Acquired amegakaryocytic thrombocytopenia after durvalumab administration.

Immune checkpoint inhibitors (ICIs), despite their ability to potentiate antitumor T-cell responses, may cause various immune-related adverse events. Most cases of thrombocytopenia induced by ICIs have revealed a pathophysiologic mechanism of immune thrombocytopenia with increased platelet destruction and preserved megakaryocytes. Acquired amegakaryocytic thrombocytopenic purpura (AATP) is an unusual disorder characterized by thrombocytopenia with markedly diminished bone marrow megakaryocytes in the presence of otherwise normal hematopoiesis. AATP caused by ICIs has not been reported on. Herein, we present the case of a 79-year-old man diagnosed with squamous cell carcinoma of the lung who developed AATP after two courses of durvalumab, a drug targeting programmed death-ligand 1. Two weeks after the second cycle, his platelet count decreased to 2.1 × 104/µL. After the patient underwent platelet transfusion, his platelet count increased to 8.1 × 104/µL the next day but subsequently decreased repeatedly even after the ICI was discontinued. Six weeks after the second cycle, he developed interstitial pneumonia and was administered prednisolone (50 mg/day). However, thrombocytopenia did not improve. Bone marrow biopsy showed scarce megakaryocytes (< 1 megakaryocyte/10 high-power fields) with preservation of myeloid and erythroid series. Myelodysplasia, myelofibrosis, or metastatic lesions were not observed. Cytogenetic analysis showed a normal male karyotype of 46XY. Hence, the patient received eltrombopag, a thrombopoietin receptor agonist, and his platelet count subsequently improved. After recovery, bone marrow aspiration revealed a normal number of megakaryocytes. AATP is rarely the type of thrombocytopenia induced by ICIs and may be successfully treated with thrombopoietin receptor agonists.

Vaccines for measles, mumps, rubella, and varicella in children.

