Nahla Barakat, PhDKing Saud University

Dept. of Pharmaceutics1431/1432

TABLETS

Tablets

• Tablets are oral solid unit dosage form of medicaments with or without suitable diluents and prepared either by molding or compression. They are solid, flat or biconvex disc in shape. •They vary greatly in shape, size and weight which depend upon amount of medicament used and mode of administration. •They also vary in hardness, thickness, disintegration and dissolution characteristics and in other aspects depending upon their intended use and method of manufacture

•They are used for local & systemic effect.

• Usually used for oral administration

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Introduction

Tablets are popular due to:1. A convenient and safe way of drug administration.2. Compared to liquid dosage form they are more physically & chemically stable.3.Enables more accurate dosing , easy to use, handle by the patient4.Can be prepared in different ways according to their use.  5. Tablets are provides a sealed covering which protects the tablets from atmospheric conditions like air, moisture and light etc.6. The manufacturing cost of tablets is low as compared to other dosage form .7. The unpleasant taste and odor of medicament(s) can be easily masked by sugar.8.Tablets provide administration of even minute dose of drug in an accurate amount.9. Tablets are formulated as a special release of products such as enteric or delayed release products.

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Disadvantages of tablet:1. It’s not suitable for poorly water-soluble or poorly absorbable drugs, less bioavailability.2. Enhances local irritant effect of some drugs or cause harm to the gastrointestinal mucosa.3.Some drugs resist compression into dense compacts.4. Hygroscopic drugs are not suitable candidate for compressed tablets.5. Drugs having bitter taste and unpleasant odor requires special treatment like coating or encapsulation which may increase their production cost.6. Drugs that are sensitive to oxygen or may also require special coating.

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General properties of Tablet dosage forms: 1.A tablet should have elegant product identity while free of defects like chips, cracks, discoloration, and contamination. 2.Should have sufficient strength to withstand mechanical shock during its production packaging, shipping and dispensing.3.Should have the chemical and physical stability to maintain its physical attributes over time 4.The tablet must be able to release the medicinal agents in a predictable and reproducible manner. 5.Must have a chemical stability over time so as not to follow alteration of the medicinal agents. 6.The appearance of the tablet should be elegant and its weight, size and appearance should be consistent

Tablet Ingredients (excipients)

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Tablets Excipients• Excipients are chosen in tablet formulation to perform a variety of functions, Like: i) For providing essential manufacturing technology functions (binders, glidants, lubricants may be added),ii)For enhancing patient acceptance (flavors, colourants may be added),iii)For providing aid in product identification (colourants may be added),iv)For Optimizing or modifying drug release (disintegrants, hydrophilic polymers, wetting agents, biodegradable polymers may be added),v)For enhancing stability (antioxidant, UV absorbers may be adde

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use: to make required bulk of the tablet . to provide better tablet properties such as to improve cohesion, to permit use of direct compression manufacturing to improve flow• Most common fillers in tablets:1. Lactose, sucrose, mannitol; frequently used, water soluble, improves tablet disintegration.2. Dicalcium phosphate dihydrate, insoluble in water, disintegrating agent is a must.3. Mannitol, dextrose, sucrose, 4. Lactose-anhydrous and spray dried lactose 5. Directly compressed starch-Sta Rx 1500 6. Hydrolyzed starch-Emdex and Celutab 7. Microcrystalline cellulose-Avicel (PH 101, 102).

1- Filler or diluent

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Requirements for a good filler:1. Chemically inert, biocompatible, cheap.2. Non-hygroscopic.3. Good biopharmaceutical properties. (water soluble or hydrophilic).4. Good technical properties (compactability )5.Have an acceptable taste.6. They must be free from all microbial contamination. 7. They do not alter the bioavailability of drug. 8. They must be color compatible. 9. They must be non toxic 10.They must be commercially available in acceptable grade11. They must be physically, chemically stable in combination with the drug

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Role: to ensure that the tablet, when in contact with a liquid, breaks up into small fragments, which promotes rapid drug dissolution.

Mode of action:  1. Facilitate water uptake into the pores of tablet,e.g. surface active agents 2.facilitate rupture of tablet by swelling during water sorption,e.g. Sodium –starch glycolate, Crosscarmelose- cross linked cellulose; modified cellulose, Ac-Di-Sol

3. Release of gases to disrupt the tablet structure, normally carbon dioxide, in contact with water. e.g. effervescent tablets. 

