A tablet is a pharmaceutical dosage form. It comprises a mixture of active substances and excipients, usually in powder form, pressed or compacted into a solid .

The excipients can include binders, glidants (flow aids) and lubricants to ensure efficient tabletting; disintegrants to promote tablet break-up in the digestive tract; sweeteners or flavours to enhance taste; and pigments to make the tablets visually attractive .

A polymer coating is often applied to make the tablet smoother and easier to swallow, to control the release rate of the active ingredient, to make it more resistant to the environment (extending its shelf life), or to enhance the tablet's appearance.

Tablets

Tablets can be classified according to their drug-release characteristics into:

I. According to drug release rate from the tablet (USP classification):

a- Immediate-release tablet:The tablet is intended to be released rapidly after administration, or the tablet is dissolved and administered as solution. It is the most common type and includes1- Disintegrating tablet (conventional or plain tablet)2- Chewable tablets3- Effervescent tablets4- Sublingual and Buccal tablets5- Lozenges6- Soluble tablets

b- Modified-release tablet:They have release features based on; time, course or location.-They should normally be swallowed intact. -Different excipients than immediate release tablets.-The drug is released from an extended-release tablet slowly at a nearly constant rate.

Delayed-release tablets

The drug is liberated from the tablet some time after administration.After this period has elapsed, the release is normally rapid.e.g. Enteric tablet, for which the drug is released in the upper part ofthe small intestine after the preparation has passed the stomach.

Multiple compressed tablets

-Tablet within a tablets: core and shell -Multilayer tablet

Immediate-release tablet:1- Disintegrating tablet (conventional or plain tablet)

- Disintegrating tablet is the most common type of tablets that is intended to be swallowed and to release the drug in a relatively short time thereafter, by disintegration and dissolution (fast and complete drug release in vivo).- It includes normally the following type of excipients; filler(with low dose drug), disintegrant, binder, glidant, lubricant and antiadherent.

- Tablet disintegration may be affected by;1- Choice of the excipients.2- Production conditions during manufacture.- 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.

Bilayer tablets

Steps of drug release from disintegrating tablets

2 -Chewable tablets

Chewable tablets are to be chewed and thus mechanically disintegrated in the mouth, so NO DISINTEGRANT IS INCLUDED IN ITS COMPOSITION.Flavoring, sweetening and coloring agents are important.Sorbitol and mannitol are common examples of fillers in chewable tablets, (mannitol has negative heat of solution which results in cooling effect and also has sweetening action)

Advantages of chewable tablets:- Provide quick and complete disintegration of the tablet and thus obtain a rapid drug effect after swallowing and dissolution.- Easy administration, especially for infants and elderly people.- Could be administered when water is not available.Examples for chewable tablets are;- Chewable Aspirin tablets (for children in the treatment of rheumatoid and to prevent clot formations in adults)-Chewable Antacid tablets

3 -Effervescent tablets:

Effervescent tablets are uncoated tablets generally containing acid substances and carbonates or hydrogen carbonates which react rapidly in the presence of water to release carbon dioxide. They are intended to be dissolved or dispersed in water before administration.

Effervescent tablets are dropped into a glass of water before administration during which CO2 is liberated. This facilitates tablet disintegration and drug dissolution; the tablet disintegrationshould be complete within few minutes.(Effervescence is a special mechanism for disintegration)CO2 is created by the reaction between carbonate or bicarbonate and a weak acid such as citric acid or tartaric acid.

Effervescent tablets are dropped into a glass of water before administration, during which carbon dioxide is liberated.

facilitates tablet disintegration and drug dissolution; the dissolution of the tablet should be complete within a few minutes.

Uses of effervescent tablets:1. Rapid drug action, e.g. analgesic drugs .2. Facilitate the intake of the drug, e.g. vitamins.

After Dissolution oftablets

buffered water solution will

be obtained

Temporarily increases the pH of the stomach

Rapid emptying of the stomach and shortening the residence time

Drug-induced gastric irritation can be avoided (short residence

time) e.g. aspirin tablets

fast drug bioavailability (As drugs are absorbed more effectively in the small intestine than in the stomach)

e.g. analgesics

As absorption of aspirin in the stomach can cause irritation

Advantages of effervescent tablets:1. To obtain rapid drug action, for example analgesics and antacids.2. To facilitate drug intake, for example vitamins.3. They are convenient, easy to use, premeasured dosage form as compared with the powdered dosage forms.4. They cannot spill as the powdered preparations can.5. They can be individually packaged to exclude moisture, thereby avoiding the problem of product instability of the unused contents during storage.

Effervescent tablets often include a flavor and a colorant.Effervescent tablets are prepared by direct compression or dry granulation.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.

Effervescent tablets package

Effervescent tablets usually contain

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

The amount of sodium bicarbonate in an effervescent tablet is often quit high (about 1 gram)

Flavor and acolourant

N.B. Binder and disintegrant are normally not included in the composition

A water-solublelubricant is

preferable in order to avoid a film of

hydrophobic lubricant on the

surface of the water after tablet dissolution

4 -Sublingual and Buccal tablets:

They are used for drug release in mouth followed by systemic uptake of the drug.

