Lester Grinspoon & James B. Bakalar have written a fascinating book about the history of cocaine use, mostly in the United States.
p. 111-115
Lethal dose: According to Gutiérrez-Noriega and Zapata Ortiz, it is 20 mg/kg orally in dogs (1.4 grams for a 150 pound man), or 10-12 mg per kg subcutaneously/intravenously (700-850 mg in a 150-pound man).
“A recent experiment on mice”: LD50 of Heroin, 57 mg/kg; LD50 of heroin worsened by small amounts of cocaine, but bettered by large amounts. According to R.D. Pickett, who did the studies, “in the doses usually used by heroin addicts (equal proportions by weight of the two drugs) cocaine potentiates heroin’s lethal effect.”
LD 50 of cocaine alone in this experiment was about 2 grams intravenously in a 150-pound man.