PK video 4: Area under the curve

Video 4 in a series of videos on the fundamentals of pharmacokinetics. This video looks at the area under the plasma drug concentration time curve (AUC) and how it's calculated. Both AUC0-t and AUC0-∞ are covered.

[@mirokarthik]

When to consider AUC0-t and AuC0-infinity

[@GrahamLappin]

On the most basic level, AUC 0-inf is the most important parameter as its used to calculate other PK parameters such as CL. Also at the most basic level, AUC 0-t is used to calculate the extrapolation to AUC 0-inf (see around 17:20 in the video).

[@KigongoFelix]

Dr. Lappin how does that log trapeziodal method come about? I do understand how the linear comes about but the log one, I really don't click.

[@GrahamLappin]

For simplicity, assume the shape of the concentration-time curve on the semi-log plot is a triangle. (ignore the absorption phase on the oral dose). The linear trapezoidal rule assumes the hypotenuse is a straight line, but it is only a straight line when concentration is on a log scale. The log trapezoidal rule takes account of this and hence provides a better estimate of the AUC. Hope this helps?

[@KigongoFelix]

@@GrahamLappin I'm trying to but let me put it this way why [(A-B)/(InA-InB)]*(D-C) AND NOT [(InA+InB)/2]*(D-C)

[@GrahamLappin]

@@KigongoFelix You are asking for the mathematical derivation of the equation - which is something I didn't intend to include. In fact, I've not done this for many years and so I'll struggle to answer this. There are explanations on line, but the mathematics is quite involved.

[@KigongoFelix]

@@GrahamLappin Alright

[@KigongoFelix]

Thanks

[@marcusviniciussouza1314]

Dr Lappin, a question: if we say that the AUC = 10 ng/mL*H, is it correct to say that the patient is exposed to this dosage throughout each hour following the administration of the drug, or after each hour past the administration?

[@GrahamLappin]

I think the units are confusing you. The units are based on multiplying the X and Y axes of the plot. The X axis is hours and the Y axis is ng/mL, so the area in ng/mL x h. You have to define the time period over which the AUC is measured. Let's say it's 0-infinity, then the total area under the curve from the point the drug is administered IV (time 0) to the point it has all been cleared from the plasma. In your example this would be 10 ng/ml x h (total AUC)