Q- A 21-year-old woman presents to the clinic for contraception. She wants to take oral contraceptives but she has concerns about their interaction to other medications. Which one of the following drugs will raise the plasm levels of OCP and increases the risk of side effects?
A-Carbamazepine
B- Ciprofloxacin
C- Phenytoin
D- Rifampin
B- Ciprofloxacin- It is the only one on the list that is a potent inhibitor of cytochrome P450 enzymes resulting in delayed metabolism of certain drugs including oral contraceptives and so; raising their plasma levels. Other drugs on the list are inducers of cytochrome P450 enzymes.
Q- Which one of the following medications acts by facilitating GABA-mediated conduction of chloride ion?
A- Baclofen
B- Buspirone
C- Midazolam
D- Morphine
C- Midazolam- Benzodiazepines bind to GABA receptor-chloride ion channels to increase the frequency of their opening. Baclofen acts centrally as a muscle relaxant. Buspirone is a selective anxiolytic acts as partial agonist at SHT receptors. Morphine activates the descending inhibitory pathways of the CNS.
Q- Which of the following is the mechanism of action of amphotericin B in treating fungal infections such as aspergillosis?
A- Binding to ergosterol to disrupt membrane permeability
B- Binding to tubulin to disrupt spindle microtubule dynamics
C- Inhibition of thymine synthesis
D- Inhibition of RNA polymerase
A-Binding to ergosterol to disrupt membrane permeability- This is the correct mechanism of action of amphotericin B in fungal infections. It is a frequent question in USMLE Step 1 and USMLE Step 2 CK.
