Comparison of the safety of seven iodinated contrast media

We aimed to determine the characteristic adverse events (AEs) of iodinated contrast media (IOCM) and to compare the safety profiles of different IOCM. This study used the database of AEs reports submitted by healthcare professionals from 15 Regional Pharmacovigilance Centers between June 24, 2009 and December 31, 2010 in Korea. All reports of IOCM, including iopromide, iohexol, iopamidol, iomeprol, ioversol, iobitridol and iodixanol, were analyzed. Safety profiles were compared between different IOCM at the system organ level using the proportional reporting ratio (PRR) and 95% confidence interval (95% CI). Among a total of 48,261 reports, 6,524 (13.5%) reports were related to the use of IOCM. Iopromide (45.5%), iohexol (16.9%), iopamidol (14.3%) and iomeprol (10.3%) were identified as frequently reported media. 'Platelet, bleeding & clotting disorders' (PRR, 29.6; 95%CI, 1.9-472.6) and 'urinary system disorders' (PRR, 22.3; 95% CI, 17.1-29.1) were more frequently reported for iodixanol than the other IOCM. In conclusion, the frequency of AEs by organ class was significantly different between individual media. These differences among different IOCM should be considered when selecting a medium among various IOCM and when monitoring patients during and after its use to ensure optimum usage and patient safety.

Platelet dysfunction in thrombosis patients treated with vitamin K antagonists and recurrent bleeding

BACKGROUND

Recurrent bleeding can complicate the treatment of thrombosis patients with vitamin K antagonists (VKA), even at a well-regulated level of anticoagulation. In this proof-of-principle study, we investigated whether alterations in platelet function or von Willebrand factor (vWf) contribute to a bleeding phenotype in these patients.

METHODS

In this case-control study 33 well-regulated patients without bleeding events (controls) and 33 patients with recurrent bleeding (cases) were retrospectively included. Thrombin generation and vWf were determined in plasma. Platelet function was assessed by light transmission aggregometry and flow cytometry using a validated panel of agonists.

RESULTS

Thrombin generation was similarly reduced in controls and cases, in comparison to normal plasma. Plasma vWf level was above the normal range in 85% of controls and 67% of the cases. vWf activity was similarly increased in all patients in comparison to healthy volunteers. Platelet aggregation was in the normal range for almost all patients irrespective of the type of agonist. However, in response to a low collagen dose, platelets from 21% of controls and 27% of cases showed diminished responses. Agonist-induced secretion of alpha- and dense-granules or integrin αIIbβ3 activation were affected in platelets from neither controls nor cases.

CONCLUSION

Recurrent bleeding in well-controlled patients on VKA therapy is not explained by anti-hemostatic changes in platelet or vWf function.

Sub-chronic toxicity study of the methanol root extract of Cnestis ferruginea

CONTEXT

Cnestis ferruginea (CF) Vahl ex DC (Connaraceae) is a shrub abundant in West Africa. Root preparations are used in traditional medicine to treat diverse conditions.

OBJECTIVE

To evaluate the sub-chronic toxicological effects of the methanol root extract of CF.

MATERIALS AND METHODS

Groups of adult rats of both sexes were treated daily with distilled water (DW) and CF at doses of 80 (sub-therapeutic dose), 400 (therapeutic dose), and 1000 (supra-therapeutic dose) mg/kg orally for 90 days. Animals were weighed weekly and observed for behavioral and morphological changes. At the end, rats were sacrificed and blood samples collected for hematological and biochemical analysis. Vital organs were harvested, weighed, and assessed for in vivo antioxidants and histopathological changes. Sperm analysis and reversibility study were done, and mortality was recorded.

RESULTS

CF at the therapeutic dose did not produce any significant irreversible deleterious effects on the weight of animals and vital organs, in vivo antioxidants, histopathological presentation, hematological, biochemical, and sperm parameters. Platelet anomaly was elicited as a delayed effect. Effects at the sub- and supra-therapeutic doses were similar but with delayed anemia in females and weight reduction and sterility in males as possible side effects. CF generally showed a potential to induce in vivo antioxidants.

DISCUSSION AND CONCLUSION

Findings suggest that CF given over an extended period possess the potential to cause induction of in vivo antioxidants especially in the ovary. Possible side effects identified with CF, which necessitate caution, include delayed platelet anomaly and anemia in females, weight reduction, and sterility in males.

