Drug delivery via the oral mucous membrane is considered to be a promising alternative to the oral route.
Sublingual route is a useful when rapid onset of action is desired with better patient compliance than orally ingested tablets. In terms of permeability, the sublingual area of the oral cavity (i.e. the floor of the mouth) is more permeable than the buccal (cheek) area, which in turn is more permeable than the palatal (roof of the mouth) area.
The portion of drug absorbed through the sublingual blood vessels by passes the hepatic first pass metabolic processes giving acceptable bioavailability. Various techniques can be used to formulate sublingual tablets. New sublingual technologies address many pharmaceutical and patient needs, ranging from enhanced lifecycle management to convenient dosing for pediatric, geriatric, and psychiatric patients with dysphagia. This article is to highlights the different sublingual dosage forms, factors affecting the sublingual absorption, advantages, various in vitro and in vivo evaluation parameters and commercially available sublingual dosage forms.
The absorption potential of oral mucosa is influenced by the lipid solubility and therefore the permeability of the solution (osmosis); the ionization (pH); and the molecular weight of the substances. For example, absorption of some drugs via oral mucosa is shown to increase when carrier pH is lowering (more acidic) and decrease with a lowering of pH (more alkaline). The cells of the oral epithelium and epidermis are also capable of absorbing by endocytosis (the uptake of particles by a cell as if by hollowly wrapping itself around it. These engulfed particles are usually too large to diffuse through its wall). It is unlikely that this mechanism is used across the entire stratified epithelium.
The sublingual artery stems from the lingual artery – the body's main blood supply to the tongue and the floor of the mouth – which arises from the external carotid artery. The proximity with the internal carotid artery allows fast access to its route supplying the greater part of the cerebral hemisphere. Osmosis In order for a drug to be effectively absorbed sublingually, it needs to be able to travel across the buccal mucous membranes; by a process of diffusion known as osmosis which applies to all forms of absorption by the body; governing both intestinal and sublingual absorption. The distribution of water across cell walls depends on the osmotic difference in the blood between the intracellular and extracellular fluid. Small particles that readily dissolve in water, rarely present a problem in permeation and diffusion, and so are able to move freely between the tissues of the body. Active transportation into cells leads to rapid metabolisation of the substances.
Molecules such as glucose (fructose) and amino acids are essential for cell metabolism and special mechanisms have evolved to facilitate their rapid diffusion and permeation across cell membranes.