Saudi Prometric Pharmacist Drug Interactions and Adverse Effects 4 — Questions and Answers
Question 1: A patient taking isotretinoin (13-cis retinoic acid) for severe acne becomes pregnant. What is the risk?
- Highly teratogenic — causes craniofacial, cardiac, and CNS defects; strict pregnancy prevention required (iPLEDGE program equivalent in Saudi Arabia) (Correct answer)
- Isotretinoin is safe in pregnancy after the first trimester
- Teratogenicity is theoretical — pregnancy outcomes are normal in clinical experience
- Only category B teratogenic risk — requires monitoring but no pregnancy prevention
Correct answer: Highly teratogenic — causes craniofacial, cardiac, and CNS defects; strict pregnancy prevention required (iPLEDGE program equivalent in Saudi Arabia)
Isotretinoin is one of the most potent human teratogens — 35% of exposed pregnancies result in malformations (craniofacial, cardiac, CNS defects) and up to 40% in spontaneous abortion. Saudi Arabia follows strict REMS/iPLEDGE-equivalent programs requiring monthly pregnancy tests, two forms of contraception, and informed consent.
Question 2: A patient on theophylline is started on erythromycin. What monitoring is most important?
- Theophylline serum levels — erythromycin inhibits CYP1A2 and increases theophylline toxicity risk (nausea, tremors, seizures, arrhythmias) (Correct answer)
- Renal function — erythromycin causes nephrotoxicity that reduces theophylline clearance
- Blood glucose — both drugs cause hyperglycemia
- Thyroid function — interaction causes hypothyroidism
Correct answer: Theophylline serum levels — erythromycin inhibits CYP1A2 and increases theophylline toxicity risk (nausea, tremors, seizures, arrhythmias)
Theophylline is primarily metabolized by CYP1A2. Erythromycin (and other macrolides, especially clarithromycin) inhibit CYP1A2, raising theophylline levels by 25–50%. Theophylline has a narrow therapeutic index (10–20 mg/L therapeutic; >20 mg/L toxic). Toxicity manifests as nausea, tachycardia, arrhythmias, and seizures.
Question 3: A patient on spironolactone develops gynecomastia. The pharmacist recommends switching to which potassium-sparing agent to avoid this side effect?
- Eplerenone — selective MRA without anti-androgenic effects causing gynecomastia (Correct answer)
- Amiloride — ENaC blocker without hormonal effects, but less potent for heart failure indication
- Triamterene — same class but lower gynecomastia risk
- Furosemide — no potassium-sparing but no gynecomastia
Correct answer: Eplerenone — selective MRA without anti-androgenic effects causing gynecomastia
Spironolactone binds not only mineralocorticoid receptors but also androgen and progesterone receptors, causing gynecomastia, breast tenderness, and menstrual irregularities. Eplerenone is a selective MRA with minimal androgen/progesterone receptor activity, providing the same cardiac benefit without hormonal side effects.
Question 4: A patient on phenelzine (MAOI) is prescribed meperidine (pethidine) for pain. What is the serious risk?
- Serotonin syndrome — meperidine has serotonin reuptake inhibition in addition to opioid agonism (Correct answer)
- Respiratory depression only
- Hypertensive crisis only (no serotonin involvement)
- No interaction — meperidine is a pure mu-opioid agonist
Correct answer: Serotonin syndrome — meperidine has serotonin reuptake inhibition in addition to opioid agonism
Meperidine (unlike most opioids) inhibits serotonin reuptake. Combined with MAOIs, it causes serotonin syndrome: hyperthermia, agitation, neuromuscular abnormalities, and cardiovascular instability — potentially fatal. Meperidine is absolutely contraindicated with MAOIs. Morphine is a safer opioid with MAOIs (direct mu agonist, no serotonergic activity).
Question 5: A patient develops orange-red discoloration of urine, tears, and sweat after starting rifampin. What is the appropriate action?
- Reassure the patient — this is an expected, harmless side effect of rifampin; do not discontinue (Correct answer)
- Suspect hepatotoxicity and check liver function tests immediately
- Discontinue rifampin — this indicates drug toxicity
- Start hydration to prevent renal toxicity from the pigment
Correct answer: Reassure the patient — this is an expected, harmless side effect of rifampin; do not discontinue
Rifampin causes harmless orange-red discoloration of urine, tears, sweat, saliva, and stool due to excretion of a rifampin metabolite. Patients must be counseled about this expected effect to prevent unnecessary alarm or discontinuation. Contact lenses may be permanently stained.
Question 6: A patient on warfarin asks about taking fish oil (omega-3 fatty acids) supplements. What is the pharmacist's advice?
- High-dose fish oil (>3 g/day omega-3) may have additive antiplatelet effect and potentially increase INR; monitor INR if high doses used (Correct answer)
- Fish oil has no interaction with warfarin at any dose
- Fish oil should be completely avoided with all anticoagulants
- Fish oil increases warfarin absorption, requiring dose reduction
Correct answer: High-dose fish oil (>3 g/day omega-3) may have additive antiplatelet effect and potentially increase INR; monitor INR if high doses used
Fish oil (omega-3 fatty acids) at high doses (>3 g/day) has antiplatelet effects and may modestly increase INR in some patients on warfarin. While the interaction is less severe than, say, aspirin + warfarin, patients should inform their pharmacist, use at recommended supplemental doses (≤1 g/day), and monitor INR if high doses are used.
Saudi Prometric Pharmacist Drug Interactions and Adverse Effects 4
A patient taking isotretinoin (13-cis retinoic acid) for severe acne becomes pregnant.
What is the risk?