Where do all the tablets go in 1986?

Where do all the tablets go in 1986? The surprising answer to this question is that our knowledge of the gastrointestinal transit of commonly prescribed drugs is remarkably patchy. As I will seek to show, however, techniques which allow a detailed description of the gastrointestinal transit, dispersion and dissolution of orally presented drugs now exist. Studies in this area are becoming increasingly important as pharmaceutical scientists develop ever more complex controlled-release formulations. Transit of these drug delivery systems through the gut has until recently been relatively unexplored with, as we shall see, sometimes lethal consequences. Many drugs are dispensed as liquids, suspensions or rapidly dispersing tablets and their gastrointestinal transit is rarely problematic because liquids and suspensions usually pass rapidly from the mouth to the small intestine, which is where most drugs are absorbed. Pharmaceutical scientists have, however, become increasingly interested in developing solid oral sustained release formulations aiming to provide the convenience of once daily dosage without toxic effects. Various methods have been used' such as coating the drug with insoluble semi-permeable membrane, incorporating it into a variety of slowly eroding matrices for example, waxes, plastics,2 or mixing it with a hydrophilic matrix-for example, hydroxypropylmethylcellulose, which on contact with water forms a gel-like coating to act as a diffusion barrier to the subsequent release of drug.3 Another approach is the osmotic pump, in which water diffuses through a semi-permeable membrane and dissolves the drug and an osmotic agent contained in the core of the capsule, the resulting solution then being expelled through a laser drilled 0.1 mm diameter hole.4 As 24 hours supply of drug together with the matrix must be incorporated into these drug delivery systems, patients may have to swallow relatively large tablets or capsules-up to 25 mm long, whose gastrointestinal transit and site of dissolution can not always be predicted. Oesophageal transit It has been recognised only relatively recently that oesophageal transit could be a major problem, when a number of instances of oesophageal ulceration were reported5 apparently because of the impaction of a wax-based slow-release form of potassium chloride. Systematic study of the relationship between transit, pill size, shape, and consistency then followed and it became abundantly clear that large tablets can often lodge in the oesophagus without exciting any subjective discomfort. Ten years ago in a seminal article entitled 'Where do all the tablets go?',6 Evans and Roberts showed that an aspirin-sized barium sulphate …