Introduction
Several neurological diseases affect millions of people worldwide, especially geriatric individuals. People need to know about these disorders and their medications as having sufficient knowledge can lead to better management and prevention of the disease.
In this article, we will discuss one of the most affected neurological disorders that is Parkinson's disease.
What is Parkinson's disease?
Parkinson’s disease is a degenerative condition caused by nerve cell damage in the substantia nigra, a region of the brain responsible for movement. These nerve cells die or become damaged, resulting in the inability to create dopamine, an important neurotransmitter.
Normally, dopamine helps to coordinate the millions of nerve and muscle cells involved in movement by functioning in a delicate balance with other neurotransmitters. This equilibrium is disrupted when there isn’t enough dopamine, which causes;
- Tremors (trembling in the hands, arms, legs, and jaw)
- Rigidity (limb stiffness)
- Slowness of movement
- Poor balance
- Poor coordination1
Symptoms of Parkinson’s disease
Symptoms may be unique to each individual with Parkinson’s disease. Early symptoms may not be obvious and, ultimately, may get ignored. Symptoms frequently begin on one side of the body and continue to worsen on that side, even after symptoms spread to the other limbs.2
Movement-related symptoms include:
- Imbalance
- Slow movement
- Rigidity
- Tremors
- Involuntary movement
Non-movement-related symptoms include:3
- Mental health disorders
- Dementia
- Sleep disorders
- Pain
- Sensory disturbances
- Cognitive impairment
Diagnosis and treatment
As of now, there are no laboratory or blood tests available for diagnosing Parkinson's disease in non-genetic patients. Typically, doctors use a neurological examination and a review of the patient's medical history to make their diagnosis.
Once a person begins treatment, improved symptoms are another sign that they have Parkinson's disease. These days, the above-mentioned common symptoms are the main basis for Parkinson's diagnosis.4
Positron emission tomography (PET) scans may be able to confirm a physician's diagnosis.
Traditional methods for diagnosis consist of:1
- Two of the three main symptoms being present
- The lack of additional neurological symptoms found during testing
- No prior history of head trauma, stroke, or other potential causes, such as the use of tranquiliser drugs
- Responding well to Parkinson's drugs, including levodopa
Although there is no cure for Parkinson's disease, medications, surgical procedures, and other therapies can alleviate symptoms. Parkinson's symptoms can be alleviated by medications that:4
- Increase dopamine levels in the brain
- Impact other brain chemicals, such as neurotransmitters that carry information between brain cells
- Reduce non-movement symptoms
Anti-parkinson medications
The different classes of medication to treat Parkinson’s disease include:
Levodopa
Levodopa works by passing the blood-brain barrier - a complex network of blood channels and cells that filter blood before it reaches the brain. Since blood enzymes degrade most of the levodopa before it reaches the brain, it is now given with an enzyme inhibitor known as carbidopa.
The use of carbidopa stops levodopa from being metabolised in the gastrointestinal tract, liver, and other organs, allowing more of it to enter the brain.5 As a result, symptom relief requires a lower dose of levodopa. This advancement also helps to lessen the acute nausea and vomiting that are frequently reported as adverse effects of levodopa. Most individuals benefit from levodopa, which alleviates symptoms of slowness, stiffness, and tremors.
Dopamine agonists
These are drugs that mimic the function of chemical messengers in the brain, prompting neurons to react similarly to dopamine. They can be prescribed alone or in combination with levodopa, and they can be used in the early stages of the disease or to increase the duration of levodopa's effectiveness.
These drugs have higher adverse effects than levodopa, thus doctors consider this when prescribing dopamine agonists to patients. Some side effects of this drug include:
- Drowsiness
- Nausea
- Vomiting
- Dry mouth
- Dizziness
- Feeling faint while standing
While these symptoms are common when starting a dopamine agonist, they usually subside after a few days. In some people, dopamine agonists might produce confusion, hallucinations, or psychosis. Therefore it is important to keep your doctor informed on all side effects you may experience from the medication so that a better prescription can be found for you.
COMT (catechol-O-methyltransferase) inhibitors
Entacapone and tolcapone are drugs used to alleviate levodopa-related fluctuations. COMT is an enzyme that breaks down levodopa in the bloodstream. Blocking COMT allows more levodopa to enter the brain, increasing therapeutic effectiveness. However, side effects may include diarrhoea and dyskinesias.
Selegiline
This medicine reduces the activity of the enzyme monoamine oxidase B (MAO-B), which metabolises dopamine in the brain, delaying the breakdown of naturally occurring dopamine and dopamine generated from levodopa. Selegiline, when taken alongside levodopa, may enhance and prolong its effectiveness.
Side effects may include:
- Heartburn
- Nausea
- Dry mouth
- Disorientation
Less common side effects should be reported to a physician and include:
- Confusion
- Nightmares
- Hallucinations
- Headaches
Anticholinergic medication
These medications act by inhibiting acetylcholine, a neurotransmitter in the brain whose effects grow more evident as dopamine levels drop. They are particularly effective for treating tremors and muscle rigidity, as well as lowering medication-induced parkinsonism.
They are generally not recommended for long-term usage in elderly people due to severe side effects.
Amantadine
This is an antiviral medicine that also helps lessen Parkinson's symptoms (unrelated to the antiviral components) and is commonly used in the early stages of the condition. It is sometimes used with an anticholinergic drug or levodopa. It may be beneficial in treating Parkinson's disease-related jerky movements.
Side effects may include:1
- Difficulties concentrating
- Disorientation
- Sleeplessness
- Nightmares
- Irritability
- Hallucinations
Amantadine may produce leg oedema and mottled skin, particularly on the legs.
Before starting these medications, you must have an in-depth conversation with your healthcare practitioner to learn when and how to take them, as well as to discuss the potential adverse effects of the medications. This will help you find which medication is best for you and the specific symptoms you may be experiencing.
It’s also important to know that your physician and pharmacist will be there to assist you with any issues or inquiries you may have.
Summary
- Parkinson's disease drugs are successful in treating symptoms and enhancing quality of life
- They can induce side effects, just like any other medication
- Before starting these medications, it is critical to have in-depth conversations with your healthcare practitioner to learn when and how to take them, as well as potential adverse effects
- Know that your physician and pharmacist will be there to assist you with any issues or inquiries
References
- American Association of Neurological Surgeons, ANNS. Parkinson’s Disease. [Internet]. aans.org. American Association of Neurological Surgeons, ANNS [updated 30 April 2024; cited 10 June 2024]. Available from: https://www.aans.org/patients/conditions-treatments/parkinsons-disease/
- Sveinbjornsdottir S. The clinical symptoms of Parkinson’s disease. Journal of Neurochemistry [Internet]. 2016 [cited 2024 Sep 9]; 139(S1):318–24. Available from: https://onlinelibrary.wiley.com/doi/10.1111/jnc.13691.
- World Health Organisation, WHO. Parkinson disease. [Internet]. who.int. World Health Organisation WHO [updated 9 august 2023; cited 10 June 2024]. Available from: https://www.who.int/news-room/fact-sheets/detail/parkinson-disease
- National Institute on Aging, NIH. Parkinson’s disease: causes, symptoms, and treatments. [Internet]. nia.nih.gov. National Institute on Aging, NIH [updated 14 April 2022; cited 10 June 2024]. Available from: https://www.nia.nih.gov/health/parkinsons-disease/parkinsons-disease-causes-symptoms-and-treatments
- Leyden E, Tadi P. Carbidopa. StatPearls [Internet]. 2023 [cited 28 August 2024]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554552/