What is a tablet? Explainer video by PharmaDrama
Tablets are the most common pharmaceutical dosage form – but why, and what are they?
In this video PharmaDrama aka Prof. Simon Gaisford discusses what tablets are, what they contain, how they are made and how you should take them. He also looks at polymer (enteric) coats and how they are used to make sustained-release (SR) and extended-release (ER) tablets.
Read the video transcript here:
Welcome to Pharma Drama, the channel where we look at the science of healthcare and healthcare products. In this video I’m going look at probably the most common type of medicine – tablets. What they are, how they are made, how they work and some tips on how to take them. So, if that sounds good to you, get yourself a drink – I’ve got… funnily enough, coffee – and let’s get into it.
Tablets are the most common type of dosage form and, indeed, are also the oldest type of dosage form; there are records of tablets being used as far back as the Egyptian empire for instance, almost 1500 years ago. Tablets as we know them today, however, were invented in 1843 when the British inventor William Brockedon applied for a patent for a machine that could compress powders to shape pills, lozenges and black lead by pressure in dies. I have to say that these days black lead tablets are not so popular, but pills and lozenges certainly are! And while we are on the topic of names, I should say that the word pill is always frowned upon by those in the pharmaceutical profession – I am not sure why but I have had it drilled into me over the years that the correct term is tablet, so I’m sticking with that, although I note that more recently the word tablet has been used for other objects – please don’t try and swallow one of these with a glass of water between meals.
So what is a tablet? It is simply a compressed powder blend. They are made by blending the drug substance (which is nearly always a white powder) with a range of other ingredients (which for some reason are called excipients and are also often white powders); the powder mix is then put into a punch and die and a lot of force is applied to squeeze (or compress) it into a hard mass. The punch and die set are what give tablets their particular shape and often indent an identifying name or feature on the surface (it’s kind of important to know what drug a tablet contains!). Tablets can be made in a range of sizes and shapes, and can be coloured, again to aid identification. In some cases, the shape and colour of a tablet can be its unique feature; I am sure if I said blue diamond tablets, you would know what the active was for instance. OK, that was Viagra, if you were wondering.
The other ingredients in a tablet are usually added for specific reasons. Once swallowed, we want a tablet to disintegrate pretty fast, but tightly compressing the powder makes it hard to disperse; therefore one common ingredient added to tablets is a disintegrant. These are compounds, like starch, that rapidly absorb water and swell – the mechanical action of swelling helps blow the tablet apart. Sometimes, however, a drug substance doesn’t compress very well (think of trying to compress ball bearings for instance) and so we add ingredients that help bind the tablet together – these are called, er… binders. We might also add ingredients to help mask the taste of the drug (most drugs are extremely bitter), to colour the tablet, to help keep the drug from degrading upon storage and so on. Sometimes, especially when the amount of drug is very low, we add an ingredient simply to bulk the tablet out a bit (to make it easier to handle) – these are called diluents. Lactose or microcrystalline cellulose are good examples.
The amount of drug contained in a tablet is important – because we have to add all these other ingredients in order to make the tablet function properly, we can’t add too much drug or the final tablet would be massive. Most tablets contain up to about half a gram of drug – any more and they become very difficult to swallow.
Every box of tablets contains one of these; a patient information leaflet. The leaflet will list all of the ingredients in the tablet and I think it’s fun to try and work out what they all do, because no manufacturer will add unnecessary ingredients to their formulation.
You will also notice that, more often than not, tablets are supplied in these; blister packs. Ever wondered why? It’s because most medicines have shelf-lives of several years, but exposure of a tablet to water or light can be very damaging. So the blister pack protects the tablet during storage but the foil is weak enough that you can push the tablet through it when you want to take it. In some cases, the blister pack can be printed with days of the week on, so it’s easy to see if you have, or have not, remembered to take your tablet each day – this is very important for contraceptive medications for instance. Sometimes you will find a desiccant packed inside the box – a desiccant is something that absorbs water, so if you see a desiccant in the box it indicates that the drug is particularly sensitive to damage by water.
