Pharmacology : Antibiotics and Stomach Irritation

So, I recently was prescribed an antibiotic for my fun, fun summer acne attack, and as is usual, the instructions warn that possible side-effects may include diarrhea, and related gastrointestinal maladies.

What’s the chemical mechanism there? Why does it happen sometimes, but not others?

Your gut has all sorts of bacteria in it, that help with the digestive process.

Systemic antibiotics, being fairly limited in intelligence, go in spraying bullets at every living micro-organism they encounter. Acne-related, or otherwise. All fall before the Might that is Tetracycline (or whatever).

Since part of your digestive system has been assaulted and is out of operation, your innards aren’t working properly. Hence, diarrhea.

Presumably some folks’ gut microbes have better body armor than others. Or some days they remember to wear their armor and some days they don’t. Or they can handle some antibiotics and not others. All in all, it’s pretty much a crapshoot (sorry!) as to whether you experience this sort of “side effect”.

Us ladies have a related issue that you guys don’t. Some antibiotics mess things up in other parts of the anatomy. Some don’t. 'nuff said?

The antibiotic in question is a topical one, Evoclin, in this case. I marvel at it’s ability to absorb through the skin in sufficient quantity to disrupt digestion.

I think it’s what’s giving me the headache right now, too, but I’ll have to give it a couple of days to make sure it’s not just a coincidence.

I hate medicine.

During the clinical trials, any problems encountered have to be counted as a side effect. If a test subject ate bad Mexican food and got diarrhea, it counts as a side effect.

That said, I’ve had both oral and IV clindamycin (the Evoclin), and have never gotten diarrhea no matter what I did. (I have gotten sick from erythromycin, but not diarrhea.)

If the possibility of diarrhea bothers you that much, eat some yogurt.


Uhh… it doesn’t.

The ‘I hate medicine’ bit is because of the headache I’m getting from it.

Mama Zappa is correct. Antibiotics kill your commensal gut bacteria. This leads to gas, bloating, cramps, and diarrhea and/or constipation.

There was a recent article in CR about "Probiotics’ and how they are a general health benefit, especially intestinally.

Eat more ‘life culture’ yogurt or take an Acidolpholous or Probiotic supplement.

That’s “live culture”. :smack:

Check the directions to see if there’s a warning in there about being in the sun with the medicine on your skin. Acne medication + sun don’t usually mix.

If you’re staying out of the sun and still getting a headache from it…er…call the doctor 'n stuff.

In addition to the changes brought on by altering the number and types of bugs in the intestines, erythromycin also can cause diarrhea because it directly stimulates GI motility. It mimics a hormone called motilin which initiates peristaltic waves. This effect is usually dose related.

Tetracyclines are more likely to cause GI upset than other families of antibiotics becaues a good portion of the dose is excreted in the bile system and ends up in the intestines. The higher concentrations lead to more bacteria being killed off.

Well, I consulted the pharmacist about my headache symptoms, and was told that it was one of the low-incidence side-effects with the medicine, and I shouldn’t worry about it.

So why does tetracycline cause photosensitivity?
How is that caused?