Chimmy, my situation is not terribly different from yours. Every time my dad calls me when he is drinking he says the same things every time -- why did my mom leave, my financial situation is declining (it is fine), I'm so lonely, etc. It is very depressed, self-deprecating talk and he usually does not remember it later. So I have a rule that we will not talk when he is drinking. I told him that this was the rule. If he calls me at night I let it go to voicemail, then I listen to the vmail before I call him back. If he turns out to be drunk when we talk I say, "Dad, you have been drinking and we agreed that I won't talk to you when you're like this. I will talk to you another time when you are sober." And then I hang up. No buts.
It has been important for me to set these boundaries -- before I limited our communication these phone conversations would really upset me, but he would barely remember them. Nothing good came of it. You are also in a situation where talking to your mother or going to see her does not result in anything good for either of you. Like you said you can't force her to stop drinking, take medicine that makes her sick, etc. The only person you can control is yourself - focus on taking care of that person. Best of luck.