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250. The answer is D. (Chapters 210-211) Drugs are commonly responsible for thrombo-cytopenia. Although all of the listed agents are associated with a reduction in platelet count, there are fewer case reports involving estrogen than those involving heparin, quinine, quini-dine, or heroin. Other drugs that cause thrombocytopenia include sulfa-containing antibiotics, amrinone, ethanol, aspirin, valproic acid, indomethacin, thiazide diuretics, phenytoin, cimetidine, penicillin, and interferon.

251. The answer is D. (Chapter 211) Patients with idiopathic thrombocytopenic purpura (ITP) have platelet antibodies that increase platelet destruction, thereby limiting the efficacy of transfusion. Patients with hypersplenism are also poor candidates for platelet transfusion because they sequester transfused platelets out of the general circulation. Most patients with platelets fewer than 50,000/^L should receive platelet transfusions to protect against bleeding complications. If platelets drop to less than 10,000/^L, platelet transfusion is strongly advised because of the risk of spontaneous bleeding, including intracranial hemorrhage. Each pack of platelets transfused raises the platelet count by approximately 10,000/^L.

252. The answer is E. (Chapter 211) Patients who have ingested significant amounts of brodifacoum require admission and treatment with massive amounts of vitamin K, possibly exceeding the pharmacy's inventory. This type of rat poison is a "superwarfarin" with a long half-life that was created to combat emerging warfarin resistance in rodent pests. Ingestion of "superwarfarin" is associated with a severe, potentially fatal coagu-lopathy. Profuse mucosal bleeding and internal hemorrhage are common clinical manifestations. Treatment of warfarin overdose depends on the clinical picture, not on the magnitude of PT prolongation. Patients may require large doses of vitamin K (50-100 mg/day) for several weeks. Fresh frozen plasma may also be required. A 10- to 15-mg dose of vitamin K should be administered subcutaneously or intramuscularly to patients who are bleeding. Intravenous vitamin K carries a risk of anaphylaxis, but 1 mg intravenously is considered a safe quantity to give. Patients may be resistant to warfarin therapy for up to 2 weeks after vitamin K administration.

253. The answer is B. (Chapter 211) Trimethoprim is a sulfa drug associated with throm-bocytopenia, not a coagulopathy secondary to vitamin K deficiency. Drug-induced deficiency of vitamin K-dependent factors is seen with cephalosporins that have an N-methylthiotetrazole side chain. These include the second-generation drug cefamandole and the third-generation drugs cefotaxime, cefoperazone, and moxalactam.

254. The answer is E. (Chapter 211) Antithrombin III is a protein that forms complexes with factors VII, IX, X, XI, and XII and prothrombin, thereby inhibiting their function. It is not vitamin K-dependent. Factors II, VII, IX, and X, protein C, and protein S are all dependent on vitamin K for proper functioning. Parenchymal liver disease decreases synthesis of factors II, VII, IX, and X. Because vitamin K is fat soluble, malabsorption, hepatic cholestasis, and poor nutrition contribute to vitamin K deficiency.

255. The answer is D. (Chapter 211) FFP is not a first-line treatment for patients with uremia and excessive bleeding because of its inability to tolerate the large volume load. Treatment of a bleeding uremic patient should include packed red blood cells, erythro-poietin, desmopressin, dialysis, conjugated estrogen, platelet transfusion, or cryoprecipi-tate infusion. Cryoprecipitate carries a risk of viral transmission and has mostly been replaced by desmopressin. FFP administration also carries a risk of virus transmission. Each unit of FFP contains 200 to 250 units of each coagulation factor. FFP is indicated in the treatment of patients with severe liver disease and bleeding.

256. The answer is E. (Chapter 211) In addition to the traumatic injury, this patient has evidence of disseminated intravascular coagulation (DIC), suggested by the prolonged PT, low fibrinogen, and decreased platelets. Clinical manifestations of DIC include bleeding, thrombosis, and purpura fulminans. This patient's continued bleeding and prolonged PT are indications for FFP and cryoprecipitate (to replete fibrinogen). Platelet transfusion is indicated when platelet count is less than 50,000/^L and there is bleeding, or if platelet count is less than 20,000/^L regardless of bleeding. Packed red blood cells should be ready in case the hemoglobin and hematocrit continue to drop. Whereas low-dose heparin (5-10 units/kg/h) is used to treat patients with purpura fulminans, low-molecular-weight heparin is not used to treat DIC. Patients with DIC who may benefit from standard heparin therapy include those with carcinoma, acute promyelocytic leukemia, or retained uterine products.

