What is a toxic dose of phenobarbital?

10g.

Injected intravenously, you need 1g of pento per 10kg of your weight. So if your weight is 65kg you need 6.5g total with pento. A 100ml bottle containing 65mg/ml has a total of 6.5g. All 100ml, a tenth of a L that is, needs to be injected into your vein.

You need more if injected otherwise.