TABLET COATING AND ITS DIFFERENT METHODS

INTRODUCTION:- Tablet is a pharmaceutical solid dosage form, comprising a mixture of active substances and excipients, commonly in powder form, pressed or compacted right into a stable. Capsules Dosage form is one of a most desired dosage form everywhere in the world. Almost all drug molecules may be formulated in a tablet and procedure of producing of drugs is very simple, and may be very bendy. Coating is a manner by using which a basically dry, outer layer of coating material is implemented to the surface of a dosage shape to achieve precise benefits. Coating may be implemented to a wide range of oral solid dosage shape, along with capsules, capsules, multi particulates and drug crystals. While coating composition is carried out to a batch of capsules in a coating pan, the tablet surfaces grow to be protected with a tacky polymeric film. Before the tablet floor dries, the carried-out coating adjustments from a sticky liquid to tacky semisolid and sooner or later to a non-sticky dry surface pans. Many stable pharmaceutical dosage forms are produced with coatings, both on the external surface of the tablet, or on substances dispensed inside gelatin tablets. The tablet ought to launch the medicament steadily and the drug should be to be had for digestion. The coating procedure can be in particular formulated to adjust how speedy the tablet dissolves and in which the lively tablets are to be absorbed into the body after ingestion.

DIFFERENT METHODS OF COATING

  1. FILM COATING:- As the sugar coating process is very time consuming and is dependent on the skills of the coating operator, this technique has been replaced by film coating technology. The process involves spraying of a solution of polymer, pigments and plasticizer onto a rotating tablet bed to form a thin, uniform film on the tablet surface. The choice of polymer mainly depends on the desired site of drug release (stomach/ intestine), or on the desired release rate. Some of the non-enteric coating polymers are Hydroxyproply methyl cellulose (HPMC), Methyl hydroxyethyl cellulose, Ethylcellulose, Povidone, etc., while the commonly used enteric coating polymers are Cellulose acetate phthalate, Acrylate polymers (Eudragit L& Eudragit S), HPMC phthalate, etc.
  2. ORGANIC FILM COATING: – Currently, the most common technology for coating solid dosage forms is the liquid coating technology (aqueous based organic based polymer solutions). In liquid coating, a mixture of polymers, pigments and excipients is dissolved in an organic solvent (for water insoluble polymers) or water (for water soluble polymers) to form a solution, or dispersed in water to form a dispersion, and then sprayed onto the dosage forms in a pan coater (for tablets) and dried by continuously providing heat, typically using hot air, until a dry coating film is formed. Organic solvent based coating provides a variety of useful polymer alternatives, as most of the polymers are soluble in the wide range of organic solvents. However, there are certain disadvantages like they are flammable, toxic, and costly and possess environmental issues. ICH guidelines also prefer the avoidance of organic solvents in pharmaceutical dosage formulations considering products safety profile. So, Pharmaceutical industries are now paying much attention in developing formulations with aqueous film coating.
  3. AQUEOUS FILM COATING: – All above problems with organic solvents resulted in shift to use of water as the preferred coating solvent. Aqueous-based coatings have been increasingly used compared with organic-based coatings. The conversion from organic solvent based coating to aqueous based coating makes the coating process more economical, though initially it may need a little investment to upgrade the coating facility. The need of this up-gradation arises due to the need of higher drying capacity (the latent heat of water is 2200kJ as compared to 550kJ for methylene chloride). This implies that one would require 4 times more energy as compared to organic solvent.
  • Primarily reduces tablet weight gain of product as compared to sugar coating by more then 98%.
  • Provides stability to the product with regards to heat, light.
  • Masking odour, bitter taste and easy acceptability of product by the patient.

Eg : Ciproflixacin, Norfloxacin