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10 USMLE Pharmacology Mechanism Questions with Answers and Explanations (Set 4)
These 10 USMLE pharmacology practice questions (Set 4) cover high-yield drug facts: disulfiram-like reactions, drugs that affect clotting, side effects of tuberculosis drugs, antiretroviral classes, beta-blocker effects on the heart and benzodiazepine reversal. Each question includes the correct answer and an explanation.
Written by Dr. Ray Makar, MD, author of the Repeated USMLE Questions eBook series.
B- Cefotetan- It is a cephalosporin antibiotic, and it can cause a disulfiram-like reaction when combined with alcohol. Disulfiram is used to treat alcohol dependence, and it works by inhibiting the enzyme aldehyde dehydrogenase, leading to an accumulation of acetaldehyde when alcohol is consumed. This causes unpleasant symptoms such as flushing, nausea, vomiting, and headache, discouraging the person from drinking alcohol.
The correct answer is B
Question 2. Which one of the following medications inhibits fibrinolysis?
A- Aminocaproic acid- It works by preventing the activation of plasminogen to plasmin, an enzyme that degrades fibrin, a key component of blood clots. By inhibiting fibrinolysis, aminocaproic acid helps stabilize blood clots and can be used in various medical conditions, such as to control bleeding in certain surgical procedures or to treat conditions associated with excessive fibrinolysis.
Heparin works by enhancing the activity of antithrombin III. This, in turn, inhibits the enzymes thrombin and factor Xa, which are crucial for blood clot formation. Lepirudin is a direct thrombin inhibitor used as an anticoagulant. Rifampin does not have an antifibrinolytic effect.
The correct answer is A
Question 3. Which one of the following medications can be reversed by administration of vitamin K?
D- Warfarin- Warfarin is an anticoagulant that works by inhibiting the synthesis of vitamin K-dependent clotting factors in the liver. These factors are II, VII, IX and X. Clopidogrel is an antiplatelet agent, Heparin is an anticoagulant that works by enhancing antithrombin III, and Tirofiban is a platelet aggregation inhibitor.
The correct answer is D
Question 4. Which one of the following drugs is associated with peripheral neuropathy?
C- Isoniazid- Isoniazid is well known for causing peripheral neuropathy as a side effect, especially in patients who are malnourished, diabetic, alcoholic, or who have kidney failure. This occurs due to pyridoxine (vitamin B6) deficiency, since isoniazid interferes with its metabolism. To prevent this, pyridoxine supplementation is often given alongside isoniazid.
The correct answer is C
Question 5. Which one of the following tuberculosis drugs is associated with optic neuritis?
B- Ethambutol- Ethambutol causes dose-related optic neuritis with decreased visual acuity, central scotoma and loss of red-green color vision. Visual acuity and color vision should be checked before and during treatment.
The correct answer is B
Question 6. Which one of the following tuberculosis drugs turns urine, tears and sweat red-orange?
D- Rifampin- Rifampin colors body fluids (urine, tears, sweat) red-orange, which can stain contact lenses. It is also a strong CYP450 inducer and can cause hepatotoxicity. Isoniazid is the TB drug most classically linked to hepatitis and peripheral neuropathy.
The correct answer is D
Question 7. Which one of the following tuberculosis drugs is associated with nephrotoxicity and ototoxicity?
A- Capreomycin- Capreomycin is an injectable second-line TB drug with aminoglycoside-like toxicity: nephrotoxicity and ototoxicity. Kidney function and hearing should be monitored.
The correct answer is A
Question 8. Which one of the following antiretroviral drugs is a protease inhibitor?
C- Ritonavir- It is a protease inhibitor used in the treatment of HIV/AIDS. Protease inhibitors work by inhibiting the activity of the HIV protease enzyme, which is essential for the replication of the virus. By blocking this enzyme, protease inhibitors prevent the virus from producing functional proteins necessary for its replication, thus helping to control the spread of the virus in the body. Etravirine is a non-nucleoside reverse transcriptase inhibitor (NNRTI). Lamivudine is a nucleoside reverse transcriptase inhibitor (NRTI). Tenofovir is also a nucleoside reverse transcriptase inhibitor (NRTI). Zidovudine is a nucleoside reverse transcriptase inhibitor (NRTI).
The correct answer is C
Question 9. Which one of the following is the effect of metoprolol on cardiac ejection time?
A- Decreased
B- Increased
C- No effect
B- Increased- Beta-blockers such as metoprolol slow the heart rate and reduce contractility. With weaker contraction, the ventricle takes longer to eject its stroke volume, so systolic ejection time increases. This is why beta-blockers are often combined with nitrates in angina: nitrates shorten ejection time and offset this effect.
The correct answer is B
Question 10. Which one of the following drugs is the most effective in midazolam paradoxical reaction?
C- Flumazenil- It is a benzodiazepine receptor antagonist that can reverse the effects of benzodiazepines, including midazolam, by competitively binding to the benzodiazepine receptors in the central nervous system. Therefore, if a paradoxical reaction occurs with midazolam, flumazenil can effectively reverse its effects.
The correct answer is C
High-yield points from this set
Cefotetan, metronidazole and some others cause a disulfiram-like reaction with alcohol.
Aminocaproic acid and tranexamic acid inhibit fibrinolysis.
Vitamin K reverses warfarin; protamine reverses heparin.
Isoniazid: peripheral neuropathy (prevent with pyridoxine) and hepatitis.
Ethambutol: optic neuritis and red-green color loss.
Rifampin: red-orange body fluids and CYP450 induction.
Capreomycin and aminoglycosides: nephrotoxicity and ototoxicity.
Drugs ending in -navir are HIV protease inhibitors.
Beta-blockers increase ejection time; nitrates decrease it.
Flumazenil reverses benzodiazepine effects (use carefully: it can trigger seizures).