2.1 Important Dosing Information
In selecting a LANOXIN dosing regimen, it is important to consider factors that affect digoxin blood levels (e.g., body weight, age, renal function, concomitant drugs) since toxic levels of digoxin are only slightly higher than therapeutic levels. Dosing can be either initiated with a loading dose followed by maintenance dosing if rapid titration is desired or initiated with maintenance dosing without a loading dose.
Consider interruption or reduction in digoxin dose prior to electrical cardioversion [see Warnings and Precautions (5.6)].
Use digoxin solution to obtain the appropriate dose in infants, young pediatric patients, or patients with very low body weight.
2.2 Loading Dosing Regimen in Adults and Pediatric Patients
For adults and pediatric patients if a loading dosage is to be given, administer half the total loading dose initially, then ¼ the loading dose every 4 to 8 hours twice, with careful assessment of clinical response and toxicity before each dose. The recommended loading dose is displayed in Table 1.
Table 1. Recommended LANOXIN Oral Loading Dose
mcg = micrograms
Age
Oral Loading Dose, mcg/kg
5 to 10 years
20 - 45
Adults and pediatric patients over 10 years
10 - 15
2.3 Maintenance Dosing in Adults and Pediatric Patients Over 10 Years Old
The maintenance dose is based on the lean body weight, renal function, age, and concomitant products [see Drug Interactions (7.1, 7.2, 7.3)].
The recommended starting maintenance dosage in adults and pediatric patients over 10 years old is displayed in Table 2. Doses may be increased every 2 weeks according to clinical response, serum drug levels, and toxicity.
Table 2. Recommended Starting LANOXIN Maintenance Dosage in Adults and Pediatric Patients Over 10 Years Old
mcg = micrograms
Age
Oral Maintenance Dose, mcg/kg/day (given once daily)
Adults and pediatric patients over 10 years
3.4 – 5.1
Table 3 displays the recommended (once daily) maintenance dose of LANOXIN in pediatric patients over 10 years old and adult patients according to lean body weight and renal function. The doses are based on studies in adult patients with heart failure. Alternatively, the maintenance dose may be estimated by the following formula (peak body stores lost each day through elimination):
Total Maintenance Dose = Loading Dose (i.e., Peak Body Stores) x % Daily Loss/100(% Daily Loss = 14 + Creatinine clearance/5)
Reduce the dose of LANOXIN in patients whose lean weight is an abnormally small fraction of their total body mass because of obesity or edema.
Table 3. Recommended Maintenance Dose (in micrograms given once daily) of LANOXIN in Pediatric Patients Over 10 Years Old and Adults by Lean Body Weight and by Renal Functiona
a Doses are rounded to the nearest dose possible using whole and/or half LANOXIN tablets. Recommended doses approximately 30 percent lower than the calculated dose are designated with an *. Monitor digoxin levels in patients receiving these initial doses and increase dose if needed.b For adults, creatinine clearance was corrected to 70-kg body weight or 1.73 m2 body surface area. If only serum creatinine concentrations (Scr) are available, a corrected Ccr may be estimated in men as (140 – Age)/Scr. For women, this result should be multiplied by 0.85. For pediatric patients, the modified Schwartz equation may be used. The formula is based on height in cm and Scr in mg/dL where k is a constant. Ccr is corrected to 1.73 m2 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 m2) = (k x Height)/Scrc If no loading dose administered.d The doses listed assume average body composition.
Corrected Creatinine Clearanceb
Number of Days Before Steady StateAchievedc
Lean Body Weightd
kg
40
50
60
70
80
90
100
lb
88
110
132
154
176
198
220
10 mL/min
62.5*
125
125
187.5
187.5
187.5
250
19
20 mL/min
125
125
125
187.5
187.5
250
250
16
30 mL/min
125
125
187.5
187.5
250
250
312.5
14
40 mL/min
125
187.5
187.5
250
250
312.5
312.5
13
50 mL/min
125
187.5
187.5
250
250
312.5
312.5
12
60 mL/min
125
187.5
250
250
312.5
312.5
375
11
70 mL/min
187.5
187.5
250
250
312.5
375
375
10
80 mL/min
187.5
187.5
250
312.5
312.5
375
437.5
9
90 mL/min
187.5
250
250
312.5
375
437.5
437.5
8
100 mL/min
187.5
250
312.5
312.5
375
437.5
500
7
2.4 Maintenance Dosing in Pediatric Patients Less Than 10 Years Old
The starting maintenance dose for heart failure in pediatric patients less than 10 years old is based on the lean body weight, renal function, age, and concomitant products [see Drug Interactions (7.1, 7.2, 7.3)]. The recommended starting maintenance dose for pediatric patients between 5 and 10 years old with normal renal function is displayed in Table 4.
