SINEMET TABLETS 25\250MG 20TAB

Indications

Approved Uses

Treatment of Parkinson's disease, post-encephalitic parkinsonism, and parkinsonism following carbon monoxide or manganese intoxication.

Dosage & Administration

Dosing by Condition

Parkinson’s disease (immediate-release): Levodopa-naïve: start 25/100 mg one tablet three times daily; increase by 1 tablet/day or every other day as needed. Conversion from levodopa alone: start at ~20-25% of prior levodopa daily dose after ≥12-hour washout. Usual maximum: keep carbidopa ≤200 mg/day (most patients need ≥70-100 mg/day carbidopa); total daily tablets/levodopa are individualized rather than a single fixed tablet maximum.

Initial Dose

The initial recommended daily dose is one tablet of SINEMET 25/100 or 10/100 three or four times a day; SINEMET 25/250 is used when more levodopa is required

Maintenance Dose

1 tablet of carbidopa 25mg/levodopa 250mg three to four times daily, adjusted based on clinical response

Maximum Dose

Maximum commonly referenced for 25/250 strength: 8 tablets/day (carbidopa 200 mg + levodopa 2000 mg) in divided doses (individualized).

Children's Dosage

Not routinely recommended; if used, dosing must be individualized and determined by a specialist.

Dose Adjustment Notes

Titrate individually and slowly to response/tolerability; dyskinesias or hallucinations often require dose reduction. When switching from levodopa alone, stop levodopa at least 12 hours before starting and begin carbidopa/levodopa at ~20-25% of the prior daily levodopa dose (then titrate). No specific renal/hepatic adjustment is defined; use caution and monitor.

How to Take

Swallow the immediate-release tablet whole with water at evenly spaced intervals; may take with food if nausea occurs, but for best and most consistent effect avoid taking with high-protein meals and consider dosing 30-60 minutes before meals or 1-2 hours after meals.

Side Effects

Common Side Effects

Common: nausea, dizziness, orthostatic hypotension, dyskinesia, somnolence, confusion/hallucinations (especially in older adults), headache; constipation and dry mouth can occur.

Side Effect Frequency

Very common (>10%): dyskinesia, nausea. Common (1-10%): dizziness, orthostatic hypotension, vomiting, hallucinations, confusion, insomnia/sleep disturbance, headache. Less common/rare: impulse-control disorders, psychosis, arrhythmias, sudden sleep onset, neuroleptic malignant syndrome-like reaction with abrupt withdrawal, melanoma risk signal.

Safety & Warnings

Contraindications

Concomitant use with nonselective MAO inhibitors (or within 14 days of stopping), narrow-angle glaucoma, hypersensitivity to carbidopa/levodopa or excipients, and suspicious undiagnosed skin lesions or history of melanoma.

Warnings & Precautions

Warn/monitor for: sudden sleep onset and impaired driving, hallucinations/psychotic-like behavior, impulse control disorders, depression/suicidality, orthostatic hypotension (especially initiation/titration), dyskinesias (may require dose reduction), melanoma/skin monitoring, and NMS-like syndrome with abrupt withdrawal; use caution in significant cardiovascular disease and in renal/hepatic impairment.

Age Restriction

Safety and efficacy not established in patients <18 years; use in children/adolescents only if specialist-directed.

Driving Warning

May Cause Drowsiness

Drug Interactions

Drug Interactions

Key interactions: nonselective MAOIs (contraindicated; hypertensive crisis), dopamine antagonists/antipsychotics and metoclopramide (reduce effect/worsen parkinsonism), antihypertensives (additive orthostatic hypotension), iron salts (reduced absorption), isoniazid (reduced levodopa effect), tricyclic antidepressants (may increase dyskinesia/hypertension), and MAO-B inhibitors (additive dopaminergic effects; monitor).

Interaction Severity

MAJOR/contraindicated: non-selective MAO inhibitors (use within 14 days) due to hypertensive crisis risk. MODERATE: dopamine antagonists (e.g., antipsychotics, metoclopramide) reduce effect; antihypertensives increase orthostatic hypotension; iron salts reduce absorption; isoniazid may reduce levodopa effect. CAUTION: MAO-B inhibitors (selegiline/rasagiline) may increase dopaminergic adverse effects (generally manageable with monitoring).

