Hyppigheden af disse bivirkninger er svær at bestemme, men anses generelt for at være meget sjældne (forekommer hos mindre end 1 person ud af 10. 000):
The frequencies of these reactions are difficult to determine but are generally considered to be very rare (affecting less than 1 person in every 10,000) − Bleeding within the brain causing death − Serious allergic reactions (including potentially fatal anaphylactic shock) which can cause skin rash, swelling of the face, lips, mouth, tongue or throat, wheezing or difficulty breathing; difficulty swallowing − Bleeding of the stomach or intestines (can lead to bloody stools or vomiting), inflammation of the intestine or colon, nausea (feeling sick) − Serious skin conditions such as Stevens-Johnson syndrome, exfoliative dermatitis and toxic epidermal necrolysis (can cause rash, blistering or peeling of the skin) − Liver failure, liver damage and severe liver inflammation (sometimes fatal or requiring liver transplant).