Hydroxyurea is an antineoplastic agent used alone or in combination with other chemotherapeutic drugs or radiation in the treatment of resistant leukemias and carcinomas of the head and neck. It is also used to increase fetal hemoglobin concentration, thus reducing the frequency of severe crisis and reducing the necessity for blood transfusions in patients with sickle cell anemia.
Hydroxyurea is an extremely toxic drug with a low therapeutic index.
Since hydroxyurea inhibits DNA synthesis, it can result in significant toxicity including myelosuppression. Furthermore, inhibition of DNA synthesis without affecting RNA synthesis may result in red blood cells becoming megaloblastic.
Overdose data is limited, but case reports exist. One such case is an accidental overdose of hydroxyurea in a 2-year-old child resulted in mild myelosuppression. The clinicians observed the patient in the emergency room for 8 hours and then discharged home. They monitored blood counts for myelosuppression for 2 weeks as an outpatient.
In another case, a woman developed agitation, widespread myoclonic jerks, oculogyric crisis, sinus tachycardia, and myelosuppression after ingesting 60 grams of hydroxyurea.
Another case series reported acute mucocutaneous toxicity in three patients with advanced acute myelogenous leukemia treated with oral high dose hydroxyurea at a dose of 10 grams for 8 to10 days. All three patients developed severe acute stomatitis. Two patients developed acute cutaneous toxicity associated with soreness, violet erythema, and edema of palms and soles, followed by intense hyperpigmentation of the skin.
Hydroxyurea is a hydroxylated analog of urea, inhibiting DNA synthesis by inhibiting ribonucleotide diphosphatase reductase and blocking the conversion of ribonucleotides to deoxyribonucleotides.
Hydroxyurea is cell cycle specific for the S phase, causing cell arrest at G1 to S.
Hydroxyurea increases HbF levels by stimulating HbF production, but the exact mechanism of HbF production is unknown. It also has antioxidant properties, alters the RBC membrane, increases red blood cell (RBC) deformability by increasing intracellular water content and decreases RBC adherence to the endothelium.
Bone marrow suppression: myelosuppression leads to anemia, leukopenia (more common) and thrombocytopenia. This toxicity is reversible by withholding the medication for 2 weeks and can potentially be resumed at a lower dose.
Hydroxyurea causes macrocytosis, seen early in treatment and may be confused with pernicious anemia. While unrelated to vitamin B12 or folic acid deficiency, prophylactic folic acid supplementation is recommended to assist with macrocytosis.
Hydroxyurea used to manage myeloproliferative disorders can cause secondary leukemias. A case series detailed three patients with essential thrombocythemia who were continuously receiving hydroxyurea for 47, 81 and 90 months had a leukemic transformation.
Long-term use of hydroxyurea can cause skin cancer; cutaneous carcinomas are a severe side effect of hydroxyurea. This can occur after several years of treatment with hydroxyurea. Patients on HU treatment need to be monitored and follow up for the long term.
There are reports of elevation of serum concentrations of hepatic enzymes in patients receiving hydroxyurea. While rare, hepatotoxicity resulting in fatal hepatic failure has been reported in patients with HIV infection receiving the drug in combination with antiretroviral agents. Fatal hepatotoxicity occurred most frequently in patients receiving combination therapy with hydroxyurea, didanosine, and stavudine.
Fatal and non-fatal pancreatitis has been reported in patients with HIV infection, during therapy with hydroxyurea and didanosine, with or without stavudine. In these patients, close monitoring of signs and symptoms of pancreatitis the recommendation, along with permanent discontinuation hydroxyurea in patients who develop signs and symptoms of pancreatitis.
Long-term treatment with hydroxyurea is associated with painful skin ulcers, aphthous ulcers, non-ulcerative toxicity with erythema and skin infiltration. Rarely, long-term therapy with hydroxyurea is associated with gangrene of the toes and digits. It is recommended to discontinue the drug.
Hydroxyurea decreases sperm count and sperm motility in males and is considered pregnancy category D. Breastfeeding is not indicated during hydroxyurea treatment.
Hydroxyurea can cause severe interstitial pneumonitis. It can even occur after several years of initial treatment with hydroxyurea. If not diagnosed, drug-induced interstitial pneumonitis can lead to lung fibrosis and respiratory failure. The recommendation is to discontinue the drug.
There is a case reported in the literature, a patient with chronic myelogenous leukemia receiving hydroxyurea treatment who had an acute myocardial infarction. The pathogenesis of this adverse effect is unclear.
Rare side effects include headache, dizziness, disorientation, hallucinations, and seizures.
As with most medicines, patients on hydroxyurea should have their electrolytes and renal function monitored, especially in patients with severe nausea, vomiting, and diarrhea. For those with myelosuppression, the practitioner should monitor signs of infection as well as CBC with differential count and platelet counts.
Treatment is symptomatic and supportive.
In patients with nausea and vomiting, treat with antiemetics and administer intravenous fluids as needed.
In patients with myelosuppression, treat with colony-stimulating factors in patients with neutropenia, platelets transfusion in patients with severe thrombocytopenia, and packed red blood cell transfusion in patients with anemia.
In patients with seizures, treat with antiepileptics.
Mild mucositis treatment is with bland oral rinses like 0.9 % normal saline, sodium bicarbonate, and water. In moderate cases with pain, a local anesthetic is added. Treatment for moderate to severe mucositis is with local anesthetic and systemic analgesics. Oral antimicrobial mouthwashes used to decrease the risk of infection.
Myelosuppression and gastrointestinal side effects were present with other chemotherapeutic agents used in combination with hydroxyurea.
If there is any concern for hydroxyurea toxicity, consultation with poison control is recommended.
Hydroxyurea toxicity management requires an interprofessional team of healthcare professionals including nursing staff, pharmacists, emergency medicine physician, internist, and hematology-oncologist. Emergency medicine physician should monitor for signs of respiratory depression and stabilize the patient’s airway. Consultation with a medical toxicologist/and or contact the poison center in patients with an unclear diagnosis may be necessary. Nurses and pharmacists should educate patients on the side effects of medication and signs of symptoms that require monitoring while taking the medication.
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