Carbiroid

• Hyperthyroidism:
  Treatment of hyperthyroidism caused by Graves’ disease or toxic multinodular goiter.
  Used to reduce thyroid hormone synthesis before thyroid surgery or radioactive iodine therapy.
• Thyrotoxic Crisis (Thyroid Storm):
  Adjunctive therapy in severe thyrotoxicosis.
• Off-label Uses:
  Occasionally used in preparation for thyroidectomy and to control hyperthyroidism during pregnancy if propylthiouracil is not tolerated.

• Adults:
  Initial dose: 15–40 mg daily in divided doses (usually 15–20 mg three times daily).
  Maintenance dose: 5–15 mg daily once stable.
  Dose adjustments based on thyroid function tests every 4–6 weeks.
• Pediatrics:
  0.4–0.8 mg/kg/day divided into 2–3 doses.
• Elderly:
  Initiate at lower doses and titrate carefully; monitor thyroid function closely.
• Renal/Hepatic Impairment:
  Use caution; no specific dose adjustments recommended but monitor liver function.
• Administration Route:
  Oral tablets; taken with or without food.
• Duration:
  Usually several months to years depending on clinical response.

Carbimazole is a prodrug that is rapidly converted in vivo to methimazole, which inhibits thyroid peroxidase. This enzyme is crucial for iodination of tyrosine residues in thyroglobulin and coupling reactions necessary for thyroid hormone synthesis (T3 and T4). By inhibiting thyroid peroxidase, carbimazole reduces the production of active thyroid hormones, thus controlling hyperthyroidism symptoms.

• Absorption:
  Well absorbed orally, with peak plasma concentrations within 1–2 hours.
• Bioavailability:
  High oral bioavailability.
• Distribution:
  Widely distributed; crosses the placenta and appears in breast milk.
• Metabolism:
  Converted rapidly to active methimazole.
• Half-life:
  Methimazole half-life is approximately 6–13 hours.
• Elimination:
  Mainly excreted in urine as metabolites.

• Pregnancy:
  Category D. Potential risk of fetal hypothyroidism and goiter; use lowest effective dose if necessary. Propylthiouracil preferred during first trimester.
• Lactation:
  Crosses into breast milk in low amounts; usually considered compatible with breastfeeding at low doses with monitoring of infant thyroid function.

• Primary: Antithyroid agent
• Subclass: Thionamide derivative

• Known hypersensitivity to carbimazole, methimazole, or excipients.
• Severe bone marrow depression or agranulocytosis history.
• Pregnancy in the first trimester (prefer propylthiouracil).

• Risk of agranulocytosis and aplastic anemia; monitor for signs of infection or bleeding.
• Hepatotoxicity reported; monitor liver enzymes if symptoms arise.
• Hypothyroidism may occur with overtreatment; monitor thyroid function.
• Monitor for rash and allergic reactions.
• Use cautiously in patients with pre-existing liver or bone marrow disorders.

Common:

• Rash, pruritus
• Nausea, gastrointestinal upset
• Arthralgia
• Mild leukopenia

Serious/Rare:

• Agranulocytosis (may present with fever, sore throat)
• Hepatitis or cholestatic jaundice
• Vasculitis
• Lupus-like syndrome
• Hypothyroidism (if overdosed)

• May increase effect of anticoagulants (e.g., warfarin) requiring monitoring.
• Concomitant use with iodine-containing contrast agents can reduce efficacy.
• May interact with beta-blockers and thyroid hormone preparations.
• No significant CYP450 enzyme involvement.

• Regular blood count monitoring recommended during first 3 months of therapy due to risk of agranulocytosis.
• Recent guidelines recommend caution in pregnancy; prefer propylthiouracil in early pregnancy and switch to carbimazole thereafter.
• Monitoring protocols emphasize individualized dose adjustments based on thyroid function tests.

• Store at 20°C to 25°C (68°F to 77°F).
• Protect from moisture and light.
• Keep container tightly closed.
• Keep out of reach of children.