this is not a journal title

I usually interpret N/A to mean not applicable, which seems to be correct in the case of amoxicillin, which is taken at the onset of flareups and therefore the question of whether it prevents them is not applicable. However, in some other cases, N/A is apparently being used in a different sense, such as with accutane. Obviously if the ability of accutane to do any of the three things in the rightmost columns fell into the not applicable category, it wouldn't even be listed here. So, it must be that the other meaning of N/A--not available, since the data have not been gathered--is now in play. If I were critiquing this as part of a scientific paper, I would say that these two cases should be disambiguated. You could, for example, replace the N/A's for accutane and sulfacetamide with -- or ? or "unknown". I would also say "unlikely" would be OK since (for the sulfa drug) antibacterials seem to have done very little for you in general and (for accutane) this is not nodular acne.