Siklos Side Effects

Generic name: hydroxyurea

Medically reviewed by Drugs.com. Last updated on Jul 20, 2023.

Note: This document contains side effect information about hydroxyurea. Some dosage forms listed on this page may not apply to the brand name Siklos.

Applies to hydroxyurea: oral capsule, oral tablet.

Serious side effects of Siklos

Along with its needed effects, hydroxyurea (the active ingredient contained in Siklos) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking hydroxyurea:

More common

• Black, tarry stools
• blood in the urine or stools
• chills
• cough
• fever
• hoarseness
• lower back or side pain
• painful or difficult urination
• pale skin
• pinpoint red spots on the skin
• sore throat
• ulcers, sores, or white spots in the mouth
• unusual bleeding or bruising
• unusual tiredness or weakness

Less common

• Blackening of the fingernails and toenails
• trouble breathing

Rare

• Confusion
• dizziness
• headache
• joint pain
• seeing, hearing, or feeling things that are not there
• seizures
• swelling of the feet or lower legs

Incidence not known

• Back, leg, or stomach pains
• bleeding gums
• bleeding under the skin
• blisters on the skin
• bluish or pale color on the skin of the fingers or toes
• chest tightness
• coldness of the fingers or toes
• crater-like lesions on the skin
• dark urine
• drowsiness
• fast heartbeat
• general body swelling
• hives, itching, skin rash
• irritation
• itching, pain, redness, or swelling on the leg
• joint stiffness or swelling
• loss of appetite
• muscle spasms (tetany) or twitching seizures
• nausea
• nosebleeds
• numbness or tingling of the fingers or toes
• pain in the fingers or toes
• sore on the leg
• swelling of the eyelids, face, lips, hands, or feet
• trembling
• trouble swallowing
• vomiting
• weight loss
• yellowing of the eyes or skin

Other side effects of Siklos

Some side effects of hydroxyurea may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

• Diarrhea
• dry skin

Less common

• Constipation
• redness of skin at the place of radiation
• weight gain

Incidence not known

• Absent, missed, or irregular menstrual periods
• bluish-brownish bands on the nails
• indigestion
• passing of gas
• stomach pain, fullness, or discomfort
• stopping of menstrual bleeding
• thinning or loss of hair

For Healthcare Professionals

Applies to hydroxyurea: compounding powder, oral capsule, oral tablet.

General

The more commonly reported adverse reactions among children have been infections and neutropenia. Among adults, hematologic, gastrointestinal symptoms, infections, headache, anorexia, and dry skin have been commonly reported.

Hematologic

Very common (10% or more): Neutropenia (13%)

Common (1% to 10%): Thrombocytopenia, anemia

Postmarketing reports: Hemolytic anemia, macrocytosis^[Ref]

Gastrointestinal

Common (1% to 10%): Nausea, upper abdominal pain, diarrhea, constipation

Postmarketing reports: Stomatitis, vomiting, gastrointestinal ulcer, oral mucositis, pancreatitis^[Ref]

Pancreatitis has occurred when hydroxyurea was administered concomitantly with antiretroviral drugs, including didanosine and stavudine.^[Ref]

Other

Common (1% to 10%): Fever, asthenia, pyrexia, fatigue, peripheral edema

Postmarketing reports: Chills, malaise^[Ref]

Dermatologic

Very common (10% or more): Dry skin (12%)

Common (1% to 10%): Skin ulcer, alopecia

Postmarketing reports: Skin ulceration, cutaneous lupus erythematosus, dermatomyositis-like skin changes, peripheral and facial erythema, nail hyperpigmentation, atrophy of skin and nails, scaling, violet papules, skin reactions (oral, ungula and cutaneous pigmentation), rash, melanonychia^[Ref]

Oncologic

Leukemia secondary to long-term hydroxyurea (the active ingredient contained in Siklos) 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.^[Ref]

Frequency not reported: Leukemia, skin cancers^[Ref]

Genitourinary

Common (1% to 10%): Urinary tract infection

Postmarketing reports: Azoospermia, oligospermia, amenorrhea, dysuria^[Ref]

Nervous system

Peripheral neuropathy has occurred when hydroxyurea (the active ingredient contained in Siklos) was administered concomitantly with antiretroviral drugs, including didanosine and stavudine.^[Ref]

Very common (10% or more): Headache (20%)

Common (1% to 10%): Dizziness

Frequency not reported: Peripheral neuropathy

Postmarketing reports: Drowsiness, convulsions^[Ref]

Hepatic

Uncommon (0.1% to 1%): Hepatotoxicity, hepatic enzyme increased, cholestasis, hepatitis

Frequency not reported: Both fatal and nonfatal hepatotoxicity have been reported in HIV-infected patients who received this drug in combination with antiretroviral agents^[Ref]

Respiratory

Common (1% to 10%): Cough, lung disorder, dyspnea, nasopharyngitis

Postmarketing reports: Diffuse pulmonary infiltrates, dyspnea, pulmonary fibrosis, interstitial lung disease, pneumonitis, alveolitis, allergic alveolitis^[Ref]

Metabolic

Common (1% to 10%): Vitamin D deficiency, other metabolic and nutrition disorders, weight gain, increased weight

Very rare (less than 0.01%): Tumor lysis syndrome

Postmarketing reports: Anorexia, severe hypomagnesemia^[Ref]

Psychiatric

Postmarketing reports: Hallucinations, disorientation^[Ref]

Renal

Postmarketing reports: Elevations in serum uric acid, blood urea nitrogen (BUN), and creatinine levels^[Ref]

Hypersensitivity

Drug-induced fever requiring hospitalization has been reported in the postmarketing period. It has been reported concurrently with gastrointestinal, pulmonary, musculoskeletal, hepatobiliary, dermatological or cardiovascular manifestations. Onset typically occurred within 6 weeks of initiation and resolved upon discontinuation of hydroxyurea (the active ingredient contained in Siklos) Upon re-administration fever reoccurred typically within 24 hours.

Postmarketing reports: Drug-induced fever

Immunologic

Common (1% to 10%): Viral infections, bacterial infections, influenza

Postmarketing reports: Systemic lupus erythematosus

Musculoskeletal

Common (1% to 10%): Arthralgia, back pain, extremity pain

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

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