Sublingual Drug Delivery System

-Sublingual Drug Delivery System are the dosage form which placed under the tongue and produce immediate systemic effect by enabling the drug absorbed directly through mucosal lining of the mouth beneath the tongue.

-The drug absorbed from stomach goes to mesenteric circulation which connects to stomach via portal vein. Thus, absorption through oral cavity avoids first-pass metabolism. 

-The tablets are usually small and flat, compressed lightly to keep them soft. The tablet must dissolve quickly allowing the API to be absorbed quickly. It’s designed to dissolve in small quantity of saliva. After the tablet is placed in the mouth below the tongue, the patient should avoid eating, drinking, smoking and possibly talking in order to keep the tablet in place.

-Swallowing of saliva should also be avoided since the saliva may contain dissolved drug. Bland excipient are used to avoid salivary stimulation.

Advantages:

-First pass - The liver is by-passed thus there is no loss of drug by first pass effect for sublingual administration, Bioavailability is higher. 

-Rapid absorption - Because of the good blood supply to the area absorption is usually quite rapid. 

-Drug stability -pH in mouth relatively neutral so a drug may be more stable.

Disadvantages:

-Holding the dose in the mouth is inconvenient. If any is swallowed that portion must be treated as an oral dose and subject to first pass metabolism. 

-Only small doses can be accommodated easily. 

Example: 

Glyceryl Trinitrate –

A potent coronary vasodilator which is used for the rapid symptomatic relief of angina.It has been found impressively effective when administered sublingually; pharmacologically active after only 1 - 2 minutes. 

Some of the drug like desoxycortisone acetate, morphine, captoprill, nifedipine and 17-B Oestradiol gives impressive absorption  when given sublingually , it has also been shown that the sublingual administration of 17-B Oestradiol requires only 1/4 of the oral dose. 

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Types of sublingual dosage forms 
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