Potency Testing Benefits and Requirements

Potency Testing Benefits and Requirements

Potency testing measures the concentration of the active pharmaceutical ingredient (API). This essential test ensures the API concentration matches its intended amount and provides value-added benefits to pharmacies including:

  • Supports product compliance checks
  • Establishes compounding process controls
  • Confirms a preparation is accurate and precise
  • Provides documentation references for regulatory audits and patient questions
  • Supports sales tools demonstrating a dedication to quality  

Potency Testing Requirements 

United States Pharmacopeia (USP <797>) 

USP <797> requires compounding pharmacies to have written procedures for identity and strength verification tests: 

  • Certify that labels of drug products include correct names and concentrations of ingredients, total volume, beyond use date, appropriate route of administration, storage conditions, and other information for safe use
  • Compare compound record to original prescription for correct identities, purities, and amounts
  • Verify correct fill volumes and correct number of units were obtained

When the strength cannot be confirmed to be accurate, based on the above three inspections, the products should be tested by methods specific for the active ingredients. 

Even if potency testing is not required, potency testing is recommended to ensure compounded drug products meet quality standards. 

Food and Drug Administration (FDA) 503B Outsourcing Facilities

The FDA interim guidance requires 503Bs to perform identity and strength verification tests for each batch:

  • Identity test can be the same test as the strength test
  • For batches < 10, allows testing on every other batch for identity and strength, or every batch bringing the total units made to 10
  • For aqueous solutions, testing for identity and strength can be performed on the bulk solution just before filling the finished drug product containers

Potency testing assures that compounded drug products meet the FDA safety requirements and have the identity and strength characteristics that the drugs claim to possess. 


ARL Potency Test Methods  

A potency test method separates, identifies, and quantifies compounds present in a sample. ARL frequently uses high-performance liquid chromatography (HPLC), ion chromatography (IC), and gas chromatography (GC) to measure API concentration by comparing a known reference standard at a known concentration to the sample (drug substance or product). USP has established that the acceptable range of most compounded drugs is ± 10%; however, it can be as great as ± 20% (as with some proteins) or as tight as ± 5% (as with potent analgesics). Pharmacies may also specify an acceptable range based on their compounded formulation.

Potency Methods: 

  • Use system suitability to verify the resolution and reproducibility of the chromatographic system are adequate for analysis
  • Give reliable results
  • Separate excipients and other API’s
  • Provide documented and reviewed test results

Potency test methods can only be considered fully validated if they are validated for the specific formulation being tested.  Compounding pharmacies make a variety of formulations to meet individual patient needs. Having fully validated test methods for every pharmacy’s formulation would require pharmacies to communicate each formulation change to the laboratory, and may require verification or revalidation of an existing test method or validation of a brand new test method.  This work would increase cost for the pharmacy and time for the patient to receive their compounded medication.   ARL offers potency testing services using both validated and non-validated methods.

ARL provides pharmacies a certificate of analysis (CofA) that states the analytical instrument or method, drug identity, concentration, and percentage of expected concentration.   For non-validated methods, ARL’s CofA states “the potency method(s) used for testing passed system suitability requirements per ARL SOP AMP-012 for non-GMP analysis. Product specific method validation is not available for the sample and specification(s) are for informational purposes only.”

For validated methods, ARL’s CofA includes a reference to the validated test method number (e.g. AMI-XXXX). The methods are validated specifically for the formulation tested and the specifications are established by the client. 

Please contact ARL (800) 393-1595 or info@arlok.com with questions.

Reference Documents: 

  • United States Pharmacopeia <797>
  • FDA Current Good Manufacturing Practice — Interim Guidance for Human Drug Compounding Outsourcing Facilities
  • Kupiec, T. “Quality Control Analytical Methods: High Performance Liquid Chromatography”. International Journal of Pharmaceutical Compounding. Vol. 8, No. 3. May/June 2004 p. 223-227
  • Kupiec, T. “Chemical Testing Aspects of USP Chapter <797> for Compounded Sterile Preparations”. International Journal of Pharmaceutical Compounding. Vol. 9, No. 2. March/April 2005 p. 136-138