Prescribing
Siklos^®

Dosing

Siklos^® is available in scored 100 mg (2x 50 mg) tablets and 1,000 mg triple-scored (4 x 250 mg) tablets to allow dose adjustment based on patient body weight and clinical response.

Where both strengths of Siklos^® (100 mg and 1,000 mg) are prescribed simultaneously, make sure that the patient and/or the parents or caregivers understand the prescription in order to avoid confusion.

Siklos^® tablets offer more tailored dose adjustments in increments as small as 50 mg to help optimize dosing.

• Children with sickle cell disease are at increased risk of infection and recurrent painful episodes during childhood, which may lead to severe organ failure. Recurrences of painful episodes or evidence of organ dysfunction are clearly associated with poor prognosis and early mortality.¹ 
• The importance of optimal dosing of hydroxyurea in sickle cell anemia patients based on patient body weight and biological and clinical response has been well established.^{2, 3} 

The Siklos^® Advantage: Body Weight adjusted dosing

Prescribing Siklos^®

• Tailored weight-adjusted dosing in 50mg increments without the need for compounding
• As the patient grows, Siklos^® allows for flexible dosing based on body weight, blood count, and clinical response.
• Follows throughout the patient’s treatment journey and various stages of growth, and now, the patient can continue taking Siklos^® into adulthood.
• Dissolvable in water for oral administration
• Siklos^® is contraindicated in patients who have demonstrated a previous hypersensitivity to hydroxyurea or any other component of its formulation.

Start Early, Stay the Course, and Switch to Siklos^®

• Start Early:

  In pediatric patients 2 years of age and older with sickle cell anemia with recurrent moderate to severe painful crises, starting Siklos^® can help reduce the frequencies of these crises and reduce the need for blood transfusions.

• Stay the Course into Adulthood:

  Siklos^® can now accompany pediatric patients into adulthood so there is no need to change medications as an adult.

• Switch your Growing Pediatric Patients to Siklos^®:

  If patients are 2 years of age or older and already on hydroxyurea, Siklos^® can accompany your patients along their treatment journeys by providing a safe and effective dissolvable dosing regimen without the need for compounding.

• Transition Growing/Teenage Patients to Siklos^®:

  Siklos^® 100 mg scored and 1,000 mg scored tablets provide tailored weight-adjusted dosing in increments as low as 50 mg. Transition your patients to Siklos^® when they need an adjustment in their Hydroxyurea dosage.

• The most common adverse reactions to Siklos^® (> 10%) include infections and myelosuppression.

Switch to Siklos^® Considerations

• Convenience
  • No refrigeration required
  • No compounding necessary
  • Longer shelf life versus compounded formulations
    • 3 years unopened and 3 months if tablet is broken
  • Dissolvable in minimal volume – 5mL of water on a spoon
  • Siklos^® tablets should be taken once daily, at the same time each day, with a glass of water
• Administration
  • Available in 100 mg and 1,000 mg - scored tablets
  • Tailored weight-based dosing
• Available for Adults
  • Siklos^® can accompany patients along their treatment journeys into adulthood as Siklos^® is now indicated for adults.
• Medicaid and Commercial Insurance Coverage

• Siklos^® is a cytotoxic drug. Follow applicable special handling and disposal procedures.

Dosage Adjustment

Daily dose should be adjusted based on patient body weight and clinical response.

• Starting dose is 20 mg per kg per day.
• A maximum dose of 35 mg/kg/day may be justified and administered under close monitoring of blood counts.

Dosing Recommendation Based on Blood Count:

Siklos is available in 100 mg and 1,000 mg tablets. The 100 mg tablets have 1 score line and can be split into 2 parts (each 50 mg). The 1,000 mg tablets have 3 score lines and can be split into 4 parts (each 250 mg). Therefore, the two strengths can be used to deliver doses of 1,000 mg, 750 mg, 500 mg, 250 mg, 100 mg, 50 mg and combinations thereof. Calculate the rounded doses to the nearest 50 mg or 100 mg strength based on clinical judgment.

Patients and/or caregivers must be able to follow directions regarding drug administration and patient monitoring and care.

Fetal hemoglobin (HbF) levels may be used to evaluate the efficacy of Siklos^® in clinical use. Obtain HbF levels every three to four months. Monitor for an increase in HbF of at least two-fold over the baseline value.

Contraindications

Siklos^® is contraindicated in patients who have demonstrated a previous hypersensitivity to hydroxyurea or any other component of its formulation.

Warnings and Precautions

• Myelosuppression:

  Hydroxyurea causes severe myelosuppression. Do not initiate treatment with hydroxyurea in patients if bone marrow function is markedly depressed. Bone marrow suppression may occur, and leukopenia is generally its first and most common manifestation. Thrombocytopenia and anemia occur less often, and are seldom seen without a preceding leukopenia.

  Some patients, treated at the recommended initial dose of 15 mg/kg/day in adults or 20 mg/kg/day in children, have experienced severe or life-threatening myelosuppression. Due to the change in body weight requiring modification of daily dose, pediatric patients have an increased risk of myelosuppression at the time of dose adjustment.

  Evaluate hematologic status prior to and every two weeks during treatment with SIKLOS. Provide supportive care and modify dose or discontinue SIKLOS as needed. Recovery from myelosuppression is usually observed within 15 days when therapy is interrupted. Resume therapy after interruption at a lower dose.

• Malignancies:

  Hydroxyurea is a human carcinogen. In patients receiving long-term hydroxyurea for myeloproliferative disorders (a condition for which Siklos is not approved), secondary leukemia has been reported. Leukemia secondary to long-term hydroxyurea has also been reported in patients with sickle cell disease. Leukemia has also been reported in patients with sickle cell disease and no prior history of treatment with hydroxyurea.

