The buccal and sublingual drug delivery
The buccal and sublingual mucosae in the oral cavity provide an excellent alternative for the delivery of certain drugs. Oral transmucosal absorption is generally rapid because of the rich vascular supply to the mucosa. These routes provide improved delivery for certain drugs that are inactivated by first-pass intestinal/hepatic metabolism or by proteolytic enzymes in the GI tract.
Sublingual administration involves placing a drug under your tongue to dissolve and absorb into your blood through the tissue there.
Buccal administration involves placing a drug between your gums and cheek, where it also dissolves and is absorbed into your blood.
The sublingual mucosa is relatively permeable and is suitable for delivery of low-molecular-weight lipophilic drugs when a rapid onset of action with infrequent dosing is required. Sublingual DDSs are generally of two different designs:
(a) rapidly disintegrating tablets and
(b) soft gelatin capsules filled with a drug in solution.
Such systems create a very high drug concentration in the sublingual region before the drug is systemically absorbed across the mucosa. Therefore, rapidly disintegrating sublingual tablets are frequently used for prompt relief from an acute angina attack.
The buccal mucosa is considerably less permeable than the sublingual area and is generally not able to provide rapid absorption properties. The buccal mucosa has an expanse of smooth muscle and relatively immobile mucosa, which makes it a more desirable region for retentive systems used for oral transmucosal drug delivery.
Thus, the buccal mucosa is suitable for sustained delivery applications, delivery of less permeable molecules, and perhaps peptide drugs.
One of the major disadvantages associated with buccal drug is the low flux, which results in low drug bioavailability. Therefore, buccal DDSs usually include a penetration (permeability enhancer) to increase the flux of drugs through the mucosa.
Another limitation associated with this route of administration is the poor drug retention at the site of absorption.
Consequently, bioadhesive polymers have been extensively employed in buccal DDSs. The duration of mucosal adhesion depends on the type and viscosity of the polymer used. Nicotine in a gum vehicle when chewed is absorbed through the buccal mucosa. Glyceryl trinitrite has been found quite effective when administered through this route.
Advantages of buccal and sublingual routes of drug administration
Some advantages of administering drugs through the oral mucosa are:
- A rapid onset of the therapeutic effect is achieved, not only by the high blood supply of the area but also by the lack of gastrointestinal (GI) factors that delay absorption (gastric emptying, presence of food, gastric disease, etc.).
- Portal circulation is avoided, which allows to improve the bioavailability of a drug (regarding the oral route) avoiding intestinal and first-pass hepatic metabolism.
- The active ingredient is not exposed to the aggressive GI medium, reason why it is possible the buccal administration of some drugs (e.g. peptides) that would otherwise be degraded by the GI pH or enzymes.
- It can be done in patients with swallowing difficulties, nausea or malabsorption syndrome, and even in unconscious patients.
- Action can be terminated by spitting out the tablet.
- Self-administration is possible.
Disadvantages of buccal and sublingual routes of drug administration
- Due to the small size of the oral cavity, only very potent drugs can be effectively delivered. The buccal mucosa offers about 200 cm2 of area for drugs absorption, i.e. about 10,000 times less than duodenum.
- Difficulty in keeping the drug in the site, as well as the need for the patient to refrain from swallowing, talking, or drinking during administration so as not to affect the residence time in which the medication is in direct contact with the mucous membrane.
- Buccal and sublingual routes of administration are not applicable to bitter or bad-tasting drugs since, in addition to patient discomfort, this type of formulations generates excessive production of saliva, which increases the risk of swallowing.
- While absorption may occur by any of paracellular and transcellular mechanisms studied, passive diffusion of drugs from the salivary aqueous phase through the membranes of oral mucosal cells predominates. Therefore, drugs of intermediate polarity are well absorbed, since excessive lipophilicity limits drug dissolution, in the same way that an increased polarity limits diffusion across cell membranes. The degree of ionization is also important: less ionized compounds at salivary pH are better absorbed.