Monday, May 31, 2010

Surviving Medical School Tip #1: The 90/10 Rule

Medical school is like drinking water from a fire hydrant. Way too much information! And the worse part is that, without any clinical experience, trying to separate the wheat from the chaff is nearly impossible. Is memorizing lipid metabolism important? Will I ever needs to read an electron micrograph of the basement membrane in the future? Will I ever need to know how many ATPs are produced by 4 rounds through the Kreb Cycle? In a word... no!

If you are a medical student, remember this: 90% of the stuff that you learn in the first two years of medical school, you will eventually forget and never use again in clinical practice (this is assuming, of course, that you are going through a 'traditional' program). The other 10% will be drilled and pounded into your brain ad nauseum until you learn it. Your clinical rotations during your third and fourth years (and your residency and thereafter) will provided that "pounding". 

When I was a medical student (a long time ago), I use to get stressed out because I couldn't retain all the information that I learned in my basic science courses. But as I moved from medical student to resident to attending, I slowly realized that almost everything that I needed to know was reinforced over and over and over again—and I didn't need to learn and retain everything with the first try. So take heart, take a deep breath, and do your best to enjoy learning about the wonders of the human body.
Sunday, May 30, 2010

Diagnosis and treatment of B12 deficiency

I never directly measure serum Vitamin B12 levels anymore. Vitamin B12 (like C-Reactive Protein) acts as an acute phase reactant and therefore can be falsely elevated even in the presence of significant B12 deficiency. A much more sensitive test is the serum methylmalonic acid (or serum MMA for short). But remember that serum MMA is inversely proportional to the Vitamin B12 level. Therefore, a B12 deficiency would cause an elevated serum MMA. The reason is as follows:
Vitamin B12 acts as a co-factor in the conversion of methylmalonyl-CoA to succinyl CoA. Therefore a deficiency of B12 would cause a build up of methylmalonyl-CoA (and therefore serum MMA). Whatever! Just clinically remember that serum MMA is inversely related to B12. 

Now once we diagnose B12 deficiency, how do we treat B12 deficiency? For years, clinicians use to give Vitamin B12 shots. They were time consuming for the doctor and painful for the patients. Now we know that B12 can simply be replaced orally. But how? If a patient has pernicious anemia and is not making any intrinsic factor, how can oral B12 get from gut to blood? If we consider that the daily recommended daily allowance of B12 is 2 mcg and we typically prescribe 2000 mcg, the answer is probably related, at least partially, to simple diffusion.

I usually repeat another serum MMA about 2-3 months after starting treatment. Then I check it on a yearly bases if normal.
Sunday, May 30, 2010

The "Rule of 6" for pediatric amoxicillin dosing

Amoxicillin is typically dosed at 40 mg per kg per day. In the U.S. which will forever be stuck in the dark ages of pounds and ounces (instead of kg and ml), many calculations are required in order to figure out how much amoxicillin to give to a kid. Here is a short cut:

   Weight in Pounds  x  6   =   mg dose of amoxicillin per dose

Let's go through an example. Assuming that you have a 40 pound child in your office, the calculation would look like this: 40 x 6 = 240. So this child would need 240 mg of amoxicillin 3x/day. The important thing to remember is that this calculation is PER DOSE (and NOT per day). And because, amoxicillin is prepared as 250 mg per teaspoon, this kid would need approximately one tsp by mouth 3x/day for 10 days. Piece of cake! And no calculators involved! This rule also works for Pen VK. And it works of Keflex and Augmentin as long as you dose both of them 3x/day. There are other antibiotics that follow the "Rule of 6" but I forgot which ones off hand.

This is a handy tip I learn from my friend and partner Ron Reynolds. And I think he even wrote a paper on it somewhere (I'll check to see if I have permission to publish the original article)...