colon-targeted delivery

Colon-targeted delivery is the trick of getting a drug to travel the whole length of the gut sealed up, then open only once it reaches the large intestine, like a parcel programmed not to unwrap until it arrives at the final stop on the line.

It is used to treat diseases of the colon itself, such as ulcerative colitis or Crohn's disease, where the drug should act locally, and also to absorb drugs (such as some peptides) that would be destroyed higher up in the gut. Several signals distinguish the colon and can be exploited: it is reached only after a long transit time, its pH differs from the small intestine, and it teems with bacteria that produce unique enzymes. Coatings that dissolve at higher pH, materials that break down only after a set time, and polymers degraded specifically by colonic bacteria are all used, often in combination.

Reaching the colon reliably is challenging because the cues are imperfect. Gut transit time varies widely with diet, disease, and the individual; pH overlaps between segments and shifts in disease; and the bacterial population differs between people and after antibiotics. The most robust products usually combine more than one mechanism, for example a pH-dependent coating over a bacteria-degradable core, to reduce the risk of releasing too early or too late.