Acquired disorders of platelet function

Platelet dysfunction is commonly acquired due to medications, procedures, medical conditions, and underlying hematologic disease. These issues are presented, the data reviewed, and recommendations given herein. Many medications and dietary supplements have platelet-inhibitory effects in vitro, although the clinical effects on bleeding risks are unclear for many. Platelet-inhibitory drugs are key in the treatment of vascular disease. Data are available to aid in the management of these medications to prevent hemorrhagic complications. Bleeding in patients with renal failure has decreased with improved dialysis and the use of erythropoietin, but remains a challenge. Platelet dysfunction accompanies cardiac valvular disease and use of cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation. Hematologic disorders including myeloproliferative disorders (MPDs), myelodysplasia, paraproteinemias, and immune thrombocytopenia (ITP) can also be associated with hemorrhagic complications due to platelet dysfunction. Knowledge of which factors affect bleeding risk and how to treat individuals with acquired platelet dysfunction are important in optimizing patient care.

Tyrosine kinase inhibitor-induced platelet dysfunction in patients with chronic myeloid leukemia

Dasatinib is associated with increased risk of bleeding among patients with chronic myeloid leukemia, even in the absence of thrombocytopenia, suggesting the presence of a hemostatic defect. We tested platelet aggregation in 91 patients with chronic myeloid leukemia in chronic phase either off-therapy (n = 4) or receiving dasatinib (n = 27), bosutinib (n = 32), imatinib (n = 19), or nilotinib (n = 9). All but 3 patients simultaneously receiving imatinib and warfarin had normal coagulation studies. All 4 patients off therapy had normal platelet aggregation. Impaired platelet aggregation on stimulation with arachidonic acid, epinephrine, or both was observed in 70%, 85%, and 59% of patients on dasatinib, respectively. Eighty-five percent of patients on bosutinib, 100% on nilotinib, and 33% on imatinib had normal platelet aggregation. Dasatinib 400 nM induced rapid and marked prolongation of closure time to collagen/epinephrine in normal whole blood on the PFA-100 system. In conclusion, dasatinib and, to some extent, imatinib produce abnormalities in platelet aggregometry testing.

[Acquired platelet function disorders: pathogenesis, classification, frequency, diagnosis, clinical management]

Given the high consumption of pharmacological agents in western societies, it is not surprising at all that drugs represent the most common cause of acquired platelet dysfunction. While acetylsalicylic acid, clopigogrel and integrin alphaIIbbeta3 (GPIIb-IIIa) receptor antagonists are well-known as prototypes of antiplatelet drugs, other widely used agents including non-steroidal anti-inflammatory drugs, antibiotics, serotonin reuptake inhibitors, and volume expanders can also impair platelet function and cause or aggravate haemorrhages. Besides pharmacological agents, certain clinical conditions are often associated with qualitative platelet disorders and bleeding diathesis. Consequently, in contrast to inherited platelet disorders, acquired platelet function defects are much more frequent in clinical practice and deserve special attention. Their pathogenesis is widespread and heterogeneous with various, sometimes overlapping abnormalities. Moreover, acquired platelet dysfunctions can occur at any age and range in severity from mild to life-threatening haemorrhages. Due to their heterogeneity, acquired platelet function disorders will be classified and discussed according to the underlying clinical setting or disease.

Severe bleeding complications during antiepileptic treatment with valproic acid in children

Valproic acid (VPA) is an antiepileptic drug frequently used in children. Although VPA can cause a variety of laboratory abnormalities affecting haemostasis, controversy exists about the clinical relevance of such haematological abnormalities. We report on 4 children with severe bleeding complications while on VPA therapy; two presented with intracranial bleeding, while two suffered from severe bleeding postoperatively. Diagnostic and therapeutic measures are discussed that help to avoid severe bleeding complications in children with VPA treatment.

Is Platelet Adhesion Assay Able To Quantify Drug-Induced Platelet Dysfunction?

