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Drug dosage identifier

Digoxin

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Dose and administration

  • Loading dose (digitalisation) is especially recommended when treating arrhythmias.
  • Give over 24 hours as 3 divided doses: Initially half of the total dose is given, then quarter of total dose every 8-12 hours x 2. Administer by slow IV infusion over 30 minutes.
  • Oral doses should be 25% greater than IV doses.
  • Do not administer IM (causes pain and tissue damage)
Postmentrual Age (weeks) Total Loading Dose Maintenance Dose Interval
  IV micrograms/kg PO micrograms/kg IV micrograms/kg PO micrograms/kg hr
≤29 15 20 4 5 24
30 to 36 20 25 5 6 24
37 to 48 30 40 4 5 12
≥49 40 50 5 6 12

 Indications

  • Treatment of heart failure caused by diminished myocardial contractility.
  • Treatment of supraventricular tachycardia, atrial flutter, and atrial fibrillation.

Contraindications and precautions

  • Known hypersensitivity to cardiac glycosides.
  • Caution in preterm infants, especially extreme immaturity.
  • Caution in infants with renal impairment.
  • Caution in infants with acute myocarditis, bradyarrhythmias (especially heart block).
  • Ventricular dysrhythmias.
  • Pre-existing hypokalaemia may precipitate adverse reactions.

Clinical pharmacology

Digoxin is a digitalis glycoside with positive inotropic and negative chronotopic actions. Increases myocardial catecholamine levels (low doses) and inhibits sarcolemmal sodium potassium - ATPase (higher doses) to enhance contractility. Indirectly increases vagal activity, thereby slowing SA and AV node conduction. Other effects include peripheral, splanchnic, and perhaps pulmonary vasoconstriction, and reduced CSF production.

Rapid but variable absorption (52-79%) from the gastrointestinal tract. IM absorption similar variability but IM injection causes pain and local soft tissue injury. Large distribution volume: Vd in term infant (12-16 L/kg) > preterm infant (4-6 L/kg). Rapid distribution to peripheral tissue compartments (elimination half life is reported as 61-170 hours in preterm infants and 35-45 hours in term infants) but the time to reach steady state is much slower. Serum concentration peaks 30-90 minutes after an oral dose with myocardial peak occurring after 4-6 hours. Accumulates in the myocardium: myocardial to serum ratio 149:1. Low binding (20%) to human plasma protein. Probably not significantly metabolised. Eliminated mainly via the kidneys (75% unchanged) by glomerular filtration and tubular secretion.

Main pharmacodynamic property of digoxin is its ability to increase the force of contraction of the myocardium - positive inotropic action. Also slows the heart rate and produces changes in activity of SA node, the atria, and AV node - negative chronotropic effect. Inotropic effect occurs within 30 minutes. Non toxic cardiac effects include shortening of QTC interval, depression of STsegment, diminished amplitude of T wave, and slowing of heart rate.

Possible adverse effects

  • Gastrointestinal disturbances (nausea, vomiting, diarrhoea).
  • Lethargy
  • Bradycardia
  • Cardiac arrhythmias (PVCs, PAT with block, bigeminy, sinus arrhythmia, sinoatrial block, atrioventricular junctional or multifocal ventricular tachycardia).
  • Toxicity is enhanced by hypokalaemia.

Special considerations

  • Dosing regime determined by maturity and renal function.
  • Serum electrolytes should be stabilised prior to digitalisation. Monitor urea, electrolytes, creatinine during therapy.
  • Obtain baseline ECG prior to first digitalising dose of digoxin, prior to the final digitalising dose and at intervals throughout treatment.
  • Serum digoxin levels should be measured during treatment. Obtain specimen 10 - 12 hours after last loading dose and repeat at intervals. Repeat after dose changed. Usual therapeutic range 1.0-2.6 nmol/L. Serum levels >4.6 nmol/L are considered to be in the toxic range.
  • Management of digoxin toxicity: stop digoxin, stabilise fluids and electrolytes, treat arrhythmias.

