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MEDICINE MONOGRAPH CODE: [6.2] ID: TIP-MED-000092

Carbimazole

Active Ingredient / Scientific Identity: Carbimazole • Class: Thioamide Antithyroid Agent (Prodrug Rapidly Converted in Vivo to Active Methimazole; Thyroid Peroxidase Inhibitor)

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THE INDIAN PHARMACIST — Educational Reference Sheet
Profile: Carbimazole ([6.2] | ID: TIP-MED-000092) • Last Reviewed: 2026-11-10
Source URL: https://theindianpharmacist.com/medicine/6-2-carbimazole/
Generic / Entity NameCarbimazole ([6.2])
Verified Indian Brands / RefGeneric Compendial Entry (No Commercial Brand Claimed)
Pharmacological ClassThioamide Antithyroid Agent (Prodrug Rapidly Converted in Vivo to Active Methimazole; Thyr
Available Dosage FormsOral Uncoated Tablets: 5 mg, 10 mg, 20 mg
Regulatory ClassificationSchedule H & Schedule G Prescription Drug ('Caution: It is dangerous to take this pre
Key Warning & Review DateRenal: No major dose adjustment required in mild-to-moderate CKD; monitor closely in severe renal failure. Hepatic: Clearance
Reviewed: 2026-11-10
Safety Matrix:⚖️ Legal Status: Schedule H & Schedule G Prescription Drug ('Caution:✔️ Standard Clinical Dispensing Precautions

1. Clinical & Scientific Overview

Carbimazole (TIP-MED-000092, Reference Code [6.2]) is classified under Thyroid, Pituitary, Adrenal & Hormonal Medicines (Ch 06) as a Thioamide Antithyroid Agent (Prodrug Rapidly Converted in Vivo to Active Methimazole; Thyroid Peroxidase Inhibitor). Within the Indian regulatory and compendial framework, it is governed under Schedule H & Schedule G Prescription Drug ('Caution: It is dangerous to take this preparation except under medical supervision' — Drugs Rules 1945).

Verified Indian Market Examples / Compendial Status:
Representative Indian Market Examples (Edition 2.7 Ch 06 [6.2], p. 72): Neo-Mercazole ( Abbott), Thyrocab (Macleods), Anti-Thyrox — Strengths & Dosage Forms: Oral Uncoated Tablets: 5 mg, 10 mg, 20 mg
Representative Indian Market Examples (Edition 2.7 Ch 06 [6.2], p. 72): Neo-Mercazole ( Abbott), Thyrocab (Macleods), Anti-Thyrox — Strengths & Dosage Forms: Oral Uncoated Tablets: 5 mg, 10 mg, 20 mg
Dosage Forms & Available Strengths:
Oral Uncoated Tablets: 5 mg, 10 mg, 20 mg
Routes: Oral / Parenteral / Topical as specified by formulation

3. Mechanism of Action & Pharmacodynamics

Thioamide Antithyroid Agent (Prodrug Rapidly Converted in Vivo to Active Methimazole; Thyroid Peroxidase Inhibitor) acting on target receptor/enzyme pathways in Thyroid, Pituitary, Adrenal & Hormonal Medicines (Ch 06): clinical efficacy is mediated via Thioamide Antithyroid Agent (Prodrug Rapidly Converted in Vivo to Active Methimazole; Thyroid Peroxidase Inhibitor) for Hyperthyroidism / thyrotoxicosis (Graves' disease, toxic multinodular goitre, toxic adenoma); pre-operative preparation before thyroidectomy; adjunct to radioactive iodine therapy..

4. Therapeutic Indications & Evidence-Supported Uses

  • Hyperthyroidism / thyrotoxicosis (Graves' disease, toxic multinodular goitre, toxic adenoma)
  • pre-operative preparation before thyroidectomy
  • adjunct to radioactive iodine therapy

🇮🇳 Jurisdiction & Indication Note: Indications and schedules reflect Indian compendial and regulatory records (CDSCO / Indian Pharmacopoeia & NFI / NLEM 2022). Where international reference labels (US FDA DailyMed / NCBI StatPearls) are cited for pharmacokinetic or mechanistic parameters, international approvals do not automatically imply CDSCO approval in India.

