PharmaCalc

Content Uniformity (CU) testing is a critical quality control procedure used to verify that each individual dosage unit in a batch contains an amount of active pharmaceutical ingredient (API) within acceptable limits. This test is required by USP <905> and Ph. Eur. 2.9.40 for all solid dosage forms including tablets and capsules.

When and Why It's Performed:

• Batch Release: Every production batch must pass CU before shipment to ensure product quality and compliance.
• Process Validation: Stage 1 and 2 of process validation involve CU testing with larger sample sizes to demonstrate process capability.
• Stability Testing: CU is monitored at each time point to detect API degradation or migration over shelf life.
• Change Validation: Process or formulation changes require CU retesting to confirm homogeneity is maintained.

The two-stage sampling plan (Stage 1 with n=10, Stage 2 with n=30) is designed to efficiently distinguish acceptable from unacceptable batches while minimizing false rejections of good products.

Content Uniformity uses an Acceptance Value (AV) approach that accounts for both the deviation of the batch mean from the reference value (100% label claim) and the variability within the sample.

Stage 1 Analysis (n=10):

Where: M = 100.0% (reference value / label claim), X̄ = sample mean assay, k = 2.4 (constant for n=10), s = standard deviation of sample.

Acceptance Criteria (Stage 1): Pass if AV ≤ 15.0%. If AV > 15.0%, proceed to Stage 2.

Stage 2 Analysis (n=30 total):

Combine results from Stage 1 (n=10) and Stage 2 additional samples (n=20) for n=30 total. Recalculate AV with k=2.0.

Acceptance Criteria (Stage 2): Pass if AV ≤ 15.0% AND no individual unit result falls outside the range 75.0–125.0% label claim. Fail if either condition is not met.

Supporting Calculations:

Scenario: A pharmaceutical manufacturer is conducting batch release testing for 500 mg paracetamol tablets. Stage 1 testing is performed with n=10 tablets sampled randomly from the batch using a HPLC assay method.

1. Calculate the Sample Mean (X̄):
   X̄ = Σxᵢ / n
   X̄ = (98.2 + 101.5 + 99.8 + 97.6 + 100.4 + 102.1 + 98.9 + 100.7 + 99.3 + 101.2) / 10
   X̄ = 999.7 / 10 = 99.97%
2. Calculate Deviations from Mean:
   Subtract X̄ from each xᵢ:
   (98.2 − 99.97) = −1.77, (101.5 − 99.97) = 1.53, (99.8 − 99.97) = −0.17,
   (97.6 − 99.97) = −2.37, (100.4 − 99.97) = 0.43, (102.1 − 99.97) = 2.13,
   (98.9 − 99.97) = −1.07, (100.7 − 99.97) = 0.73, (99.3 − 99.97) = −0.67, (101.2 − 99.97) = 1.23
3. Calculate Sum of Squared Deviations:
   Σ(xᵢ − X̄)² = (−1.77)² + (1.53)² + (−0.17)² + (−2.37)² + (0.43)² + (2.13)² + (−1.07)² + (0.73)² + (−0.67)² + (1.23)²
   = 3.13 + 2.34 + 0.03 + 5.62 + 0.18 + 4.54 + 1.14 + 0.53 + 0.45 + 1.51
   = 19.47
4. Calculate Sample Standard Deviation (s):
   s = √[Σ(xᵢ − X̄)² / (n−1)]
   s = √[19.47 / (10−1)] = √[19.47 / 9] = √2.164 = 1.47%
5. Calculate Acceptance Value (AV) for Stage 1:
   AV = |M − X̄| + k × s
   AV = |100.0 − 99.97| + 2.4 × 1.47
   AV = 0.03 + 3.53
   AV = 3.56%
6. Compare Against Acceptance Criterion (Stage 1):
   Acceptance Criterion: AV ≤ 15.0%
   Result: 3.56% ≤ 15.0% ✓
   Check all individual results within 75–125%? Yes (range: 97.6–102.1%, all within range) ✓

Interpretation: The batch exhibits excellent content uniformity with a low acceptance value well below the 15% limit. The mean assay is very close to 100% label claim (99.97%), and the sample standard deviation is minimal (1.47%), indicating homogeneous distribution of API throughout the batch.