USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 161:

  Which of the following drugs binds to, and prevents disassembly of, microtubules?

  A. busulfan

  B. cisplatin

  C. mercaptopurine

  D. paclitaxel

  E. vinblastine

  Correct Answer: D

  Section: Pharmacology

  Paclitaxel (choice D) is a plant alkaloid that interferes with microtubule disassembly. Busulfan (choice A)

  and cisplatin (choice B) are alkylating agents that interfere with DNAmobilization and replication.

  Mercaptopurine (choice C) is an antimetabolite that interferes with purine synthesis. Vinblastine (choice E)

  and vincristine and vinorelbine are mitotic poisons that prevent cancer cell division by interfering with

  microtubule assembly and thus immobilizing the mitotic spindle apparatus. Their indications and toxicities

  are quite different from those of paclitaxel.

• Question 162:

  Which of the following drugs corrects the anemia of pernicious anemia and prevents the neurological consequences of the disease?

  A. beta-carotene

  B. ferrous sulfate

  C. folic acid

  D. hydroxocobalamin E. vitamin E

  Correct Answer: D

• Question 163:

  Which of the following laxatives acts osmotically to increase the water content of the stool?

  A. cascara

  B. docusate

  C. glycerine

  D. magnesium hydroxide

  E. senna

  Correct Answer: D

  Section: Pharmacology Magnesium hydroxide is an osmotic laxative that retains water in the lumen of the colon. Cascara (choice A) is a naturally occurring plant product that stimulates the bowel and causes evacuation within 612 hours when given orally. Docusate (choice B) is a stool-softening agent that acts entirely within the lumen. Glycerine (choice C), given by suppository, is a stool softener. Senna (choice E) is a stimulant and bulk-forming agent that increases the volume of the stool and stimulates evacuation.

• Question 164:

  Which of the following drugs reduces LDL cholesterol by inhibiting an intestinal transport protein?

  A. atorvastatin

  B. cholestyramine

  C. ezetimibe

  D. gemfibrozil

  E. niacin

  Correct Answer: C

  Section: Pharmacology Ezetimibe is an important newer drug that inhibits cholesterol and bile acid absorption from the gut by inhibiting the epithelial transport protein NPC1L1. Atorvastatin (choice A) reduces both LDL and triglycerides, but does not inhibit VLDL secretion. Cholestyramine (choice B) inhibits the reabsorption of bile acids and cholesterol from the gut and actually increases triglycerides in some patients. Gemfibrozil (choice D) activates lipoprotein lipase in peripheral tissues and reduces VLDL levels and triglycerides. It does not reduce hepatic secretion of VLDL. Niacin (choice E) is the most effective drug available for reducing triglycerides and also reduces LDL cholesterol by reducing the hepatic secretion of its precursor, VLDL particles.

• Question 165:

  Which of the following drugs is considered a first-line agent in the chronic treatment of rheumatoid arthritis and in the treatment of choriocarcinoma?

  A. cyclosporine

  B. hydroxychloroquine

  C. methotrexate

  D. sulfasalazine

  E. thalidomide

  Correct Answer: C

  Section: Pharmacology Methotrexate in very low dosage has proven effective in slowing the progression of rheumatoid arthritis and has low toxicity. It is also one of the most effective (in much higher dosage) antimetabolite cancer chemotherapeutic drugs used in choriocarcinoma. Cyclosporine (choice A) is not used in either condition but is a first-line drug in transplant immunopharmacology. Hydroxychloroquine (choice B) is a disease-modifying antirheumatoid arthritis drug, but has no efficacy in the treatment of cancer. It is more toxic and less effective in rheumatoid arthritis than methotrexate. Sulfasalazine (choice D) is also effective in slowing the progression of joint damage in rheumatoid arthritis but has no efficacy in cancer. Thalidomide (choice E) is effective in erythema nodosum leprosum and multiple myeloma but has not been demonstrated to be effective in rheumatoid arthritis or choriocarcinoma.