The platelet adhesion assay (PADA) is an innovative method for the detection of both normal, pathologically increased or decreased platelet adhesiveness. Adhesion is the first important phase of platelet activation, followed by shape change and aggregation. Adhesion is triggered by glycoproteins (GP) on the platelet surface, mainly by GPIIb/IIIa, and to a lesser extent also by GPIb/V/IX. Since fibrinogen serves as adhesive protein for GPIIb/IIIa receptors, and since the PADA uses polymer particles that become coated with fibrinogen, the PADA is able to monitor GPIIb/IIIa receptor antagonists and to detect overdosing, potentially leading to bleeding complications. Ex vivo, citrated whole blood from healthy volunteers and patients was spiked with increasing GPIIb/IIIa inhibitor concentrations and PADA was measured. Comparing these results with GPIIb/IIIa receptor occupancy, determined by FACS, a basic consistency of the data was shown. Via intracellular signaling, the adenosine diphosphate (ADP) receptor mechanism is closely involved in the activation of GPIIb/IIIa receptors so that also ADP receptor antagonists of the thienopyridine type, especially clopidogrel, can be quantitatively determined by the PADA. In patients under clopidogrel therapy, the therapeutic effect was monitored and also individual dose adjustments were realized. Furthermore, patients having partial or full clopidogrel resistance were identified. Overdoses can be detected as well.

Application of flow cytometry to platelet disorders

Flow cytometry is a powerful and versatile tool that can be used to yield definitive information regarding the phenotypic status of platelets. The method provides a quantitative assessment of the physical and antigenic properties of platelets (e.g., surface expression of receptors, bound ligands, components of granules, or interactions of platelets with other platelets, other blood cells, or components of the plasma coagulation system), thereby facilitating the diagnosis of inherited or acquired platelet disorders (e.g., Bernard-Soulier syndrome, Glanzmann thrombasthenia, storage pool disease), the pathological activation of platelets (e.g., in the setting of acute coronary syndromes, cerebrovascular ischemia, peripheral vascular disease, cardiopulmonary bypass), and changes in the ability of platelets to activate via specific stimuli (e.g., efficacy of antiplatelet therapies). Accordingly, this review summarizes the key technical and methodologic components of flow cytometric analysis of platelets, as well as specific examples of its application to diagnosis and patient care.

Cyclosporin A does not affect platelets in children with idiopathic nephrotic syndrome

The immunosuppressive agents administered to maintain the remission of idiopathic nephrotic syndrome (INS) may have a deleterious effect on several cell types. The aim of this study was to analyze platelet activation and reactivity in children with INS treated with cyclosporin A (CyA). The study groups comprised 16 children with remission of INS induced by CyA and 16 children with glucocorticosteroid-induced remission 8 weeks from the onset of INS relapse. Fifteen healthy children served as controls. Surface expression of CD61, CD62P, and CD42b on resting and thrombin-stimulated platelets was analyzed with flow cytometry. No differences between groups were found in CD61, CD62P, and CD42b surface expression, but markers of the coagulation cascade and fibrinolysis or endothelial injury (F1+2 prothrombin fragments, tissue plasminogen activator inhibitor 1) were elevated in patients treated with CyA compared with children on steroids and healthy controls. No correlations between markers of platelet function and CyA concentration were found. We postulate that CyA administration in nephrotic patients causes an activation of thrombinogenesis but does not influence platelet activation and reactivity in INS.

The Hemostatic Defect of Cardiopulmonary Bypass

Cardiac surgery involving cardiopulmonary bypass is a common yet complex procedure that results in considerable disruption of hemostasis during and following surgery. Despite the relatively common and widespread use of this procedure, there remains a significant peri-operative risk of both thrombosis and hemorrhage in some patients. This is known as the hemostatic defect of cardiopulmonary bypass. Strategies including the use of pharmacological agents, hemodilution, autologous blood transfusion, rapid in-theatre monitoring of hemostatic potential with fine-tuning of the degree of heparinization, minimally invasive surgery and the use of biologically coated cardiopulmonary bypass equipment have been employed to ameliorate the effects of cardiopulmonary bypass on hemostasis. However there exists a fine line between preventing hemorrhage and promoting thrombosis. Likewise attempts to prevent thrombosis may result in increased hemorrhage. Research into many strategies for minimizing the hemostatic defect of cardiopulmonary bypass is incomplete, with safety and efficacy the subjects of intensive investigation.

