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It is strange how two tablets can belong to the same but at the same time to a different category depending on how the tablet itself is classified. For example, chewable tablets and effervescent tablets have two different routes of administration but both belong to the category of uncoated tablets. Uncoated tablets are prepared by compression of granules in which no coating is added after compression. They may be single-layer or multi-layer tablets.

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Difference between coated and uncoated tablets – When is the coating necessary?

If you’re wondering when coating a tablet is necessary, there’s not just one answer. Uncoated tablets are rougher and don’t really taste good. This makes them harder to swallow especially for children, as they also leave a bad aftertaste in the mouth. So coating is important to mask an unpleasant taste. Another reason may be that the active ingredient the tablet is made of is acid sensitive, so an enteric coating may help resist stomach acidity.

On the other way around, the enteric coating can also help protect the stomach from a more aggressive drug. Apart from that, the coating reduces also tablet friability and it can modify or control drug release. In uncoated tablets, any excipient or added substance is not specifically intended for this purpose.

Problems that can occur during uncoated tablets manufacturing

During uncoated tablet manufacturing, various problems can arise. Capping and lamination are two of these and refer to the separation of the tablet. Capping is the horizontal separation of the upper or lower part of the tablet from its main body; while lamination is the separation of the tablet into several horizontal layers.

Capping and lamination may occur immediately after compression or after several hours or days. To avoid this, it is advisable to test the tablet for friability to see if the problem is present or not.

The main causes can be air entrapment in granules or particles, granules that are too dry, improper tooling, or incorrect setup of the press. Tablet lamination and capping can be prevented by precompression.

If the tablet has excessive binder, sticking can happen. It refers to when tablet materials adhere to the die wall. Picking is used to describing when a portion of material is removed from the tablet surface by a punch due to embossing design. Plating punch faces with chromium can be a solution to produce non-adherent punch faces.

Disintegration time for uncoated tablets

Disintegration is the ability of a tablet to break down into smaller particles to allow the drug to be absorbed by the body. The disintegration test is paramount for tablets that are intended for mouth administration except for chewable tablets.

The disintegration tester consists of a basket that can hold six tablets. The basket is raised and lowered into a beaker that has water as the immersion fluid, unless there is another medium specified, having the temperature at 35 °C to 39 °C.

After running the device for the specified time, if all the tablets are disintegrated completely, they are good to go. If one or two tablets fail the test, it must be repeated on 12 additional tablets. If not less than 16 out of 18 tablets tested are disintegrated, the requirements are met.

Friability test for uncoated tablets

Friability test says to you how much mechanical stress tablet withstand during manufacturing, packaging and transit or when they are handled by consumers. A Friabilator is the laboratory instrument used for friability test. The device consists of  a plastic chamber, the rotating drum, where you can place your preweighed tablets. Now you can rotate the drum 100 times and after removing them from the drum, just weight the tablet again.

If they have lost less than 0.5 to 1.0%, they are considered acceptable. Chewable and effervescent tablets have high friability weigh losses, so they have different specification and require special packaging. Basically, with the friability test, you can know the difference in the weight of uncoated tablets before and after the test. In this way, you can evaluate the physical strength of uncoated tablets

Which type of excipients do you have to use in uncoated tablets?

During uncoated tablet manufacturing, you cannot think to start without having your excipients. They play an important role and fulfill different functions – they can improve the taste or modify the disintegration time or the time and place of substance release. Saying that they are everything other than APIs, i.e. active pharmaceutical ingredients. When making uncoated tablets, there are some types of excipients you have to use.

For example, excipients used in orally disintegrating tablets (ODT) are sucrose, mannitol or sorbitol. Since this type of tablet disintegrates very quickly upon contact with saliva, disintegrants such as polyvinylpyrrolidone or sodium starch glycolate play a fundamental role here. In effervescent tablets instead, excipients used are citric acid, sodium citrate, fumaric acid, tartaric acid, with citric acid being one of the most important.

Processing steps involved in uncoated-tablets making

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