2- Disintegrant

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The Method of Disintegrant Addition:

1. Mixed with other ingredients prior to granulation & thusincorporated within the granules (intragranular addition).2. Mixed with the dry granules before the complete powder mix is compacted (extragranular addition).3. incorporated as both an intragranular and an extragranular portion.

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Commonly Used Disintegrants:

1. Starch: - conc. Up to 5-20% of tablet weight- Swell in contact with water2. Super disintegrants (e.g. crrosecarmelose, sodium starch glycolate (Explotab), Crosspovidone-cross linked povidone)Swells up to ten fold within 30 seconds when contact water.3. Clays: bentonite, Veegum 10 % level in coloured tablet only

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Role: Ensure that granules and tablets can be formed with the required mechanical strength ( glue that holds powders together to form granules ).- In dry powder form- In solution- Examples:starch paste 5-25% gelatin solution 10-20%, gum acacia, tragacanth, 10-25%Liquid glucose 50%,Cellulose derivativePolyvinylpyrrolidone 2% (PVP), PEG

3- Binder and adhesive

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Role: Lubricants prevent adherence of granule/powder to die wall and promote smooth ejection from the die after compaction, reduce inter particle friction and improve the rate of flow of the tablet granulation

• Mechanisms of Action :1. Fluid lubrication.2. Boundary lubrication.

4- Lubricant

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Disadvantages of lubricants1. Lubricants tend to be hydrophobic, so their levels (typically 0.3 – 2%) need to be optimized:– Under-lubricated blends tend to flow poorly and show compression sticking problems– Over-lubricated blends can adversely affect tablet hardness and dissolution rate, as well as tablet strength.

– To overcome these problems;- Optimum conc. < 2%- Addition of SAA (surfactant)

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Commonly used LubricantsA. Water- insoluble (Fatty acids-based) lubricant• Magnesium Stearate• Calcium Stearate• Stearic Acid, stearic acid salt• Talc• Silica derivative- colloidal silica such as Cab-O-Sil, Aerosil in 0.25-3% conc. • liquid Paraffin, propylene glycol (PG)

B. water-soluble lubricant- PEG 6000; less effective- Magnesium lauryl sulfate; good lubrication and surface wetting effect

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Role: Improve flowability of the powder They are added during direct compaction and to granulation before tabletting ( they reduce interparticulate friction)..• Common Glidants:1. Talc (at concentration 1-2 %).2. Colloidal silica (0.2 %).3. Corn Starch 5-10%

5- Glidants

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Role: Reduce adhesion between the powder andthe punch faces thus prevent particles sticking to the punches

• Many lubricants, such as magnesium stearate, have also antiadherent properties. Also talc and cornstarch, colloidal silica, can act as antiadherents.

6- Antiadherant

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Adsorbents are the agents that can retain large quantities of liquids. Therefore liquids like Vitamin E can be incorporated into tablets by addition of adsorbents .Most commonly used adsorbents in pharmaceuticals are anhydrous calcium phosphate, starch, magnesium carbonate, bentonite, kaolin, magnesium silicate, magnesium oxide and silicon dioxide. Generally the liquid to be adsorbed is first mixed with the adsorbent prior to incorporation into the formulation. Silicon dioxide when added can play as both glidant and an adsorbent role in the formula.

7- Adsorbent

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8- Flavour

Use: give the tablet a more pleasant taste or to mask an unpleasant one. (Chewable tablet)

• Flavouring agents are often thermolabile and so cannot be added prior to an operation involving heat.• They are often mixed with the granules as an alcohol solution.

Ex: Flavour oil

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9- Colorant

Uses: It is added to tablets to aid identification, Improve patient compliance.Mask of off color drugProduction of more elegant product.

All coloring agents must be approved and certified by FDA. Two forms of colors are used in tablet preparation – FD &C and D & C dyes. These dyes are applied as solution in the granulating agent or Lake form of these dyes. Lakes are dyes absorbed on hydrous oxide and employed as dry powder coloring.

