Cardiac glycosides with thiazide diuretics

Other drugs that may interact with cardiac glycosides include the following Albuterol, amphotericin B, beta-blockers, calcium, disopyramide, loop diuretics, nondepolarizing muscle relaxants, potassium-sparing diuretics, succinylcholine, sympathomimetics, thiazide diuretics, thioamines, and thyroid hormones. 

Alterations in the serum potassium level are hazardous because they may result in cardiac arrhythmias. Drugs that may cause hyperkalemia despite normal renal function include potassium itself, -blockers, digitalis glycosides, potassium-sparing diuretics, and fluoride. Drugs associated with hypokalemia include barium, B-agonists, caffeine, theophylline, and thiazide and loop diuretics. 

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. 

No interactions are expected at standard therapeutic doses. At higher doses or with long-term use, licorice may potentiate potassium depletion of high-ceiling loop diuretics and thiazide diuretics, stimulant laxatives (Mills and Bone 2005), and corticosteroids such as prednisolone (Cheng et al. 2004 De Smet 1993), and may potentiate the action of cardiac glycosides such as digoxin (Kelly 1990). 

Concomitant use of senna or sickle-pod senna is cautioned with antiarrhythmic drugs, thiazide diuretics, corticosteroids, licorice, and botanicals containing cardiac glycosides, as long-term use of senna or sickle-pod senna as a laxative can cause or exacerbate potassium loss (Brinker 2001 De Smet 1993 ESCOP 2003). 

Concomitant use of diuretic herbs with prescription loop diuretics, thiazide diuretics, osmotic diuretics, and potassium-sparing diuretics may cause excessive fluid loss. Reductions in potassium levels caused by diuretics may increase the toxicity of cardiac glycosides, such as digoxin, and their combination should be avoided (Anon 2010). 

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. 

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