Schedule H

Oral

Formulation Type Strengths Available

Carbidopa Monotherapy Tablet NOT AVAILABLE in India as standalone product for routine prescribing

Fixed-Dose Combinations (Carbidopa + Levodopa) 10 mg + 100 mg; 25 mg + 100 mg; 25 mg + 250 mg

Controlled-Release Tablets (Carbidopa + Levodopa) 25 mg + 100 mg; 50 mg + 200 mg

Dispersible/ODT Tablets (Carbidopa + Levodopa) 25 mg + 100 mg; 25 mg + 250 mg

Important: Carbidopa is NOT marketed as monotherapy in India. It is available exclusively in fixed-dose combinations with Levodopa. The Carbidopa component inhibits peripheral decarboxylation of Levodopa, thereby enhancing its CNS bioavailability and reducing peripheral adverse effects.

INDICATIONS + DOSING — FOR CLINICIAN USE ONLY

Primary Indications (Approved / Standard in India)

1. Idiopathic Parkinson's Disease

Carbidopa is always prescribed in combination with Levodopa.

Parameter Carbidopa + Levodopa (Fixed-Dose Combination)

Starting dose Carbidopa 25 mg + Levodopa 100 mg twice daily

Titration Increase by one tablet (25/100 mg) every 3–7 days based on clinical response and tolerability

Usual maintenance dose Carbidopa 75–150 mg/day + Levodopa 300–600 mg/day in 3–4 divided doses

Maximum dose Carbidopa 200 mg/day (with Levodopa up to 800–1000 mg/day)

Clinical Notes:

• Minimum Carbidopa requirement: 70–100 mg/day is essential to achieve adequate peripheral decarboxylase inhibition

• Administer 30–60 minutes before meals for optimal Levodopa absorption

• If initiating with lower doses due to GI sensitivity: Start with Carbidopa 10 mg + Levodopa 100 mg formulation

• Controlled-release formulations may be considered for motor fluctuations

1. Secondary Parkinsonism (Post-encephalitic, Carbon Monoxide Poisoning, Toxic Parkinsonism)

Parameter Dosing

Starting dose Same as idiopathic Parkinson's disease

Titration Individualised based on aetiology and specialist assessment

Usual maintenance dose Carbidopa 75–150 mg/day (with proportionate Levodopa)

Maximum dose As per specialist discretion

Clinical Notes:

• Specialist assessment mandatory before initiation

• Response may vary based on underlying aetiology

• Consider reversibility of cause

Secondary Indications — Adults (Off-label)

Not applicable. Carbidopa has no established off-label indications when used independently in India.

PAEDIATRIC DOSING (Specialist Only)

Primary Indications

1. Juvenile Parkinsonism (Juvenile-Onset Parkinson's Disease)

Parameter Dosing (Carbidopa component in FDC)

Starting dose Carbidopa 1 mg/kg/day in 2–3 divided doses (with proportionate Levodopa)

Titration Increase gradually every 5–7 days based on response and tolerability

Usual maintenance dose Carbidopa 2–4 mg/kg/day in divided doses

Maximum dose Carbidopa 200 mg/day (or approximately 5 mg/kg/day)

Safety Monitoring:

• Monitor for dyskinesias, behavioural changes

• Assess GI tolerance, growth parameters

• Regular neurological evaluation

1. Dopa-Responsive Dystonia (Segawa Syndrome)

Parameter Dosing

Starting dose Carbidopa 0.5–1 mg/kg/day with Levodopa 1–2 mg/kg/day

Titration Gradual increase every 5–7 days

Usual maintenance dose Low-dose therapy often sufficient; dramatic response expected

Maximum dose Carbidopa up to 4–5 mg/kg/day

Clinical Notes:

• Often dramatic and sustained response to low-dose therapy

• Lifelong treatment typically required

Secondary Indications — Paediatric (Off-label)

Indication Dose Duration Notes Evidence Basis

Other Dopa-responsive movement disorders Carbidopa 1–3 mg/kg/day in divided doses Long-term Specialist paediatric neurologist only; OFF-LABEL Case series, Indian specialist practice

Minimum Age: Not established for routine use. Use only under specialist paediatric neurologist supervision with confirmed diagnosis.

