68 y/o male was prescribed Primidone 50 mg. t.i.d. for essential tremor. Began b.i.d., then increased to t.i.d. and has been taking it for approximately 6 months. In the past two months, I ve noticed a drastic change in his behavior...almost childlike, very spontaneous and impulsive. While on vacation recently, he absolutely seemed manic----like he couldn t stop talking and he truly rambled on and on, then made unusual expensive purchases----not his usual behavior. He s a workaholic normally but, two weeks ago worked a total of 39 hours nonstop as an auto mechanic. He even drank an energy drink to keep himself going and felt he HAD to get all of the work done that day! The following morning, he complained with right arm pain on awakening, then chest aching and ended up having a STEMI, was transported emergently by air for cardiac cath, stent and angioplasty of the LAD s where they bifurcate. Following three hospital days, he was told, of course, to avoid heavy lifting or any work for two weeks. He s worked at least 10 hours a day since post MI day 9, does c/o chest pain at least once daily but slows down for a few minutes, then charges right back into work again! He admits he feels tightly wound and that he just can t stop! His actions and comments are definitely more manic and spontaneous than ever before. Any chance Primidone could be the culprit?