| Metoprolol is the active ingredient being used to treat the condition.
Metoprolol succinate (Toprol XR) and Metoprolol Tartrate(lopressor) are 2 different dosage forms (forms of the medication).
M.Succinate is an extended-release medication and M.Tartrate is an immediate-release medication.
The only other difference I would be able to think of is that M.Tartrate, being an immediate release, would most likely require the patient to take additional pills throughout the day.
*This is due to metoprolol's short half life, which means the drug will be excreted from the body quickly since it's released immediately, and half life determines when to dose the drug once it's gone from the body. Shorter half life means taking more of the medication sooner than if it were an extended release.
With the extended release, the drug will stay slowly release over a longer period of time, so the patient probably wouldn't have to take more than one or two pills per day.
Most medications have these 2 options and then some because every patient varies with how they can take medication and it's helpful when dosing to know there are options.
Hope this helped :-D | 
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