film coating

Film coating is a thin skin of polymer sprayed onto a tablet, like a fine layer of paint or varnish. It clings tightly to the tablet's contours and adds only a small amount of weight, yet it can mask a bitter taste, smooth the surface so it is easier to swallow, give a recognisable colour, and protect the drug from light, air or moisture.

The coat is applied in a rotating drum: tablets tumble while a liquid containing a film-forming polymer (such as hydroxypropyl methylcellulose), a plasticiser, pigments and a solvent is sprayed on, and warm air dries each layer as it lands. Modern coatings use water as the solvent where possible, avoiding flammable organic solvents. The whole film is usually only a few percent of the tablet's weight.

An ordinary film coat dissolves quickly in the stomach and barely changes how fast the drug is released — it is mainly cosmetic and protective. To actually control where or when the drug is released, a special functional coat such as an enteric or extended-release coat is needed instead.