Coating is one of the oldest pharmaceutical processes that is still practiced today. It is a process by which an essentially dry, outer layer of coating material is applied to the surface of an appropriate substrate order to confer specific benefits over uncoated variety.
Some of the original reasons for coating solid dosage forms, such as pills, granules, and tablets, were
a. to mask or minimize the unpleasant smell or taste of a drug or biologically active extract present that may come during partial dissolution of the drug in buccal fluids during absorption,
b. to prevent corrosive action of the active ingredients on the mucous membranes of the gastrointestinal tract,
c. to improve swallowability and palatability by increasing surface smoothness in the mouth,
d. to improve the stability of the active component in the solid dosage form,
e. to improve the aesthetic appearance of the pills or tablets, etc.
There are essentially four major methods for applying coatings to solid-dosage forms: sugar coating, film coating, compression coating and microencapsulation. This article will focus on the differences between film coating and sugar coating but before then let’s take a look at what film coating and sugar coating are.
Contents
What is film coating?
Film coating is quite a complex process that can be simplified to represent one that involves the deposition of a thin, but uniform polymer-based formulations onto the surface of solid dosage forms (tablets, capsules, powders, granules, or pallets) under conditions that permit:
- Balance between, and control of, the coating liquid delivery rate and drying process
- Uniform distribution of the coating materials across the surface of the product being coated
- Optimization of both visual and functional quality of the final coated product.
Two major groups of film coating materials may be distinguished:
- those that are nonenteric and, for the most part, cellulose derivatives, and
- those that can provide an enteric effect and are commonly esters of phthalic acid.
Within both groups, it is general practice to use a mixture of materials to give a film with the optimum range of properties.
Read more on Film coating processes
What is sugar coating?
The process of sugar coating, which has its origins in the confectionery industry, involves the successive deposition of aqueous sugar solution on the tablet cores as they are rotated and tumbled in a revolving pan by spraying sugar solution or suspensions into pans and drying off the solvent.
A typical sugar-coating process encompasses five stages:
- Sealing
- Subcoating
- Smoothing
- Color coating
- Polishing
- Printing
While each of these stages is varied, the common feature throughout is that the process requires repeated applications of coating liquid, each application followed by a period during which the tablets are allowed to tumble freely to allow complete distribution of the coating materials, and finally a drying period when moisture is removed from the coating prior to the next application.
Read more on sugar-coating processes
Differences between film coating and sugar coating
The differences between film coating and sugar coating are summarized below
| Features | Film coating | Sugar coating | |
| Tablets | Appearance | Retain contour of original core Usually not as shiny as sugar coat type | Rounded with high degree of polish |
| Weight increase because of coating material | 2 – 3 % | 30 – 50 % | |
| Logo or “break lines” | Possible | Not possible | |
| Other solid dosage form | Coating of multi-particulates very important in modified-release form | Coating possible but little industrial importance | |
| Process | Operator training required | Process tends itself to automation and easy training operator | Considerable |
| Adaptability to Good Manufacturing Practice (GMP) | High | Difficulty may arise | |
| Process stages | Multistage process | Usually single stage | |
| Functional coating | Easily adaptable for controlled release | Not usually possible apart from enteric coating | |
| Typical batch coating time | 1.5 – 2 hours | 8 hours, but easily longer |
References
- Ghosh, T. and Jasti, B. (2005). Theory and Practice of Contemporary Pharmaceutics. London: CRC Press LLC.
- Lieberman, H. A., Lachman, L. and Schwartz, J. B. (1990). Pharmaceutical Dosage Forms: Tablets. New York: Marcel Dekker, Inc.