BACKGROUND: Measles, mumps, rubella, and varicella (chickenpox) are serious diseases that can lead to serious complications, disability, and death. However, public debate over the safety of the trivalent MMR vaccine and the resultant drop in vaccination coverage in several countries persists, despite its almost universal use and accepted effectiveness. This is an update of a review published in 2005 and updated in 2012. OBJECTIVES: To assess the effectiveness, safety, and long- and short-term adverse effects associated with the trivalent vaccine, containing measles, rubella, mumps strains (MMR), or concurrent administration of MMR vaccine and varicella vaccine (MMR+V), or tetravalent vaccine containing measles, rubella, mumps, and varicella strains (MMRV), given to children aged up to 15 years. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library 2019, Issue 5), which includes the Cochrane Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to 2 May 2019), Embase (1974 to 2 May 2019), the WHO International Clinical Trials Registry Platform (2 May 2019), and ClinicalTrials.gov (2 May 2019). SELECTION CRITERIA: We included randomised controlled trials (RCTs), controlled clinical trials (CCTs), prospective and retrospective cohort studies (PCS/RCS), case-control studies (CCS), interrupted time-series (ITS) studies, case cross-over (CCO) studies, case-only ecological method (COEM) studies, self-controlled case series (SCCS) studies, person-time cohort (PTC) studies, and case-coverage design/screening methods (CCD/SM) studies, assessing any combined MMR or MMRV / MMR+V vaccine given in any dose, preparation or time schedule compared with no intervention or placebo, on healthy children up to 15 years of age. DATA COLLECTION AND ANALYSIS: Two review authors independently extracted data and assessed the methodological quality of the included studies. We grouped studies for quantitative analysis according to study design, vaccine type (MMR, MMRV, MMR+V), virus strain, and study settings. Outcomes of interest were cases of measles, mumps, rubella, and varicella, and harms. Certainty of evidence of was rated using GRADE. MAIN RESULTS: We included 138 studies (23,480,668 participants). Fifty-one studies (10,248,159 children) assessed vaccine effectiveness and 87 studies (13,232,509 children) assessed the association between vaccines and a variety of harms. We included 74 new studies to this 2019 version of the review. Effectiveness Vaccine effectiveness in preventing measles was 95% after one dose (relative risk (RR) 0.05, 95% CI 0.02 to 0.13; 7 cohort studies; 12,039 children; moderate certainty evidence) and 96% after two doses (RR 0.04, 95% CI 0.01 to 0.28; 5 cohort studies; 21,604 children; moderate certainty evidence). The effectiveness in preventing cases among household contacts or preventing transmission to others the children were in contact with after one dose was 81% (RR 0.19, 95% CI 0.04 to 0.89; 3 cohort studies; 151 children; low certainty evidence), after two doses 85% (RR 0.15, 95% CI 0.03 to 0.75; 3 cohort studies; 378 children; low certainty evidence), and after three doses was 96% (RR 0.04, 95% CI 0.01 to 0.23; 2 cohort studies; 151 children; low certainty evidence). The effectiveness (at least one dose) in preventing measles after exposure (post-exposure prophylaxis) was 74% (RR 0.26, 95% CI 0.14 to 0.50; 2 cohort studies; 283 children; low certainty evidence). The effectiveness of Jeryl Lynn containing MMR vaccine in preventing mumps was 72% after one dose (RR 0.24, 95% CI 0.08 to 0.76; 6 cohort studies; 9915 children; moderate certainty evidence), 86% after two doses (RR 0.12, 95% CI 0.04 to 0.35; 5 cohort studies; 7792 children; moderate certainty evidence). Effectiveness in preventing cases among household contacts was 74% (RR 0.26, 95% CI 0.13 to 0.49; 3 cohort studies; 1036 children; moderate certainty evidence). Vaccine effectiveness against rubella is 89% (RR 0.11, 95% CI 0.03 to 0.42; 1 cohort study; 1621 children; moderate certainty evidence). Vaccine effectiveness against varicella (any severity) after two doses in children aged 11 to 22 months is 95% in a 10 years follow-up (rate ratio (rr) 0.05, 95% CI 0.03 to 0.08; 1 RCT; 2279 children; high certainty evidence). Safety There is evidence supporting an association between aseptic meningitis and MMR vaccines containing Urabe and Leningrad-Zagreb mumps strains, but no evidence supporting this association for MMR vaccines containing Jeryl Lynn mumps strains (rr 1.30, 95% CI 0.66 to 2.56; low certainty evidence). The analyses provide evidence supporting an association between MMR/MMR+V/MMRV vaccines (Jeryl Lynn strain) and febrile seizures. Febrile seizures normally occur in 2% to 4% of healthy children at least once before the age of 5. The attributable risk febrile seizures vaccine-induced is estimated to be from 1 per 1700 to 1 per 1150 administered doses. The analyses provide evidence supporting an association between MMR vaccination and idiopathic thrombocytopaenic purpura (ITP). However, the risk of ITP after vaccination is smaller than after natural infection with these viruses. Natural infection of ITP occur in 5 cases per 100,000 (1 case per 20,000) per year. The attributable risk is estimated about 1 case of ITP per 40,000 administered MMR doses. There is no evidence of an association between MMR immunisation and encephalitis or encephalopathy (rate ratio 0.90, 95% CI 0.50 to 1.61; 2 observational studies; 1,071,088 children; low certainty evidence), and autistic spectrum disorders (rate ratio 0.93, 95% CI 0.85 to 1.01; 2 observational studies; 1,194,764 children; moderate certainty). There is insufficient evidence to determine the association between MMR immunisation and inflammatory bowel disease (odds ratio 1.42, 95% CI 0.93 to 2.16; 3 observational studies; 409 cases and 1416 controls; moderate certainty evidence). Additionally, there is no evidence supporting an association between MMR immunisation and cognitive delay, type 1 diabetes, asthma, dermatitis/eczema, hay fever, leukaemia, multiple sclerosis, gait disturbance, and bacterial or viral infections. AUTHORS' CONCLUSIONS: Existing evidence on the safety and effectiveness of MMR/MMRV vaccines support their use for mass immunisation. Campaigns aimed at global eradication should assess epidemiological and socioeconomic situations of the countries as well as the capacity to achieve high vaccination coverage. More evidence is needed to assess whether the protective effect of MMR/MMRV could wane with time since immunisation.