Non-steroidal anti-inflammatory drugs: indications for use

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely used of all therapeutic agents. Although they are effective analgesics they do have significant adverse side-effects. Before treatment is started the prescriber should always weigh efficacy against possible side-effects. NSAIDs vary in their selectivity for inhibiting the two types of cyclo-oxygenase. An NSAID should therefore be chosen on the basis of the incidence of associated side-effects.

Effects of DDAVP administrated subcutaneously in dogs with aspirin-induced platelet dysfunction and hemostatic impairment due to chronic liver diseases

To evaluate the hemostatic effects of desmopressin (DDAVP) in dogs with aspirin-induced platelet dysfunction and hemostatic impairment in chronic liver diseases, 3 microg/kg DDAVP was administrated subcutaneously. In aspirin-induced platelet dysfunction dogs (n=5), prolonged BMBT (buccal mucosal bleeding time) was shortened significantly after DDAVP injection (2.2 +/- 1.2 min, P<0.05). In dogs with chronic liver diseases (n=4), activated partial thromboplastin time (APTT) tended to shorten by 0.9 to 3.0 sec, and prolonged BMBT was shortened in two cases for 4.2 and 1.7 min after DDAVP injection. Therefore, the present results indicated that DDAVP shortened the prolonged BMBT in dogs with aspirin-induced platelet dysfunction and chronic liver disease. DDAVP might be helpful in hemostasis under invasive procedures such as biopsy or surgery for dogs with hemostatic impairment.

[Increased perioperative blood loss during treatment with paroxetine]

A 63-year-old man who took paroxetine for depression developed massive peroperative haemorrhage during a pancreaticoduodenectomy as a result of paroxetine-induced thrombocytopathy. He lost 4 litres of blood. After administration of 8 units of fresh frozen plasma and 2 times 5 units of thrombocyte concentrate, hemostatic control was obtained and the operation could be continued. Paroxetine is a non-tricyclic serotonin reuptake inhibitor prescribed for the treatment of depression. Since this drug also blocks serotonin reuptake in platelets, a clinically significant platelet dysfunction can occur under certain conditions. Because serotonin promotes platelet aggregation, too low an amount of serotonin in the platelets can result in thrombocytopathy. Before major surgery, it is advised to perform extensive clotting tests if there is any hint of haemorrhagic diathesis in the anamnesis. In case of a prolonged bleeding time, paroxetine treatment should be stopped perioperatively.

Purpura due to aspirin-induced platelet dysfunction aggravated by drinking alcohol

We report a rare case of prominent purpura induced by aspirin and enhanced by alcohol. A 44-year-old woman presented with a history of generalized purpura. She drank alcohol once or twice a week and regularly took an analgesic preparation, containing aspirin and acetaminophen, for alleviation of headaches. When purpura was evident the patient's liver function was within normal limits and her coagulation time was normal but her bleeding time was prolonged. Red blood cell, white blood cell and platelet counts were normal but a poor response to platelet agonists demonstrated platelet dysfunction. After stopping the analgesic and abstaining from alcohol for 5 days, platelet aggregation, in response to the agonists, returned to normal and purpura disappeared. When the patient took further doses of the analgesic preparation for 3 days for headache relief, but did not drink alcohol, platelet aggregation was again abnormal but purpura was only slight.

Heparin-induced platelet dysfunction and cardiopulmonary bypass

BACKGROUND

Cardiopulmonary bypass is associated with impaired platelet macroaggregation. Heparin contributes to platelet dysfunction before extracorporeal circulation. In vitro heparinization of whole blood does not impair macroaggregation. Heparin releases several endothelial proteins; thus heparin may inhibit macroaggregation indirectly.

METHODS

Patients undergoing operations using cardiopulmonary bypass and ABO blood group compatible volunteers were studied. Whole blood impedance aggregometry assessed macroaggregation in response to collagen (0.6 microg ml(-1)) in blood diluted either with normal saline or with platelet poor plasma, obtained from patients at different stages of cardiopulmonary bypass.

RESULTS

Before heparinization, blood diluted with its own platelet poor plasma recorded an impedance change of 13.0 (4.7 to 15.6) Ohms. Platelet poor plasma obtained after heparinization or during extracorporeal circulation reduced this response to 3.7 (1.1 to 8.4) and 2.0 (1.1 to 3.3) Ohms, respectively (both p < 0.0001 versus pre-heparin; n = 13). Macroaggregation in blood from volunteers was similarly inhibited by patients' platelet poor plasma (n = 30). The macroaggregatory response in blood sampled after heparinization for cardiopulmonary bypass, decreased gradually from 11.4 (8.2 to 15.9) Ohms immediately after sampling to 1.7 (1.4 to 4.1) Ohms 2 hours later (p < 0.0001; n = 11).

