News, Parkinson

Do you know your medication?

1 September 2020

Antiparkinsonian Drugs

 The goal of antiparkinsonian drugs is to allow you to maintain your daily activities, to remain socially engaged and to exercise. Your journey with Parkinson’s disease is unique and your medical treatment needs to be adapted to your own personal needs.

The majority of drugs used to treat Parkinson’s disease temporarily raise dopamine levels in the brain. They act as substitutes for the dopamine deficit associated with the degeneration of dopaminergic neurons. Your condition is unique; thus, finding the best combination of drugs, their respective dosage and the schedule for administering them can take time.

These parameters are relatively standard when initiating treatment. However, your body is ultimately the deciding factoring in measuring your response to your treatment. You need to tell your neurologist if you observe day-to-day variations in the efficacy of your treatment or dyskinesia.

Levodopa is, to this day, the most effective drug for treating the symptoms of Parkinson’s disease, mainly rigidity and slowness of movement.

Levodopa is absorbed at the intestinal level and transported through the bloodstream to the brain. Once in the brain, it is transformed into dopamine and stored in nerve cells in order to replace the missing dopamine. Levodopa is always combined with another molecule, carbidopa in Sinemet® and benserazide in Prolopa®, allowing a greater quantity of levodopa to enter the brain.

Levodopa is usually ingested in the form of tablets. Its maximum effect is obtained 30 to 60 minutes after taking it. You should not take it alongside proteins (ex: dairy products, eggs, meat, soy, nuts, peas) that can limit its absorption. Its duration of actions varies from person to person and the progression of their disease. It varies from two hours to a couple of hours.

You can get the most out of your treatment by following a few simple tips.

Once the optimal dose has been found to treat your symptoms (ex: 2 tablets of 25/100 each time), this dose will generally not be increased over time. However, the frequency with which your treatment is administered during the day will increase in conjunction with the degeneration of neurons. This increase is not linked to your body adapting to the repeated administrations of the drug.

Levodopa induces nausea which can be managed by taking the tablets with non-protein foods (ex: crackers, applesauce), by increasing very gradually the doses, or by separating said doses from that of other drugs and medication. It can also cause drops in pressure when going from a sitting or a lying position to standing up.

When the drug starts to kick in (approximately 30 minutes after taking it), or if the dose is too high, you could experience dyskinesia, which are involuntary, non-stereotypic, anarchic, random, sudden and irregular movements of short duration affecting all or part of the body, present while resting or moving.

After a couple of years, the effect of levodopa can fluctuate throughout the day. This phenomenon in which the medication is not working optimally, known as an “off” period, returns you to a state in which your symptoms are no longer under control. You need to report these situations to your neurologist.

Levodopa can also be administered through a pump directly in the small intestine (DuodopaTM). This method of constant administration allows for a decrease in efficacy fluctuations throughout the day.

These drugs belong to the class of dopamine agonists. They work by imitating dopamine in the brain.

These drugs are slightly less effective than levodopa, but they have a longer duration of action which makes them particularly interesting for managing the variations in efficacy of levodopa. They are used as an initial treatment or alongside levodopa during the more advanced stages of the disease.

The frequency with which they are taken is generally once a day and the absorption of the drug is not disturbed by the contents of the stomach. You can thus take it during your meals.

This drug class has two major side effects. Among antiparkinsonian drugs, they are the ones who have the biggest tendency to provoke hallucinations. Thus, they are not recommended for people who have already this kind of episodes or who are living with dementia. On the other hand, these drugs can also induce compulsive behavior in regard to food, sexuality, consumption, games and the Internet.

Loved ones are key in recognising these new behaviours. If you observe these changes, tell your neurologist immediately and they will gradually reduce the dose.

Apomorphine is also a dopamine agonist used when needed to manage the efficacy transition between two doses of levodopa. It is administered by injection through a pen during the “off” periods.

The effect of apomorphine begins within the first ten minutes after injection and lasts almost an hour. The level of efficacy is similar to that of levodopa.

The administration of the drug requires a specific protocol to find the dose that’s right for you. This protocol, the length of which is a day the hospital, must be done by specialised neurologist.

 

Other than the secondary effects associated with this drug class, apomorphine can lead to important episodes of nausea and vomiting during the first days of treatment and a drop in blood pressure.

A sublingual version of apomorphine should be available sometime in 2021.

Entacapone stops the enzyme responsible for the deterioration of levodopa. Levodopa, consequently, becomes available for longer, thus making it an appropriate choice for people who have a short response to levodopa (less than 3 hours). The addition of entacapone usually prolongs the effects of levodopa by 30 to 60 minutes, which reduces the “off” periods.

Entacapone also increases the magnitude of levodopa’s effect, which can cause dyskinesia. Urine can also become orange.

The drug Comtan® is generally taken in association with each dose of levodopa, unless they are too close together.

The drug Stalevo® contains three molecules (levodopa, carbidopa, et entacapone), which limits the moments in which the treatment is administered, but makes it more difficult to adjust the dose of levodopa.

These drugs belong to the class of inhibitors of monoamine oxidase-B, an enzyme which deteriorates dopamine in the brain. Levodopa, consequently, becomes available for longer. These drugs must be taken in the morning to avoid insomnia.

These drugs present a moderate efficacy in treating the symptoms of Parkinson’s disease. Their major advantage lies in the simplicity of their once-a-day administration, the duration of their action, and the low frequency of side effects. However, they are contraindicated with most antidepressants, pain medication and syrups for a wet cough. Food such as chocolate, offal and ripened cheese are also contraindicated.

For a long time, these two drugs were thought to be able to slow down the progression of the disease. After a review of the research data, American health authorities concluded that the amount of proof backing the neuroprotective effect of these drugs was insufficient.

Amantadine is one of the rare antiparkinsonian drugs to not act directly on dopaminergic neurons in the substantia nigra. It acts on another type of neuron, glutamatergic neurons. By blocking them, amantadine allows for the liberation of dopamine in the brain.

Amantadine is sometimes used in the first stages of the disease or later on, in association to treat dyskinesia induced by levodopa.

The side effects of amantadine are limited. It sometimes causes a purplish, lace-shaped discoloration under the skin of the legs.

These drugs are anticholinergics. They block the effect of a neurotransmitter called acetylcholine, usually over-present in the brain of people living with Parkinson’s disease. This drug class dates back to the pre-levodopa era.

Their efficacy is limited for rigidity, but it can help alleviate certain symptoms of trembling, particularly for young people diagnosed.

The main drawback of this drug is its long list of side effects. They can provoke hallucinations, vision problems, a dry mouth, constipation and can cause glaucoma.

These drugs are thus less used, as other more effective and safe antiparkinsonian drugs are now available.

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