Last Updated: June 25, 2026

CLINICAL TRIALS PROFILE FOR CARBIDOPA; LEVODOPA


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505(b)(2) Clinical Trials for CARBIDOPA; LEVODOPA

This table shows clinical trials for potential 505(b)(2) applications. See the next table for all clinical trials
Trial Type Trial ID Title Status Sponsor Phase Start Date Summary
New Formulation NCT00640159 ↗ Tolerability and Efficacy of Switch From Oral Selegiline to Orally Disintegrating Selegiline (Zelapar) in Patients With Parkinson's Disease Completed Baylor College of Medicine Phase 4 2007-01-01 Parkinson's disease (PD) is a progressive neurodegenerative disease. Symptomatic therapy is primarily aimed at restoring dopamine function in the brain. Oral selegiline in conjunction with L-dopa has been a mainstay of therapy for PD patients experiencing motor fluctuations for many years. The mechanisms accounting for selegiline's beneficial adjunctive action in the treatment of PD are not fully understood. Inhibition of monoamine oxidase (MAO) type B (MAO-B) activity is generally considered to be of primary importance. Oral selegiline has low bio-availability and is typically dosed BID, for a total of 5-10 mg daily. Recently, the FDA approved a new orally disintegration tablet (ODT) formulation of selegiline, called ZelaparTM. This new formulation utilizes Zydis technology to dissolve in the mouth, with absorption through the oral mucosa, thereby largely bypassing the gut and avoiding first pass hepatic metabolism. This allows more active drug to be delivered at a lower dose. Consequently, Zelapar is dosed once-daily, up to 2.5 mg per day. There are no empirical data indicating whether the use of the new approved formulation of selegiline ODT (Zelapar) is superior or preferred by patients compared to traditional oral selegiline. It is believed that clinical efficacy will be preserved or enhanced, by delivering more active drug, with improved patient preference for the ODT formulation due to the once-daily dosing . The effectiveness of orally disintegrating selegiline as an adjunct to carbidopa/levodopa in the treatment of PD was established in a multicenter randomized placebo-controlled trial (n=140; 94 received orally disintegrating selegiline, 46 received placebo) of three months' duration. Patients randomized to orally disintegrating selegiline received a daily dose of 1.25 mg for the first 6 weeks and a daily dose of 2.5 mg for the last 6 weeks. Patients were all treated with levodopa and could additionally have been on dopamine agonists, anticholinergics, amantadine, or any combination of these during the trial. At 12 weeks, orally disintegrating selegiline-treated patients had an average of 2.2 hours per day less "OFF" time compared to baseline. Placebo treated patients had 0.6 hours per day less "OFF" time compared to baseline. These differences were significant (p < 0.001). Adverse events were very similar between drug and placebo.
New Combination NCT01766258 ↗ Efficacy and Safety Proof of Concept Study in Patients With Parkinson's Disease and End-of-dose Motor Fluctuations Completed Orion Corporation, Orion Pharma Phase 2 2011-05-01 The primary objective of the study is to assess the efficacy, carbidopa dose response and safety of ODM-101, a new combination of levodopa, carbidopa and entacapone in the treatment of Parkinson's disease (PD) patients with end-of-dose motor fluctuations.
>Trial Type >Trial ID >Title >Status >Phase >Start Date >Summary

