Amitriptyline is one of the few meds it's possible to OD on reliably through cardiac switch. I can't seem to find the LD50 (dose deadly for half the population) in humans, but in the DDAMP cocktail mentioned in the PePH, Nitschke says you need 8g of amitriptyline along with other meds. If the OD is done on amitriptyline alone, I'd increase the dosage a bit, although you're remarkably thin and Nitschke, I don't know why, does not take one's weight into account when calculating the fatal dose. 10g should be more than enough.