Pharmaceutical Analysis · Short notes

Pharmacopoeial Assays: Short Notes & Cheat Sheet

Pharmacopoeias and monographs, content limits, dissolution and uniformity tests, microbiological and biological assays, and classic drug assays.

Short notes

Read these before you attempt the topic's MCQs.

A product complies only if it passes every part of the monograph, not just the assay.

Major pharmacopoeias: British (BP), United States (USP–NF), European (Ph. Eur.), International (Ph. Int.) and Japanese (JP). Pakistan recognises official pharmacopoeias such as the BP and USP for drug specifications.
A monograph gives the definition and content limits, identification tests, purity tests (related substances, loss on drying, sulfated ash, heavy metals), the assay method and storage.
APIs usually must contain about 98.0–102.0%, and tablets about 95.0–105.0% (or 90–110%) of the labelled amount, depending on the monograph.
A(1%, 1 cm) is the specific absorbance of a 1% w/v solution in a 1 cm cell, used for UV assays (e.g. paracetamol).

USP dissolution apparatus: 1 basket (commonly 100 rpm), 2 paddle (commonly 50 rpm), 3 reciprocating cylinder, 4 flow-through cell, 5 paddle over disk, 6 rotating cylinder, 7 reciprocating holder.
Dissolution acceptance is staged: S1 tests 6 units (each ≥ Q + 5%), S2 adds 6 more, S3 adds 12 more. Q is often 75–80% dissolved.
Content uniformity is required for low-dose products (under 25 mg or under 25% of tablet weight); otherwise weight variation may be used.
BP uniformity of weight for tablets: ±10% up to 80 mg, ±7.5% for 80–250 mg, ±5% above 250 mg. No more than 2 of 20 may deviate, and none by double the limit.
Sterility, bacterial endotoxin (LAL) and microbial limit tests apply to the relevant dosage forms.

Bioassays are used when chemical methods cannot measure biological potency.
Antibiotic potency is measured microbiologically by the cylinder-plate (agar diffusion) or turbidimetric method.
Historic bioassays include insulin (blood sugar in rabbits or convulsions in mice) and heparin (clotting of sheep plasma); many are now replaced by chemical or chromogenic methods.
Results are expressed in international units (IU) against a reference standard.

High-yield facts in one place. Cover the right-hand column and test yourself.

Basket 1, Paddle 2: USP apparatus 1 is the basket and apparatus 2 is the paddle, the two most used.

Content uniformity, not weight variation, is required for low-dose tablets.
Dissolution stage S1 tests 6 units, not 20.
Antibiotic potency by microbiological assay is reported in units or µg of activity, not simply chemical purity.
A monograph's identification tests alone do not establish purity or content.

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