• Question 166:

  An unconscious man is brought to the emergency room. He was at home when discovered, but he works as a foreman in a chemical packaging plant. His blood pressure and heart rate are normal. He is sweating profusely, has constricted pupils, and auscultation of the lungs indicates rales and wheezing. Widespread subcutaneous muscle twitches are apparent. He has had urinary and fecal incontinence. Which of the following chemicals is the most likely cause of this poisoning?

  A. isobutyl nitrite

  B. metallic mercury

  C. morphine

  D. parathion

  E. phencyclidine

  Correct Answer: D

  Section: Pharmacology When a person who is exposed to chemicals in the workplace is intoxicated, both drugs of abuse and workplace exposures must be considered. The signs of this patient's intoxication match the classic picture of cholinesterase inhibitor poisoning as summarized by the mnemonic "dumbels:" diarrhea, rination, miosis, bronchospasm, excitation, lacrimation, and sweating and salivation. Isobutyl nitrite (choice A), an industrial chemical also used as a recreational drug for sex enhancement, causes tachycardia, methemoglobinemia, and signs of tissue hypoxia. Mercury (choice B) causes chemical pneumonitis and pulmonary edema. Chronic mercury exposure causes behavioral abnormalities. Morphine (choice C) causes miosis but reduces gastrointestinal activity. Phencyclidine (choice E) causes hallucinations, combativeness, and sympathetic discharge.

• Question 167:

  Which of the choices in the table below most accurately describes the actions of vitamin D and arathyroid hormone on calcium and phosphate in the blood?

  

  A. Option A

  B. Option B

  C. Option C

  D. Option D

  E. Option E

  Correct Answer: D

  Section: Pharmacology Although there are several forms of vitamin D and both vitamin D and parathyroid hormone act on the intestine, kidney, and bone, the net effect of vitamin D is to increase serum calcium and phosphate, while parathyroid hormone increases serum calcium and decreases phosphate. None of the other options (choices AC, E) correctly reflects the actions of vitamin D or parathyroid hormone.

• Question 168:

  The increased risk of blood clots in women who use certain combined estrogen/progestin birth control pills is well established. Which of the following best explains this association?

  A. impaired glucose tolerance

  B. increased Factor II, VII, IX, and X levels produced by estrogens

  C. increased plasminogen levels produced by progestins

  D. increased thyroxine-binding globulin

  E. increased triglyceride levels produced by progestins

  Correct Answer: B

  Section: Pharmacology Increased clotting factor synthesis (and decreased antithrombin III synthesis) caused by estrogens are the major factors responsible for increased incidence of thromboembolic phenomena. Glucose tolerance is impaired (choice A) in some women by progestins and would not be expected to affect clotting. Plasminogen (choice C) is increased by estrogens, not progestins, but would decrease clotting. Thyroxine-binding globulin (choice D) is also increased by estrogen, but would have little effect on clotting.

  Triglycerides (choice E) are increased by estrogens and would have little or no effect on clotting.

• Question 169:

  Which of the following drugs is used to accelerate pulmonary maturation in the fetus in women with premature labor?

  A. aminoglutethimide

  B. betamethasone

  C. mifepristone

  D. misoprostol

  E. prostacyclin

  Correct Answer: B

  Section: Pharmacology Glucocorticoids help accelerate maturation of the lungs in the fetus at the end of term. In preterm labor, these drugs help prevent respiratory failure in the newborn. Betamethasone is the preferred corticosteroid for this purpose because it is poorly bound in the maternal serum and transfers into the fetal circulation more readily. The other drugs listed (choices A, CE) are of no value in this setting.

• Question 170:

  Exhibit:

  

  Please refer to the exhibit.

  Which of the following mechanisms most accurately describes the blocking action of methimazole?

  A. A

  B. B

  C. C

  D. D

  E. E

  Correct Answer: B