Other Positive inotropic Agents

phosphodiesterase inhibitors such as inamrinone and milrinone are classified as positive inotropic agents because they increase myocardial con- 

Gastrointestinal symptoms anorexia nausea vomiting abdominal pain Visual disturbances halos 

A-V junctional escape rhythms, junctional tachycardia atrial rhythms with slowed A-V conduction or A-V block 

Dopamine and dobutamine are sometimes used to stimulate the heart in cases of acute or severe heart failure (see Chapter 20). Dopamine and dobutamine exert a fairly specific positive inotropic effect, presumably through their ability to stimulate beta-1 receptors on the myocardium.60 Other beta-1 agonists (epinephrine, prenalterol, etc.) will also increase myocardial contractility, but most of these other beta-1 agonists will also increase heart rate or have other side effects that prevent their use in congestive heart failure. Dopamine and dobutamine are usually reserved for patients with advanced cases of congestive heart failure who do not respond to other positive inotropic drugs (e.g., digitalis).6,72 

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P-Adrenergic stimulation improves cardiac performance by positive inotropic effects and vasodilation. Dobutamine (see p. 66) is the most commonly used inotropic agent other than digitalis. Dobutamine leads to an increase in intracellular cAMP, which results in the activation of protein kinase. Slow calcium channels are one important site of phosphorylation by protein kinase. When phospho-rylated, the entry of calcium ion into the myocardial cells increases, thus enhancing contraction (Figure 16.11). Dobutamine must be given by intravenous infusion, and is primarily used in the treatment of acute heart failure in a hospital setting. 

Acnisal salicylic acid, aconiazide [inn] is an isoniazid analogue and an ANTITUBERCULAR and ANTIBACTERIAL AGENT, aconitine is an alkaloid from monk s hood or wolfsbane (Aconitum napellus) and other Aconltum spp. (Ranunculaceae). It is a NEUROTOXiN implicated in poisoning by A. spp., especially, 4. chasmanthum in India. Experimentally, it is a SODIUM-CHANNEL ACTIVATOR that binds to Na -channels, slows inactivation, shifts inactivation to a more negative value, and alters ion specificity. This results in repetitive firing of neurons, with marked effects on the heart including positive inotropism and arrhythmias. Aconitine (and the related alkaloid delphinine) were formerly used in... 

V. Drug or laboratory interactions. The positive inotropic effects of inamrinone are additive with other inotropic agents, including digitalis glycosides. These drugs can be used together, but the patient should be monitored for cardiac dysrhythmias. 

P effects, nonselective (i.e. pj + Pj) isoprenaline (isoproterenol). Its uses as bronchodilator (P2), for positive cardiac inotropic effect and to enhance conduction in heart block (p, pp have been largely superseded by agents with a more appropriately selective profile of effects. Other agents with nonselective P effects, ephedrine, orciprenaline, are also obsolete for asthma. 

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