Immune Thrombocytopenia Secondary to Hodgkin's Lymphoma in Children

BACKGROUND: Immune thrombocytopenia (ITP) is an autoimmune disorder of variable origin that results in bleeding and decreased platelet count. Autoimmune abnormalities have been described in patients with malignancies including non-Hodgkin's lymphoma but are rarely described in patients with Hodgkin's lymphoma. OBJECTIVES: To describe an unusual presentation of Hodgkin's lymphoma in an unusual age and alarm pediatricians of the challenging diagnosis. METHODS: We present two cases that highlight an unusual clinical presentation of childhood Hodgkin's lymphoma occurring at an atypical age. RESULTS: Over a 4-year period, two children aged 5 and 6 years were admitted for suspected ITP, both had cervical lymphadenopathy. Bone marrow examination showed no evidence of tumor or fibrosis. Biopsy of the lymph node was possible only after administration of intravenous immunoglobulins and normalization of the platelet count. Platelet counts increased after initiation of chemotherapy. CONCLUSIONS: The identification of the clinical presentation of ITP as a possible presentation of Hodgkin's lymphoma is important to facilitate timely diagnosis and management.

Acquired Amegakaryocytic Thrombocytopenia in Adult-onset Still's Disease: Successful Combination Therapy with Tocilizumab and Cyclosporine.

Adult-onset Still's disease (AOSD) sometimes demonstrates hematologic disorder, whereas acquired amegakaryocytic thrombocytopenia (AAT) involvement is extremely rare. We herein report a 67-year-old woman with relapse of AOSD who concomitantly developed AAT. Thrombocytopenia along with high disease activity of AOSD was resistant to high-dose prednisolone, even in combination with methotrexate and tacrolimus. However, alternative treatment with cyclosporine after administering tocilizumab resulted in the improvement of thrombocytopenia, ultimately demonstrating that combination therapy based on suppressing the intractable disease activity of AOSD and subsequently adding a reliable immunosuppressant was required to achieve remission.

Prevention of relapse in patients with acquired thrombotic thrombocytopenic purpura undergoing elective surgery: a case series.

Essentials Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease. Surgery is a possible trigger of acute TTP episodes and no guidelines are available. Six patients with severe ADAMTS-13 deficiency during remission underwent elective surgery. Patients were prophylactically treated to restore ADAMTS-13 activity and no relapses occurred. SUMMARY: Background Severe ADAMTS-13 deficiency has been recognized as the main risk factor for recurrence of thrombotic thrombocytopenic purpura (TTP). Several conditions, including surgery, may influence the levels of ultra-large von Willebrand factor and ADAMTS-13, acting as a trigger for an acute TTP event. Objectives To report our experience of management of six patients with acquired TTP who underwent elective surgery after prophylactic treatment to restore ADAMTS-13 activity levels. Patients Six patients followed for acquired TTP with severe ADAMTS-13 deficiency during remission were candidates for seven elective surgeries (inguinal hernioplasty, cholecystectomy, laparoscopic hysterectomy, oophorectomy, parotidectomy and two total hip arthroplasties). Results Four patients were treated with prophylactic plasma exchange (PEX) therapy immediately before surgery. One patient was treated with PEX therapy before her first surgery and with preemptive rituximab once her second surgery was scheduled. Because rituximab increased ADAMTS-13 levels only partially, she required one PEX procedure the day before her second surgery. One patient was treated with azathioprine after rituximab failure, obtaining a progressive increase of ADAMTS-13 activity to more than 40%. This level allowed her to undergo total hip arthroplasty without additional treatment. All surgeries were successful and no complications or relapses occurred. Conclusions Six patients with acquired TTP underwent seven successful surgical procedures using prophylaxis to restore ADAMTS-13 activity. Further observational studies or randomized clinical trials are needed to confirm whether prophylactic PEX could be the key factor in preventing relapse.

Thrombocytopenic purpura following envenomation by the nose-horned viper (Vipera ammodytes ammodytes): Two case reports.

