The precise mechanism by which Hydroxyurea produces its cytotoxic effects cannot, at present, be described. However, the reports of various studies in tissue culture in rats and man lend support to the hypothesis that Hydroxyurea causes an immediate inhibition of DNA synthesis without interfering with the synthesis of ribonucleic acid or of protein. This hypothesis explains why, under certain conditions, it may induce teratogenic effects. Three mechanisms of action have been postulated for the increased effectiveness of concomitant use of Hydroxyurea therapy with irradiation on squamous cell (epidermoid) carcinomas of the head and neck. In vitro studies utilizing Chinese hamster cells suggest that Hydroxyurea is lethal to normally radioresistant S – stage cells, and holds other cells of the cell cycle in the G-1 or pre-DNA synthesis stage where they are most susceptible to the effects of  irradiation. The third mechanism of action has been theorized on the basis of in vitro studies of HeLa cells; it appears that Hydroxyurea, by inhibition of DNA synthesis, hinders the normal repair process of cells damaged but not killed by irradiation, thereby decreasing their survival rate; RNA and protein synthesis have shown no alteration.



Intermittent Therapy

80 mg/kg administered orally as a single dose every third day.

Continuous Therapy

20 to 30 mg/kg administered orally as a single dose daily.

The intermittent dosage schedule offers the advantage of reduced toxicity since patients on this dosage regimen have rarely required complete discontinuance of therapy because of toxicity.

Concomitant Therapy with Irradiation

(Carcinoma of the head and neck)

80 mg/kg administered orally as a single dose every third day. Administration of Hydab should be begun atleast seven days before -initiation of irradiation and continued during radiotherapy as well as indefinitely afterwards provided that the patient may be kept under adequate observation and evidences no unusual or severe reactions. Irradiation should be given at the maximum dose considered appropriate for the particular therapeutic situation; adjustment of irradiation dosage is not usually necessary when Hydab is used concomitantly.


Until the intermittent therapy regimen has been evaluated, continuous therapy (20 to 30 mg/kg administered orally as a single dose daily) is recommended. An adequate trial period for determining the antineoplastic effectiveness of Hydab is 6 weeks of therapy. When there is regression in tumor size or arrest in tumor growth, therapy should be continued indefinitely.


Significant tumor response to Hydab (Hydroxyurea Capsules USP) has been demonstrated in melanoma, resistant chronic myelocytic leukemia, and recurrent, metastatic, or inoperable carcinoma of the ovary.

Hydab used concomitantly with irradiation therapy is intended for use in the local control of primary squamous cell (epidermoid) carcinomas of the head and neck, excluding the lip.

Product Information

Hydab (Hydroxyurea Capsules USP) is available as a capsule containing Hydroxyurea USP 500mg.

For the use only of a Registered Medical Practitioner or a Hospital or a Laboratory