Classifications of the tablets.

1. Orally ingested tablets.

• Compressed tablets.
• Multiple compressed tablets/layered tablets
• Sustained action tablets
• Enteric coated tablets.
• Gelatine coated tablets.
• Sugar coated tablets.
• Film coated tablets.
• Chewable tablets.

2. Oral cavity uses tablets.
   • Buccal Tablets
   • Sublingual tablets
   • Lozenges
   • Dental cones
3. Tablets administered by other routes.
   • Implantation tablets
   • Vaginal tablets
4. Tablets used to prepare solutions.
   • Effervescent tablets
   • Dispensing tablets
   • Hypodermic tablets
   • Tablet triturates
5. Based on the action (Modified tablets).

• Sustained release.
• Extended-release.
• Fast dissolving.
• Double layered

Ingredients used for the tablet’s preparations.

1. API (active pharmaceutical ingredients)— These are the actual chemical compound which reacts with the body constituents and shows their effects on required area.
2. Excipients/additives— These are the inert material which are helps in preparation of tablets and maintain their originality. Excipients does not have any properties to altered the chemical reaction/composition of the API.

Functions of excipients.

• Impart weight, accuracy, & volume.
• Improve solubility
• Increase stability
• Enhance bioavailability
• Modifying drug release
• Assist product identification
• Increase patient acceptability
• Facilitate dosage form design.

Some additives are.

• Diluent / Filler— API are present in the smaller quantity in the tablets which are not enough to produce the bulk of tablets so, diluents/filler are used to make the bulk of tablets. Examples— Sorbitol, mannitol, dextrose, calcium sulphate dihydrate, anhydrous lactose etc.
• Binder and adhesive— They impart a cohesiveness to the tablet formulation (both direct compression and wet– granulation method) which ensures the tablet remaining intact after compression. They improve the free-flowing qualities by the formation of granules of desired size and hardness. Examples— Acacia, tragacanth, cellulose, starch, gelatine, glucose etc.
• Disintegrants—It facilitate the disintegration/breakup properties of the tablets in the GIT after the administration. Examples— Starch, alginate, cellulose etc.
• Lubricants— Lubricants are intended to prevent adhesion of the tablet materials to the surface of dies and punches, reduce inter particle friction and may improve the rate of flow of the tablet granulation. Example: Stearic acid, Magnesium stearate, Talc, PEG (Polyethylene glycols), Surfactants.
• Glidants— Glidants intended to promote flow of granules or powder material by reducing the friction between the particles. Example: Corn Starch, Talc, Silica derivative.
• Colouring agents— Colour helps in the product identification along with masking the undesirable colour. Example— FD & C yellow 5‐ Tartrazine, FD & C green 3‐ Fast Green, FD & C blue 1‐ Brilliant Blue etc.
• Flavouring agents— Example— flavour oil is used
• Sweetening agent—Example— Mannitol, Saccharin, aspartame etc.

Preparation of the tablets— Prepare by the three methods.

1. Wet granulation method— It is the most common and widely used method. Steps are follows as-

Raw material—weighing—screening—wet massing—sieving/milling—drying—screening—mixing—compression.

2. Dry granulation method— This method is used for tablet preparation, in case tablet ingredients are highly sensitive to moisture, or unable to with stand elevated temperatures during drying, slugging may be used to form the granules. Steps are follows as-

Raw material—weighing—screening—mixing—slugging—milling—screening—mixing—compression.

3. Direct compression— Direct compression involves direct compressing the powdered material into tablets. Steps are follows as-

Raw material—weighing—screening—wet massing—mixing—compression.

Factors affecting during tablet manufacturing (Defects)/(Imperfections).

1. Formulation related— Sticking, picking, binding.
2. Tablets processing— Capping, lamination, cracking, chipping.
3. Machine— Double Impression.

Uncoated tablets

Compressed tablets— These are rougher, may be more difficult to swallow and often leave a bad taste in the mouth swallowed. They are made from powdered, crystalline or granular materials, alone or in combination with suitable excipients.

These are standard uncoated tablets made by compression using wet granulation, direct compression or double compression. It provides rapid disintegration and drug release. They are mostly intended to exert local action in GIT. It typically includes water insoluble drugs such as antacid and adsorbents.

Multiple compressed/layered tablets— These are compressed tablets made by more than one compression cycle. Such tablets are prepared by compressing additional tablet granulation on a previously compressed granulation. The operation may be repeated to produce multilayered tablets of two or three layers.

