Unexpected delayed-type hypersensitivity skin reactions to the ultra-low-molecular-weight heparin fondaparinux

Non-immediate heparin and heparinoid cutaneous allergic reactions: a role for fondaparinux

Non-immediate allergic cutaneous reactions to heparins have been increasingly reported, typically manifesting as large, eczematous plaques at sites of subcutaneous injection. Patients may demonstrate cross-reactivity between unfractionated heparin, low molecular weight heparin and semi-synthetic heparinoids, making finding an alternative difficult. Fondaparinux has been identified as a useful alternative in such patients; here we present the first two documented cases in Australia and a literature review.

Anticoagulation via anti-Factor Xa inhibition

Hospital-acquired deep vein thrombosis (DVT) affects 10-25% of medical patients and up to 60% of surgical patients. While thromboprophylaxis is without a doubt under utilized in the hospital setting, there is also a need for more efficacious agents. Fondaparinux, the first of a new class of agents Factor Xa inhibitiors, has recently come into clinical use. It is a synthetic pentasaccharide and indirect Factor Xa inhibitor with a predictable antithrombotic action. Being a synthetic product, there are no concerns about supply, nor viral or prion protein contamination. Initial large international trials in orthopaedic patients demonstrated its superior efficacy to standard thromboprophylaxis. Further trials confirmed its superior efficacy in venous thromboembolism (VTE) prevention, both in medical and surgical patient groups, as well as treatment of pulmonary embolism and DVT. Its use has also recently been evaluated in acute coronary syndromes and angioplasty. Fondaparinux currently has licenses in the UK for thromboprophylaxis and treatment of VTE and a license for the management of acute coronary syndrome is likely to be forthcoming. It has a favourable side effect profile and if the price is acceptable, is likely to take over from low molecular weight heparins in these indications as the drug of choice on the grounds of efficacy and safety.

Delayed-type hypersensitivity to low molecular weight heparins and heparinoids: cross-reactivity does not depend on molecular weight

BACKGROUND

Cross-reactivity is a widespread phenomenon in patients who develop cutaneous delayed-type hypersensitivity (DTH) reactions to low molecular weight heparins (LMWHs). As molecular weight is believed to be a key determinant of sensitization to heparins, the recently developed LMWH bemiparin, with the lowest molecular weight of all LMWHs, appeared to be a significant improvement.

OBJECTIVES

To evaluate cross-reactivity between bemiparin and several other LMWHs and heparinoids by means of subcutaneous testing. Methods Test doses of bemiparin and several other LMWHs/heparinoids were given to eight patients with a history of local eczematous reactions after subcutaneous injection of enoxaparin.

RESULTS

Seven of eight patients showed cross-reactivity following subcutaneous injection of bemiparin. In addition, nearly all tested substances caused local eczematous reactions in at least some patients, with the exception of fondaparinux, which was well tolerated by all patients. Of all substances tested, bemiparin had the highest cross-reactivity with enoxaparin. Substances with a lower molecular weight did not cross-react less frequently than the others.

CONCLUSIONS

No significant correlation was found between the molecular weight of the tested substances and the frequency of DTH reactions. In patients with DTH to enoxaparin, the LMWH bemiparin is not a suitable alternative.

Hypersensitivity reactions to anticoagulant drugs: diagnosis and management options

Anticoagulants, including heparins, coumarins, hirudins, and some of the previously used plasma volume expanders, belong to the most widely used drugs. Hypersensitivity reactions from these agents are uncommon. However, they may have a considerable impact on patient safety and treatment decisions. Therefore, early diagnosis of potentially life-threatening adverse events and identification of alternatives is clinically important. This review contains an update on current knowledge about hypersensitivity reactions caused by the different anticoagulants. In addition, it discusses pathophysiologic mechanisms, diagnostic possibilities, and management options. The most common hypersensitivity reactions are erythematous plaques, occurring with a delay after subcutaneous application of heparins. Seldom they turn into maculopapular exanthema. Other hypersensitivity reactions are rare but may be life-threatening, e.g. skin necrosis because of heparin-induced thrombocytopenia. Skin and provocation tests with immediate and late readings are the most reliable diagnostic tools for heparin- or hirudin-induced urticaria/anaphylaxis or heparin-induced delayed plaques. If necrosis from heparins or coumarins is suspected, skin tests are contraindicated. In anaphylactic reactions caused by dextrans or hydroxyethyl starch skin tests are useless. Most in vitro tests have a low sensitivity and are not generally available. Therefore, in some anticoagulant-associated hypersensitivity reactions detailed allergologic investigation may help to identify safe treatment alternatives. However, several tests may be needed, and the procedures are usually time-consuming.

Fondaparinux is a safe alternative in case of heparin intolerance during pregnancy

Heparin is the drug of choice for the treatment or the prevention of thromboembolic disease during pregnancy. However, treatment options are limited when heparin cannot be used because of hypersensitivity skin reactions. Despite the recent availability of new anticoagulant agents, data relating to their use during pregnancy are lacking. This report describes the successful management with fondaparinux, during 150 days, of a pregnant patient with protein S deficiency and prior deep vein thrombosis (DVT) who developed heparin and danaparoid hypersensitivity.

Fondaparinux as anticoagulant in a pregnant woman with heparin allergy

We report a patient who had a history of deep vein thrombosis in a previous pregnancy. She was treated with heparins without any reactions in the index pregnancy. Subsequently, when the patient became pregnant again, she developed an acute cutaneous reaction to the low molecular heparin enoxaparin 3 weeks after initiation of therapy. She developed a similar reaction to delteparin as well. She was therefore treated with warfarin until 36 weeks of gestation. Then she was treated with fondaparinux (Arixtra, Sanofi-Synthelabo, Paris, France) 2.5 mg daily for the remainder of the pregnancy. Delivery was at term by induction of labour. Fondaparinux was stopped on the day of the induction of labour. It was re-started 6 h post-delivery and the patient was anticoagulated with warfarin in the post-partum period. There were no bleeding tendencies or recurrences of thrombosis during fondaparinux therapy. Both mother and baby were well after delivery.