2. Drug quantification from plasma is commonly performed by using techniques such as HPLC or LC/MS. However, these methods do have limitations, and investigators may choose to use a radiolabeled analog of a drug instead. Radioligands are molecules that contain radioactive isotopes, commonly 3H or 14C. This technique allows investigators to quantify drug concentration from radiation measurements. The following measurements were made in 250 g rats following oral administration of 18.2 µCi of a 14C-labeled drug of interest: Time (min) Plasma Radiation Levels (µCi/L) 0 0.0 2 9.7 4 19.2 7 25.3 9 37.8 12 39.6 14 45.8 17 48.8 20 52.0 25 56.4 30 59.2 35 60.1 40 61.1 45 62.1 50 62.8 60 63.1 70 62.1 80 60.1 90 57.3 100 55.5 110 53.7 120 52.2 150 48.0 180 45.0 240 39.0 Note that a µCi is a measure of the amount of radioactivity and hence is a measure of the amount of drug present. Given that the oral bioavailability of this drug is known to be essentially 100%, estimate the following from this data: (5 points per variable; total of 30 points for parts a-f) (a) elimination rate constant, k (b) elimination half-life, t1/2,elim (c) absorption rate constant, ka (d) absorption half-life, t1/2,abs (e) volume of distribution, V (f) clearance, CL
2. Drug quantification from plasma is commonly performed by using techniques such as HPLC or LC/MS. However, these methods do have limitations, and investigators may choose to use a radiolabeled analog of a drug instead. Radioligands are molecules that contain radioactive isotopes, commonly 3H or 14C. This technique allows investigators to quantify drug concentration from radiation measurements. The following measurements were made in 250 g rats following oral administration of 18.2 µCi of a 14C-labeled drug of interest: Time (min) Plasma Radiation Levels (µCi/L) 0 0.0 2 9.7 4 19.2 7 25.3 9 37.8 12 39.6 14 45.8 17 48.8 20 52.0 25 56.4 30 59.2 35 60.1 40 61.1 45 62.1 50 62.8 60 63.1 70 62.1 80 60.1 90 57.3 100 55.5 110 53.7 120 52.2 150 48.0 180 45.0 240 39.0
Note that a µCi is a measure of the amount of radioactivity and hence is a measure of the amount of drug present. Given that the oral bioavailability of this drug is known to be essentially 100%, estimate the following from this data: (5 points per variable; total of 30 points for parts a-f) (a) elimination rate constant, k (b) elimination half-life, t1/2,elim (c) absorption rate constant, ka (d) absorption half-life, t1/2,abs (e) volume of distribution, V (f) clearance, CL
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