Calculation of Digoxin Required for Compounding
To compound 10 bottles each of digoxin oral solution at concentrations of 50 mcg/mL and 1 mg/mL (30 mL per bottle), a total of 0.32 grams of digoxin is required.
Step-by-Step Calculation
Let's calculate the amount of digoxin needed for each concentration separately:
For 50 mcg/mL concentration:
- Volume per bottle: 30 mL
- Number of bottles: 10
- Total volume: 30 mL × 10 = 300 mL
- Digoxin needed: 50 mcg/mL × 300 mL = 15,000 mcg = 0.015 g
For 1 mg/mL concentration:
- Volume per bottle: 30 mL
- Number of bottles: 10
- Total volume: 30 mL × 10 = 300 mL
- Digoxin needed: 1 mg/mL × 300 mL = 300 mg = 0.3 g
Total digoxin required:
- 0.015 g + 0.3 g = 0.315 g ≈ 0.32 g (rounded to the nearest hundredth)
Clinical Considerations When Compounding Digoxin
When compounding digoxin solutions, several important clinical considerations should be kept in mind:
Narrow therapeutic index: Digoxin has a narrow therapeutic window (0.5-0.9 ng/mL is the optimal therapeutic range) 1, 2, making accurate compounding essential to prevent toxicity.
Toxicity risk: Digoxin toxicity can cause severe bradycardia, life-threatening arrhythmias, and high degrees of AV nodal blockade 3. Precise measurement and compounding are critical.
Verification process: Double-check all calculations and have a second pharmacist verify both the calculation and the final compounded product due to digoxin's high-risk status.
Appropriate equipment: Use calibrated equipment and analytical balances capable of accurately measuring small quantities of digoxin.
Documentation: Maintain thorough records of the compounding process, including exact weights, dilutions, and quality control checks.
Treatment of Potential Digoxin Toxicity
In case of accidental overdose or toxicity from compounded digoxin:
Digoxin-specific Fab antibody fragments should be administered to patients with severe life-threatening cardiac glycoside toxicity 3.
One vial of antidigoxin Fab is standardized to neutralize 0.5 mg of digoxin 3.
For known ingested amounts: administer 2 vials of Fab for every milligram of digoxin ingested 3.
For unknown amounts: calculate using the formula: serum digoxin concentration (ng/mL) × weight (kg)/100 3.
In critical cases, empirically administer 10 to 20 vials 3.
Remember that accurate compounding of digoxin is essential for patient safety given its narrow therapeutic index and potential for serious toxicity.