Posology : מינונים

4.2. Posology and method of administration
Posology:
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.

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 exampleif patients are switched from oral to the I.V. formulation the dosage should be reduced by approximately 33%.

Adults and paediatric populations over 10 years

Rapid oral loading:
If medically appropriate, rapid digitalisation may be achieved in a number of ways, such as 750 to 1500 micrograms (0.75 to 1.5 mg) as a single dose.

Where there is less urgency, or greater risk of toxicity e.g. in the elderly, the oral loading dose should be given in divided doses six hours apart, with approximately half the total dose given as the first dose.
Clinical response should be assessed before giving each additional dose (see section 4.4).

Slow oral loading:
In some patients, for example those with mild heart failure, digitalisation may be achieved more slowly with doses of 250 to 750 micrograms (0.25 to 0.75 mg) daily for one week followed by an appropriate maintenance dose. A clinical response should be seen within one week.
The choice between slow and rapid oral loading depends on the clinical state of the patient and the urgency of the condition.

Maintenance dose:
The maintenance dosage should be based upon the percentage of the peak body stores lost each day through elimination. The following formula has had wide clinical use: Maintenance dose = Peak body stores x daily loss in percent
100

Where: Peak body stores = personalized loading dose daily loss (in percent) = 14 + creatinine clearance (Ccr)/5

Ccr is creatinine clearance corrected to 70 kg bodyweight or 1.73 m2 body surface area. If only serum creatinine (Scr) concentrations are available, a Ccr (corrected to 70 kg bodyweight) may be estimated in men as

Ccr =   (140 - age)
Scr (in mg/100 ml)
NOTE: Where serum creatinine values are obtained in micromol/l, these may be converted to mg/100 ml (mg %) as follows:

Scr(mg/100 ml) =    Scr (micromol/l) x 113.12
10,000

=     Scr (micromol/l)
88.4
Where 113.12 is the molecular weight of creatinine.
For women, this result should be multiplied by 0.85.
N.B. These formulas cannot be used for creatinine clearance in children.

In practice, this will mean that most patients with heart failure will be maintained on 125 to 250 micrograms (0.125 to 0.25 mg) digoxin daily; however in those who show increased sensitivity to the adverse effects of digoxin, a dose of 62.5 micrograms (0.0625 mg) daily or less may suffice.

Conversely, some patients may require a higher dose.

Neonates, infants and paediatric populations up to 10 years of age
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 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: 
Preterm neonates less than 1.5 kg        -      25 micrograms/kg per 24 h.
Preterm neonates 1.5 kg to 2.5 kg        -      30 micrograms/kg per 24 h.
Term neonates to 2 years         -              45 micrograms/kg per 24 h.
2 to 5 years                     -              35 micrograms/kg per 24 h.
5 to 10 years                    -              25 micrograms/kg per 24 h.
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 to 8 h, assessing clinical response before giving each additional dose.

Maintenance dose:
The maintenance dose should be administered in accordance with the following schedule: Preterm neonates: daily dose = 20 % of 24h loading dose.

Term neonates and children up to 10 years: daily dose = 25 % of 24h loading dose.

These dosage schedules are meant as guidelines and careful clinical observation and monitoring of serum digoxin levels (see section 4.4) should be used as a basis for adjustment of dosage in these paediatric patient groups.

Elderly
The possibility of reduced renal function and lower lean body mass should be taken into account when dealing with elderly patients. If necessary, the dosage should be reduced and adjusted to the changed pharmacokinetics to prevent elevated serum digoxin levels and the risk of toxicity. The serum digoxin levels should be checked regularly and hypokalaemia should be avoided.

Renal impairment
The dosing recommendations should be reconsidered if patients are elderly or there are other reasons for the renal clearance of digoxin being reduced. A reduction in both initial and maintenance doses should be considered (See Section 4.4).

Method of administration
For oral use only.
Lanoxin Elixir is supplied with a graduated pipette and this should be used for measurement of all doses.
Lanoxin Elixir should not be diluted.