Two specifications, and the paperwork that crosses between them

An incoming-material specification and a finished-preparation release answer different questions. The first says what a lot of material must measure before the pharmacy accepts it. The second is a decision about a batch that did not exist when the material arrived. A certificate of analysis is evidence for the first and an input to the second. It is not a release for the second, and reading it as one is the common error.

For a 503A pharmacy the certificate is statutory. 21 U.S.C. 353a(b)(1)(A) conditions the exemption on bulk drug substances that comply with an applicable USP or NF monograph where one exists, that are made by an establishment registered under section 510 of the Federal Food, Drug, and Cosmetic Act, and that are accompanied by valid certificates of analysis. Section 353b(a) sets parallel conditions for an outsourcing facility but does not exempt it from 501(a)(2)(B), which carries current good manufacturing practice.

Part 211 is worth reading even where it does not bind you, because it sets the conditions on which a certificate may be accepted. 21 CFR 211.84(d)(2) lets a supplier's report of analysis stand in for the receiver's own testing for purity, strength and quality, but only where the receiver runs at least one specific identity test itself and establishes the reliability of the supplier's analyses through validation at appropriate intervals.

The endotoxin limit for a compounded sterile preparation: K/M, worked end to end

USP General Chapter 85 defines it in two parts. The endotoxin limit for parenteral drugs, defined on the basis of dose, equals K/M, where K is a threshold pyrogenic dose of endotoxin per kg of body weight and M is the maximum recommended bolus dose of product per kg of body weight. Where the product is injected at frequent intervals or infused continuously, M is instead the maximum total dose administered in a single hour period.

K is fixed by the route and is never calculated: 5 EU/kg for any route other than intrathecal, and 0.2 EU/kg intrathecal. M is the input no supplier can give you. It comes from the prescriber's order and the preparation record. Worked on an M of 5 mg on a 70 kg basis, the two inputs the formula needs:

The limit belongs to the preparation, not to the vial, and Chapter 85 allows it to be carried in EU/mL, EU/mg or EU per Unit of biological activity. The maximum valid dilution follows from the same numbers, and a reading taken past it is not a valid test.

Now read the limit backward onto the material. Endotoxin is not removed by compounding, so every contribution has to fit inside it. An ingredient released at not more than 10 EU/mg leaves the preparation well inside 70 EU/mg. One released at not more than 100 EU/mg does not, and no downstream step will fix it. An EU/mg figure is the most useful number on an incoming certificate.

Chapter 797 sets when the finished preparation is tested for endotoxins: Category 3 injectable preparations compounded from one or more nonsterile components, and Category 2 injectable preparations compounded from one or more nonsterile components where the beyond-use date requires sterility testing. Where no monograph limit exists, the preparation must not exceed the limit calculated as described in Chapter 85. That calculation is the pharmacy's to make.

• M = 5 mg divided by 70 kg = 0.0714 mg per kg
• Endotoxin limit = K divided by M = 5 EU per kg divided by 0.0714 mg per kg = 70 EU per mg
• At a finished concentration of 5 mg per mL, the same limit is 350 EU per mL
• Maximum valid dilution = (70 EU per mg x 5 mg per mL) divided by a labeled reagent sensitivity of 0.005 EU per mL = 70,000

Where each analysis sits

Placing the four analyses is most of the work. The question is not whether a test exists, but whose specification it belongs to and what unit the number arrives in.

Sterility is a statement about a batch, not about a vial

USP General Chapter 71 is two methods, membrane filtration and direct inoculation, run in two media. Fluid Thioglycollate Medium is incubated at 32.5 plus or minus 2.5 degrees. Soybean-Casein Digest Medium is incubated at 22.5 plus or minus 2.5 degrees and suits fungi and aerobic bacteria. Both run for not less than 14 days.

The sample is small, and the chapter is plain about it. For parenteral preparations, Table 3 sets the minimum number of items tested in each medium: 10 percent or 4 containers, whichever is greater, up to 100 containers; 10 containers from 101 to 500; and 2 percent or 20 containers, whichever is less, above 500. A pass means a sample drawn that way grew nothing in 14 days.

Chapter 797 adds its own arithmetic. Testing follows Chapter 71 or a validated alternative shown to be noninferior, for which it points to Validation of Alternative Microbiological Methods, Chapter 1223. The maximum batch size for a preparation requiring sterility testing is 250 final yield units, a figure the Expert Committee derived from Chapter 71 Table 3.

Method suitability sets the calendar, and it is the question to put to a contract laboratory before asking for a turnaround. Chapter 71 requires its Method Suitability Test to show that contamination can actually be recovered from that formulation. It is run per formulation, on a new product and again whenever the experimental conditions change, not per batch, and the chapter permits it to run simultaneously with the sterility test itself. The 14 day incubation does not compress, and a turbid medium triggers a transfer to fresh medium at 14 days and not less than 4 more days.