CONCLUSIONS

In vivo heparinization induces plasma changes that inhibit platelet macroaggregation. This is an indirect, delayed inhibition that is transferable in vitro to normal platelets.

Thrombotic microangiopathy as a complication of high-dose chemotherapy for breast cancer

Five hundred and eighty-one patients with stage II-IV breast cancer were treated at Duke University Medical Center with high-dose chemotherapy, followed by hematopoietic support. All patients received a conditioning regimen of cyclophosphamide, cisplatin and carmustine. Of these patients, 15 (2.6%) developed symptoms similar to the hemolytic-uremic syndrome with evidence of thrombotic microangiopathy (TMA). The time of onset ranged from 75 days to 281 days post-transplant, with a median of 143 days. Hemolytic anemia and thrombocytopenia, without alternative cause, were required for diagnosis. All patients were treated with steroid therapy. In addition, 12 patients were treated primarily with plasmapheresis, and received a median of 46 treatments. Additional therapy included staphylococcal protein A column apheresis (eight patients), vincristine (three patients) and danazol (one patient). The mortality rate was 11 of 15 patients (73%). These patients had a median survival of 41 days from diagnosis of TMA (range 2-76 days). The four survivors are alive at 76, 186, 1837 and 2387 days from diagnosis of TMA. Three of these patients received twice daily plasmapheresis and protein A column apheresis therapy. One patient recovered without specific therapy. TMA is an infrequent complication of high-dose chemotherapy, but is associated with a high mortality. It frequently follows significant pulmonary drug toxicity. Survival may be improved with early diagnosis and aggressive plasmapheresis therapy.

Do patients with epistaxis have drug-induced platelet dysfunction?

Aspirin and other non-steroidal anti-inflammatory drugs (NSAID) are being used increasingly. A positive correlation has been shown between epistaxis and the use of NSAID in the over 50s. This prospective study compared the NSAID intake and platelet function in 50 patients with epistaxis and 50 controls. Standard haematological parameters and the platelet response to collagen and arachidonic acid aggregation and adenosine triphosphate release were measured. The patients showed a significant increase in NSAID intake (P < 0.01, 95% confidence for the difference in the medians = 4-36%) and hypertension (for diastolic blood pressure > 100 mmHg, P < 0.01, 95% confidence for the difference in the medians = 5.9-16.1). The patients showed a significant reduction in platelet aggregation to collagen (P = 0.025). Non-steroidal anti-inflammatory drugs produce a significant platelet dysfunction which should be considered in the multifactorial aetiology of epistaxis.

A study on the efficacy of a phospholipid solution in dogs with aspirin-induced thrombocytopathy

The aim of the present study was to test the haemostyptic properties of a phospholipid complex with platelet factor-3 (PF-3) activity in platelet-dependent haemostatic disorders. The substance was investigated in an animal model comprising six investigational groups (five dogs each). A thrombocytopathy was created in the dogs belonging to groups 1-5 by intravenous administration of 20 mg/kg body weight (BW) acetylsalicylic acid (ASA). Two hours later a human albumin solution (5%) (control group) or a phospholipid complex with PF-3 activity was injected or infused intravenously in different dosages. In dogs pre-treated with ASA, injection of 2 ml/kg BW of the phospholipid complex shortened capillary bleeding time, which was prolonged as a consequence of ASA-treatment. This effect lasted for 4 h at least. The capability of the platelets to aggregate increased 5 min after intravenous injection of the phospholipid without differences in the respective groups. At the same time platelet counts dropped to approximately 50%, but increased again distinctly after 30 min. When the phospholipid complex was administered to clinically healthy dogs who had not been treated with ASA, this resulted in prolongation of the capillary bleeding time as well as a significant platelet drop in the peripheral blood. Although these were only short-term effects after administration of the phospholipid complex, a disadvantageous effect cannot be excluded in patients suffering from haemorrhagic diathesis. For this reason, a phospholipid complex with PF-3 activity cannot be recommended as a therapeutic agent for platelet-dependent coagulation disorders in the dog.

