Potency testing measures the concentration of the active pharmaceutical ingredient (API) in a drug product. This critical test should be conducted before drug distribution, confirming that the API concentration is within specification of the labeled amount.
USP sets the acceptable potency range of ±10% for compounded preparations. However, this range may vary depending on the API, for example, ±20% for certain proteins and as narrow as ±5% for potent analgesics. Pharmacies may also establish internal specifications based on the specific formulation and its intended use.
When compounding with a pre-filled IV bag, the total volume of the bag varies based on the manufacturer's excess volume, known as overfill, and the compounding method used. Pharmacies may:
- Add active pharmaceutical ingredient(s) to the solution; or,
- Withdraw solution before adding the active pharmaceutical ingredient(s) to the solution
ARL recommends adding a fill volume test with a potency test to ensure quality and consistency of potency results in the final preparation. The fill volume test measures the total volume of the IV bag, which includes the base solution volume, overfill, and the admixture volume.
After the total volume is determined, the laboratory uses this measurement to calculate potency results, reflecting the drug concentration per bag. Without this total volume assessment, potency results for IV bags may appear artificially low and out-of-specification (OOS), even if the correct drug amount was added.
Example: Two IV bags labeled as 100 mL contain different overfill amounts, such as 104 mL and 107 mL. If the pharmacy adds the same API quantity to both the 104 mL and 107 mL bags, the API concentration will differ between the two bags. This variation may lead to one bag’s potency results within specification, and the second bag’s results out of specification.
Pharmacies can minimize the risk of potency failures by ordering a fill volume test with a potency test for IV bags, ensuring that the drug concentration accurately reflects the API of the finished drug product. For more information on potency testing for IV bags, contact 800-393-1595 or info@arlok.com.