Fundamentals of Pharmacology for Veterinary Technicians Chapter 8

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1 Figure 8-1

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10 TABLE 8-1 Blood Flow Through the Heart The right atrium receives blood from all tissues, except the lungs, through the cranial and caudal venae cavae. Blood flows from here through the tricuspid valve into the right ventricle. (This is systemic circulation.) The right ventricle pumps the blood through the pulmonary semilunar valve and into the pulmonary artery, which carries it to the lungs. (This is pulmonary circulation.) The left atrium receives oxygenated blood from the lungs through the four pulmonary veins. The blood flows through the mitral valve into the left ventricle. (This is pulmonary circulation.) The left ventricle receives blood from the left atrium. From the left ventricle, blood goes out through the aortic semilunar valve and into the aorta and is pumped to all parts of the body, except the lungs. (This is systemic circulation.) Blood is returned by the venae cavae to the right atrium and the cycle continues. Table 8-1

11 TABLE 8-2 Catecholamine Receptors Receptor Example of Clinical Use Effect when StimulatedAffecting Receptor α 1 Constriction of peripheral Constricts blood vessels blood vessels within the area and prevents rapid diffusion of drug away from the injection site (for example, epinephrine can be injected with a local anesthetic) α 2 Reduces blood pressure Reduces blood pressure, but has CNS effect that can cause drowsiness and sedation β 1 Increases heart rate and force Treats animals with of heart contractions; decreased cardiac function increases blood glucose β 2 Causes bronchodilation Treats diseases where bronchodilation is needed Table 8-2

12 TABLE 8-3 Antiarrhythmic Drugs Class of Antiarrhythmic Drug Name Action Class IA: Local Anesthetics A. quinidine (Cin-Quin, Cardioquin, A. Suppresses myocardial excitability This group works as local anesthetics Quinidex ) and increases conduction times. to the nerves and myocardial membrane Used orally to treat atrial and ventricular arrhythmias. Side effects include vomiting, diarrhea, and weakness. B. procainamide (Pronestyl, B. Suppresses myocardial excitability Procamide SR, Procan SR) and increases conduction times. Used orally to treat premature ventricular contractions (PVC), ventricular tachycardia, and some atrial tachycardias. Side effects are vomiting, diarrhea, and weakness. Class 1B: Membrane Stabilization A. lidocaine (Xylocaine, Lidocaine for A. Depresses myocardial excitability. This group works by blocking the Injection 1% and 2%) Used IV to control PVCs and treat influx of sodium into the cell, ventricular tachycardia. Side effects thus stabilizing the myocardium are rare. and preventing depolarization B. tocainide (Tonocard ) B. Action similar to lidocaine, but is only given orally. Used orally to treat ventricular arrhythmias (ventricular tachycardia and PVCs). Side effects include ataxia, vomiting, and hypotension. Table 8-3

13 to TABLE 8-3 Continued treat ventricular arrhythmias (ventricular tachycardia and PVCs). Side effects include ataxia, vomiting, and hypotension. Class of Antiarrhythmic Drug Name Action Class 1B: Membrane Stabilization C. mexiletine (Mexitil ) C. Action is similar to lidocaine, but is (cont.) used orally. Used to treat ventricular arrhythmias (ventricular tachycardia and PVCs). Side effects include vomiting and unsteadiness. Class II: Beta-Adrenergic Blockers propranolol (Inderal, Intensol ) Reduces automaticity by blocking β 1 This group works by blocking and β 2 receptors, thus reducing beta-adrenergic receptors or by oxygen demand by the myocardium. preventing release of norepinephrine Used to treat hypertrophic from the adrenergic neuron cardiomyopathy and some ventricular arrhythmias. Side effects include bradycardia, lethargy, and depression. Class III: Action Potential Prolongation bretylium (Bretylol ) Increases the duration of the action This group works by lengthening the amiodarone (Cordarone ) potential. Both are used for emergency time between action potentials, treatments of ventricular tachycardia which decreases the sinus rate and fibrillation. These drugs are used in animals that are resistant to other drugs. Side effects include hypotension and vomiting. Class IV: Calcium-Channel Blockers A. verapamil (Isoptin, Calan ) A. Blocks calcium passage, relaxing This group works by blocking channels vascular smooth muscle to lower that allow calcium to enter the blood pressure and inhibit the myocardial cell. The entry of calcium cardiac conduction system. Given into the cell facilitates muscle orally and IV to treat supraventricular contractility tachycardia and atrial flutter. B. nifedipine (Procardia, Adalat ) B., C. Blocks calcium passage, dilating C. diltiazem (Cardizem ) coronary and peripheral blood vessels which results in the reduction of cardiac workload. Both are used Table 8-3 Continued

14 TABLE 8-4 Diuretic Drugs Diuretic Category Action Examples Side Effects Thiazide diuretics Inhibit sodium and chloride hydrochlorothiazide Hypokalemia (low blood reabsorption from the distal (HydroDIURIL ) potassium levels) convoluted tubule of the chlorothiazide (Diurel ) nephron hydroflumethiazide (Saluron ) bendroflumethiazide (Corzide ) Loop diuretics Inhibit reabsorption of sodium furosemide (Lasix, Disal, Hypokalemia and chloride in the loop Diuride ) of Henle, reducing the ability ethacrynic acid (Edecrin ) of the kidneys to concentrate urine; more potent than thiazides in promoting sodium and water excretion Potassium-sparing diuretics Work in a variety of ways 1. spironolactone (Aldactone ) Hyperkalemia 1. Inhibit aldosterone (mineralocorticoid that normally increases sodium retention and thus water in the kidney) 2. Block sodium reabsorption 2. trimterene (Dyazide ) in the distal convoluted tubule 3. Inhibit sodium reabsorption 3. amiloride (Midamor ) in the distal convoluted tubule Osmotic diuretics Large molecules that can be mannitol (Osmitrol ) Vomiting, electrolyte filtered by the glomerulus but glycerin (Osmoglyn ) imbalance have limited capability of being reabsorbed into the blood. High concentration of osmotic agent is left in the kidney tubule, which carries large amounts of fluid with it Carbonic anhydrase Block the action of carbonic acetazolamide (Diamox ) Gastrointestinal disturbances, Table 8-4