5. Educational Dosage Context, Formulations & Administration

Educational Dosing & Regimen Summary: General Adult Reference: Initial Blocking Phase: 15 mg to 40 mg daily (as a single daily dose or divided 8–12 hourly) for 4–8 weeks until euthyroid; Maintenance Phase: gradually reduced to 5 mg to 15 mg once daily for 12–18 months. (Note: 10 mg Carbimazole converts to ~6 mg active Methimazole). Follow endocrinologist prescription.

Administration & Meal Timing: With or without food (usually taken after meals to minimize mild gastric discomfort). | Once daily after breakfast (for maintenance doses ≤15 mg), or divided two to three times daily after meals during high-dose initiation.

6. Pharmacokinetics, Metabolism & Renal/Hepatic Adjustment

Absorption & Disposition:
Absorption, distribution, metabolism, and excretion follow class pharmacokinetic profile; verify patient renal/hepatic function.
Metabolism & Biotransformation:
Renal: No major dose adjustment required in mild-to-moderate CKD; monitor closely in severe renal failure. Hepatic: Clearance is reduced in hepatic impairment; use lowest effective dose and monitor LFTs closely.
Elimination & Renal Adjustment:
Renal: No major dose adjustment required in mild-to-moderate CKD; monitor closely in severe renal failure. Hepatic: Clearance is reduced in hepatic impairment; use lowest effective dose and monitor LFTs closely.
Hepatic Impairment Considerations:
Renal: No major dose adjustment required in mild-to-moderate CKD; monitor closely in severe renal failure. Hepatic: Clearance is reduced in hepatic impairment; use lowest effective dose and monitor LFTs closely.

7. Contraindications, Precautions & High-Risk Warnings

Contraindications & Red-Flag Precautions:
  • Contraindicated in history of carbimazole-induced agranulocytosis, severe bone marrow depression, acute pancreatitis, and severe cholestatic liver disease. Teratogenicity Warning: Crosses the placenta and causes congenital defects (aplasia cutis, choanal/oesophageal atresia) during the first trimester of pregnancy—switch to Propylthiouracil (PTU) before conception or during the 1st trimester!

Key Clinical Precautions: Renal: No major dose adjustment required in mild-to-moderate CKD; monitor closely in severe renal failure. Hepatic: Clearance is reduced in hepatic impairment; use lowest effective dose and monitor LFTs closely.

8. Adverse Effects Profile

Common & Mechanism-Related Adverse Effects:
  • Pruritic maculopapular skin rash/urticaria (3–5%), arthralgia, mild nausea, headache, transient benign leukopenia, alopecia.
  • Agranulocytosis (0.2–0.5% of patients, occurring mostly during the first 2–3 months of therapy: absolute neutrophil count <500/mcL presenting abruptly with high fever, severe sore throat, painful mouth ulcers, or chills—LIFE-THREATENING EMERGENCY!), cholestatic jaundice/hepatitis, acute pancreatitis, ANCA-positive vasculitis, over-treatment hypothyroidism.
Serious / Dose-Limiting Adverse Effects:
  • Monitor for severe hypersensitivity, organ toxicity, or dose-limiting adverse events.

9. Major Drug–Drug, Drug–Food & Drug–Herb Interactions

  • As hyperthyroidism resolves to euthyroidism, the hypermetabolic clearance of other drugs slows down: Warfarin sensitivity changes, and Serum Digoxin and Theophylline levels increase significantly as the patient becomes euthyroid (requiring dose reduction of digoxin/theophylline and beta-blockers)

10. Clinical Monitoring, Patient Counselling & Storage

Clinical & Laboratory Monitoring: Monitor clinical response, baseline renal/hepatic parameters, and relevant serum biomarkers.

Pharmacist Patient Counselling Points:

  • Patient Counselling Checklist: Mandatory Agranulocytosis Verbal & Written Warning: Instruct every patient starting Neo-Mercazole/Carbimazole: 'If you develop a sore throat, mouth ulcers, or fever—especially during the first 3 months—STOP taking the tablet immediately and visit the clinic that same day for an urgent Complete Blood Count (CBC) test before taking any more doses.' Also explain that clinical improvement takes 2–4 weeks because preformed thyroid hormone stored in the gland must first be depleted (a beta-blocker like propranolol is often given initially for rapid relief of tremors and palpitations).
  • Meal & Clock Timing Instruction: With or without food (usually taken after meals to minimize mild gastric discomfort). (Once daily after breakfast (for maintenance doses ≤15 mg), or divided two to three times daily after meals during high-dose initiation.)
  • Missed Dose Protocol: Take as soon as remembered on the same day; do not double.
  • Geriatric Dispensing Pearl: In elderly patients, hyperthyroidism often presents as 'apathetic thyrotoxicosis' (atrial fibrillation, unexplained weight loss, or heart failure without classic tremors or goitre). Monitor digoxin and anticoagulant doses closely as thyroid levels normalise.

