Overview, Advantage And Disadvantage Of Pharmaceutical Rectal Tablet

The rectal tablet can be considered a good alternative to the oral tablet for the paediatric population because these dosage forms are neither to be swallowed nor need to be taste-masked. It is an old and acceptable means of treatment. The volume and nature of rectal fluid, its buffer capacity, pH and surface tension play a large part in this but are subject to wide variation, even within a single subject, resulting in variability of absorption by this route. Rectal tablets have both systemic and local effects.

Rectal tablet

Rectal Tablet Composition

Rectal tablets are composed of solid supports impregnated with medicinal substances. They are solid dosage forms containing drugs that are either dispersed or dissolved in a suitable lipophilic base or hydrophilic base.

Lipophilic bases are immiscible with body fluids and readily melt at body temperature to release the drug on the mucosal surface, whereas hydrophilic bases need to dissolve in the physiological fluids for drug release.

Anatomy Of Rectum

In humans the rectum comprises the last 12-19cm of the colon and the rectal epithelium is formed by a single layer of columnar or cuboidal cells and goblets cells; its surface area is about 200-400 cm. The absorbing surface area of the rectum is considerably smaller than that of the small intestine, as the former lack villi and microvilli. However, the epithelium in the rectum and the upper intestinal tract are histologically similar, giving them comparable abilities to absorb drugs. The veins of the rectum comprise the superior hemorrhoidal vein, which drains into the inferior mesenteric and portal system, and the middle and inferior hemorrhoidal veins, which enter the systemic venous circulation via the internal iliac veins. However, it is a little known fact that the inferior and middle hemorrhoidal veins bypass the liver and do not undergo first-pass metabolism. Therefore, the drugs delivered through rectal tablet to the lower and middle hemorrhoidal veins are absorbed rapidly and effectively. The rectum is an interesting area for drug absorption because it is not buffered and has a neutral pH. It also has a very little enzymatic activity, thus enzymatic degradation does not occurring. The rectal mucus is more capable of tolerating various drug related irritations than the gastric mucosa.

In adults, rectal tablets should be inserted in the lower part of the rectum to avoid the absorption of the drug by the upper haemorrhoidal vein which supplies blood to the portal vein. In addition, the empty rectum presents a constant and static environment as compared to the upper gastrointestinal tract, where the environment varies greatly depending on the section (e.g. pH, volume of stomach vs. duodenum) and in fasted or fed conditions. The volume of liquid is reported as relatively low (1–3 mL) and the pH neutral (pH 7–8) with low buffer capacity. Its surface area is smaller than the upper gastrointestinal tract, but larger than nasal and buccal absorptive surfaces.

Advantages Of Rectal Tablet

1. Better product stability even at room temperature

2. No irritation to the gastric mucosa

3. Drugs that need high doses can easily be formulated

4. Suitable for drugs that possess limited absorption in the upper gastrointestinal tract

5. Drugs unstable to proteolytic enzymes are formulated as rectal tablet

6. Exhibit a high hepatic first pass effect

7. Suitable for person who cannot easily swallow tablets or capsules

8. Rectal tablet are generally inexpensive to manufacture

9. can also be self-administered by patients without the need for a medically trained person in comparison to parenteral dosage forms

Disadvantages Of Rectal Tablet

1. Possibility of premature expulsion of the dosage form before sufficient absorption takes place.

2. Suppositories containing such compounds as Aspirin and Penicillin G sodium have limited product stability even under refrigeration

3. Irregular drug absorption

4. Discomfort

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