- Assuming first order kinetics what fraction of an IV drug dose remains in the body after 4 half-lives?
- The t1/2 of a drug is 6 hours. What fraction is left in the body at 21h post drug administration?
- Twenty percent of a drug dose remains in the body at t=10hours. What is the half-life of the drug?
- The plasma concentration of a drug administered by IV bolus injection may be described by the following equation:
Ct = 0.92e -0.35t
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where Ct is in units of mg/L and the time (t) is in hours.
If the dose is 50mg calculate the following:
- The plasma concentration at 6.5h post dosing.
- The plasma half-life.
- The volume of distribution.
- The area under the plasma concentration versus time curve.
- The total clearance.
- Drug X is administered as an IV bolus dose of 100mg and the following plasma concentrations were obtained with time:
|Plasma Concentration (mg/L)||2.6||2.4||2.1||1.2||0.75||0.45||0.2|
Calculate the volume of distribution, plasma half-life and clearance of X.
X was subsequently administered via the oral route at a dose of 200mg as both an aqueous solution and as a formulated product. The measured areas under the plasma concentration time curves were 14.3 mg/L.h and 12.6 mg/L.h for the solution dose and formulated product respectively.
Using this data calculate the relative and absolute bioavailability of X.
- Drug W on IV administration to an experimental animal at a dose of 10mg/kg (animal weight 2.3kg) gave the following plasma concentrations with time:
Using the above data:
- Draw a diagram of a compartmental model that describes the plasma disposition of the drug and indicate any relevant rate constants.
- Write an equation describing the plasma concentration versus time curve (use numbers rather than symbols as much as possible).
- Calculate the values of the rate constants you have indicated in part (a).
- What is the terminal half-life of drug W?
- What is the volume of distribution of W and what is the initial dilution volume (volume of the central compartment)?
- Calculate the area under the plasma concentration versus time curve and compare this value with that obtained using the trapezoidal method.
- Drug Y is administered orally to a patient at a dose of 100mg and the following plasma concentrations were obtained with time:
|Plasma Concentration (mg/L)||0.33||1.0||1.8||2.02||2.0||1.6||1.0||0.6||0.38|
Calculate the absorption and elimination rate constants, the volume of distribution and clearance of Y assuming that F, the bioavailability, is equal to 0.75.
If the 100mg oral dose is repeated at 8 hourly intervals calculate the maximum, minimum and average steady-state plasma concentrations.
- Drug A is administered IV to a patient according to the following table:
At 4.00pm on day 2 a plasma sample was analysed for A and a concentration of 6mg/L was obtained.
Is this measured concentration consistent with the expected value?
Volume of distribution of A is 14.5L and clearance is 40mL/min.