Discussions that mention methylphenidate

ADD / ADHD board


Index,

I want to explain the apparent contradiction that 10mg is NOT larger than 5mg.

You are absolutely correct.

MrsSparky, you should find this helpful in understanding your son's reaction to a "higher" dose patch.

The answer lies in the definition of "dose." For our purposes let's define "dose" as the highest plasma level reached in any given day.

Assuming Daytrana releases the exact same dose hourly then mg/hr release = 0.9 for a 10mg patch that lasts 9 hours.

Let's use 4 hours as our half-life figure and assume no mg/mL plasma loss up until hour 4. What is peak plasma level for a 10mg patch? About 3.6 mg around hour 4. That would hold until hour 9 then drop off for the next 4 hours to virtually 0.

Like I said, you are absolutely correct because peak plasma for a 5mg IR tab would be 5mg at hour two. The 10mg patch NEVER gets plasma concentrations that high and for the first four hours is significantly lower unless Daytrana releases more upfront. That I don't know.

Here are some facts and figures I scared up you might enjoy.

Peak plasma concentrations for methylphenidate are reached between 1 and 3 hours after ingestion with 2 hours being average. Half-life is reached in 2 to 4 hours with 3 hours as average.

The average bioavailability for methylphenidate is 30% with individual differences ranging from 11% to 52%. The difference between 52 and 11 is 41 (52-11=41). Who skews the average? Adults. Peak plasma levels of 10.8 and 7.8 ng/mL were measured 2 hours after administration of 0.30 mg/kg in children and adults respectively.

These numbers easily explain the wide variation in efficacy experienced.

Definitions:
Bioavailability: how much is absorded and produces the intended action.
Peak plasma concentration: highest methylphenidate level per volume of blood.
Half-life: Time in hours when half the peak-plasma value is reached. Hours are measured from ingestion.

The numbers above are pulled from research documents.

Bob