INTRODUCTION:

Tablet is a pharmaceutical dosage form comprising a mixture of active substances and excipients, usually in powder form, pressed or compacted from a powder into a solid dose. The excipients can include glidants (flow aids), diluents, binders or granulating agents and lubricants to ensure efficient tableting; disintegrants to promote tablet break-up in the digestive tract; sweeteners or flavours to enhance taste; and pigments to make the tablets visually attractive. A polymer coating is often applied to enhance the tablet's appearance or to make the tablet smoother and easier to swallow and to control the release rate of the active ingredient, to make it more resistant to the environment (extending its shelf life). “Caplets” are those tablets which are in the shape of capsules. Medicinal tablets and capsules are often called pills.¹

Tablet Coating:

Coating is a process by which an essentially dry, outer layer of coating material is applied to the surface of a dosage form in order to confer specific benefits that broadly ranges from facilitating product identification to modifying drug release from the dosage form. After making a good tablet, one must often coat it.^1-3 Coating may be applied to multiple range of oral solid dosage form, including tablets, capsules, multiparticulates and drug crystals. When coating composition is applied to a batch of tablets in a coating pan, the tablet surfaces become covered with a tacky polymeric film. Before the tablet surface dries, the applied coating changes from a sticky liquid to tacky semisolid and eventually to a non-sticky dry surface pans. The entire coating process is conducted in a series of mechanically operated acorn-shaped coating pans of galvanized iron stainless steel or copper. The smaller pans are used for experimental, developmental, and pilot plant operations, the larger pans for industrial production.²

Tablet Coating:

It comprises the following things:

· A modern tablet coating system combines several components: A coating pan · A spraying system · An air handling unit A dust collector⁶

· Advantages of tablet coating: Tablet coatings must not make tablets stick together during the coating process, must follow the fine contours of embossed characters or logos on tablets and must be stable and strong enough to survive the handling of the tablet. Printing on tablets can also be done by coatings, if required. Coatings are necessary for tablets giving a smoother finish, makes large tablets easier to swallow and also to mask the unpleasant taste.³

· Disadvantages of tablet coating: Limitations of sugar coating such as relatively high cost, long coating time and high bulk have led to the use of other coating materials. · However the process of coating is tedious and time-consuming and it requires the expertise of highly skilled technician³

Enteric coated tablet:

An enteric coating is a barrier that controls the location of oral medication in the digestive system where it is absorbed. The word “enteric” indicates small intestine; therefore, enteric coatings prevent release of medication before it reaches the small intestine. The enteric coated polymers remain unionise at low pH, and therefore remain insoluble. But as the pH increases in the GIT, the acidic functional groups are capable of ionisation, and the polymer swells or becomes soluble in the intestinal fluid. Materials used for enteric coatings include CAP, CAT, PVAP and HPMCP, fatty acids, waxes, shellac, plastics and plant fibers. There are four reasons for putting such a coating on a tablet or capsule ingredient: ü Protection of active pharmaceutical ingredients, from the acidic environment of the stomach (e.g. enzymes and certain antibiotics). ü to prevent gastric distress or nausea from a drug due to irritation (e.g. sodium salicylate). ü for the delivery of drugs that are optimally absorbed in the small intestine to their primary absorption site in their most concentrated form. ü to provide a delayed-release component for repeat action. ü Required for minimizing first pass metabolism of drugs³

Mechanism of enteric coated tablet:

ETP tablets are composed of three layers, a drug containing core tablet (rapid release function), the press coated swellable hydrophobic polymer layer (Hydroxy propyl cellulose layer (HPC), time release function) and an enteric coating layer (acid resistance function). The tablet does not release the drug in the stomach due to the acid resistance of the outer enteric coating layer. The enteric coating layer rapidly dissolves after gastric emptying and the intestinal fluid begins to slowly erode the press coated polymer (HPC) layer. Rapid drug release occurs when the erosion front reaches the core tablet since the erosion process takes a long time as there is no drug release period (lag phase) after gastric emptying. The duration of lag phase (drug release period) is controlled either by the weight or composition of the polymer (HPC) layer.¹

Evaluation of Core and Coated Tablet:

The core and coated tablets were evaluated for hardness, friability, weight variation, disintegration time, thickness, drug content and in vitro release studies.⁷

· Hardness: The tablet crushing strength was measured by using Monsanto tablet hardness tester. A tablet is placed between the anvils and the crushing strength, which causes the tablet to break, was recorded¹⁹.

