18-24 hours to the patient. This type of intensive administration of "loading" doses can
cause toxic reactions since digitalis preparations have only a moderate safety margin.
b. Although a patient's condition may have responded to digitalization, he may
have to continue to take a digitalis product for a long period. The physician must
determine the amount of drug the patient must take on a daily basis in order for the
patient's heart to perform at its optimal level. Maintenance doses are ordered which are
just enough to replace the amount of digitalis eliminated since the administration of the
last dose. The maintenance dose is then taken each day to maintain the quantity of
drug required to keep the patient's heart beating efficiently. Although these daily
maintenance doses are much lower than the original digitalizing doses, the risk of
toxicity remains.
3-7. DIGITALIS PRODUCTS
a. Digoxin (Lanoxin). Digoxin is the most common cardiac glycoside used to
treat congestive heart failure. The drug is usually administered intravenously (IV) for
digitalization in a total dosage of from 1 to 1.5 milligrams. This drug may be given orally
if the physician desires. The maintenance dose ranges from 0.125 milligram to 0.5
milligram daily, but normally 0.25 milligram of digoxin is given each day to the patient.
The side effects of digoxin include anorexia (loss of appetite), arrhythmias, nausea and
vomiting, and yellowish-green vision. Digoxin should be used with caution in patients
who have kidney problems because the kidneys are the primary route of excretion for
this agent. This drug should be used with caution in patients who have low serum
potassium. Digoxin is available in 0.125 milligram, 0.25 milligram, and 0.5 milligram
tablets; 0.05 milligram, 0.1 milligram and 0.2 mg liquid filled capsules; or in an injectable
solution of 0.1 milligram per milliliter in 1 milliliter containers and 0.25 milligram per
milliliter in 2 milliliter containers. It is also available in a 0.05 milligram per milliliter
pediatric elixir. The bioavailability is improved with the liquid filled capsules such that
0.1mg of the capsule is equivalent to 0.125 mg of the tablet. Many times the physician
will prescribe the pediatric elixir with directions for the patient to take a certain total daily
dose (e.g., 0.125 milligram). You must interpret this as milliliters (or cubic centimeters-
cc's) in order for the patient to dose himself with the calibrated dropper supplied with the
preparation. As you probably realize, you might have to use your pharmaceutical
calculation skills to calculate the dose of the drug solution.
b. Digitoxin (Crystodigin). Digitoxin is another cardiac glycoside obtained
from Digitalis purpurea. Although rarely used, you must be aware of this agent as it can
be confused with digoxin. This product must be used with caution in patients with liver
problems since this drug is excreted primarily in the bile and consequently, has a long
half-life (5 to 7 days). The drug is available as a 0.1 mg and 0.2 mg tablet.
MD0806
3-5