Sounds like they both (UK and USA versions) have an ethylcellulose coating London Red. Should be fine, try it and don't worry so much.
All of the other delayed-relase mesalamines have a thin polymer-based coating, an MMX, examples include lialda, delzicol, asacol, etc. "A gastro-resistant, pH-dependent film of methacrylic acid copolymers covers the MMX Multi Matrix System®", which behaves differently in release point and rate. That'd be a bigger change. UK Pentasa
Pentasa® releases active drug slowly throughout the entire small intestine and colon.
"PENTASA tablets consist of ethylcellulose-coated microgranules of mesalazine. Following administration and tablet disintegration the microgranules act as discrete slow-release formulations which allow a continuous release of drug from duodenum to rectum at all enteral pH conditions. The microgranules enter the duodenum within an hour of administration, independent of food co-administration. In healthy volunteers the average small intestinal transit time is approximately 3-4 hours.."
Source: /www.medicines.org.uk/emcmobile/medicine/668#PHARMACODYNAMIC_PROPSUsa Pentasa
PENTASA is an ethylcellulose-coated, controlled-release formulation of
mesalamine designed to release therapeutic quantities of mesalamine throughout the