Active Ingredient: Digoxin
Digoxin is indicated in the management of certain supraventricular arrhythmias, particularly chronic atrial fibrillation and flutter, where its major beneficial effect is to reduce the ventricular rate.
For this indication, competent medicine agencies globally authorize below treatments:
Oral
25 - 45 ug per kg of body weight
From 25 To 45 ug per kg of body weight once every day
The following schedules are intended as an initial guide but each patient has to be tailored individually according to age, lean body weight and renal function for his/her needs:
Suggested doses are intended only as an initial guide.
In cases where cardiac glycosides have been taken in the preceding two weeks the recommendations for initial dosing of a patient should be reconsidered and a reduced dose is advised.
The difference in bioavailability between injectable digoxin and oral formulations must be considered when changing from one dosage form to another. For example if patients are switched from oral to the I.V. formulation the dosage should be reduced by approximately 33%.
In the newborn, particularly in the premature infant, renal clearance of digoxin is diminished and suitable dose reductions must be observed, over and above general dosage instructions.
Beyond the immediate newborn period, children generally require proportionally larger doses than adults on the basis of body weight or body surface area, as indicated in the schedule below. Children over ten years of age require adult dosages in proportion to their body weight.
Oral loading dose: This should be administered in accordance with the following schedule: pre-term neonates less than 1.5kg (25 micrograms/kg body weight over 24 hours); pre-term neonates 1.5-2.5kg (30 micrograms/kg body weight over 24 hours); term neonates to 2 years (45 micrograms/kg body weight over 24 hours); 2-5 years (35 micrograms/kg body weight over 24 hours); 5-10 years (25 micrograms/kg body weight over 24 hours).
The loading dose should be administered in divided doses with approximately half the total dose given as the first dose, and further fractions of the total dose given at intervals of 4-8 hours, assessing clinical response before giving each additional dose.
Maintenance: The maintenance dose should be administered in accordance with the following schedule: pre-term neonates (daily dose is 20% of 24 hour loading dose); term neonates and children up to 10 years (daily dose is 25% of 24 hour loading dose).
These dosage schedules are meant as guidelines and careful clinical observation and monitoring of serum digoxin levels should be used as a basis for adjustment of dosage in these paediatric patient groups. If cardiac glycosides have been given in the two weeks preceding commencement of digoxin therapy, it should be anticipated that optimum loading doses of digoxin will be less than those recommended above.
Measurements of plasma levels of digoxin are useful in individualising therapy during the early stages of treatment, for detecting poor patient compliance and for diagnosing toxicity. Serum concentrations of digoxin may be expressed in conventional units of ng/ml or SI units of nmol/L. To convert ng/ml to nmol/L, multiply ng/ml by 1.28.
The serum concentration of digoxin can be determined by radioimmunoassay. Blood should be taken 6 hours or more after the last dose of digoxin. There are no rigid guidelines as to the range of serum concentrations that are most efficacious but most patients will benefit, with little risk of toxic symptoms and signs developing, with digoxin concentrations from 0.8 nanogram/ml, ng/ml (1.02 nanomol/litre, nm/L) to 2.0ng/ml (2.56nm/L). Above this range toxic symptoms and signs become more frequent and levels above 3ng/ml (3.84nm/L) are quite likely to be toxic. However, in deciding whether a patient’s symptoms are due to digoxin, the patent’s clinical state together with the serum potassium level and thyroid function are important factors. Other glycosides, including metabolites of digoxin, can interfere with the assays that are available and one should always be wary of values, which do not seem commensurate with the clinical state of the patient.
Intravenous
20 - 35 ug per kg of body weight
From 20 To 35 ug per kg of body weight once every day
Digoxin is for administration by slow intravenous infusion.
The dose of digoxin for each patient has to be tailored individually according to age, lean body weight and renal function. Suggested doses are intended only as an initial guide.
If cases where cardiac glycosides have been taken in the preceding two weeks, the recommendations for initial dosing of a patient should be reconsidered and a reduced dose is advised.
The difference in bioavailability between injectable digoxin and oral formulations must be considered when changing from one dosage form to another. For example if patients are switched from oral to the I.V. formulation the dosage should be reduced by approximately 33%.
Emergency parenteral digitalisation (in patients who have not been given cardiac glycosides within the preceding two weeks):
If cardiac glycosides have been given in the two weeks preceding commencement of digoxin therapy, it should be anticipated that optimum loading doses of digoxin will be less than those recommended below.
In the newborn, particularly in the premature infant, renal clearance of digoxin is diminished and suitable dose reductions must be observed, over and above general dosage instructions.
Beyond the immediate newborn period, children generally require proportionally larger doses than adults on the basis of body weight or body surface area, as indicated in the schedule below. Children over 10 years of age require adult dosages in proportion to their body weight.
The I.V. loading dose in the above groups should be administered in accordance with the following schedule:
Pre-term neonates:
Less than 1.5kg: 20 micrograms/kg over 24 hours
Pre-term neonates:
1.5-2.5kg: 30 micrograms/kg over 24 hours
Full-term neonates:
To age 2 years: 35 micrograms/kg over 24 hours
Age 2-5 years: 35 micrograms/kg over 24 hours
Age 5-10 years: 25 micrograms/kg over 24 hours
The loading dose should be administered in divided doses with approximately half the total dose given as the first dose and further fractions of the total dose given at intervals of 4-8 hours, assessing the clinical response before giving each additional dose. Each dose should be given by intravenous infusion over a period of 10-20 minutes.
The maintenance dose should be administered in accordance with the following schedule:
Preterm neonates:
daily dose = 20% of 24-hour loading dose (intravenous or oral)
Term neonates and children up to 10 years:
daily dose = 25% of 24-hour loading dose (intravenous or oral)
These dosage schedules are meant as guidelines and careful clinical observation and monitoring of serum digoxin levels should be used as a basis for adjustment of dosage in these paediatric patient groups.
Digoxin injection can be administered undiluted or diluted with a 4-fold or greater volume of 0.9% Sodium Chloride Injection, 0.18% Sodium Chloride/4% Glucose Injection or 5% Glucose Injection. A 4-fold volume of diluent equates to adding one 2 ml ampoule of digoxin to 6 ml of injection solution. The use of less than a 4-fold volume of diluent could lead to precipitation of digoxin.
Digoxin Injection may be diluted with the following solutions:
Sodium Chloride Intravenous Infusion BP 0.9% w/v
Glucose Intravenous Infusion BP 5.0% w/v
Sodium Chloride (0.18% w/v) and Glucose (4% w/v) Intravenous Infusion BP
When diluted in the ratio of 1 to 250 (i.e. one 2ml ampoule containing 500 micrograms digoxin added to 500ml of infusion solution), Digoxin Injection B.P. is known to be compatible with the above mentioned infusion solutions and stable for up to 48 hours at room temperature (20-25°C).
Dilution should be carried out either under full aseptic conditions or immediately prior to use. Any unused solution should be discarded.
Each dose should be given by intravenous infusion over of 10-20 minutes.
The total loading dose should be administered in divided doses with approximately half of the total dose given as the first dose and further fractions of the total dose given at intervals of 4-8 hours. An assessment of clinical response should be performed before giving each additional dose.
The intramuscular route is painful and is associated with muscle necrosis. This route cannot be recommended.
Rapid intravenous injection can cause vasoconstriction producing hypertension and/or reduced coronary flow. A slow injection rate is therefore important in hypertensive heart failure and acute myocardial infarction.
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