USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 191:

  Serotonin (5-HT) is one of several mediators of the signs and symptoms of carcinoid tumor. When released from this neoplasm, most of the manifestations of 5-HT are the result of activation of the 5-H receptor. These manifestations are therefore likely to include which of the following effects?

  

  A. bronchospasm

  B. constipation

  C. skeletal muscle weakness

  D. tachycardia

  E. ulceration of the stomach or duodenum

  Correct Answer: A

• Question 192:

  Which of the following drugs causes hyperchloremic metabolic acidosis and may cause hyperammonemia in a patient with cirrhosis?

  A. acetazolamide

  B. amiloride

  C. furosemide

  D. hydrochlorothiazide

  E. spironolactone

  Correct Answer: A

  Section: Pharmacology Acetazolamide acts in the proximal tubule to block carbonic anhydrase, greatly increasing bicarbonate excretion and alkalinizing the urine while causing metabolic acidosis. In cirrhosis, ammonia is excreted in larger amounts because urea production in the liver is limited. If an acid urine (necessary for converting ammonia to ammonium ion) cannot be produced, the ammonia is promptly reabsorbed, causing hyperammonemia and hepatic encephalopathy. None of the other drugs (choices BE) causes hyperammonemia in cirrhotic patients.

• Question 193:

  Antiarrhythmic drugs have a variety of adverse effects that must be monitored carefully. Which of the following drugs is associated with discoloration of the skin, photosensitivity, thyroid dysfunction, and pulmonary complications?

  A. amiodarone

  B. diltiazem

  C. ibutilide

  D. lidocaine

  E. procainamide

  Correct Answer: A

  Section: Pharmacology Amiodarone is a large, insoluble molecule that deposits in skin (and the cornea) and causes photosensitivity. It contains two iodine atoms, which may be responsible for binding to thyroid receptors and the observed thyroid problems. It is associated with pulmonary fibrosis (sometimes fatal), but the mechanism is unknown. In spite of these adverse effects, it is extremely useful in arrhythmia treatment. Diltiazem (choice B) is associated with constipation and cardiac depression; ibutilide (choice C) with torsade de pointe arrhythmia, lidocaine (choice D) with convulsions, and procainamide (choice E) with torsade de pointe arrhythmia and drug-induced lupus.

• Question 194:

  A 73-year-old patient has heart failure that has worsened over the past 12 months. Which of the following drugs is likely to slow progression even though it has no direct positive or negative effects on cardiac contractility?

  A. digoxin

  B. dobutamine

  C. losartan

  D. nesiritide

  E. propranolol

  Correct Answer: C

  Section: Pharmacology Losartan, an AT1 angiotensin receptor antagonist, has been shown to slow the progression of heart failure, in common with the ACE inhibitors, beta blockers, and spironolactone, which also slow progression of this disease. Positive inotropic agents such as digoxin (choice A) and dobutamine (choice B) do not slow progression although they may be useful for reducing symptoms. Nesiritide (choice D) is a peptide that causes vasodilation and sodium diuresis and may have value in acute but not chronic failure. Propranolol (choice E) probably slows progression of heart failure but it has direct negative inotropic effects on the heart.

• Question 195:

  Which of the following beta-lactam drugs has good activity against beta-lactamase-producing organisms and penetrates readily into cerebrospinal fluid?

  A. amoxicillin

  B. cefazolin

  C. clavulanic acid

  D. imipenem

  E. ticarcillin

  Correct Answer: D

  Section: Pharmacology Imipenem is the only drug listed that is effective against many beta-lactamase-producing organisms and penetrate the bloodbrain barrier. Clavulanic acid C. is an inhibitor of beta lactamase and is used with an antibiotic but is not an antibiotic itself. None of the other drugs (choices A, B, D, and E) readily penetrate in the cerebrospinal fluid.

• Question 196:

  Diltiazem as used in angina pectoris has several beneficial actions that contribute to the prevention of the anginal symptoms. Which of the following actions is detrimental in angina?

  A. reduced arterial blood pressure

  B. increased diastolic heart size

  C. reduced systolic myocardial fiber tension

  D. bradycardia

  E. slowed AV conduction

  Correct Answer: B

  Section: Pharmacology Calcium channel blockers cause a decrease in arterial pressure, heart rate, and cardiac contractility, all of which help to reduce myocardial oxygen requirement and thereby reduce angina pain. However, the reduction in contractility increases diastolic cardiac size, which increases oxygen requirement and is therefore detrimental. The other effects listed (choices A, C, and E) are all valid beneficial actions of calcium blockers in angina. Slowed AV conduction E. occurs, but is of no significance in angina.

• Question 197:

  A 57-year-old man presents with angina. He uses 1 or 2 nitroglycerin tables sublingually when he experiences chest pain. Which of the following drugs may interact to cause serious hypotension if taken 6 hours or less before the nitrate?

  A. clonidine

  B. diltiazem

  C. metronidazole

  D. phentolamine

  E. sildenafil

  Correct Answer: E

  Section: Pharmacology Nitrates release nitric oxide in smooth muscle and cause relaxation by facilitating the production of cGMP. Sildenafil (and related drugs for erectile dysfunction, tadalafil and vardenafil) inhibit the inactivation of cGMP. When sildenafil and a nitrate are combined, excessive amounts of cGMP accumulate and may cause severe hypotension. The other drugs listed (choices Athrough D) have no significant interactions with nitrates.

• Question 198:

  A 50-year-old man presents with a blood pressure of 160/100. He is to be started on hydrochlorothiazide. Which of the following is a common adverse effect of hydrochlorothiazide?

  A. atrioventricular (AV) blockade

  B. constipation

  C. drug-induced lupus erythematosus

  D. potassium wasting

  E. tachycardia

  Correct Answer: D

  Section: Pharmacology Because thiazides decrease the reabsorption of sodium in the distal convoluted tubule, aldosterone secretion is increased and a compensatory response is evoked that releases potassium in response to increased sodium reabsorption in the cortical collecting tubule, therefore, potassium- wasting results. Other adverse effects of thiazides include increased blood glucose, uric acid, and lipids. None of the other choices (AB, E) are adverse effects of thiazide administration.

• Question 199:

  Mifepristone has antagonist action at which of the following receptors?

  A. beta adrenoceptors

  B. dopamine receptors

  C. insulin receptors

  D. low-density lipoprotein receptors

  E. progesterone receptors

  Correct Answer: E

  Section: Pharmacology Mifepristone, also known as RU 486, is an effective antagonist at progesterone and glucocorticoid receptors. It has no effect on the other receptors listed (choices AD).

• Question 200:

  The location of the lesion in Horner syndrome (either preganglionic or postganglionic) can be determined by the use of certain sympathomimetics. Which of the following agents would distinguish between a preganglionic versus a postganglionic lesion?

  A. amphetamine

  B. atenolol

  C. epinephrine

  D. isoproterenol

  E. phenylephrine

  Correct Answer: A

  Section: Pharmacology Indirectly acting sympathomimetics (e.g., amphetamines, cocaine) are useful in this situation because their action requires the presence of intact postganglionic noradrenergic neurons. Thus administration of hydroxyamphetamine into the eye will cause mydriasis in a Horner patient if the lesion is preganglionic (postganglionic neuron intact), but not if the lesion is postganglionic. In contrast, directacting sympathomimetics (choices C, D, E) will have the same effect regardless of the location of the lesion. Beta antagonists (choice B) will not produce any effect on the pupil.