  Skin cancer has also been reported in patients receiving long-term hydroxyurea. Advise protection from sun exposure and monitor for the development of secondary malignancies.

• Embryo-Fetal Toxicity:

  Based on the mechanism of action and findings in animals, SIKLOS can cause fetal harm when administered to a pregnant woman. Hydroxyurea was embryotoxic and teratogenic in rats and rabbits at doses 0.8 times and 0.3 times, respectively, the maximum recommended human daily dose on a mg/m2 basis. Advise pregnant women of the potential risk to a fetus.

  Advise females of reproductive potential to use effective contraception during and after treatment with SIKLOS for at least 6 months after therapy. Advise males of reproductive potential to use effective contraception during and after treatment with SIKLOS for at least 6 months after therapy.

• Vasculitic Toxicities (Including Leg Ulcers):

  Cutaneous vasculitic toxicities, including vasculitic ulcerations and gangrene, have occurred in patients with myeloproliferative disorders during therapy with hydroxyurea. These vasculitic toxicities were reported most often in patients with a history of, or currently receiving, interferon therapy. Due to potentially severe clinical outcomes for the cutaneous vasculitic ulcers reported in patients with myeloproliferative disease (a condition for which SIKLOS is not approved), treatment with SIKLOS should be discontinued and/or its dose reduced if cutaneous vasculitic ulcerations develop. Rarely, ulcers are caused by leukocytoclastic vasculitis.

  Avoid use of SIKLOS in patients with wounds on the legs (leg ulcers).

• Risks with Concomitant Use of Antiretroviral Drugs:

  Pancreatitis, hepatotoxicity, and peripheral neuropathy have occurred when hydroxyurea was administered concomitantly with antiretroviral drugs, including didanosine and stavudine.

• Risks with Concomitant Use of Live Virus Vaccine:

  Avoid use of live virus vaccine in patients taking SIKLOS. Concomitant use of hydroxyurea with a live virus vaccine may potentiate the replication of the vaccine virus and/or may increase the adverse reactions of the vaccine virus and result in severe infections. Patient’s antibody response to vaccines may be decreased. Consider consultation with a specialist.

• Macrocytosis

  SIKLOS may cause macrocytosis, which is self-limiting, and is often seen early in the course of treatment. The morphologic change resembles pernicious anemia, but is not related to vitamin B12 or folic acid deficiency. This may mask the diagnosis of pernicious anemia. Prophylactic administration of folic acid is recommended.

• Test Interference

  Interference with Uric Acid, Urea, or Lactic Acid Assays is possible, rendering falsely elevated results of these in patients treated with hydroxyurea.

• Hemolytic Anemia

  Cases of hemolytic anemia in patients treated with hydroxyurea for myeloproliferative diseases have been reported. Patients who develop acute jaundice or hematuria in the presence of persistent or worsening of anemia should have laboratory tests evaluated for hemolysis (e.g., measurement of serum lactate dehydrogenase, haptoglobin, reticulocyte, unconjugated bilirubin levels, urinalysis, and direct and indirect antiglobulin [Coombs] tests). In the setting of confirmed diagnosis of hemolytic anemia not related to the disease and in the absence of other causes, discontinue SIKLOS.

Administration

Siklos^® should be taken once daily, at the same time every day, with a glass of water. For patients who are not able to swallow the tablets whole, they can be dispersed immediately before use in a small quantity of water in a teaspoon.

Siklos^® is a cytotoxic drug.

Siklos^® tablets must be handled with care.

View and print Handling and Breaking Instructions

View and print Dissolving Instructions

See how a Siklos^® tablet dissolves in water

Patient Counseling Information

Advise patient or caregiver to read the FDA-approved patient labeling: Instructions for Use and Medication Guide.

• There is a risk of myelosuppression. Emphasize the importance of monitoring blood counts every two weeks throughout the duration of therapy to patients taking Siklos^®. Please read Warnings and Precautions in Section 5 of PI. Advise patients to report signs and symptoms of infection or bleeding immediately to their HCP or, in case of emergency, to call 911.
• Advise patients that there is a risk of cutaneous vasculitic toxicities and secondary malignancies including leukemia. Advise use of sun protection. Please read Warnings and Precautions in Section 5 of PI.
• Advise females of reproductive potential of the potential risk to a fetus should they become pregnant while taking Siklos^®. Advise patients to inform their healthcare provider of a known or suspected pregnancy. Advise females and males of reproductive potential to use contraception during and after treatment with Siklos^® for at least 6 months after therapy.
• Advise females to discontinue breastfeeding during treatment with Siklos^®. See Section 8.2 of PI.
• Advise male patients of potential risk to fertility.
• Advise patients with HIV infection to contact their physician for signs and symptoms of pancreatitis, hepatic events and peripheral neuropathy. See Section 7.1 of PI.
• Because Siklos^® tablets are scored, advise patients on how to take Siklos^® properly.
• Where both strengths of Siklos^® (100 mg and 1,000 mg) are prescribed simultaneously, make sure that the patient and/or the parents or caregivers understand the prescription in order to avoid confusion.

References

1. Ferster, A. et al. Hydroxyurea for treatment of severe sickle cell anemia: a pediatric clinical trial. Blood 88, 1960-1964 (1996).
2. Ware et al. Hematology Am Soc Hematol Educ Program. 2015;2015:436-432.
3. Strouse et al. Pediatr Blood Cancer. 2012 August ; 59(2): 365–371.
4. Siklos^® (hydroxyurea) tablets, for oral use [Prescribing Information]. Addmedica, December 2021.