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Pronunciation |
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(di
ji TOKS
in) |
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U.S. Brand
Names |
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Crystodigin® |
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Generic
Available |
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Yes |
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Pharmacological Index |
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Antiarrhythmic Agent, Class IV |
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Use |
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Treatment of congestive heart failure, atrial fibrillation, atrial flutter,
paroxysmal atrial tachycardia, and cardiogenic shock |
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Pregnancy Risk
Factor |
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C |
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Contraindications |
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Hypersensitivity to digitoxin or any component (rare); digitalis toxicity;
beriberi heart disease; A-V block; idiopathic hypertrophic subaortic stenosis;
constrictive pericarditis; ventricular fibrillation; ventricular
tachycardia |
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Warnings/Precautions |
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Use with caution in patients with hypoxia, hypothyroidism, or acute
myocarditis. Do not use to treat obesity. Patients with incomplete A-V block
(Stokes-Adams attack) may progress to complete block with digitalis drug
administration. Use with caution in patients with acute myocardial infarction,
severe pulmonary disease, idiopathic hypertrophic subaortic stenosis,
Wolff-Parkinson-White syndrome, sick sinus syndrome (bradyarrhythmias), amyloid
heart disease, and constrictive cardiomyopathies. Adjust dose with renal or
hepatic impairment and aged patients. Elderly may develop exaggerated
serum/tissue concentrations due to decreased lean body mass, total body water,
and age-related reduction in renal/hepatic function. Exercise will reduce serum
concentrations of digoxin due to increased skeletal muscle
uptake. |
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Adverse
Reactions |
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1% to 10%: Gastrointestinal: Anorexia, nausea, vomiting
<1% (Limited to important or life-threatening symptoms): Sinus
bradycardia, A-V block, S-A block, atrial or nodal ectopic beats, ventricular
arrhythmias, bigeminy, trigeminy, atrial tachycardia with A-V block, drowsiness,
headache, fatigue, lethargy, vertigo, disorientation, hyperkalemia with acute
toxicity, feeding intolerance, abdominal pain, diarrhea, neuralgia, blurred
vision, halos, yellow or green vision, diplopia, photophobia, flashing lights
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Overdosage/Toxicology |
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Symptoms of acute overdose: Vomiting, hyperkalemia, sinus bradycardia, S-A
arrest and A-V block are common, ventricular tachycardia, and fibrillation may
occur
Chronic intoxication: Visual disturbances, weakness, sinus bradycardia,
atrial fibrillation with slowed ventricular response, and ventricular
arrhythmias
After GI decontamination, treat hyperkalemia if >5.5 mEq/L with sodium
bicarbonate and glucose with insulin or Kayexalate®. Treat
bradycardia or heart block with atropine or pacemaker and other arrhythmias with
conventional antiarrhythmics. Use Digibind® for severe
hyperkalemia, symptomatic arrhythmias unresponsive to other drugs, and for
prophylactic treatment in massive overdose. |
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Drug
Interactions |
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CYP3A3/4 enzyme substrate
Levothyroxine (and other thyroid supplements) may decrease digitoxin blood
levels.
Enzyme inducers (phenytoin, phenobarbital, rifampin) may reduce the blood
levels of digitoxin.
Amiloride may reduce the inotropic response to digitoxin.
Amiodarone reduces renal and nonrenal clearance of digitoxin and may have
additive effects on heart rate.
Beta-blocking agents (propranolol) may have additive effects on heart rate.
Calcium preparations: Rare cases of acute digitalis glycoside toxicity have
been associated with parental calcium (bolus) administration.
Moricizine may increase the toxicity of digitalis glycosides (mechanism
undefined).
Propafenone increases digoxin blood levels. Effects may also occur with
digitoxin. Monitor closely.
Propylthiouracil and methimazole may increase digitoxin blood levels by
reducing thyroid hormone.
Quinidine increases digitoxin blood levels substantially; monitor blood
levels/effect closely. Other related agents (hydroxychloroquine, quinine) should
be used with caution.
Verapamil, diltiazem, bepridil, and nitrendipine increase digoxin
concentrations, and may have similar effect on digitoxin. Other calcium channel
blocking agents do not appear to share this effect.
Drugs which cause hypokalemia (thiazide and loop diuretics, amphotericin B):
Hypokalemia may potentiate toxicity of digitalis glycosides.
These medications have been associated with reduced blood levels of digitalis
glycosides which appear to be of limited clinical significance:
Aminoglutethimide, antacids (magnesium- and aluminum-containing), sucralfate,
sulfasalazine, ticlopidine.
