Pharmacokinetics Flashcards
What is the primary pathway of drug degradation in the gut?
Answer
A Oxidation B Phase II conjugation reactions C Hydrolysis D Proteolysis E P-glycoprotein efflux drug transportation
C-Hydrolysis
A chemist wishes to increase the rate of gut dissolution of a new tablet formulation. Which of the following would be the most useful option to consider for most medications?
Answer
A
Decreasing the surface area of the tablet.
B
Increasing the surface area of the tablet.
C
Adding an emulsifying agent.
D
Instructing the patient to take thirty minutes after the morning dose of a proton pump inhibitor.
E
Instructing the patient to take thirty minutes after the morning dose of an antacid.
B
Increasing the surface area of the tablet.
In order to increase tablet dissolution the chemist could increase the tablet’s surface area and/or decrease the size.
A new antibiotic for community-acquired pneumonia (CAP) was recently FDA approved. The drug was presented at the Pharmacy and Therapeutics Committee meeting. The drug monograph included the following information:
Community-acquired pneumonia dosing (IV): 675 mg IV Q8H
Community-acquired pneumonia dosing (PO): 675 mg PO TID
Protein binding: 18%
Metabolism: partially hepatic
Half-life (elimination): 1.6 - 2.1 hours
What hospital policy/protocol should this drug be added to?
Answer
A The CAP Policy B The Antibiogram Protocol C The Therapeutic Interchange Protocol D The Pharmacokinetic Policy E The High Risk Medication Protocol
C
The Therapeutic Interchange Protocol
Refer to page 147 of the 2017 RxPrep Course Book. Drugs like this are easily converted to the oral formulation in the same dose. Most hospitals have a “Therapeutic Interchange” Protocol or “IV to PO” Protocol (approved by the Medical Staff) that allows medications to be converted if certain criteria are met (e.g., the patient is able to take oral medications).
When a drug is administered intravenously, which of the following steps does not occur?
Answer
A Absorption B Distribution C Metabolism D Excretion E All of the steps (absorption, distribution, metabolism and excretion) occur when a drug is administered intravenously
A
Absorption
When a drug is given IV, there is no absorption. The drug directly enters the systemic circulation.
AUC values of drug X following IV administration of 50 mg and oral administration of 100 mg were found to be 70 mg x hr/mL and 90 mg x hr/mL respectively. Calculate the absolute bioavailability of drug X. (Answer must be numeric; no units or commas; round final answer to the nearest WHOLE number.)
64
100% x (50/100) x (90/70)= 64%
Which formula is used to describe the rate of drug dissolution (or the rate at which the drug dissolves)?
Answer
A Michaelis-Menten B Noyes-Whitney C Henderson-Hasselbach D Remington's Coefficient E Stimmel's
B
Noyes-Whitney
Refer to page 147 of the 2017 RxPrep Course Book. The rate of dissolution is described by the Noyes-Whitney equation.
An intravenous drug is administered as a 225 mg dose. The resulting AUC is 52 mg x hr/mL. Bioavailability of the oral formulation is 50%. Calculate the clearance of this drug in mL/hr. (Answer must be numeric; no units or commas; round final answer to the nearest HUNDREDTH.)
Answer
4.33
Incorrect
Bioavailability is 100% (F = 1) following intravenous administration. Bioavailability of the oral formulation is not needed for this calculation. Cl = 225 / 52 = 4.33 mL/hr.
A dose of 750 mg of acetaminophen is administered to a patient. A blood sample is drawn two hours after the dose is administered. The concentration of acetaminophen is measured as 8 mcg/mL. Acetaminophen has a volume of distribution of 51 L. How many milligrams of drug remain in the body 2 hours after the dose is administered? (Answer must be numeric; no units or commas.)
408
Choose the correct statement/s that describe the elimination half-life (t½). (Select ALL that apply.)
Answer
A
The half-life is the time required for the plasma concentration of the drug to decrease by 50%.
B
If a drug is eliminated via zero order kinetics, the half life is always the same.
C
The elimination half-life refers to the time it takes for half of the dose to be absorbed through the gut lining.
D
After approximately 5 half-lives, the elimination is considered to be nearly complete.
E
The half-life can be calculated if the elimination rate constant (ke) is known.
A
The half-life is the time required for the plasma concentration of the drug to decrease by 50%.
D
After approximately 5 half-lives, the elimination is considered to be nearly complete.
E
The half-life can be calculated if the elimination rate constant (ke) is known.
A patient has overdosed on phenytoin and is experiencing symptoms of phenytoin toxicity. The prescriber asks how much drug the patient has consumed because he wishes to calculate how long it will take the patient to clear the drug. The pharmacist offers the following correct advice. (Select ALL that apply.)
Answer
A
Phenytoin exhibits Michaelis-Menten elimination.
B
Once the metabolizing enzymes are saturated, phenytoin elimination follows zero-order elimination. The elimination will not correlate in a linear fashion with the amount of drug consumed.
C
With significant overdose the patient will display extreme irritability, anxiety and difficulty sleeping and concentrating.
D
With significant overdose the patient will exhibit CNS depressant effects.
E
Phenytoin initially follows first-order elimination.
A
Phenytoin exhibits Michaelis-Menten elimination.
B
Once the metabolizing enzymes are saturated, phenytoin elimination follows zero-order elimination. The elimination will not correlate in a linear fashion with the amount of drug consumed.
D
With significant overdose the patient will exhibit CNS depressant effects.
E
Phenytoin initially follows first-order elimination.
When a drug such as phenytoin is overdosed, the elimination changes from first to zero-order. This is because the enzymes that metabolize phenytoin are full of the drug (or saturated) and cannot metabolize the extra drug. The additional phenytoin will not be subjected to first-pass (it will pass through the saturated liver) and increase the serum concentration dramatically. This is called Michaelis-Menten, or saturable, kinetics. Overdose of phenytoin produces CNS-depressant effects.
A patient is receiving vancomycin 1,250 mg IV Q12H. The following drug levels are available and orders to hold vancomycin are received after the first level comes back.
1/8: 41.45 mcg/mL at 1800 1/8: 35.6 mcg/mL at 2230 1/9: 22.55 mcg/mL at 1200 1/9: 17.8 mcg/mL at 1900 1/9: 16.36 mcg/mL at 2130
What is the patient’s vancomycin half-life in hours? (Answer must be numeric; no units or commas; round the final answer to the nearest TENTH.)
20.5
