An Overview on: Sublingual Route for Systemic Drug Delivery

International Journal of Research in Pharmaceutical and Biomedical Sciences ISSN: 2229-3701can create problem in swallowing the food andpotential for food lodge in the throat increases.The absorption is transfer of the drug from its siteof administration into systemic circulation, so itcan be said that absorption is directly proportionallayer thickness. The absorption of the drug followsin this way Sublingual > Buccal > Gingival >Palatal. Due to high permeability and rich bloodsupply, the sublingual route can produce rapidonset of action so the drug with short deliveryperiod can be delivered and dose regimen isfrequent. The drug gets diluted in the saliva andfrom there the drug is adsorbed across the oralcavity.For example: Glyceryl nitrate-a potent coronaryvasodilator which is used for rapid symptomaticrelief of angina. After administration its getspharmacologically active after 1-2 minutes. Oralspray was found to provide rapid relief ofsymptom with first class metabolism. The extent offirst class metabolism when compared to thesublingual spray decreased to 48% with sublingualtablets and 28% with the oral dose. Nitrate whichappears in the plasma concentration can bemaintained for 24 hours when administratedsublingually 9 .The Mechanism of Sublingual AbsorptionThe absorption potential of the buccal mucosa isinfluenced by the lipid solubility and therefore thepermeability of the solution (osmosis), theionization (pH), and the molecular weight of thesubstances. For example, absorption of some drugsvia the buccal mucosa is shown to increase whencarrier pH is lowering (more acidic) and decreasewith a lowering of pH (more alkaline). The cells ofthe oral epithelium and epidermis are also capableof absorbing by endocytosis (the uptake of particlesby a cell as if by hollowly wrapping itself around it.These engulfed particles are usually too large todiffuse through its wall). It is unlikely that thismechanism is used across the entire stratifiedepithelium. It is also unlikely that active transportprocesses operate within the oral mucosa.However, it is believed that acidic stimulation anduptake into the circulatory system.The mouth is lined with a mucous membranewhich is covered with squamous epithelium andcontains mucous glands. The buccal mucosa issimilar to the sublingual mucosal tissue.The salivary glands consist of lobules of cellswhich secrete saliva through the salivary ducts intothe mouth. The three pairs of salivary glands arethe Parotid, the Sub mandibular and the Sublingualwhich lies on the floor of the mouth. The more acidthe taste the greater the stimulation of salivaryoutput, serving also to avoid potential harm to acidsensitive tooth enamel by bathing the mouth incopious neutralizing fluid. With stimulation ofsalivary secretion oxygen is consumed andvasodilator substances are produced, and theglandular blood flow increases, due to increasedglandular metabolism.The sublingual artery travels forward to thesublingual gland, it supplies the gland and branchesto the neighboring muscles and to the mucousmembranes of the mouth, tongue and gums. Twosymmetrical branches travel behind the jaw boneunder the tongue to meet and join at its tip. <strong>An</strong>otherbranches meets and anastomoses with the submental branches of the facial artery. The sublingualartery system stems from the lingual artery – thebody’s main blood supply to the tongue and thefloor of the mouth – which arises from the externalcarotid artery. The proximity with the internalcarotid artery allows fast access to its routesupplying the greater part of the cerebralhemisphereDrugs for sublingual administrationSublingual drug administration is applied in thefield of cardiovascular drugs, steroids, somebarbiturates and enzymes. It has been a developingfield in the administration of many vitamins andminerals which are found to be readily andthoroughly absorbed by this method. Sublinguallyabsorbed nutrition, which avoids exposure to thegastric system and liver, means direct nutritionalbenefits, particularly important for sufferers ofgastro‐intestinal difficulties such as ulcers,hyperactive gut, coeliac disease, those withcompromised digestion, the elderly and invalids –the nutritional benefit is independent ofgastro‐intestinal influences (10,11) . Examples of drugsadministered by this route include antianginal likenitrites and nitrates, anti hypertensive likenifedipine, analgesics like morphine andbronchodilators like fenoterol. Certain steroids likeestradiol and peptides like oxytocin can also beadministered e.g. fentanyl citrate, apomorphine,prochlorperazine dimaleate {PRO}, and hydrazineHCl {HYD}.Sublingual formulationSublingual tabletsThey are to be placed under the tongue and produceimmediate systemic effect by enabling the drugabsorbed directly through mucosal lining of themouth beneath the tongue. The drug absorbed fromstomach goes to mesenteric circulation whichconnects to stomach via portal vein. Thusabsorption through oral cavity avoids first passmetabolism. The tablets are usually small and flat,compressed lightly to keep them soft. The tabletmust dissolve quickly allowing the API to beabsorbed quickly. It is designed to dissolve in smallquantity of saliva. After the tablet is placed in themouth below the tongue, the patient should avoideating, drinking, smoking and possibly talking inVol. 3 (2) Apr – Jun2012 www.ijrpbsonline.com 915