Wednesday, October 15, 2008
The Pharmacokinetics of Speed
Meth lingers longer than coke, targets different brain areas.
Scientists at the Brookhaven National Laboratory, already famous for their work on positron emission tomography (PET) scans, have traced the pathways by which methamphetamine lingers in the brain longer than cocaine. The Brookhaven Lab, managed by the U.S. Department of Energy (DOE) tested non-drug abusing volunteers. The results will be published in the November 1 issue of Neuroimage.
The researchers injected the 19 volunteers with radioactively tagged doses of the drugs. Scanning cameras then recorded the concentration and distribution of the tagged molecules. Both cocaine and methamphetamine enter the brain quickly—part of the reason why the two drugs are so reinforcing. However, cocaine clears the brain just as quickly, while meth does not. Moreover, the study demonstrated that methamphetamine is much more widely distributed throughout the brain than cocaine, which tends to exclusively target the dopamine-rich limbic reward pathways. “This slow clearance of methamphetamine from such widespread brain regions may help explain why the drug has such long-lasting behavioral and neurotoxic effects,” said Joanna Fowler, lead author of the study.
The researchers also looked at a more controversial hypothesis—widespread reports that methamphetamine abuse among African Americans is markedly lower than it is among Caucasians. These reports lead Fowler and her colleagues to question “whether biological or pharmacokinetic differences might explain this difference.”
The answer? Evidently not. According to a Brookhaven press release, “Surprisingly, the researchers found significant differences in cocaine pharmacokinetics between African Americans and Caucasians, with the African Americans exhibiting higher uptake of cocaine, a later rise to peak levels, and slower clearance.” When it came to speed, however, the scientists failed to detect any racial differences in uptake.
Fowler’s conclusion: “Variables other than pharmacokinetics and bioavailability account for the lower prevalence of methamphetamine abuse in African Americans.”
She added that “the differences observed for cocaine pharmacokinetics are surprising considering there are no differences in cocaine abuse prevalence between these two ethnic groups.”
This may come as a surprise to people who have been taught by news coverage and crime dramas to think of the crack problem as a “black problem.” But it may also indicate an inherent physiological preference for cocaine among African Americans, regardless of stated levels of abuse prevalence. As usual, more studies are needed.
Image Credit: Brookhaven National Laboratory News