Residual solvents: read the statement, not only the number

USP General Chapter 467 applies to existing drug substances, excipients and products, all subject to relevant control of the solvents likely to be present. The classes are a toxicological ranking, not a testing schedule: Class 1 to be avoided, Class 2 to be limited, Class 3 of low toxic potential.

Class 2 has two ways of being expressed, and confusing them is where a certificate becomes hard to read. Option 1 uses the ppm figures in Table 2, calculated as 1000 multiplied by the permitted daily exposure and divided by the daily quantity in grams, assuming a product weight of 10 g a day: acetonitrile at 4.1 mg gives 410 ppm. Option 2 works from the exposure against the actual daily quantity, so one component may sit above its Option 1 figure if the sum stays under.

The most useful part of the chapter for a buyer is the part telling a supplier what it may write. Under Reporting Levels of Residual Solvents it offers three statements: only Class 3 solvents are likely to be present, with loss on drying under 0.5 percent; only named Class 2 solvents are likely to be present, all below the Option 1 limit; or the two combined. Likely to be present means the solvent used or produced in the final manufacturing step, plus solvents from earlier steps not removed consistently by a validated process. A certificate carrying one of those three, with the Class 2 solvents named, is doing what the chapter asks. One claiming conformance and naming nothing is not.

One point is specific to peptides. Trifluoroacetic acid, common in solid-phase synthesis and preparative chromatography, is in none of the three classes. It sits in Table 4, Other Residual Solvents, described as those for which no adequate toxicological data on which to base a permitted daily exposure was found. There is no compendial ppm limit, so control of it belongs in the specification agreed with the manufacturer.

Elemental impurities, in the unit a buyer can use

USP General Chapter 232 sets the limits and Chapter 233 the procedures, aligned with ICH Q3D. The limits are permitted daily exposures in micrograms per day, attaching to a finished drug product, which is awkward for a buyer, because an ingredient certificate reports a concentration.

ICH Q3D(R2) closes the gap. Table A.2.2 gives permitted concentrations in micrograms per gram and states in its caption that they apply to drug products, drug substances and excipients at a daily intake of not more than 10 grams. A micrograms per gram figure therefore reads straight against the parenteral column: cadmium 0.2, lead 0.5, arsenic 1.5, mercury 0.3, cobalt 0.5, vanadium 1, nickel 2.

Which elements have to be looked at is a separate question, and Table 5.1 answers it. For a parenteral, the four Class 1 elements and the three Class 2A elements belong in the risk assessment whether or not anything was intentionally added, along with lithium, antimony and copper from Class 3. Anything intentionally added is in for every route, which pulls a palladium, platinum or nickel catalyst into the assessment.

What this means for a buyer

Four questions cover most of what a certificate should already have told you.

Two things follow. 21 CFR 211.167(a) puts sterility and pyrogen testing on each batch of drug product purporting to be sterile or pyrogen-free, which is the preparation and not the ingredient. And M belongs to the preparer: K is fixed by the route, and the number the arithmetic produces is what an incoming certificate is read against.

The register prints an assay floor against each entry, and material ships with a certificate of analysis for its lot. The four questions above are worth putting to any source, including this one.

• What is the bacterial endotoxin figure in EU per mg, and against what release limit? A conformance statement with no figure compares to nothing.
• Which residual solvents are likely to be present in the sense Chapter 467 defines, and which of its three reporting statements does the certificate make?
• Which elemental impurities were assessed, at what concentration in micrograms per gram?
• What method established identity, and is it separate from the purity assay?

Sources

1. United States Pharmacopeia USP General Chapter 85, Bacterial Endotoxins Test
2. United States Pharmacopeia USP General Chapter 71, Sterility Tests
3. International Council for Harmonisation ICH Q3C(R9), Impurities: Guideline for Residual Solvents
4. United States Pharmacopeia USP General Chapter 797, Pharmaceutical Compounding - Sterile Preparations, sections 9.3.1 12.2 and 12.3
5. United States Pharmacopeia USP General Chapters 232, Elemental Impurities - Limits, and 233, Elemental Impurities - Procedures
6. International Council for Harmonisation ICH Q3D(R2), Guideline for Elemental Impurities, Tables A.2.1 A.2.2 and 5.1
7. United States Code 21 U.S.C. 353a, Pharmacy compounding
8. United States Code 21 U.S.C. 353b, Outsourcing facilities
9. Code of Federal Regulations 21 CFR 211.84, Testing and approval or rejection of components, drug product containers, and closures
10. Code of Federal Regulations 21 CFR 211.167, Special testing requirements
11. US Food and Drug Administration Pyrogen and Endotoxins Testing: Questions and Answers, final guidance