Levodopa

Absorption

Orally inhaled levodopa reaches a peak concentration in 0.5 hours with a bioavailability than is 70% that of the immediate release levodopa tablets with a peripheral dopa decarboxylase inhibitor like carbidopa or benserazide.

Toxicity

There is no readily available data for the use of levodopa in pregnancy. Rabbits treated with levodopa and carbidopa produced smaller litters and their offspring developed visceral and skeletal deformities. Levodopa may lower prolactin and interfere with lactation but there is limited human data to demonstrate this effect. Levodopa is present in human breast milk and so the potential effects of nursing while taking levodopa should be considered before prescribing levodopa to nursing mothers. There is currently a lack of data on the safety and effectiveness of using levodopa in pediatric patients. Patients over 65 years of age are more likely to experience adverse effects associated with taking levodopa, however this generally is not sufficient to exclude this patient group from treatment.

Description

Levodopa is an amino acid precursor of dopamine with antiparkinsonian properties. Levodopa is a prodrug that is converted to dopamine by DOPA decarboxylase and can cross the blood-brain barrier. When in the brain, levodopa is decarboxylated to dopamine and stimulates the dopaminergic receptors, thereby compensating for the depleted supply of endogenous dopamine seen in Parkinson's disease. To assure that adequate concentrations of levodopa reach the central nervous system, it is administered with carbidopa, a decarboxylase inhibitor that does not cross the blood-brain barrier, thereby diminishing the decarboxylation and inactivation of levodopa in peripheral tissues and increasing the delivery of dopamine to the CNS.

Description

L-Dopa—also known as levodopa, 3-hydroxy-L-tyrosine, and dozens of other names—has been known for at least 90 years as a naturally occurring amino acid that is the biological precursor to the neurotransmitter dopamine.?L-Dopa is administered to increase dopamine levels in Parkinson’s disease patients; unlike dopamine, it can cross the blood–brain barrier.

Chemical properties

L-Dopa [59-92-7], levodopa, crystallizes as colorless, odorless, and tasteless needles from water, mp 276-278℃(decomp.). It is freely soluble in dilute hydrochloric and formic acids but practically insoluble in ethanol, benzene, chloroform, and ethyl acetate. Solubility in water is 66 mg/40 mL. In the presence of moisture, l-dopa is rapidly oxidized by atmospheric oxygen, with darkening.

Originator

Larodopa,Roche,US,1970

The Uses of Levodopa

Levodopa is an immediate precursor of dopamine and product of tyrosine hydroxylase. It derived from vanillin is widely used for treatment of Parkinson’s disease, most often in combination with peripheral decarboxylase inhibitors such as benserazide and carbidopa.

Indications

Levodopa on its own is formulated as an oral inhalation powder indicated for intermittent treatment of off episodes in Parkinson's patients who are already being treated with carbidopa and levodopa. Levodopa is most commonly formulated as an oral tablet with a peripheral dopa decarboxylase inhibitor indicated for treatment of Parkinson's disease, post-encephalitic parkinsonism, and symptomatic parkinsonism following carbon monoxide intoxication or manganese intoxication.

Background

Levodopa is a prodrug of dopamine that is administered to patients with Parkinson's due to its ability to cross the blood-brain barrier. Levodopa can be metabolised to dopamine on either side of the blood-brain barrier and so it is generally administered with a dopa decarboxylase inhibitor like carbidopa to prevent metabolism until after it has crossed the blood-brain barrier. Once past the blood-brain barrier, levodopa is metabolized to dopamine and supplements the low endogenous levels of dopamine to treat symptoms of Parkinson's. The first developed drug product that was approved by the FDA was a levodopa and carbidopa combined product called Sinemet that was approved on May 2, 1975.

What are the applications of Application

Levodopa is an immediate precursor of dopamine and product of tyrosine hydroxylase

Definition

ChEBI: Levodopa is an optically active form of dopa having L-configuration. Used to treat the stiffness, tremors, spasms, and poor muscle control of Parkinson's disease.

Manufacturing Process

Levodopa can be prepared from 1-3-dinitrotyrosine, 3-(3,4-methylenedioxyphenyl)-l-alanine, and l-tyrosine, and by fermentation of l-tyrosine.
A charge of 1,000 g of ground velvet beans was extracted with 9 liters of 1% aqueous acetic acid at room temperature over a 20-hour period with occasional stirring during the first 4 hours. The liquor was decanted and thebean pulp slurry was vacuum filtered through a cake of acid-washed diatomaceous earth in a Buechner funnel. The decanted liquor was combined with the filtrate and concentrated under vacuum and a nitrogen atmosphere to a volume of 900 ml. After treating with acid-washed activated carbon, the concentrate was then filtered through acid-washed diatomaceous earth.
After concentrating the filtrate to approximately 400 ml, solids started crystallizing out at which time the filtrate was cooled by refrigerating at 5°C for several hours. Filtration gave 18.7 g of L-Dopa, MP 284° to 286°C (dec.); [α]D 8.81° (1% solution in aqueous 4% HCl). The infrared spectrum and paper chromatography indicated very good L-Dopa according to US Patent 3,253,023.
Various synthetic routes are also described by Kleeman and Engel.

brand name

Bendopa (Valeant); Dopar (Shire); Larodopa (Roche).

