Drug Interactions and Adverse Effects Flashcards

A patient taking isotretinoin (13-cis retinoic acid) for severe acne becomes pregnant. What is the risk?

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.

A patient on theophylline is started on erythromycin. What monitoring is most important?

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.

A patient on spironolactone develops gynecomastia. The pharmacist recommends switching to which potassium-sparing agent to avoid this side effect?

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.

A patient on phenelzine (MAOI) is prescribed meperidine (pethidine) for pain. What is the serious risk?

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).

A patient develops orange-red discoloration of urine, tears, and sweat after starting rifampin. What is the appropriate action?

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.

A patient on warfarin asks about taking fish oil (omega-3 fatty acids) supplements. What is the pharmacist's advice?

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.