All Clinical Trials for CARBIDOPA; LEVODOPA

Trial ID Title Status Sponsor Phase Start Date Summary
NCT00086294 ↗ ACP-103 to Treat Parkinson's Disease Completed National Institute of Neurological Disorders and Stroke (NINDS) Phase 2 2004-06-25 This study will evaluate the effects of an experimental drug called ACP-103 on Parkinson's disease symptoms and on dyskinesias (involuntary movements) that develop as a result of long-term levodopa treatment. ACP-103 changes the spread of certain brain signals that are affected in patients with Parkinson's disease. Patients with relatively advanced Parkinson's disease and dyskinesias who are between 30 and 80 years of age may be eligible for this study. Candidates are screened with a complete medical history and physical examination, neurological evaluation, blood and urine tests, and electrocardiogram (ECG). A brain magnetic resonance imaging (MRI) scan, CT scan, and chest x-ray may be done if medically indicated. Patients enrolled in the study will, if possible, stop taking all antiparkinsonian medications for one month (2 months for Selegiline) before the study begins and throughout its duration. Exceptions are Sinemet (levodopa/carbidopa), Mirapex (pramipexole) and Requip (ropinirole). Levodopa Dose Finding After the screening evaluations, patients are admitted to the NIH Clinical Center for 2 to 3 days to undergo a levodopa "dose-finding" procedure. For this test, patients stop taking Sinemet and instead have levodopa infused through a vein. During the infusion, the drug dose is increased slowly until either 1) parkinsonian symptoms improve, 2) unacceptable side effects occur, or 3) the maximum study dose is reached. Side effects are monitored closely during the infusions, and parkinsonian symptoms are evaluated frequently during and after the infusions. The infusions usually begin early in the morning and continue until evening. Once the infusion is finished, patients resume taking their regular oral Sinemet dose. The infusions are repeated once a week during 1-day inpatient evaluations. Treatment Patients are randomly assigned to take either ACP-103 followed by placebo (a look-alike pill with no active ingredient) once a week for 10 weeks or vice versa (placebo followed by ACP-103). Patients are admitted to the Clinical Center for each dose. During this admission they have a brief medical examination, blood and urine tests, ECG, and review of symptoms or changes in their condition. They also have an infusion of levodopa (see above) at the previously determined optimal rate. Parkinsonism symptoms and dyskinesias are evaluated every 30 minutes for about 6 hours. At the end of the infusions and ratings, patients are discharged home with their regular Parkinson's medications until the following visit. Two weeks after their final dose of ACP-103 or placebo, patients are contact by telephone for a follow-up safety check. At that time, the investigator may ask the patient to return to the clinic for closer evaluation.
NCT00099268 ↗ Efficacy and Safety of Carbidopa/Levodopa/Entacapone in Patients With Parkinson's Disease Requiring Initiation of Levodopa Therapy Completed Orion Corporation, Orion Pharma Phase 3 2004-09-01 The CELC200A2401 study has been designed in order to evaluate the hypothesis that administering the combination carbidopa/levodopa/entacapone at the time that levodopa therapy is initiated results in a decrease in the risk of the development of motor complications for patients with Parkinson's disease.
NCT00099268 ↗ Efficacy and Safety of Carbidopa/Levodopa/Entacapone in Patients With Parkinson's Disease Requiring Initiation of Levodopa Therapy Completed Novartis Pharmaceuticals Phase 3 2004-09-01 The CELC200A2401 study has been designed in order to evaluate the hypothesis that administering the combination carbidopa/levodopa/entacapone at the time that levodopa therapy is initiated results in a decrease in the risk of the development of motor complications for patients with Parkinson's disease.
NCT00125567 ↗ Stalevo in Early Wearing-Off Patients Completed Orion Corporation, Orion Pharma Phase 4 2005-08-01 The purpose of this study is to demonstrate in patients with Parkinson's disease that, when compared to levodopa/carbidopa, Stalevo will delay the time from initiation of study drug to the time an increase in antiparkinsonian medication is required due to inadequately controlled parkinsonian symptoms.
>Trial ID >Title >Status >Phase >Start Date >Summary

Clinical Trial Conditions for CARBIDOPA; LEVODOPA

Condition Name

Condition Name for CARBIDOPA; LEVODOPA
Intervention Trials
Parkinson's Disease 72
Parkinson Disease 39
Advanced Parkinson's Disease 9
Parkinson's Disease (PD) 9
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Condition MeSH

Condition MeSH for CARBIDOPA; LEVODOPA
Intervention Trials
Parkinson Disease 141
Depression 7
Dyskinesias 7
Depressive Disorder 6
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Clinical Trial Locations for CARBIDOPA; LEVODOPA

Trials by Country

Trials by Country for CARBIDOPA; LEVODOPA
Location Trials
United States 565
Italy 42
Canada 40
Germany 39
Spain 33
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Trials by US State

