In earlier years it was thought that apamin was a rather nontoxic compound (LD = 15 mg/kg in mice) compared to the other compounds in bee venom.  The current lethal dose values of apamin measured in mice are given below. There are no data known specific for humans.
Intraperitoneal (mouse) LD: 3.8 mg/kg
Subcutaneous (mouse) LD: 2.9 mg/kg
Intravenous (mouse) LD: 4 mg/kg
Intracerebral (mouse) LD: 1800 ng/kg
Parenteral (mouse) LD: 600 mg/kg