TYPES OF TABLETS

Generally, tablets are classified by their route of administration/function.
Primary classification of tablets can be given as follow:
I) Tablets ingested orally

1. Standard compressed tablets
2. Multiple compressed tablets
3. Delayed action and enteric coated tablets
4. Film coated tablets
5. Sugar coated tablets

II) Tablets used in the oral cavity

1. Buccal and sublingual tablets
2. Troches and lozenges
3. Dental cones

III) Tablets administered by other routes

1. Implantation tablets
2. Vaginal tablets

IV) Tablets used to prepare solution

1. Effervescent tablets
2. Dispensing tablets
3. Hypodermic tablets
4. Tablet triturates

Standard coated tablets

Methods of manufacturing: wet granulation, double compaction or direct compression.

These tablets usually rapidly disintegrate and releases drug.
Drugs intended for local effects in GIT: Tablets contain water insoluble drug. E.g. adsorbents and antacids.
Drugs intended to produce systemic effect: Drugs possess some aqueous solubility. Their effect occur by disintegration of tablet --> formation of small fragments--> dissolution of drug in fragments --> then absorption of drug through membrane --> distribution in the body.

Dissolution--> surface related phenomenon
As particle size decreases--> surface area increases.
As surface area increases--> rate of dissolution increases.

Multiple compressed tablets
These are layered and compression coated tablets. Their types are i) two or three layered tablets, ii) a tablet within a tablet, iii) a tablet within a tablet within a tablet.
Reasons for preparation of such tablets:

1. To separate physically and/or chemically incompatible ingredients.
2. To produce repeat action or prolonged action product.
3. In multiple compressed tablet, one layer provides initial dose by rapid disintegration and other layer then slowly disintegrate to release drug in intestinal environment.

Limitation: unpredictable and uncontrolled release of drugs is achieved. Action of product depends on gastric emptying.

Delayed action and enteric coated tablets

Delayed action tablets are intended to release drug after some time (a delay) or after the tablet passes certain passage in GIT.

Example: Enteric coated tablets. These are intended to release the drug in intestinal environment.
Purpose: 1) to protect acid labile drugs from degradation, 2) to exert local action in the intestine e.g. in intestinal worm or parasite infection.

Sugar coated tablets
Sugar coating (sugar syrup coating) is usually performed to mask the unpleasant taste and odor of the drug. Here a smaller tablet is compressed and sealing is done by coating it with enteric coating or cellulose materials. 
Then it is coated with multiple layers of syrup and finally polished.

Film coated tablets
A solution of polymer(s) in an organic solvent(s) is sprayed over tablets in order to form a thin film on the tablets. Film coating provides mechanical strength to tablets, masks the unpleasant odor and taste.

Chewable tablets
These are intended to be chewed in mouth prior to swallowing. E.g. antacids. Antacids are high dose & bigger tablets which cannot be swallowed easily. In this case preparation of  chewable tablets is feasible. Bitter tasting drugs cannot be formulated as chewable tablets. 

Buccal and sublingual tablets (systemic effect)
These tablets are intended to be held in the mouth where they release drug which is absorbed through oral mucosa. 
Buccal tablets--> held between cheek & gums or in cheek pouch.
Sublingual tablets--> held beneath the tongue.
The absorption from oral mucosa releases drug directly into the general circulation avoiding first pass metabolism.
Advantages:
a. Avoids contact with gastric acid thereby avoiding decomposition of certain drugs. E.g. certain steroids and hormones.
b. Rapid onset of drug action occurs e.g. vasodilator drugs.
c. First pass effect ( hepatic drug metabolism) is avoided.
These tablets do not disintegrate but slowly dissolve in mouth for the period of 15 to 30 minutes.
Bland excipients (which do not stimulate salivation) are selected to avoid swallowing of drug.

Troches and lozenges (Local effect)
These tablets are also held in oral cavity but their actions are local in mouth or throat.
E.g. Formulation for sore throat or coughing treatment.
These contain local anesthetics, various antiseptics & antibacterial agents, demulcents, astringents & antitussives.
Lozenges are commonly known as cough drops.

Lozenges are hard candy tablets prepared by fusion or candy molding process while troches are prepared by compression as other tablets.

Dental cones
These are placed in an empty socket in gums following tooth extraction in order to avoid bacterial infection or to stop bleeding.
Drugs having antibacterial actions or with astringent/coagulant properties are formulated for this purpose.

Implantation tablets
These are also known as depot tablets and are designed for subcutaneous implantation in animals or man.
Purpose: to provide prolonged drug effect for one month to a year.
These tablets are small, cylindrical or rosette shaped & are not more than 8mm in length.
Safety problems:
a. Need for a surgical technique to discontinue therapy.
b. Tissue toxicity problems in the area of the implantation site.
These are mostly used in the animals to administer growth hormones to food producing animals.
Ear of the animal is used for such implants.

Vaginal tablets
Vaginal tablets/ inserts are designed to undergo slow dissolution and drug release in the vaginal cavity.
These are ovoid or pear shaped tablets.
Drug categories--> antibacterial, antiseptics, astringent or steroids.

These were the general types of tablets classified according to the route of administration.

If you want me to add information about any other type of tablet or detail about any one of the above,  leave a comment! 😊