Chemistry of Throat Lozenges

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I’ve been suffering the effects of a sore throat these past few days (the curse of the end of term cold), which inevitably got me thinking about the chemical compounds in the throat lozenges I’ve been binging on. Whilst there are a range of possible active ingredients, many throat lozenges use one (or two) of three particular compounds. This graphic takes a look at them, and how they help provide relief!

There are three compounds commonly used in throat lozenges: amylmetacresol, dichlorobenzyl alcohol, and hexylresorcinol. In many cases, amylmetacresol and dichlorobenzyl alcohol are actually used in combination, whilst hexylresorcinol seems to be more commonly used in isolation. That’s the helpful compounds identified, then, but how exactly do they help?

Firstly, all three of the compounds mentioned have antiseptic properties, capable of killing some strains of bacteria. This is, of course, helpful in cases of sore throats with a bacterial cause, but according to studies these only account for no more than 20% of throat infections. The remaining cases are caused by viruses, and some studies even place the percentage for viral infections as the cause of sore throats as high as 95% of cases. Lozenges containing the combination of amylmetacresol and dichlorobenzyl alcohol have been shown to be able to kill a small selection of viruses, but this and their antiseptic action alone doesn’t seem to account for their soothing effects.

To an extent, how they exert these effects still hasn’t been fully explained, but recent studies suggest that the soothing nature of a throat lozenge is due to the interaction of the compounds therein with sodium channels. To put it incredibly simply, sodium channels are effectively like gates that allow sodium ions to enter cells under certain conditions. This can have a variety of purposes, but the role we’re interested in is that of pain.

A type of sodium channels called voltage-gated sodium channels help convey nerve signals to the brain, to signal pain, or soreness in the case of a sore throat. It’s these that the compounds in throat lozenges have been shown to interact with. They have been shown to bind to these sodium channels, blocking them and thereby inducing an anaesthetic effect, preventing the usual signalling of soreness to the brain. Their effect is comparable to that of some commonly used local anaesthetic compounds, and may help explain why they’re effective in the relief of soreness and discomfort in the case of sore throats.

Of course, these aren’t the only compounds in throat lozenges. Flavouring compounds will also be included, in order to make the lozenges more palatable. Some lozenges include menthol, the minty compound that also induces a cooling effect in the mouth and throat, and which has antiseptic and anaesthetic properties of its own. Other anaesthetics, such as benzocaine, can be included, and treatment for other symptoms can also be catered for; antitussives (cough suppressants) such as dextromethorphan can be added to the formulation, as well as decongestants like phenylephrine.

If you want more of the science behind banishing the symptoms of colds, check out the chemistry of decongestants! Remember, you can reach all of the previous medicinal chemistry graphics on the infographics index page here.

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