Drug stability and degradation
Practice questions with explanations

C. The specific product's stability data for the temperature and duration involved, obtained from the manufacturer or immunisation programme

Some vaccines tolerate defined excursions and can be released, while others cannot, and the decision requires the recorded temperature and duration. Guessing risks either wasting scarce stock or administering an ineffective vaccine to someone who believes they are protected, which is arguably the greater harm.

D. Hydrolysis

Water attacks the carbonyl carbon, splitting esters into an acid and an alcohol and amides into an acid and an amine. Esters hydrolyse far more readily than amides, which is why procaine has a short duration while lignocaine, an amide, is more stable. Hydrolysis is catalysed by hydrogen and hydroxide ions, so buffering to the pH of maximum stability is a standard formulation strategy.

D. Freezing denatures and aggregates the protein, irreversibly destroying activity

Insulin is a protein whose activity depends on its three-dimensional structure; ice crystal formation disrupts it and causes aggregation that cannot be reversed by thawing. The practical counselling points are to store spare cartridges in the body of the refrigerator rather than against the back wall or in the freezer compartment, to protect from heat and direct sun, and to inspect for cloudiness or clumping before use.