What is the difference between metoprolol 50 mg and metoprolol succ er 50 mg

Metoprolol Succ ER is an extended medication, hence the ER in the name, it is released in your body over time. Motoprolol is release within a few short hours after taking it, thus the effects don't last as long as the ER version.

Metoprolol is a beta blocker and usually used for hypertension (high blood pressure).

I am now on the Succinate and my Doc tells me to increase from 50 mg to 75 mg.
I have a recent supply of the Tartrate so can I use 25 mg of this and then 50mg of the ER ?

I'm not a doctor or pharmacist but I would say no. The Succinate (ER ) version stays in the body for about a day while the Tartrate does not. Nor should you split a 50mg tab of the Succinate