Saudi Prometric Pharmacist Clinical Pharmacy and Therapeutics 3 — Questions and Answers
Question 1: A patient with Parkinson's disease is on levodopa/carbidopa therapy. What is the purpose of carbidopa in this combination?
- Peripheral DOPA decarboxylase inhibitor — prevents peripheral levodopa conversion, increasing CNS levodopa delivery and reducing side effects (Correct answer)
- Central dopamine agonist that enhances levodopa's effect
- Monoamine oxidase inhibitor preventing dopamine breakdown
- Catechol-O-methyltransferase (COMT) inhibitor
Correct answer: Peripheral DOPA decarboxylase inhibitor — prevents peripheral levodopa conversion, increasing CNS levodopa delivery and reducing side effects
Carbidopa inhibits peripheral aromatic L-amino acid decarboxylase (DOPA decarboxylase), preventing levodopa from being converted to dopamine in the bloodstream. This reduces peripheral dopamine side effects (nausea, hypotension) and allows more levodopa to enter the CNS, requiring lower doses.
Question 2: Which drug is first-line for treatment of Helicobacter pylori eradication failure after standard triple therapy?
- Bismuth quadruple therapy (PPI + bismuth + metronidazole + tetracycline) for 10–14 days (Correct answer)
- Repeat the same triple therapy for 4 more weeks
- Add a fourth antibiotic to the original regimen
- Switch to fluoroquinolone-based triple therapy only
Correct answer: Bismuth quadruple therapy (PPI + bismuth + metronidazole + tetracycline) for 10–14 days
When first-line clarithromycin-based triple therapy fails, bismuth quadruple therapy (PPI + bismuth subsalicylate + metronidazole + tetracycline) for 10–14 days is recommended as second-line. Fluoroquinolone-based triple therapy is an alternative but resistance is increasing.
Question 3: A pharmacist is counseling a patient starting allopurinol for chronic gout. When should allopurinol be initiated?
- 2–4 weeks after resolution of the acute attack, with co-prescription of colchicine or NSAID prophylaxis initially (Correct answer)
- Immediately during the acute attack to reduce future attacks
- Only when serum uric acid exceeds 10 mg/dL
- After the second acute gout attack, not the first
Correct answer: 2–4 weeks after resolution of the acute attack, with co-prescription of colchicine or NSAID prophylaxis initially
Allopurinol should be started 2–4 weeks after the acute attack has resolved to avoid prolonging the current attack (rapid changes in urate can trigger inflammation). Initial prophylactic colchicine or NSAID (at low dose) is prescribed for 3–6 months to prevent flares triggered by urate lowering.
Question 4: A patient on phenytoin is started on oral contraceptives. What is the clinical concern?
- Phenytoin induces CYP3A4, increasing OC metabolism and reducing contraceptive efficacy — use alternative contraception (Correct answer)
- Oral contraceptives increase phenytoin toxicity
- Phenytoin inhibits OC metabolism, increasing estrogen levels
- No significant interaction exists between phenytoin and oral contraceptives
Correct answer: Phenytoin induces CYP3A4, increasing OC metabolism and reducing contraceptive efficacy — use alternative contraception
Phenytoin (and carbamazepine, rifampin) induces CYP3A4 and other enzymes that metabolize ethinyl estradiol and progestins in oral contraceptives, reducing plasma levels by 50–80%. This can cause contraceptive failure. Patients need non-hormonal backup or higher-dose OC with agreement from prescribers.
Question 5: A patient with community-acquired pneumonia (CAP) of moderate severity is to be treated as an outpatient. What is the preferred antibiotic regimen?
- Amoxicillin-clavulanate + macrolide (or respiratory fluoroquinolone alone) (Correct answer)
- IV vancomycin + cephalosporin
- Trimethoprim-sulfamethoxazole alone
- Amoxicillin + clindamycin
Correct answer: Amoxicillin-clavulanate + macrolide (or respiratory fluoroquinolone alone)
Outpatient CAP treatment: for low-risk patients, amoxicillin alone or amoxicillin-clavulanate + a macrolide covers typical and atypical organisms. A respiratory fluoroquinolone (levofloxacin/moxifloxacin) alone is an alternative. The combination covers S. pneumoniae and atypical pathogens (Mycoplasma, Chlamydophila, Legionella).
Question 6: A patient with epilepsy becomes pregnant. Which antiepileptic drug is most teratogenic and should be avoided?
- Valproate (valproic acid) — highest risk of neural tube defects and cognitive impairment (Correct answer)
- Lamotrigine — equally teratogenic to valproate
- Levetiracetam — associated with cleft palate
- Phenobarbital — not teratogenic in pregnancy
Correct answer: Valproate (valproic acid) — highest risk of neural tube defects and cognitive impairment
Valproate has the highest teratogenicity of all antiepileptics, causing neural tube defects (spina bifida), cardiac defects, cleft palate, cognitive impairment (fetal valproate syndrome), and neonatal withdrawal. It is contraindicated in women of childbearing age unless no alternatives exist (with folic acid 5 mg/day and counseling).
Saudi Prometric Pharmacist Clinical Pharmacy and Therapeutics 3
A patient with Parkinson's disease is on levodopa/carbidopa therapy.
What is the purpose of carbidopa in this combination?