Platelet function defects associated with hemorrhage or thrombosis

Platelet dysfunction, especially acquired forms, is a common cause of hemorrhage, especially when associated with trauma or surgery. Although the hereditary platelet function defects are generally quite rare, hereditary storage pool disease is common enough to be suspected in an individual, usually a child, with characteristic historical and clinical findings. The acquired platelet function defects, especially those resulting from drugs, are common and should promptly be suspected in patients developing easy and spontaneous bruising, mild-to-moderate mucosal membrane hemorrhage, or unexplained bleeding associated with trauma or surgery. The template bleeding time is generally useful as a screening test of platelet function, but a normal template bleeding time, in the face of a suggestive history, suggestive clinical findings, or in a patient frankly bleeding, is not reliable, and platelet aggregation or lumiaggregation should be done in appropriate clinical situations. Also, prolongation of the template bleeding time is an unreliable predictor of clinical bleeding propensity. The mainstay of therapy for almost all these defects, if bleeding is significant, is the liberal infusion of appropriate numbers of platelet concentrates. The acquired platelet function defects should also be managed by attempts to treat or control the underlying disease, if possible, and offending drugs or potentially offending drugs should immediately be stopped.

Evaluation of platelet hyperfunction in hemodialysis patients receiving recombinant human erythropoietin

There are data suggesting that recombinant human erythropoietin (rHuEPO) may induce thromboses in hemodialysis patients, possibly due to alterations in platelet function. In an earlier study, we found evidence of platelet hyperfunction in several patients 4 to 8 weeks following the start of rHuEPO therapy, which was begun shortly after hemodialysis was initiated. Studies were performed to examine the effects of rHuEPO on whole blood platelet aggregation and adenosine triphosphate (ATP) release independent of changes in hematocrit or the uremic state. Eight hemodialysis patients without and four with a history of vascular access clotting had platelet aggregation tests performed at baseline while receiving rHuEPO, off rHuEPO for 2 weeks, and 4 to 6 weeks after restarting the drug. While the plasma EPO level decreased significantly after the 2-week period off rHuEPO (P < 0.0001), the hematocrit did not change at any of the three time periods. Whole blood platelet aggregation in response to adenosine diphosphate (ADP), collagen, and ristocetin was not significantly altered on or off rHuEPO in either patient group. Platelet hyperfunction, determined by aggregation or ATP release either spontaneously or in response to low-dose ADP or ristocetin, was not seen in any patient. These data suggest that the increase in access clotting is not the result of platelet hyperfunction induced directly by rHuEPO.

Acquired platelet function defects

Platelet dysfunctions, especially acquired forms, are common causes of hemorrhage, especially when associated with trauma or surgery. Although the hereditary platelet function defects are generally quite rare, hereditary storage-pool disease is common enough to be suspected in an individual, usually a child, with characteristic historical and clinical findings. The acquired platelet function defects, especially those resulting from drugs, are very common and should promptly be suspected in patients developing easy and spontaneous bruising, mild to moderate mucosal membrane hemorrhage, or unexplained bleeding associated with trauma or surgery. The template bleeding time is generally useful as a screening test of platelet function, but a normal template bleeding time, in the face of a suggestive history, suggestive clinical findings, or in the patient frankly bleeding, is not reliable, and platelet aggregation or lumi-aggregation should be done in appropriate clinical situations. Also, prolongation of the template bleeding time is an unreliable predictor of clinical bleeding propensity. The mainstay of therapy for essentially all these defects, if bleeding is significant, is the liberal infusion of appropriate numbers of platelet concentrates. The acquired platelet function defects should also be managed by attempts to treat or control the underlying disease, if possible, and offending drugs or potentially offending drugs should immediately be stopped.

