Starting Material Sampling Plan Calculator (n, p and r Plans)

About the Starting Material Sampling Plan Calculator (n, p and r Plans)

Works out how many containers of a batch of starting material to sample under the three plans of the WHO guidelines for sampling of pharmaceutical products (TRS 929, Annex 4): the n plan (n = 1 + √N), the p plan (p = 0.4 √N) and the r plan (r = 1.5 √N), for N containers received. It names the plan WHO gives for your material — uniform or not, herbal, from a recognized source or not, for full testing or mainly for identity — and applies EU GMP Annex 8's rule on testing the identity of every container.

The n value is rounded to the nearest whole number with every container sampled up to 4, p and r are rounded up, as the WHO text says, and the tool shows where WHO's own Table 1 lists another value. It chooses the containers to open (or the samples to test individually) at random, splits a p plan's samples into pools, and lays out a sampling sheet for the batch record. A list of batches runs in one go. Without a pass it shows a free preview: the plan, the rules that apply and the verdict, with every computed figure hidden; the figures, the working, the sheet and the PDF, Excel and Print exports unlock with a Premium pass.

Common uses

• Warehouse and quality control staff planning the sampling of an incoming delivery, batch by batch.
• Regulators and procurement agencies sampling consignments with the WHO plans.
• Auditors and trainers checking a sampling SOP against the WHO formulas and Table 1.
• Preparing the sampling sheet with the containers chosen at random for the batch record.

The three plans

• n plan: for uniform material from a recognized source, used with great caution. Samples are taken from n containers chosen at random; each is checked for appearance and identity, and if they agree they are combined into one composite sample for testing. WHO does not recommend it for manufacturers' control laboratories that analyse and release or reject each consignment, and with 4 containers or fewer every one is sampled.
• p plan: for uniform material from a recognized source when the main purpose is the identity test. A sample is taken from every container and tested for identity; if they agree, they are pooled into p final samples.
• r plan: for material suspected to be non-uniform or from a source that is not well known, and for herbal starting materials. A sample is taken from every container and tested for identity; if they agree, r samples chosen at random are tested individually and then combined for the retention sample.

WHO wrote these plans mainly for drug regulatory authorities and procurement agencies and notes that they are not necessarily appropriate for manufacturers, although the principles help.

Identity of every container

EU GMP Annex 8 says that the identity of a complete batch of starting materials can normally only be ensured if individual samples are taken from all the containers and an identity test is performed on each. Sampling only a proportion is permissible with a validated procedure, which takes account of the manufacturer and supplier, their quality system, the manufacturing conditions and the material. Annex 8 calls such a procedure improbable for materials supplied by intermediaries such as brokers where the source is unknown or not audited, and for starting materials of parenteral products. WHO likewise says sampling plans are not recommended for sampling starting materials for identification tests. In the US, 21 CFR 211.84 requires at least one identity test on each component and bases the number of containers on statistical criteria, the supplier's history and the quantity needed.

WHO’s Table 1 and the formula

Table 1 of the WHO guidelines lists n for up to 90 containers, p for up to 225 and r for up to 44. For most N it agrees with the formulas, but not everywhere: for n it lists 2 for 3 containers and 3 for 4 (the text samples every container up to 4) and 4 for 13 (the formula gives 5); for p it lists 2 for 2 to 6 containers (the formula gives 1); for r it lists 7 for 22 containers (the formula gives 8). The report shows both values whenever they differ, and you choose which one to use.

Sources

• WHO TRS 929, Annex 4: WHO guidelines for sampling of pharmaceutical products and related materials — the plans, Table 1 and Appendix 5
• EU GMP, EudraLex Volume 4 — Annex 8 (sampling of starting and packaging materials) and Chapter 5 (production)
• 21 CFR 211.84 — testing and approval or rejection of components

Limitations

• The plans are WHO’s examples for starting materials. Packaging materials and finished products need sampling standards such as ISO 2859-1, as WHO says.
• Your approved sampling procedure and your regulator decide which plan, rounding and table you follow.
• The containers are numbered 1 to N; the random choice changes when you draw again, so keep the sheet that was used.
• Up to 2,000 containers per batch and 200 batches per list.
• MySmartCoPilot is not affiliated with or endorsed by the World Health Organization or the European Commission; the tool applies their published guidance.

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