Different Types Of Tablets

apsules are easier to swallow and are used by manufacturers when the drug can’t be compacted into a solid tablet. They are also useful when the drug needs to be mixed with oil or other liquid to aid absorption in the body. It is normally a shell or container made of gelatin that contains the drug.

There are two types of capsules, hard or soft.

Hard capsules

Hard capsules, which are more commonly seen, are made up of a rigid shell in two pieces that fit together and is then filled with the drug. This formulation is normally more suitable for drug powders and can only be used if the drug will be easily dissolved in the stomach.
Soft capsules

Soft capsules are formed in a single piece and are more suitable for oils e.g. Fish oils, or drugs that need to be dissolved in oils or other liquids to aid the drug to be absorbed in the stomach. In soft capsules the drug is combined with an appropriate solvent in the centre of the capsule and the capsule shell melts within minutes in the stomach.

Drugs are easily absorbed from these mixtures offering two distinct advantages; 1) quicker effect, which is good for immediate pain relief, 2) Drug absorbed more effectively, so lower doses can be used which in turn means the soft capsules can be made smaller, making swallowing easier.

Suppositories are designed for anal administration and usually consist of the active drug(s) and a base which is designed to melt at room temperature. Once the suppository has been rectally administered the base will then break down and the drug will be released. The formulation and design is no more complex than this.

Most suppositories are prescribed for local effects such as treating constipation or haemorrhoids. The anal route however provides an excellent route for drug absorption and therefore can be used in patients with swallowing difficulties or for drugs where avoidance of the stomach is preferable e.g. NSAIDs. Additionally by avoiding the stomach the drug also misses the liver and therefore in many cases more of the drug will get into the system and a lower dose can be administered. For this reason it is important to check the bioavailability of a suppository compared to a tablet when swapping between the two.

Except in the case of constipation it is important to administer suppositories after bowels have been evacuated otherwise an evacuation itself could cause the suppository to be expelled prematurely

A special refers to a formulation without a product license that has been formulated in accordance with a prescriber’s instructions for a specific patient. ‘Specials’ are most commonly liquid formulations prepared for patients with swallowing difficulties, where a licensed liquid formulation is not available.

Patients with swallowing difficulties have specialist clinical needs that often cannot be met by licensed medicinal products. Consequently, the law allows for the manufacture and supply of ‘specials’; unlicensed medicinal products manufactured for use by a specific individual patient, on the prescriber’s direct personal responsibility.

Specials do not have a marketing authorisation and consequently cannot legally be advertised. Similarly ‘Specials’ cannot lawfully be manufactured and supplied if an equivalent product is available.

If a special is manufactured in the UK, the manufacturer must hold a specials licence which is issued by the Medicines and Healthcare Products Regulatory Agency (MHRA) and ensures a safe, quality assured product.

Inhalers are used to deliver drugs to the body via the lungs for the treatment or prevention of diseases of the airways such as asthma, chronic obstructive pulmonary disease or cystic fibrosis. This route is however not reserved solely for this purpose. Which a large surface area and good blood supply the lungs can also be used for delivering drugs throughout the body e.g. antivirals for the treatment of influenza. More recently manufacturers have designed inhalers with some success to administer insulin via this route

By giving the drug directly to where it is needed means it is likely to work quicker. Also smaller doses are needed when delivered direct to where it’s needed, rather than using tablets or injections, therefore reducing the risk of side effects.

The inhaled route is however of limited value to patients who can’t swallow tablets or capsules as most medicines are not available via this route.

Patches are designed to enable drugs to pass through the relatively impermeable skin into the body and are often referred to as TTS (transdermal therapeutic systems). Due to the effectiveness of the skin as a barrier this route is only suitable for chemicals with the appropriate characteristics and for drugs where only small doses are required for therapeutic effect. Figure 1 provides a diagrammatic representation of a patch formulation.

By utilising patches as a method of drug administration the release of the drug can be controlled and therefore peaks and troughs in the drugs level in the body can be avoided. If a patient suffers side effects the patch can be removed and furthermore patches can hold sufficient amounts of the drug to enable them to only require changing after extended periods of time.

