Minimum Interfacial Bonding Strength for Bilayer Tablets Determined Using a Survival Test

Purpose: To identify the minimum interfacial bonding strength (IBS) required for bilayer tablets to sustain the stresses experienced during manufacturing, transportation, and handling. Methods: Bilayer tablets of a number of formulations with systematically varied IBS were prepared on a materials testing macine. Five bilayer tablets with the same IBS were repeatedly dropped at a fixed height in a friabilator and integrity of the interface was periodically examined. The number of tablets free from observable defects at the interface was plotted as a function of the number of drops. The IBS for all five tablets to remain intact after 1000 drops was taken as the minimum IBS for a given formulation. Results: The minimum IBS depends on both layer composition and tablet size. For bilayer tablets made with more brittle materials or a larger size, a higher minimum IBS is required to pass the survival test. The incorporation of HPMC leads to a lower minimum IBS. An IBS of 0.26 MPa is sufficient for all bilayer tablet formulations and sizes to pass the survival test in this work. Conclusions: A minimum IBS of 0.26 MPa is recommended as a tentative criterion for bilayer tablets of most materials to avoid quality issues arising from inadequate IBS.