Ah Anika....taking handfuls of meds is just So.Much.Fun, right? I wanted to chime in with my experience also. Again, as others have mentioned, I am not a doctor, so I can only tell you about my experiences. As for everyone's advice to ask your doctor - definitely! I will often write a list of questions to ask my doctor before going to see him, as I tend to get a little overwhelmed and end up forgetting to ask most of them if they aren't written down. If your doctor doesn't respond to your questions in a way that helps you understand, push for a different/better answer from him/her. My favorite method is..."Oh, thanks so much for answering that, but could you translate your answer into English now for me?" (with a big grin). I'm a little luckier than most, as my dad is a Neurophysiologist and taught in the medical school at Ohio State University for 30 years so if I don't completely understand something, I call him and make HIM translate it for me.
Anway....I am currently taking Sulfasalazine twice a day, 17.5 mg of MTX every Saturday, 80 mg of Prednisone every Saturday, a blood pressure pill, 1000mg of Metformin twice a day (diabetes), cyclobenzaprine up to every 6 hours for muscle spasms, an NSAID twice a day, an allergy pill twice a day, folic acid, Gabepentin twice a day (nerve pain), and a bunch of others that I can't remember right at the moment. My point here, is that I have taken MTX, Sultasalazine, a biologic and prednisone all at the same time, but I would certainly ask your doctor if he intended for you to continue taking both the plaquenil and mtx at the same time. I guess my main question to you would be...is it all working for you? If it is, if you feel that your psoriasis and PsA are in good control with all those meds, I'm not sure if I would want to go off of anything. Every person, every body is different. If you've found a cocktail that works for you - great! If you don't feel that it is in good control, then a change is definitely in order.
Also...make sure he/she is monitoring your bloodwork at least every 6 months to check your liver function. Mine does a CBC and a CMP at least that often, and sometimes throws in other blood tests as well just to see what is going on in my body. The ESR is a test that we've given up worrying about, as it supposedly indicates the level of inflammation that is in your body, but always comes up normal for me - even though there is clearly a great deal of inflammation in various joints always.
So anyway, this is my two cents worth. Please let us know what is happening after your next appointment. Inquiring minds and all....