Yes, a physician has to prescribe this drug. It is often the oncologist who ordered the chemo who prescribes it, but it can be another provider. Here is a brief description of the generic medication from the Mayo web site:

Pegfilgrastim injection is used to treat neutropenia (low white blood cells) that is caused by cancer medicines. It is a synthetic (man-made) form of a substance that is naturally produced in your body called a colony stimulating factor. Pegfilgrastim helps the bone marrow to make new white blood cells.

When certain cancer medicines are used to fight cancer cells, they also affect the white blood cells that fight infections. Pegfilgrastim is used to reduce the risk of infection while you are being treated with cancer medicines. It is also used to improve survival in cancer patients who have been exposed to radiation.

This medicine is available only with your doctor's prescription.