A few weeks ago, I tested positive for strep throat. I was given an antibiotic, and told to take one capsule per day for seven days, I think.
This week, my wife has a throat infection - not strep. She also got an antibiotic, and has to take one per day for a week. (Two capsules for her first dose, though).
I’m considerably taller and heavier than she is.
Why did we get the same dosage? Or, more generally, how do doctors decide how much and how long to prescribe antibiotics or medicine in general?
Last winter, when I and Mr Mad (1 foot taller, 100 lbs heavier) got one prescription (same pills, just twice as many in the bottle – and $22 bucks cheaper!) for strep, I asked the pharmacist. Her explanation, translated through my general self-centered misery, as well as the mists of time, was that the antibiotic dosage is for the germs, not the “host organism.” I remember the “host organism” part very clearly, for some reason.
My next question was “why do they make pills to treat sore throats so freakin’ big?” She declined to answer that question to my satisfaction.
I hope a more detailed, accurate answerer posts – I’d like an explanation while I’m coherent enough to understand.
In truth, there is very, very little evidence to guide how much or how long one needs to be treated in order to obtain a cure.
It is reasonable to suppose that the dose of antibiotic is pretty well independent of the patient’s size. After all, you’re trying to kill all the bacteria, an amount which is pretty well independent of the patient’s size (unlike, say, treating hypertension where the extent of the problem is the whole body, so to speak).
Still, other things sometimes do need to be taken into account when prescribing antibiotics, especially kidney function (since many antibiotics are cleared out of the body by the kidneys and some of them can damage the kidneys) and the simultaneous administration of other drugs.
Several issues at play here. When confirmed diagnosis of strep throat (Group A beta hemolytic strep), the antibiotic of choice for those not allergic remains Penicillin. There is much misconception about the appropriate dose, but in the standard medical literature, it has been shown that oral Penicillin in the dose of 500mg twice daily for 10 days is the optimal regimen, regardless of weight of patient (as long as we are talking about adults). There are single injectable doses as well that are also proven effective, but many opt out because it involves an intramuscular injection which is not without pain.
The other issue is “throat infection-not strep”. One of the major issues facing our modern medical society these days is inappropriate use of antibiotics for infections for which antibiotics have no place. Of the many situations where antibiotics are inappropriately used, non-strep throat infections, bronchitis, and sinusitis, are major culprits. These are all infections caused by viruses, for which antibiotics have NO utility. In fact, the use of antibiotics in these situations is a major cause for emerging antibiotic resistance to really serious infections. For a glimpse of the problems, here is a link to the CDC http://www.cdc.gov/drugresistance/community//technical.htm
This whole situation is a challenge to physicians and patients alike - folks go to the doctor because they are sick, they want something that will make them better and doctors want to do something. When was the last time you went to the doctor and got “advice” without a prescription? Were you happy with the encounter, did you feel that what it cost you to visit the doctor was worth the “advice”. Most folks expect a prescription when they go to the doc; after all, why go to the doc if you don’t need prescription drugs - we all know how much valuable medical advice is available for free on the internet.
I know that on the micro level, one needless prescription for an infection that it won’t really help (but could it, you ask, when there is no way to prove it with a simple test as is the case with many viral infections) seems hardly worth getting uptight about, but it is. There are a number of infections now in hospitals across the country for which there are dwindling numbers of available antibiotics to treat, and in fact the reason for that lies at the very doorsteps of doctors visits for which antibiotics are prescribed for “throat infections-not strep”.
In a related vein, there is very little data to support the commonly held notion that intravenous (IV) antibiotic therapy is superior to that delivered by the oral route (po).
AFAIK, there are only a very few studies comparing the two routes head-to-head in the treatment of many common infections. Those studies that have been done failed to demonstrate the superiority (or inferiority) of one route compared to the other. The best evidence in this regard is for pneumonia and pyelonephritis (kidney infection).
IMO, IV antibiotics should be reserved for those who can’t take po, whose GI tract isn’t functioning, or who require essentially unchanging blood levels of the antibiotic. YMMV. (There will never be RCT’s for most of this anyway, since “therapeutic equipoise” would be impossible, let alone ethics approval).
Funny, that’s not what my doctor has told me on the various occasions I’ve had bronchitis (or sinus infections, for that matter). He said that although it’s true that often antibiotics are prescribed for infections that are viral rather than bacterial, there are still plenty of infections of the types that you mention that are indeed bacterial.