A rapid systemic drug effect can thus be obtained without first-path liver metabolism, because the drug diffuses into the blood, directly through tissues under the tongue in case of sublingual tablets and through oral mucosa in case of buccal tablets.

They are often small and porous, the latter facilitating fast disintegration and drug release.

Sublingual tablets are placed under the tongue.

Ex. 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. Nitroglycerine suffers from first-pass metabolism if taken orally. Also other cardiovascular drug, barbiturates, and vitamins are prepared as sublingual tablet dosage form.

Buccal tablets are placed in the side of the cheek for absorption through oral mucosa.N.B. Buccal tablets may be also prepared for their localapplication.

5-LozengesThey are tablets that dissolve slowly in the mouth and so release the drug dissolved in the saliva.Lozenges may be used for;- Local medication for mouth or throat, e.g. local anesthetics, antiseptics and antibiotics. - Systemic drug uptake.

Compressed lozenges:are made by using tablet machine with large and flat punches, with high pressure is applied to produce hard tablets, so that they dissolve slowly in mouth.

Bradoral® compressed loyenges for treatment of sore throat

NO DISINTEGRANT IS INCLUDED IN COMPRESSED LOZENGES COMPOSITION

Other additives (binder and filler) must have pleasant tasteor feeling during dissolution. High concentration of fillers which are mainly sugars as glucose, sorbitol or mannitol. High concentration of binder is used. Common binder used in compressed lozenges is gelatin.

6 -Soluble tablets

Soluble tablets are uncoated or film-coated tablets. They are intended to be dissolved in water before administration.The solution produced may be slightly opalescent due to the added excipients used in the manufacture of tablets.

Modified-release tablet

1-Extended-release tablet 2- Delayed-release tablet

Allowing the reduction in dosing frequency.

Drug release is delayed due to physiological conditions e.g. pH (a lag period followed by normal release).

The best example is enteric coated tablets, the drug is released in the upper part of the small intestine after which the preparation has passed the stomach.

If the drug is sensitive to acid, or is irritant to the stomach lining, an enteric coating can be used.

Cumulativeamount of drug released

Immediate releasetablet

Del

ayed

rele

ase

tabl

et

Extended releasetablet

Time

Slowly release the drug in the GIT at a constant rateProlonged release and sustained release (12-24 hours)

-The aim is to increase the time period during which a therapeutic concentration level in the blood is maintained

-To increase the release time for drugs that can cause local irritation in the stomach or intestine if they are released quickly (iron salts)

II. According to method of manufacturing:a- Compressed tablet:

It is obtained by compressing uniform volume of particles using "Tablet compression machine". It's used for large scale production.

b. Molded tablets:

Molding means shaping and hardening of semi- solid mixture of drug and excipients.It is obtained using ʺtablet mold“. It is restricted for small-dose tablet and for small scale production.

Tablet mold

Tablets administered by other routes

These tablets are administered by other routes except for the oral cavity and so the drugs avoided from passing through the gastrointestinal 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 tablets

•These tablets undergo slow dissolution and drug release in the vaginal cavity of women. The shape kept ovoid or pear shaped to facilitate retention in vagina .

•These tablets release generally antibacterial, antiseptics or astringents to treat vaginal infections or release steroids for systemic absorption.

•The tablet should be made compatible with plastic tube inserters which are designed to place the tablet in the upper region of vaginal tract.

Implants

•These tablets are inserted into subcutaneous tissue by surgical procedures where they are very slowly absorbed over a period of one month or one year.

•A special injector with a hollow needle and plunger is used to administer the rod shaped tablet for other shapes surgery is required. The tablets may be pellets cylindrical or rosette shaped with diameter not more than 8 mm. They are sterile formulation without excipients and made hard with large particle size to achieve gradual drug release. Mainly, these tablets are prepared to deliver growth hormones.

Coated tabletsDefinition:

Coated tablets are defined as tablets covered with one or more layers of mixtures of various substances with theintention of (adding) conferring benefits and properties to the dosage form over the uncoated one.

Film-coated tabletsSugar-coated tabletsPress-coating (Enteric-coated tablets)

Sugar coated tablets:Sugar coated tablets:1- Protect tablets from moisture1- Protect tablets from moisture2- Mask odor and flavor2- Mask odor and flavor3- Elegance3- Elegance

Film coated tablets: Film coated tablets:1- Thin film coat1- Thin film coat2- Soluble or insoluble polymer film2- Soluble or insoluble polymer film Enteric coated tablets: Enteric coated tablets: compressed tablets coated with substances that resist solution in gastric fluid but disintegrate in the intestine. It can be used for tablets containing drug substances which are inactivated or destroyed in the stomach, for those which irritate the mucosa or as a means of delayed release of the medication.