Small-Volume Dissolution Testing of Pediatric Mini-Tablets Using Miniaturized USP Apparatuses: Regulatory and Methodological Considerations

Mini-tablets (MTs) have gained increasing importance as age-appropriate dosage forms, particularly for pediatric patients, due to their ease of swallowing and flexible dosing capabilities. Despite their growing use, regulatory guidance and standardized quality control (QC) methods specifically adapted to MTs, especially extended-release (ER) formulations, are still lacking. This study investigates the suitability of two miniaturized dissolution apparatuses for evaluating ER MTs: a Mini-Paddle system, which is a geometrically downscaled version of the compendial Paddle (USP 2) apparatus, and a small-volume Reciprocating-Holder (USP 7) apparatus. Two commercially available pediatric ER MT drug products containing melatonin and sodium valproate were tested individually and in deliberately manipulated batches to assess the methods' sensitivity and discriminatory power. The Mini-Paddle apparatus reliably quantified drug release from melatonin MTs but encountered limitations with low-dose sodium valproate MTs, requiring the pooling of multiple units, which masked individual variability. Conversely, the small-volume Reciprocating-Holder enabled sensitive, single-unit testing for both products, effectively detecting batch-to-batch differences despite very low drug loads. Neither apparatus currently holds official compendial status, emphasizing the urgent need for regulatory recognition and standardized methodologies. This study highlights the critical need for sensitive, miniaturized dissolution methods tailored to the unique challenges of MTs to ensure consistent quality, safety, and efficacy, particularly in vulnerable populations. Future work should focus on harmonizing and validating miniaturized dissolution systems to support QC and regulatory acceptance of MT formulations.