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.
Table 146-1 CARDIOVASCULAR DRUG DOSING—CANINE AND FELINE PATIENTS
| 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
Furosemide
• Parenteral administration of furosemide is associated with a rapid onset of diuresis, usually within 30 minutes of injection. IV administration also may be associated with release of beneficial venodilating prostaglandins. However, fast intravenous administration may also acutely stimulate the sympathetic nervous system and the rennin-angiotensin-aldosterone system, leading to an initial increase in systemic vascular resistance, blood pressure, heart rate, and left ventricular filling pressure; therefore, IV use should be reserved for severe CHF.
• Furosemide is a “high-ceiling” diuretic, demonstrating a graded dose-response effect. The drug must be delivered by renal blood flow to be effective. Reduced renal blood flow from CHF or volume depletion; renal failure; an NSAID such as aspirin; or hypoproteinemia can negatively impact delivery of furosemide to the proximal tubule. Malabsorption or decreased delivery of furosemide may be relevant in explaining refractory ascites in cases of severe right-sided CHF.
• Furosemide preparations include proprietary veterinary and generic veterinary formulations of 12.5 and 50 mg tablets; 20, 40, and 80 mg tablets (for human patients); injectable 1% and 5% solutions (10 mg/ml and 50 mg/ml); and 1% syrup (10 mg/ml).
• The usual parenteral dosage range for hospital therapy is 1 to 4 mg/kg; IV, IM, SC two to four times daily as needed. Cats tolerate lower dosages of diuretics when compared to dogs and are more likely to develop hypokalemia and azotemia.
• In life-threatening CHF, furosemide should be given by slow IV bolus. An alternative method of administration that may be more effective is constant rate IV infusion of furosemide. Following an initial bolus of 0.5 to 1 mg/kg, the dose earmarked for the next 24 hours can be constantly infused with a small volume pump.
• Oral furosemide is used for long-term treatment of CHF. Dosages are typically 2 to 6 mg/kg one to three times daily, titrated to the magnitude of fluid retention. Oral furosemide seems less potent (presumably from poorer absorption or renal delivery) when compared to parenteral furosemide at equal doses. One strategy for treating refractory ascites or pulmonary edema in the chronic CHF patient involves intermittent subcutaneous administration of furosemide at home. Injections are given in place of the regularly scheduled oral treatment. This can be initiated three times weekly and increased or decreased as necessary. Chronic subcutaneous administration may lead to granuloma like swellings in some dogs.
Adverse Effects
• Consequences in the patient may include azotemia, hypochloremia, metabolic alkalosis, and potentially hypokalemia (though this effect is usually blunted by adequate food intake and by an ACEI).
• Hypokalemia and hypomagnesemia predispose to premature complexes, digitalis intoxication, loss of efficacy of class I anti-arrhythmic drugs, and increased likelihood of drug-induced ventricular arrhythmias in animals treated with class III anti-arrhythmics.
• Excessive diuretic doses can be detected by regular measurement of blood pressure and the serum BUN, creatinine, and electrolytes.
• Azotemia is very common in dogs and especially in cats requiring daily furosemide treatment. Mild to moderate azotemia is acceptable in a patient with persistent fluid accumulation because the edema or effusion is likely to worsen if furosemide dosage is decreased. In contrast, the dose of furosemide should be reduced in a patient with azotemia and no evidence of edema.
Spironolactone
• Spironolactone prevents sodium reabsorption, spares potassium and magnesium, and most importantly, it antagonizes the cardiotoxic effects of aldosterone on the myocardium. Early use of this drug should be considered in CHF owing to potentially favorable effects on preventing myocardial fibrosis.
• Spironolactone is available in 25- and 50-mg tablets. Typical dosages for cardioprotection range from 6.25 to 25 mg once or twice daily and generally fall within a dosage range of 0.5 to 2 mg/kg daily. Dosages are somewhat empiric and related to severity of CHF and patient size; in human patients, even low dosages are cardioprotective.
• Hyperkalemia occasionally occurs from the combined effects of the spironolactone added to an ACEI. For this reason, potassium supplements should not be administered concurrently with spironolactone.
Hydrochlorothiazide
• HCT is available in a variety of tablet sizes, some of which represent combination products. HCT is often formulated with spironolactone (25 mg of each in the 50-mg tablet) or triamterene (to spare potassium) as these combinations increase the diuretic effect while sparing potassium.
• The usual dose of HCT is 1 to 2 mg/kg daily provided the drug can be tolerated. Unfortunately, the “sequential nephron blockade” of fluid and electrolyte reabsorption during combination diuretic therapy is frequently too potent: the result is rapid volume and electrolyte depletion.
• To minimize the risk of acute renal failure and electrolyte disturbances, HCT is administered every other day for the first week of therapy, and serum chemistries and blood pressure are then reevaluated.
• If renal function and electrolytes remain stable, the frequency of dosing can be increased to once daily administration, added to the previously established furosemide-spironolactone regimen.
Nesiritide
• Nesiritide (labeled for human use) appears to be effective in dogs. It enhances urinary output and reduces aldosterone effects in furosemide-treated dogs; increases urine volume in normal dogs and those with experimental CHF; and demonstrates minimal electrophysiologic effects on the canine heart.
