Palatal mucosa as a route for systemic drug delivery: A review

Rapid developments in the field of molecular biology and gene technology resulted in generation of many macromolecular drugs including peptides, proteins, polysaccharides and nucleic acids in great number possessing superior pharmacological efficacy with site specificity and devoid of untoward and toxic effects. However, the main impediment for the oral delivery of these drugs as potential therapeutic agents is their extensive pre-systemic metabolism, instability in acidic environment resulting into inadequate and erratic oral absorption. Parenteral route of administration is the only established route that overcomes all these drawbacks associated with these orally less/inefficient drugs. But, these formulations are costly, have least patient compliance, require repeated administration, in addition to the other hazardous effects associated with this route. Over the last few decades pharmaceutical scientists throughout the world are trying to explore transdermal and transmucosal routes as an alternative to injections. Historically, oral transmucosal drug delivery has received intensive interest since ancient times for the most widely utilized route of administration for the systemic delivery of drugs. In more recent years, better systemic bioavailability of many drugs has been achieved by oromucosal route. Among the various transmucosal sites available, soft-palatal mucosa was also found to be the most convenient and easily accessible novel site for the delivery of therapeutic agents for systemic delivery as retentive dosage forms, because it has abundant vascularization and rapid cellular recovery time after exposure to stress. Smooth surface of the soft palate and its good flexibility are prerequisites to prevent mechanical irritation and local discomfort. The objective of this review is to provide an update on the most promising advances in novel non-invasive soft-palatal route and the conceptual and technical approaches to the design and formulation of soft-palatal drug delivery systems. In this area, the development of mucoadhesive delivery systems appears to be the most promising strategy.