Excipient

Every drug product is API plus excipients. Excipients are not pharmacologically active at the dose used but are not inert — they govern tablet hardness, disintegration time, dissolution, palatability, parenteral isotonicity, suspension stability, capsule shell elasticity, and the chemistry of degradation pathways. A typical immediate-release tablet contains the API plus 5-10 excipients (e.g. microcrystalline cellulose as filler, lactose as diluent, croscarmellose sodium as disintegrant, magnesium stearate as lubricant, hypromellose for film coating, talc as anti-tack, iron oxide for colour). The same molecule formulated with different excipients can produce dramatically different in-vivo performance — which is why excipient changes are tightly controlled by post-approval-change variation regulations.

• Diluents / fillers — bulk out the tablet to a workable weight (lactose, microcrystalline cellulose, mannitol).
• Binders — hold the granulation together (PVP, HPMC, starch paste).
• Disintegrants — break the tablet apart in GI fluid (croscarmellose sodium, sodium starch glycolate).
• Lubricants — reduce die-wall friction during compression (magnesium stearate, stearic acid).
• Glidants — improve powder flow into the die cavity (colloidal silicon dioxide).
• Coatings — film coat for taste, stability, modified release (hypromellose, ethylcellulose, methacrylates).
• Preservatives — prevent microbial growth in multidose liquids (benzyl alcohol, parabens, sorbic acid).
• Buffers — control pH for stability or compatibility (citrate, phosphate, acetate).
• Antioxidants — protect against oxidative degradation (BHT, ascorbic acid, sodium metabisulfite).
• Solvents / vehicles — dissolve and deliver (water for injection, ethanol, propylene glycol).
• Surfactants — wet, solubilise, emulsify (polysorbates, lecithin).
• Capsule shells — gelatin or HPMC; with bovine / fish / vegetal source disclosure.
• Sweeteners / flavours / colours — palatability, especially paediatric.

Excipient GMP is not full ICH Q7 (which applies to APIs) but is a risk-proportionate framework. The IPEC-PQG joint guide and the EU Commission's 2015 formalised-risk-assessment guideline together establish the expectation: the finished-dose manufacturer assesses each excipient on its source, route of administration, criticality to product performance, and known risks (TSE/BSE, nitrosamine source-3, elemental impurities, microbial bioburden) and assigns a GMP rigour level. High-risk excipients (parenteral, novel modified-release polymers, animal-derived materials) require near-Q7 supplier GMP plus tight audit; low-risk excipients (commodity chemicals for solid-dose) require qualified supplier + CoA + receiving controls. The risk assessment is documented per excipient per product, and re-reviewed on supplier change, source change, or new risk emergence (e.g. the nitrosamine cascade after 2018).

FDA maintains the Inactive Ingredient Database — every excipient ever approved in a US-marketed drug product, with its maximum daily exposure (MDE) by route of administration. Formulators reference the IID to confirm that the proposed excipient at the proposed level falls within precedent; a new excipient or an above-IID level triggers an additional safety evaluation (and often a separate excipient-master-file submission). The IID is the practical 'allowed list' for US formulation work. The EU equivalent is captured in the Ph.Eur. monographs plus the EMA's published lists of authorised excipients per product class.

Most commercial excipients have a compendial monograph in USP-NF, Ph.Eur. and JP — the monograph defines identity tests, assay limits, impurity limits (including ICH Q3C residual solvents and ICH Q3D elemental impurities), microbial limits, and the official test methods. Buying excipient 'USP-NF / Ph.Eur. grade' means the supplier certifies the lot meets all the monograph requirements; the CoA is the lot-specific evidence. Where a monograph does not exist or where a product needs tighter limits than the monograph (parenteral grade, microbe-free, specific particle-size distribution), the finished-dose manufacturer issues an in-house specification on top of (not in place of) the compendial monograph.

Two impurity programmes specifically catch excipients. Nitrosamines source-3 — contamination introduced through an excipient (e.g. nitrites in plant-derived materials reacting with amines on contact with the API) — was a major remediation programme after 2018 and remains a standing risk assessment requirement for every drug product. ICH Q3D elemental impurities — Class 1 (As, Cd, Hg, Pb), Class 2A (Co, V, Ni), Class 2B (Ag, Au, Ir, Os, Pd, Pt, Rh, Ru, Se, Tl) and Class 3 (Ba, Cr, Cu, Li, Mo, Sb, Sn) — apply to the finished drug product, but the dominant source of most elemental impurities is the excipients (especially mined materials like talc, kaolin, calcium carbonate). Both programmes require excipient-supplier-data inclusion in the risk assessment.

1. Risk assessment per excipient per product not done — single global statement used to cover dozens of materials.
2. Supplier-qualification audit cycle slipped on commodity excipients ('they're just lactose') — the same materials that drove melamine, glycerin / DEG and nitrosamine crises.
3. Compendial-grade purchased but in-house parenteral specification not added — endotoxin, particulate or microbial limits inadequate for the dosage form.
4. Q3D elemental impurity risk-assessment not refreshed after a supplier change.
5. IID exceeded for an excipient at a particular route without the additional safety justification.
6. Animal-derived materials (gelatin, lactose, magnesium stearate) without TSE/BSE certification (EMA/410/01 rev.3).
7. Excipient change made under a downstream CBE-30 / Type IA when it was actually a major variation.

• Excipient material master: function category, monograph reference (USP/Ph.Eur./JP), in-house spec on top, IID precedent reference, TSE/BSE status, Q3D risk-assessment status, source-3 nitrosamine risk-assessment status, halal / kosher / vegan / non-GMO certifications where applicable.
• Per-excipient per-product risk assessment record linked to the formulation; supplier change, source change or new risk-class emergence reopens it automatically.
• Every received lot has CoA captured and reconciled against the approved spec — automatic attribute-level pass/fail.
• Q3D rolling assessment combining excipient elemental contributions with the API contribution for the finished product PDE.
• Nitrosamine source-3 register per product, with periodic re-evaluation scheduled.
• Animal-derived excipient TSE/BSE certificates tracked with expiry; expiring certificates block new receipts until renewed.
• Supplier audit cycle calibrated to the IPEC risk tier; missed audit slips the excipient onto restricted use.