12–24h (as per dog)
Butorphanol Torbutrol 0.5 mg/ml for injection DOG: 0.25–0.5 mg/kg, SQ, IM for sedation
Torbutrol tablets, 1, 5, 10 mg DOG: 0.5 mg/kg PO q6–12h as an antitussive
CAT: 0.2–0.3 mg/kg in a cocktail with acepromazine
(0.05–0.1 mg/kg), SQ, IM
Carvedilol Coreg tablets, 3.125, 6.25, 12.5 mg DOG: initiate dosage in canine DCM at 0.05–0.1 mg/kg PO q12h for 2 weeks; up-titrate the dose every 2–4 weeks provided marked lethargy, progressive CHF, or relative bradycardia develop (HR < 100/minute during examination) do not develop. Typical dose target is 0.2–0.4 mg/kg PO q12h for canine DCM.
Digoxin Lanoxin, Cardoxin, USP tablets, 0.125, 0.25 mg DOG: 0.0055–0.0075 mg/kg q12h, PO
Elixirs of 0.05 mg/ml and 0.15 mg/ml CAT: ¼ of a 0.125 mg Lanoxin tablet q48 to 72 hours
Lanoxin for injection, 0.25 mg/ml
Dihydrocodone Hycodan, 5-mg tablets DOG: 1.25–5.0 mg, PO q8–24h for cough
Diltiazem Cardizem and USP tablets, 30, 60, 90, 120 mg DOG: 0.5–2.0 mg/kg PO q8h (up-titrate dose)
Dilacor XR capsules 120, 180, 240 mg DOG/CAT: 0.1 mg/kg IV (can repeat every 15 minutes to 0.5 mg/kg while monitoring arterial blood pressure).
Cardizem CD capsules 120, 180, 240 mg CAT: 0.5–2.0 mg/kg PO q8–12h for standard diltiazem; ½ of a 60 mg Dilacor pellet (taken from the capsule) q12–24h
Diltiazem for injection 50 mg/ml PO; or compounded Cardizem CD starting at 30 mg PO q12h
Dobutamine Dobutrex for injection, 250 mg (20 ml vial) DOG: 2.5–20 mcg/kg/min, constant rate IV infusion.
CAT: 2.5–10 mcg/kg/min CRI
Dopamine Intropin, USP for injection, 200 mg, 400 mg vials 2–10 mcg/kg/min, constant rate IV infusion
Enalapril Enacard, USP tablets: 1.25, 2.5, 5, 10, 20 mg DOG: 0.25–0.5 mg/kg PO q12–24h (initial daily dose typically 0.5 mg/kg daily)
CAT: 0.25–0.5 mg/kg PO q12–24h (as per dog)
Epinephrine Adrenaline, USP 1:1000 (1 mg/ml), 1:10,000 DOG, CAT: 0.05–0.2 mg/kg, IV or intratracheal (only for status asthmaticus or cardiopulmonary-cerebral resuscitation)
Esmolol Brevibloc for injection, 100 mg/ml (10-ml vial) DOG, CAT: Initial IV loading dose of 100 to 500 mcg/kg administered over one minute, followed by a 25–150 mcg/kg/min constant rate infusion.
Furosemide Furosemide for injection, 10 mg/ml and 50 mg/ml DOG: 2–6 mg/kg q8–12h as needed, IV, IM, SQ, PO
Veterinary Lasix tablets, 12.5, 50 mg CAT: 1–4 mg/kg q12h as needed, IV, IM, SQ, PO
Furosemide USP tablets, 20, 40, 50, 80 mg Following initial bolus, CRI can be used to deliver 24h dose
Furosemide 1% oral syrup (10 mg/ml)
Heparin USP Heparin USP for injection CAT: 150–250 units/kg initial dose, SQ, IV
50–200 units/kg q8h, SQ
Hydralazine Apresoline, USP tablets, 10, 25, 50 mg DOG: 1–3 mg/kg PO, q12h (up-titrate dose to ABP effect)
Hydrochlorthiazide Hydrodiuril, USP tablets, 25, 50 mg DOG, CAT: 1–4 mg/kg q24–48h, PO
Isosorbide dinitrate Sorbitrate, Isordil, USP tablets, 5, 10 mg DOG: 2.5–5 mg orally bid
Lidocaine Xylocaine, USP for injection, 2% (20 mg/ml, without epinephrine) DOG: 2 mg/kg IV bolus, can repeat up to 8 mg/kg over a 10- minute period; 25–75 mcg/kg/minute constant rate IV infusion (check blood potassium concentration if no effect);
CAT: 0.25–1.0 mg/kg, slow IV injection over a 3–5-minute period

