A 58-year-old man with a lung lesion develops hyponatremia (Na 127 mEq/L). He appears euvolemic clinically and urine electrolytes reveal a high Na (>20 mmol/L) and high osmolality. Which of the following is the most likely mechanism for the low serum sodium?
The mediator of hyponatremia is likely antidiuretic hormone (ADH). Although controlling water permeability is the main function under ADH control, there is some evidence that ADH influences sodium transport in the cortical collecting duct. ADH can also act as a neurotransmitter. Autonomic effects of ADH in the CNS include bradycardia, increase in respiratory rate, suppression of fever, and alteration of sleep patterns.
A 38-year-old woman develops palpitations, weight loss, and heat intolerance. On examination, she has a mild tremor, an enlarged thyroid, and resting tachycardia. Biochemical tests confirm the diagnosis and she is started on methimazole. Which of the following is the most likely mechanism of this drug?
Methimazole is an effective treatment for hyperthyroidism. Methimazole interferes with thyroid function mainly by inhibition of thyroidal organic binding and coupling reactions. In contrast to other agents such as perchlorate, the action of thioamides is not prevented by large doses of iodide.
A 69-year-old man develops renal failure. Which of the following drugs requires a major adjustment in dosage?
Most of the fluoroquinolones are renally excreted and therefore require dose adjustment in renal failure. Exceptions are moxifloxacin and pefloxacin, which are metabolized by the liver. The other antibiotics do not require any adjustment for renal failure. Ampicillin needs to be adjusted only with severe renal failure.
A 69-year-old man with stable angina is given nitroglycerin. Which of the following is the most likely effect of this medication?
The benefit of nitroglycerin is probably due to diminution in cardiac output and work of the heart. Nitroglycerin generally dilates most veins and arteries, and this result in both a decreased preload and a decreased afterload for the heart. This leads to decreased myocardial oxygen requirements. Although coronary artery dilation also occurs, it is probably not as important in relieving anginal pain.
A 15-year-old boy is prescribed tetracycline for facial acne. Which of the following is the most common side effect of tetracycline?
GI symptoms are the major side effects of tetracycline. Stomatitis, glossitis, and diarrhea are seen and may be related to superinfections. Hepatic toxicity has been reported but is rare except in massive doses or during pregnancy. Tetracyclines can cause discoloration of teeth in children and in fetuses of mothers given the drug during pregnancy.
A 48-year-old man presents with fever, cough, and purulent sputum production. His chest x-ray (CXR) reveals a right middle lobe infiltrate and he is started on intravenous (IV) antibiotics after sputum and blood cultures are obtained. The following day his sputum cultures grow Streptococcus pneumoniae, which is sensitive to penicillin. He is better now so you step him down to oral treatment with amoxicillin rather than penicillin. Which of the following is the most likely reason why oral amoxicillin is preferred over penicillin?
Polar side chains added to penicillin molecules made these compounds acid stable and, therefore, improved absorption. Intake of food prior to ingestion of ampicillin will decrease absorption. In cases of severe renal impairment, the dose should be adjusted downward.
A 29-year-old woman develops deep vein thrombosis (DVT) in the third trimester. Which of the following statements regarding heparin therapy is correct?
Heparin must be given parenterally (usually intravenously or subcutaneously) to be active, and its activity is monitored by the partial thromboplastin time (PTT), not the PT. It is safer than oral anticoagulants in pregnancy and does not deplete clotting factors as its mode of action. Rather, it potentiates the effect of antithrombin III on the clotting cascade. It can be neutralized by administration of protamine. Because protamine can cause a bleeding tendency by its own actions, it is used only when bleeding is severe, and in the lowest possible dose. When low-molecular weight-heparin is used, it has a more predictable pharmacokinetic profile which allows for a weight-adjusted dosage without laboratory follow-up.
A 72-year-old man is prescribed hydrochlorothiazide for hypertension. Which of the following is the most likely symptomatic side effect?
The most common symptomatic side effect in men is impotence, and it should be specifically looked for. The most serious complications relate to fluid and electrolyte imbalance and include hyponatremia, hypokalemia, and volume contraction.
A 63-year-old woman with hypertension is started on a beta-blocker. Which of the following conditions require caution in prescribing this medication?
Beta-blockers are frequently used in the treatment of hypertrophic cardiomyopathy and for migraine prophylaxis and might prevent aortic dilatation in Marfan syndrome. It rarely causes clinical problems in patients with claudication, but if AV conduction defects are present (either by disease or use of other drugs), life-threatening bradyarrhythmias can occur.
A 69-year-old man is given a multivitamin containing B12. Which of the following is most characteristic of vitamin B 12 absorption?
Vitamin B 12 absorption is best in the distal ileum. Receptors for the intrinsic factor are present in the distal ileum, but mass action absorption also occurs with large doses. However, the oral route is still felt to be unreliable if hematologic or neurologic effects are present. The Schilling test, with and without intrinsic factor, can help diagnose the exact cause of B 12 deficiency.
