'being a pharmacist' - which paragraph is better?

Hi, Which one do you like better? Also, if you have suggestions to make it better (e.g. grammar, annotation, wording...), please let me know!!!

Thanks in advance!!!

Because of the amount of responsibilities it requires, being a pharmacist is a profession far harder than one might think. One little mistake on measuring the medication can be potentially fetal. Also, pharmacists must know what many of the medications do and if there are any side effects and incompatibilities with other medications that the patient might be on.

OR

Because of the amount of responsibilities it requires, being a pharmacist is a profession far harder than one might think. They must be very careful that they have measured the medication correctly, because one little mistake can be potentially fatal. And, they pharmacists must know what many of the medications do and if there are any side effects and incompatibilities with other medications that the patient might be on.

I like the second one a lot better, it flows much easier in the head of the reader. Also the first one has a few grammar and spelling mistakes. As for the second one I would change the second sentence and on to this:

"Pharmacists must be very careful of measuring the right amount of medication because any small mistake could be fatal. They must also keep in mind the benefits and side effects of each medicine and their incompatibilities with other medications."

Good luck!

I prefer the second.
I'm not a native speak English, so I'm not able to correct the mistakes.
However, I'm a student of pharmacy and like better the second one