Detection of antibiotic-induced platelet dysfunction in whole blood using flow cytometry

Using flow cytometry and activation-dependent monoclonal antibodies, we have developed a technique based on forward angle-light scatter (FALS) and immunofluorescence that simultaneously detects human platelet activation, secretion, and aggregation in whole blood. To detect the effects of cefotetan and latamoxef, both of which contain an N-MTT side chain, and of free N-MTT and cefoxitin, which does not contain the N-MTT side chain, on platelet activation and secretion, platelets were stained by the indirect method using a murine-produced platelet specific activation-dependent monoclonal antibody, S12, and a goat anti-mouse IgG fluorescein-conjugated antibody. S12 binds to a 140kd alpha granule membrane protein (GMP-140) that is expressed during secretion. Single parameter, 256 channel, log integrated green fluorescence histograms were generated, and negative and positive fluorescent populations were defined. Latamoxef and cefotetan reduced the number of platelets expressing S12 by more than 43%. In contrast, cefoxitin reduced the number of platelets expressing S12 by only 13.5%. The inhibition of GMP-140 expression per platelet was calculated by converting the log data to linear fluorescence intensity. Latamoxef and cefotetan inhibited expression of GMP-140 by 88% and 87% respectively. Free N-MTT inhibited its expression by 68%. In contrast cefoxitin reduced GMP-140 expression per platelet by only 45%.

Effect of chitosan on lingual hemostasis in rabbits with platelet dysfunction induced by epoprostenol

Chitosan, a complex carbohydrate derivative of shellfish exoskeleton, is shown to enhance lingual hemostasis in rabbits treated with a known antagonist of platelet function, epoprostenol (prostacyclin or PGI2). Bleeding times were measured for bilateral (15 mm x 2 mm) tongue incisions in 10 New Zealand white rabbits. Using a randomized, blinded experimental design, one incision in each animal was treated with chitosan and the other was treated with control vehicle without chitosan. Extraoral bleeding and coagulation times were measured for each animal before, during, and after infusion of epoprostenol. Continuous infusion of epoprostenol increased mean systemic bleeding time 95%. In this platelet dysfunction animal model, lingual incisions receiving the experimental substance showed a 56% improvement in bleeding time in comparison with lingual incisions receiving control solution (P = .003).

Platelets acquire a secretion defect after high-dose chemotherapy

Patients receiving high-dose chemotherapy (HDC) and autologous bone marrow transplantation (ABMT) may experience life-threatening hemorrhagic myocarditis. The authors investigated whether HDC was associated with an acquired platelet defect. Platelet aggregation and release were evaluated after HDC in ten patients with either metastatic breast carcinoma or melanoma. Platelets underwent shape change and a primary wave of aggregation. High-dose chemotherapy was associated with the inhibition of secondary aggregation of platelets induced by adenosine diphosphate (ADP), arachidonic acid, prostaglandin H2 (PGH2) analog (U44619), and collagen. Although electron microscopic study of the platelets revealed normal morphologic features with an adequate number of dense bodies and alpha-granules, release of adenosine triphosphate (ATP) from dense granules was less than 20% of normal. The acquired platelet defect occurred before development of thrombocytopenia. Aggregation of platelets from normal volunteers was not inhibited by either the addition of the chemotherapeutic agents, chemotherapy metabolites, or the patients' sera. In conclusion, HDC induces an acquired abnormality in platelet secretion and aggregation which may contribute to the development of hemorrhagic complications after ABMT.

Platelet-mediated bleeding caused by broad-spectrum penicillins

One hundred fifty-six hospitalized adult patients treated with ticarcillin, piperacillin, mezlocillin, or cefotaxime (control) were prospectively observed for determination of frequencies of platelet dysfunction and bleeding. Increases in bleeding times (greater than or equal to 5 min above pretreatment values) occurred in 73% of patients receiving ticarcillin, 43% receiving piperacillin, 25% receiving mezlocillin, and 17% receiving cefotaxime (P less than .0001); chemotherapy, thrombocytopenia, age of greater than or equal to 60 years, dose of greater than or equal to 12 g per day, and duration of treatment of six or more days were significant covariables. Significant bleeding occurred in 34% of patients treated with ticarcillin, 17% with piperacillin, 2% with mezlocillin, and 5% with cefotaxime (P = .0005); chemotherapy, thrombocytopenia, primary marrow disorders affecting platelet function, prolonged prothrombin time, and azotemia were significant covariables. Bleeding was associated with an elevated pretreatment bleeding time, an increase in bleeding time during treatment, and the maximal observed bleeding time during treatment (P less than .0001).