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Example:Yellow 6- FD & C sunset yellowyellow 5- FD & C Tartrazinegreen 3- FD & C Fast Greenblue 1- FD & C Brilliant Blueblue 2 – FD & C Indigotinered 3- FD & C Erythrosine FD & C red 22 – FD & C Eosin Y

It is added during coating.• It can also be added prior to compaction. ( can be added as an insoluble powder or dissolved in the granulation liquid

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10- Sweetener

They are used in chewable tablet to exclude or limit the use of sugar in the tablets.e.g. Mannitol, lactose, sucrose, Dextrose 72% as sweet as sucrose.Saccharin, 500 times sweeter than sucrose. Disadvantage: has a bitter after taste and carcinogenic.Aspartame, largely replace saccharin., 180 times sweeter than sucroseDisadvantage: lack of stability in the presence of moisture.

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11. BuffersBuffers are added to maintain a required pH since a change in pH may cause significant alteration in stability. Most commonly used buffering agent in tablet formulation includes sodium bicarbonate, calcium carbonate, and sodium citrate.

12. AntioxidantsAntioxidants are added in tablet formulation: to protect drug from undergoing oxidation.

Chelators may also act as antioxidant.

Most commonly used antioxidants include ascorbic acid and their esters ,alpha-tocopherol , ethylene diamine tetra acetic acid , sodium metabisulfite , sodium bisulfite , Butylated Hydroxy Toluene (BHT) , Butylated Hydroxy Anisole (BHA) , citric acid , and tartaric acid .

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13. Chelating agents tend to form complexes with trace amount of heavy metal ions inactivating their catalytic activity in the oxidation of medicaments. Ethylenediamine tetracetic acid and its salts, Dihydroxy Ethyl Glycine, Citric Acid and Tartaric Acid are most commonly used chelators.

14. Dissolution EnhancersThey are the agents that alter the molecular forces between ingredients to enhance the dissolution of solute in the solvent. Fructose, Povidone, Surfactants are used as dissolution enhancer.

15. Dissolution RetardantsDissolution Retardants are incorporated into tablet formulation only when controlled release of drug is required. Waxy materials like stearic acid and their esters can be used as dissolution retardants.

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16. Wetting Agents in tablet formulation aid water uptake and thereby enhancing disintegration and assisting in drug dissolution.

Incorporation of anionic surfactant like Sodium Lauryl Sulphate (SLS) is known to enhance the dissolution. SLS improves permeation of drug through biological membrane since it destroys the path through which drug has to pass and thus minimizing the path length for the drug to travel. Wetting agents are mainly added when hydrophobic drug is to be formulated into tablet. SLS, Sodium diisobutyl sulfosuccinate are used as wetting agent in tablet formulation.

11. High Purity

API has to be in pure form otherwise impurities can catalyze series of chemical reactions, e.g. in case of hydrocortisone impurity of cupric ion causes oxidation of ketone functional group.

API should meet specifications given in the respective Pharmacopoeia.

2. High stability

The API should be stable against photolysis, oxidation, hydrolysis, etc. to keep the formulation a simple one. Sensitive particles require careful handling during manufacturing.

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3. Good compatibility with excipientsThere should not be any kind of interaction between excipient and API. Excipients have to be inert in nature. However there are some reported examples of API-excipient interactions like Lisinopril reacts with lactose and undergoes browning reaction leading to darkening on storage. So, avoid the use of lactose and use other fillers for API containing primary amine. To ascertain drug and excipient interaction, 1:1 mixture is prepared and stored under accelerated/ICH conditions. The amount of drug degraded shall be determined to select the most suitable excipient.

4. Optimum bulk powder propertiesBulk powder properties have to be optimum to:i) Prevent segregation.ii) Have optimum size tablet particularly for low potency-low density API.iii) Have good flow.

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5. Optimum and Uniform particle size-particle size distributionAPI should have uniform particle size and close particle size distribution because it has pronounce effect on uniformity of content, uniformity of weight, disintegration time, granule friability, drying rate kinetics of wet granulation, flowability, compressibility, stability, dissolution, bioavailability, etc. • The flow and compression characteristics are important from the viewpoint of industrial pharmacist. • Strong tablets are obtained if fine particles are used due to increase in surface area and surface energy.

6. Spherical shapeSpherical shaped particles exhibit good flow as compared to needle shaped particles. • Particles with irregular shape may exhibit hindered flow due to interlocking between particles. • This point is very important since it is directly related with weight of tablet and uniformity.

