Buccal drug delivery: what's new and what does the future hold?

Abstract

The buccal mucosa is the stratified squamous epithelial tissue inside lining of the cheeks. It is a favorable site of drug absorption since the tissue is non-keratinized, relatively immobile and strongly supplied with blood by a dense capillary-vessel network; moreover, it is highly tolerant to allergens, resistant to potentially harmful agents and has a relatively low enzymatic activity. The tissue consents quick onset of effect, offers an easily accessible and generally well-accepted site for drug delivery, is a useful route of administration in patients in an unconscious state (e.g., when swallowing is impaired), and is suitable for retentive dosage forms of administration. Buccal mucosa allows drug delivery for both locoregional and systemic treatments. Locoregional delivery has a number of applications, including treatment of local conditions, such as mucositis, bacterial and fungal infections, aphthous stomatitis, vesiculobullous diseases, and potentially malignant disorders and oral cancer. On the other hand, the tissue is appropriate for delivering systemically acting drugs. The actives directly enter general circulation through capillary vessels, bypassing the first-pass metabolism in the intestine and liver, avoiding presystemic drug elimination or chemical/enzymatic degradation within the gastrointestinal tract thus leading to high bioavailability. “If low concentrations of drug are required to gain access to the blood, transbuccal drug delivery may be very satisfactory for safe and well-accepted future clinical applications” [1–3]. Controlled delivery of drugs through the buccal mucosa should be considered like a slow intravenous infusion. These characteristics contribute to optimal pharmacokinetic behavior of drugs after administration of smaller doses than in conventional oral formulations [4]. Nevertheless, similar to other mucosal membranes, the buccal mucosa has some disadvantages, including short residence time and small absorption area. The major limitation to buccal drug delivery is the barrier property of the tissue which has inadequate permeability for certain molecules, resulting in low drug bioavailability. Drug absorption is very satisfactory only for those actives that possess adequate physicochemical properties and the ability to permeate across the tissue. Accordingly, the formulative approach alone could be not sufficient for an effective control of drug delivery through the mucosa, and limited rate of absorption should be adjusted by simultaneous chemical and physical enhancement, including supersaturation and eutectic formation [4,5]. Buccal dosage forms reside in a tastesensing organ, and organoleptic aspects of formulation could become crucial limiting factors for drug application. Suitable palatal properties are often required to get optimal acceptability of dosage form or for masking less desirable properties of the active component [6]. Despite offering the possibility of improved systemic drug delivery, buccal administration has been utilized for relatively few pharmaceutical products so far. Conventional dosage forms, such as solutions, are commercially available for Buccal drug delivery: what’s new and what does the future hold?