RATIONALE: Two clinical cases are reported of envenomation by the nose-horned viper (Vipera ammodytes ammodytes) venom of a 9-year-old boy and of an 84-year-old woman. PATIENT CONCERNS: Both patients had been bitten on their extremities by such a snake in August near Split, a town in southern Croatia. DIAGNOSES: Clinical manifestation of envenomation was severe in the case of the boy, being characterized by a severe coagulopathy. This was only just apparent in the case of the elderly woman, who suffered extensive local edema and hematoma at the site of the bite, together with a neurotoxic effect-bilateral ptosis. This was the first occasion of thrombocytopenic purpura being observed in patients envenomed by nose-horned viper venom. This unexpected clinical finding was characterized by an unusually profound thrombocytopenia of 5 and 10 × 10/L platelets of the respective patients on their admission to the hospital, together with purpura, observed on the face and thorax of both individuals. In the most serious cases, such pathology can be life threatening if not promptly recognized and treated. INTERVENTIONS: The patients recovered quickly on receiving the specific antivenom along with all the usual supportive treatments. OUTCOMES: No serious sequels were noticed at the moment of discharge. LESSONS: Our finding constitutes an important message to clinicians to consider the possibility of such complications in the case of nose-horned viper envenomation.

A Rare Case of Thrombotic Thrombocytopenic Purpura Caused by Pancreatitis and Clopidogrel.

BACKGROUND Thrombotic thrombocytopenic purpura is mostly characterized by symptoms and signs of hemolytic anemia, thrombocytopenia, renal impairment, fever and neurologic dysfunction. It is not always necessary to have all 5 characteristic symptoms, and presentations can vary. It can be congenital or acquired by any etiology that causes deficiency or dysfunction of ADAMST13 enzyme. CASE REPORT We present a case of a 71-year-old man who presented to our hospital initially with abdominal pain. He was diagnosed with pancreatitis, and conservative management was started with pain control and hydration. During the hospital course, the patient developed anemia that was hemolytic in nature, acute kidney injury and thrombocytopenia. He was then diagnosed as having TTP secondary to pancreatitis with additive effect of clopidogrel, as he had recently been started on clopidogrel due to percutaneous coronary intervention. He was started on prompt treatment with plasma exchange and intermittent dialysis, and he achieved full recovery after that. CONCLUSIONS TTP is a potentially fatal disease with high mortality risk. It is judicious to recognize and have high suspicion of TTP being caused by such rare causes (pancreatitis and clopidogrel), as immediate recognition and treatment can enhance survival.

Amegakaryocytic Thrombocytopenia and Subsequent Aplastic Anemia Associated with Apparent Epstein-Barr Virus Infection.

Acquired amegakaryocytic thrombocytopenia (AAT), a rare entity characterized by severe thrombocytopenia and the absence of megakaryocytes in the bone marrow, may mimic or precede the diagnosis of aplastic anemia (AA). Here, we describe a patient who presented with apparent Epstein-Barr virus (EBV)-associated immune thrombocytopenia resistant to several lines of therapies, which was in fact a form of AAT with some features of AA. He eventually responded to therapy with eltrombopag, cyclosporine A (CSA), and antithymocyte globulin (ATG) and recovered completely. EBV infection is known to cause a variety of benign and malignant hematologic disorders, including bone marrow failure. However, to the best of our knowledge, this is the first case report of EBV-associated AAT. Treatment options for AAT are still not well defined, and even response to eltrombopag together with CSA and ATG does not always imply successful therapy. The natural history of EBV infection may well be sufficient to explain unexpected eventual recovery.

[Acquired amegacaryocytic thrombocytopenic purpura hiding acute myeloid leukemia]. / Un purpura thrombopénique amégacaryocytaire acquis qui cache une leucémie aigue myéloblastique.

Acquired amegakaryocytic thrombocytopenic purpura is a very rare condition characterized by severe thrombocytopenia linked to the reduction or disappearance of megakaryocytes in the bone marrow. It may be primary idiopathic or secondary to many pathological conditions including hematologic disorders. We report the case of a 24-year-old patient admitted for haemorrhagic syndrome caused by immunological thrombocytopenic purpura. The diagnosis was acquired amegakaryocytosis after the failure of corticotherapy and the performance of myelography. The patient was treated with ciclosporin with rapid progression to acute myeloblastic leukemia. The progression of acquired amegakaryocytosis to acute leukemia is reported but it is generally not so rapid and above all it is preceded by myelodysplastic syndrome or medullary aplasia. This study highlights the importance of a close follow-up of these pathologies with a benign-like appearance.

[A Patient with Basaloid Carcinoma of the Esophagus Removed Surgically after Pre-Operative Chemotherapy Who Developed TTP during Post-Operative Chemotherapy].