Food Interaction

High-protein meals can reduce and delay levodopa absorption and clinical response; if fluctuations occur, separate doses from protein (e.g., take 30-60 minutes before or 1-2 hours after meals) or redistribute protein to later in the day; taking with a small low-protein snack is acceptable for nausea.

Special Populations

Children

Not routinely recommended; if used, dosing must be individualized and determined by a specialist.

Elderly

Start at lower doses and titrate slowly; elderly patients are more susceptible to orthostatic hypotension, confusion, hallucinations, and impulse control disorders; monitor closely

Liver Impairment

No specific dose adjustment defined; use with caution in hepatic impairment (especially severe) and monitor.

Storage & Patient Advice

Stopping the Medicine

Do not stop abruptly; taper gradually under prescriber supervision to avoid an NMS-like syndrome.

Overdose

Symptoms: nausea/vomiting, agitation/confusion, dyskinesias, hypotension or hypertension, tachycardia/arrhythmias; may include blepharospasm/muscle twitching. Management: urgent emergency care, supportive treatment with cardiac monitoring; consider GI decontamination if early; no specific antidote (pyridoxine is not reliably effective when carbidopa is present).

Patient Counseling

Take exactly as prescribed and do not stop abruptly; may take with food for nausea but separate from high-protein meals if response fluctuates; rise slowly to reduce dizziness/orthostasis; avoid driving/operating machinery until effects are known due to somnolence/sudden sleep; report dyskinesia, hallucinations/confusion, new or changing skin lesions, and impulse-control behaviors; harmless dark discoloration of urine/sweat/saliva may occur; review all medicines/supplements (notably iron and dopamine antagonists).

Monitoring Requirements

Monitor clinical response and motor fluctuations/dyskinesia; blood pressure (especially orthostatic); mental status (hallucinations, impulse-control disorders, sleep attacks); periodic hepatic, hematopoietic, cardiovascular, and renal function during long-term therapy; and regular skin examinations for melanoma.

Pharmacology

Mechanism of Action

Levodopa is a dopamine precursor that crosses the blood-brain barrier and is converted to dopamine in the CNS; carbidopa inhibits peripheral aromatic L-amino acid (DOPA) decarboxylase, reducing peripheral conversion of levodopa, increasing CNS availability, and decreasing peripheral adverse effects (e.g., nausea).

Onset of Action

Immediate-release onset is typically ~20-60 minutes (often 30-60 minutes); optimal regimen/overall benefit may require days to weeks of titration (and longer as disease and dosing are optimized).

Half-Life

Levodopa: ~1.5 hours when co-administered with carbidopa (vs ~0.5-1 hour alone); Carbidopa: ~1-2 hours.

Bioavailability

Levodopa oral bioavailability is variable and incomplete (commonly ~30% and increased when combined with carbidopa), and carbidopa bioavailability is also variable; a fixed value such as 'levodopa 99%' is not correct for oral tablets.

Metabolism

Levodopa: extensively metabolized by aromatic L-amino acid decarboxylase (AADC) to dopamine and by COMT to 3-O-methyldopa, with downstream MAO/aldehyde dehydrogenase metabolism of catecholamines; Carbidopa: limited metabolism (primarily to inactive metabolites) and acts as a peripheral AADC inhibitor.

Excretion

Primarily renal excretion: levodopa is excreted mainly in urine as metabolites (e.g., DOPAC/HVA and 3-O-methyldopa), with only a small fraction unchanged; carbidopa is excreted mainly in urine largely as metabolites with a smaller portion unchanged.

Product Information

Available Dosage Forms

For carbidopa/levodopa products: immediate-release tablet (e.g., SINEMET), extended-release tablet (e.g., SINEMET CR), orally disintegrating tablet (e.g., Parcopa), extended-release capsule (e.g., Rytary), and enteral suspension/intestinal gel for infusion (carbidopa/levodopa enteral). Inhalation powder is levodopa-only (not carbidopa/levodopa).

Composition per Dose

Each tablet: 250mg Levodopa, 25mg Carbidopa (as anhydrous).

OTC Alternatives

No OTC alternative

Controlled Substance

No

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