DIGOXIN (Page 2 of 5)

CONTRAINDICATIONS:

CONTRAINDICATIONS:

Digitalis glycosides are contraindicated in patients with ventricular fibrillation or in patients with a known hypersensitivity to digoxin.

WARNINGS

WARNINGS:
Sinus Node Disease and AV Block: Because digoxin slows sinoatrial and AV conduction, the drug commonly prolongs the PR
interval. The drug may cause severe sinus bradycardia or sinoatrial block in patients with preexisting sinus node disease and may
cause advanced or complete heart block in patients with preexisting incomplete AV block. In such patients consideration should be
given to the insertion of a pacemaker before treatment with digoxin.
Accessory AV Pathway (Wolff-Parkinson-White Syndrome): After intravenous digoxin therapy, some patients with paroxysmal
atrial fibrillation or flutter and a coexisting accessory AV pathway have developed increased antegrade conduction across the
accessory pathway bypassing the AV node, leading to a very rapid ventricular response or ventricular fibrillation. Unless conduction
down the accessory pathway has been blocked (either pharmacologically or by surgery), digoxin should not be used in such patients.
The treatment of paroxysmal supraventricular tachycardia in such patients is usually direct-current cardioversion.
Use in Patients with Preserved Left Ventricular Systolic Function: Patients with certain disorders involving heart failure
associated with preserved left ventricular ejection fraction may be particularly susceptible to toxicity of the drug. Such disorders
include restrictive cardiomyopathy, constrictive pericarditis, amyloid heart disease, and acute cor pulmonale. Patients with idiopathic
hypertrophic subaortic stenosis may have worsening of the outflow obstruction due to the inotropic effects of digoxin.

PRECAUTIONS

PRECAUTIONS:

Use in Patients with Impaired Renal Function: Digoxin is primarily excreted by the kidneys; therefore, patients with impaired

renal function require smaller than usual maintenance doses of digoxin (see DOSAGE AND ADMINISTRATION). Because of

the prolonged elimination half-life, a longer period of time is required to achieve an initial or new steady-state serum concentration

in patients with renal impairment than in patients with normal renal function. If appropriate care is not taken to reduce the dose of

digoxin, such patients are at high risk for toxicity, and toxic effects will last longer in such patients than in patients with normal renal

function.

Use in Patients with Electrolyte Disorders: In patients with hypokalemia or hypomagnesemia, toxicity may occur despite serum

digoxin concentrations below 2 ng/mL, because potassium or magnesium depletion sensitizes the myocardium to digoxin. Therefore,

it is desirable to maintain normal serum potassium and magnesium concentrations in patients being treated with digoxin. Deficiencies

of these electrolytes may result from malnutrition, diarrhea, or prolonged vomiting, as well as the use of the following drugs or

procedures: diuretics, amphotericin B, corticosteroids, antacids, dialysis, and mechanical suction of gastrointestinal secretions.

Hypercalcemia from any cause predisposes the patient to digitalis toxicity. Calcium, particularly when administered rapidly by the

intravenous route, may produce serious arrhythmias in digitalized patients. On the other hand, hypocalcemia can nullity the effects of

digoxin in humans; thus, digoxin may be ineffective until serum calcium is restored to normal. These interactions are related to the

fact that digoxin affects contractility and excitability of the heart in a manner similar to that of calcium.

Use in Thyroid Disorders and Hypermetabolic States: Hypothyroidism may reduce the requirements for digoxin. Heart failure and/

or atrial arrhythmias resulting from hypermetabolic or hyperdynamic states (e.g., hyperthyroidism, hypoxia or arteriovenous shunt) are

best, treated by addressing the underlying condition. Atrial arrhythmias associated with hypermetabolic states are particularly resistant

to digoxin treatment. Care must be taken to avoid toxicity if digoxin is used.

Use in Patients with Acute Myocardial Infarction: Digoxin should be used with caution in patients with acute myocardial

infarction. The use of inotropic drugs in some patients in this setting may result in undesirable increases in myocardial oxygen demand

and ischemia.

Use During Electrical Cardioversion: It may be desirable to reduce the dose of digoxin for 1 to 2 days prior to electrical

cardioversion of atrial fibrillation to avoid the induction of ventricular arrhythmias, but physicians must consider the consequences

of increasing the ventricular response if digoxin is withdrawn. If digitalis toxicity is suspected, elective cardioversion should be

delayed. If it is not prudent to delay cardioversion, the lowest possible energy level should be selected to avoid provoking ventricular

arrhythmias.

