Reconstitution

Reconstitution is the dissolving of a lyophilised cake into a liquid so that it can be injected. The arithmetic is the point of the step: the solid mass in the vial is fixed, so the concentration of the resulting solution is that mass divided by the volume of diluent added, and every later volume-to-amount relationship depends on it. Approved lyophilised products name both the diluent and its volume on the label, because the manufacturer validated cake, diluent and solution as one system, not as interchangeable parts.

The physical chemistry is less forgiving than it looks. Cakes are formulated to dissolve quickly when the diluent runs down the vial wall, and slow or incomplete dissolution is itself a signal about the cake, its water content or its storage history. Vigorous agitation generates foam, and foam means a large air-liquid interface, which is where peptides unfold and aggregate. The diluent also determines whether the solution is preserved, and so whether it can be entered more than once.

Reconstitution converts a solid whose stability is measured in months or years into a solution whose stability is measured in days or weeks. The beyond-use date starts at reconstitution rather than at manufacture, and it depends on the preservative system, the storage temperature and the container. A powder that survived shipping badly may still dissolve perfectly, since dissolution does not test potency.

The characteristic grey-market error is treating the milligram figure on a vial label as the mass of peptide present. Net peptide content, counterion mass and deliberate overfill all sit between label and reality, so a calculator dividing the label figure by a volume produces false precision. A second error is inferring quality from appearance: a clear solution shows that the solid dissolved and nothing about identity, purity or sterility.