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Digitoxin

The Elephant Formulary
© 2003-06 Susan K. Mikota DVM and Donald C. Plumb, Pharm.D.
Published by Elephant Care International -
www.elephantcare.org


Elephant specific information, if available, is in blue.

Chemistry - A cardiac glycoside, digitoxin occurs as a bitter tasting, odorless, white to pale buff colored, microcrystalline powder. It is practically insoluble in water and one gram is soluble in approximately 150 ml of alcohol.

 

Storage/Stability/Compatibility - Digitoxin tablets should be stored at room temperature (15-30°C) and kept in well-closed containers. Digitoxin injection is hydrolyzed at pH’s less than 3. It is said to be compatible with most available IV solutions and it is not compatible with acids or alkalies.

 

Uses/Indications - Like digoxin, digitoxin is indicated for heart failure or atrial arrhythmias, but because it is metabolized by the liver to a greater extent, some clinicians feel that it should be used instead of digoxin in patients with diminished renal function. Others believe that digoxin may be used in these patients if adequate serum level monitoring is performed and dosage adjustments are made as necessary. Digitoxin is not routinely used in cats and some clinicians state it is contraindicated in this species.

 

Pharmacokinetics - Digitoxin has only one steroidal hydroxyl group (versus two for digoxin) and therefore is much less polar. It is rapidly and nearly completely absorbed in the small intestine after oral administration. It is unknown if the presence of food alters either the rate or extent of absorption.

 

Digitoxin is highly protein bound (97% in humans, 70-90% in dogs) and values generally are the same in uremic patients. It is unknown if digitoxin enters the milk.

 

Digitoxin is extensively metabolized and the elimination half-life usually remains unchanged in renal failure patients. The elimination half-life in dogs has been reported range from 8-49 hours. Like digoxin, this apparent interpatient variability suggests that digitoxin serum levels must be monitored to optimize therapy and reduce the chance for toxicity. Digitoxin is usually not recommended for use in cats because of its “very long” half-life, but one study reported a t1/2 of only 32 hours, although other values have been reported to be longer than 100 hours.

 

Pharmacology, Contraindications/Precautions,

 

Adverse Effects/Warnings, Overdosage, Drug Interactions -

See the information listed for digoxin.

 

Doses -

Horses:

a)   0.03 - 0.06 mg/kg PO for digitalization; 0.01 mg/kg PO for maintenance (Robinson 1987)

 

Monitoring Parameters -

1)   Serum levels

Because of this drug’s narrow therapeutic index, and interpatient variability, it is strongly recommended to monitor serum levels to help guide therapy. Unless the patient (dog) received an initial loading dose, at least 36 hours should pass after starting therapy to monitor serum levels to allow levels to approach steady-state. Suggested therapeutic serum levels in the dog are 15-35 ng/ml (Neff-Davis 1985). Toxicity is usually associated with levels greater than 40 ng/ml. Levels at the higher end of the suggested range may be necessary to treat some atrial arrhythmias, but may also result in higher incidences of adverse effects. Usually a trough level (just before next dose or at least 4-10 hours after the last dose) is recommended.

2)   Appetite/weight

3)   Cardiac rate, ECG changes

4)   Serum electrolytes

5)   Clinical efficacy for CHF (improved perfusion, decreased edema, increased venous (or arterial) O2 levels).

 

Client Information - Contact veterinarian if animal displays changes in behavior, vomits, has diarrhea, lack of appetite, symptoms of colic (horses), becomes lethargic or depressed.

 

Dosage Forms/Preparations/FDA Approval Status/Withholding Times -

 

Veterinary-Approved Products: None

 

Human-Approved Products:

Digitoxin Tablets 0.05 mg, 0.1 mg; Crystodigin® (Lilly); (Rx)

 

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