A patient who is on long-term treatment with warfarin sodium (Waran) with the prothrombin complex (

Fråga: A patient who is on long-term treatment with warfarin sodium (Waran) with the prothrombin complex (PK) in the therapeutic range (10-25 percent) now wants to travel to a part of the world where gammaglobulin prophylaxis is recommended. What is the risk for bleeding, and what precautions should be undertaken in this patient if an intramuscular injection is given?

Sammanfattning: When an intramuscular injection is considered in a patient treated with anticoagulantic drugs due to embolism or thrombosis it might be possible to give the injection providing that the warfarin treatment is discontinued for a few days. The benefit from the injection has, however, to be balanced against the risk for a deep intramuscular haemorrhage.

Svar: In the well-known textbook Martindale there is nothing written about possible dangers of intramuscular injections during treatment with anticoagulant drugs. A total of 226 haematological adverse reactions have been reported to the Swedish Adverse Drug Reaction Committee (SADRAC) in connection with warfarin treatment. Approximately half of them were cerebral haemorrhages and only 12 were classified as haematomas. It is not stated whether any of these haematomas were caused by intramuscular injections.

A representative from the manufacturer (1) recommends physicians to avoid intramuscular injections in patients treated with warfarin. The risk for bleeding is considerably lower when the intravenous or the subcutaneous routes are used. The doctor in charge at the coagulation unit at Karolinska Hospital (2) recommends that, if intramuscular injections are to be given, the warfarin treatment should be withdrawn for a few days to enable the PK-value to rise to approximately 40 per cent. A temporary withdrawal of the therapy is not harmful if the indication is anticoagulant treatment due to pulmonary embolism or venous thrombosis. However, such a procedure is contraindicated in patients with cardiac valve prothesis. If an injection is given the thinnest possible needle should be used and pressure applied on the injection site for approximately 20 minutes afterwards.