|
Parkinson’s disease is a progressive, incurable neurological disease. The three main symptoms are slowness of movement (bradykinesia), tremor and rigidity (stiffness).
Treatment for this disease has been continually changing over the past 30 years, especially with the introduction of levodopa. Present-day medicine helps improve symptoms, delays the onset of total physical dependence and hence delays morbidity and mortality, which result due to progressive immobility.
Initially the use of drug treatment should be withheld and the patient’s progress monitored. Drug treatment should begin once significant functional disability sets in and the treatment regime should be monitored regularly, especially regarding timing of doses, benefit obtained and the severity of any side-effects.
Dopaminergic drugs:
LEVODOPA is used with a dopa-decarboxylase inhibitor, which prevents peripheral degeneration of levodopa to dopamine, which does not cross the blood-brain barrier. It is the amino-acid precursor of dopamine, which helps replace the depleted striatal dopamine and so helps to decrease rigidity and bradykinesia. This drug has less effect on tremor. The extracerebral dopa-decarboxylase inhibitors used are benserazide (co-beneldopa) and carbidopa (co-careldopa).
The reduced levels of peripheral dopamine decreases possible side effects such as nausea, vomiting and cardiovascular problems. There is also a shorter time lapse between the onset of therapeutic effects and a smoother clinical response. However, there usually is an increase in abnormal involuntary movements and psychiatric complications.
Levodopa should be given in low doses and gradually increased. The final dose should be a compromise between increased mobility and minimal side effects. After 1½ to 2 years, there maybe a gradual decline in the therapeutic effects of the drug. This may led to the ‘on-off’ effect, which causes fluctuations in normal performance during ‘on’ times and weakness and akinesia (no movement) during ‘off’ periods. ‘End-of-dose’ deterioration may occur; where the duration of the benefits of the drug becomes progressively shorter.
SELEGILINE is a monoamine-oxidase-B inhibitor used in severe parkinsonism with levodopa to help decrease ‘end-of-dose’ deterioration. ENTACAPONE is also used with co-beneldopa and co-careldopa to help decrease ‘end-of-dose’ deterioration.
BROMOCRIPTINE, CARBERGOLINE, LYSURIDE and PERGOLIDE are ergot derivatives, which act on surviving dopamine receptors. However, there is no advantages of these drugs over that of levodopa. It also helps with ‘off’ periods but its use is limited due to its numerous side effects: abnormal involuntary movements, confusion and it may also cause neuropsychiatric problems and retroperitoneal fibrosis.
ROPINIROLE a dopamine D2 receptor agonist helps all symptoms and its side effects are similar to those of bromocriptine.
AMANTADINE has the mildest effects on the disease and only a few patients benefit from its effects. However, it is relatively free of side effects.
APOMORPHINE a potent stimulator of D1 and D2 receptors which may help stabilizes unpredictable ‘off’ instances from levodopa treatment.
TOLCAPONE is no longer used due to reports serious hepatotxicity.
If a patient is suffering from pulmonary disease, peptic ulcers, cardiovascular disease, diabetes mellitus, osteomalacia, open-angle glaucoma, skin melanoma and/or psychiatric illness caution should be taken when using levodopa. Closed-angle glaucoma is a contraindication to treatment.
Side effects which may result are: anorexia, nausea, vomiting, postural hypotension, dizziness, tachycardia, arrhythmias, red discoloration of urine and other body fluids, abnormal involuntary movements and psychiatric symptoms. Depression, drowsiness, headaches, flushing, sweating, gastro-intestinal bleeding and peripheral neuropathies have also been reported.
Antimuscarinic drugs:
These drugs are also known, as ‘anticholinergic’ drugs are less effective on Parkinson’s then levodopa. However, they are usually used to supplement levodopa. These drugs correct the central imbalance of excess acetycholine, which results due to a decrease in dopamine. They help decrease tremor and rigidity but have little effect on bradykinesia. They also help reduce symptoms caused by drug-induced parkinson (ex. with antipsychotics).
There is no real difference between different antimuscarinic drugs, however patients tend to tolerate each one differently. They may be taken before a meal if the individual suffers from a dry mouth or after if gastro-intestinal symptoms occur. The most common are ORPHENADRINE, BENZHEXOL, BENZTROPINE and PROCYCLIDINE.
Caution should be advised when using these drugs if the patient has cardiovascular disease, hepatic or renal impairment and with the elderly. Untreated urinary retention, glaucoma and gastro-intestinal obstruction are contraindications for use of the above drugs.
Other side effects, which may result, are dizziness, blurred vision, urinary retention, tachycardia, hypersensitivity, nervousness and with a high dose, the patient may be prone to mental confusion, excitement and psychatric disturbances.
| 
