Parnaparin. A review of its pharmacology, and clinical application in the prevention and treatment of thromboembolic and other vascular disorders.

Parnaparin is a low molecular weight (LMW) heparin which, like other members of its class, apparently demonstrates a greater antithrombotic effect relative to its anticoagulant activity when compared with the unfractionated heparin (heparin) from which it is derived. Moreover, subcutaneous parnaparin has a greater bioavailability and longer half-life than heparin, permitting once-daily administration for the prophylaxis of deep venous thrombosis (DVT) or the treatment of established vascular disorders. Prophylaxis with a 7-day regimen of parnaparin 3200 or 6400 IUaXa/day has consistently been associated with a lower incidence of confirmed DVT compared with usual prophylactic regimens of heparin. This intertreatment difference reached statistical significance in a large multicentre study involving a total of 610 surgical patients (3.2% for parnaparin vs 6.3% for heparin). Thus far, however, comparisons of parnaparin with other LMW heparins for this indication are unavailable. Parnaparin has demonstrated equivalent efficacy to heparin in the treatment of established vascular disorders, including phlebopathies and related syndromes, as well as peripheral arterial occlusive disease. Parnaparin also showed some benefit as an adjunctive therapy in patients with angina pectoris. The risk of general bleeding appears to be similar with parnaparin or heparin, although parnaparin results in fewer haematomas at the site of injection, partly because of the less frequent administration regimen. Parnaparin has also been associated with a lower incidence of pain and/or burning sensation at the injection site compared with heparin. As with other LMW heparins, the possibility that parnaparin will be infrequently associated with thrombocytopenia cannot be excluded. Thus, parnaparin may be preferred over traditional heparin for the prophylaxis of thromboembolic events in surgical patients (particularly those at high risk for DVT), as well as the treatment of established vascular disorders with a thrombotic aetiology. Compared with heparin, parnaparin offers the advantages of a more convenient administration regimen coupled with improved local tolerability. However, the therapeutic advantages of parnaparin relative to other LMW heparins have yet to be established in large scale comparative trials.