diethylcarbamazine, synthetic anthelmintic drug effective against certain parasitic filarial worms, which are endemic throughout most of the subtropical and tropical regions of the world. These parasites infect the blood and lymph channels in humans, causing the debilitating disease filariasis. Diethylcarbamazine is effective in treating filariasis caused by Wuchereria bancrofti (Bancroft filariasis), Onchocerca volvulus (onchocerciasis, or river blindness), and Loa loa (loiasis). The drug is administered orally.