SPEX Exam SPEX Pharmacology 4

Question 1

A patient with severe hepatic impairment (Child-Pugh Class C) requires analgesia. Which opioid analgesic has the LEAST risk of accumulation due to its reliance on glucuronidation rather than CYP450 hepatic metabolism?

Accepted Answer

Hydromorphone

Answer

Hydromorphone undergoes primarily glucuronidation to hydromorphone-3-glucuronide, making it less reliant on CYP450 enzymes that are severely impaired in Child-Pugh C cirrhosis. While morphine also undergoes glucuronidation, its active metabolite morphine-6-glucuronide accumulates dangerously in hepatic impairment. Fentanyl and oxycodone are CYP3A4-dependent and pose higher accumulation risk in hepatic failure.

Question 2

Which mechanism best explains why selective serotonin reuptake inhibitors (SSRIs) cause a paradoxical initial increase in anxiety during the first 1–2 weeks of treatment, before their anxiolytic effect emerges?

Accepted Answer

Acute surge in synaptic serotonin activating 5-HT2C receptors before autoreceptor desensitization

Answer

When SSRIs acutely block serotonin reuptake, the initial surge of synaptic 5-HT preferentially stimulates anxiogenic 5-HT2C receptors. Over 1–2 weeks, somatodendritic 5-HT1A autoreceptors in the raphe nuclei desensitize, allowing sustained increased 5-HT output that eventually predominates through anxiolytic 5-HT1A postsynaptic signaling. The desensitization of autoreceptors (option A) is what resolves anxiety, not causes it.

Question 3

A pharmacist counsels a patient on warfarin who has started taking rifampin for latent TB. The patient's INR has dropped from 2.5 to 1.2 over two weeks. If rifampin is discontinued, what is the MOST critical risk in the following 1–2 weeks?

Accepted Answer

Supratherapeutic anticoagulation as enzyme induction reverses and warfarin levels rise

Answer

Rifampin is a potent inducer of CYP2C9 and CYP3A4, which dramatically increases warfarin clearance, requiring higher doses to maintain therapeutic INR. When rifampin is stopped, the induction reverses over 1–2 weeks, but if the warfarin dose was increased to compensate, the now-uninduced enzymes allow warfarin to accumulate to supratherapeutic — potentially hemorrhagic — levels. Close INR monitoring and proactive dose reduction are essential upon rifampin discontinuation.

Question 4

Which pharmacokinetic property of digoxin makes renal dosage adjustment uniquely critical compared to most other cardiac glycosides?

Accepted Answer

Digoxin is primarily eliminated unchanged by glomerular filtration and tubular secretion

Answer

Unlike many drugs, digoxin is eliminated predominantly (60–80%) as unchanged drug via renal excretion — through both glomerular filtration and active tubular secretion by P-glycoprotein. It is NOT significantly metabolized hepatically, undergoes minimal first-pass effect, has a very large volume of distribution (Vd ~7 L/kg), and is only ~25% protein-bound. This means renal impairment directly and proportionally reduces clearance, and dialysis is largely ineffective due to its enormous Vd.

Question 5

A patient taking phenelzine (an irreversible MAOI) for refractory depression requires treatment for a urinary tract infection. Which antibiotic is MOST likely to precipitate a life-threatening serotonin syndrome in this patient?

Accepted Answer

Linezolid

Answer

Linezolid is an oxazolidinone antibiotic with clinically significant MAO inhibitory activity. When combined with a serotonergic drug or another MAOI like phenelzine, it can precipitate life-threatening serotonin syndrome. The FDA has issued warnings against combining linezolid with serotonergic agents. Trimethoprim-sulfamethoxazole does not significantly inhibit MAO or increase serotonin. Nitrofurantoin and fosfomycin lack MAO or serotonergic activity. Linezolid's antibiotic classification often masks its MAO-inhibiting risk.

SPEX Exam Practice Test

SPEX Exam Practice Test

SPEX Exam SPEX Pharmacology 4