Is it safe to take 200mg vitamin B6 with isoniazid 300mg daily? The B6 was cheaper otc. I was prescribed 50mg vitamin B6 from my doctor originally.

Probably safe but... High doses of vit. B6 can cause neuropathy (inflammation/irritation of nerves). 200 mg is at the border of the amount that could cause this. Authorities advise not taking more than 100 mg, but 200 mg/day for months is the lowest amount proven to cause problems. Capsules with 50-100 mg of b6 are inexpensive & widely available at health food stores. You can take the 200 mg but buy a lower dose next.
Limit B6. Do not take more than 50 mg of b6 per day--it can cause nerve problems.