It’s not easy to interpret doctor’s prescriptions
The Sunday Nation
Nairobi,
30 September 2012
A couple of years ago, I won two free pizzas for answering a seemingly simple puzzle. The question was: a doctor gives you three tablets at 12 o’clock and tells you take one every hour. What time will you finish the dose?
It is tempting to reason it this way: one tablet taken every hour means that three will require three hours. Therefore, the dose will be completed in three hours time, that is, at 3pm. But that would be the wrong way to go about it.
We can get the correct answer by counting like nursery school children, thus: The first tablet is taken at 12pm; the second one an hour later, that is 1pm; and the third (and last) one at 2pm! Confused? Go over it again…
Things can get more complicated. My doctor recently prescribed a cream ointment to be applied on a skin irritation. The instructions were to apply three times a day for three days… “if the irritation doesn’t disappear, come back and see me” he added.
If I start the treatment on a Monday evening; on what day should I stop applying the ointment? Is it Wednesday? Now, if the medication was in tablet form, the pharmacist would dispense the exact number to last “for the three days”. In that case, I would have continued taking them until they got finished – I wouldn’t need to count the days.
But a cream is “uncountable” so I had to do the count. Starting from Monday evening, the first “application day” ends on Tuesday at lunch time; the second one starts on Tuesday evening and ends on Wednesday afternoon; the third (and final) day starts on Wednesday evening and ends on Thursday afternoon.
Now that’s not the result that most people would expect: Wednesday appears be a more logical answer. But that would be two days; not the three that the doctor ordered. We can also confirm this result by another method.
By telling me to apply the ointment three times a day for three days, the doctor must have intended for use it a total of nine times. I applied once on Monday; three times on Tuesday; and thrice again on Wednesday. Now 1 + 3 + 3 = 7. There are two more applications remaining to make nine. These were done on Thursday morning and afternoon…QED
Perhaps this counting problem is one of the reasons why patients fail to complete the prescribed dose leading to the development of drug-resistant strains of diseases. And if that be the case, then there is for doctors to change the way they give instructions for taking medicines.
They should clearly state the starting and ending day and time. That is, something like, “take one teaspoon two times a day, starting from Monday evening and ending on Saturday morning”. It might sound like a mouthful, but it is not as confusing as the traditional method.
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