These medications have been associated with increased digitalis glycoside
blood levels which appear to be of limited clinical significance: Famciclovir,
flecainide, ibuprofen, itraconazole, cimetidine, famotidine, fluoxetine,
nefazodone, omeprazole, ranitidine, trimethoprim. |
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Mechanism of
Action |
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Digitalis binds to and inhibits magnesium and adenosine triphosphate
dependent sodium and potassium ATPase thereby increasing the influx of calcium
ions, from extracellular to intracellular cytoplasm due to the inhibition of
sodium and potassium ion movement across the myocardial membranes; this increase
in calcium ions results in a potentiation of the activity of the contractile
heart muscle fibers and an increase in the force of myocardial contraction
(positive inotropic effect); digitalis may also increase intracellular entry of
calcium via slow calcium channel influx; stimulates release and blocks re-uptake
of norepinephrine; decreases conduction through the S-A and A-V
nodes |
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Pharmacodynamics/Kinetics |
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Absorption: 90% to 100%
Distribution: Vd: 7 L/kg
Protein binding: 90% to 97%
Metabolism: Hepatic, 50% to 70%
Time to peak: 8-12 hours
Half-life: 7-8 days
Elimination: 30% to 50% excreted unchanged in urine/feces
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Usual Dosage |
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Oral:
<1 year: 0.045 mg/kg
1-2 years: 0.04 mg/kg
>2 years: 0.03 mg/kg which is equivalent to 0.75 mg/m2
Maintenance: Approximately
1/10
of the digitalizing dose
Adults: Oral:
Rapid loading dose: Initial: 0.6 mg followed by 0.4 mg and then 0.2 mg at
intervals of 4-6 hours
Slow loading dose: 0.2 mg twice daily for a period of 4 days followed by a
maintenance dose
Maintenance: 0.05-0.3 mg/day
Most common dose: 0.15 mg/day
Dosing adjustment in renal impairment: Clcr <10
mL/minute: Administer 50% to 75% of normal dose.
Hemodialysis: Not dialyzable (0% to 5%)
Dosing adjustment in hepatic impairment: Dosage reduction is
necessary in severe liver disease. |
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Dietary
Considerations |
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Should be administered with water 30 minutes before or 2 hours after meals,
with high-fiber foods and foods high in calcium; avoid natural
licorice |
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Reference Range |
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Therapeutic: 20-35 ng/mL; Toxic: >45 ng/mL |
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Cardiovascular
Considerations |
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Digoxin has a more established role in the treatment of heart failure and
atrial fibrillation/flutter |
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Dental Health: Local
Anesthetic/Vasoconstrictor
Precautions |
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Use vasoconstrictor with caution due to risk of cardiac arrhythmias with
digitoxin |
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Dental Health:
Effects on Dental Treatment |
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Sensitive gag reflex may cause difficulty in taking a dental
impression |
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Patient
Information |
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Do not discontinue medication without physician's advice; instruct patients
to notify physician if they suffer loss of appetite, visual changes, nausea,
vomiting, weakness, drowsiness, headache, confusion, or
depression |
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Nursing
Implications |
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Observe patients for noncardiac signs of toxicity: anorexia, vision changes
(blurred), confusion, and depression |
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Dosage Forms |
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Tablet: 0.1 mg, 0.2 mg |
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References |
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Baciewicz AM, Isaacson ML, and Lipscomb GL,
"Cholestyramine Resin in the Treatment of Digitoxin Toxicity," Drug Intell
Clin Pharm, 1983, 17(1):57-9.
Hess T, Riesen W, Scholtysik G, et al,
"Digitoxin Intoxication With Severe Thrombocytopenia: Reversal by Digoxin-Specific Antibodies,"
Eur J Clin Invest, 1983, 13(2):159-63.
Nolan PE and Mooradian AD, "Digoxin," Bressler R and Katz MD eds,
Geriatric Pharmacology, New York, NY: McGraw-Hill, 1993, 7:151-63.
Park GD, Goldberg MJ, Spector R, et al,
"The Effects of Activated Charcoal on Digoxin and Digitoxin Clearance," Drug
Intell Clin Pharm, 1985, 19(12):937-41.
Taboulet P, Baud FJ, Bismuth C, et al,
"Acute Digitalis Intoxication - Is Pacing Still Appropriate?" Clin
Toxicol, 1993, 31:261-73. |
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