Heart disease cardiac glycosides

Secondary hypotension is a sign of an underlying disease that should be treated first. If stroke volume is too low, as in heart failure, a cardiac glycoside can be given to increase myocardial contractility and stroke volume. When stroke volume is decreased due to insufficient blood volume, plasma substitutes will be helpful in treating blood loss, whereas aldosterone deficiency requires administration of a mineralocor-ticoid (e.g., fludrocortisone). The latter is the drug of choice for orthostatic hypotension due to autonomic failure. A parasympatholytic (or electrical pacemaker) can restore cardiac rate in bradycardia. 

Taurine (2-aminoethanesulfonic acid 4.235) is an inhibitory neurochemical that probably acts primarily as a neuromodulator rather than a neurotransmitter. It is formed from cysteine, and its accumulation can be prevented by the cardiac glycoside ouabain. Although receptor sites and specific actions cannot be elucidated without an antagonist, taurine has been implicated in epilepsy and, potentially, in heart disease. There are a large number of physiological effects attributed to taurine, among them cardiovascular (antiarrythmic), central (anticonvulsant, excitability modulation), muscle (membrane stabilizer), and reproductive (sperm motility factor) activity. Analogs of taurine, phthalimino-taurinamide (4.236) and its iV-alkyl derivatives, are less polar than taurine and are potent anticonvulsant molecules. 

In summary, many patients with symptoms of heart failure take a cardiac glycoside, a diuretic, and an ACE inhibitor. Diuretics and a glycoside such as digoxin improve symptoms, but have little effect on survival. ACE inhibitors improve symptoms and prolong survival, but the disease still progresses. 

Adverse effects Thiazide diuretics induce hypokalemia and hyperuricemia in 70% of patients, and hyperglycemia in 10% of patients. Serum potassium levels should be monitored closely in patients who are predisposed to cardiac arrhythmias (particularly individuals with left ventricular hypertrophy, ischemic heart disease, or chronic congestive heart failure) and who are concurrently being treated with both thiazide diuretics and digitalis glycosides (see p. 160). Diuretics should be avoided in the treatment of hypertensive diabetics or patients with hyperlipidemia. 

There are many disorders of the cardiovascular system and blood. Common cardiovascular disorders are cardiac failure, ischaemic heart disease, arrhythmias and hypertension. Although these conditions cannot be cured by drug therapy, there are many drugs available to help control them. Cardiac glycosides are useful in cardiac failure and arrhythmias because they improve myocardial contractility and slow conduction through the heart. 

Established interactions. The CSM in the UK advises that, as potentially serious hypokalaemia may result from beta2 agonist therapy, particular caution is required in severe asthma, as this effect may be potentiated by theophylline and its derivatives, corticosteroids, diuretics, and by hypoxia. Hypokalaemia with concurrent use of thiazide and loop diuretics may be reduced or even abolished by the addition of spironolactone or high-dose triamterene. Plasma potassium levels should therefore be monitored in patients with severe asthma. Hypokalaemia may result in cardiac arrhythmias in patients with ischaemic heart disease and may also affect the response of patients to drugs such as the digitalis glycosides and an-tiarrhythmics. 

Na+ -p K+) Adenosinetriphosphatase is the membrane-bound enzyme that transports sodium and potassium in opposite directions across the cell membrane to create the ion gradients that are utilized to perform physiological functions. The cardiac glycosides and aglycons, such as digoxin, ouabain, and strophanthidin, are natural products that have been used therapeutically for centuries in the treatment of heart disease. Their only known biochemical effect is to inhibit specifically (Na+-j-K ) adenosinetriphosphatase and consequently decrease or completely stop active cation flux. 

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