Lack of pharmacokinetic influence on levodopa by bromocriptine

Influence of the dopamine agonist alpha-dihydroergocryptine on the pharmacokinetics of levodopa in patients with Parkinson's disease

This study investigated whether chronic coadministration of alpha-dihydroergocryptine (DHEC) altered the plasma pharmacokinetics of individualized treatments with levodopa in 12 patients with Parkinson's disease. Steady-state pharmacokinetics of plasma levodopa (L-Dopa) under combined treatment were compared with those under treatment with L-Dopa alone. There was no evidence of increased exposure to L-Dopa caused by concomitant treatment with DHEC. In contrast, additional treatment with DHEC reduced the overall exposure to L-Dopa (17.5% reduction in area under the curve; 95% CI: 23%-6%). This effect was small but statistically significant for the area under the plasma concentration-time curve, whereas tmax (time of maximum plasma concentration) and peak-to-trough fluctuation were not affected. Cmax (maximum plasma concentration), on average, was reduced to a similar extent (-14.5%; 95% CI: 38% to -17%), albeit not significantly. The magnitude of the interaction does not suggest changing the current clinical practice of up-titrating DHEC and subsequently adapting L-Dopa to the individual needs of patients.

Efficacy and safety of tianeptine in the treatment of depressive disorders in comparison with fluoxetine*

Depression is treated by a great variety of antidepressant treatments. SSRIs (such as fluoxetine) are well known: it is, however, sure that further progress is needed and the search for antidepressants with other mechanisms of action (such as tianeptine) or different efficacy is still of interest. A multinational study compared tianeptine with fluoxetine in 387 patients with Depressive Episode, or Recurrent Depressive Disorder, or Bipolar Affective Disorder (ICD-10), in a double-blind parallel group design. They were treated for six weeks. At inclusion, no significant difference between groups was shown. Final MADRS scores were 15.7 and 15.8 with tianeptine and fluoxetine, respectively (ITT population) (p = 0.944). MADRS responders were 58% and 56% with tianeptine and fluoxetine, respectively (p = 0.710). No statistical difference was observed for the other efficacy parameters. Thirty-six withdrawals occurred in each group, without any difference for the reasons of discontinuation. There was no major difference between groups for the other safety parameters. In this study, both tianeptine and fluoxetine exhibited a good efficacy and safety. Copyright 1999 Elsevier Science B. V. All rights reserved.

Pharmacokinetic optimisation in the treatment of Parkinson's disease

The current symptomatic treatment of Parkinson's disease mainly relies on agents which are able to restore dopaminergic transmission in the nigrostriatal pathway, such as the dopamine precursor levodopa or direct agonists of dopamine receptors. Ancillary strategies include the use of anticholinergic and antiglutamatergic agents or inhibitors of cerebral dopamine catabolism, such as monoamine oxidase type B inhibitors. Levodopa is the most widely used and effective drug. Its peculiar pharmacokinetics are characterised by an extensive presystemic metabolism, overcome by the combined use of extracerebral inhibitors of the enzyme aromatic-amino acid decarboxylase and rapid adsorption in the proximal small bowel by a saturable facilitated transport system shared with other large neutral amino acids. Drug transport from plasma to the brain is mediated by the same carriers operating in the intestinal mucosa. The main strategies to assure reproducibility of both drug intestinal absorption and delivery to the brain and clinical effect include standardisation of levodopa administration with respect to meal times and a controlled dietary protein intake. The levodopa plasma half-life is very short, resulting in marked plasma drug concentration fluctuations which are matched, as the disease progresses, with swings in the therapeutic response ('wearing-off' phenomena). 'Wearing-off' phenomena can be also associated, at the more advanced disease stages with a 'negative', both parkinsonism-exacerbating and dyskinetic effect of levodopa at subtherapeutic plasma concentrations. Dyskinesias may be also related to high-levodopa, excessive plasma concentrations. Recognition of the different levodopa toxic response patterns can be difficult on a clinical basis alone, and simultaneous monitoring of levodopa concentration-effect relationships may prove useful to disclose the underlying mechanism and in planning the correct pharmacokinetic management. Controlled-release levodopa formulations have been developed in an attempt to smooth out fluctuations in plasma profiles and matched therapeutic responses. The delayed levodopa absorption and lower plasma concentrations which characterise controlled-release formulations compared with standard forms must be taken into account when prescribing dosage regimens and can be complicating factors in the management of the advanced disease stages. The pharmacokinetic and pharmacodynamic characterisation of the other antiparkinsonian agents is hampered by the lack of sensitive and specific analytical methods to measure their very low plasma drug concentrations and by the difficulty in quantitatively assessing overall moderate drug clinical effects. In clinical practice an optimal dosage schedule is still generally found for each patient on an empirical basis. Future strategies should focus on the search for pharmacological agents with a better kinetic profile, particularly a higher and reproducible bioavailability and a predictable relationship between plasma drug concentration and clinical response. Treatments aimed not only at controlling the symptoms, but also at slowing the neurodegenerative process, are currently under intensive investigation.

Effect of age on the pharmacokinetics of oral levodopa in patients with Parkinson's disease

The influence of age on the kinetics of a standard oral dose of levodopa administered with an inhibitor of peripheral dopa decarboxylase enzymes (benserazide) has been evaluated in 40 patients with Parkinson's disease (age 34-78 y) on chronic therapy. They were divided into 2 groups, on the basis of age below (21 patients, Group A) or above (19 patients, Group B) 65 y. The area under the plasma concentration-time curve (AUC) of levodopa was significantly greater in the older group (547 versus 428 mumol.l-1.min in Group B), coupled with a reduced apparent oral clearance (8.1 versus 10.7 ml.min-1.kg-1) and a longer plasma elimination half-life (67.6 versus 54.6 min). The age of the patients was positively correlated with the AUC of levodopa (r = 0.474) and its plasma elimination half-life (r = 0.391), and was negatively correlated with clearance (r = -0.489). The findings confirm previous data on volunteers that showed a reduction in the systemic clearance of levodopa due to age, which would probably account for the finding of a greater AUC of levodopa in older patients. The observed, age-mediated differences in levodopa pharmacokinetics, albeit statistically significant, were moderate and were likely to be of only minor importance for the dosing schedule.