Anaphylactoid reaction to enoxaparin in a patient with deep venous thrombosis

Shake it off: A curious case of rigors

Heparin-induced Anaphylactoid reactions are rare systemic reactions to heparin exposure. Although the exact pathogenesis of the reaction is unclear, in vivo platelet activation from inflammation may play a role. The reaction involves anti-platelet factor 4, a common factor also noted to be involved in heparin-induced thrombocytopenia (HIT). Like HIT, prompt identification of the reaction, immediate discontinuation of heparin, and supportive care are the mainstays of treatment to avoid severe and potentially fatal outcomes. Previous cases have described heparin-induced anaphylactoid reactions in the setting of heparin-induced thrombocytopenia. However, we will present a case of an isolated heparin-induced anaphylactoid reaction without HIT.

Hypersensitivity reactions to low molecular weight heparins: different patterns of cross-reactivity in 3 patients

Low molecular weight heparins (LMWHs) are used for a variety of indications. The most common type of hypersensitivity reactions to LMWHs are delayed-type hypersensitivity reactions (DHR). Immediate-type hypersensitivity reactions (IHR) occur only sporadically. Cross-reactivity of different LMWHs is a common and unpredictable problem. We present 2 cases of patients who developed DHR to nadroparin and enoxaparin, respectively. The third case presents a patient who developed IHR to nadroparin. Skin tests confirmed the hypersensitivity in all cases. In the cases of DHR, a skin test negative LMWH was identified and was tolerated in a challenge test. In the IHR case, cross-reactivity to all tested LMWHs was established. We hypothesize that the degree of cross-reactivity might depend on the type of hypersensitivity reaction with immediate reactions linked to more extensive cross-reactivity than delayed reactions. This is important to consider because, at least in some cases, a safe alternative LMWH can be identified.

In vivo activation and functions of the protease factor XII

Combinations of proinflammatory and procoagulant reactions are the unifying principle for a variety of disorders affecting the cardiovascular system. Factor XII (FXII, Hageman factor) is a plasma protease that initiates the contact system. The biochemistry of the contact system in vitro is well understood; however, its in vivo functions are just beginning to emerge. The current review concentrates on activators and functions of the FXII-driven contact system in vivo. Elucidating its physiologic activities offers the exciting opportunity to develop strategies for the safe interference with both thrombotic and inflammatory diseases.

Fatal anaphylactoid reaction associated with heparin-induced thrombocytopenia

Acute systemic (anaphylaxis and anaphylactoid) reactions have been well described in patients with heparin-induced thrombocytopenia (HIT). Both necrotizing and non-necrotizing skin lesions at heparin injection sites have been reported and may occur in 10–20% of patients with HIT. We report herein a patient treated with subcutaneous enoxaparin sodium who developed non-necrotizing erythematous skin lesions at enoxaparin sodium injection sites. A subsequent intravenous bolus of unfractionated heparin produced a fatal anaphylactoid reaction. This suggests that caution should be exercised in the administration of intravenous heparin to patients with non-necrotizing erythematous skin lesions at prior heparin injection sites.

Mast cells increase vascular permeability by heparin-initiated bradykinin formation in vivo

Activated mast cells trigger edema in allergic and inflammatory disease. We report a paracrine mechanism by which mast cell-released heparin increases vascular permeability in vivo. Heparin activated the protease factor XII, which initiates bradykinin formation in plasma. Targeting factor XII or kinin B2 receptors abolished heparin-triggered leukocyte-endothelium adhesion and interfered with a mast cell-driven drop in blood pressure in rodents. Intravital laser scanning microscopy and tracer measurements showed heparin-driven fluid extravasation in mouse skin microvessels. Ablation of factor XII or kinin B2 receptors abolished heparin-induced skin edema and protected mice from allergen-activated mast cell-driven leakage. In contrast, heparin and activated mast cells induced excessive edema in mice deficient in the major inhibitor of factor XII, C1 esterase inhibitor. Allergen exposure triggered edema attacks in hereditary angioedema patients, lacking C1 esterase inhibitor. The data indicate that heparin-initiated bradykinin formation plays a fundamental role in mast cell-mediated diseases.

Drug allergy: an updated practice parameter

Adverse drug reactions (ADRs) result in major health problems in the United States in both the inpatient and outpatient setting. ADRs are broadly categorized into predictable (type A and unpredictable (type B) reactions. Predictable reactions are usually dose dependent, are related to the known pharmacologic actions of the drug, and occur in otherwise healthy individuals, They are estimated to comprise approximately 80% of all ADRs. Unpredictable are generally dose independent, are unrelated to the pharmacologic actions of the drug, and occur only in susceptible individuals. Unpredictable reactions are subdivided into drug intolerance, drug idiosyncrasy, drug allergy, and pseudoallergic reactions. Both type A and B reactions may be influenced by genetic predisposition of the patient