Patches can be used to deliver a variety of drugs for a wide range of conditions and therefore may provide an alternative to tablets and capsules in some patients.

Examples of patch formulations include:

Hyoscine patches for motion sickness or hypersalivation.
Fentanyl & buprenorphine patches for pain.
Nicotine patches to aid smoking cessation.
Glyceryl trinitrate patches for angina and heart failure.
Oxybutynin patches for incontinence.

Pharmaceutically produced liquid medicines can either be called liquids, solutions, syrups or mixtures. Liquid medicines are largely designed for patients who are unable to swallow tablets or capsules and therefore are prescribed mainly for children and the elderly and are designed to ensure that the drug is dispersed evenly throughout, the taste of the drug is masked by sweeteners and flavourings and a usual dose is given in 5ml which is a sensible amount to swallow. The consistency is also considered by manufacturers as gloopy liquids are easier to manage and are less likely to be aspirated.
[Figure 1 Diagrammatic representation of a liquid.]

Water is the most commonly used solvent however due to drug Instability in water some liquid medicines contain stabilisers. Occasionally alternative liquid solvents such as glycerol or alcohol are used. Where the drug doesn’t dissolve in the liquid solvent manufacturers use suspending agents to ensure the even drug distribution. Figure four provides a diagrammatic representation of what may be found in a liquid medicine. It can be seen that these are not simple formulations and considerably more complex than a crushed tablet in water.

‘Modified release’ means that the escape of the drug from the tablet has been modified in some way. Usually this is to slow the release of the drug so that the medicine doesn’t have to be taken too often and therefore improves compliance. The other benefit from modifying release is that the drug release is controlled and there are smaller peaks and troughs in blood levels therefore reducing the chance of peak effects and increasing the likelihood of therapeutic effectiveness for longer periods of time.

Tablets and capsules which are designed to provide modified release often have the letters MR, LA, XL, CR or SR in their names e.g. Diffundox MR, Elantan LA, Dilzem XL Calcicard CR, Dilcardia S,. Sometimes the words ‘slow’ or ‘retard’ can be used to denote modified release e.g. Diclomax retard, Voltarol retard & Slow K.

There are a number of ways in which a medicine can have its release modified. Perhaps the most famous is that used in Contac 400 capsules. The pellets inside are of different thicknesses and therefore the thinnest release the drug first and the thickest last (Figure 1).
Modified Release

Another method used is to put the drug in thick goo which breaks down slowly itself and therefore releases the drug slowly. One method which has been tried in the past has been to put a non dissolving coating around the tablet or capsule, laser a small hole in it and then let the drug only release through the hole. In such cases patients frequently report passing the tablet or capsule whole and worrying whether it is actually working. Frequently they are however just passing the outer coat in their stools as this is how the medicine is designed to work and the drug has long been absorbed.

Modified release products usually have a higher than normal amount of the drug within them and therefore if they are crushed the whole dose will be released very quickly and could be dangerous.

For this reason modified release products should never be crushed or modified before being taken.

If a tablet is described as having an ‘enteric coating’ (e/c) or ‘gastro-resistant’ it means that there is a coating which is designed to hold the tablet together in acid conditions i.e. the stomach and therefore release the drug in the intestines.

There are three reasons for putting such a coating on a tablet or capsule ingredient:

• To protect the stomach from the drug
• To protect the drug from the stomach
• To release the drug after the stomach e.g. in the intestines

The drugs which most commonly cause stomach ulcers like aspirin, diclofenac and naproxen are frequently available with enteric coatings. Omeprazole is itself broken down in acid and therefore the drug generally has an enteric coating around it either as a granule in the capsules or as a granule in the dispersible form. Sulfasalazine is used either for the treatment of arthritis or for the treatment of Crohn’s disease which is inflammation of the intestines. When used for arthritis it is very often given without an enteric coating so that it can be absorbed more quickly, whereas for Crohn’s where it is needed in the intestines to work it is given with an enteric coating.

It can be seen that an enteric coating is therefore there usually for a good reason and therefore such tablets or the contents of enteric coated capsules should never be crushed before being taken.