Tablets: Types and Classification

As per Unites States Pharmacopeia (USP) "A tablet is a solid dosage form containing a medicinal substance or substances, usually prepared with the aid of suitable pharmaceutical excipients. It is intended for oral administration and is typically made by compression of powder into a hard, compact unit.""

Compressed Tablets

These are simple tablets, manufactured through compression of medicinal agents (drugs), with other formulation additives or excipients i.e. diluents, binders, disintegrating agents etc.

Multiple Compressed Tablets

These tablets are prepared by more than one compression of powder or granules. These are also called Layered tablets. These tablets are prepared by initial compression of powder to form one layer of the tablet.

Then additional Powder or granules added over that first layer, and again compressed. Due to this second compression, another layer of tablet Forms over the first layer, and produces multiple layered tablets.

This separation achieved due to physical and chemical incompatibilities between two or more drug components or to achieve different release pattern of drug from different tablet layers.

Enteric Coated Tablets

Enteric coated tablets have delayed drug release pattern. They are coated with polymer (Cellulose Acetate Pthalate, Hydroxy propyl methyle cellulose etc.) in such a way, that they can Pass the stomach without disitegration and can protect the incorporate drug from acidic environment of Stomach.

Enteric coated tablet passes the stomach undegraded and can disintegrate in intestine (at basic pH) and release the drug.

Film Coated Tablets

Film coated tablets are compressed tablets, but coated by a thin layer of any polymer, usually coloured. Film coating is achieved to mask the unpleasant taste and odour of any bitter drug. Film coating is also Used to change the release pattern of any drug.

Chewable Tablets

These tablets are rapidly disintegrating when chewed or break through teeth in oral cavity. These tablets are Smooth surfaced and having creamy base, which is generally flavoured and coloured.

These tablets are specially designed for the elderly and children’s patients, which have problems in swallowing the tablets. e.g. Some Antacid tablets

Buccal Tablets

These tablets are prepared by mixing the powdered drug with polyacrylic acid or cellulose derivatives and any other excipients (if required) and then compression. These tablets are intended to place between cheek and teeth and dissolve in buccal cavity or buccal pouch to release the drug in mouth, which is absorbed through oral mucosa. These tablets are prepared with objective to protect the drug from acidic environment of stomach.

Sublingual Tablets

These tablets are placed under the tongue and cannot be chew or swallowed. Sublingual tablets dissolves promptly or rapidly under the tongue and instantly release the drug, which is readily absorb through fine blood capillaries found under the tongue.

These tablets provide higher and rapid bioavailability of therapeutic drugs.

Troches and Lozenges

These are disc shaped preparations, generally having drugs with flavouring agents in a hard candy or sugar base. These are intended to dissolve slowly in mouth. Generally used for local anesthetics, Antibacterial agents, anti-tussive agents.

Dental Cones

Dental cones are compressible tablets, meant for placing them in the empty socket of extracted tooth. They are used for local effect, i.e. for delivery of antibacterial drugs to prevent bacterial infections at gums, or for astringent action to prevent bleeding.

Implantable Tablets

These are long-acting sterile tablets, and are designed to release the drug for a prolong Time, even for some months and years. These are specially designed tablets, formulated with drug release rate controlling excipients and polymers.

These tablets are placed under the skin or inserted subcutaneously by means of minor surgery.

Vaginal Tablets

These are also called vaginal inserts. These are uncoated, oval or bullet shaped tablets, use to deliver the Drugs for local effect, mainly for antibacterial and anti-fungal drug delivery.

Effervescent Tablets

These tablets are based on rapid disintegration or breakdown of the tablet in physiological media or water. These tablets are prepared by compressing the drug generally with organic acid (citric or tartaric acid) and Sodium carbonate.

These effervescent granules (organic acid + bicarbonate) produces gas when comes in the contact with water. Due to gas formation the tablet gets breaks instantly and release the drug.

Hypodermic Tablets

These are soft, readily soluble tablets, used for instant preparation of parenteral solutions. These tablets are dissolved in water for injection and after complete dissolution, the prepared solution is administered through parenteral route by injection.

These tablets are now in limited use because of sterility issues.

Tablet Triturates

These are small cylindrical shaped tablets having potent drug in small amount. These tablets are dissolved in small amount of water and consume orally.

Aperture Tablets

In this type of tablets, a aperture or a hole of sub-milimeter range is created with the help of laser beam. This aperture is created for optimization of drug release pattern from the inside of the tablet. The drug Incorporate inside the tablet is released through this aperture. By varying the size and numbers of aperture, the drug release pattern can be changed.

Divisible Tablets

These tablets have grooves at upper and / or lower bottom of the tablet as a line for division. From these grooves the tablets can be easily broken into two parts, without affecting drug release pattern.

Concave-Convex Tablet

These are different from flat tablets. The edges are not much sharp as compared to flat tablets. The surface of tablet body is either elevated (convex) or low-lying (Concave). This shape of tablet prevents them from attrition during coating process and rounded body make them easy to swallow.

Delayed Release Tablets

These tablets are intended to release the drug after a certain time after administration. Delayed release tablets can control the release of drug to deliver them at any specific time interval, when the tablet reaches to any specific site,

i.e. if the drug released at Intestine – Enteric Coated Tablet

if the drug released at Colon - Colon targeted Tablets

Extended-Release Tablets

These tablets allow the drug to release for a prolong time durations and can minimize the dose frequency.

They are of following types

Sustained Release Tablets- these tablets can release a drug for a sustained duration of time period.

Controlled Release Tablets- These tablets can also release the drug throughout a time duration, but the drug release rate is constant throughout the time duration.