Solid Dosage Forms: Tablets

n. Immediate-Release Tablets

Immediate-release tablets are tablets designed to disintegrate and release their medication with no special rate-controlling features, such as special coatings and other techniques. This is the most common type of tablet and examples include, chewable, effervescent, sublingual and buccal tablets.

o. Rapid-release Tablets

Rapid-release tablets, also called rapidly dissolving tablets, rapidly disintegrating tablets, orally-dispersible tablets, quick disintegrating tablets, mouth dissolving tablets, fast disintegrating tablets, fast-dissolving tablets, rapid-dissolving tablets, or porous tablets are characterized by disintegrating or dissolving in the mouth within 1 minute, some within 10 seconds, leaving an easy-to-swallow residue.

Tablets of this type are prepared using very water-soluble excipients designed to wick water into the tablet for rapid disintegration or dissolution without chewing.

Rapid-release tablets offer increased convenience and ease of administration with the potential to improve compliance, especially when swallowing conventional solid oral-dosage forms presents difficulties for the patient.

Notwithstanding these advantages, there are a number of disadvantages and difficulties associated with formulating rapid-release tablets, including drug loading, taste masking, friability, manufacturing costs, and stability of the product.

Examples of rapid-release tablets include Clarinex Reditabs [desloratadine], Schering.

p. Extended-Release Tablets

Extended-release tablets sometimes called controlled-release tablets, prolonged-release, delayed release or sustained release tablets are tablets designed to release their medication in a predetermined manner over a prolonged period of time. These tablet types are categorized into

• Those that respond to some physiological condition to release the drug, such as enteric coatings;
• Those that release the drug in a relatively steady, controlled manner; and
• Those that combine combinations of mechanisms to release pulses of drug such as repeat action tablets.

A typical example of this tablet type is Divalproex-Sodium-Extended-Release-Tablets.

q. Vaginal Tablets/ Vaginal Inserts

Vaginal tablets are uncoated, bullet-shaped, or ovoid tablets designed for vaginal administration. They are prepared by compression and are shaped to fit tightly on plastic inserter devices that accompany the product.

Following insertion, retention and slow dissolution of the tablet occur, releasing the medicaments to provide the local pharmacological effect (e.g. for the treatment of bacterial or fungal infection).

Vaginal tablets may also be used to provide systemic absorption of therapeutic agents. Examples include Gyno-Tiocosid (Neimeth), Gynesatum- Clotrimazole vaginal Tablet (Chazmax Pharmaceutical Industries Limited), Nystamark-Nystatin Vaginal Tablet (Mark Pharmaceuticals) etc.

r. Implantation Tablets/ Implants

These are long-acting sterile tablets designed to provide continuous release of drugs, often over a period of months or a year. They are placed subcutaneously for systemic or local delivery.

Implants are mainly used for the administration of hormones such as testosterone steroids for contraception. They usually contain rate-controlling excipients in addition to the active ingredient(s).

Several types of implants are available including pellets, resorbable microparticles, polymer implants, in situ–forming gel/solid implants, metal/plastic implants, and drug-eluting stents.

Examples of implantation tablets include Implanon – etonogestrel (Organon), Disulfiram Tablet for Implantation etc.

Tablet Excipients/ Ingredients

In tablet formulation, many materials are usually combined at various quantities to produce a tablet that is of good standard. These materials serve different and specialized functions in the tablet. The type and quantity of each raw material used is dependent on the intended tablet type and formulation technique. Tablet Excipients include:

• Binders /granulating fluid –e.g., include acacia gum, tragacanth, corn starch, methylcellulose, gelatin, panwar gum, ghatti gum, mucilage of isapol husks, carboxymethylcellulose, methylcellulose, polyvinylpyrrolidone and sugars, such as sucrose, glucose, dextrose, molasses, and lactose etc.
• Bulking agents/ diluents/fillers – g., anhydrous lactose, spray dry lactose, microcrystalline cellulose, corn starch, dicalcium phosphate, calcium sulfate, lactose, cellulose, kaolin, mannitol, sodium chloride, etc.
• Disintegrating agents – e.g., starch, clays, celluloses, algins, gums, and cross-linked polymers (croscarmellose, crospovidone, and sodium starch glycolate) etc.
• Lubricants – g., metallic stearate (0.1-0.2 % w/w) e.g., magnesium stearate, calcium stearate, stearic acid (0.25-1 %), hydrogenated vegetable oil, corn starch, boric acids, sodium chloride, sodium lauryl sulphate etc.
• Glidants – e.g., colloidal silicon dioxide Cab-o-sil (Cabot), Talc (asbestos-free) etc.
• Colouring agents/ Colourants – e.g., FD&C Blue No. 1, FD&C Blue No. 2, FD&C Green No. 3, D&C Green No. 5, D&C Red No. 6, D&C Red No. 21. D&C Red No. 22, D&C Red No. 27 etc.
• Flavoring agents/ Flavorants – e.g., Aspartame (Pfzer)
• Adsorbent – e.g., silicon dioxide, magnesium oxide, starch, magnesium silicate etc.