To avoid incompatibility, the ingredients of the formulation except the incompatible material are compressed into a tablet and then incompatible substance along with necessary excipients are compressed over the previously compressed tablet.

Coated tablets

This tablet readily lends itself into a repeat action. Outer layer provides the initial dose while the inner core releases the drug later on. Hence, it is useful for releases of two active pharmaceutical ingredients (APIs), one immediate release formulation which is entrapped in coat and the other sustained release formulation entrapped in the core. Colton 232, Stock 538 and Manesty Drycota 900 are equipment’s utilized for preparing compression coated tablets

• Enteric coated tablets— The enteric coated tablets are coated with the material resistant to acidic medium (stomach environment) and hence are not able to release drug in stomach. Whereas, it easily releases drug in intestine (alkaline) media. Hence, drugs have to pass through stomach and the time of release of drug is delayed and hence called delayed action tablet
• Sugar coated tablets— These are compressed tablets containing a sugar coating. Such coatings are done to mask the bitter and unpleasant odour and the taste of the medicament. The sugar coating makes the tablet elegant and it also safeguard the drug from atmospheric effects. The patient acceptability also increases due to the sweet taste of tablet. Widely utilized in preparing multivitamin and multivitamin mineral combination
• Film coated tablets— The compressed tablets having a film coating of some polymer substance, such as hydroxy propyl cellulose, hydroxy propyl methyl cellulose and ethyl cellulose. The film coating protects the medicament from atmospheric effects. Film coated tablets are generally tasteless, having little increase in the tablet weight and have less elegance than that of sugar-coated tablets.
• Gelatine coated tablets— The gelatine coating imparting a low coefficient of friction and thus an increased slipperiness and swallowability to the tablet without the stickiness or thickness.

Various modified tablets

Sustained release— Sustained release dosage form is defined as well characterized and reproducible dosage form, which is designed to control drug release profile at a specified rate to achieve desired drug concentration either in blood plasma or at target site.

Advantages

• Reduced see-saw fluctuations.
• Total amount of dose decreases.
• Improved patient compliance.
• Increased safety of drugs

Disadvantages

• Chances of dose dumping.
• Dose retrieval is difficult.
• High cost of formulation.
• Need for additional patient education.
• Reduced potential for accurate dose adjustment

Extended-release—

Extended-release tablets and capsules are commonly taken only once or twice daily. Typically extended-release products provide an immediate release of drug which promptly produces the desired therapeutic effect which then is followed by gradual and continual release of additional amounts of drug to maintain this effect over a predetermined period of time. The sustained plasma drug levels provided by extended- release drug products often eliminate the need for night dosing, which provides benefit to the patient.

Advantages

• Reduction in drug blood level fluctuations
• Frequency reduction in dosing
• Enhanced patient convenience and compliance
• Reduction in adverse side effects
• Reduction in overall health care costs

Disadvantages-

• Loss of flexibility in adjusting the drug dose and/or dosage regimen.
• Increased risk of sudden and total drug release or dose dumping due to failure of technology of the dosage unit.

Fast dissolving tablets — A tablet that dissolve or disintegrates quickly in the oral cavity upon the contact with saliva, resulting in solution or suspension of administered medicine.

• Sub lingual tablets are also fast dissolving, when these are contacts with the sublingual mucosa then dissolve rapidly and shows their actions.
• Effervescent tablets along with the active medicament contain ingredients like sodium bicarbonate, citric acid and tartaric acid which react in the presence of water liberating carbon dioxide and producing effervescence leading to disintegration of the tablet, thus fastens solution formation and increase the palatability.
• Dispersible tablets are uncoated or film coated tablets intended to be dispersed in water before administration giving a homogeneous dispersion. Typically, a dispersible tablet is dispersed in about 5 to 15 ml of water (e.g., in a tablespoonful or a glass of water) and the resulting dispersion is administered to the patient.

Double layered/bilayer tablets— Bilayer tablets are novel drug delivery systems where combination of two drugs in a single unit having different release profiles can be delivered. Bilayer tablets improve patient compliance, prolong the drug(s) action and can deliver two incompatible drugs in a single formulation. Bilayer tablets have one layer of active ingredient for immediate release and a second layer for delayed release, either as a second dose or in an extended-release fashion.