Eight parkinsonian patients participated in a pharmacokinetic pharmacodynamic study of sequential doses of controlled-release carbidopa (CD)/levodopa (LD) at 4-hour intervals, with serial blood samples obtained before and after each dose. Effect measurements obtained with each blood sample included tapping and walking speed as well as a global assessment of motor function. Analysis of the data by extended least squares regression for linear, Emax, and sigmoid Emax pharmacodynamic models revealed that linear relationships do not provide the best fit between LD plasma concentrations and clinical effects after controlled-release CD/LD. The data are fit best to models that are curvilinear in nature. LD plasma concentrations greater than 2.0 micrograms/ml resulted in sustained effects on walking and global scores while the greatest rate of change in walking and global scores occurred at 0.9 micrograms/ml. LD plasma concentrations fluctuating around 0.9 micrograms/ml may result in the "on/off" effects seen in Parkinson's disease.
We have treated 102 Parkinson patients with bromocriptine for up to 6 years; most of these posed problems of management when referred to us. Forty-two continue to take bromocriptine, at a mean dose of 49 mg daily (range 10-160), in combination with some 50% of their previous optimal dose of levodopa (with or without a decarboxylase inhibitor). We consider the main indications for bromocriptine are severe dyskinesia, early morning dystonia, and "wearing off" reactions. Contraindications include hallucinations, delusions, substantial confusion, acute myocardial infarction, active peptic ulceration, and active pleuropulmonary disease.
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