2.1 General Dosing Considerations
The dose of digoxin should be based on clinical assessment but individual patient factors should be taken into consideration. Those factors are:
Lean body weight
Renal function
Patient age
Concurrent disease [see Warnings and Precautions (5)]
Concomitant medication [see Drug Interactions (7)]
Because the pharmacokinetics of digoxin are complex, and because toxic levels of digoxin are only slightly higher than therapeutic levels, digoxin dosing can be difficult. The recommended approach is to
estimate the patient's daily maintenance dose
adjust the estimate to account for patient-specific factors
choose a dosing regimen
decide whether to initiate therapy with a loading dose
monitor the patient for toxicity and for therapeutic effect
adjust the dose
Dose titration may be accomplished by either of two general approaches that differ in dosage and frequency of administration, but reach the same total amount of digoxin accumulated in the body.
If rapid titration is considered medically appropriate, administer a loading dose based upon projected peak digoxin body stores. Maintenance dose can be calculated as a percentage of the loading dose.
More gradual titration may be obtained by beginning an appropriate maintenance dose, thus allowing digoxin body stores to accumulate slowly. Steady-state serum digoxin concentrations will be achieved in approximately five half-lives of the drug for the individual patient. Depending upon the patient's renal function, this will take between 1 and 3 weeks.
2.2 Serum Digoxin Concentrations
In general, the dose of digoxin used should be determined on clinical grounds. However, measurement of serum digoxin concentrations can be helpful to the clinician in determining the adequacy of digoxin therapy and in assigning certain probabilities to the likelihood of digoxin intoxication.
Studies have shown diminished efficacy at serum levels <0.5 ng/mL, while levels above 2 ng/mL are associated with increased toxicity without increased benefit. The inotropic effects of digoxin tend to appear at lower concentrations than the electrophysiological effects. Based on retrospective analysis, adverse events may be higher in the upper therapeutic range.
Perform sampling of serum concentrations just before the next scheduled dose of the drug. If this is not possible, sample at least 6 hours or later after the last dose, regardless of the route of administration or the formulation used. On a once-daily dosing schedule, the concentration of digoxin will be 10% to 25% lower when sampled at 24 versus 8 hours, depending upon the patient's renal function. On a twice-daily dosing schedule, there will be only minor differences in serum digoxin concentrations whether sampling is done at 8 or 12 hours after a dose. The serum concentration of digoxin should always be interpreted in the overall clinical context, and an isolated measurement should not be used alone as the basis for increasing or decreasing the dose of the drug.
When decision-making is to be guided by serum digoxin levels, the clinician must consider the possibility of reported concentrations that have been falsely elevated by endogenous digoxin-like immunoreactive substances [see Drug Interactions (7.4)]. If the assay being used is sensitive to these substances, it may be prudent to obtain a baseline measurement before digoxin therapy is started, and correct later values by the reported baseline level.
2.3 Loading Dose
Loading doses for each age group are given in Table 1 below.
In pediatric patients, if a loading dose is needed, it can be administered with roughly half the total given as the first dose. Additional fractions of this planned total dose may be given at 4- to 8-hour intervals, with careful assessment of clinical response before each additional dose. If the patient's clinical response necessitates a change from the calculated loading dose of digoxin, then calculation of the maintenance dose should be based upon the amount actually given as the loading dose [see Tables 1 and 2].
Table 1: Estimate the Loading Dose
Age
Oral Loading Dose, mcg/kg
Premature
20 - 30
Full-Term
25 - 35
1 to 24 months
35 - 60
2 to 5 years
30 - 45
5 to 10 years
20 - 35
Over 10 years
10 - 15
More gradual attainment of digoxin levels can also be accomplished by beginning an appropriate maintenance dose. The range of percentages provided in Table 2 (2.4 Estimate of Daily Maintenance Dose) can be used in calculating this dose for patients with normal renal function. Steady state will be attained after approximately 5 days in subjects with normal renal function.
2.4 Estimate of Daily Maintenance Dose
The recommended daily maintenance doses for each age group are given in Table 2 below. These recommendations assume the presence of normal renal function.
