MAs and nurses call in prescriptions all the time. These are basically done under the authority of the physician. If my MA tells me that so and so has a UTI, and I ask her to prescribe Bactrim DS tablets po bid for 5 days, I have no problem with that.
I also think I have as much chance of an error as she does. And, I wouldn't use the word "allowed" as almost all pharmacies will accept a telephone order from an MA.
I just read an article yesterday entitled, "Physicians need to work to the level of their license." meaning to delegate other tasks.
My MA will refill meds like Mycolog II and Zyrtec, Zantac, etc. I can't be bothered worring about that. I do check them, and I will change it if necessary or say, "We need to see that patient." She doesn't just prescribe meds on her own or call in Vicodin.