In injectable suspensions, the particle size of the drug substance is a critical formulation parameter affecting the dissolution. Ho et al. found that an injectable suspension with smaller drug particles exhibited faster dissolution and improved systemic exposure. Variations in exposure due to drug particle size are also related to the local histological response, and nanoparticles are more widely distributed in the tissues and less likely to become fibrotic. Similar results between drug particle size and pharmacokinetics have been reported for the commercially available injectable nanosuspension of rilpivirine. 22)23) Leng et al. reported that an injectable suspension of paliperidone palmitate with larger drug particles showed better absorption than did one with smaller particles. 24) Therefore, an appropriate particle size must be selected depending on the drug substance.