USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 141:

  A 35-year-old opera singer has been treated for hypertension with enalapril. Although his blood pressure has been reduced, he complains that he is now unable to perform because of a dry cough. Which of the following acts by a similar but not identical mechanism and is much less likely to cause cough?

  A. captopril

  B. clonidine

  C. losartan

  D. prazosin

  E. propranolol

  Correct Answer: C

• Question 142:

  A 35-year-old woman with hypertension is planning to become pregnant. Which of the following is contraindicated in pregnancy?

  A. clonidine

  B. hydralazine

  C. hydrochlorothiazide

  D. losartan

  E. methyldopa

  Correct Answer: D

  Section: Pharmacology Losartan causes renal damage in the fetus, and renal impairment in renovascular disease. It is contraindicated in pregnancy. Clonidine (choice A) causes some sedation and rebound hypertension when stopped suddenly, but is not contraindicated in pregnancy. Hydralazine (choice B) causes a reversible type of lupus erythematosus. Hydrochlorothiazide (choice C) may cause hypokalemia, dilutional hyponatremia, elevated lipids, hyperuricemia, and glucose intolerance. Methyldopa (choice E) causes sedation and formation of red blood cell antibodies, but has been shown to be safe in pregnancy.

• Question 143:

  Which of the following antitubercular agents is a strong inducer of hepatic cytochrome P450?

  A. ethambutol

  B. isoniazid

  C. rifampin

  D. streptomycin

  E. sulfisoxazole

  Correct Answer: C

  Section: Pharmacology Rifampin selectively inhibits bacterial DNA-dependent RNA polymerase. It is very useful in treating mycobacterial infections since it can penetrate cells and kill intracellular organisms. It is one of the most potent inducers of cytochrome P450 known, leading to increased hepatic clearance of many other drugs including the oral anticoagulants, cyclosporine, propranolol, digitoxin, corticosteroids, and oral contraceptives. Ethambutol (choice A) is often combined with isoniazid in antitubercular regimens. Clearance is primarily via renal excretion. Isoniazid (choice B) is the most widely used antitubercular agent. It functions by inhibiting mycolic acid biosynthesis. Isoniazid is cleared by metabolism via Nacetylase and hydrolytic activity. Streptomycin (choice D) was the first effective drug for the treatment of tuberculosis, but, because of its ototoxicity and nephrotoxicity and the development of less toxic agents, use of streptomycin is limited to more severe forms of the disease. Sulfisoxazole (choice E) may rarely be used in antitubercular regimens in combination with other drugs. Clearance is primarily via glomerular filtration.

• Question 144:

  Resistance to which of the following drugs occurs when the bacterium expresses higher quantities of a drug-efflux pump?

  A. amoxicillin

  B. clarithromycin

  C. doxycycline

  D. gentamicin

  E. vancomycin

  Correct Answer: C

  Section: Pharmacology Resistance to tetracyclines such as doxycycline (choice C) is associated with production of an efflux pump or alteration of the 30S ribosomal-binding site. Resistance to beta lactams such as amoxicillin (choice A) usually results from production of beta lactamase. Macrolides such as clarithromycin (choice B), erythromycin, and azithromycin bind to the 50S ribosome in susceptible organisms and prevent protein synthesis. Simple methylation of the binding site prevents the bacteriostatic action of these drugs and many bacteria have such mutation. Resistance to aminoglycosides such as gentamicin (choice D) is usually due to synthesis of inactivating enzymes by the bacteria. Resistance to vancomycin (choice E) is still unusual but can occur through the modification of the D-ala-D-ala- binding site in peptidoglycan.

• Question 145:

  Which of the following antiviral agents uses viral thymidine kinase as part of its activation pathway?

  A. acyclovir

  B. amantadine

  C. foscarnet

  D. saquinavir

  E. zidovudine

  Correct Answer: A

  Section: Pharmacology Acyclovir is an acyclic guanine nucleoside analog that undergoes activation by phosphorylation by herpesviral thymidine kinase (but not the host thymidine kinase) to form the acyclovir triphosphate form and causes DNA chain termination. Amantadine (choice B) is a tricyclic amine that inhibits uncoating of influenza A virus. It is also used for the treatment of parkinsonism. Foscarnet (choice C) is a pyrophosphate analog that inhibits herpesvirus nucleic acid synthesis at the level of the viral DNA polymerase. Saquinavir (choice D) is an HIV protease inhibitor. Zidovudine (choice E) is an antiretroviral thymidine analog. The triphosphate is a competitive inhibitor of reverse transcriptase and a DNA chain terminator. The monophosphate is a competitive inhibitor of thymidine kinase.