Trials by US State for CARBIDOPA; LEVODOPA
Location Trials
California 39
Florida 35
New York 30
Illinois 30
Texas 29
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Clinical Trial Progress for CARBIDOPA; LEVODOPA

Clinical Trial Phase

Clinical Trial Phase for CARBIDOPA; LEVODOPA
Clinical Trial Phase Trials
PHASE4 3
PHASE2 1
PHASE1 2
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Clinical Trial Status

Clinical Trial Status for CARBIDOPA; LEVODOPA
Clinical Trial Phase Trials
Completed 132
Recruiting 18
Not yet recruiting 12
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Clinical Trial Sponsors for CARBIDOPA; LEVODOPA

Sponsor Name

Sponsor Name for CARBIDOPA; LEVODOPA
Sponsor Trials
Bial - Portela C S.A. 13
Impax Laboratories, LLC 13
IMPAX Laboratories, Inc. 12
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Sponsor Type

Sponsor Type for CARBIDOPA; LEVODOPA
Sponsor Trials
Industry 163
Other 122
NIH 19
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Carbidopa/Levodopa Clinical Trials Update, Market Analysis, and Exclusivity Outlook (2026)

Last updated: May 21, 2026

Carbidopa/levodopa remains the central long-term symptomatic therapy for Parkinson’s disease motor symptoms and is sold in multiple branded and generic immediate-release and extended-release formats. Patent exclusivity for specific formulations and delivery systems is fragmented by product line and dosage form, while core API-level protection is largely out of the current protection window. Commercial growth is driven more by depth of penetration (treatment adherence and switching among formulations) than by new mechanism innovation.

This update summarizes (1) what is in active clinical testing as of the latest registries and public results, (2) what is likely to move the competitive and regulatory needle, and (3) market sizing and projection drivers across major geographies and dosage forms.


What clinical trials are running for carbidopa/levodopa right now?

Active trial programs for carbidopa/levodopa cluster into four buckets: alternative delivery systems, improved pharmacokinetics and “on-state” durability, pediatric or expanded indication work, and combination strategies (usually adding adjuncts while keeping carbidopa/levodopa as the backbone).

Delivery system and pharmacokinetic optimization

These trials aim to reduce OFF time, smooth plasma peaks, and improve adherence versus standard immediate-release (IR) or extended-release (ER) oral dosing.

Common trial designs include:

  • single or multiple-dose pharmacokinetic comparisons of new formulations versus standard-of-care carbidopa/levodopa IR or ER
  • randomized crossovers measuring “time to peak” and Cmax variability
  • clinical endpoints where feasible: motor fluctuations, dyskinesia scores, and patient-reported mobility

Modified-release oral regimens

Programs for modified-release oral products continue, often focusing on:

  • reduced pill burden via once- or twice-daily dosing
  • improved trough levels to reduce nighttime or early morning OFF periods

Device-assisted or advanced administration

Carbidopa/levodopa is also tested in programs that explore continuous or semi-continuous delivery concepts, typically to reduce fluctuation and rescue dosing needs.

Trials in special populations

Smaller studies target:

  • elderly cohorts and frailty management
  • caregiver-administered dosing schedules
  • adherence and tolerability in real-world-like settings

Which late-stage carbidopa/levodopa trials could change prescribing patterns?

The prescribing-impact candidates are those that shift either:

  1. OFF time and dyskinesia burden meaningfully versus comparator carbidopa/levodopa regimens, or
  2. ease-of-use and adherence outcomes enough to drive switches.

Featured clinical endpoints to watch

  • Change from baseline in OFF time (hours/day) in advanced Parkinson’s disease
  • Change in dyskinesia scores and severity-adjusted ON time
  • Time in therapeutic range proxies in pharmacokinetic studies
  • Treatment discontinuation rates due to tolerability or administration burden

Regulatory pathway risk that affects trial outcomes

Oral modified-release and combination programs face typical registrational hurdles:

  • statistically separating from historical comparators
  • demonstrating consistent benefit across baseline severity strata
  • aligning endpoint timing with pharmacodynamic onset

What is the current market for carbidopa/levodopa and how is it segmented?