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7. Good flowabilityFlow is important for having uniformity of weight and uniformity of drug content. It can be measured using angle of repose, Carr’s index and Hausner ratio.

The methods used to improve flow are summarized belowi) Addition of glidantsii) Addition of fines: Addition of fines up to certain extent improves flow. This is because of filling of void space and decrease in surface roughness.iii) By wet granulation: Wet granulation gives regular sphere shaped granules and removes static charge, thus, flow property improved.

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8. Optimum moisture contentMoisture content has to be optimum because of the following reasons:i) Total lack of moisture results into brittle tablet.ii) Moisture affects flow, which in turn affects uniformity of content.iii) High amount of moisture gives stickiness, which will affect compaction. iv) Picking/sticking may be observed.

Moisture content can be controlled by:i) Use of anhydrous salts.ii) Use of non-aqueous solvent.iii) Optimum drying time.iv) Addition of finely powdered adsorbent like magnesium oxide

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9. Absence of static charge on surfaceIt is important because of the following reasons:i) Affects uniformity of dose and weight variation (flow worsen if attractive forces generated).ii) During mixing it may cause segregation and lead to non-uniformity of content if API and excipients are charged.iii) Charged API may adhere to feed frame and result into serious damage to tablet equipment.In order to remove charge certain treatments can be given like granulation, addition of diluents or lubricant, surface coating with help of colloidal silica, etc.

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10. Good organoleptic propertiesMany API are unpalatable and unattractive in their natural form. In such cases, tablet formulation require certain care. API has to be checked for colour and taste.

I. ColourIdeally API should be colourless. For coloured API, the following steps shall be considered:i) Select appropriate excipient to avoid mottling.ii) Incorporate API in smallest particle size.iii) Incorporate colour in dry form along with binder and activate mixture by addition of water or other activator.iv) Coating can be applied to conceal non-uniform colour (sugar coated multivitamin tablet

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II. TasteIt is very important for tablets because they come in contact with taste buds. Ideally API should have no taste. Sometimes it might have unpleasant taste like bitter e.g. Chloramphenicol, Clindamycin, etc. The following taste masking options can be tried:i) Use of prodrug to decrease API solubility in saliva or to reduce affinity for taste receptor e.g. Chloramphenicol Palmitate.ii) Sugar coating or film coating.iii) Addition of sweeteners like mannitol in case of fast dissolving tablet or chewable tablet.iv) Use of drug-ion exchange adsorbent in formulation.v) Drug β-cyclodextrin complex may exhibit good taste profile and good compressibility as well.

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Excipients Function

Diluent Diluents make the required bulk of the tablet when the drug dosage itself is inadequate to produce tablets of adequate weight and size

Binder Binders are added to tablet formulations to add cohesiveness to powders, thus providing the necessary bonding to form granules, which under compaction form a cohesive mass or a compact which is referred to as a tablet.

Disintegrants A disintegrant is added to most tablet formulations to facilitate a breakup or disintegration of the tablet when placed in an aqueous environment.

TABLE.1. EXCIPIENT WITH THEIR FUNCTIONS IN TABLET FORMULATION

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Antifrictional Agents

Function

Lubricant Lubricants are intended to reduce the friction during tablet formation in a die and also during ejection from die cavity.

Antiadherants Antiadherents are added to reduce sticking or adhesion of any of the tablet granulation or powder to the faces of the punches or to the die wall

Glidants Glidants are intended to promote the flow of tablet granulation or powder mixture from hopper to the die cavity by reducing friction between the particles.

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MISCELLANEOUS

Function

Wetting agent Wetting agents are added to tablet formulation to aid water uptake during disintegration and assist drug dissolution. 

Dissolution retardant

Dissolution retardants as the name suggest, retards the dissolution of active pharmaceutical ingredient(s).

Dissolution enhancer

Dissolution enhancers as the name suggest, enhance the dissolution rate of active pharmaceutical ingredient(s).

buffers Buffers are added to provide suitable micro environmental pH to get improved stability and / or bioavailability.

Adsorbents Adsorbents are capable of retaining large quantities of liquids without becoming wet; this property of absorbent allows many oils, fluid extracts and eutectic melts to be incorporated into tablets.