Monitoring of Diuretic Therapy
Monitor diuretic therapy as follows:
• Examine the jugular veins. If prominent or distended, volume depletion is not likely an issue and higher diuretic doses are likely to be tolerated.
• Measure the serum electrolytes to screen for hyponatremia, hypochloremia (disregard if mild), hypokalemia (never disregard). Hypomagnesemia often tracks hypokalemia.
• Metabolic alkalosis may be evident by increased or normal bicarbonate concentration in the face of a low serum chloride. As with hypochloremia, this abnormality is typically ignored unless moderate or severe.
• Diuretic complications are treated by reducing the diuretic dosage and, if necessary, infusing crystalloids (5% dextrose in water or 0.45 NaCl/2.5% dextrose; either fluid should be supplemented with potassium chloride at 10-20 mEq KCl per 500 ml fluid).
• Patients with primary renal disease and CHF pose a treatment challenge, as volume depletion reduces renal blood flow. It is difficult to support renal function and still control edema or effusions in patients with advanced CHF.
• Provided the patient is drinking, chronic administration of subcutaneous fluids is illogical, as the same effect can be obtained by simply lowering the diuretic dosage (which generally worsens the CHF).
• Mild to moderate azotemia often must be accepted if CHF therapy is to be successful. Hemodialysis would be optimal for controlling uremia and volume status but is not widely available or accessible.
POSITIVE INOTROPIC DRUGS (CARDIOTONICS)
Digoxin
• Following oral or IV administration, digoxin inhibits the sodium–potassium ATPase that activates a sodium calcium exchanger, which increases calcium influx. The inotropic effect is mild when compared to potent drugs such as dobutamine or pimobendan.
• Digoxin also sensitizes arterial baroreceptors, leading to a withdrawal of sympathetic activity and increased vagal efferent tone to the heart. This effect slows the sinus node rate at rest and decreases the ventricular rate response to atrial fibrillation (by impairing AV nodal conduction).
• Canine data suggest that digoxin may inhibit the renin–angiotensin system and decrease sympathetic nerve discharge.
• Digoxin administered orally decreases systemic vascular resistance, venous tone, and central venous pressure and induces diuresis in patients with CHF.
• Digoxin given IV may cause systemic and coronary vasoconstriction and can produce transient myocardial ischemia. Therefore, IV administration is not recommended.
• Digoxin is mainly a drug for management of advanced CHF caused by predominately systolic dysfunction. The drug is particularly indicated in the setting of atrial fibrillation and CHF.
• Digoxin plays no role in the acute hospital therapy of CHF unless it is complicated by atrial fibrillation.
• We do not prescribe digoxin for occult (asymptomatic) heart disease as other drugs (ACEI and beta-blockers) are more likely to be cardioprotective and digoxin may aggravate ventricular ectopy.
• Overt contraindications to digitalization include frequent or complex ventricular ectopy; moderate to severe renal failure (reduced elimination); myocarditis, sinus node disease, or heart block (vagal effects can depress nodal functions); hypokalemia (increases potential for arrhythmias); ventricular pre-excitation (AV block may lead to preferential conduction down the accessory pathway); and known individual hypersensitivity (typically anorexia) to the drug.
• Drug interactions may occur with quinidine, verapamil, and amiodarone resulting in increased serum digoxin concentration.
• Digoxin is administered typically by the oral route. Intravenous use is uncommon today in small animals. Available digoxin preparations include tablets (0.125, 0.25, 0.5 mg) and elixirs (0.05 and 0.15 mg per ml). The usual daily dose for the dog is 0.0055 to 0.0075 mg/kg, PO, twice daily.
• Monitoring of therapy can be accomplished by client interview for adverse signs; auscultation for arrhythmias; an ECG when heart rhythm disturbances are detected; and most importantly, a serum digoxin level. Following a week of consistent treatment, a blood sample is obtained 8 to 12 hours post dosing; the therapeutic goal for a trough level is 0.8 to 1.2 ng/ml.
Catecholamines
• Dobutamine HCl is an injectable catecholamine (synthetic analogue of dopamine) with dose-dependent positive inotropic effects that are far greater than digitalis glycosides. Effects on blood vessels are dose-dependent and depend on the predominant drug effect and availability of sympathetic receptors.
• Both beta and alpha effects are inotropic, but myocardial beta-receptor density is far greater in dogs and cats.
• Myocardial receptor density is altered in chronic canine CHF, and the beta-receptor density (especially beta1) is reduced. Accordingly, the dose of dobutamine required for cardiac stimulation may be higher than that used for healthy dogs in other settings (as with anesthesia). Constant rate infusion can lead to further down regulation of beta-receptors occurring within several hours (tachyphylaxis), requiring higher doses to maintain the same inotropic effects.
• In resistance arterioles, the beta2 effect of catecholamines causes vasodilation, while alpha-receptor stimulation constricts the vessels.
