I’m on a schedule of antibiotics to treat a wicked sinus infection and started wondering something this morning. I’m supposed to take these horse pills for 10 days straight, to maintain the same level of antibiotic in my system for that period of time. So what happens to yesterday’s dose? Does it get used up fighting the infection? Does it get excreted? Does it just get tired of the whole thing and retire? I slept through microbiology in college…can anybody who didn’t help me out here?
Different antibiotics work differently.
What are you on?
Avelox 400mg Once daily.
That’s a fluoroquinone. What it does is it inhibits the DNA gyrase enzymes which your bacteria use to unwind their DNA strands so that they can then replicate.
Avelox is good at entering into various bodily fluids, like the mucous in your sinuses, which is probably why it was prescribed for your sinus infection.
Your body gets rid of the antibiotic by excreting it in your urine and/or breaking it down in your liver and excreeting it through your bile. The dosing interval for any antibiotic is set by how quickly your body gets rid of it.
So basically what the drug has done is sterilized the little beasties so they die off naturally, as opposed to killing them outright? What’s the life expectancy of a staph bacillus, anyway?
Don’t forget about the action of your own immune system- I suspect that it does most of the bacterial killing, not old age.
Antibiotics that do that are said to be bacteriostatic.
Antibiotics that kill them outright are bacteriocidal. I’m too lazy to look it up, but I’m fairly sure fluroquinolones are bacteriocidal.
Antibiotics usually attack bacterial (or fungal) invaders without decimating your native cells by taking advantage of a property that they have, that you don’t. This may involve how bacteria build or maintain cell walls (bacteria and people have different sizes and wall make-up; not having a cell wall to protect it from the elements is tantamout to dying), or make proteins needed to function. DNA and RNA are required to make proteins and some antibiotics interfere with the bacterial version of that. Some antibiotics stop the bacteria from making necessary chemicals required for synthesis (e.g. Septra interferes with folate production). Some antibiotics are bacteriocidal and kill the cell directly (rather than bacteriostatic which is more indirect).
A little more here: Homepage | Tufts University School of Medicine
Most gets excreted by the kidneys or in the poop. Very little actually finds the bacteria. The drug distributes throughout all the tissues of the body with varying penetration. Fluorquinolones get into secretions pretty well making them great for airway or urine. Generally, after around 3-4 doses, your trough level (the dose in your body tissues right before you take the next dose) is pretty close to a steady state, and has reached the level needed to treat the infection in most tissues, with some important exceptions like brain and bone with this class of drugs.
Moxifloxacin has a pretty broad spectrum of bugs that it treats – Gram positives, gram negatives, atypicals, both aerobic and anaerobic, hell it even covers Mycobacterium tuberculosis. This range and its ability to get into secretions makes it a great drug for treating sinusitis, which is usually due to Gram positive S. pneumo, or two or three different Gram negatives. IMHO, a little too good of a drug for sinusitis which is a) rarely bacterial and therefore antibiotics are not usually necessary and b) due to only two or three different bugs which are easily treated with a narrower range antibiotic like amoxicillin. Moxiflox has a distressingly high rate of C. diff colitis, which happens when you get out the big gun drugs…
Well, whatever it is doing it is doing well. I knew the Dope would come through. No colitis yet, and I’m on pill #3. (Crosses fingers.)