depakote,keppra,and elevated serum amonia(ammonia)

A few months ater starting Keppra(and stopping dilantin),my husband's VPA (ER) level was 121.For years,his level was steady-between 80 and 90.He had markedly increased hand tremors and somnolence.We were told by neurologist and pharmacist-still in therapeutic range-Keppra could not have caused the increased VPA level.Two months later,we returned to the neurologist at my (never marry a nurse) insistence.My husband now had leg cramps,was stuporous,very irritable,slept  14 to 16 hrs. a day,and had "liver flap".In march,his LFTs were normal.It was during this visit on june 19 that I first learned about Depakote and hperamonemia.We reduced his dosage by 500 mg. and did no labsuntil 13 days later.His VPA was 112,and plasma amonia (ammonia) was 101 ug/dl.Could Keppra be causing the increased VPA level and that in turn is causing the increased plasma amonia (ammonia)?Pharmacist and neurologist say "no".I say there si no literature I have been able to find-and the only variable has been d/c ing the phenytoin and adding Keppra.Also,we are out of options as far as any other AEDs-we've done the gamut over the years-including UCSF epilepsy Center.My husband's seizures are rare,but when they do occur.they are Grand Mal-and usually staus-I stop  them with SL versed.So-any ideas?Should we repeat labs?Next apt. is not until Aug 20 and with amonia (ammonia) still at 101-I'm a little worried-though he is clinically better-not back to baseline for him.