Category : Science and Education
Archive   : DRUGMAN.ZIP
Filename : PHARM4A

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.


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References:
1. Arnold SB, et al: Long-term digitalis therapy improves left
ventricular function in heart failure. NEJM 1980; 303:1443.
2. Cohn JN (editor): New concepts in the mechanisms and treatment of
congestive heart failure (Symposium). Am J Cardiol 1985; 55: 1A.
3. Cohn JN, et al: Effect of vasodilator therapy on mortality in chronic
congestive heart failure. Results of a Veterans Administration
Cooperative study. NEJM 1986; 314: 1547.
4. Digitalis. (Symposium) J Am Coll Cardiol 1985; 5: 1A.
5. Doherty JE: Clinical use of digitalis glycosides. An update. Cardiol-
ogy 1985; 72:225.
6. Franciosa JA, Dunkman WB, Leddy CL: Hemodynamic effects of
vasodilators and long-term response in heart failure. J Am Coll Car-
diol 1984; 3: 1521.
7. Jaski BE, et al: Positive inotropic and vasodilator actions of mil-
rinone in patients with severe congestive heart failure. Dose response
relationships and comparison to nitroprusside. J Clin Invest 1085; 75:
643.




(PgDn key for more references)


8. Maekawa K, Liang C-S, Hood WB: Comparison of dobutamine and dopamine
in acute myocardial infarction. Effects of systemic hemodynamics,
plasma catecholamines, blood flows and infarct size. Circulation 1983;
67:750.
9. Smith TW, et al: Digitalis glycosides: Mechanisms and manifestations
of toxicity. (in 3 parts) Prog Cardiovasc Dis 1984; 26:413,495; 27:21.















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