Interactions

Management of Digoxin administration

Description

The IV preparation is available in two concentrations:

  • The preparation in use will depend on availability and may change without notice. Check all calculations carefully to ensure that the correct dose is given.
  • Lanoxin paediatric injection: clear, colourless solution 25 micrograms/ml in 2ml ampoules.
  • Lanoxin paediatric injection: 100micrograms/ml in 1ml ampoules.
    Note: the 100 microgram/ml preparation is a Section 29 medication and the names of the infants receiving this preparation and the names of the specialist responsible for prescribing it must be recorded.

Paediatric elixir for oral use: clear yellow solution 50 micrograms/ml in 50ml bottles.

Prescription

  • Loading (digitalising) doses are charted on the stat page of the prescription chart in micrograms/dose.
  • Maintenance doses are charted on the prescription chart in micrograms/dose.

Administration

Slow IV Infusion

  1. Administered and checked by nurses with Neonatal Drug Certification.
  2. A dose concentration of 25 micrograms/ml should be used. Use either:
    Paediatric strength ampoule (25 mcg/ml). Do NOT dilute further OR
    Dilute 100 microgram/ml ampoule to 25 microgram/ml: Mix 1ml of 100 microgram/ml digoxin with 3ml of sterile water for injection.
  3. Filter prior to administration through a 5 micron filter or a Pall filter.
  4. Administer by slow IV infusion over 30 minutes using a syringe pump.
  5. Compatible with NS, D5W at a 25 micrograms/ml strength.
  6. Do NOT mix with other drugs, IV solution, blood or blood products.
  7. Continuous cardiac monitoring must be performed while the infusion is in progress and subsequently.
  8. Flush line with NS before and after infusion of digoxin.

Oral

  1. Can be administered with or without food. Milk does not impair absorption of the drug.
  2. Infant Gaviscon has been reported to decrease the amount of digoxin absorbed.

Nursing considerations

  1. Take apex beat for one full minute before administration. Document. Note rate, rhythm and quality. Withhold digoxin and notify doctor immediately if changes are apparent and/or apex rate is <100/min in the preterm infant or <80/min in the term infant. For IV administration continuous cardiac monitoring is essential.
  2. Monitor and assess patient response to therapy.
  3. Assess for signs of adverse effects and/or toxicity.
  4. Monitor for dysrrhythmias, respiratory congestion and peripheral oedema.
  5. Weigh daily.
  6. Monitor fluid balance.
  7. Monitor blood pressure.

Storage

  • Ampoules: Store at room temperature <30° C. Protect from light.
  • Paediatric elixir: Store at room temperature <25° C. Protect from light.

References

  1. Roberts RJ. Cardiovascular drugs. In: Roberts RJ. Drug therapy in infants: Pharmacologic principles and clinical experience. Philadelphia: WB Saunders, 1984, p138-56.
  2. Johnson GL, Desai NS, Pauly TH, Cunningham MD. Complications associated with digoxin in low-birth-weight infants. Pediatrics 1982; 69:463.
  3. Nyberg L, Wettrell G. Pharmacokinetics and dosage of digoxin in neonates and infants. EurJ ClinPharmacol 1980; 18:69.
  4. Pinsky WW, Jacobsen JR, Gillette PC, Adams J, Monroe L, McNamara DG. Dosage of digoxin in premature infants. J Pediatr 1979; 96:639-42.
  5. Park MK. Use of digoxin in infants and children, with specific emphasis on dose. J Pediatr 1986; 108:871-7.
  6. Product disclosure. Wellcome Australia
  7. Nursing 97 Drug Handbook Springhouse 1997, p205-6.

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Document Control

  • Date last published: 30 September 1998
  • Document type: Drug Dosage Guideline
  • Services responsible: ADHB Pharmacy, Neonatology
  • Editor: Sarah Bellhouse
  • Review frequency: 2 years