Why do we go to the trouble of making tablets in the first place, I hear you ask? And the answer is… that there are many reasons! The main reason is to control the dose. Many drugs have no effect at low concentration and side effects at high concentrations, so making sure the dose is correct is very important. These ibuprofen tablets contain 200 mg of drug each, and the manufacturer has to perform many quality control checks to make sure this is true. The second reason is to mask taste – I said already but many drugs taste extremely bitter and you wouldn’t be able to swallow them as pure powders, so blending them within a tablet makes them a lot more palatable. It is also easier to swallow a tablet than a load of white powder!
When drugs taste particularly horrible, it is also possible to coat the tablet with something much nicer. Often sugar is used, but in some instances a polymer coat is applied. Sugars, as you might imagine, dissolve very fast and so don’t really affect how quickly a tablet disperses. Sometimes, however, we don’t actually want the tablet to dissolve fast (say because the drug degrades in stomach acid, or because we want the drug to be released over a longer period of time, if it’s a once per day formulation for instance). This is where polymer coats are useful – some polymers only dissolve at certain pH values, and so can be used to target whereabouts along the gut the tablet will dissolve (handily the pH of the human gut generally increases as we move from tum to bum, so we can fine tune the release characteristics of a medicine by carefully selecting the type of polymer used for the coating). We call the polymer an enteric-coat and when they are used in this way we say the tablet is a modified-release formulation. If the polymer coat is designed to dissolve at a specific point in the digestive tract we say the tablet is an extended release formulation and if it is designed to provide a continuous barrier, so that drug is released slowly over time, we say it’s a sustained-release formulation. This is what ‘ER’ and ‘SR’ stand for on some packaging.
Why are tablets so popular? That comes down to ease of manufacture. It’s relatively easy to manufacture a large batch of tablets (say 100,000 to 1 million) quickly and cheaply. Because the punch and die sets ensure all the tablets are the same, if the powder blend put into the tabletting machine is uniform, each tablet should have the same dose. However, because punch and die sets are very expensive, and changing the powder blend will change the way the powder compresses, tablets are usually only available in a limited number of dose strengths. This is fine when the dose of a drug is not particularly important (say for ibuprofen) but it’s a significant issue when the dose of a drug is very important (say for warfarin).
When you are proscribed a course of tablets, the label on the packet will tell you how many tablets to take, when to take them and whether they should be taken with food or on an empty stomach. This information is very important! If more than one tablet per day is proscribed, then taking them at regular intervals helps keep the concentration of drug in your blood at a reasonably constant level – if you take tablets too frequently you can end up with too high a concentration of drug and if you leave too long a gap the concentration can get too low. These effects are particularly important if you can’t remember if you’ve taken your tablet so have another ‘just in case’. This can really cause a spike in blood concentration and that could be very bad. So if you are taking tablets for a long time, or have to take many medications simultaneously, a good idea is to use one of these – a dosette box. Although it won’t ensure you take the tablet at the right time of day, it will ensure you don’t under or over dose!
Finally, are you one of those people who cut tablets? Sometimes people find tablets too large to swallow or sometimes people need a dose that is not available. Where a tablet has a score line across the top it’s usually fine to cut, but I hope you can see from above that if a tablet has a polymer coat, such that it’s an ER or SR formulation, cutting it will be a very bad idea, as the protective function of the polymer will be lost. The same principle applies to crushing a tablet and suspending it in water or fruit juice – it’s easier to swallow, but if it was designed as an ER or SR formulation, you may actually be stopping the product from working properly.
And that is all we need to talk about – hopefully you have a better understanding of what tablets are, how they work and how you should take them. If you found the video useful please hit the like button and consider subscribing – it really helps the channel. Otherwise, thank you so much for watching, and I’ll see you again soon.
See our explanation article on binders:
