Hi,i'm taking 400 acyclovir for herpes twice a day.i having trouble swallowing them.is one tablet effective.

Probably not: With acyclovir for herpes, even 400 mg twice daily is on the low side; 400 mg once a day pr 200 mg twice definitely is not enough. Maybe twice a day you can take 200 mg, wait a few minutes, then take the other one. Otherwise, contact the doctor or clinic who prescribed it to discuss other options, such as 200 mg 4-5 times a day, or perhaps the liquid suspension usually given to children.