The human experience with intravenous levodopa

1) Shan H. Siddiqi, M.D., Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri, USA.

2) Natalia K. Abraham, M.D., School of Epidemiology, Public Health and Preventive Medicine, University of Ottawa, Ottawa, Ontario, Canada.

3) Christopher L. Geiger, M.D., Department of Internal Medicine, University of Washington, Seattle, Washington, USA.

4) Morvarid Karimi, M.D., Department of Neurology, Washington University School of Medicine, St. Louis, Missouri, USA.

5) Joel S. Perlmutter, M.D., Departments of Neurology, Radiology, and Anatomy & Neurobiology, Division of Biology and Biomedical Sciences, and Programs in Occupational Therapy and Physical Therapy, Washington University School of Medicine, St. Louis, Missouri, USA.

6) Kevin J. Black, M.D., Departments of Psychiatry, Neurology, Radiology, and Anatomy & Neurobiology, and Division of Biology and Biomedical Sciences, Washington University School of Medicine, St. Louis, Missouri, USA. ORCID 0000-0002-6921-9567

Address correspondence to Dr. Black at Campus Box 8134, 660 S. Euclid Ave., St. Louis, Missouri, USA, or

Copyright © 2015, the authors.

NOTE: This was an early draft of an article whose final published version now appears as:

Siddiqi SH, Abraham NK, Geiger CL, Karimi M, Perlmutter JS and Black KJ (2016) The Human Experience with Intravenous Levodopa. Front. Pharmacol. 6:307. doi: 10.3389/fphar.2015.00307



Objective: To compile a comprehensive summary of published human experience with levodopa given intravenously, with a focus on information required by regulatory agencies.

Background: While safe intravenous use of levodopa has been documented for over 50 years, regulatory supervision for pharmaceuticals given by a route other than that approved by the U.S. Food and Drug Administration (FDA) has become increasingly cautious. If delivering a drug by an alternate route raises the risk of adverse events, an investigational new drug (IND) application is required, including a comprehensive review of toxicity data.

Methods: Over 200 articles referring to intravenous levodopa (IVLD) were examined for details of administration, pharmacokinetics, benefit and side effects.

Results: We identified 144 original reports describing IVLD use in humans, beginning with psychiatric research in 1959-1960 before the development of peripheral decarboxylase inhibitors. At least 2781 subjects have received IVLD, and reported outcomes include parkinsonian signs, sleep variables, hormones, hemodynamics, CSF amino acid composition, regional cerebral blood flow, cognition, perception and complex behavior. Mean pharmacokinetic variables were summarized for 49 healthy subjects and 190 with Parkinson disease. Side effects were those expected from clinical experience with oral levodopa and dopamine agonists. No articles reported deaths or induction of psychosis.

Conclusion: At least 2781 patients have received i.v. levodopa with a safety profile comparable to that seen with oral administration.


Parkinson disease (PD), the second most common neurodegenerative disease, is associated with impairments in dopaminergic neurotransmission in the basal ganglia. Replacement of dopamine has been the cornerstone of treatment for PD. Because dopamine does not cross the blood-brain barrier (BBB), its immediate precursor levodopa (L-3,4-dihydroxphenylalanine, L-DOPA) is administered since it crosses the BBB (Birkmayer 2001, Hornykiewicz 1963, Cotzias 1967). Although purified levodopa was first ingested by mouth in 1913 (Roe 1997), when levodopa was first used for medical treatment in the late 1950s, it was given by the intravenous rather than the oral route (Pare 1959, Birkmayer 2001).

Oral levodopa has become the preferred method of treatment clinically, but intravenous levodopa administration still holds advantages over the oral form for some research studies. First, the rapid administration of intravenous levodopa is often necessary for certain study designs, including those focused on pharmacokinetics. Additionally, intravenous administration leads to more predictable plasma levodopa concentrations because oral medications have highly variable absorption characteristics, especially in PD patients (Bushmann 1989), with differences in absorption based on sex and age (Robertson 1989, Kompoliti 2002). Intravenous levodopa permits researchers to keep brain levodopa concentrations constant while assessing physiological responses over time. Furthermore, intravenous levodopa has sometimes been used clinically in patients who cannot tolerate oral medications, such as PD patients during surgery or on total parenteral nutrition.