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Excipients Function

Antioxidants Antioxidants are added to maintain product stability, they act by being preferentially oxidized and gradually c.onsumed over shelf life of the product

Chelating agents

Chelating agents are added to protect against autoxidation; they act by forming complexes with the heavy metal ions which are often required to initiate oxidative reactions.

Colours Colours are added to tablet formulation for following purposes: to disguise off colour drugs, product identification and for production of more elegant product.

Flavours Flavours are added to tablet formulation in order to make them palatable enough in case of chewable tablet by improving the taste.

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1- Disintegrating tablets• Most common type is intended to be swallowed and releases the drug in a relatively short time after disintegration and dissolution thus fast & complete drug release in vivo (conventional or plain tablets).

• A disintegrating tablets include the following types of excipients: filler (if the dose of drug is low), disintegrant, binder, glidant, lubricant and antiadherent.

Steps of drug release from disintegrating tablets

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Conventional tablet may be single layer or multilayer. Multilayer tablets are prepared by repeated compression of powders and are made primarily to separate incompatible drugs from each other.Tablet, multilayer: This is a solid dosage form that contains medicinal substances that have been compressed to form a multiple-layered tablet or a tablet-within-a-tablet (the inner tablet being the core and the outer portion being the shell).

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2- Chewable tablets• They are chewed so mechanically disintegrated in the mouth.• The drug is not dissolved in the mouth but swallowed and dissolves in the stomach or intestine., • and it does not leave a bitter or unpleasant after-taste.

Advantages of chewable tablets:1. Quick and complete disintegration of the tablet - and hence obtain a rapid drug effect after swallowing and dissolution. e.g. antacid tablets.2. Facilitate the intake of the tablet for elderly and children who have difficulty in swallowing; e.g. vitamin tablets.3. Can be taken when water is not available.

Mannitol is normally used as a base due to low hygroscopy and more importantly, it gives pleasant, cooling sensation.

They are similar in composition to conventional tablets except that a disintegrant is normally not included.

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3. Lozenges• They are tablets that dissolve slowly in the mouth and so release the drug dissolved in the saliva.• They can thus be described as slow-release tablets for local drug treatment.

Use of lozenges:Local medication in the mouth or throat in common cold, to treat cough by: antiseptics, antibiotics, demulcents, antitussive agents or astringents.

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Lozenges are usually contain:

1.They are similar in composition to conventional tablets.2. Disintegrants are not included in Lozenges tablets.3. Colour, sweetener and flavour.4.High concentration of Fillers which are mainly sugars, such as glucose, sorbitol or mannitol.5. Other additives (binder and filler) must have pleasant taste.

6. Common binder used in compressed lozenges is gelatin

7. The tablet generally contains sucrose or lactose and gelatin solution to impart smooth taste

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Hard candy lozenges, e.g. Halls®, may be made by molding into a hard candy lozenges using candy making machine, For thermostable drugs, warm, highly conc. flavored syrup is used as a base and the lozenges are formed by molding and drying.

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4- Sublingual and buccal tablets

Used for drug release in the mouth followed by systemic uptake of the drug.• Rapid systemic drug effect can thus be obtained without first-pass liver metabolism.• Sublingual tablets are placed under the tongue and buccal tablets are placed in the side of the cheek.• They are often small and porous, to facilitate fast disintegration and drug release.

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Sublingual tablets are placed under the tongue, Example:Nitroglycerin sublingual tablet; it exerts its action within two minutes for rapid relief of "Angina pectoris" attack, because the sublingual area is rich in blood supply.• Also other cardiovascular drugs, barbiturates, and vitamins are prepared as sublingual tablet dosage form

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Buccal tablets are placed in the side of the check for absorption through oral mucosa.• N.B. Buccal tablets may be also prepared for their local application.

Buccal tablets are intended to be placed on the gum or in the cheek to allow the drug absorbed. • Because the medicine can be held for a longer period of time on the gum, medicines which need to be released at a slower rate can be given via this route. • This route is used for anti-nausea drugs and nicotine replacement gums.

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5. Dispersible tablet These tablets disintegrate either rapidly in water, to form a stabilized suspension, or disperse instantaneously in the mouth to be swallowed without the aid of water. It’s preferred for pediatric patients who cannot swallow a solid dosage form and the AP I is unstable if formulated in liquid formulation. Also helpful for patients having prolonged illness who are prone to nauseatic sensations if they have to swallow a tablet. Faster onset of action as compared to standard compressed tablet. The common examples of API formulated in this dosage form are analgesics e.g., aspirin, ibuprofen, etc.