Laboratory Test Monitoring: Patients receiving digoxin should have their serum electrolytes and renal function (serum creatinine

concentrations) assessed periodically; the frequency of assessments will depend on the clinical setting. For discussion of serum

digoxin concentrations; see DOSAGE AND ADMINISTRATION section.

Drug Interactions: Potassium-depleting diuretics are a major contributing factor to digitalis toxicity. Calcium, particularly if

administered rapidly by the intravenous route, may produce serious arrhythmias in digitalized patients. Quinidine, verapamil,

amiodarone, propafenone, indomethacin, itraconazole, alprazolam, and spironolactone raise the serum digox-in concentration due

to a reduction in clearance and/or in volume of distribution of the drug, with the implication that digitalis intoxication may result.

Erythromycin and clarithromycin (and possibly other macrolide antibiotics) and tetracy-cline may increase digoxin absorption

in patients who inactivate digoxin by bacterial metabolism in the lower intestine, so that digitalis intoxication may result (see

CLINICAL PHARMACOLOGY: Absorption). Propantheline and diphenoxylate, by decreasing gut motility, may increase digoxin

absorption. Antacids, kaolin-pectin, sulfasalazine, neomycin, cholestyramine; certain anticancer drugs, and metoclopramide may

interfere with intestinal digoxin absorption, resulting in unexpectedly low serum concentrations. Rifampin may decrease serum

digoxin concentration, especially in patients with renal dysfunction, by increasing the non-renal clearance of digoxin. There have

been inconsistent reports regarding the effects of other drugs [e.g., quinine, penicillamine] on serum digoxin concentration. Thyroid

administration to a digitalized, hypothyroid patient may increase the dose requirement of digoxin. Concomitant use of digoxin and

sympathomimetics increases the risk of cardiac arrhythmias. Succinylcholine may cause a sudden extrusion of potassium from muscle

cells, and may thereby cause arrhythmias in digitalized patients. Although beta-adrenergic blockers or calcium channel blockers and

digoxin may be useful in combination to control atrial fibrillation, their additive effects on AV node conduction can result in advanced

or complete heart block.

Due to the considerable variability of these interactions; the dosage of digoxin should be individualized when patients receive

these medications concurrently. Furthermore, caution should be exercised when combining digoxin with any drug that may cause

a significant deterioration in renal function, since a decline in glomerular filtration or tubular secretion may impair the excretion of

digoxin.

Drug/Laboratory Test Interactions: The use of therapeutic doses of digoxin may cause prolongation of the PR interval and

depression of the ST segment on the electrocardiogram. Digoxin may produce false positive ST-T changes on the electrocardiogram

during exercise testing. These electrophysiologic effects reflect an expected effect of the drug and are not indicative of toxicity.

Carcinogenesis, Mutagenesis, Impairment of Fertility: There have been no long-term studies performed in animals to evaluate

carcinogenic potential; nor have studies been conducted to assess the mutagenic potential of digoxin or its potential to affect fertility.

Pregnancy: Teratogenic Effects: Pregnancy Category C: Animal reproduction studies have not been conducted with digoxin. It

is also not known whether digoxin can cause fetal harm when administered to a pregnant woman or can affect reproductive capacity.

Digoxin should be given to a pregnant woman only if clearly needed.

Nursing Mothers: Studies have shown that digoxin concentrations in the mother’s serum and milk are similar. However, the

estimated exposure of a nursing infant to digoxin via breast feeding will be far below the usual infant maintenance dose. Therefore,

this amount should have no pharmacologic effect upon the infant. Nevertheless, caution should be exercised when digoxin is

administered to a nursing woman.

Pediatric Use: Newborn infants display considerable variability in their tolerance to digoxin. Premature and immature infants are

particularly sensitive to the effects of digoxin, and the dosage of the drug must not only be reduced but must be individualized

according to their degree of maturity. Digitalis glycosides can cause poisoning in children due to accidental ingestion.

Geriatric Use: The majority of clinical experience gained with digoxin has been in the elderly population. This experience has

not identified differences in response or adverse effects between the elderly and younger patients. However, this drug is known to

be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal

function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, which

should be based on renal function, and it may be useful to monitor renal function (see DOSAGE AND ADMINISTRATION).

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