DHA Pharmacist 4 — Questions and Answers
Question 1: A patient is prescribed warfarin and starts taking clarithromycin for a respiratory infection. What is the most likely pharmacokinetic interaction?
- Clarithromycin induces CYP2C9, decreasing warfarin levels
- Clarithromycin inhibits CYP3A4 and CYP2C9, increasing warfarin levels (Correct answer)
- Clarithromycin displaces warfarin from plasma proteins, reducing efficacy
- Clarithromycin enhances renal clearance of warfarin
Correct answer: Clarithromycin inhibits CYP3A4 and CYP2C9, increasing warfarin levels
Clarithromycin is a potent CYP3A4 and CYP2C9 inhibitor, which reduces warfarin metabolism and increases its anticoagulant effect, raising bleeding risk.
Question 2: Under DHA regulations, which category of medications requires a triplicate prescription in the UAE?
- Antibiotics
- Controlled substances (narcotics and psychotropics) (Correct answer)
- Antihypertensives
- Anticoagulants
Correct answer: Controlled substances (narcotics and psychotropics)
UAE law requires controlled substances such as narcotics and psychotropics to be dispensed only on triplicate prescriptions issued by licensed practitioners.
Question 3: A pediatric patient weighing 20 kg requires amoxicillin at 40 mg/kg/day divided every 8 hours. What is the correct dose per administration?
- 133 mg
- 200 mg
- 267 mg (Correct answer)
- 400 mg
Correct answer: 267 mg
Total daily dose = 40 mg/kg × 20 kg = 800 mg/day; divided every 8 hours gives 800 ÷ 3 ≈ 267 mg per dose.
Question 4: Which parameter best describes the fraction of an oral drug that reaches systemic circulation unchanged?
- Volume of distribution
- Clearance
- Bioavailability (Correct answer)
- Half-life
Correct answer: Bioavailability
Bioavailability (F) is defined as the fraction of an administered dose that reaches the systemic circulation in its active form.
Question 5: A patient on methotrexate for rheumatoid arthritis is also prescribed ibuprofen. What is the primary concern?
- Ibuprofen induces methotrexate metabolism, reducing efficacy
- NSAIDs reduce renal clearance of methotrexate, causing toxicity (Correct answer)
- Ibuprofen displaces methotrexate from its receptor
- Combined use causes QT prolongation
Correct answer: NSAIDs reduce renal clearance of methotrexate, causing toxicity
NSAIDs inhibit renal prostaglandin synthesis, reducing renal blood flow and tubular secretion of methotrexate, leading to methotrexate accumulation and toxicity.
Question 6: According to DHA pharmacy standards, what is the minimum required action when a pharmacist identifies a clinically significant prescribing error?
- Dispense the medication and note the error in the patient file
- Contact the prescribing physician before dispensing to clarify or correct the order (Correct answer)
- Refuse dispensing and send the patient back to the clinic without explanation
- Substitute with a safer alternative without notifying the prescriber
Correct answer: Contact the prescribing physician before dispensing to clarify or correct the order
DHA standards mandate that pharmacists contact the prescribing physician to resolve clinically significant errors before dispensing, ensuring patient safety.
Question 7: Which of the following is the mechanism of action of proton pump inhibitors (PPIs)?
- Competitive antagonism of H2 receptors on parietal cells
- Irreversible inhibition of H+/K+-ATPase on parietal cells (Correct answer)
- Neutralization of gastric acid by forming salts
- Stimulation of mucus production in the gastric lining
Correct answer: Irreversible inhibition of H+/K+-ATPase on parietal cells
PPIs irreversibly inhibit the H+/K+-ATPase (proton pump) on the luminal surface of gastric parietal cells, blocking the final step of acid secretion.
DHA Pharmacist 4
A patient is prescribed warfarin and starts taking clarithromycin for a respiratory infection.
What is the most likely pharmacokinetic interaction?