· Friability Tablet strength: was tested by Roche friabilator. Twenty tablets were accurately weighed and placed in the friabilator and operated for 100 revolutions in 4 min. The tablets were dedusted and the percentage weight loss was calculated by reweighing the tablets. The tablets that loose less than 1% weight were considered to be compliant.

· Weight variation: In weight variation, twenty tablets were selected at random and average weight was determined using an electronic balance. Tablets were weighed individually and compared with average weight.

· Disintegration time: Disintegration time was determined using the disintegration apparatus USP in 0.1N HCl for 2 hrs. and then in phosphate buffer pH 6.8 for 1 hour maintaining the temperature at 37± 2°C.

· Thickness: The thickness of the tablet was measured by using vernier calipers.

· Drug content studies: Ten tablets were weighed individually and powdered; an amount equivalent to 5 mg of drug was taken and 50ml of 95% ethanol was added and was shaken for 30 minutes. Sufficient ethanol (95%) was added to produce 100ml. It was centrifuged and suitable volume of the supernatant liquid equivalent to 0.5mg of drug was pipette out and diluted to 50ml with 95% ethanol. The solution was filtered (through 0.45μm). Drug content was measured at 236nm using UV/Visible single beam spectrophotometer.

· In vitro drug release studies: 7.7.1 In gastric and intestinal pH in vitro drug release study of enteric coated tablets was carried out by using USP XXIV six station dissolution rate test apparatus with paddle stirrer. The dissolution rate was studied in 900 ml of 0.1 N HCl (pH 1.2) maintained at a temperature of 37±1ºC with a speed of 50rpm for first two hours followed by phosphate buffer (pH 7.4) for further four hours. Samples of 5ml were withdrawn after every hour, filtered (through 0.45μm) and replaced with 5ml of fresh dissolution medium. The samples were suitably diluted if necessary and estimated spectrophotometrically at 236nm by using UV/Visible single beam spectrophotometer and cumulative percentage drug release was calculated.^1,2

CONCLUSION:

From the above review, we can conclude that tablets are made enteric-coated for avoiding the first pass metabolism, gastric irritation and degradation and to direct the drug to the target intestines. Enteric coated tablets could be used to treat Streptococcal infections of the throat (strep throat) and the skin and can also be used in treating lung infections (pneumonias) caused by Streptococcal pneumoniae, Mycoplasma pneumoniae and Legionella pneumophila (Legionnaires disease). The choice of the polymer and the thickness of the coated layer are critical to control the pH solubility profile of the enteric coated dosage form.

REFERENCES:

1. Lachman L, Lieberman HA, Joseph LK. The Theory and Practice of Industrial Pharmacy. Varghese Publishing House; Mumbai; Third Edition: 297-321.

2. Lachman L, Liberman H, Kanig J. The Theory and Practice of Industrial Pharmacy; Third Edition: 293-345, 346- 373.

3. Review article on recent advances in enteric coating Singh Deep Husain.

4. Aulton M. Pharmaceutics: The Science of Dosage Form Design. International Student Edition: 304-321, 347-668.

5. Ansel H, Allen L, Jr. Popovich N. Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems; Eighth edition.

6. Kumar Vinay. KV, Sivakumar T and Tamizh mani. T, Colon targeting drug delivery system: A review on recent approaches, International Journal of Pharmaceutical and Biomedical Science, 2011; 2: 11-19.

7. Anil K. Philip and Betty Philip, Colon Targeted Drug Delivery Systems: A Review on Primary and Novel Approaches, Oman Medical Journal, 2010; 25(02): 70-78.

Received on 05.10.2021 Modified on 09.11.2021

Asian J. Pharm. Tech. 2022; 12(2):176-178.

DOI: 10.52711/2231-5713.2022.00029