Itching can also be due to the usual medications of PV (hydroxyurea= Hydrea or cytodrox), and there is another possible medications to check with ur doctor, or eventually doing phlebotomy (blood letting) .
if you are on treatment, you should do frequent blood tests, to check on electrolytes, as the treatment kill cells , and their contenance is released in blood
(calcium, magnesium, phosphorus, uric acid, etc)
Anti-histaminic drugs do well (zyrtec, or atarax, Xyzall,etc). PV is a very rare disease, 2/100 000 per year, so there is no real specific medication for itching, except surveillance, and taking old or new generations of anti-histaminic medications