Hello,
      I had gone through your question carefully and can understand your concern very well.
      I would like to tell you that most of the time, 
ALT is very specific for 
liver disorders. As you are on 
Isoniazid for last 2.5 months and one of the severe side effects of this drug is 
hepatitis, but its very rare. Risk is increases as the age advances, so if you are more than 50 years of age, then chances of developing hepatitis is more as compared to younger ones.
       Levels of ALT and AST are increased during 1st few months of starting treatment, but usually ALT levels return to normal after 3-4 months of treatment. 
       So in your case, as you have started isoniazid since 2.5 months and levels of ALT is not that much high, so at this point it doesn't seem to be an urgency and need any kind of evaluation, but i would recommend you to repeat the ALT and AST levels every monthly to rule out hepatitis. If the levels are consistently high after 4 months, then you need to consult a physician and need to be discussed about this.
      Hope this answers your question and let me know if you have any further relevant queries, i will be happy to guide you further.