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P A R T 8
Drugs acting on the cardiovascular system
30 minutes when given intravenously). It is widely
distributed throughout the body. Digoxin is primar
ily excreted unchanged in the urine. Because of this,
caution should be used in the presence of renal impair
ment because the drug may not be excreted and could
accumulate, causing toxicity.
Contraindications and cautions
Cardiac glycosides are contraindicated in the presence
of allergy to any component of the digitalis preparation.
Digoxin is contraindicated in the following conditions:
ventricular tachycardia or fibrillation,
which are poten-
tially fatal arrhythmias and should be treated with other
drugs
; heart block or sick sinus syndrome,
which could
be made worse by slowing of conduction through the
atrioventricular node
; idiopathic hypertrophic subaortic
stenosis (IHSS)
because the increase in force of contrac-
tion could obstruct the outflow tract to the aorta and
cause severe problems
; acute MI
because the increase in
force of contraction could cause more muscle damage
and infarct
; renal insufficiency
because the drug is
TABLE 44.1
DRUGS IN FOCUS Cardiotonic agents
Drug name
Dosage/route
Usual indications
Cardiac glycosides
digoxin (Lanoxin,
Sigmaxin)
Adult: loading dose 0.75–1.25 mg PO or
0.125–0.25 mg IV, then maintenance dose of
0.125–0.25 mg/day PO; decrease dose with
renal impairment
Paediatric (dose based on age):
10–60 mcg/kg PO or 8–50 mcg/kg IV loading
dose, maintenance is 25%–30% of loading
dose
Treatment of acute heart failure, atrial
arrhythmias
Phosphodiesterase inhibitor
milrinone (Primacor)
50 mcg/kg IV bolus over 10 minutes; then
0.375–0.75 mcg/kg/min IV infusion; do not
exceed 1.13 mg/kg per day; reduce dose in
renal impairment
Short-term management of HF in adults
receiving digoxin and diuretics
BOX 44.1
Drug therapy across the lifespan
Cardiotonic agents
CHILDREN
Digoxin is used widely in children with heart defects
and related cardiac problems.The margin of safety for
the dosage of this drug is very small with children.The
dosage needs to be very carefully calculated and should
be double-checked by another healthcare provider before
administration.
Children should be monitored closely for any sign
of impending digitalis toxicity and should have serum
digoxin levels monitored.
The phosphodiesterase inhibitors are not recommended
for use in children.
ADULTS
Adults receiving any of these drugs need to be instructed
as to what adverse reactions to report immediately.
They should learn to take their own pulse and should
be encouraged to keep track of rate and regularity on a
calendar.They may be asked to weigh themselves in the
same clothing and at the same time of the day to monitor
for fluid retention. Any changes in diet, gastrointestinal
activity, or medications should be reported to the
healthcare provider because of the potential for altering
serum levels and causing toxic reactions or ineffective
dosing.
PREGNANCY AND BREASTFEEDING
The safety for the use of these drugs during pregnancy
has not been established.They should not be used
in pregnancy unless the benefit to the mother clearly
outweighs the potential risk to the fetus.The drugs do
enter breast milk, but they have not been associated with
any adverse effects in the neonate. Caution should be
used, however, if one of these drugs is needed during
breastfeeding.
OLDER ADULTS
Older adults frequently are prescribed one of these drugs.
They, like children at the other end of the life spectrum,
are more susceptible to the toxic effects of the drugs and
are more likely to have underlying conditions that could
interfere with their metabolism and excretion.
Renal impairment can lead to accumulation of digoxin
in the body. If renal dysfunction is present, the dosage
needs to be reduced and the person monitored very
closely for signs of digoxin toxicity.
The total drug regimen of the older person should be
coordinated, with careful attention to interacting drugs or
alternative therapies.
For backup in situations of stress or illness, a significant
other should be instructed in how to take the person’s
pulse and the adverse effects to watch for while the person
is taking this drug.
