In a patient on multiple-daily-dose gentamicin, which measured concentration best signals accumulation and a higher risk of nephrotoxicity and ototoxicity?

A raised pre-dose (trough) concentration

Which pharmacodynamic index best predicts the efficacy of beta-lactam antibiotics such as piperacillin?

Time the free level stays above the MIC

Peak concentration to MIC ratio

Pharmacokinetics and therapeutic drug monitoring

50 Gulf Prometric Pharmacist (DHA, DOH, MOH, SCFHS, QCHP) practice questions on Pharmacokinetics and therapeutic drug monitoring, part of Pharmaceutics, Pharmacokinetics and Calculations. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
A drug has a volume of distribution of 35 L and a clearance of 3.5 L/h. What is its elimination half-life?
1. A0.1 hours
2. B10 hours
3. C6.9 hours
4. D24 hours
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Answer: C · 6.9 hours
The elimination rate constant is k = CL / Vd = 3.5 / 35 = 0.1 per hour. The half-life is 0.693 / 0.1 = 6.93 hours. Steady state would be reached after about 5 half-lives, roughly 35 hours.
- A: 0.1 hours is a confusion with the rate constant.
- B: Ten hours is the reciprocal of k and ignores the 0.693.
- D: Twenty-four hours does not follow from the numbers.
Remember this
t1/2 = 0.693 x Vd / CL.
Question 2 · Medium
In a patient on multiple-daily-dose gentamicin, which measured concentration best signals accumulation and a higher risk of nephrotoxicity and ototoxicity?
1. AA normal creatinine alone
2. BA low 24-hour urine level
3. CA raised pre-dose (trough) concentration
4. DA low peak concentration
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Answer: C · A raised pre-dose (trough) concentration
A trough that stays above the target shows the drug is not clearing between doses, so tissue exposure is prolonged. Toxicity correlates with sustained exposure, not the peak. Troughs also warn of falling renal function before creatinine rises much.
- A: Creatinine rises late and can lag behind accumulation.
- B: A urine level is not used for monitoring aminoglycosides.
- D: A low peak means underdosing, not accumulation.
Remember this
A persistently raised aminoglycoside trough signals accumulation and toxicity risk.
Question 3 · Hard
A drug is 90% renally excreted. A patient has a creatinine clearance of 30 mL/min (normal 120 mL/min), and the usual dose is 600 mg every 12 hours. Using the Giusti-Hayton method, what is the adjusted dose for the same interval?
1. AAbout 300 mg
2. BAbout 450 mg
3. CAbout 150 mg
4. DAbout 195 mg
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Answer: D · About 195 mg
The renal function ratio is 30/120 = 0.25. The adjustment factor Q = 1 - fe x (1 - ratio) = 1 - 0.9 x 0.75 = 1 - 0.675 = 0.325. The adjusted dose is 600 x 0.325 = 195 mg every 12 hours.
- A: 300 mg is half the dose and ignores the numbers.
- B: 450 mg is three quarters of the dose.
- C: 150 mg is 25% and ignores the non-renal fraction.
Remember this
Q = 1 - fe x (1 - patient CrCl / normal CrCl); adjusted dose = usual dose x Q.
Question 4 · Easy
Which pharmacodynamic index best predicts the efficacy of beta-lactam antibiotics such as piperacillin?
1. ATotal daily AUC to MIC ratio
2. BTrough concentration alone
3. CTime the free level stays above the MIC
4. DPeak concentration to MIC ratio
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Answer: C · Time the free level stays above the MIC
Beta-lactams show time-dependent killing: once the level is a few times above the MIC, higher peaks add little, and what matters is the percentage of the dosing interval that the free concentration exceeds the MIC (fT>MIC). This is the basis for frequent dosing and extended or continuous infusions in severe infection.
- A: AUC to MIC best predicts vancomycin and fluoroquinolone efficacy.
- B: A trough alone is not the efficacy index for beta-lactams.
- D: Peak to MIC ratio drives aminoglycoside killing.
Remember this
Beta-lactam efficacy depends on the time the free drug stays above the MIC.
Question 5 · Easy
A drug with first-order elimination is stopped. About what fraction of the amount in the body remains after 3 half-lives?
1. A25%
2. B12.5%
3. C33%
4. D6.25%
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Answer: B · 12.5%
Each half-life removes half of what is left: 100% to 50% after one, 25% after two and 12.5% after three. After 4 to 5 half-lives only about 3-6% remains, which is why a drug is usually regarded as eliminated by then.
- A: 25% remains after two half-lives.
- C: 33% assumes a fixed third is lost each time, which is not first-order.
- D: 6.25% remains after four half-lives.
Remember this
After n half-lives the fraction remaining is (1/2) to the power n; 3 half-lives leave 12.5%.
Question 6 · Hard
A gentamicin level is 8 mg/L one hour after the end of an infusion and 2 mg/L six hours later. Assuming first-order elimination, how long after the first level will the concentration fall to 1 mg/L?
1. A4.5 hours
2. B9 hours
3. C6 hours
4. D12 hours
Answer and explanation in LearnFree account
Question 7 · Medium
A patient on oral digoxin is having a serum level taken to check for toxicity. When should the sample be drawn relative to the last dose?
1. AImmediately after the next dose
2. BAt least 6-8 hours after the dose
3. C30 minutes after the dose
4. DAt the time of peak absorption, 1 hour after
Answer and explanation in LearnFree account
Question 8 · Medium
Oral propranolol needs a much higher dose than intravenous propranolol for the same effect. The main reason is:
1. AExtensive first-pass hepatic extraction
