Odd bit of pharmacology


in Science

I learned an interesting fact at my second Wadham High Table dinner in as many days. Apparently, the antibiotic tetracycline binds aggressively with calcium. This is why you can’t drink milk when you are taking it, since the drug will bond to the milk and not enter your bloodstream. For the same reason, it builds up inside bones and teeth that are growing. If you examine a skeleton from a person who took tetracycline, the bones that were growing at the time can be made to fluoresce.

Because tetracycline turns brown when exposed to light, people who take these drugs while their teeth are still growing are likely to have them turn brown permanently.

{ 7 comments… read them below or add one }

Edward May 11, 2007 at 7:39 pm

Actually, you wouldn’t give tetracycline to someone with strep because it doesn’t work. Nice thing about strep is that they’re about the only bug left that are still susceptible to ordinary run-of-the-mill penicillin.

But yes, if you give tetracycline to a kid under 12 or a pregnant woman, you’ll need a really really good lawyer…

Note: I think you can still drink milk (though don’t quote me on it). I think it is just not within 2 hours of taking the drug. I think it is generally recommended anyway that you don’t eat anything before/after taking it because its bioavailability is best on an empty stomach.

R.K. May 11, 2007 at 4:57 pm

I guess this is one reason doctors tell you not to share prescriptions.

You get strep, they give you tetracycline, your child gets it, you share your antibiotics with him or her, your kid gets brown teeth.

Milan May 12, 2007 at 2:54 am


I was told that tetracycline doesn’t kill intestinal bacteria important to digestion because it is absorbed early. As such, it makes sense that the milk vulnerability doesn’t last too long.

Boo May 12, 2007 at 1:17 pm

Who told you that information? Just curious if it was any tutor I may know.

Anon May 12, 2007 at 5:48 pm

I bet they have used the glowing bone thing on a show like CSI at some point.

Edward May 15, 2007 at 2:48 am

I think the reason it doesn’t kill intestinal bacteria is because there is so widespread resistance to tetracycline. They were the original broad spectrum drugs back in the day (the ’60s I think), but they were overused and became fairly useless rather quickly. Just about the only thing it kills now are STDs and zits (and for acne, it is more the skin-drying side effect than the antimicrobial effect).

I am under the impression that even if an antibiotic is absorbed early, it can still kill intestinal bacteria. Some of the antibiotics given by I.V. (cloxacillin, clindamycin) are notorious for wiping intestinal flora, which can give rise to things like C. difficile. Probably has something to do with the gut being really richly vascularized and some kind of reverse transport across the epithelial cells.

Am writing an exam on this stuff this weeks, so that’s probably why lots of random stuff about it…

Milan May 15, 2007 at 1:19 pm


Thanks for the information. It makes sense that blood flow would carry antibiotics absorbed early in the digestive tract into the intestines.

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