I don't have myoclonus, but I am on BOTH Keppra (2000 mg) and Lamictal (450 mg) for my seizures. Never had any major problems with either of them (the initial titration onto Lamictal was very nasty, but after I got to my target dose the side effects subsided).

Just an FYI-- Keppra is known to cause mood issues (ranging from mild crankiness and crying to agression and anger) in some people, so just be aware of and keep an eye out for.

Good Luck !
L2L