Read more on tablet excipients

How Tablets are Manufactured

Tablets are commonly manufactured by one of the following manufacturing processes:

Wet granulation

1. Milling of drugs and excipients.
2. Mixing of drugs and excipients (excluding the lubricant).
3. Preparation of binder dispersion.
4. Mixing of binder solution with powder to form a coarse mass.
5. Coarse sieving
6. Drying of moist granules.
7. Sieving of the dried granules and mixing with disintegrant and lubricant.
8. Compression into tablets.

Click to read more on tablet manufacture by wet granulation method 

Dry granulation (slugging or roller compaction/ chilsonisation)

1. Milling of drugs and excipients.
2. Mixing of milled powders.
3. Compression of mixed powders into slugs (big tablets).
4. Milling and sieving of the slugs.
5. Mixing with disintegrant and lubricant.
6. Compression into tablets.

Click to read more on tablet manufacture by dry granulation method

Direct compression

1. Milling of drugs and excipients.
2. Mixing of powders, disintegrant and lubricant.
3. Compression into tablet

Click to read more on tablet manufacture by direct compression method

Advantages of Tablets in the Pharmaceutical industry

• Tablets are elegant in appearance and convenient to use.
• They are superior to other dosage forms with respect to chemical, physical and microbiological stability.
• Tablets provide stable and an accurately measured dosage of drug substance to patients.
• Tablets can be formulated to protect unstable drug substances or disguise unpalatable excipients.
• Tablets are generally inexpensive to manufacture.
• It is easier to mask the unpleasant taste of some APIs in tablets thus improving patient acceptability.
• Tablets may be formulated to contain two or more drug substances (even if they are physically or chemically incompatible), thus reducing multiple tablet use.
• Tablets may be easily manufactured to show product identification using coloured coatings, embossed markings, and printing.
• Tablets may be designed to release their active substance at a particular site within the gastrointestinal tract to reduce side effects, promote absorption at that site or provide a local effect (e.g. ulcerative colitis).
• With the exception of proteins which are denatured in the gastrointestinal tract, all classes of therapeutic agents may be administered orally in the form of tablets

Disadvantages of Tablets

• The manufacture of tablets requires a series of unit operations (weighing, milling, drying, mixing etc.) thus there is an increased level of product loss at each stage in the formulation process.
• The absorption of medicament from tablets is dependent on physiological factors, such as gastric resident/emptying time, and thus, vary from one .patient to another.
• The compression properties of certain drug substance are poor and may present problems in their subsequent formulation and manufacture as tablets.

Conclusion

Tablets remain popular as a dosage form, due to the various advantages afforded both to the manufacturer and to the patient. Although the basic mechanical approach for most tablet manufacture has remained the same, efforts are continuously made to understand more clearly the physical characteristics of powder compaction and the factors affecting the availability of the drug substance from the dosage form after oral administration.

References

• Allen L. V and Ansel H. C. (2014). Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems. Philadelphia: Lipincott Williams and Wilkins.
• http://www.pharmaceutical-technology.com/products/softgels-for-clinical-studies
• Jariwala, D. M., Patel, H. P., Desai, C. T., Shah., S. A. and Shah, D. R. (2016). A Review on Multiple Compressed Tablets. Journal of Pharmaceutical Science and Bioscientific Research, 6(3): 371-375.
• Jones D. (2008). Fasttrack Pharmaceutics – Dosage Form and Design. London: Pharmaceutical Press.
• Sakr, A. A and Alanazi, F. K (2012). Oral Solid Dosage Form. In L.A Felton (Eds.), Remington  Essentials of Pharmaceutics (pp. 581-610). London: Pharmaceutical Press