Table 4. Recommended Starting LANOXIN Maintenance Dosage in Pediatric Patients Between 5 and 10 Years Old
Age
Daily Oral Maintenance Dose, mcg/kg/day
Dose Regimen, mcg/kg/dose
5 to 10 years
6.4 – 12.9
3.2 – 6.4 Twice daily
The recommended maintenance dose (to be given twice daily) is presented in Table 5.
Table 5. Recommended Maintenance Dose (in micrograms given twice daily) of LANOXIN in Pediatric Patients <10 Years of Agea Based upon Lean Body Weight and Renal Functiona,b
a Recommended are doses to be given twice daily.b The doses are rounded to the nearest dose possible using whole and/or half LANOXIN tablets. Recommended doses approximately 30 percent lower than the calculated dose are designated with an *. Monitor digoxin levels in patients receiving these initial doses and increase dose if needed.c The modified Schwartz equation may be used to estimate creatinine clearance. See footnote b under Table 2.d If no loading dose administered.
Corrected Creatinine Clearancec
Number of Days Before Steady StateAchievedd
Lean Body Weight
kg
20
30
40
50
60
lb
44
66
88
110
132
10 mL/min
-
62.5
62.5*
125
125
19
20 mL/min
62.5
62.5
125
125
125
16
30 mL/min
62.5
62.5*
125
125
187.5
14
40 mL/min
62.5
62.5*
125
187.5
187.5
13
50 mL/min
62.5
125
125
187.5
187.5
12
60 mL/min
62.5
125
125
187.5
250
11
70 mL/min
62.5
125
187.5
187.5
250
10
80 mL/min
62.5*
125
187.5
187.5
250
9
90 mL/min
62.5*
125
187.5
250
250
8
100 mL/min
62.5*
125
187.5
250
312.5
7
2.5 Monitoring to Assess Safety, Efficacy, and Therapeutic Blood Levels
Monitor for signs and symptoms of digoxin toxicity and clinical response. Adjust dose based on toxicity, efficacy, and blood levels.
Serum digoxin levels < 0.5 ng/mL have been associated with diminished efficacy, while levels above 2 ng/mL have been associated with increased toxicity without increased benefit.
Interpret the serum digoxin concentration in the overall clinical context, and do not use an isolated measurement of serum digoxin concentration as the basis for increasing or decreasing the LANOXIN dose. Serum digoxin concentrations may be falsely elevated by endogenous digoxin-like substances [see Drug Interactions (7.4)]. If the assay is sensitive to these substances, consider obtaining a baseline digoxin level before starting LANOXIN and correct post-treatment values by the reported baseline level.
Obtain serum digoxin concentrations just before the next scheduled LANOXIN dose or at least 6 hours after the last dose. The digoxin concentration is likely to be 10% to 25% lower when sampled right before the next dose (24 hours after dosing) compared to sampling 8 hours after dosing (using once-daily dosing). However, there will be only minor differences in digoxin concentrations using twice daily dosing whether sampling is done at 8 or 12 hours after a dose.
2.6 Switching from Intravenous Digoxin to Oral Digoxin
When switching from intravenous to oral digoxin formulations, make allowances for differences in bioavailability when calculating maintenance dosages (see Table 6).
Table 6. Comparison of the Systemic Availability and Equivalent Doses of Oral and Intravenous LANOXIN
Absolute Bioavailability
Equivalent Doses (in micrograms)
LANOXIN Tablets
60 - 80%
62.5
125
250
500
LANOXIN Intravenous Injection
100%
50
100
200
400