Drugs, drugs, everywhere: Throat lozenges edition

Hey everyone. My wonderful and ever patient girlfriend is fighting a nasty cold right now, and has taken to using throat lozenges made by Strepsils to make her sore throat less sore. I got my hands on the lozenge box and discovered that they contain not one, but two active ingredients. Hokey doodle! Each lozenge of Strepsils extra Black Cherry contains 2.4 mg of hexylresorcinol and 4 mg of menthol.

Menthol is a cyclic terpene alcohol that makes plants belonging to the genera Mentha (the mints) smell and taste the wonderful way that they do. It is able to produce a cooling sensation by stimulating a receptor found in skin and mucous membranes called TRPM8 that usually responds to cool temperatures (i.e. 8-28 degrees Celsius). At concentrations of 1% of less, menthol depresses skin sensory receptors, resulting a local anaesthetic effect. At concentrations between 1.25 and 16%, it actually stimulates sensory receptors, countering the effects of any irritants. In either case, topical pain relief (including relief from a sore throat) is achieved. At concentrations above 30%, menthol actually can induce cold pain. Menthol also somehow kills bacteria and fungi, making it a reasonably good antiseptic.

Hexylresorcinol (also called 4-hexylresorcinol) has a long history of use as a drug and ingredient in cosmetics. It works as an antiseptic, and can therefore be found in soaps, skin cleaners, and throat lozenges. Back in the day, before the development of more selective agents, hexylresorcinol was widely used as an antihelmintic. Meaning you could potentially use throat lozenges to get rid of parasitic worms if they were growing inside of you. Awesome. Hexylresorcinol can also be used to prevent shrimp black spot (melanosis), an unappealing surface discoloration of shrimp caused by the enzymatic production of pigmented compounds, as well as the browning and decay of fresh-cut mangoes and apples. It accomplishes these tasks by inhibiting enzymes called polyphenol oxidases.

Strepsils is probably named for Streptococcus, a genus of bacteria that includes a number of species capable of causing sore throats. They've been making it since 1958, so I guess it must do something. That said, if you've got friggin' Strep throat, you want prescription antibiotics and not some OTC throat lozenges. Trust me on this one.

Incidentally, the fine folks at Wikipedia have informed me that cough drops are not the same things as throat lozenges. You see, cough drops are designed to reduce coughing, while throat lozenges are designed to sooth a sore throat.

- Frankos VH, Schmitt DF, Haws LC, McEvily AJ, Iyengar R, Miller SA, Munro IC, Clydesdale FM, Forbes AL, Sauer RM. Generally recognized as safe (GRAS) evaluation of 4-hexylresorcinol for use as a processing aid for prevention of melanosis in shrimp. Regul Toxicol Pharmacol. 1991 Oct;14(2):202-12.
- Patel T, Ishiuji Y, Yosipovitch G. Menthol: a refreshing look at this ancient compound. J Am Acad Dermatol. 2007 Nov;57(5):873-8. Epub 2007 May 10. Review.

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