Mylostat500 mg

Mylostat is an antimetabolite (ribonucleotide reductase inhibitor) with the following evidence-based indications:

Established / FDA-approved uses

• Sickle cell disease (SCD): Reduces the frequency of painful vaso-occlusive crises and the need for blood transfusions in adults and children with SCD, primarily by inducing fetal hemoglobin (HbF) production.
• Chronic myeloid leukemia (CML): Used for cytoreduction, particularly during the initial control of leukocyte counts before or alongside definitive therapy.
• Essential thrombocythemia and polycythemia vera: Used to reduce platelet or red cell counts and thrombotic risk in these myeloproliferative disorders, especially in high-risk patients.

Guideline-supported / combination uses

• Locally advanced squamous cell carcinoma of the head and neck and carcinoma of the cervix: Used as part of combination regimens with radiation therapy; not effective as monotherapy for these indications.

Off-label uses (commonly reported, not FDA-approved)

• Refractory psoriasis (second-line, when standard therapies fail).
• Selected myeloproliferative neoplasms and hypereosinophilic syndromes, under specialist supervision.

Use of Mylostat should always be directed and monitored by a qualified physician, typically a hematologist or oncologist.

Each capsule/tablet contains Hydroxyurea as the active ingredient, commonly available in strengths such as 500 mg (capsule) and other locally marketed strengths. Oral liquid formulations also exist internationally. Excipients vary by manufacturer; refer to the specific product's package insert for the complete excipient list.

Mylostat is an orally administered antineoplastic and antimetabolite agent. Chemically it is a simple hydroxylated urea derivative that inhibits the enzyme ribonucleotide reductase, blocking the conversion of ribonucleotides to deoxyribonucleotides and thereby interfering with DNA synthesis. It is used both as a cytoreductive agent in certain hematologic malignancies and myeloproliferative disorders, and, at lower doses, as a disease-modifying therapy in sickle cell disease through induction of fetal hemoglobin.

Mylostat belongs to the antimetabolite class of antineoplastic agents, specifically classified as a ribonucleotide reductase inhibitor. It is also recognized as a fetal hemoglobin-inducing agent used in hemoglobinopathy management.

Hydroxyurea inhibits the enzyme ribonucleoside diphosphate reductase, which catalyzes the rate-limiting step in the conversion of ribonucleotides to deoxyribonucleotides required for DNA synthesis. This action arrests cells in the G1/S phase of the cell cycle without significantly affecting RNA or protein synthesis, making it relatively selective for rapidly dividing cells.

In sickle cell disease, Hydroxyurea increases the production of fetal hemoglobin (HbF) in red blood cells, partly through nitric oxide-mediated pathways. Elevated HbF reduces intracellular sickle hemoglobin polymerization, decreasing red cell sickling, hemolysis, and the frequency of vaso-occlusive events. It also reduces neutrophil and reticulocyte counts and improves red cell hydration and deformability.

Hydroxyurea is rapidly absorbed after oral administration, with peak plasma concentrations reached within 1-4 hours. It is partly metabolized hepatically (via urease-related pathways) and partly excreted unchanged renally, with an elimination half-life of approximately 3-4 hours.

Mylostat capsules should be swallowed whole with a full glass of water, without opening, chewing, or crushing them, to avoid inhalation or skin contact with the cytotoxic powder. If a caregiver must handle capsules, gloves are recommended, and hands should be washed thoroughly afterward. It may be taken with or without food, generally at the same time each day to maintain consistent blood levels.

Clinically significant interactions with Mylostat include:

• Other myelosuppressive agents or radiation therapy: Concurrent use increases the risk of additive bone marrow suppression; requires closer hematologic monitoring.
• Antiretroviral therapy (e.g., didanosine, stavudine): Concurrent use has been associated with an increased risk of pancreatitis, hepatotoxicity, and peripheral neuropathy; combination should be avoided or used only with careful monitoring.
• Live vaccines: Immunosuppression from Mylostat may reduce vaccine efficacy or increase infection risk from live vaccines; live vaccinations should generally be avoided during therapy.
• Uricosuric agents: Mylostat can increase serum uric acid levels, which may require dose adjustment of urate-lowering therapy.

Always inform the prescribing physician of all other medications, including over-the-counter drugs and supplements, before starting Mylostat.

Boxed warnings associated with Mylostat include myelosuppression, secondary leukemia risk, cutaneous vasculitic toxicities, and embryo-fetal toxicity (detailed further under Precautions and Warnings, and Pregnancy and Lactation).