A 79-year-old man on quinidine for paroxysmal atrial fibrillation develops thrombocytopenia. Which of the following is the most likely mechanism for this syndrome?
Thrombocytopenia usually occurs after weeks or months of therapy. It is due to formation of drug-platelet complexes that evoke a circulating antibody. Thrombocytopenia and bleeding can be severe but resolve rapidly on discontinuing the drug. The antibody is longlasting, and reintroduction of quinidine, even in a small dose, can rapidly cause thrombocytopenia. Other hypersensitivity reactions to quinidine include hepatitis, bone marrow suppression, and a lupus syndrome. The most common side effects of quinidine are gastrointestinal and include nausea, vomiting, and diarrhea.
A 19-year-old man takes an overdose of lysergic acid diethylamide (LSD). Which of the following clinical findings are mostly to be seen in this individual?
Sympathomimetic effects such as pupillary dilatation, piloerection, hyperthermia, and tachycardia are common in an overdosage of LSD. Other symptoms include dizziness, weakness, drowsiness, nausea, and paresthesias. The hallucinogenic effects can last for hours and are mainly visual.
A 19-year-old college student smokes cannabis on a regular basis. Which of the following clinical findings is most likely to be seen an hour after inhalation?
The most common therapeutic use of cannabis is as an antiemetic during cancer chemotherapy. It might have some analgesic and anticonvulsant properties. Its ability to lower intraocular pressure has not been therapeutically useful in glaucoma. However, all the possible therapeutic effects of cannabis are accompanied by psychoactive effects, which include impaired cognition and perception, prolonged reaction time, and impaired memory and learning.
An 83-year-old woman has chronic congestive heart failure (CHF) due to grade IV left ventricular function (ejection fraction <20%). She requires 80 mg/day of furosemide as part of her treatment. Which of the following metabolic abnormalities is most likely to be seen while she is taking this medication?
In addition to dehydration, hypokalemia, hypochloremia, and alkalosis also result from excessive use of furosemide. Loop diuretics such as furosemide act primarily to inhibit electrolyte reabsorption in the thick ascending limb of the loop of Henle. The degree of diuresis is greater than in other classes of diuretics.
A 73-year-old man with gastroesophageal reflux is prescribed ranitidine. Which of the following is the most likely effect of this medication?
Ranitidine is an H2-blocker that reversibly competes with histamine for binding to H2 receptors on gastric parietal cells. Its effect is profound on basal acid secretion, but it also has a significant effect on stimulated (e.g., food, hypoglycemia, vagal stimulation) acid production.
A 69-year-old man with poorly controlled hypertension is on hydrochlorothiazide and metoprolol. Compliance with medications and salt restriction is reviewed with the patient and he is also prescribed nifedipine for optimal control of his blood pressure. Which of the following is the mechanism of action for this medication?
Nifedipine is a synthetic agent that is a potent, long-acting systemic vasodilator for the treatment of coronary vasospasm. It is also effective for hypertension. At doses used clinically, nifedipine does not block transmission through the AV node. The vasodilatation can result in a reflex increase in heart rate.
A 28-year-old woman with bipolar disorder has a lithium level of 2.3 mEq/L (normal range 0.6–1.25 mEq/L). Which of the following side effects is most likely to occur?
Lithium is used primarily for bipolar affective disorder, either to treat mania or prevent recurrences of the bipolar disorder. It has also been used in severe unipolar depression. Acute intoxication can result in vomiting, diarrhea, tremor, ataxia, coma, and convulsions. Leukocytosis is also a side effect of lithium therapy. Polyuria and polydipsia secondary to acquired nephrogenic diabetes insipidus is a common side effect. Both acute and chronic intoxication can be lethal. The toxic and therapeutic levels of lithium are very close, and patients on lithium require close medical observation, including measurement of serum lithium levels.
A 74-year-old man with a previous episode of gout is given allopurinol. Which of the following is the most likely mechanism of action for this medication?
Allopurinol effectively blocks uric acid production by inhibiting xanthine oxidase. Allopurinol is indicated in patients with a history of uric acid calculi of the urinary tract. In addition, it is often used in patients with malignancy (e.g., leukemia, lymphoma), particularly when chemotherapy or radiation therapy is being used.
A 69-year-old woman, with poor dietary habits and alcoholism, is found to have a macrocytic anemia with hypersegmented neutrophils. Which of the following is the most appropriate diagnostic test?
Folate deficiency can be secondary to small bowel disease, alcoholism, inadequate intake, disease states with high cell turnover (hemolytic anemia), drugs (methotrexate), and pregnancy. The concentration of folate in plasma changes rapidly with changes in food intake, so the diagnosis of anemia secondary to folate deficiency is made more reliable by measuring red blood cell folate.
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