Quiz 1

I will be periodically posting medical quizzes followed by answers and brief explanations. These quizzes represent medical problems and conditions that may be encountered by medical professionals. They are mainly intended as quick educational tips for medical students and residents, in addition to nephrology fellows. Although, I will make every effort to ensure the accuracy of the information presented, I am not responsible for any unintended mistakes or inappropriate use or application of the information presented. You should always consult with your supervising attending when you are taking care of your patients.

The Quiz

You are evaluating a patient who was admitted with a serum sodium of 125 meq/l. He is slightly symptomatic from the hyponatremia. you calculate that he needs 240 meq of sodium to correct his serum sodium to 131 meq/l over a 24 hours period. The patient refuses the insertion of an IV line and asks you to correct his "sodium problem" using an oral medication. The pharmacist informs you that NaCl tablets are available in 600 mg strength.

How many NaCl tablets should you prescribe for the patient to take in the next 24 hours?

Please scroll down to read the answer

Many medical professionals when prescribing salt tablets, they order 1 or 2 tablets twice or three times per day. Although, this may lead to some rise in serum sodium , it will not achieve the above target of 6 meq/l in 24 hours. To convert mg to mmol, you need to

divide the weight in mg ( 600 ) by the molecular mass of NaCl (23+35.5=58.5):

600/58.5= 10.256 , each 600 mg tablet contains about 10.25 meq of Na, so you need to prescribe about 23.5 tablets in a 24 hour- period to raise the serum sodium by 6 meq/l.

It is important to remember that the above calculation is an estimate of the correction and the patient may end up with a serum sodium that is above or below the target. This is easy to explain, if you remeber that serum sodium concentration is determined by the ratio between total body sodium (and K) and total body water. So the final serum sodium achieved will depend on other factors such as total water and sodium (and K) intake and losses (urine, stool, sweat...)

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