Veterinary Clinical Medicine-I (General and Systemic)

Cardiac drugs - An introduction

CARDIAC DRUGS

Vasodilators

• ACE Inhibitors: They inhibit angiotensin I → angiotensin II conversion and alters production of aldosterone. It decreases peripheral vasoconstriction and Na ⁺ and H₂O retention. They are Afterload and preload reducers. Vasodilation and reverse remodeling occurs. The “–pril: drugs such as Enalapril (Enocard), used for DCM.  Benazapril acts same way and has hepatic clearance and SID. Side effects include renal failure ( ↓ GFR), hypotension. Do not use in conjunction with NSAIDs (like Rimadyl).
• Hydralazine – Pure arteriolar vasodilator. Potent afterload reducer, ↓ BP. Indicated for chronic valve diz and DCM. Must titrate dose. Side effects include hypotension and ↑ HR.
• Amlodipine – Ca⁺⁺ channel blocker. Arteriolar vasodilator. Treat hypertension in cats (w/out heart diz) and in conjunction w/ ACE inhibitor in dog for more ↓ afterload.
• Nitroglycerin – Preload reducer, venous capacitance. Emergency use for CHF, blood in shunted to capacitance vv.

Antiarrhythmics

• Procainamide – Membrane stabilizer. Slowed conduction, less automaticity. IV emergency tx of ventricular arrythmias.
• Lidocaine – Membrane stabilizer. Emergency tx for ventricular arrythmias. IV, short t_½, so slow IV drip.
• Propanolol – Class II β blocker. Negative chronotrope and inotrope. For atrial tachycardia and HCM to ↓ heart and ↑ filling time. Side effects include bronchoconstriction, bradyarrythmias, hypotension, heart failure, hypoglycemia.
• Atenolol – Class II β blocker, specific to β₁. Don’t see bronchiolar effects.
• Diltiazem - Ca⁺⁺ channel blocker. Negative chronotrope and inotrope, ↓ conduction. Atrial tachycardia and HCM.
• Digoxin – Cardiac glycoside. Positive inotrope, negative chronotrope. Supraventricular tachycardias, CHF, DHF. Side effect is arrhythmogenicity, N, V, D via stimulation of CRTZ. Dose on lean body weight.

Positive Inotropes

• Dobutamine – Direct β₁ stimulation. Positive inotrope and chronotrope. Emergency CHF. CRI. Arrythmogenic.
• Epinephrine - α₁, α₂, β₁, β₂ stimulation. Potent vasopressor dt positive inotrope and chronotrope. Emergency tx of cardiac standstill. Very arrythmogenic.

Diuretics

• Furosemide – K⁺ wasting diuretic, use when congestive diz. See Diuretics.
• Spironolactone – Antialdosterone diuretic; blocks effects at distal tubules, spares K⁺, eliminates Na⁺ and Cl^-. Not potent by itself, use in combo w/ other diuretics. Good for ascites. Careful in combo w/ ACE inhibitor. Also has reverse remodeling effects on the heart, antifibrotic.