Parkinson's disease is characterized by motor and psychiatric problems according to "Adams and Victor's Principles of Neurology" by Drs.Allan Ropper and Martin Samuels. Motor problems include a resting tremor, rigidity, instability and difficulty moving. Psychiatric symptoms include sleepiness, insomnia, mood swings and trouble sleeping. The exact cause is not known but there are a number of known genetic contributions. Many of the symptoms of the disease are linked to decreased secretion of dopamine in an area of the brain known as the substantia nigra. Many therapies aim to increase the dopamine level in this area of the brain, and should be pursued with the consultation of a healthcare professional.
Levodopa
Levodopa, also known as L-dopa , is a precursor to dopamine in the body as noted by "Harrison's Principles of Medicine" by Anthony S Fauci M.D. The precursor chemical is given instead of dopamine because dopamine cannot cross the blood vessels into the brain, whereas L-dopa can. After it crosses into the brain the enzyme dopa decarboxylase transforms it into dopamine. L-dopa is generally given with a drug such as carbidopa that inhibits the conversion of L-dopa to dopamine outside of the brain to minimize side-effects. Side effects include dizziness, GI symptoms such as nausea, vomiting, diarrhea and constipation, sleep problems and nightmares may also occur. More serious side effects can include unusual movements, and psychiatric problems such as thoughts of suicide, hallucinations and compulsive behaviors.
Dopamine Agonists
"Basic and Clinical Pharmacology" by Drs. Bertram Katzung, Susan Masters, and Anthony Trevor notes that dopamine agonists are drugs that mimic the action of dopamine. These drugs include apomorphine which is injectable, and the oral medications bromocriptine, pergolide, pramipexole and ropinirole. Side effects may include nausea, constipation, sleepiness, insomnia, hallucinations and swelling. Some of these drugs may also contribute to the development of problems with the valves of the heart. They may also be associated with compulsive behaviors.
MAO-B Inhibitors
MAO-B inhibitors such as selegiline block the breakdown of dopamine in the brain and thereby increase its levels. MAO-B inhibitors decrease the need for levodopa, and cannot be combined with certain other drugs such as many of the anti-depressants. More common side-effects include nausea, abdominal pain, dizziness, confusion, hallucinations and dry mouth.
Amantadine
Amantadine has mild effects in treating Parkinson's symptoms. The exact mechanism of action is unknown but it does increase dopamine release from nerve cells in the brain, inhibits its re-uptake back into the nerves and stimulates dopamine receptors. It can cause skin rashes and swelling around the ankles. Less commonly it can cause hallucinations, nightmares and confusion.
References
- "Adams and Victor's Principles of Neurology"; Allan Ropper and Martin Samuels; 9th Ed; 2009
- "Harrison's Principles of Medicine"; Anthony S Fauci et al; 17th Ed; 2008
- "Basic and Clinical Pharmacology"; Bertram Katzung, Susan Masters, and Anthony Trevor; 11th Ed; 2009