2. BComplete urinary excretion before absorption
3. CVery high plasma protein binding
4. DIrreversible binding to the gastric mucosa
Answer and explanation in LearnFree account
Question 9 · Easy
A loading dose is determined mainly by which pharmacokinetic parameter?
1. ARenal function only
2. BVolume of distribution
3. CElimination half-life
4. DClearance
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Question 10 · Hard
In a crossover study, an intravenous injection of 40 mg yielded an AUC of 30 mg.h/L, while a 100 mg tablet of the same compound yielded 36 mg.h/L. What is the tablet's absolute bioavailability?
1. A1.20
2. B0.40
3. C0.75
4. D0.48
Answer and explanation in LearnFree account
Question 11 · Medium
After 50 mg intravenously, a drug's AUC is 20 mg.h/L. After 50 mg by mouth the AUC is 14 mg.h/L. The absolute oral bioavailability is:
1. A0.3
2. B0.7
3. C0.14
4. D1.43
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Question 12 · Easy
With repeated dosing at a constant interval and no change in clearance, steady state is reached after about:
1. A2 dosing intervals regardless of half-life
2. B1 half-life
3. C4 to 5 half-lives
4. D10 half-lives
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Question 13 · Medium
A patient is stable on a drug with linear kinetics. The dose is doubled with the same interval. Which statement is correct?
1. ACss roughly doubles, but needs 8 to 10 half-lives to be reached
2. BCss roughly doubles, but is reached in half the time
3. CCss roughly doubles, reached after about 4 to 5 half-lives
4. DThe steady-state concentration stays the same after the change
Answer and explanation in LearnFree account
Question 14 · Medium
When should a vancomycin trough sample be taken for a patient on a 12-hourly schedule at steady state?
1. AWithin 30 minutes before the fourth dose
2. B30 minutes after the first dose
3. CAt any time
4. D6 hours after the first dose
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Question 15 · Hard
Digoxin tablets (bioavailability 70%) are to be used to load an 80 kg patient to 1.4 micrograms/L, taking the volume of distribution as 6 L/kg. What total oral loading dose is needed?
1. A9,600 micrograms
2. B672 micrograms
3. C470 micrograms
4. D960 micrograms
Answer and explanation in LearnFree account
Question 16 · Medium
Why has the 2020 vancomycin guideline moved away from targeting troughs of 15 to 20 mg/L in serious MRSA infections?
1. ATroughs cannot be measured accurately in a hospital laboratory
2. BThey add nephrotoxicity without clearly better outcomes than AUC dosing
3. CVancomycin no longer needs any monitoring in serious infection
4. DTroughs above 15 mg/L are always subtherapeutic in serious infection
Answer and explanation in LearnFree account
Question 17 · Medium
A man stable on digoxin 0.25 mg daily is started on amiodarone for atrial fibrillation. What is the most appropriate pharmacist recommendation?
1. AStop digoxin permanently
2. BDouble the digoxin dose to keep the same effect
3. CContinue the same dose, because the drugs do not interact
4. DReduce the digoxin dose by about one-third to one-half and monitor the serum level
Answer and explanation in LearnFree account
Question 18 · Hard
A 170 cm man weighs 110 kg and his ideal body weight is 70 kg. Gentamicin is dosed at 5 mg/kg using adjusted body weight (ideal weight plus 0.4 x excess weight). What is the dose?
1. A280 mg
2. B350 mg
3. C430 mg
4. D550 mg
Answer and explanation in LearnFree account
Question 19 · Easy
Phenytoin is unusual because within its therapeutic range its elimination is:
1. AIndependent of the hepatic enzymes
2. BUnaffected by the dose
3. CSaturable (Michaelis-Menten kinetics)
4. DPurely renal and linear
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Question 20 · Hard
A patient has a vancomycin concentration of 30 mg/L at 2 hours after the end of an infusion and 12 mg/L at 10 hours. What is the approximate half-life?
1. A8 hours
2. B6 hours
3. C4 hours
4. D12 hours
Answer and explanation in LearnFree account
Question 21 · Easy
What is the usual therapeutic range for total serum phenytoin?
1. A30-50 mg/L
2. B10-20 mg/L
3. C1-5 mg/L
4. D50-100 mg/L
Answer and explanation in LearnFree account
Question 22 · Medium
In the neurology clinic, a hospital pharmacist in Riyadh is asked to interpret a trough phenytoin report: total concentration 6 mg/L, serum albumin 2.5 g/dL, normal kidney function. What does the Sheiner-Tozer correction give for the equivalent normal-albumin concentration?
1. A12 mg/L
2. B6 mg/L
3. C15 mg/L
4. D10 mg/L
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Question 23 · Medium
A 250 mg capsule and a 100 mg intravenous injection of the same drug are compared in one volunteer, giving exposures (AUC) of 30 and 20 mg.h/L respectively. Calculate the absolute bioavailability of the capsule.
1. A0.75
2. B1.5
3. C0.6
4. D0.4
Answer and explanation in LearnFree account
Question 24 · Medium
A patient starts once-daily gentamicin 7 mg/kg, and the hospital uses the Hartford nomogram. How is the drug level usually monitored?
1. AOne random level 6 to 14 hours after the start of the dose
2. BA peak and a trough around the third dose
3. CA level within 30 minutes before every dose
4. DNo level is needed if renal function is normal
Answer and explanation in LearnFree account
Question 25 · Medium
A drug has a clearance of 4 L/h and a target average steady-state concentration of 10 mg/L. Its bioavailability is 100%. What oral dose should be given every 12 hours?
1. A40 mg
2. B960 mg
3. C480 mg
4. D120 mg
Answer and explanation in LearnFree account

