Yesterday I had a round of minor surgery. When all was said and done, the surgical site was cauterized with what a nineteenth century physician would have called "lunar caustic" -- silver nitrate to a modern chemist or physician. I have to admit my first geeky thought was, "how does that work?"
Silver nitrate has been used for a long time as a cauterizing agent. In 1826 John Higginbottom, a British physician wrote An essay on the application of the lunar caustic in the cure of certain wounds and ulcers. My physician used a solution of AgNO3, Higginbottom almost certainly used a solid mixture of silver nitrate and silver chloride, but other than that the basic treatment protocol hasn't changed in almost 200 years. Higginbottom notes that the application "smarts" and I would guess that it must have. I felt it, even with a good local anesthetic. The good 19th physician also prescribed adjuvant therapy ("I took away ten ounces of blood and administered purgative medicine") which my physician sensibly eschews!
So why is the stuff called lunar caustic? The caustic part is obvious, silver nitrate is an effective oxidizing agent for organic molecules, including biomolecules. Alchemists associated silver with the moon, its Latin name, argentum derives from "white, shining".
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Such a romantic name for a chemical, shame we've stopped using them really. I've never heard of that particular use for silver nitrate before, only its utility in getting rid of my unwanted chloride ions.
ReplyDeleteSilver nitrate is used pretty commonly as a cauterizing agent. It's pretty easy to control where it goes, and so collateral tissue damage is limited. It's also been used as an antiseptic, to prevent eye infections in newborns.
ReplyDeleteI think I knew abou the antiseptic use for newborns, and remember being quite surprised by the idea. It seems almost too simple a molecule. I guess I'm too used to fiendishly complex organic molecules with medicinal uses and so I skate over the inorganic ones like silver nitrate, cisplatin (and derivatives) etc.
ReplyDeleteUnlike cisplatin which is (for such a small molecule) so selective in targer, I think silver nitrate works in these setting because it's so unselective, it just chews up any organic molecule it encounters. Bacterial walls included. I guess what suprises me about the use in the eye is that in dilute form it's still effective on the bacteria while not eating the eye.
ReplyDeleteMichelle, is the silver the key ingredient? That is, is the nitrate essentially a spectator ion? Also, since silver is the oxidizing agent, then it is reduced, so does that mean that applying this solution leaves behind silver metal? (not bulk metal per se but colloidal particles, possibly even nanoparticles?)
ReplyDeleteMark,
ReplyDeleteYes, the reaction does leave behind reduced silver (generally seems to be considered colloidal - but I can't find a good reference).
Thanks Michelle,
ReplyDeleteI am also a geek (but with no medical or advanced chemistry background)that likes to know why these things work.(especially on ones own body) Presumably it was a serendipidous observation that established silver nitrate worked as a "safe" cauteriser. Perhaps as Mark suggested the silver also has an effective role as an antiseptic (eg now used in dressings) which gives the treatment extra utility. FYI I had a slight wound on my finger by the lateral (not base) quick which grew a "proud flesh" blob without skin etc. The "lunar caustic" worked amazingly quickly, painlessly and effectively, and new skin and quick has repaired the damage.