Dopamine transporter occupancies in the human brain induced by therapeutic doses of oral methylphenidate.
OBJECTIVE
The therapeutic effects of methylphenidate in the treatment of attention deficit disorder have been attributed to its ability to increase the synaptic concentration of dopamine by blocking the dopamine transporters. However, the levels of dopamine transporter blockade achieved by therapeutic doses of methylphenidate are not known. This study measured, for the first time, dopamine transporter occupancy by orally administered methylphenidate in the human brain and its rate of uptake in the brain.


METHODS
Positron emission tomography (PET) and [11C]cocaine were used to estimate dopamine transporter occupancies after different doses of oral methylphenidate in seven normal subjects (mean age=24 years, SD=7). In addition, the pharmacokinetics of oral methylphenidate were measured in the baboon brain through use of PET and [11C]methylphenidate administered through an orogastric tube.


RESULTS
At 120 minutes after administration, oral methylphenidate produced a dose-dependent blockade of dopamine transporter; means=12% (SD= 4%) for 5 mg, 40% (SD=12%) for 10 mg, 54% (SD=5%) for 20 mg, 72% (SD=3%) for 40 mg, and 74% (SD=2%) for 60 mg. The estimated dose of oral methylphenidate required to block 50% of the dopamine transporter corresponded to 0.25 mg/kg. Oral methylphenidate did not reach peak concentration in brain until 60 minutes after its administration.


CONCLUSIONS
Oral methylphenidate is very effective in blocking dopamine transporters, and at the weight-adjusted doses used therapeutically (0.3 to 0.6 mg/kg), it is likely to occupy more than 50% of the dopamine transporters. The time to reach peak brain uptake for oral methylphenidate in brain corresponds well with the reported time course to reach peak behavioral effects.
Medical Department, Brookhaven National Laboratory, Upton, NY 11973, USA. volkow@bnl.gov
N D
ND
Volkow
G J
GJ
Wang
J S
JS
Fowler
S J
SJ
Gatley
J
J
Logan
Y S
YS
Ding
R
R
Hitzemann
N
N
Pappas
D000284:Administration, Oral; D000328:Adult; D000818:Animals; D001289:Attention Deficit Disorder with Hyperactivity / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism*; D001923:Brain Chemistry / Q000187:drug effects*; D002250:Carbon Radioisotopes; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003042:Cocaine; D004298:Dopamine / Q000378:metabolism*; D018492:Dopamine Antagonists / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D050483:Dopamine Plasma Membrane Transport Proteins; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008774:Methylphenidate / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D009419:Nerve Tissue Proteins; D010215:Papio; D014055:Tomography, Emission-Computed
D002250:Carbon Radioisotopes; D002352:Carrier Proteins; D018492:Dopamine Antagonists; D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D008774:Methylphenidate; D003042:Cocaine; D004298:Dopamine