Buccal and Sublingual Forms

Buccal and sublingual dosage forms deliver drugs through the oral mucosa directly into the systemic circulation, bypassing the gastrointestinal tract and first-pass hepatic metabolism. These routes provide rapid onset of action and improved bioavailability for drugs that would otherwise be extensively metabolized in the liver or degraded in the stomach. The oral mucosa is highly vascularized and permeable, making it an attractive site for drug delivery.

What Are Buccal and Sublingual Forms?

Sublingual administration involves placing a drug under the tongue, where it is absorbed through the sublingual mucosa into the lingual vein, which drains into the superior vena cava and bypasses the portal circulation. Buccal administration places the drug between the cheek and the gum, where absorption occurs through the buccal mucosa into the facial vein and then into the systemic circulation. The sublingual route provides faster absorption than the buccal route because the sublingual mucosa is thinner and more permeable, but the buccal route offers a larger surface area and a more sustained absorption profile.

Types of Buccal and Sublingual Forms

Sublingual tablets are small, fast-dissolving tablets designed to disintegrate rapidly under the tongue and release the drug for absorption. Nitroglycerin sublingual tablets are the classic example, providing rapid relief from angina pectoris. Buccal tablets are designed to adhere to the buccal mucosa and release drug over an extended period. These tablets contain bioadhesive polymers that help them remain in place for hours.

Sublingual and buccal films are thin, flexible sheets that adhere to the oral mucosa and dissolve quickly, releasing the drug for absorption. Films offer convenient administration without water and are used for drugs such as fentanyl for breakthrough pain and buprenorphine for opioid dependence. Sublingual sprays deliver a metered dose of drug as a fine mist under the tongue, providing rapid absorption. Lozenges are solid dosage forms that dissolve slowly in the mouth, releasing drug for buccal absorption. They are used for both local effects, such as throat infections, and systemic effects, such as nicotine replacement.

When to Use

Buccal and sublingual forms are indicated when rapid onset of action is needed, such as nitroglycerin for acute angina, fentanyl for breakthrough cancer pain, and buprenorphine for opioid withdrawal. They are also valuable for drugs with poor oral bioavailability due to extensive first-pass metabolism, such as testosterone and certain peptides. The buccal route is particularly useful when sustained absorption over several hours is desired, as the buccal mucosa provides a stable absorption environment.

When Not to Use

These forms are not appropriate for patients with oral mucosal lesions, infections, or dry mouth conditions that impair dissolution and absorption. Irritating or unpalatable drugs are poorly tolerated by the oral mucosa. Patients who eat or drink while the dosage form is in place may swallow the drug prematurely, resulting in reduced bioavailability. Buccal and sublingual forms are generally unsuitable for drugs that require large doses, as the oral mucosa has limited surface area for absorption.

Advantages

Practical Benefits

Rapid onset of action, often within minutes
Convenient administration without water or swallowing
Easy to use and discreet compared to injections
Avoidance of needles, improving patient acceptance

Clinical Benefits

Bypass of first-pass hepatic metabolism, improving bioavailability
Avoidance of gastrointestinal degradation for acid-labile drugs
Direct entry into systemic circulation for predictable absorption
Reduced gastrointestinal side effects compared to oral administration
Ability to terminate drug delivery by removing the dosage form

Disadvantages

Clinical Limitations

Limited to potent drugs with good mucosal permeability
Smaller surface area restricts total drug absorption
Saliva flow can cause drug swallowing and reduced bioavailability
Mucosal irritation or ulceration with chronic use

Taste and texture may be unpleasant and affect adherence
Eating, drinking, and talking may dislodge the dosage form
Dry mouth reduces dissolution and absorption
Smoking and oral hygiene habits affect drug absorption

Best Practices for Administration

For sublingual administration, the tablet should be placed under the tongue and allowed to dissolve completely without chewing or swallowing. The patient should avoid eating, drinking, or smoking until the tablet has fully dissolved. For buccal administration, the tablet should be placed between the upper cheek and gum and held in place until dissolution is complete. The application site should be alternated to prevent mucosal irritation. Patients should be advised about the importance of not swallowing the dosage form prematurely.

Special Considerations

Patients with xerostomia or dry mouth from medications or medical conditions may have impaired dissolution and absorption of buccal and sublingual forms. Rinsing the mouth with water before administration can help if dry mouth is a concern. Sublingual nitroglycerin may cause a transient burning sensation, which confirms that the tablet is active and properly dissolving. Drugs absorbed through the oral mucosa enter the systemic circulation directly, so lower doses are typically needed compared to oral administration, and clinicians must be careful to avoid overdose when converting from oral to sublingual or buccal routes.

Conclusion

Buccal and sublingual dosage forms provide a practical and effective alternative to oral and injectable routes for drugs requiring rapid onset or improved bioavailability. Their convenience, rapid absorption, and avoidance of first-pass metabolism make them valuable for acute conditions and for drugs with poor oral pharmacokinetics. Proper patient education on administration technique is essential for consistent therapeutic effect.