Drug Preparation(s) Usual Dosageß
Lisinopril Prinivil unscored tablets, 2.5, 5, 10, 20, 40 mg DOG: 0.25–0.5 mg/kg q12–24h, PO
Magnesium 20% MgCl2 solution for injection (contains DOG: 0.75–1 mEq/kg/24h IV infusion (50% of total dose can be given in 2–4 hours if necessary)
1.97 mEq of Mg++ per mL) For ventricular fibrillation: 0.15–0.30 mEq/kg IV over 5–10 min
Metoprolol tartrate Toprol-XL scored tablets, 25 mg DOG: Start at ¼ of a 25 mg tablet once daily; up-titrate every 2 weeks to 12.5 mg q12h, PO (for a 20–30 kg dog)
Mexiletine Mexitil, USP capsules, 150, 200, 250 mg DOG: 5–8 mg/kg q8h, PO
Mexitil, 250 mg for injection DOG: 2.5 mg/kg bolus IV given over 10 min, followed by 30 mcg/kg/min for 3 hours CRI, followed by 5–8 mcg/kg/min CRI for 24–48 hours IV (currently available in Europe)
Nitroprusside sodium Nitropress, Nipride 50 mg/vial Usual dosage range is 2–10 mcg/kg/min CRI
Begin at 0.5–1 mcg/kg/minute and uptitrated
If possible limit infusion to 24 hours
Nitroglycerine ointment (2%) Nitrol, Nitro-bid, Nitrostat, USP 15 mg per inch DOG: ¼–1 inch topically q12h; Patch: 2.5–10 mg (small-giant dog)
Minitran transderm patches 2.5, 5, 10, 15 mg/24 hr CAT: ¼ inch topically q12h
Pimobendan Vetmedin capsules, 1.25, 2.5, 5 mg DOG: 0.3–0.6 mg/kg/day, divided; usual dose is 0.25 mg/kg q12h PO (give 1 hour before feeding)
Prazosin Minipress, 1-, 2-, 5-mg capsules 1 mg/15 kg q8–12h PO
Procainamide Pronestyl, USP for injection, 100 mg/ml; 500 mg/ml DOG: 2 mg/kg (IV) to a maximum total dose of 20 mg/kg over a 30-minute period; 25–40 mcg/kg/min IV infusion; 8–20 mg/kg, IM or SQ q4–6h; 10–20 mg/kg q8h PO (sustained release preparation)
Procainamide SR, USP capsules and tablets, 250, 375, 500 mg CAT: 3–8 mg/kg q6–8h IM or PO
Propranolol Inderal, USP for injection, 1-mg ampoule DOG, CAT: 20–60 mcg/kg over 5–10 min, IV
Tablets, 10, 20, 40, 60, 80 mg DOG: 0.5–1.0 mg/kg q8h, PO (use with caution in CHF)
Inderal LA capsules, 60, 80, 120, 160 mg Can up-titrate dose from 0.1 mg/kg q8h, PO
CAT: 2.5–5.0 mg dose q8h, PO (use with caution in CHF)
Spironolactone Aldactone, USP tablets, 25 mg DOG: 0.5 mg/kg–1.0 mg/kg q12–24h, PO
Sotalol Betapace, USP scored tablets, 80, 160, 240 mg DOG: 1–2 mg/kg q12h, PO
Tocainide Tonocard, USP tablets, 400, 600 mg DOG: 10–20 mg/kg q8h (rarely prescribed today; available in Europe)
Verapamil Isoptin, 5-, 10-mg ampoules for injection; DOG: 0.05 mg/kg, IV every 10–30 minutes to a maximum cumulative dose of 0.2 mg/kg
Isoptin, Calan, 40-, 80-, 120-mg tablets
Warfarin Coumadin 1-, 2-mg scored tablets CAT: 0.5 mg PO, initial daily dose; compounding may be needed

Check dosing information and standard textbooks for specific dosing recommendations.

Prescription of many of these drugs in small animal patients constitutes an extra-label use and vary across different countries; Clients should be so advised. Recommendations are based on current standards of veterinary practice.

Many drugs must be titrated to effect, especially in dogs and cats with congestive heart failure. Consider drug interactions when prescribing multiple drugs.