A 63-year-old man presented with the chief complaint of an unpleasant feeling in the chest after a meal.Esophagogastroduodenoscopy revealed interminglement of ulcer infiltration type lesions and protruding lesions in the lower esophagus.A large type 1 protruding lesion was located mainly in the esophagogastric junction(EGJ)and it progressed towards the stomach.A hypertrophic and protruding lesion on the lower esophageal wall and a 6 cm tumor in the major axis of the fornix were observed on thoracic and abdominal CT, and an endocrine cell carcinoma or basaloid carcinoma were suggested after biopsy.Finally, we diagnosed a basaloid carcinoma after immunohistochemistry analysis.We administered 4 courses of TS-1 plus CDDP as pre-operative chemotherapy.Because of a significant reduction in tumor size, approximately 5 months after first presentation, we performed esophageal resection by right thoracotomy and laparotomy, and reconstructive surgery for the thoracic gastric duct.The pathological diagnosis was basaloid carcinoma with multiple foci of squamous cell carcinoma.After surgery, we continued chemotherapy with TS-1 plus CDDP, which was previously effective, but a liver metastasis appeared 8 months later.We discontinued chemotherapy because of a prominent decline in platelets.Because of the clinical symptoms, we diagnosed secondary thrombotic thrombocytopenic purpura accompanied by a malignant tumor.We implemented plasma exchange and steroid pulse therapy, but this patient experienced no therapeutic effect and died.

Seronegative Antiphospholipid Syndrome with Anti-phosphatidylethanolamine Antibody in a Boy.

Antiphospholipid syndrome (APS) is an autoimmune disease caused by antiphospholipid antibodies. At our institution, APS is diagnosed on the basis of the Sapporo criteria, which consist of thrombosis and recurrent pregnancy-related complications and the following laboratory findings: the presence of lupus anticoagulant, anticardiolipin antibody, or anti-ß2 glycoprotein 1 antibody. However, we sometimes treat patients we strongly suspect of having APS but who do not satisfy the laboratory criteria. To accommodate such suspected cases, a subtype of APS termed seronegative APS has been proposed. Here, we report on a man with chronic thromobocytopenic purpura since the age of 3 years and multiple cerebral infarctions since the age of 14 years who finally received a diagnosis of seronegative APS with positive antiphosphatidylethanolamine antibodies.

Platelet transfusions in platelet consumptive disorders are associated with arterial thrombosis and in-hospital mortality.

While platelets are primary mediators of hemostasis, there is emerging evidence to show that they may also mediate pathologic thrombogenesis. Little data are available on risks and benefits associated with platelet transfusions in thrombotic thrombocytopenic purpura (TTP), heparin-induced thrombocytopenia (HIT) and immune thrombocytopenic purpura (ITP). This study utilized the Nationwide Inpatient Sample to evaluate the current in-hospital platelet transfusion practices and their association with arterial/venous thrombosis, acute myocardial infarction (AMI), stroke, and in-hospital mortality over 5 years (2007-2011). Age and gender-adjusted odds ratios (adjOR) associated with platelet transfusions were calculated. There were 10 624 hospitalizations with TTP; 6332 with HIT and 79 980 with ITP. Platelet transfusions were reported in 10.1% TTP, 7.1% HIT, and 25.8% ITP admissions. Platelet transfusions in TTP were associated with higher odds of arterial thrombosis (adjOR = 5.8, 95%CI = 1.3-26.6), AMI (adjOR = 2.0, 95%CI = 1.2-3.3) and mortality (adjOR = 2.0,95%CI = 1.3-3.0), but not venous thrombosis. Platelet transfusions in HIT were associated with higher odds of arterial thrombosis (adjOR = 3.4, 95%CI = 1.2-9.5) and mortality (adjOR = 5.2, 95%CI = 2.6-10.5) but not venous thrombosis. Except for AMI, all relationships remained significant after adjusting for clinical severity and acuity. No associations were significant for ITP. Platelet transfusions are associated with higher odds of arterial thrombosis and mortality among TTP and HIT patients.

High procalcitonin and thrombocytopenic purpura in a case of Kikuchi-Fujimoto disease.

Kikuchi-Fujimoto disease is a mild and rare idiopathic disease, particularly in children. It is mostly characterized by painful cervical lymphadenopathy and/or prolonged fever and confirmed by histology. We report a case of Kikuchi-Fujimoto disease in a 14-year-old teenager with high procalcitonin concentration and thrombocytopenic purpura.