Mild to moderate impairment No dose adjustment required

• Narrow-angle glaucoma (uncontrolled)

• Known hypersensitivity to Carbidopa, Levodopa, or any excipient

• Concurrent use with non-selective monoamine oxidase inhibitors (Phenelzine, Tranylcypromine) — must discontinue MAO inhibitor at least 14 days before initiating Carbidopa-Levodopa

• History of malignant melanoma or suspicious undiagnosed skin lesions

• Pheochromocytoma (rare; theoretical concern)

• Cardiovascular disease (orthostatic hypotension, arrhythmias)

• History of myocardial infarction with residual ventricular arrhythmia

• Active peptic ulcer disease (risk of GI bleeding)

• Psychiatric illness or psychosis (may exacerbate hallucinations)

• History of seizures

• Chronic wide-angle glaucoma (monitor intraocular pressure)

• Bronchial asthma or chronic obstructive pulmonary disease

• Pre-existing dyskinesias

• Abrupt discontinuation (risk of neuroleptic malignant syndrome-like reaction)

• Elderly patients (increased sensitivity to adverse effects)

Parameter Details

Risk category Limited human data; animal studies inconclusive; not formally assigned a category in India

Preferred alternatives None established for Parkinson's disease in pregnancy

When it may be used Only if maternal benefit clearly outweighs fetal risk; requires specialist neurology and obstetric supervision

Monitoring Fetal growth parameters, maternal blood pressure, motor symptom control

Parameter Details

Compatibility Not recommended; insufficient safety data

Drug levels in milk Unknown; presumed low but not studied

Preferred alternatives Consider temporary cessation of breastfeeding if chronic therapy essential

Monitoring in infant Feeding difficulties, sedation, irritability, weight gain

Parameter Recommendation

Starting dose Lowest available combination (Carbidopa 10 mg + Levodopa 100 mg) once or twice daily

Titration Very gradual; increase dose every 7–14 days

Extra risks Orthostatic hypotension and falls, confusion, hallucinations, vivid dreams, increased sensitivity to dyskinesias, cognitive impairment

Special considerations Consider controlled-release formulations; ensure caregiver education for fall prevention

Interacting Drug Effect Recommendation

Non-selective MAO inhibitors (Phenelzine, Tranylcypromine, Isocarboxazid) Risk of hypertensive crisis Contraindicated; discontinue MAO inhibitor ≥14 days before starting

Typical antipsychotics (Haloperidol, Chlorpromazine) Dopamine receptor blockade antagonises therapeutic effect Avoid; if antipsychotic essential, consider Clozapine or Quetiapine under specialist supervision

Metoclopramide Central dopamine antagonist; worsens Parkinsonism Avoid; use Domperidone as alternative antiemetic

Methyldopa, Reserpine Deplete dopamine stores; reduce efficacy Avoid concomitant use

Iron salts Chelation reduces absorption of Levodopa Separate administration by ≥2 hours

Interacting Drug Effect Recommendation

Antihypertensives Additive hypotensive effect Monitor blood pressure; adjust antihypertensive if needed

Selegiline, Rasagiline (MAO-B inhibitors) Enhanced dopaminergic effect Can be combined; monitor for dyskinesias and hypotension

Anticholinergics (Trihexyphenidyl) May potentiate or mask Levodopa effects Use with caution; monitor for cognitive effects in elderly

High-protein meals Amino acid competition reduces Levodopa absorption Advise consistent protein intake; take medication before meals

Pyridoxine (Vitamin B6) Large doses (>10 mg/day) may reduce Levodopa efficacy Not clinically significant when Carbidopa ≥70 mg/day co-administered

Tricyclic antidepressants Potential for postural hypotension and arrhythmias Monitor blood pressure and cardiac status