Diuretics are a standard of chronic congestive heart failure (CHF) therapy and are administered for two main purposes: (1) diuresis of the patient with pulmonary edema or body cavity effusions and (2) prevention of the chronic sodium and water retention that characterizes chronic CHF. Diuretics are also anti-hypertensive agents but do not represent an important treatment approach for high arterial blood pressure (ABP) in dogs and cats. Diuretics should be administered with a sodium-restricted diet that is proportional to the severity of CHF.


Furosemide is the most often used diuretic. It acts by inhibiting the co-transporter of chloride in Henle’s loop with resultant losses of chloride, sodium, water, calcium, magnesium, potassium, and water-soluble vitamins in the urine. Bumetanide and torsemide are related human drugs infrequently used in veterinary practice.


Spironolactone is a potassium- (and magnesium) sparing diuretic that antagonizes the effects of aldosterone by binding to mineralocorticoid receptors in the distal collecting duct. Though a weak diuretic, it is often added to a comprehensive CHF therapy regimen that includes furosemide, an ACEI, and a positive inotrope. Eplerenone is a related drug that is not widely used in veterinary practice.


Hydrochlorothiazide (HCT) is occasionally used in combination with furosemide and spironolactone for management of refractory fluid retention. HCT primarily blocks the sodium transporter in the distal convoluted tubule and the connecting segment but also has action across the proximal tubule. This effect inhibits sodium, chloride, and water reabsorption. HCT is a moderately potent diuretic, but when used in combination with furosemide, the diuretic impact is greatly magnified as HCT prevents distal sodium reabsorption that escapes the effects of the loop diuretic.

Monitoring of Diuretic Therapy

Diuretics contract plasma volume and dosing must be adjusted to control fluid accumulation while preventing hypotension, weakness, dehydration, electrolyte disturbances, and azotemia. In most cases, simple monitoring of ABP along with serum creatinine and BUN are sufficient to ensure the dose is not excessive.

Most adverse effects develop within the first two to three weeks unless other medications change or complications develop (e.g., digoxin toxicity with vomiting).

Monitor diuretic therapy as follows:


Positive inotropic drugs increase the availability of calcium to cardiomyocytes, thereby enhancing the strength of heart contraction. This class of drugs includes the digitalis glycosides (digoxin, digitoxin), catecholamines (dobutamine, dopamine), phosphodiesterase inhibitors (milrinone), and calcium sensitizers (pimobendan).


Digoxin is the oldest inotropic drug in common use. (Digitoxin is used rarely and will not be discussed.) Digoxin is indicated in therapy of moderate to severe CHF caused by dilated cardiomyopathy, chronic valvular heart disease, or untreated congenital heart disease in dogs. It is rarely prescribed to cats. Digoxin is especially useful when CHF is complicated by atrial fibrillation or frequent premature atrial complexes. The cardiac glycosides have not been shown to prolong survival in CHF.

While some veterinarians use the examination heart rate to decide if they will prescribe digoxin, there is no established basis for this approach or for predicting the potential benefit of the drug. Digoxin does little to mitigate heart rate due to high sympathetic tone, stress, or exercise; heart rate benefits of increased vagal tone are most evident in the resting state.


The catecholamines used most often in emergent management of CHF are dobutamine and dopamine. These drugs stimulate cardiac beta- and alpha–receptors to increase contractility in a dose-dependent manner via the second messenger effect (increased generation of cyclic AMP or IP3for beta- and alpha–receptor stimulation, respectively). In patients with CHF, the heart rate generally increases slightly during infusion of catecholamines. The effects of catecholamines on systemic arterioles are dose dependent but include vasodilation at lower doses (beta2 effect) and vasoconstriction (alpha effects) at higher infusion rates.


The word “inodilator” pertains to positive inotropic drugs that also demonstrate significant vasodilator effects. The combination of increased myocardial contractility and left ventricular afterload reduction result in a potent increase in ventricular stroke volume.


Pimobendan (Vetmedin) is classified as a calcium sensitizer, as well as a phosphodiesterase inhibitor with vasodilator properties. It is approved for veterinary use in many countries and completing clinical trials in other countries (including the USA). Pimobendan is an inodilator with a novel mode of action on contractility. Whereas digitalis and catecholamines increase the transport of calcium into the cardiomyocyte, pimobendan increases the sensitivity of the actin-myosin contractile apparatus to available calcium.

Compared to other inotropic drugs, pimobendan offers a number of advantages.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Cardiovascular Drugs

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