257. The answer is C. (Chapter 211) One milligram of protamine sulfate will neutralize 100 units of standard-molecular-weight heparin and is indicated in the setting of severe bleeding after the heparin infusion has been stopped. Bleeding is a common complication of heparin use and occurs in about one-third of patients. One to seven percent of patients will have serious or life-threatening bleeding. Concomitant use of cimetidine, nonsteroidal antiinflammatory drugs (NSAIDs), aspirin, warfarin, and steroids increase a patient's bleeding risk. Underlying conditions that also increase risk of bleeding include history of renal failure, gastrointestinal bleeding, ethanol use, malignancy, recent trauma, and bleeding diatheses. Thrombocytopenia is a common complication of heparin use.

258. The answer is E. (Chapter 211) Heparin-associated thrombocytopenia with anti-platelet antibody formation is uncommon but is potentially life threatening. Patients with previous exposure to heparin may have an immediate reaction, whereas patients without previous exposure will more likely develop antibodies over the next 6 to 10 days. Arterial thrombosis is a possible complication. If platelet levels fall below 50,000/^L, heparin transfusion must be stopped; some clinicians have advocated future avoidance of heparin. A more common form of heparin-associated thrombocytopenia without antibody formation occurs in about 25 percent of patients. A transient decrease in platelet count occurs, but seldom below 100,000/^L. The etiology is postulated to be due to platelet aggregation and splenic sequestration.

259. The answer is D. (Chapters 211, 216) Thrombolytic drugs have been used to treat massive, acute pulmonary emboli. With treatment, reperfusion is improved and pulmonary artery pressures are decreased. However, clinical trials that conclusively demonstrate improved survival are lacking.

260. The answer is D. (Chapter 211) Thrombocytopenia is the most common hemato-logic complication of HIV infection. Immune platelet destruction, such as that seen with ITP, is also common. Anemia frequently occurs secondary to decreased erythropoiesis and bone marrow suppression from infection or drug therapy. A lupus-type anticoagulant prolongs the PTT and may appear and disappear in concert with the onset and treatment of opportunistic infections. Anti-cardiolipin antibodies, another type of acquired circulating antibody, increase the patient's risk of thrombosis. TTP is an uncommon complication of HIV infection. It may actually herald HIV infection when appearing with a pentad of fever, thrombocytopenia, neurologic symptoms, renal insufficiency, and microangiopathic hemolytic anemia.

261. The answer is A. (Chapter 211) Factor VIII inhibitors prolong the PTT (reflecting the intrinsic coagulation cascade), but not the PT (reflecting the extrinsic coagulation cascade). This same pattern is seen in patients with hemophilia A (factor VIII deficiency). The incidence of factor VIII inhibitors is low, estimated at 0.2 to 1.0 per million, but the mortality rate approaches 50 percent. Patients develop massive spontaneous ecchymoses and hematomas. About half of affected people are otherwise healthy and older than 65 years. Associated underlying autoimmune disorders include systemic lupus erythematosus (SLE), rheumatoid arthritis, and ulcerative colitis. Associated lymphopro-liferative disorders include multiple myeloma, Waldenstrom's macroglobulinemia, and benign monoclonal gammopathy. Pregnancy and the immediate postpartum period are also associated. A factor VIII-specific assay shows low or absent factor VIII activity. Treatment involves repletion or supplementation of factor VIII and prothrombin.

262. The answer is E. (Chapter 211) Lupus anticoagulant, an antiphospholipid antibody, is often an incidental laboratory finding. Only 5 to 15 percent of patients have SLE, and clinical bleeding is rare unless the patient has an underlying predisposing condition such as hypoprothrombinemia, significant thrombocytopenia, or uremia. Patients with lupus anticoagulant display mild to moderate PTT prolongation and a normal or slightly prolonged PT. Arterial and venous thrombosis occurs in 23 to 53 percent of patients. Recurrent fetal loss is secondary to placental vessel thrombosis and infarction.

263. The answer is A. (Chapter 211) This patient has impending airway compromise and should be emergently intubated. After the airway is secured, factor VIII should be replaced and computed tomography (CT) of the neck should be performed. Patients with hemophilia are at risk for spontaneous bleeding and posttraumatic bleeding. Because this patient with hemophilia A has a potentially life-threatening hemorrhage, he requires an initial dose of factor VIII of 50 units/kg. If no factor VIII concentrate is readily available, cryoprecipitate (100 units of factor VIII per bag) or FFP (1 unit of factor VIII/mL) can be administered as a temporizing measure.