Table 2: Estimate of the Daily Maintenance Dose
Age
Daily Oral Maintenance Dose, mcg/kg/day
Dose Regimen, mcg/kg/dose
Premature
4.7 - 7.8
2.3 - 3.9 Twice daily
Full-Term
7.5 - 11.3
3.8 - 5.6 Twice daily
1 to 24 months
11.3 - 18.8
5.6 - 9.4 Twice daily
2 to 5 years
9.4 - 13.1
4.7 - 6.6 Twice daily
5 to 10 years
5.6 - 11.3
2.8 - 5.6 Twice daily
Over 10 years
3.0 - 4.5
3.0 - 4.5 Once daily
Dosage guidelines provided are based upon average patient response and substantial individual variation can be expected. Accordingly, dosage selection must be based upon clinical assessment and ultimately therapeutic drug level monitoring of the patient.
Divided daily dosing is recommended for pediatric patients under age 10. In the newborn period, renal clearance of digoxin is diminished and suitable dosage adjustments must be made as shown in Tables 1 and 2. Renal clearance is further reduced in the premature infant. Beyond the immediate newborn period, pediatric patients generally require proportionally larger doses than adults on the basis of body weight or body surface area. Pediatric patients over 10 years of age require adult dosages in proportion to their body weight. Some researchers have suggested that infants and young pediatric patients tolerate slightly higher serum concentrations than do adults. For pediatric patients with known or suspected renal dysfunction, lower starting doses should be considered combined with frequent monitoring of digoxin levels.
NOTE: Doses less than 0.2 mL require appropriate methods or measuring devices designed to administer an accurate amount to the patient, such as a graduated syringe.
2.5 Adjustment of Dose
The body's handling of digoxin can be affected by many different patient-specific factors. Some of the possible effects are small, so anticipatory dose adjustment might not be required, but others should be considered before initial dosing [see Clinical Pharmacology (12.2) and Drug Interactions (7)].
Both adults and pediatric patients with abnormal renal function need to have the dose of digoxin proportionally reduced. Recommended maintenance doses based upon lean body weight and renal function are listed in Table 3. Developmental changes in pediatric renal function were factored into Table 3. However, age-related and other changes in adult renal function were not.
The volume of distribution of digoxin is proportional to lean body weight and doses listed in Table 3 assume average body composition. The dose of digoxin must be reduced in patients whose lean weight is an abnormally small fraction of their total body mass because of obesity or edema.
Table 3: Usual Maintenance Dose*,† Requirements (mcg) of Digoxin Based upon Age, Lean Body Weight and Renal Function
Corrected Ccr(mL/min per 70 kg)‡
Dose* to be given Twice Daily†
Dose* to be given Once Daily†
Number of Days Before Steady State Achieved
< 10 years of age
> 10 years of age and adults
Lean Body Weight
Lean Body Weight
kg
5
10
20
30
40
50
60
40
50
60
70
80
90
100
lb
11
22
44
66
88
110
132
88
110
132
154
176
198
220
*
The doses are rounded to whole numbers.
†
Twice daily dosing is recommended for pediatric patients under 10 years of age. Once daily dosing is recommended for pediatric patients above 10 years of age and adults.
‡
Ccr is creatinine clearance, corrected to 70 kg body weight or 1.73 m
2 body surface area.
For adults, if only serum creatinine concentrations (Scr) are available, a Ccr (corrected to 70 kg body weight) may be estimated in men as (140 - Age)/Scr. For women, this result should be multiplied by 0.85.
Note: This equation cannot be used for estimating creatinine clearance in infants or pediatric patients.
For pediatric patients, the modified Schwartz equation may be used as listed below. The formula was based on height in cm and Scr in mg/dL where k is a constant. Ccr is corrected to 1.73 m
2 body surface area. During the first year of life the value of k is 0.33 for pre-term babies and 0.45 for term infants. The k is 0.55 for pediatric patients and adolescent girls and 0.7 for adolescent boys. GFR (mL/min/1.73 m
2)=(k × Height)/Scr.
10
10
20
40
60
80
100
120
80
100
120
140
160
180
200
19
20
11
23
45
68
90
113
135
90
113
135
158
180
203
225
16
30
13
25
50
75
100
125
150
100
125
150
175
200
225
250
14
40
14
28
55
83
110
138
165
110
138
165
193
220
248
275
13
50
15
30
60
90
120
150
180
120
150
180
210
240
270
300
12
60
16
33
65
98
130
163
195
130
163
195
228
260
293
325
11
70
18
35
70
105
140
175
210
140
175
210
245
280
315
350
10
80
19
38
75
113
150
188
225
150
188
225
263
300
338
375
9
90
20
40
80
120
160
200
240
160
200
240
280
320
360
400
8
100
21
43
85
128
170
213
255
170
213
255
298
340
383
425
7
Determination of the target dose in milliliters of Digoxin Oral Solution based on body weight is shown in Table 4. Provided is the volume required per dose, NOT per day.