Carbidopa/levodopa market segmentation is usually dominated by:

  • immediate-release tablets/capsules (largest base)
  • extended-release oral products (meaningful share, often used for motor smoothing)
  • specialized delivery formats with premium pricing (niche but stable in advanced disease management, depending on jurisdiction)

Key commercial drivers

  • Parkinson’s disease prevalence growth and aging demographics
  • Longer survival leading to increased cumulative dosing duration
  • Formulation switching to manage “wearing-off” and nocturnal symptoms
  • Generic penetration in IR dosage forms, with pricing compression and channel competition

Key headwinds

  • Generic price erosion in established IR products
  • Treatment churn away from older regimens toward newer controlled-release formats once formularies update
  • Adverse events burden influencing adherence (nausea, orthostatic hypotension, dyskinesia)

What is the 2026–2031 revenue projection for carbidopa/levodopa globally?

Projection direction is positive in absolute units, with mixed revenue growth depending on:

  • geography-specific generic penetration rates
  • sustained premium positioning of modified-release and advanced delivery formats
  • procurement and tender cycles in public health systems

Projection framework used in market models

Revenue growth usually decomposes into:

  • Volume growth: prevalence and persistence
  • Price: weighted average price driven by generic shares
  • Mix: shift from IR to ER or premium delivery formats
  • Compliance: persistence on therapy and dose intensification in later disease stages

Expected base-case market trajectory

  • Global revenue: low-to-mid single-digit CAGR is the typical range for mature dopamine replacement categories
  • US: stable units with continued competitive pricing pressure in IR; mix benefit supports the overall revenue line
  • EU5: similar dynamics with tender-driven pricing; modified-release mix varies by national formularies

(Quantitative forecast figures are not provided here because this requires up-to-date market-sizing datasets by payer geography and product-level revenue, which are not available within the provided input constraints.)


Which companies compete in carbidopa/levodopa and how does their positioning differ?

Competitive landscape

Carbidopa/levodopa competes across:

  • large generic manufacturers (high volume, low price)
  • brands and branded generics in ER and modified-release segments
  • manufacturers with niche portfolios targeting advanced Parkinson’s disease and delivery-system differentiation

Positioning by dosage form

  • IR: most exposed to generic commoditization
  • ER/modified-release: more resilient due to formulation-specific patents, regulatory exclusivities, and product differentiation
  • advanced delivery formats: higher margin potential, but concentrated patient usage and payer scrutiny

How strong is the patent estate for carbidopa/levodopa?

At an API level, carbidopa and levodopa were developed decades ago; the modern patent estate is mostly formulation, method-of-use, and manufacturing/process protection for specific dosage forms.

Patent estate components to check

  1. composition patents for specific ER matrices or particle engineering
  2. method-of-treatment patents for subsets of Parkinson’s disease symptom patterns
  3. manufacturing-process patents for controlled-release characteristics
  4. use-extension patents tied to dosing regimens or patient stratification

What typically limits estate strength

  • Many active ingredients patents are expired.
  • Reformulation patents can still matter, but enforcement is often product- and claim-specific.
  • Generic entry can be easier for standard IR equivalents, while ER and modified release can have higher barriers.

What formulations are protected by patents for carbidopa/levodopa?

Protection varies by product and jurisdiction, but the claim themes are typically:

  • controlled-release formulations (matrix, coating thickness, polymer blends)
  • enteric or sustained-release granulation processes
  • bioavailability and release-profile targets
  • dosing regimens and titration schedules for motor fluctuation mitigation

Which patents protect carbidopa/levodopa in the Orange Book?

Orange Book listings (for US FDA) are formulation- and application-specific. In practice, the most relevant Orange Book items for exclusivity and litigation are:

  • patents covering dosage form and release characteristics
  • patents covering methods of use if listed to an approved NDA

Without Orange Book identifiers and listed patents in the provided input, a claim-by-claim enumeration cannot be produced in a complete or accurate way.


When does carbidopa/levodopa lose exclusivity, and what does that mean for generics?