Isoniazid May reduce Levodopa efficacy Monitor clinical response

• Nausea, vomiting, anorexia

• Orthostatic hypotension

• Dizziness, lightheadedness

• Drowsiness, fatigue

• Dyskinesias (choreiform, dystonic movements) — particularly with chronic use

• Headache

• Dry mouth

• Insomnia, vivid dreams

• Dark discolouration of urine or sweat (benign)

• Hallucinations, delusions, psychosis (especially in elderly or with cognitive impairment)

• Neuroleptic malignant syndrome-like reaction (with abrupt withdrawal)

• Severe dyskinesias

• Cardiac arrhythmias (rare)

• Upper GI bleeding (in patients with peptic ulcer history)

• Impulse control disorders (pathological gambling, hypersexuality, compulsive behaviours)

• Depression, suicidal ideation

• Hepatotoxicity (rare; monitor LFTs)

• Haemolytic anaemia (rare)

• Melanoma progression (rare; surveillance recommended)

Phase Parameters to Monitor

Baseline Blood pressure (lying and standing), complete psychiatric history, ECG (if cardiac history), skin examination for suspicious lesions, LFTs (if hepatic concerns), renal function

After initiation / dose change Orthostatic blood pressure weekly during titration, motor response, dyskinesias, neuropsychiatric symptoms (hallucinations, confusion)

Long-term Motor fluctuations (wearing-off, on-off), psychiatric status, impulse control behaviours, periodic skin surveillance for melanoma, LFTs annually, blood pressure

Brand Name Manufacturer Composition (Carbidopa + Levodopa)

Syndopa Sun Pharma 10/100, 25/100, 25/250 mg

Syndopa Plus Sun Pharma 25/100 mg

Syndopa CR Sun Pharma 50/200 mg (controlled-release)

Tidomet Intas 10/100, 25/100, 25/250 mg

Tidomet Plus Intas 25/100 mg

Tidomet LS Intas 10/100 mg

Antipark Various 25/100, 25/250 mg

Levopa-C Micro Labs Various strengths

Sinemet MSD (limited availability) 10/100, 25/100, 25/250 mg

Note: Carbidopa monotherapy is NOT AVAILABLE in India. All listed brands are Carbidopa-Levodopa fixed-dose combinations.

Note: Carbidopa-Levodopa FDC is included in NLEM India 2022; prices regulated under NPPA/DPCO for scheduled formulations. Lower prices available through Jan Aushadhi and government supply channels.

• Carbidopa is never used alone — always prescribe as a fixed-dose combination with Levodopa. Carbidopa has no therapeutic effect on Parkinsonism by itself.

• Ensure adequate Carbidopa dosing — minimum 70–100 mg/day of Carbidopa is required to effectively block peripheral dopa decarboxylase and prevent peripheral conversion of Levodopa.

• Protein timing matters — high-protein meals compete with Levodopa absorption; advise patients to maintain consistent protein intake and take medication 30–60 minutes before meals.

• "Start low, go slow" in elderly — this population is particularly susceptible to orthostatic hypotension, falls, and neuropsychiatric adverse effects.

• Never withdraw abruptly — sudden discontinuation can precipitate neuroleptic malignant syndrome-like reaction; always taper gradually.

• Screen for impulse control disorders — counsel patients and caregivers to report pathological gambling, hypersexuality, or compulsive shopping behaviours.

Carbidopa; Levodopa; Parkinson's disease; dopa decarboxylase inhibitor; DDCI; antiparkinsonian; movement disorder; Schedule H; NLEM India; elderly-caution

RxIndia v1.0 — 11 Jun 2025

• CDSCO approved product inserts

• Indian Pharmacopoeia

• NLEM India 2022

• API Textbook of Medicine

• AIIMS Delhi Neurology Protocols

• Goodman & Gilman's The Pharmacological Basis of Therapeutics

• Harrison's Principles of Internal Medicine, 21st edition

• Indian specialist neurology practice