A 50-year-old man with severe P. falciparum malaria develops disseminated intravascular coagulation (DIC). His blood results show: platelets 18 × 10⁹/L, PT 28 seconds (normal <14), APTT 55 seconds (normal <35), fibrinogen 0.6 g/L, D-dimers markedly elevated. What is the most important intervention alongside IV artesunate?