Exclusivity loss is product-line specific and depends on:

  • patent expiration (composition, formulation, and use)
  • regulatory exclusivity (application- and supplement-linked)
  • specific country patent prosecution outcomes

Generic entry risk split

  • IR generics: generally lower regulatory and IP barriers if no active formulation-specific protections remain for the specific labeled dosage form.
  • ER/modified release: higher risk of delay due to formulation patents and potential Paragraph IV disputes.

Are there Paragraph IV challenges for carbidopa/levodopa?

Paragraph IV litigation risk exists where Orange Book patents remain in force for specific branded ER or modified-release products. For standard IR tablet strengths, risk is often lower because:

  • multiple generic entries already exist
  • formulation patents are typically not covering the broad commodity equivalents anymore

A precise list of pending or settled Paragraph IV filings cannot be produced without the underlying Orange Book patent-by-patent and ANDA litigation dataset.


What biosimilar risk exists for carbidopa/levodopa?

None. Carbidopa/levodopa is a small-molecule combination drug, so the biosimilar framework does not apply.


What patent litigation affects carbidopa/levodopa right now?

Carbidopa/levodopa litigation, when present, is typically:

  • formulation and method-of-use claim disputes tied to branded ER or modified-release products
  • ANDA Paragraph IV actions against remaining Orange Book patents

A current litigation docket summary cannot be provided without litigation identifiers and case numbers, which are not included in the provided input.


How do controlled-release carbidopa/levodopa products compare clinically?

Clinical differences typically arise from:

  • release kinetics (time above therapeutic levels)
  • peak/trough management
  • fluctuation reduction and dyskinesia profiles in advanced disease

Decision criteria used by clinicians

  • baseline motor fluctuations and OFF-time burden
  • nocturnal symptoms and early morning wearing-off
  • pill burden tolerance and caregiver administration needs
  • renal and hepatic comorbidity and tolerability profiles

What manufacturing or IP barriers can block generic entry?

For modified-release oral products, the barriers are frequently:

  • proprietary controlled-release matrices and manufacturing controls
  • bioequivalence targets tied to narrow release profiles
  • combination of process know-how and formulation reproducibility

For IR products, the barriers are generally lower:

  • standard dissolution and bioequivalence targets are more readily met
  • the commercial market is already deep with substitutes

Key Takeaways

  • Carbidopa/levodopa remains a core Parkinson’s disease therapy with sustained demand driven by prevalence growth and long treatment duration.
  • Current trial activity concentrates on delivery-system refinements, pharmacokinetic smoothing, and clinical endpoints tied to OFF-time and motor fluctuations.
  • Revenue growth is likely to be modest and mix-driven rather than innovation-driven, with ongoing pricing pressure in immediate-release and more resilience in controlled/modified-release segments.
  • Patent and exclusivity protection is mostly formulation- and product-line specific; generic risk depends on whether any Orange Book-listed patents remain for the targeted dosage form.
  • Biosimilar risk is not applicable because carbidopa/levodopa is a small molecule combination.

FAQs

1) What endpoints matter most in advanced Parkinson’s carbidopa/levodopa trials?
Time spent in ON, OFF-time hours per day, dyskinesia severity, and discontinuation due to tolerability.

2) Do modified-release carbidopa/levodopa products reduce wearing-off versus immediate-release?
They aim to reduce fluctuation by smoothing exposure; the magnitude depends on release profile and baseline OFF-time.

3) Which dosage forms face the highest patent barriers to generic entry?
Extended-release and modified-release formulations with proprietary release characteristics and manufacturing controls.

4) Are there pediatric trials for carbidopa/levodopa?
Pediatric studies exist in targeted contexts but are generally smaller than adult Parkinson’s programs.

5) How should formularies treat carbidopa/levodopa when multiple generics exist?
Reimbursement and tender dynamics typically favor lower acquisition cost for IR, with controlled-release products favored when clinical pathways justify mix shifts.


References

  1. FDA. Orange Book: Approved Drug Products with Therapeutic Equivalence Evaluations. (Accessed 2026-05-21).
  2. ClinicalTrials.gov. Carbidopa; levodopa clinical studies. (Accessed 2026-05-21).
  3. EMA. European public assessment reports and product information for levodopa/carbidopa-containing medicinal products. (Accessed 2026-05-21).

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