264. The answer is D. (Chapter 212) DDAVP is a synthetic peptide, not a blood product, so there is no risk of viral transmission. For hemophilia A patients who respond, the rise in factor VIII levels occurs within 1 h of administration. The usual dose is 0.3 ^g/kg intravenously or subcutaneously every 12 h for three to four doses, after which temporary tachyphylaxis may occur. DDAVP is postulated to work by causing a release of von Willebrand factor (vWF) from endothelial cells. Increased levels of vWF are able to carry additional factor VIII in the plasma. Mild hyponatremia may occur because of the effect similar to that of anti-diuretic hormone.

265. The answer is B. (Chapter 213) Acute chest syndrome, characterized by fever, dyspnea, tachypnea, hypoxia, pleuritic chest pain, leukocytosis, and pulmonary infiltrates, is this patient's most likely diagnosis. Despite the later development of consolidation, initial chest x-ray is often unremarkable. Acute chest syndrome occurs when a pulmonary infarct becomes secondarily infected, and it is seen in 30 percent of patients with sickle cell disease, accounting for 15 percent of adult deaths. It may be difficult to differentiate between acute chest syndrome and pneumonia or pulmonary infarction, and most hema-tologists recommend empiric antibiotics. If pulmonary embolism is suspected, V/Q or spiral CT is indicated. Pulmonary angiography carries the risk of further exacerbating pulmonary sickling and should be avoided. Aggressive hydration may precipitate adult respiratory distress syndrome.

266. The answer is D. (Chapter 213) Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an inherited enzyme disorder that affects up to 10 percent of the world's population. This deficiency leaves senescent red blood cells vulnerable to oxidative stress and causes hemoglobin to precipitate in the form of Heinz bodies. It is X-linked and manifests in male heterozygotes and female homozygotes. Hemolytic crises occur after bacterial or viral infection, metabolic acidosis, fava bean ingestion, or exposure to oxi-dant drugs. The most common oxidant drugs are sulfa drugs such as TMP-SMX, chloro-quine, pyridium, and nitrofurantoin. With rhabdomyolysis, the urinalysis is positive for blood (myoglobin), but red cells are absent on microscopy. Pyridium will color urine orange. Over a period of several days, a patient with gallbladder obstruction would have pain and might have a urine positive for bilirubin but negative for urobilinogen because the conjugated bilirubin would not reach the intestine.

267. The answer is D. (Chapter 214) This patient has thrombotic thrombocytopenic purpura. This disorder is characterized by a microangiopathic hemolytic anemia that results in microthrombi in capillaries and arterioles throughout the body, especially in the brain, heart, kidneys, pancreas, and adrenal glands. Schistocytes are present on peripheral smear. Treatment includes ICU admission, steroids, and plasma exchange transfusion using FFP. Because platelets can exacerbate thrombosis, transfusion should be avoided unless there is uncontrolled hemorrhage.

268. The answer is E. (Chapter 217) This patient has evidence of acute spinal cord compression in the thoracic region, demonstrated by bilateral radiculopathy. Aggressive work-up and treatment may help prevent permanent neurologic disability. He requires urgent neurosurgical consultation, high-dose steroids, magnetic resonance imaging, and a Foley catheter. Acute spinal cord compression is common in patients with multiple myeloma, lymphoma, and metastatic breast, lung, and prostate cancers. It can also occur in the setting of epidural hematoma, infection, or fracture.

269. The answer is E. (Chapter 217) This patient has severe hypercalcemia that could adversely affect cardiac, neurologic, and muscular function. Saline infusion (1 to 2 L) followed by 80 mg intravenous furosemide are standard initial therapies. Glucocorticoids are efficacious for the treatment of hypercalcemia in the setting of lymphoma, hemato-logic emergencies, and metastatic lung and breast cancers. Peak effectiveness is not reached for several days. Bisphosphonate and mithramycin are also highly efficacious treatments. One gram of inorganic phosphate, infused over an 8-h period, and never as a bolus, will rapidly reduce serum calcium, but potential adverse effects include accelerated soft-tissue calcifications, hypocalcemia, hypotension, renal failure, and death.

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