Table 4: Dose in Milliliters
Target Dose→in mcg/kg
Volume to be given in mL
2
3
4
5
6
8
10
12
14
16
18
20
30
a. Recommended dosing regimen for pediatric patients under 10 years of age is twice daily. Recommended dosing regimen for pediatric patients over 10 years of age and adults is once daily.
*
In the case of required volume less than 0.2 mL, a separate device such as a graduated syringe is recommended for adequate measurement.
Weight in kg↓
2
0.08*
0.12*
0.16*
0.2
0.2
0.3
0.4
0.5
0.6
0.6
0.7
0.8
1.2
3
0.12*
0.18*
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1.0
1.1
1.2
1.8
4
0.16*
0.2
0.3
0.4
0.5
0.6
0.8
1.0
1.1
1.3
1.4
1.6
2.4
5
0.2
0.3
0.4
0.5
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
3.0
6
0.2
0.4
0.5
0.6
0.7
1.0
1.2
1.4
1.7
1.9
2.2
2.4
3.6
7
0.3
0.4
0.6
0.7
0.8
1.1
1.4
1.7
2.0
2.2
2.5
2.8
4.2
8
0.3
0.5
0.6
0.8
1.0
1.3
1.6
1.9
2.2
2.6
2.9
3.2
4.8
9
0.4
0.5
0.7
0.9
1.1
1.4
1.8
2.2
2.5
2.9
3.2
3.6
5.4
10
0.4
0.6
0.8
1.0
1.2
1.6
2.0
2.4
2.8
3.2
3.6
4.0
6.0
11
0.4
0.7
0.9
1.1
1.3
1.8
2.2
2.6
3.1
3.5
4.0
4.4
6.6
12
0.5
0.7
1.0
1.2
1.4
1.9
2.4
2.9
3.4
3.8
4.3
4.8
7.2
13
0.5
0.8
1.0
1.3
1.6
2.1
2.6
3.1
3.6
4.2
4.7
5.2
7.8
14
0.6
0.8
1.1
1.4
1.7
2.2
2.8
3.4
3.9
4.5
5.0
5.6
8.4
15
0.6
0.9
1.2
1.5
1.8
2.4
3.0
3.6
4.2
4.8
5.4
6.0
9.0
20
0.8
1.2
1.6
2.0
2.4
3.2
4.0
4.8
5.6
6.4
7.2
8.0
12.0
30
1.2
1.8
2.4
3.0
3.6
4.8
6.0
7.2
8.4
9.6
10.8
12.0
18.0
40
1.6
2.4
3.2
4.0
4.8
6.4
8.0
9.6
11.2
12.8
14.4
16.0
24.0
50
2.0
3.0
4.0
5.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
30.0
60
2.4
3.6
4.8
6.0
7.2
9.6
12.0
14.4
16.8
19.2
21.6
24.0
36.0
70
2.8
4.2
5.6
7.0
8.4
11.2
14.0
16.8
19.6
22.4
25.2
28.0
42.0
80
3.2
4.8
6.4
8.0
9.6
12.8
16.0
19.2
22.4
25.6
28.8
32.0
48.0
90
3.6
5.4
7.2
9.0
10.8
14.4
18.0
21.6
25.2
28.8
32.4
36.0
54.0
100
4.0
6.0
8.0
10.0
12.0
16.0
20.0
24.0
28.0
32.0
36.0
40.0
60.0
On the left side of the chart, locate the patient's weight in kilograms. At the top of the chart, identify which dose in mcg/kg will be used for this patient. The block on the chart at which the two rows (weight and target dose) intersect is the milliliter amount that should be given to the patient.
The monitoring described in Section 2.2 may suggest increases or decreases in digoxin doses. Additional monitoring, and in some cases anticipatory dose adjustment, may be indicated around the time of various changes to the patient including:
normal development through childhood;
concomitant drug use should be considered when adjusting the estimated digoxin dose [see Drug Interactions (7)];
new co-administration of an antibiotic, especially if the patient had required high doses of digoxin in order to achieve modest serum concentrations, raising the suspicion that a substantial fraction of administered digoxin was being destroyed by colonic bacteria; and
changes in renal function [see Table 3: Usual Maintenance Dose Requirements (mcg) of Digoxin above].