PEBC Treatment Planning 4 — Questions and Answers
Question 1: A patient taking phenytoin for seizures is prescribed fluconazole for a fungal infection. What is the expected pharmacokinetic outcome?
- Fluconazole induces CYP2C9, reducing phenytoin levels
- Fluconazole inhibits CYP2C9, increasing phenytoin levels and toxicity risk (Correct answer)
- No significant interaction exists between these two drugs
- Phenytoin reduces fluconazole efficacy via P-glycoprotein induction
Correct answer: Fluconazole inhibits CYP2C9, increasing phenytoin levels and toxicity risk
Fluconazole is a potent CYP2C9 inhibitor; since phenytoin is primarily metabolized by CYP2C9, co-administration can lead to significantly elevated phenytoin levels and toxicity.
Question 2: A child with otitis media has a penicillin allergy documented as 'hives and swelling.' What antibiotic is the most appropriate alternative?
- Cefuroxime, because cross-reactivity with penicillin is negligible with cephalosporins
- Azithromycin, to avoid all beta-lactams due to severe allergy history (Correct answer)
- Amoxicillin-clavulanate, because hives are not a true allergy
- Ciprofloxacin, as the safest alternative in pediatric patients
Correct answer: Azithromycin, to avoid all beta-lactams due to severe allergy history
Hives and swelling suggest a possible IgE-mediated reaction; avoiding all beta-lactams and choosing azithromycin is the safest approach in this clinical context.
Question 3: A patient is prescribed methotrexate for rheumatoid arthritis. What supplement should ALWAYS be co-prescribed to reduce toxicity?
- Vitamin B12 1000 mcg daily
- Folic acid 1–5 mg daily (Correct answer)
- Vitamin D 1000 IU daily
- Iron 325 mg daily
Correct answer: Folic acid 1–5 mg daily
Folic acid supplementation significantly reduces methotrexate-associated adverse effects such as mucositis, nausea, and hepatotoxicity without diminishing its therapeutic efficacy.
Question 4: When selecting an antibiotic for a urinary tract infection (UTI) in a patient with a sulfonamide allergy, which commonly used UTI agent must be avoided?
- Nitrofurantoin
- Trimethoprim-sulfamethoxazole (TMP-SMX) (Correct answer)
- Ciprofloxacin
- Fosfomycin
Correct answer: Trimethoprim-sulfamethoxazole (TMP-SMX)
TMP-SMX contains sulfamethoxazole, a sulfonamide antibiotic, and must be avoided in patients with documented sulfonamide allergy.
Question 5: A patient newly diagnosed with type 2 diabetes has an A1C of 9.5% and is otherwise healthy. According to Canadian Diabetes Association guidelines, what is the preferred initial pharmacotherapy?
- Lifestyle modification alone for 3 months before initiating any drug
- Metformin monotherapy titrated to maximum tolerated dose
- Metformin plus a second agent due to high A1C unlikely to be controlled with monotherapy (Correct answer)
- Insulin glargine once daily as A1C is above 9%
Correct answer: Metformin plus a second agent due to high A1C unlikely to be controlled with monotherapy
Canadian guidelines recommend combination therapy at diagnosis when A1C is ≥1.5% above target, as monotherapy is unlikely to achieve glycemic goals in this scenario.
Question 6: Which parameter best determines whether a patient requires a loading dose when initiating a new medication?
- A short half-life indicating rapid drug elimination
- A large volume of distribution requiring more drug to achieve therapeutic concentrations quickly (Correct answer)
- High protein binding reducing free drug availability
- Low bioavailability requiring dose adjustment
Correct answer: A large volume of distribution requiring more drug to achieve therapeutic concentrations quickly
A large volume of distribution means drug is extensively distributed into tissues, requiring a loading dose to rapidly achieve therapeutic plasma concentrations without waiting for steady state.
Question 7: A breastfeeding mother requires treatment for mild-to-moderate postpartum depression. Which antidepressant is generally considered the preferred choice due to its safety profile in breastfeeding?
- Paroxetine, due to its highest milk transfer ratio
- Sertraline, due to low milk-to-plasma ratio and extensive safety data (Correct answer)
- Fluoxetine, due to its short half-life limiting infant exposure
- Amitriptyline, as TCAs are preferred over SSRIs postpartum
Correct answer: Sertraline, due to low milk-to-plasma ratio and extensive safety data
Sertraline has low transfer into breast milk and the most extensive safety data in breastfeeding, making it the first-line choice for postpartum depression.
PEBC Treatment Planning 4
A patient taking phenytoin for seizures is prescribed fluconazole for a fungal infection.
What is the expected pharmacokinetic outcome?