Esophageal transit of solid oral dosage forms – impact of different surface materials characterized in vitro and in vivo by MRI in healthy volunteers

Acceptable swallowability and complete esophageal transit are decisive for the safe and effective administration of solid oral dosage forms. This applies in particular to the main user group of medicines, older adults, who often suffer from swallowing difficulties. It is well known that surface properties play an important role in this respect. In the past, this has led to the development of numerous coating formulations for tablets with improved swallowability. However, in vitro and especially in vivo data investigating a positive effect of different coating materials is limited. Therefore, we investigated coating materials being based on polyvinyl alcohol, hydroxypropyl methylcellulose, and a copolymer of methacrylate in respect to their influence on swallowability and esophageal transit of a tablet formulation. They were compared to uncoated tablets as well as to hard gelatin capsules. Three in vitro assays suitable for routine use in pharmaceutical development were performed: i.) Wettability test in artificial saliva; ii.) Swelling measurement in artificial saliva; iii.) Measurement of the adhesion between surface materials and a simulated mucosa surface. All three assays resulted in a differentiation of the surface materials. The coated tablets showed favorable behavior compared to uncoated tablets and hard gelatin capsules. To test the effect of the different materials in vivo, an intervention study was conducted. 36 adults were included and the likeliness of prolonged esophageal transit of (un-)coated tablets as well as a hard gelatin capsule of the same weight was objectively evaluated by means of magnetic resonance imaging. While hard gelatin capsules showed highest rates for prolonged esophageal transit, the tendency for adhesion was reduced for uncoated tablets, and least for coated tablets, i.e., prolonged esophageal transit in 22.2 %, 11.1 %, and ≤5.6 % of the cases, respectively. Further differentiation of the coating materials was not possible. Subjective evaluations of each participant with respect to subjective swallowability and esophageal transit did not correlate well with the objective measurements by means of magnetic resonance imaging. The use of coatings in general has a positive influence on esophageal transit. However, the selection of coating type seems to be of greater importance in respect to patients' oral perception of the dosage forms compared to their influence on the probability for prolonged esophageal transit.