PharmPK Discussion - Significance of triexponential vs biexponential plasma curve

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On 1 Mar 2015 at 01:09:19, Nisha K R (nishavenkatesh.-a-.YAHOO.CO.IN) sent the message


Dear All,

I work with radiotracers. A tracer injected as IV bolus had a triexponential plasma curve in young
rats and a biexponential plasma curve in aged rats. Also the K1/k2 (equivalent to k12/k21 in drug
pharmacokinetics if I am not mistaken) for the brain is higher in the young animals and lower in the
aged. What could be the significance of these?

This tracer is not a P-gp substrate. The aged animals were twice as heavy as the young. The tracer
uptake into fat was not significantly different, but lower in the aged animals. Other than brain,
the only other organs showing a significant reduction in uptake in the aged animals were the liver
and kidney.

Best Regards,
Nisha

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On 3 Mar 2015 at 14:57:57, Edward O'Connor (efoconnor.-at-.gmail.com) sent the message
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Maturation of the blood csf and blood brain barrier?
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On 3 Mar 2015 at 14:59:37, Andréa Diniz (dinizepires.-a-.hotmail.com) sent the message
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Hello Nisha
Did you add covariate (weight) to your model?
Andrea
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On 4 Mar 2015 at 16:29:01, Nisha K R (nishavenkatesh.-at-.yahoo.co.in) sent the message


Hello Andrea,

Thank you for replying. Weight has been accounted for in the corrections for quantity of
radioactivity injected (x MBq/Kg). This would assume a linear relationship which is not strictly
correct. However we did not see any relationship between weight and K1/k2.

Nisha
--
Hello Edward,

We initially thought this might be a reason, but then wondered if so wouldn't both K1 and k2 change
similarly and therefore no change occur in K1/k2?

Nisha

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