National drug control authorities hold the responsibility to monitor the quality of all drug products marketed in the territory of their competence. The extent to which routine surveillance, as opposed to assessment of suspect products, should be undertaken will depend upon the capacity of the national quality-control laboratory, the extent to which the quality of products is assessed prior to registration, the extent to which the requirements for good manufacturing practice are implemented, and the number of products that are imported from abroad.
A systematic programme of drug quality surveillance should aim at regular sampling of all marketed products whether registered for sale or compounded in pharmacies. Each product should be assessed at least once every two to three years, but particular attention should be accorded to products that are of prime importance to public health programmes or that are potentially dangerous, unstable, or difficult to formulate properly.
The programme of sampling should be drawn up by the responsible laboratory, if necessary under the guidance of the drug control authority, on a yearly or half-yearly basis. This programme should not only list the products to be sampled during a given period, but should also specify the sampling procedures and the size of the samples to be collected, taking into account the need for retention samples. The programme should determine to what extent each brand of a given product will be sampled and which local authority or inspector will be responsible for each sampling operation, and it should indicate to which laboratory (if more than one exists) each sample should be sent. Such a programme enables the facilities of each laboratory to be used to best advantage.