| Pharmacokinetics & Pharmacodynamics |
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Which of the following types of drugs will have maximum oral bioavailability?
A. Drugs with high first-pass metabolism. B. Highly hydrophilic drugs. C. Largely hydrophobic, yet soluble in aqueous solutions. D. Chemically unstable drugs. E. Drugs that are P-glycoprotein substrates.
C. Highly hydrophilic drugs have poor oral bioavailability, because they are poorly absorbed due to their inability to cross the lipid-rich cell membranes. Highly lipophilic (hydrophobic) drugs also have poor oral bioavailability, because they are poorly absorbed due their insolubility in aqueous stomach fluids and therefore cannot gain access to the surface of cells. Therefore, drugs that are largely hydrophobic, yet have aqueous solubility have greater oral bioavailability because they are readily absorbed.
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Which of the following is true about the blood–brain barrier?
A. Endothelial cells of the blood–brain barrier have slit junctions. B. Ionized or polar drugs can cross the blood–brain barrier easily. C. Drugs cannot cross the blood–brain barrier through specific transporters. D. Lipid-soluble drugs readily cross the blood–brain barrier. E. The capillary structure of the blood–brain barrier is similar to that of the liver and spleen.
D. Lipid-soluble drugs readily cross the blood–brain barrier because they can dissolve easily in the membrane of endothelial cells. Ionized or polar drugs generally fail to cross the blood–brain barrier because they are unable to pass through the endothelial cells, which do not have slit junctions.
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A drug with a half-life of 10 hours is administered by continuous intravenous infusion. Which of the following best approximates the time for the drug to reach steady state?
A. 10 hours. B. 20 hours. C. 33 hours. D. 40 hours. E. 60 hours.
D. A drug will reach steady state in about four to five half-lives. Thus, for this drug with a half-life of 10 hours, the approximate time to reach steady state will be 40 hours.
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Alkalization of urine by giving bicarbonate is used to treat patients presenting with phenobarbital (weak acid) overdose. Which of the following best describes the rationale for alkalization of urine in this setting?
A. To reduce tubular reabsorption of phenobarbital. B. To decrease ionization of phenobarbital. C. To increase glomerular filtration of phenobarbital. D. To decrease proximal tubular secretion. E. To increase tubular reabsorption of phenobarbital.
Correct answer = A. As a general rule, weak acid drugs such as phenobarbital can be eliminated faster by alkalization of the urine. Bicarbonate alkalizes urine and keeps phenobarbital ionized, thus decreasing its reabsorption
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A 55-year-old male patient (70 kg) is going to be treated with an experimental drug, Drug X, for an irregular heart rhythm. If the Vd is 1 L/kg and the desired steadystate plasma concentration is 2.5 mg/L, which of the following is the most appropriate intravenous loading dose for Drug X?
A. 175 mg. B. 70 mg. C. 28 mg. D. 10 mg. E. 1 mg.
A. For IV infusion, Loading dose = (Vd) × (desired steady-state plasma concentration). The Vd in this case corrected to the patient’s weight is 70 L. Thus, Loading dose = 70 L × 2.5 mg/L = 175 mg.
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