ammonia,depakote and keppra

My husband is a 60 y/o male-dxed with eoilepsy about ten years ago.His seizures are rare,but are grand mal and usually status.I am a retired RN and give SL versed to abort the seizures.We have been through the gamut of AEDs and have been to UCSF epilesy Center.We finally settled on good old fashioned VPA (ER) and Dilantin-they provided the best control,the least somnolence,and (bonus) were cheapest.On our neurologist's advice ,we transitioned from phenytoin to Keppra,while continuing 2500 mg VPA daily.(He's always failed monotherapy.)We made the change as he was"sleeping his life away."Subsequent to completing the change,VPA level was 118 and LFTs were fine.Of note,his depakote levels have always been 70 to 90.This was in March.Over the last few months,my husband had increased hand tremors,increased somnolence and irritability,and  had difficulty with simple tasks and conversation.We returned to the neurologist in June-he had "liver flap" by then.That is when we learned about VPA and ammonia.We did no labs.We reduced Depakote by 500 mg . 12 days post reduction in dose,his  serum ammonia was 101ug/dl and VPA was 112.We did no other labs.My husband is less stuporous,but not back to baseline.We cannot get an apt.until Aug 20.I have 3 questions.I  am convinced the Keppra caused increased VPA level which in turn caused the increased ammonia.I can find no literature on this.Can we continue  VPA  if we add carnitine?And is ammonia level of 101ug/dl acceptable(safe) until our apt.next month?My husband is otherwise healthy-noHTN,no hx durgs or ETOH.He is a retired marine mammologist and I am a (happily) retired RN.Thnak you for your consideration of this complex and mutifactorial issue.