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Re: Ritalin-140mgs? daily

Posted by undopaminergic on June 14, 2008, at 10:44:11

In reply to Ritalin-140mgs? daily, posted by Dade on June 10, 2008, at 7:35:30

My usual dose is 216 mg in a 24 hour period of wakefulness, followed by more than 12 hours of sleep.

Dr. Nora Volkow (current director of the NIDA, by the way) and co-authors published their findings on dose-effect releationships for immediate release oral methylphenidate in the article referenced below:
Am J Psychiatry. 1998 Oct;155(10):1325-31. PMID 9766762

The dose is measured in milligrams (mg) or milligrams per kg of body weight (mg/kg), while the effect is defined as the percentage of dopamine (DA) reuptake inhibition or in other words, percent of dopamine transporter (DAT) blockade.

The article found the following dose-effect relationships to be approximately correct for a single dose of immediate release methylphenidate taken by a person weighing 80 kg:
5 mg (0.06 mg/kg) ~ 12% DAT blockade
10 mg (0.13 mg/kg) ~ 40% DAT blockade
20 mg (0.25 mg/kg) ~ 54% DAT blockade
40 mg (0.50 mg/kg) ~ 72% DAT blockade
60 mg (0.75 mg/kg) ~ 74% DAT blockade

To calculate the total daily dose, the above doses need to be multiplied by the number of doses per day actually taken - usually 2-4.

According to my calculations, the above doses of immediate release (IR) methylphenidate (MPH) correspond to Concerta extended release (XR) tablets as follows:
5 mg IR MPH ~ 18 mg Concerta XR MPH
10 mg IR MPH ~ 36 mg Concerta XR MPH
20 mg IR MPH ~ 72 mg Concerta XR MPH
40 mg IR MPH ~ 144 mg Concerta XR MPH
60 mg IR MPH ~ 216 mg Concerta XR MPH

Generally, clincally useful doses result in at least 50% dopamine reuptake inhibition. In other words, 160 mg/day is not at all unreasonable. Of course, many do well on lower doses, whereas others will require even more.




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