Current U.S. FDA regulations focus heightened scrutiny to ensure safety of research studies with drugs delivered by a route for which the drug has not been approved. This heightened scrutiny, however, created practical obstacles to research with intravenous levodopa, as described for instance by Rascol and colleagues (p. 250 Rascol 2001). Specifically, an IND (Investigational New Drug) application must be submitted if risks of intravenous levodopa are significantly higher than those of oral levodopa (§21 CFR 312.2(b)(iii)). An IND application must include a comprehensive review of preclinical and human pharmacology. Therefore, the overall goal of this paper is to facilitate research use of IV levodopa by compiling a literature review that comprehensively summarizes the human experience with intravenously administered levodopa. We tabulate the extent of human exposure, side effects, benefits, and efficacy. We also summarize pharmacokinetic (PK) and pharmacodynamic parameters from these studies.


The authors searched MEDLINE and OVID, reviewed selected books, searched toxicity databases, and followed references cited in those sources. Articles written completely in languages other than English, German, Italian, Spanish, or Portuguese were excluded. Search terms included (levodopa / L-dopa / DOPA) AND (intravenous / intravascular / infusion / injection / i.v.); limit to humans; search date through May, 2015. Information from studies using oral or intraduodenal L-DOPA administration was excluded except for PK/PD tables. Studies in which IV levodopa was always coadministered with monoamine oxidase inhibitors (MAOIs) or catechol-O-methyltransferase (COMT) inhibitors were excluded. Levodopa methyl ester (Juncos 1987) and DL-dopa (Pare 1959) were included, but PK/PD calculations were corrected for the difference in molecular weights. Co-administered drugs were reported if included by the authors.

We recorded total dose, maximum infusion rate, and pharmacokinetic (PK) and pharmacodynamic (PD) parameters where available, including steady state volume of distribution (VOD), clearance, distribution half life (\(t_{\frac{1}{2}\alpha}\)), and elimination half life (\(t_{\frac{1}{2}}\) or \(t_{\frac{1}{2}\beta}\)), \(E_{max}\), and \(EC_{50}\)). Reported data were used to calculate any missing PK parameters where possible. Additionally, any reports on efficacy were noted. Side effect frequency was recorded if reported. The number of subjects and subject conditions (Parkinson disease, other disease states or healthy volunteers) were recorded for each study.

Average PK parameters were calculated across studies, weighted by the number of subjects.


139 articles reporting intravenous levodopa administration were identified. Most subjects with parkinsonism were diagnosed with idiopathic PD, but some studies reported a variety of etiologies including postencephalitic and vascular parkinsonism and PSP. PD patients differed in their history of prior drug treatment before the studies with conditions including de novo, fluctuating, on-off, and stable. Some subjects were treated with levodopa for conditions other than PD (see Table 1: Patient Populations and Response Parameters), including other movement disorders (dystonia, progressive supranuclear palsy [PSP], neuroleptic malignant syndrome [NMS], primary psychiatric disorders (schizophrenia, mood disorders, personality disorders), endocrine disorders (diabetes mellitus, essential obesity, hypopituitarism), hepatic disease (alcoholic cirrhosis, steatohepatitis, hepatic encephalopathy), cardiac valvular disease, and asthma. Healthy controls were also included in some studies.

Pharmacokinetic data were reported for a total of 251 human subjects (see Table 2: Pharmacokinetics of IV Levodopa). Co-administration of a peripheral decarboxylase inhibitor (PDI) lowered the clearance and elimination half-life of intravenously administered levodopa, while there was no notable effect of PDIs on volume of distribution.

The pharmacodynamic data (see Table 3: Reports of Human Experience with IV Levodopa) obtained from the literature surveyed a total of 2781 human subjects, with a significant variety of patient groups studied and a multitude of response parameters (see Table 1). From these articles, no side effects were reported for a total of 1260 subjects. The highest total dose was 4320 mg in one day, given to a patient with idiopathic PD and carcinoma of the retina. The patient reported no adverse effects at this dose. The highest single bolus dose was 200 mg, while the highest steady infusion rate was 5 mg/kg/hr.

Concomitantly administered peripheral decarboxylase inhibitors included carbidopa and benserazide. Often, PDIs affected clearance and volume of distribution (as mentioned above), minimized gastrointestinal symptoms, and allowed subjects to be given lower doses of levodopa.

Othet concomitant drugs were also listed, to help explain any side effects that might be caused by concomitant drug administration rather than by levodopa alone. These included adenosine receptor antagonists (istradefylline, tozadenant [SYN115] aminophylline, caffeine), stimulants (amphetamines, methylphenidate), dopamine receptor agonists (apomorphine, terguride, SKF38393), monoamine oxidase (MAO) inhibitors, dextromethorphan, estradiol, paroxetine, and dantrolene.

A variety of neurological, psychiatric, cardiovascular, and other physiological effects of levodopa were monitored (see Table 1). There were no reported deaths. There were no instances of psychosis, even when attempting to elicit it in susceptible subjects (Goetz 1998). Th