Pharmacokinetic-pharmacodynamic modelling in the early development phase of anti-psychotics: a comparison of the effects of clozapine, S 16924 and S 18327 in the EEG model in rats.

1. The use of pharmacokinetic/pharmacodynamic (PK/PD) analysis in early compound development was investigated in the rat for two developmental anti-psychotic compounds with clozapine as a positive control. 2. Three plasma samples were collected from each of eight animals according to a pre-defined sampling matrix allowing a total of 12 time points for PK analysis. Quantitative electroencephalography (QEEG), particularly the theta and beta frequencies, was used as a measurement of pharmacological effect. 3. PK/KD modelling of the sparse PK data available relative to a rich set of PD data was achieved using a population approach in NONMEM (IV). Individual PK parameter estimates were incorporated into a PK/PD model. 4. Qualitative EEG changes in rat and human were similar for clozapine, but different for the two developmental compounds, suggesting that changes in these PD parameters may not be specifically related to the anti-psychotic activity. 5. Although no definitive data are available concerning the signal specificity of EEG frequency bands with respect to dopaminergic or serotonergic receptor activity, qualitative and quantitative differences seen in EEG parameters are likely to result from the multiple receptor occupancy for these compounds. 6. The results confirm the value of population PK/PD modelling in conjunction with sparse sampling to enable determination of concentration effect relationships in the pre-clinical development programme of CNS-active drugs.

Transdermal administration of piribedil reverses MPTP-induced motor deficits in the common marmoset.

The ability of transdermal administration of the dopamine D2/D3 agonist piribedil (1-[3,4-methylenedioxybenzyl)]-4-[(2-pyrimidinyl)]piperazine) to reverse hypokinesia and other motor deficits observed in MPTP-treated common marmosets was investigated. Piribedil (2.5-10.0 mg/animal), applied directly to the skin of the abdomen as a paste, produced a long-lasting and concentration-dependent reversal of motor deficits. The antiparkinsonian actions of piribedil occurred within 10 minutes of drug administration and lasted as long as 10 hours. Transdermally applied piribedil produced a pattern of locomotor activity characteristic of normal motor behavior in this species. Symptoms of nausea (marked excessive salivation, retching, and/or vomiting) were not observed after transdermal application of piribedil. Additionally, pretreatment with the peripheral dopamine antagonist domperidone enhanced the antiparkinsonian effects of piribedil. Application to the skin of monolayer or bilayer patches impregnated with piribedil also produced a marked increase in locomotor activity and reversal of motor deficits. After application of various patch fractions (whole, one-half, or one-fourth), the increase in locomotor activity and reversal of disability correlated well with the surface area of skin covered. Measurement of serum levels of piribedil after single application of bilayer patches showed a positive relationship between drug levels and antiparkinsonian activity. Repeated daily application of piribedil bilayer patches for 5 days to MPTP-treated common marmosets primed to show dyskinesia by previous exposure to L-Dopa produced antiparkinsonian activity accompanied by dyskinetic movements. Transdermal administration of dopamine agonists such as piribedil may provide a useful means of producing a long-lasting reversal of motor deficits in Parkinson's disease while avoiding acute adverse effects such as nausea.