DIGITALIS GLYCOSIDES: PROPERTIES
Pharmacokinetics and drug selection
* Absorption: Nearly 100% of an oral dose of digitoxin and 70-90% of
a dose of digoxin will be absorbed.
* Elimination: Digitoxin is metabolized in the liver and eventually ex-
creted by the kidneys; digoxin is metabolized to a lesser extent and
eliminated primarily by the kidneys. Patients with severe heart fail-
ure have a prolongation of digoxin half-life.
* Accumulation: Because of their long half-lives (see Table 4-1), the
cardiac glycosides accumulate in the body when given daily. Thus cau-
tion is indicated when increasing dosage since the new steady state
will not be achieved for 4-6 days (digoxin) or 3-5 weeks (digitoxin).
* Selection of a glycoside: Digoxin is the most suitable drug in 90-95%
of patients. It has a reasonably rapid onset of action and a shorter
half-life than digitoxin. Digitoxin is sometimes useful in patients
with rapidly changing renal function because its half-life is rela-
tively insensitive to such changes. It is doubtful that other drugs in
this group need ever be used except in rare instances of hyper-
sensitivity to the above 2 agents.
(PgDn key for references)
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