Therapeutic Function

Antiparkinsonian

Biological Functions

Levodopa (L-DOPA), the most reliable and effective drug used in the treatment of parkinsonism, can be considered a form of replacement therapy. Levodopa is the biochemical precursor of dopamine. It is used to elevate dopamine levels in the neostriatum of parkinsonian patients. Dopamine itself does not cross the blood-brain barrier and therefore has no CNS effects. However, levodopa, as an amino acid, is transported into the brain by amino acid transport systems, where it is converted to dopamine by the enzyme L-aromatic amino acid decarboxylase.
If levodopa is administered alone, it is extensively metabolized by L-aromatic amino acid decarboxylase in the liver, kidney, and gastrointestinal tract. To prevent this peripheral metabolism, levodopa is coadministered with carbidopa (Sinemet), a peripheral decarboxylase inhibitor. The combination of levodopa with carbidopa lowers the necessary dose of levodopa and reduces peripheral side effects associated with its administration.

General Description

Levodopa belongs to a group of the most effective drugs for treating the type of Parkinsonism not caused by medicinal agents. The first significant breakthrough in the treatment of PDcame about with the introduction of high-dose levodopa. Fahn referred to this as a revolutionary development intreating parkinsonian patients. The rationale for the use oflevodopa for the treatment of PD was established in theearly 1960s. Parkinsonian patients were shown to have decreasedstriatal levels of DA and reduced urinary excretionof DA. Since then, levodopa has shown to be remarkablyeffective for treating the symptoms of PD.

Biochem/physiol Actions

3,4-Dihydroxy-L-phenylalanine or L-DOPA is a natural isomer of the immediate precursor of dopamine that crosses the blood-brain barrier. It is used for the treatment of Parkinson′s disease and is a product of tyrosine hydroxylase.

Pharmacokinetics

Levodopa is able to cross the blood-brain barrier while dopamine is not. The addition of a peripheral dopa decarboxylase inhibitor prevents the conversion of levodopa to dopamine in the periphery so that more levodopa can reach the blood-brain barrier. Once past the blood-brain barrier, levodopa is converted to dopamine by aromatic-L-amino-acid decarboxylase.

Side Effects

Get medical help immediately if you have any symptoms: fever, unusual muscle stiffness, severe confusion, sweating, fast/irregular heartbeat, and rapid breathing. A severe allergic reaction to this drug is rare. This medication may cause saliva, urine, or sweat to turn dark. This effect is harmless.

Safety Profile

Poison by ingestion. Moderately toxic by intravenous and intraperitoneal routes. Human systemic effects by ingestion: somnolence, hallucinations and distorted perceptions, toxic psychosis, motor activity changes, ataxia, dyspnea. Experimental teratogenic and reproductive effects. Questionable human carcinogen producing skin tumors. Human mutation data reported. An anticholinergic agent used as an anti Parhnsonian drug. When heated to decomposition it emits toxic fumes of NOx

Synthesis

Levodopa, (-)-3-(3,4-dihydroxyphenyl)-L-alanine (10.1.1), is a levorotatory isomer of dioxyphenylalanine used as a precursor of dopamine. There are a few ways of obtaining levodopa using a semisynthetic approach, which consists of the microbiological hydroxylation of L-tyrosine (10.1.1), as well as implementing a purely synthetic approach.
Oxidation of L-tyrosine, for selective introduction of a hydroxyl group at C3 of the tyrosine ring, can be accomplished in a purely synthetic manner by using a mixture of hydrogen peroxide and iron(II) sulfate mixture in water as an oxidant with permanent presence of oxygen.

The third method of levodopa synthesis consists of the acetylation of tyrosine using acetylchloride in the presence of aluminum chloride and the subsequent oxidative deacylation of the formed 3-acetyltyrosine (10.1.2) using hydrogen peroxide in sodium hydroxide solution.

Metabolism

Levodopa is either converted to dopamine by aromatic-L-amino-acid decarboxylase or O-methylated to 3-O-methyldopa by catechol-O-methyltransferase. 3-O-methyldopa cannot be metabolized to dopamine. Once levodopa is converted to dopamine, it is converted to sulfated or glucuronidated metabolites, epinephrine E, or homovanillic acid through various metabolic processes. The primary metabolites are 3,4-dihydroxyphenylacetic acid (13-47%) and homovanillic acid (23-39%).

Metabolism

Metabolism of levodopa and dopamine may proceed by four pathways: decarboxylation, O-methylation, transamination, and oxidation. Levodopa is decarboxylated to dopamine by the enzyme AAAD. This enzyme is ubiquitously distributed in the gut, liver, and kidney. The gastric and intestinal wall contains AAAD, which significantly metabolizes levodopa. At least half of an oral levodopa dose is decarboxylated during absorption and first-pass hepatic metabolism. Further decarboxylation may occur by AAADC during successive circulation through these tissues. Approximately 70% of the levodopa metabolites appear as dopamine and its degradation products, indicating that decarboxylation is the primary route of metabolism.

storage

-20°C

Purification Methods

Likely impurities are vanillin, hippuric acid, 3-methoxytyrosine and 3-aminotyrosine. DOPA recrystallises from large volumes of H2O forming colourless white needles; its solubility in H2O is 0.165%, but it is insoluble in EtOH, *C6H6, CHCl3, and EtOAc. Also crystallise it by dissolving it in dilute HCl and adding dilute ammonia to give pH 5, under N2. Alternatively, crystallise it from dilute aqueous EtOH. It is rapidly oxidised in air when moist, and darkens, particularly in alkaline solution. Dry it in vacuo at 70o in the dark, and store it in a dark container preferably under N2. It has at 220.5nm (log 3.79) and 280nm (log 3.42) in 0.001N max HCl. [Yamada et al. Chem Pharm Bull Jpn 10 693 1962, Bretschneider et al. Helv Chim Acta 56 2857 1973, NMR: Jardetzky & Jardetzky J Biol Chem 233 383 1958, Beilstein 4 IV 2492, 2493.]