Are nurses allowed to call in perscriprions for patients?

Yes, with limits... Nurse practitioners are able to call in (or direct someone to call in) a prescription for a patient. In many offices, a triage or phone nurse is often directed to call in prescriptions for patients.
Not prescribe. They may call a script over the phone that a doctor or physician assistant prescribes, but nurses do not have prescription privileges. At least in ohio they dont.