USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 91:

  Which of the following antidepressants is most selective in blocking reuptake of serotonin as compared with norepinephrine?

  A. amitriptyline

  B. citalopram

  C. desipramine

  D. imipramine

  E. trazodone

  Correct Answer: B

  Section: Pharmacology Citalopram is one of the highly selective SSRIs, as is its (S) isomer, escitalopram. Most older, tricyclic, and heterocyclic antidepressants block--to varying degrees--reuptake of both norepinephrine and serotonin amine neurotransmitters into the presynaptic nerve terminals. Different agents are relatively selective for one or the other amine. Amitriptyline (choice A), desipramine (choice C), imipramine (choice D), and trazodone (choice E) are members of the tricyclic/heterocyclic group and all have mixed effects on both norepinephrine and serotonin reuptake. Desipramine (choice C) is the most selective agent for blocking uptake of norepinephrine. The selective serotonin uptake inhibitors offer the advantage that they do not produce sedation or autonomic side effects, in contrast to many of the tricyclic and heterocyclic antidepressants.

• Question 92:

  Which of the following quantitative comparisons of haloperidol (H) and olanzapine (O) is most accurate?

  

  A. Option A

  B. Option B

  C. Option C

  D. Option D

  E. Option E

  Correct Answer: B

  Section: Pharmacology Haloperidol is an older oral and parenteral antipsychotic drug with high extrapyramidal but low autonomic toxicity. Olanzapine is a new oral antipsychotic agent with low extrapyramidal and autonomic activity.

• Question 93:

  Which of the following best describes the mechanism of action of oral anticoagulants such as warfarin?

  A. act as a template for complexing thrombin and antithrombin III

  B. break down thrombin

  C. form an active complex with plasminogen

  D. inhibit calcium binding to coagulation factors

  E. inhibit hepatic carboxylation of coagulation factor precursors

  Correct Answer: E

• Question 94:

  Below figure illustrates a current concept of the control of gastric acid secretion. Which of the following drugs acts at the site labeled "ATPase"?

  

  A. aluminum hydroxide

  B. misoprostol

  C. omeprazole

  D. ranitidine

  E. sucralfate

  Correct Answer: C

• Question 95:

  Which of the following statements is most correct regarding the use of drugs in hypertension?

  A. ACE inhibitors are contraindicated if the patient is pregnant

  B. beta-blockers are contraindicated if hypertension is associated with heart failure

  C. calcium channel blockers are contraindicated if the patient also has obstructive pulmonary disease

  D. diuretics are contraindicated in hypertension associated with diabetes

  E. vasodilators are contraindicated in a patient taking a diuretic

  Correct Answer: A

  Section: Pharmacology ACE inhibitors are absolutely contraindicated in pregnancy because they cause renal malformations or agenesis in the fetus. Beta blockers (choice B) are very useful in chronic heart failure with or without hypertension. Calcium channel blockers (choice C) have no detrimental effects in obstructive pulmonary disease. Diuretics are extremely useful in most forms of hypertension (choice D). Because strong vasodilators (choice E) evoke powerful compensatory responses (salt and water retention, tachycardia), drugs like minoxidil are almost always used together with drugs such as diuretics that prevent the compensatory responses.

• Question 96:

  Which of the following is a recombinant human antibody used in advanced breast cancer?

  A. adalimumab

  B. etanercept

  C. infliximab

  D. sirolimus

  E. trastuzumab

  Correct Answer: E

• Question 97:

  Exhibit:

  

  Please refer to the exhibit.

  Apatient is to receive chemotherapy for cancer. The oncologist plans to use ondansetron to reduce the

  nausea and vomiting associated with the chemotherapeutic agents. What is the mechanism of action of

  ondansetron?

  A. A

  B. B

  C. C

  D. D

  E. E

  Correct Answer: E

• Question 98:

  Which of the following correctly describes the actions of baclofen?

  A. agonist at glutamate receptors

  B. antagonist at neuronal nicotinic receptors

  C. agonist at gamma-aminobutyric acid receptors

  D. agonist at glycine receptors

  E. antagonist at skeletal muscle ryanodine receptors

  Correct Answer: C

• Question 99:

  Apatient has glaucoma following cataract surgery, a moderate elevation of intraocular pressure that often follows replacement of the crystalline lens. Which of the following is a rational choice for treatment and the correct mechanism for that drug?

  A. atracurium--increased outflow of aqueous humor

  B. dorzolamide--increased outflow of aqueous humor

  C. latanoprost--decreased synthesis of aqueous humor

  D. pilocarpine--decreased synthesis of aqueous humor

  E. timolol--decreased synthesis of aqueous humor

  Correct Answer: E

  Section: Pharmacology Beta blockers such as timolol reduce intraocular pressure by reducing synthesis of aqueous by the ciliary epithelium. Atracurium (choice A) is a nondepolarizing neuromuscular blocking agent that is of no value in glaucoma. Dorzolamide (choice B) is a topically active carbonic anhydrase inhibitor that inhibits the synthesis, not the outflow, of aqueous humor. Latanoprost (choice C) is a PGF-2 alpha analog used topically to increase aqueous outflow. Pilocarpine (choice D) is a muscarinic cholinomimetic that increases aqueous outflow.

• Question 100:

  Carbidopa is often used in patients with Parkinson's disease. Which of the following best describes the mechanism of action of carbidopa?

  A. activates D2 receptors in the basal ganglia

  B. inhibits the metabolism of dopamine in the blood and peripheral tissues

  C. inhibits the metabolism of dopamine in the brain

  D. inhibits the metabolism of levodopa in peripheral tissues

  E. inhibits the metabolism of levodopa in the brain

  Correct Answer: D

  Section: Pharmacology Carbidopa is a peripheral inhibitor of dopa decarboxylase. Dopa decarboxylase is an enzyme present in large amounts in the GI tract and peripheral tissues, and in smaller amounts in the nerve terminals of dopaminergic neurons in the basal ganglia. It is required for the conversion of DOPA to dopamine in the biosynthesis of dopamine and norepinephrine. However, when the prodrug levodopa is used for parkinsonism, over 90% is metabolized in the periphery by the enzyme to dopamine and inactive products and only about 3% of the administered dose enters the brain. Because dopamine does not cross the blood- brain barrier, dopamine formed outside the brain is of no value in treating parkinsonism. When carbidopa is given with levodopa, less levodopa is metabolized in the gut and other peripheral tissues, so more (about 10%) is available to enter the CNS. Carbidopa does not cross the bloodbrain barrier, so it does not prevent conversion of levodopa to active dopamine in the basal ganglia. Combination therapy thus reduces the peripheral effects of levodopadopamine and allows patients to receive more benefit and less toxicity from a given dose of levodopa. Choices AC and E are incorrect.