Levodopa neuroleptic drugs

Figure 7.8 Dopamine and motor function. When nigrostriatal dopamine activity is normal so is motor function. Any reduction in this DA activity, as in Parkinson s disease, results in reduced motor activity, i.e. akinesia. By contrast, too much DA activity, as in Huntington s Chorea, produces abnormal motor function, i.e. dyskinesia. The latter may be controlled by neuroleptic drugs (DA antagonists) but they can swing the balance in DA activity sufficiently to produce akinesia (Parkinsonism). DA agonists (and levodopa) may overcome akinesia but can induce DA overactivity and dyskinesia (peak dose effect) (see Chapter 15)...

Levodopa and neuroleptic drugs can interfere with the effects of each other at dopamine receptors the patient should be monitored for deterioration in both parkinsonism and mental state. If an antiemetic is required in a patient taking levodopa, one that does not affect central dopamine receptors should be chosen. 

There is some evidence that the atypical neuroleptic drug clozapine can alleviate levodopa-induced dyskinesia while itself providing additional relief in Parkinson s disease (SEDA-18, 159) clozapine may also relieve levodopa-induced psychosis (SEDA-17,166). 

Do not abruptly discontinue use of the antiparkinsonism drugs Neuroleptic malignant-like syndrome may occur when the antiparkinsonism drugs are discontinued or the dosage of levodopa is reduced abruptly. The nurse carefully observes the patient and reports the following symptoms muscular rigidity, elevated body temperature, and mental changes... 

Antimuscarinic drugs such as atropine have been used to modest effect in the treatment of PD for more than a century attenuating tremor and rigidity but with little effect on akinesia. Currently benzhexol and benztropine are sometimes added to levodopa therapy but peripheral effects such as dry mouth, blurred vision and constipation are unpleasant. They are also often used to counteract neuroleptic-induced extrapyramidal effects. 

A number of unapproved uses of antipsy- chotic drugs also exist. CPZ and haloperidol were used early on to treat phencyclidine (PCP)-induced psychosis. Psychoses associ- ated with depression, bipolar disorder, and Alzheimer s disease are commonly treated with haloperidol, risperidone, or olanzapine. Psychotic symptoms in Parkinson s disease patients caused by levodopa and/or dopaminergic agonists have been alleviated with quetiapine, because EPS-prone typical neuroleptics contraindicated in Parkinson s disease. 

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