Hydroxyurea and periodicity in myeloproliferative disease

Three patients, one with polycythaemia vera (PV) and two with chronic myeloid leukaemia (CML), are described who had cycling of blood counts which became apparent whilst receiving hydroxyurea therapy. Significant periodicity was confirmed with the use of the Lomb periodogram. This is Fourier power spectral analysis tailored for unevenly sampled data. The patient with PV had marked oscillations of platelet counts with a periodicity of 29 d and an amplitude of (202-588) x 10(9)/L. Smaller oscillations of neutrophil, monocyte and lymphocyte numbers and Hb levels occurred with a similar periodicity. Anticipatory changes in hydroxyurea dosage or the maintenance of a constant dose did not abolish periodicity, but a change in therapy to the non-cycle-specific drug anagrelide dampened and abolished the cycling. One of the patients with CML had tremendous and clear oscillations in white cell, platelet and Hb levels, with a mean periodicity of 74 d. The other had erratic counts which were confirmed to be significantly periodic (64 d), on spectral analysis. A change in therapy to busulphan in both these patients again dampened and abolished the cycling. Hydroxyurea, which is a cell-cycle-specific agent, probably exacerbates the periodicity which may be present in some patients with myeloproliferative disease. A change in therapy to non-cycle-acting compounds such as busulphan or anagrelide results in much more stable counts in such patients.