The influence of bromocriptine on the pharmacokinetics of levodopa in Parkinson's disease.

Several hypotheses have explained the beneficial effect of adding bromocriptine (BR) to levodopa (LD) in Parkinson's disease (PD) by interaction at the striatal level. In the present study we show the influence of BR on plasma LD values in an acute loading experiment (125 mg LD + 12.5 mg carbidopa [DCI] given alone and together with 2.5 mg BR at 0 time; 4 h observation). On the basis of this influence we have been able to differentiate between three groups of patients: (a) in six patients (five of them with frequent off episodes) LD values were significantly lower (p less than 0.05) when both drugs were given together (area under the curve [AUC] +/- SE 2.10 +/- 0.42 micrograms/ml/h vs. 4.96 +/- 1.10 micrograms/ml/h); (b) in eight patients (one with frequent akinesia) LD levels were significantly higher (p less than 0.003) when both drugs were given together (AUC +/- SE 4.05 +/- 0.51 micrograms/ml/h vs. 1.94 +/- 0.19 micrograms/ml/h); (c) in six patients (without motor fluctuations) no difference in LD levels was noted (AUC +/- SE 3.91 + 0.62 micrograms/ml/h vs. 3.81 +/- 0.70 micrograms/ml/h). The clinical evaluation (Webster scale) did not show substantial differences, except for increased dyskinesia, which correlated with higher LD levels. In summary, we suggest that the diminution of motor fluctuations and the occurrence of dyskinesias when BR is added to LD may stem from changes in LD plasma levels. These findings would be taken into consideration in the interpretation of therapeutic response fluctuations under combined treatment.