Which of the following is an adverse effect of fondaparinux?

• A. Thrombocytopenia
• B. Hyperkalemia
• C. Hypertension
• D. Bleeding

Answer: (D)

Fondaparinux works by enhancing antithrombin III inhibition of factor Xa, which reduces thrombin generation and overall clot formation. Because it is an anticoagulant, the main adverse effect to monitor is bleeding. This makes bleeding the best answer. While rare cases of thrombocytopenia can occur and fondaparinux has a lower risk of heparin-induced thrombocytopenia than heparins, the hallmark adverse effect most commonly associated with fondaparinux is bleeding. Hyperkalemia and hypertension are not typical direct effects of this drug. Bleeding risk increases with factors like older age, low body weight, higher dose, and impaired renal function, since fondaparinux is cleared by the kidneys.