To me the interesting part was that the incidence of bacterial vs. viral infections sometimes varies according to the medical history of the person being treated; for example, I am asthmatic, and he told me that asthmatics are much more likely than non-asthmatics to come down with bacterial rather than viral bronchitis. (Oh, and my doc knows me well enough to know that I will gladly not take an antibiotic if it isn’t necessary, and more than once he has sent me home without a prescription and told me to wait it out.)
The idea that it’s the amount of bacteria that matters rather than the host size doesn’t hold water. A larger person on the same dosage will presumably have a lower concentration of the antibiotic in his or her body, and this will be less inhibitory to the bacteria.
That doesn’t make sense to me. Staph, at least, can infect pretty much any tissue. I’d believe that strep may be the only *common *throat bacteria, but it’s not the only possible throat bacteria.
Yeast, while not a bacteria, can also infect the throat.
After a sports injury once, I told the doctor that I was taking the recommended dose (2 capsules each time) of Advil, and she said, “For someone your size, take three or four.” (I’m 6’3".) Seemed logical to me.
I always liked the 81 mg of aspirin every day. Eighty-one! 82 mg is clearly too much, and 80 mg just isn’t worth it!
I suppose so, but, this may be made almost irrelevant in that most antibiotic doses are overkill.
It is also not the case that the concentration of the drug is necessarily proportional to body “size”. The concentration of antibiotic (and other drugs) is influenced by the so-called “volume of distribution” (which often exceeds the patient’s volume!), protein binding, tissue penetration, use of other drugs which influence the antibiotic’s metabolsim, and I’m sure more that I’ve just forgotten.
Antibiotic treatment for common pharyngitis (your typical sore throat) has only been proven to be effective when the strep bacteria is confirmed. Although studies in the medical literature show that treatment with penicillin can shorten the duration of the symptoms with strep throat, the major reason for treating pharyngitis caused by strep is to prevent the serious complication of group A strep infection - Rheumatic fever with potential heart damage, etc. Because strep is relatively contagious, antibiotic treatment also makes sense from a population health perspective too since reducing the broader population risk of Rheumatic fever is highly desirable. Most otherwise healthy people will, through their own immune systems, eliminate a strep throat without antibiotics. Rarely, complications from a common strep pharyngitis could occur such as an abcess around/behind the tonsil thus providing another potential reason to treat all documented strep throats with antibiotic. Other non-virus infections of the throat are real (yeast, gonorrhea come to mind), though extremely rare compared to viral pharyngitis. When identified, they of course need specific treatment, but again, sore throats are usually not these entities.
In the absence of strep, the vast majority of other sore throats are indeed caused by viruses. It is the treatment with antibiotics of these instances of “throat infection - not strep”, which occurs far more commonly than the medical community would like to admit, and leads to the problems with emerging antibiotic resistance. I’m sure you can find many anecdotal stories from people who didn’t have strep, got antibiotics, and felt quickly better - this promotes the unreasonable prescription of antibiotics, but it is not medically justified.
Of course, in all decisions clinical, individual patient factors (i.e. asthmatic, smoker, weakened immune system for whatever reason) may prompt a physician to be more aggressive in the prescription of antibiotics for bronchitis and sinusitis, but again there is ample evidence that a large portion of those infections are viral. As can be seen by exploring the link provided to the CDC in my earlier post, there are well supported reasons for being far more judicious in prescribing antibiotics for these varieties of upper respiratory infections. One of the simple clinical strategies is, when there is no reason to move aggressively to antibiotic therapy, to simply wait a while - bronchitis and sinusitis that persists beyond 10-14 days is more likely to be bacterial, and thus would warrant treatment.
Excessive antibiotic use is a huge problem and it is compounded by the fact that in many clinical scenarios, it may not be possible to accurately “rule out” bacterial infection - is it better to treat with antibiotics on the chance that it is bacterial - depends completely on the individual situation which only you and your doctor can address at that time. But, if you stop going to the doc expecting to get antibiotics for every little sniffle, sore throat, cough, and congestion you can contribute to solving the problem.
81 miligrams is not a carefully calibrated dose. It just happens to be approximately a quarter of a standard 325mg aspirin pill, so 81mg pills were used as baby aspirin back before we knew not to give aspirin to babies. 325 miligrams arrived, I believe, because it’s five grains (a grain being 65 miligrams, though I don’t know the origin of the grain.) Since there’s no way to determine some exact ideal dose, a lot of this is just due to the vagaries of history.
How are standard doses calculated for new medicines, anyway? How do they figure out that this pill needs 5 miligrams, and this one needs 10, and this one needs 400? Since they’re usually nice round numbers, I’m guessing even with all our modern techniques it’s still basically an estimate.
