What Is Content Uniformity Testing?
Short answer
Content uniformity testing measures the amount of drug in individual dosage units, such as single capsules or tablets, to show that each one is close to the label claim. A potency assay tells you the batch average; content uniformity tells you how much one unit varies from the next. USP General Chapter <905> sets the standard procedure and acceptance criteria.
Why uniformity matters
A batch can hit its label claim on average and still have individual capsules that are high or low. USP’s chapter on uniformity of dosage units starts from that point: each unit in a batch should contain an amount of drug within a narrow range around the label claim (USP <905>). For a patient taking one capsule at a time, the individual unit is what counts.
This isn’t theoretical. In a limited FDA survey of compounded products bought online in 2001, 10 of 29 products (34%) failed one or more quality tests. Nine failed potency, all on the low side, at 59% to 89% of expected potency, and one oral product failed content uniformity as well as potency (FDA survey report). FDA also notes that compounded drugs are not FDA-approved, so FDA does not verify their quality before they are marketed (FDA). Testing is how a pharmacy shows its own batches are consistent.
Assay vs content uniformity vs weight variation
| Test | What it measures | What it tells you |
|---|---|---|
| Assay (potency) | Drug content of a composite of units, as % of label claim | Whether the batch average is right |
| Content uniformity | Drug content of each of several individual units | Whether units match each other and the label |
| Weight variation | Weight of individual units, with content estimated from the assay | Uniformity, when the drug is spread evenly through the fill |
USP <905> allows either content uniformity or weight variation, and content uniformity can be used in every case. Weight variation is limited to certain dosage forms, such as hard capsules and uncoated tablets containing 25 mg or more of a drug that makes up 25% or more of the unit by weight (USP <905>). For low-dose units, weighing a capsule can’t show whether the drug was evenly mixed, so content uniformity is the test to run.
How the USP <905> test works
- Test 10 units individually, usually by HPLC, and express each result as a percent of label claim.
- Calculate the acceptance value (AV), a single number that combines how far the average is from target with how spread out the results are.
- Stage 1: the batch passes if the AV for the first 10 units is 15.0 or less.
- Stage 2: if not, test 20 more units. The 30-unit AV must still be 15.0 or less, and every individual unit must fall within 75% to 125% of the reference value used in the calculation (USP chapter FAQs).
For drug manufacturers, federal rules also list capsule weight variation and adequacy of mixing among the in-process controls that protect batch uniformity (21 CFR 211.110).
Who should run content uniformity testing?
- Compounding pharmacies and 503B outsourcing facilities validating a new capsule or tablet formulation, a new blending process, or a new strength.
- Anyone with a low-dose product, where small mixing errors become large percentage errors.
- Consumers and businesses who suspect capsules from the same bottle aren’t behaving the same way.
Testing at Renew Lab Group
Our Houston lab runs HPLC and LC-MS potency and purity testing for compounding pharmacies, businesses and consumers. We can assay individual units from a batch and report each result alongside the average, so you see the spread as well as the potency. See our compounding pharmacy potency testing, HPLC testing lab, testing for individuals, how accurate HPLC potency testing is and how to read HPLC results. To request testing, call 936-379-5515 or email info@renewlabgroup.com.
Related questions
What is the difference between content uniformity and weight variation?
Content uniformity measures the drug in each unit directly. Weight variation weighs each unit and estimates its drug content from the batch assay, which only works when the drug is evenly distributed. USP <905> limits weight variation to certain dosage forms (USP <905>).
How many units are tested for content uniformity?
Under USP <905>, 10 units first. If the acceptance value is above 15.0, 20 more are tested, for 30 in total (USP chapter FAQs).
Is content uniformity the same as potency testing?
No. A potency assay gives the average drug content of a batch. Content uniformity shows how much individual units vary around that average. A batch can pass one and fail the other.
Can Renew Lab Group test my compounded capsules for uniformity?
Yes. Our Houston lab can assay individual capsules or tablets by HPLC and report each result. For a quote, call 936-379-5515 or email info@renewlabgroup.com.
Talk to the lab about content uniformity testing
Tell us what you need tested and we’ll recommend a method and send a quote. Contact us at 936-379-5515 or info@renewlabgroup.com for current pricing, turnaround and sample requirements. Samples can be dropped off at our lab at 6001 Central Crest, Houston, TX 77092.
Sources
- USP: General Chapter <905> Uniformity of Dosage Units
- USP: Uniformity of Dosage Units, chapter FAQs
- FDA: Report, Limited FDA Survey of Compounded Drug Products
- FDA: Compounding and the FDA, questions and answers
- 21 CFR 211.110: Sampling and testing of in-process materials and drug products (Cornell LII)
Researcher resources
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