Posttransfusion purpura occurrence and potential risk factors among the inpatient US elderly, as recorded in large Medicare databases during 2011 through 2012.

BACKGROUND: Posttransfusion purpura (PTP) is a serious transfusion complication resulting in sudden thrombocytopenia with bleeding. The study's objective was to assess PTP occurrence and potential risk factors among the inpatient US elderly, ages 65 and older, during 2011 through 2012. STUDY DESIGN AND METHODS: This retrospective claims-based study utilized large Medicare databases for calendar years 2011 and 2012. Transfusions of blood and blood components were identified by recorded ICD-9-CM procedure codes and revenue center codes, and PTP was ascertained via ICD-9-CM diagnosis code. Our study evaluated PTP rates (per 100,000 inpatient transfusion stays) among elderly Medicare beneficiaries, overall and by age, sex, race, number of units, and blood components transfused. Multivariate regression analyses were used to assess potential risk factors. RESULTS: Among 4,336,338 inpatient transfusion stays for elderly beneficiaries during the study period, 78 had a PTP diagnosis code recorded, an overall rate of 1.8 per 100,000 stays. PTP occurrence varied by the blood components, units transfused, and other characteristics. Significantly higher odds of PTP were found for platelet (PLT)-containing transfusions, with greater number of units transfused, as well as for elderly with histories of cardiac arrhythmias (odds ratio [OR], 2.65; 95% confidence interval [CI], 1.43-4.93), coagulopathy (OR, 1.79; 95% CI, 1.01-3.21), leukemia (OR, 2.37; 95% CI, 1.07-5.26), transplant (OR, 2.68; 95% CI, 1.41-5.09), and other conditions. CONCLUSION: Our population-based study suggests a substantially higher PTP risk with PLT-containing transfusions. The study also suggests increased PTP risk with greater number of units transfused as well as the importance of underlying health conditions and prior recipient alloimmunization for PTP occurrence among the elderly.

Drug-induced immune thrombocytopenia: incidence, clinical features, laboratory testing, and pathogenic mechanisms.

Drug-induced immune thrombocytopenia (DIIT) is a relatively uncommon adverse reaction caused by drug-dependent antibodies (DDAbs) that react with platelet membrane glycoproteins only when the implicated drug is present. Although more than 100 drugs have been associated with causing DIIT, recent reviews of available data show that carbamazepine, eptifibatide, ibuprofen, quinidine, quinine, oxaliplatin, rifampin, sulfamethoxazole, trimethoprim, and vancomycin are probably the most frequently implicated. Patients with DIIT typically present with petechiae, bruising, and epistaxis caused by an acute, severe drop in platelet count (often to <20,000 platelets/pL). Diagnosis of DIIT is complicated by its similarity to other non-drug-induced immune thrombocytopenias, including autoimmune thrombocytopenia, posttransfusion purpura, and platelet transfusion refractoriness, and must be differentiated by temporal association of exposure to a candidate drug with an acute, severe drop in platelet count. Treatment consists of immediate withdrawal of the implicated drug. Criteria for strong evidence of DIIT include (1) exposure to candidate drug-preceded thrombocytopenia; (2) sustained normal platelet levels after discontinuing candidate drug; (3) candidate drug was only drug used before onset of thrombocytopenia or other drugs were continued or reintroduced after resolution of thrombocytopenia, and other causes for thrombocytopenia were excluded; and (4) reexposure to the candidate drug resulted in recurrent thrombocytopenia. Flow cytometry testing for DDAbs can be useful in confirmation of a clinical diagnosis, and monoclonal antibody enzyme-linked immunosorbent assay testing can be used to determine the platelet glycoprotein target(s), usually GPIIb/IIIa or GPIb/IX/V, but testing is not widely available. Several pathogenic mechanisms for DIIT have been proposed, including hapten, autoantibody, neoepitope, drug-specific, and quinine-type drug mechanisms. A recent proposal suggests weakly reactive platelet autoantibodies that develop greatly increased affinity for platelet glycoprotein epitopes through bridging interactions facilitated by the drug is a possible mechanism for the formation and reactivity of quinine- type drug antibodies.