Why Dissolution Test Apparatus Calibration with Salicylic Acid Tablets was Stopped

Historically, salicylic acid tablets were used as calibration standards for dissolution test apparatus (mainly USP Apparatus 1 & 2) to check performance. However, this practice was discontinued by the United States Pharmacopeia (USP) in 2010 and replaced with mechanical calibration.

Key Reasons for Discontinuation

1. Variability in Tablet Performance

   • Salicylic acid tablets were highly sensitive to manufacturing variations (compression force, particle size, moisture content), which caused inconsistent dissolution results even in properly working apparatus.

2. Limited Discriminatory Ability

   • Passing/failing dissolution based solely on salicylic acid tablet performance could give false positives (failing a good apparatus) or false negatives (passing a faulty apparatus).

3. Lack of Root Cause Identification

   • Tablet-based testing only indicated a failure without clarifying whether the cause was paddle/basket speed, wobble, temperature, or vessel alignment.

4. Focus Shift to Mechanical Calibration

   • USP introduced Performance Verification Test (PVT) using prednisone tablets, then moved towards enhanced mechanical calibration — measuring physical parameters (shaft wobble, centering, vessel verticality, temperature) to ensure reproducibility.

5. Regulatory Harmonization

   • FDA and USP aligned with ICH and global standards preferring mechanical calibration as it is more reproducible, traceable, and directly linked to apparatus performance.

Current Practice

• Salicylic acid tablets are no longer used for dissolution calibration.

• Labs now follow:

  • Mechanical Calibration (measuring apparatus geometry, temperature, and RPM accuracy)

  • Prednisone Tablets PVT (USP reference standard) for apparatus performance check.

In short:
Salicylic acid tablets were stopped due to poor reproducibility, lack of diagnostic value, and regulatory preference for mechanical calibration, which ensures consistent and reliable dissolution testing.