Good Distribution Practices
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Direct answer
A medicine that leaves the factory perfect can still reach a patient useless, and Good Distribution Practices (GDP) is the quality system built to close that gap. GDP governs storage, transport, receipt and documentation from the manufacturer's premises to the dispensing point, temperature being the chief hazard. The WHO framed it as Annex 5 of Technical Report Series No. 957 (2010), since consolidated into one guideline on good storage and distribution practices for medical products. It is why a pentavalent vial travels at 2-8°C wearing a vaccine vial monitor.
What you must remember
- Boundary with GMP: GMP ends at final packaging and release; GDP takes over for procurement, warehousing, transport and delivery — sourcing only from valid wholesale licence holders (Forms 20-B, 21-B).
- Temperature vocabulary is one-mark territory: cold 2-8°C; cool 8-15°C; controlled room temperature 20-25°C with excursions 15-30°C; "store below 30°C" is the label wording common in India's hot climate.
- UIP cold chain ladder: walk-in cooler 2-8°C; deep freezer and walk-in freezer -15°C to -25°C (OPV is stored frozen); ice-lined refrigerator (ILR) at 2-8°C needs only about 8 hours of power daily, with roughly 20 hours holdover — domestic refrigerators (about 4 hours) never qualify.
- Vaccine vial monitor (VVM): square-inside-circle heat indicator, four stages; discard at stage 3 (square darker than circle) — it reads cumulative heat, not freezing.
- Shake test for adsorbed vaccines suspected frozen (DPT, DT, TT, hepatitis B, pentavalent): shake beside a frozen control; persistent slow-settling flakes mean discard.
- Issue by FEFO; quarantine unreleased, returned and recalled stock under status labels; restock returns only when documents prove storage conditions held.
- Temperature-map warehouses and vehicles across seasons with loggers calibrated to traceable standards; recalls are graded Class I-III by risk and closed only by effectiveness checks.
How a pentavalent vial crosses India without losing potency
The exam case on GDP is one batch's journey from plant to session site. At dispatch, released stock leaves in insulated cold boxes with conditioned ice packs and a calibrated logger — the shipment's passport, checked before unloading on arrival. At the Government Medical Stores Depot they enter a walk-in cooler at 2-8°C; batch, expiry, label and VVM stage are verified before the consignment leaves quarantine. At the district cold chain point they sit in an ILR that rides out power cuts on its ice lining, the handler recording temperature twice daily.
Transport to the session uses vaccine carriers with four or five conditioned ice packs — conditioned until the ice sloshes inside, the surface near 0°C, so adsorbed vaccine never touches a freezing surface. Diluents must be cooled to 2-8°C for at least 24 hours before reconstitution. At the site the nurse reads the VVM — stage 1 or 2 passes, stage 3 is discarded regardless of expiry — and if freezing is suspected, the shake test against a deliberately frozen control decides. Under the WHO multi-dose vial policy, opened DPT, TT, hepatitis B and pentavalent vials serve later sessions up to 28 days if the VVM stays usable and storage holds at 2-8°C; reconstituted BCG and measles vaccines are discarded within 6 hours or at session end, whichever is earlier. The chain is graded by its worst temperature event; only documentation proves it held.
Where students slip
The costliest error is treating cold as anything below 8°C. A logger chart reading 0.5°C for three hours is not a pass — freezing is an excursion too, and it ruins adsorbed vaccines even under the ceiling; a viva examiner will hand you that chart and expect a rejection reasoned through the shake test. The second slip is VVM stage 2 versus 3: the monitor senses heat alone, so a frozen vial can carry a perfect stage 1 — the reason both checks run side by side. Third, the boundary: GDP begins where GMP ends and applies just as fully to a room-temperature paracetamol shipment — mapping, vehicle qualification and counterfeit control have nothing to do with the cold chain.
Frequently asked questions
Which WHO document forms the basis of Good Distribution Practices?
Annex 5 of WHO Technical Report Series No. 957 (2010), now consolidated into the WHO guideline on good storage and distribution practices.
At what temperature is a vaccine held through the immunization cold chain?
Between 2°C and 8°C at every point, with OPV the exception kept frozen at -15°C to -25°C in deep freezers until distribution.
At which VVM stage must a vaccine vial be discarded?
Stage 3, when the inner square matches or darkens past the circle; stages 1-2 remain usable within expiry even after brief heat exposure.
When is the shake test performed, and on which vaccines?
Whenever an adsorbed vaccine — DPT, DT, TT, hepatitis B, pentavalent — is suspected of freezing: shake it beside a frozen control vial and discard if flakes settle slowly and cling to the glass.
Why must domestic refrigerators not store vaccines?
Holdover is only about 4 hours, temperature is uneven, and the freezer compartment inside can expose vaccines to sub-zero damage.