Simple, add a new var like "g_itemid_antidote", then add this in plugin_init:
PHP Code:
g_itemid_antidote = zp_register_extra_item("Antidote", 40, ZP_TEAM_HUMAN)
After that, add:
PHP Code:
public zp_extra_item_selected(id, itemid)
{
if(itemid != g_itemid_antidote || zp_get_zombie_count() <= 3)
return
infect_antidote(id)
}
And for the cure_user part, take a look at zp source code.