Delayed action tablets
Enteric coated tablet is such an example of delayed action tablet.

Why use this formulation :
  • The Active Pharmaceutical Ingredient irritates gastric mucosa, for example aspirin or strong electrolytes
  • Drugs that produce nausea and vomiting.
  • Active Pharmaceutical Ingredient is sensitive to low pH, for example erythromycin
  • release the drug undiluted, for example intestinal antibacterial, antiseptic agents, intestinal vermifuge, etc.
This dosage form is intended to hydrate and begin to dissolve in duodenum (pH 4 to 6) or in small intestine where pH increases to 7 to 8. The presence of esterases or bile salts like surface active agents plays a role in drug release.

Read more : Delayed Release Drug

Targeted tablets
When we need to release the API at a specific site in the elementary tract, targeted drug delivery is a preferred option. Depending upon the composition and release mechanism of a tablet, the drug is delivered to a particular region. Under this category, we have two types of tablet:

I. Gastro retentive Tablet
This type of dosage form is to be opted when API release is desired in stomach (Antacids, APIs used against H.pylori infection) or site of absorption is either stomach or upper part of small intestine.

Gastroretentive systems can remain in the gastric region for several hours and hence can significantly prolong the gastric residence time of drugs. Prolonged gastric retention improves bioavailability, reduces drug waste, and improves solubility for drugs that are less soluble in a high pH environment of small intestine. It has applications also for local drug delivery to the stomach and proximal small intestine.

Floating Tablet

To retain the drug for longer time period in stomach, following approaches can be used:
  • Low density tablet (effervescent or non effervescent)
  • Tablets that can expand in gastric environment (swelling or by unfolding) and thus increasing the size so that it cannot cross the pyloric sphincter.
  • Using mucoadhesive polymers that stick to mucosa of stomach and provide slow drug release.
Supine position is to be avoided and also high level of fluid is necessary or if the swelling formulation leaves stomach before it swells it’s ineffective. API that formulated as gastro retentive tablets are Diazepam, Levodopa, Benserazide, and Ciprofloxacin.

II. Colonic tablets
Colonic tablet deliver the drug into colon without dilution in other regions of gastrointestinal tract or the drug has poor absorption in stomach or small intestine.The pH in this region varies from 6.4 - 7 and presence of microbial flora plays as important role in drug release especially in this region.

Various mechanisms are adopted for drug release in this area are coating with pH sensitive polymer e.g., Eudragit®S100, Eudragit® L100, biodegradable polymer like polymers which are sensitive to colonic bacteria, bioadhesive polymers which selectively sticks to colonic mucosa e.g., polycarbophils or polyethans, redox sensitive polymers that respond to redox potential in colon which expresses the total metabolic and bacterial action.

Chewable tablets
The tablet which is intended to be broken and chewed in between the teeth before ingestion and thus mechanically disintegrated in the mouth. Antacid and vitamin tablets are usually prepared as chewable tablets. It is given to the children who have difficulty in swallowing and to the adults who dislike swallowing.

The added advantage of this medication is that it can be taken at any time or when water is not available.

Mannitol is normally used as a base due to low hygroscopy and more importantly, it gives pleasant, cooling sensation. Flavoring, sweetening and coloring agents are important. Antacid tablets are invariably prepared as chewable to obtain quick ingestion relief as well as the antacid dose is too large to swallow and the activity is related to particle size. Another example is multivitamin tablet which a patient can take as a daily dose.

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).

Dispersible tablet
Dispersible tablets are uncoated or film-coated 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. Dispersible tablets usually disintegrate within three minutes when put in water or a small amount of breast milk. The common examples of API formulated in this dosage form

Advantages of dispersible tablets are:
  • more convenient for active pharmaceutical ingredients with insufficient stability in water.
  • more easily transportable and they generate less handling and transportation costs for the same amount of active ingredient (less volume, less weight)
  • easier to produce and the production costs are less, which makes them more affordable than standard liquid formulations.
  • faster onset of action as compared to standard compressed tablet.
  • can be used in very young children (0 – 6 months).
  • helpful for patients having prolonged illness who are prone to nauseatic sensations if they have to swallow a tablet.
  • are easy to dispense and: they require minimal manipulation by health professionals and parents prior to use which minimises the risk of errors.
  • require a small amount of water for administration.
  • can be dispersed in breast milk.
The properties of the water dispersible tablet, such as porosity, hardness, disintegration time and increase in viscosity after dispersion are necessary to investigate during manufacturing which decides the product performance.
  • As for liquid formulations, the taste of a dispersible tablet is a crucial parameter that will condition the acceptability by the child and the adherence to treatment.
  • Taste masking is obtained by adding flavours and/or sweeteners to the formulation.
  • Dispersible tablets have less physical resistance than regular tablets; they are more sensitive to moisture and may degrade at higher humidity conditions. Each tablet must be protected from the ambient humidity.
  • The quality of the packaging is critical to guarantee the conservation of the product.
  • Dispersible tablets are usually packed in blisters (aluminium/PVC) or strips (aluminium).
  • The manufacturer guarantees the stability of the dispersible tablet in the primary packaging (blister or strip).

Read more:

Oral Tablets for Ingestion (Part III)