25 more Pharmacokinetics and therapeutic drug monitoring questions

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Pharmacokinetics and therapeutic drug monitoring

A drug has a volume of distribution of 35 L and a clearance of 3.5 L/h. What is its elimination half-life?

In a patient on multiple-daily-dose gentamicin, which measured concentration best signals accumulation and a higher risk of nephrotoxicity and ototoxicity?

A drug is 90% renally excreted. A patient has a creatinine clearance of 30 mL/min (normal 120 mL/min), and the usual dose is 600 mg every 12 hours. Using the Giusti-Hayton method, what is the adjusted dose for the same interval?

Which pharmacodynamic index best predicts the efficacy of beta-lactam antibiotics such as piperacillin?

A drug with first-order elimination is stopped. About what fraction of the amount in the body remains after 3 half-lives?

A gentamicin level is 8 mg/L one hour after the end of an infusion and 2 mg/L six hours later. Assuming first-order elimination, how long after the first level will the concentration fall to 1 mg/L?

A patient on oral digoxin is having a serum level taken to check for toxicity. When should the sample be drawn relative to the last dose?

Oral propranolol needs a much higher dose than intravenous propranolol for the same effect. The main reason is:

A loading dose is determined mainly by which pharmacokinetic parameter?

In a crossover study, an intravenous injection of 40 mg yielded an AUC of 30 mg.h/L, while a 100 mg tablet of the same compound yielded 36 mg.h/L. What is the tablet's absolute bioavailability?

After 50 mg intravenously, a drug's AUC is 20 mg.h/L. After 50 mg by mouth the AUC is 14 mg.h/L. The absolute oral bioavailability is:

With repeated dosing at a constant interval and no change in clearance, steady state is reached after about:

A patient is stable on a drug with linear kinetics. The dose is doubled with the same interval. Which statement is correct?

When should a vancomycin trough sample be taken for a patient on a 12-hourly schedule at steady state?

Digoxin tablets (bioavailability 70%) are to be used to load an 80 kg patient to 1.4 micrograms/L, taking the volume of distribution as 6 L/kg. What total oral loading dose is needed?

Why has the 2020 vancomycin guideline moved away from targeting troughs of 15 to 20 mg/L in serious MRSA infections?

A man stable on digoxin 0.25 mg daily is started on amiodarone for atrial fibrillation. What is the most appropriate pharmacist recommendation?

A 170 cm man weighs 110 kg and his ideal body weight is 70 kg. Gentamicin is dosed at 5 mg/kg using adjusted body weight (ideal weight plus 0.4 x excess weight). What is the dose?

Phenytoin is unusual because within its therapeutic range its elimination is:

A patient has a vancomycin concentration of 30 mg/L at 2 hours after the end of an infusion and 12 mg/L at 10 hours. What is the approximate half-life?

What is the usual therapeutic range for total serum phenytoin?

In the neurology clinic, a hospital pharmacist in Riyadh is asked to interpret a trough phenytoin report: total concentration 6 mg/L, serum albumin 2.5 g/dL, normal kidney function. What does the Sheiner-Tozer correction give for the equivalent normal-albumin concentration?

A 250 mg capsule and a 100 mg intravenous injection of the same drug are compared in one volunteer, giving exposures (AUC) of 30 and 20 mg.h/L respectively. Calculate the absolute bioavailability of the capsule.

A patient starts once-daily gentamicin 7 mg/kg, and the hospital uses the Hartford nomogram. How is the drug level usually monitored?

A drug has a clearance of 4 L/h and a target average steady-state concentration of 10 mg/L. Its bioavailability is 100%. What oral dose should be given every 12 hours?