Oral Fast Dissolving Films of Promethazine Hydrochloride Employing Natural Surfactants: A Comprehensive Review of Formulation Science, Pharmacology and Evaluation Strategies

Oral fast dissolving films (OFDFs) have emerged as one of the most patient-centric advances in solid-dosage drug delivery, dissolving within seconds on the tongue without the need for water and thereby resolving the swallowing difficulties that beset paediatric, geriatric, bedridden and non-cooperative populations. Promethazine hydrochloride, a first-generation phenothiazine antihistamine with potent antiemetic and sedative activity, is an attractive candidate for film-based delivery because its conventional oral formulations suffer from extensive hepatic first-pass metabolism (absolute bioavailability ≈ 25%), delayed onset of action and an intensely bitter taste that compromises compliance. This review consolidates current knowledge on the design of promethazine OFDFs, with particular emphasis on the substitution of synthetic surfactants by biocompatible natural surfactants such as lecithin and triterpenoid saponins. The physiology of oral mucosal absorption and of the emetic reflex is examined to justify the rapid-onset rationale, followed by a detailed drug profile, a survey of film-forming polymers and functional excipients, the mechanistic basis of surfactant-mediated solubility enhancement, the principal manufacturing techniques, and the complete battery of physicochemical, mechanical and biopharmaceutical evaluation parameters. Illustrative analytical data, recent literature and global market trends are presented graphically. Natural-surfactant OFDFs of promethazine represent a green, biocompatible and commercially relevant strategy for achieving rapid antiemetic relief, although challenges in drug loading, taste masking and large-scale reproducibility remain to be fully addressed.