• Dopamine, the precursor to nor-epinephrine, has similar effects but causes more tachycardia and pulmonary and systemic vasoconstriction than dobutamine for equivalent inotropic doses. For these reasons, dopamine is used less often in CHF but is preferred if bradycardia or severe hypotension is present.
• Indications for catecholamines—The principal use of dobutamine or dopamine in CHF is therapy of cardiogenic shock, which can be defined clinically as severe CHF accompanied by hypotension (systolic ABP <80 mm Hg and a mean ABP <50 mm Hg) with evidence of poor perfusion (pale mucous membranes and elevated blood lactate). This situation is often accompanied by hypothermia and in cats is also associated with sinus bradycardia (HR <160/min). Dobutamine also can be used to support the dog with chronic refractory CHF that is retaining fluid and is unresponsive to high dose diuretic therapy.
• The immediate goal of catecholamine therapy in CHF is the short-term (24-48 hours) support of myocardial contractility to achieve a higher stroke volume and cardiac output. Such therapy, when administered with other drugs for heart failure such as diuretics and nitrates, frequently stabilizes the patient. Ideally this benefit will occur mainly through an increase in stroke volume, without excessive increases in heart rate or vascular resistance.
• Clinical measures of improvement during catecholamine infusion include increases in ABP and urinary output; enhanced tissue perfusion, as judged by heightened level of consciousness, normal rectal temperature, pink mucous membrane color, and shortened refill time; and improved muscle strength.
• Clinical use of dobutamine in dogs with CHF involves a constant rate intravenous infusion with initial suggested rate of 2.5 mcg/kg/min. Dobutamine is added to 5% dextrose solution and infusion controlled by an automated dose syringe or infusion pump.
• The initial dose can be increased in 30 to 60 minutes to 3.75 or 5 mcg/kg/min and then up-titrated as needed to clinical effect.
• Objective markers of drug effect are increases in rectal temperature and ABP. A target ABP of 90 to 100 mm Hg systolic is a reasonable goal, and the infusion should be maintained at a level to prevent higher ABP or tachycardia.
• After 24 to 48 hours of dobutamine, the infusion can be reduced by 50% every 2 to 4 hours with monitoring of ABP. If blood pressure is maintained at >85 mm Hg systolic, the drip can be discontinued.
• If ABP fails to increase in dogs with cardiogenic shock, consideration should be given to adding or substituting dopamine for more potent vasoconstriction. Dose rates are indicated in Table 146-1.
• Atrial fibrillation is not a contraindication for use of dobutamine. In most cases, ventricular rate response is unchanged or actually slows during dobutamine infusion, presumably from improved ABP and withdrawal of endogenous sympathetic tone. Digoxin can be used in combination with dobutamine to help control ventricular response rate.
• Cats with CHF, hypotension, and bradycardia can benefit from infusions of dobutamine. This includes feline patients that have suffered a myocardial infarction superimposed on pre-existent cardiomyopathy.
• Typically an infusion of 2.5 mcg/kg/min is initiated. Infusion rates exceeding >7.5 mcg/kg/min are uncommonly needed.
• The infusion rate can be increased every 30 to 60 minutes to achieve an ABP of 90 to 120 mm Hg systolic. In most cases, heart rate also will increase to more appropriate levels for a cat with CHF.
• Contraindications for catecholamines are mostly relative. Ventricular ectopy may worsen and should be carefully monitored by ECG monitor. Hypokalemia may worsen with catecholamine infusion, so electrolyte imbalances should be corrected.
Inodilators
Pimobendan
Compared to other inotropic drugs, pimobendan offers a number of advantages.
• It is far more potent than digoxin and does not cause anorexia. Furthermore, pimobendan is not reported to impact off-loading of calcium from the contractile apparatus, which suggests it will not impair diastolic function (a potential problem with digitalis).
• Pimobendan is superior to pure phosphodiesterase inhibitors in canine models of CHF, emphasizing the benefit of the calcium sensitization.
• Pimobendan is administered by the oral route yet still carries a potent inotropic effect. For this reason, it serves as a second choice to dobutamine (or dopamine) infusion for hospital treatment of low cardiac output. ABP must be followed to insure that excessive vasodilation does not develop secondary to PDE inhibition. Thus, while dobutamine is the drug of choice for cardiogenic shock, pimobendan may be more practical in many practice situations.
• Unlike digoxin, catecholamines, and pure PDE-III inhibitors, pimobendan is noteworthy for an apparent lack of sensitization to ventricular arrhythmias.
• Pimobendan is indicated in the therapy of heart failure in dogs caused by dilated cardiomyopathy and is also beneficial in treatment of CHF due to chronic valvular heart disease or untreated congenital heart diseases in dogs. It has also been used for “prevention” of CHF in breeds with advanced occult DCM such as that encountered in the Doberman pinscher. Where available, pimobendan has often replaced digoxin for treatment of canine CHF.
• There is no logical reason for prescribing pimobendan to the exclusion of “standard CHF therapy” of furosemide and an ACE-inhibitor, along with dietary sodium restriction. This trio provides an excellent pharmacologic profile for treatment of advanced CHF in dogs.
• It is likely that pimobendan will be useful in cats with CHF, though extra-label feline use requires far more study.
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