Drug-induced interstitial pneumonitis in essential thrombocythemia treated with anagrelide

Anagrelide, a phospholipase A2 inhibitor, is widely used in the management of essential thrombocythemia. To date, anagrelide has only rarely been reported to be associated with the development of drug-induced interstitial pneumonitis. We herein report two cases of anagrelide-associated interstitial pneumonitis. The patients were a 67-year-old woman and a 75-year-old man, both with essential thrombocythemia. Both cases developed interstitial pneumonitis at 8 weeks after administration of anagrelide. Because anagrelide-induced interstitial pneumonitis was suspected from CT scan and bronchoalveolar lavage fluid findings, anagrelide-therapy was discontinued and corticosteroid administration was initiated. Anagrelide withdrawal and corticosteroid administration resulted in marked symptom amelioration. A lymphocyte stimulation test using anagrelide was positive in both cases. As interstitial pneumonitis is a rare adverse event during anagrelide-therapy administration, physicians must be vigilant in identifying drug-induced interstitial pneumonitis in patients treated with anagrelide because early detection can decrease the severity and prevent mortality.