Common side effects

• Myelosuppression (leukopenia, anemia, thrombocytopenia) - the most common dose-limiting effect
• Macrocytosis (usually a benign, expected finding rather than a sign of vitamin deficiency)
• Gastrointestinal disturbances: nausea, vomiting, diarrhea, constipation, stomatitis
• Skin changes: rash, hyperpigmentation, scaling, alopecia, and dryness
• Headache and fever

Less common but serious effects

• Cutaneous vasculitic ulcerations and, rarely, gangrene (see Precautions and Warnings)
• Secondary skin malignancies with long-term use
• Secondary leukemia with prolonged therapy in myeloproliferative disease
• Pulmonary toxicity (interstitial lung disease) - rare

Patients should promptly report unusual bruising, bleeding, fever, skin ulcers, or persistent illness to their physician.

Mylostat is teratogenic and embryotoxic in animal studies and can cause fetal harm when administered to a pregnant woman. It should be used during pregnancy only if clearly needed and the potential benefit justifies the potential risk to the fetus, and only under close specialist supervision. Women of reproductive potential should use effective contraception during treatment with Mylostat and for a period after discontinuation; men being treated should also use contraception, as effects on sperm (including possible mutagenicity) have been reported.

Mylostat is excreted into breast milk; breastfeeding is generally not recommended during treatment due to the potential for serious adverse reactions in the nursing infant. Consult a physician before breastfeeding while taking this medicine.

Myelosuppression

Mylostat commonly causes dose-related bone marrow suppression, which can be severe. Regular complete blood counts (CBC) should be performed before starting therapy and periodically throughout treatment; dose adjustment or temporary discontinuation may be required if significant cytopenias occur.

Secondary Leukemia

Long-term use of Mylostat, particularly in myeloproliferative disorders, has been associated with an increased risk of secondary leukemia. The benefits of therapy should be weighed against this risk, especially for prolonged treatment courses.

Cutaneous Vasculitic Toxicities

Vasculitic ulcerations and gangrene have been reported, particularly in patients with a current or past history of interferon therapy. Mylostat should be discontinued if cutaneous vasculitic ulcers develop, and it should generally not be resumed following such an event.

Secondary Skin Malignancies

Patients on long-term Mylostat therapy should have periodic skin examinations for malignant or pre-malignant skin lesions.

Embryo-fetal Toxicity

See Pregnancy and Lactation for detailed guidance; effective contraception is required during treatment.

Renal and Hepatic Impairment

Use with caution and appropriate dose adjustment in patients with renal or hepatic impairment (see Dosage and Administration).

Macrocytosis

Macrocytosis is an expected pharmacologic effect and does not necessarily indicate folate or vitamin B12 deficiency, though such deficiencies should be excluded if clinically suspected.

Mylostat should be taken exactly as prescribed by a physician; do not stop, extend, skip doses, or share this medicine with others without medical advice.

Overdosage with Mylostat may present with mucocutaneous symptoms, acute worsening of myelosuppression, and gastrointestinal symptoms. In case of a known or suspected overdose, seek immediate medical attention or contact emergency services / a poison control center right away. Do not attempt to manage a suspected overdose at home; supportive care and close hematologic monitoring should be provided under medical supervision.

Store at room temperature (below 30°C), away from light and moisture. Keep out of reach of children. Capsules should remain in their original container.

Renal Impairment

Dose reduction is required in patients with significant renal impairment; close monitoring for toxicity is recommended (see Dosage and Administration).

Hepatic Impairment

Use with caution; data on formal dose adjustment are limited, so close clinical and laboratory monitoring is advised.

Elderly

Older patients may be more sensitive to the myelosuppressive effects of Mylostat and may require lower starting doses with close monitoring.

Pediatric Use

See Pediatric Uses for detailed information.

Immunocompromised Patients

Increased susceptibility to infection due to myelosuppression; live vaccines should generally be avoided during therapy.

Duration of Mylostat therapy is individualized and determined by the treating physician based on the indication, clinical response, and laboratory monitoring. In sickle cell disease and myeloproliferative disorders, treatment is typically long-term/chronic, with periodic reassessment of blood counts and clinical benefit. Therapy should not be stopped abruptly without medical advice.

Antineoplastic agent; antimetabolite; ribonucleotide reductase inhibitor; fetal hemoglobin-inducing agent.

Hydroxyurea inhibits ribonucleoside diphosphate reductase, blocking conversion of ribonucleotides to deoxyribonucleotides and arresting cells in the G1/S phase of the cell cycle, which underlies its cytoreductive effect in hematologic malignancies. In sickle cell disease, it additionally stimulates fetal hemoglobin (HbF) synthesis, reducing sickle hemoglobin polymerization and its downstream complications.

Mylostat is approved for use in pediatric patients 2 years of age and older with sickle cell disease to reduce the frequency of painful crises, using weight-based dosing with careful titration and monitoring of blood counts. Safety and efficacy in children younger than 2 years with sickle cell disease, and in pediatric patients for other indications (e.g., myeloproliferative disorders), have not been well established, and use in these settings should be guided by a pediatric hematologist/oncologist.