Husband is demeaning since he can't drive and ridicules me in everything I do! Refuses to do anything to improve his health. Advice?

I don't know how long he is taking this antidepressant now, but it takes easily a month to know if there is or is not improvement. You say he is realizing he has a memory issue. Has he admitted/discussed with you? If he has that is a very good sign actually; the more common approach is denial.
Is this behavior of your husband's a radical change from his usual attitude to life?
I am so sorry you are going through this.

Sounds like this is how your husband is dealing with the changes he's witnessing in his life and brain. I don't believe that it's all that uncommon, unfortunately, but I get that it's hard for you to put up with. Give him time to adjust to his "new normal" and when he's having a more calm moment, try and have a conversation about what your concerns are, and reassure him that you love him, and that you're not going anywhere, and that you just want what's best for him. And I certainly wouldn't give up on the antidepressants, as there are many, many options out there. If often takes several tries before someone finds the one(sometimes 2)that works for them. Wishing you the best.

Stop expecting a person who is depressed by the loss of his abilities (and the inevitable intimations of mortality) to help himself or to be considerate to you.

Ask either this or another appropriate mental health practitioner to explain to him in clear terms what is probably happening to his brain, his mood, and his behaviour; and then to prescribe a treatment plan, including antidepressants, which he will actually be able to follow.

I.e. one which does not depend on his having any self-motivation to speak of at the moment.

Meanwhile, protect yourself by blanking out, as well as you are able, any criticisms or pessimistic jibes from him - dismiss them on the grounds that these are not his real thoughts, and do not have any real basis. Don't listen to him any more than you'd ask a person with temporary sight loss for advice on a new hair tint. But DO listen to him when (if?) he talks about how *he's* feeling, and really listen.

In addition to all that Beatty advised, call the doctor and ask for a trial of a different antidepressent.

This is what people do though, isn't it? Take out their anger on their nearest & dearest 😔.

He may well be angry at not driving or losing his independence, but it is unfair to direct it at you.

Does he stop this behaviour if you tell tell him 'enough'?

If not, I think I would be leaving the room every time there was any rudeness, ridicule or verbal abuse. Find hobbies at the other end of the house, go out a lot, watch the tv wearing headphones.

Is he physically independent?