• Question 146:

  Which of the following antiviral drugs is correctly associated with the appropriate primary toxicity?

  A. amantadine--neutropenia

  B. didanosine--pancreatitis

  C. ribavirin--hepatitis

  D. ritonavir--hemolytic anemia

  E. zidovudine--CNS stimulation, GI complaints

  Correct Answer: B

  Section: Pharmacology Didanosine causes pancreatitis in a significant number of patients treated for AIDS. Amantadine (choice A) is used in the prevention and treatment of influenza and causes CNS stimulation and light headedness. Ribavirin (choice C) is used for the treatment of respiratory syncytial virus in infants and causes dose-dependent hemolytic anemia in about 10% of patients. Ritonavir (choice D), a protease inhibitor used in AIDS, causes hepatitis. Zidovudine (choice E), another drug used in AIDS, causes neutropenia as its primary doselimiting effect.

• Question 147:

  Which of the following acts as a folate antagonist in the treatment of malaria?

  A. amodiaquine

  B. chloroquine

  C. mefloquine

  D. proguanil

  E. quinine

  Correct Answer: D

  Section: Pharmacology Proguanil is a prodrug that is converted to cycloguanil, an inhibitor of malarial dihydrofolate reductase. Amodiaquine (choice A) and chloroquine (choice C) are similar and probably interfere with metabolism of heme in the vacuoles of the parasite. Mefloquine (choice C) and quinine (choice E) have unknown mechanisms of action but are not folate antagonists.

• Question 148:

  A patient is admitted for acute coronary syndrome with signs of impending myocardial infarction. She undergoes angioplasty with double coronary stenting to maintain the patency of her coronary vessels. Which of the following drugs will probably be administered to prevent clotting in the region of the wire mesh stents?

  A. clopidogrel

  B. low-molecular-weight heparin

  C. regular heparin

  D. tissue plasminogen activator (t-PA)

  E. warfarin

  Correct Answer: A

  Section: Pharmacology Foreign material (such as a stent) in blood vessels invites clotting and the stented vessel will rapidly occlude if clotting is not prevented. The primary process in the formation of this arterial clot is platelet aggregation, so an antiplatelet drug such as clopidogrel is suitable (choice A). Abciximab and tirofiban are also sometimes used in this setting. Heparin (both forms, choices B and C) and warfarin (choice E) are useful in the prevention of venous thrombosis. t-PA (choice D) is useful in accelerating the dissolution of a fibrin clot (e.g., after myocardial infarction), but is not useful in this situation.

• Question 149:

  A drug being developed as an antiarrhythmic agent was studied in the laboratory using microelectrode techniques for measuring the transmembrane potential. The results of this study are shown in below figure. Which of the following standard antiarrhythmic agents does the new drug most resemble?

  

  A. adenosine

  B. ibutilide

  C. lidocaine

  D. procainamide

  E. propranolol

  Correct Answer: B

• Question 150:

  Apatient is being treated for metastatic prostate cancer. Which of the following agents is used parenterally in prostate cancer to reduce luteinizing hormone (LH) release from the pituitary even though it initially increases LH release?

  A. diethylstilbestrol

  B. finasteride

  C. flutamide

  D. ketoconazole

  E. leuprolide

  Correct Answer: E

  Section: Pharmacology Leuprolide is a GnRH agonist that when given in pulsatile fashion stimulates pituitary LH release, but when given continuously, or in a depot preparation, suppresses LH release and reduces plasma testosterone levels to castration levels. Because it is a peptide, it must be given parenterally. It is used extensively in the treatment of metastatic prostate cancer. Diethylstilbestrol (choice A) is an oral nonsteroidal synthetic estrogen that is now rarely used in the treatment of prostate cancer. Use of this agent produces undesirable feminization and is reserved for cases unresponsive to other agents. Finasteride (choice B) is an orally active inhibitor of the 5-alpha-reductase that converts testosterone to dihydrotestosterone in the prostate. Because conversion of testosterone to dihydrotestosterone is essential for the androgenic effects in the prostate, inhibition of the 5-alpha-reductase decreases the stimulation of the prostate. Unfortunately, the drug has limited efficacy in prostate malignancy. Finasteride is used for the treatment of benign prostatic hyperplasia because it produces a moderate decrease in prostate size and improvement in urinary flow. It is also used for the treatment of androgenic hair loss. Flutamide (choice C) is a nonsteroidal antiandrogen occasionally used in the treatment of prostate cancer that is unresponsive to leuprolide. It is active orally. Ketoconazole (choice D) is an oral antifungal agent that has the property of inhibiting the cytochrome P450 isoforms involved in steroid biosynthesis. It has been used in the treatment of prostate cancer with mixed results.