Medical treatment for<unk>  should be directed at the underlying cause (for example treating parasitic infection or malignancy).<unk>  without evidence of organ dysfunction may be observed with monitoring for evidence of organ involvement.
Treatment of hypereosinophilic syndrome has a number of options including corticosteroids, hydroxyurea, interferon-alpha, imatinib and other tyrosine kinase inhibitors, IL-5 antibodies, and other cytotoxic and immunomodulatory agents.
Corticosteroids are most commonly used as first line therapy. They are able to produce a rapid decrease in eosinophil counts, which is valuable if there is already evidence of organ dysfunction related to high eosinophil levels. 
0.5-1mg/kg/day of prednisone (or the equivalent dose of another steroids) is the recommended starting dose.  Patients with non-severe disease manifestations can start with lower doses
Steroids are tapered over time, with second line agents added if needed to maintain control.
In one study, corticosteroids were able to induce remission in 85% of patients at 1 month
Hydroxyurea is the most commonly used second-line agent for hypereosinophilic syndrome.  Typical dose range is 500mg-2g per day.  Hydroxyurea acts at the level of the bone marrow to reduce production of new<unk> . As such it is not suitable if a rapid lowering in eosinophil levels is needed.  Hydroxyurea is not usually used alone, it is most often used as an additional steroid-sparing agents.
Interferon-alpha is also a second-line, steroid sparing agent.  Use of this agent is limited by its toxicities.  Interferon-alpha also has activity on lymphocytes, so it may be particularly effective in<unk>  secondary to lymphocytic malignancies.
Imatinib and related TKIs have shown promise in treating chronic<unk>  leukemia due to similar molecular re-arrangements as CML.  This family of TKIs is very well tolerated.  These drugs are most effective in patients who have the FIP1L1-PDGFRA rearrangement driving a clonal expansion in the bone marrow.
Other cytotoxic agents have been used in isolated cases, but lack strong evidence
In severe cases refractory to other therapy, stem cell transplant may be considered if the cause of the<unk>  is a primary bone marrow process.
0.5-1mg/kg/day of prednisone (or the equivalent dose of another steroids) is the recommended starting dose.  Patients with non-severe disease manifestations can start with lower doses
Steroids are tapered over time, with second line agents added if needed to maintain control.
In one study, corticosteroids were able to induce remission in 85% of patients at 1 month
Eosinophilia medical therapy
Sjögren's syndrome medical therapy
Uveitis medical therapy
Goodpasture syndrome medical therapy
Scleroderma medical therapy
Mast cell leukemia medical therapy
Mixed connective tissue disease medical therapy
Cryoglobulinemia medical therapy