Tablet Dosage Forms

Tablets represent the most popular and widely used dosage form in pharmaceutical history. Defined as solid unit dosage forms containing medicinal substances with or without suitable diluents, tablets are prepared by compression or molding. They vary in shape, size, weight, hardness, thickness, disintegration, and dissolution characteristics, depending on their intended use and method of administration.

Advantages of Tablets

The prevalence of tablets is due to the numerous advantages they offer over other dosage forms such as liquids, capsules, or injectables. From a manufacturing perspective, they are the most economical form to produce, especially in large quantities. The compression process allows for high-speed production with precise dosing accuracy. For the patient, tablets are portable, compact, and easy to administer. Furthermore, they offer superior chemical and physical stability compared to liquids, as the solid state generally protects the active ingredient from degradation by oxidation, hydrolysis, or photolysis.

Tablets also provide flexibility in formulation design. Manufacturers can coat them to mask unpleasant tastes, protect the drug from the stomach's acidic environment, or control the release rate of the medication. They can also be designed to dissolve quickly in the mouth or slowly in the gastrointestinal tract, depending on the therapeutic requirement.

Components of a Tablet

While the active pharmaceutical ingredient (API) is the therapeutic component, it typically constitutes only a small portion of the tablet's total weight. The majority of the tablet consists of excipients, which are inert substances added to facilitate the manufacturing process or to impart specific physical properties to the dosage form.

• Diluents (Fillers): Added to bulk up the tablet to a practical size for compression, especially when the API is very potent and required in small amounts (e.g., lactose, microcrystalline cellulose).
• Binders: Ensure that the granules or powder particles stick together during compression (e.g., polyvinylpyrrolidone, starch).
• Disintegrants: Promote the breakup of the tablet into smaller granules or particles in the gastrointestinal tract to increase the surface area for drug dissolution (e.g., croscarmellose sodium, sodium starch glycolate).
• Lubricants: Reduce friction between the tablet and the die wall during ejection to prevent sticking (e.g., magnesium stearate).
• Glidants: Improve the flow properties of the powder blend to ensure consistent filling of the die.

Classification of Tablets

Tablets are categorized based on their route of administration or their specific function. Understanding these categories is essential for healthcare professionals to ensure proper usage and patient counseling.

Compressed Uncoated Tablets

These are the simplest form of tablets, composed of active ingredients and excipients compressed into a solid form. They are intended to be swallowed whole, chewed, or dispersed in water prior to administration. Because they are uncoated, they rely entirely on the disintegrant to break apart in the body. They are generally the least expensive to manufacture but may have an unpleasant taste or cause gastric irritation if the drug is acidic or alkaline.

Compressed Coated Tablets

Coating is applied to tablets for various reasons, including masking the taste of bitter drugs, protecting the API from environmental factors (moisture, light), improving appearance, or controlling the release of the drug.

• Sugar-coated Tablets: Historically common, these involve multiple layers of sugar applied to a core. While effective at masking taste, they are time-consuming to produce and thicker than modern alternatives.
• Film-coated Tablets: These are covered with a thin layer of polymer (e.g., cellulose derivatives). They are thinner than sugar-coated tablets, dissolve more quickly, and are less prone to chipping. Most modern tablets are film-coated.
• Enteric-coated Tablets: These have a special polymer coating that resists dissolution in the acidic environment of the stomach (pH < 3). They dissolve only in the alkaline environment of the small intestine. This is crucial for drugs that are destroyed by stomach acid (like erythromycin) or those that irritate the gastric lining (like aspirin).

Effervescent Tablets

Effervescent tablets are designed to produce a solution when dropped into water. They contain a mixture of an acid (e.g., citric acid) and a carbonate or bicarbonate base (e.g., sodium bicarbonate). Upon contact with water, these ingredients react to produce carbon dioxide, causing the tablet to break apart and dissolve. This results in a fizzy solution that masks the taste of the drug and can enhance palatability, particularly for pediatric and geriatric patients.

Chewable Tablets

These tablets are intended to be chewed and swallowed with saliva or dissolved in the mouth before swallowing. They usually contain a pleasant flavoring agent and a sweetener to improve palatability. They are often used for antacids, multivitamins, and medications for children who have difficulty swallowing whole tablets.

Orally Disintegrating Tablets (ODTs)

Also known as mouth-dissolving tablets, ODTs are a modern evolution of the traditional tablet. They are placed on the tongue, where they disperse or dissolve rapidly in saliva without the need for water. This dosage form is highly beneficial for patients with dysphagia (difficulty swallowing) or those who need rapid on-set of action. They typically use specific superdisintegrants or lyophilization (freeze-drying) processes to achieve the desired porosity and rapid dissolution.

Buccal and Sublingual Tablets

These tablets are small, flat, and usually soft in texture. They are placed in the buccal pouch (between the gum and cheek) or under the tongue (sublingual). The medication is absorbed directly through the oral mucosa into the systemic circulation, bypassing the first-pass metabolism in the liver. This provides a rapid onset of action. Examples include nitroglycerin tablets for angina pectoris and certain hormonal supplements.

Modified-Release Tablets

These are complex formulations designed to release the drug at a specific rate or at a specific location in the gastrointestinal tract. They are divided into two main categories:

• Extended-Release (ER) or Sustained-Release (SR): These tablets release the drug slowly over an extended period, maintaining plasma concentrations within the therapeutic window for longer durations. This reduces the frequency of dosing (e.g., once or twice daily instead of four times daily).
• Delayed-Release: As seen with enteric-coated tablets, the drug release is delayed until the tablet reaches a specific region of the intestine.

Implantation Tablets

These are sterile, compressed tablets intended for subcutaneous implantation. They provide a sustained release of drug over extended periods, ranging from weeks to months. They are used for hormone therapies and psychiatric treatments.

Conclusion

The tablet remains a cornerstone of modern pharmaceutical therapy due to its versatility, stability, and patient compliance. From simple immediate-release compressed powders to sophisticated multi-layered modified-release systems, tablet technology continues to evolve. By selecting the appropriate excipients and manufacturing techniques, pharmaceutical scientists can tailor the release profile, absorption rate, and overall efficacy of a medication to meet diverse clinical needs. Understanding the nuances of these different tablet types enables pharmacists and physicians to provide accurate guidance to patients, ensuring the medication is taken correctly and effectively.