When Does a Dissolution Batch Actually Fail? A Worked USP <711> S1, S2, S3 Example for Immediate Release Dosage Forms

Why Stage Testing Exists

Dissolution results vary from unit to unit even when a batch is perfectly homogeneous. Testing every unit against a single pass/fail cutoff would either reject good batches on ordinary variability or let poor batches through. USP <711> solves this with a three-stage, escalating sample-size design: start with 6 units, and only pull more units — under progressively looser criteria — if the first stage doesn't clearly pass.

This structure means a batch can pass at S1 with just 6 units, or it can still pass at S2 or S3 with 12 or 24 units respectively, provided the additional data supports it. A batch only fails outright if it fails S3.

The Acceptance Criteria (Immediate-Release)

Per USP <711>, unless otherwise specified in the individual monograph, the requirements are met if the quantities of active ingredient dissolved conform to the following:

Q is the amount of active ingredient specified to dissolve, expressed as a percentage of label claim. The 5%, 15%, and 25% values are also percentages of label claim, so Q and these tolerances are always in the same units.

Reading the Table Correctly

•      S1 is strict but requires the fewest units: every single one of the 6 units must clear Q + 5%.

•      S2 relaxes the target to the average of all 12 units, but adds a floor — no individual unit may fall below Q − 15%.

•      S3 relaxes further on individual units (up to 2 of 24 may fall between Q − 15% and Q − 25%) but still requires the 24-unit average to meet Q.

•      Testing stops the moment a stage's criteria are met — there is no requirement to continue to S2 or S3 if S1 passes.

Worked Example

Consider an immediate-release tablet with Q = 80% at the specified time point. That places the S1 threshold at Q + 5% = 85%, and the S2 individual-unit floor at Q − 15% = 65%.

Stage 1 (S1) — 6 Units

Units 3 (84%) and 5 (79%) fall below the 85% threshold, shown in red. S1 requires every unit to clear that bar, so this batch does not pass at S1 — even though 4 of 6 units look strong — and testing proceeds to S2.

Stage 2 (S2) — 6 Additional Units

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Frequently Asked Questions

• What does “Q” mean in dissolution testing?

  “Q” represents the percentage of the labeled active ingredient that must dissolve within a specified time period according to regulatory specifications.

• How many stages are included in USP <711> dissolution testing?

  USP <711> dissolution testing generally includes three stages:

  • Stage 1 (S1) 

  • Stage 2 (S2) 

  • Stage 3 (S3)

  Testing may stop early if acceptance criteria are met at S1 or S2.

• What happens during Stage 1?

  In Stage 1:

  • Six dosage units are tested. 

  • Each unit must meet the required dissolution criteria, typically Q + 5%. 

  If all six units pass, testing ends successfully. 

• What happens if Stage 1 fails?

  If Stage 1 fails:

  • An additional six dosage units are tested in Stage 2. 

  • The combined average and individual results are evaluated against USP <711> acceptance criteria.

• What are the acceptance criteria for Stage 2?

  For Stage 2:

  • A total of 12 units are evaluated. 

  • The average of all units must be equal to or greater than Q. 

  • No individual unit should fall below Q − 15%.

• What happens during Stage 3?

  If Stage 2 still fails:

  • Twelve more units are tested, resulting in 24 total units. 

  • Additional limits such as Q − 25% are evaluated alongside the overall average.

• When can dissolution testing stop?

  Testing may stop:

  • After Stage 1 if all criteria are met. 

  • After Stage 2 if Stage 2 criteria are satisfied. 

  Stage 3 is only required if Stage 2 fails.

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