Storage, Stability & Dispensing Safeguards: Store below 25°C–30°C in original moisture- and light-resistant packaging out of reach of children. Available forms: Oral Uncoated Tablets: 5 mg, 10 mg, 20 mg

11. Visual Pharmacology & Mechanism Diagram (svg-v339-01-adme-12-step-journey)

THE 12-STEP ORAL DRUG JOURNEY THROUGH THE HUMAN BODY (LADME) Note: IV bolus enters Step 6 directly (F = 100%); Sublingual & Transdermal routes bypass Step 4–5 Portal First-Pass Metabolism 1. Oral Administration • Tablet / Capsule swallowed • Gastric emptying to duodenum pH 1.5–3.5 (Stomach) 2. Disintegration & Dissolution • Tablet breaks into granules • API dissolves in GI fluid Noyes-Whitney Dissolution Rate 3. GI Epithelial Absorption • Crosses intestinal villi • Passive / Active / P-gp efflux Small Intestine (Large Surface Area) 4. Portal Circulation • Mesenteric veins → Portal vein • Delivers blood to liver sinusoids Pre-systemic Venous Conduit 5. First-Pass Metabolism • Gut & hepatic CYP450 extraction • High: GTN, Propranolol, Morphine Determines Bioavailability (F = f_a × (1-E_H)) 6. Systemic Circulation • Hepatic vein → IVC → Heart • Unbound vs Albumin-bound drug Only FREE drug is active 7–8. Tissue Distribution (Vd) • Capillary permeation to organs • Blood-Brain & Placental barriers Vd = Dose / C_0 (L or L/kg) 9. Target Site of Action • Receptors (GPCR, Ion channel) • Enzymes & Carrier Transporters Pharmacodynamic Effect (E_max, EC50) 10. Hepatic Biotransformation • Phase I (CYP450 Oxidation/Hydrolysis) • Phase II (Glucuronidation/Sulfation) Converts lipophilic drug → hydrophilic metabolite 11. Renal & Biliary Elimination • Nephron: Filtration + Secretion − Reabsorption • Biliary excretion & Enterohepatic recycling Total Clearance CL_tot = CL_renal + CL_hepatic 12. Excretion from the Body • Urine (Primary polar metabolite route) • Bile/Faeces, Expired Air, Sweat, Milk Elimination Half-Life t1/2 = (0.693 × Vd) / CL
svg-v339-01-adme-12-step-journey — 8.1 Complete 12-Step Journey of an Orally Administered Drug (ADME): Figure 8.1: The 12-step physiological journey of a typical orally administered solid dosage form through Liberation, Absorption, Distribution, Metabolism, and Excretion (LADME). Note: Parenteral (IV), sublingual, and inhalational routes bypass gastrointestinal absorption and/or hepatic first-pass metabolism.

12. Authoritative References, Regulatory Sources & Editorial Disclaimer

Primary Compendial & Guideline Reference: Indian Pharmacist Desk Reference — Professional Edition 2.7 (2026–27) • Ch 06 [6.2] (p. 72)

Official Verification Portals: Indian Pharmacopoeia Commission (IPC) & National Formulary of India (NFI) • Central Drugs Standard Control Organization (CDSCO) • Ministry of Health & Family Welfare — NLEM 2022 • NCBI Bookshelf / StatPearls Pharmacology Reference • DailyMed (US FDA Official Prescribing Reference)

Last Medically & Pharmaceutically Reviewed: 2026-11-10 • Verification Status: HANDBOOK_SOURCE_CONTENT

Educational & Clinical Disclaimer: This reference profile is published solely for pharmacy education, academic study, and professional clinical reference. It does not substitute for patient-specific clinical judgement, qualified specialist oncology/medical supervision, or official CDSCO/IP prescribing information. Never self-medicate with prescription, Schedule H/H1/X, NDPS, or oncology medicines.

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Educational Reference Notice: This printout from THE INDIAN PHARMACIST (https://theindianpharmacist.com/medicine/6-2-carbimazole/, Last Reviewed: 2026-11-10) is an educational reference sheet for students and healthcare learners. It is NOT an official prescribing guideline or patient-specific treatment order.