Platelet dysfunction associated with Wilms tumor and hyaluronic acid

Acquired von Willebrand disease (AVWD) has been described in two cases of nephroblastoma. We studied a patient with nephroblastoma who presented with a coagulopathy suggestive of AVWD. The subject had undetectable levels of F.VIIIR:Ag, diminished F.VIIIR:WF (16.3%), F.VIII:C activity (37%), and lack of platelet aggregation to ADP, epinephrine, collagen, and arachidonic acid. These results were associated with abnormally high serum levels (850 mg/dl) of hyaluronic acid (HA), which made the patient's serum hyperviscous. Examination of the neoplasm revealed HA in the tumor matrix. All abnormalities of coagulation resolved after chemotherapy and extirpation of the neoplasm, which produced normal serum HA levels. To study the effects of HA on platelet function, we added HA to normal platelet-poor plasma (NPP), which rendered F.VIIIR:Ag undetectable; treatment of HA with hyaluronidase eliminated F.VIIIR:Ag assay interference caused by HA. F.VIII:C activity decreased in vitro when HA was mixed with normal platelet-poor plasma (NPP). HA reduced the initial slope of normal platelet aggregation. Partial correction of platelet aggregation occurred after hyaluronidase treatment of HA-spiked PRP. Experiments in rabbits exposed to HA (serum level 400 mg/dl) demonstrated abnormalities similar to those noted in the patient. Shear rate studies of whole blood containing HA (500 mg/dl) yielded high shear stress, 27-136 dynes/cm2 over shear rates of 10-216 sec-1. We conclude that the coagulopathy demonstrated in this case is secondary to hyperviscosity produced by elevated levels of HA, which interferes with the assay for F.VIIIR:Ag. Thus the acquired coagulopathy associated with other cases of nephroblastoma may present as spurious von Willebrand disease.

Alcohol and stroke

Alcohol might contribute to stroke in several ways: induction of cardiac arrhythmias and cardiac wall motion abnormalities which predispose to cerebral embolism, induction of hypertension, enhancement of platelet aggregation and activation of the clotting cascade, and reduction of cerebral blood flow by stimulation of cerebral vascular smooth muscle contraction or by altering cerebral metabolism. While these pathophysiological mechanisms have gained enthusiastic experimental and theoretical support, the findings are preliminary and will require further large-scale clinical and epidemiological analyses to substantiate their roles as causal factors or potentiators of stroke. Documentation of measurable platelet and coagulation cascade abnormalities reported in healthy volunteers who have ingested alcohol will need to be confirmed on a broader scale in stroke patients with recent ethanol consumption. The risk of stroke in those with alcohol-induced atrial fibrillation and cardiomyopathy must be ascertained for the general population. While the experimental evidence is exciting and provocative, epidemiological evidence also suggests a link between alcohol consumption and stroke. Regular alcohol ingestion is associated with hypertension, fatal and nonfatal intracranial hemorrhage, cerebral infarction, and increased risk of death from stroke. Recent, less stringently controlled studies suggest that alcohol consumption is a risk factor for cerebral infarction in young adults with occasional ethanol intoxication and middle-aged women and young men with occasional alcohol intoxication and regular heavy drinking. Alcohol may also be a risk factor for subarachnoid hemorrhage.

Epinephrine reverses the inhibitory influence of aspirin on platelet-vessel wall interactions

The effect of in vitro aspirin treatment and alpha adrenergic receptor stimulation on the interaction of platelets with the subendothelium was studied using citrated human blood obtained from normal control donors. Reconstituted blood following drug treatment was circulated through a chamber which housed everted segments of deendothelialized rabbit aorta. The wall shear rate was 800 sec-1. Surface coverage of platelets were morphometrically evaluated. Aspirin treatment significantly reduced platelet thrombi on exposed subendothelium. However, platelet spreading was increased. There was no significant difference in the total percent coverage of platelets in the vascular surface between the aspirin treated group and normal controls. Epinephrine exposure of aspirin treated platelets completely reversed the effect of alterations induced in platelet behavior by aspirin. Epinephrine exposed aspirin treated platelets had as many platelet thrombi on exposed subendothelium as normal control platelets. In addition, epinephrine treatment decreased the spreading of aspirin treated platelets on the vascular surface. Results of the present study and our earlier findings suggest that the epinephrine induced membrane modulation may be a major mechanism for protecting the hemostatic role of platelets after their function is compromised in vivo and in vitro. The failure of aspirin to offer significant protection in many clinical trials may be due to the presence of a salvage pathway in platelets provided by the mechanism of membrane modulation.