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6- Melts tabletMelt tablets are placed on the tongue and are designed to dissolve directly in the mouth's saliva. The contents are then swallowed with saliva and consequently water does not have to be administered with these medicines. This is particularly useful in patients who are at risk of aspiration and therefore unable to swallow tablets with water concurrently.

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7- Oro-dispersible tabletsOro-dispersible tablets are similar to melts and are designed to disperse in the mouth and to be washed down with saliva. Like sub-lingual, buccal and melts, oro-dispersible products require an adequate amount of saliva production

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8- Vaginal tabletsVaginal tablets are compressed tablets meant for insertion into vaginal cavity and designed to undergo slow dissolution and drug release in the cavity. Sometimes vaginal suppositories or pessaries are prepared by compression which are known as vaginal tablets. These are usually ovoid or almond in shape to facilitate the retention in vagina. It is used to release antibacterial agents, astringents and antiseptics to treat vaginal infection or possibly to release steroids for systemic absorption. Soluble additives are used for the preparation of these tablets. These are often formulated with buffering agent to provide favorable pH to stimulate the action of the given medicament(s).

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Tablets used to prepare solution1. Soluble tablet• Soluble tablets are uncoated or film- coated tablets.• Tablets are solids of uniform shape and dimensions, usually circular, with either flat or convex faces.• Water soluble tablets are intended for application after dissolution in water and contain an active ingredient should be totally soluble in water at used concentrations. •All the excipients used to formulate these tablets are required to be completely soluble in water

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2- Effervescent tabletsEffervescent tablets are dropped into a glass of water before administration, during which carbon dioxide is liberated.CO2 facilitates tablet disintegration and drug dissolution; the dissolution of the tablet should be complete within a few minutes.

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Advantages of effervescent tablets:1. Rapid drug action, e.g. analgesic drugs .2. Facilitate the intake of the drug, e.g. vitamins.3. Fast drug bioavailability

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Effervescent tablets are usually contained:

 

Carbonate or bicarbonate and a weak acid such as citric or tartaric.

Flavor and a colourant

A water-soluble lubricant is preferable

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Effervescent tablets should be:protected from moisture, so that a special package is needed;each tablet is completely covered with aluminum foil and kept in a water-proof container, often including a desiccant. Effervescent tablets may be packed in blister packs.

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3. Hypodermic tablet These tablets contain one or more readily water soluble ingredients and are intended to be added in water for injection of sterile water to form a clear solution which is to be injected parenterally. They were widely used by rural physician due to its portability. One bottle of sterile water was carried by the doctor to prepare many types of injectables. It can be used for medicaments whose stability in water is very poor.

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ORAL TABLETS FOR INGESTION These tablets are meant to be swallowed intact along with a sufficient quantity of potable water. Exception is chewable tablet. Over 90% of the tablets manufactured today are ingested orally. This shows that this class of formulation is the most popular world wide and the major attention of the researcher is towards this direction.

Standard compressed tabletsMultiple compressed tablets     I. Compression coated tablet     II. Layered tablet    Modified Release tabletDelayed action tabletTargeted tablet     I. Floating tablet    II. Colon targeting tabletChewable tablet Dispersible tablet

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TABLETS USED IN THE ORAL CAVITY The tablets under this group are aimed release API in oral cavity or to provide local action in this region. The tablets under this category avoids first-pass metabolism, decomposition in gastric environment, nauseatic sensations and gives rapid onset of action. The tablets formulated for this region are designed to fit in proper region of oral cavity.

Lozenges and troches Sublingual tabletBuccal tabletMouth dissolved tablet

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TABLETS ADMINISTERED BY OTHER ROUTES These tablets are administered by other route except for the oral cavity and so the drugs are avoided from passing through gastro intestinal tract. These tablets may be inserted into other body cavities or directly placed below the skin to be absorbed into systemic circulation from the site of application

Vaginal tabletImplants

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TABLETS USED TO PREPARE SOLUTION The tablets under this category are required to be dissolved first in water or other solvents before administration or application. This solution may be for ingestion or parenteral application or for topical use depending upon type of medicament used.

Effervescent tabletHypodermic tabletSoluble tablet