Packaging, storage and shelf-life

Stock rotation looks like bookkeeping but it is pharmacology applied to a shelf. The physical problem is that a stored drug slowly loses potency, and the label records the date beyond which that loss is no longer acceptable. Rotation exists so that no batch reaches that date still sitting at the back of the shelf. FEFO, first to expire first out, is the primary rule: the drug soonest to expire is placed in front of the shelf and the later-expiring one behind. FIFO, first in first out, handles a specific tie: when drugs with the same expiration date are received at different times, the earlier arrival is dispensed first. LIFO, last in first out, handles the case that surprises beginners: it is used when the last drug to be received is sooner to expire, so the newest arrival must leave first. Notice that all three rules are decided by dates that are already printed on the pack, which is why the label must never be turned away from the dispenser. The wider storage rules support the same goal: heavy products on the lower shelves, lighter ones on the upper shelves, alphabetical arrangement by generic or trade name, and storage on shelves, in cupboards and in the refrigerator according to the product. The beginner’s misconception is that rotation is only about tidiness or about money. It is about potency: a patient given a batch that has lost activity is under-treated, and a health worker who trusts an expired pack is trusting a label rather than the drug inside.

An expiry date is the end of the period during which the manufacturer guarantees that the formulation still meets its specification of potency and quality under the recommended storage conditions. Shelf-life is that period, calculated as the date of expiry minus the date of manufacture. The lecture notes give a concrete arithmetic: a drug manufactured on 01/02/2007 and expiring on 31/01/2012 has a shelf-life of five years. They also give a reading rule for incomplete dates: when the manufacturing or expiry date is given as month and year only, the drug remains potent until the last day of that month. Two practical consequences follow. First, the date was calculated for the recommended storage conditions, so a product kept in heat or sunlight may degrade faster than the label implies; the special storage instructions are part of the expiry promise, not decoration. Second, the date is a boundary and not a switch: a well-stored product does not become poisonous on the stated day, but its guaranteed potency ends there, and potency is what the prescriber counted on when choosing the dose. The beginner’s misconception runs in two directions — one student believes an expired medicine is necessarily toxic, another assumes it is always still fine because “it was kept in a cupboard”. Neither is a substitute for the label and the storage instructions. In practice, check both dates, respect the storage instruction, and remove stock according to the rotation rules before the boundary is reached.