Description and indication for use
Digoxin is a crystalline cardiac glycoside
obtained from the leaves of Digitalis Lantata.
Digoxin has a positive inotropic action on
the heart, increasing the systolic force of contraction, achieving more
complete ventricular emptying, and resulting in increased cardiac output,
decreased cardiac enlargement, and reduced venous pressure and improvement in
renal function. Increased cardiac output
improves peripheral circulation with mobilisation of oedematous fluid, improved
renal blood flow and resultant diuresis.
The increase in cardiac work is accomplished without a commensurate
increase in oxygen consumption.
Digoxin increases vagal tone in the heart,
resulting in slowing of the sino-atrial node rate and further depression of
conduction in the atrioventricular bundle.
Indications include treatment of congestive
heart failure due to decreased myocardial contractility and as an anti-arrhythmic
for supraventricular arrhythmias, especially paroxysmal atrial tachycardia.
NOTE: Injection contains Propylene Glycol 40% and Alcohol 10%.
Dose
O and IV:
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VLBW digitalising dose:
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10 microgram/kg following at 8 hourly intervals
by 5 mcg/kg for 2 doses.
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Term digitalising dose:
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10 microgram/kg/dose 8 hourly for 3 doses.
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Maintenance dose:
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5 microgram/kg/dose 12 hourly.
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Digitalisation
with loading doses is only necessary in the management of arrhythmias or in
acute congestive heart failure, otherwise start
with maintenance doses.
IV dosing is seldom advantageous over oral.
Monitor serum levels.
Reconstitution/Dilution
Ampoule = 50 microgram in 2 mL (25 mcg/mL).
(Note:
also 500 microgram in 2 mL - ADULT available).
IV:
Withdraw 1 mL of 25 micrograms/mL solution
and add to 4 mL of water for injection (in a 5 mL syringe) = 25 mcg in 5 mL = 5 mcg/mL.
Discard excess volume to obtain required
dose or withdraw dose using another syringe.
Route and method of administration
IV:
Give slowly over at least 5 minutes.
IM:
DO
NOT GIVE IM.
Absorption from IM injection is unpredictable.
Side effects
Principally associated with signs of
overdosage.
Electrolyte imbalances.
Precipitation or aggravation of congestive
cardiac failure.
Signs of overdosage include vomiting,
salivation and diarrhoea, drowsiness, bradycardia and arrhythmias.
Special precautions
CAUTION in patients with electrolyte disturbances, especially hypokalaemia
as this may predispose the patient to Digoxin toxicity.
CAUTION in patients with ischaemic heart disease, acute myocarditis, lung
disease.
Contraindications
Signs of toxicity.
Ventricular dysrhythmias.
Atrial flutter or fibrillation with slow
ventricular rates.
Second and third degree heart block.
Reduced dose necessary in renal impairment.
Compatible solutions
Glucose 5%.
Sodium chloride 0.9% and sodium chloride
0.45%.
Incompatibilities
Administer
alone.
Drug interactions
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Indomethacin
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May impair renal function which will increase Ddigoxin levels due to reduced elimination. A reduction in Digoxin maintenance dose is recommended.
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Frusemide, Amphotericin B, Dexamethasone,
Prednisolone
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All may cause hypokalaemia, predisposing patient
to Digoxin toxicity.
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Chlorothiazide
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May cause hypokalaemia/hypercalcaemia,
predisposing patient to Digoxin toxicity.
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Antacids
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Can reduce oral absorption of Digoxin.
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Calcium and Phenytoin
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May potentiate bradycardia produced by Digoxin.
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Suxamethonium,
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Use cautiously in patients receiving Digoxin as
arrhythmias may occur.
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Spironolactone
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Interacts with Digoxin in 2 different ways.
May block
tubular secretion of Digoxin, reducing clearance and increasing plasma levels
of Digoxin.
May interfere
with Digoxin immunoassay, resulting in falsely elevated Digoxin levels.
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Amiodarone
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May reduce renal and non-renal clearance of Ddigoxin, resulting in raised, possibly toxic Digoxin serum levels.
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Cisapride
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May reduce effectiveness of Digoxin by decreasing
oral absorption.
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Erythromycin
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May increase serum Digoxin levels in some
patients, due to alteration of GI flora.
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Liothyronine, Thyroid Hormonal Replacement
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Increases the metabolic rate, which requires a
dosage increase of Digoxin.
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Verapamil
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May cause Digoxin toxicity by reducing renal and
extra renal elimination of digoxin.
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Nursing responsibilities
Infant must have a cardiorespiratory
monitor on at all times to assess response to therapy.
Observe infant for response to
medication. Report signs of toxicity.
Collect serum levels weekly, with level
taken at least 6 hours after the dose.
Therapeutic range 1 to 2.5 nanomol/L.
Serum electrolytes should be monitored.
Take apical pulse for one full minute
before giving Digoxin, noting rate, rhythm, quality. Withhold Digoxin if change apparent and
notify Medical Officer immediately (especially if heart rate is < 90 to 110
beats/minute).