Reduction of Steady-State Valproate Levels by Other Antiepileptic Drugs

Steady-state plasma valproate (VPA) levels were analyzed in 37 children after 6 weeks of VPA therapy. Twenty-six patients were receiving other antiepileptic drugs in addition to VPA (experimental group). Eleven patients who received VPA alone served as controls. The mean VPA dose was not statistically different for the two groups (experimental group, 35.4 mg/kg/ day, 11.6 SD; control group, 31.1 mg/kg/day, SD 6.6) The mean plasma VPA level was significantly lower for the experimental group (63.0 Μg/m1, SD 21.8) than for the control (99.3 Μg/m1), SD 23.3) ( p < 0.01). VPA levelrdose ratio (LDR) was also reduced in the experimental group (1.92, SD 0.75) as compared to controls (3.26, SD 0.65) ( p < 0.01). Within the experimental group the VPA levels and VPA LDR were significantly reduced in patients receiving either phenytoin or phenobarbital. The data suggest that other antiepileptic drugs significantly alter the steady-state level to dose relationship for VPA. RÉSUMÉ Le taux plasmatique À l'Équilibre du valproate de sodium (VPA) a ÉtÉÉtudiÉ chez 37 enfants aprÈs 6 semaines de thÉrapeutique. Vingt six patients reÇoivent d'autres mÉdicaments antiÉpileptiques associÉs au VPA (groupe expÉrimental) alors que 11 sujets tÉmoins ne reÇoivent que le VPA seul. La posologie moyenne du VPA n'est pas significativement diffÉrente entre les deux groupes (35,4 mg/kg/jour ± 11,6 centre 31,1 mg/kg/jour ± 6,6). Le taux plasmatique de VPA est significativement plus bas dans le groupe experimental (63,0 Μg/ml ± 21,8) contre 99,3 Μg/ml ± 23,3 dans le groupe tÉmoin ( p < 0,01). Le rapport taux plasmatique/posologie (LDR) a ÉtÉ diminuÉ dans le groupe expÉrimental (1,92 ± 0,75) par rapport au groupe tÉmoin (3,26 ± 0,65), p < 0,01 en particulier chez les malades recevant de la phÉnytoÏne ou du phÉnobarbital. La posologie moyenne du VPA n'Étant pas significativement diffÉrente dans les deux groupes, les faits observÉs suggÈrent que l'addition d'autres antiÉpileptiques est capable de modifier le taux À l'Équilibre du VPA plasmatique en fonction de la dose administrÉe. RESUMEN Se analizaron los niveles estables de valproato en plasma (VPA) en 37 niÑos despuÉs de 6 semanas de terapia con VPA. Ventiseis pacientes recibÍan otros fÁrmacos ademÁs de VPA (grupo experimental) y once sÓlo tomaban VPA y sirvieron como controles. La dosis media de VPA no fue significativamente distinta en los dos grupos (grupo experimental: 35,4 mg/kg/dÍa, DS 11,6; grupo control: 31.1 mg/kg/dÍa, DS 6,6). El nivel plasmÁtico medio de VPA fue significativamente inferior en el grupo experimental (63,0 Μg/ml, DS 21,8) que en el control (99,3 Μg/ml, DS 23,3), p < 0,01. La relaciÓn nivel de VPA: dosis (LDR) estaba tambiÉn reducida en el grupo experimental (1,92, DS 0,75) al compararla con los controles (3,26, DS 0,65), p < 0,01. Dentro del grupo experimental los niveles de VPA y la LDR estaban significativamente reducidos en pacientes que tomaban fenitoÍna o fenobarbital. La dosis media no fue diferente entre los grupos experimental y control. Estos datos sugieren que la ingestiÓn de otros fÁrmacos alteran de modo significativo los niveles estables de VPA en relaciÓn con la dosis. ZUSAMMENFASSUNG In steady-state befindliche Plasma Valproatspiegel (VPA) wurden bei 37 Kindern nach 6 wÖchiger VPA-Therapie analysiert. 26 Patienten erhielten zusÄtzlich zum VPA andere Antiepileptika (experimentelle Gruppe). 11 Patienten, die VPA alleine bekamen, dienten als Kontrollen. Die mittlere VPA-Dosis war in beiden Gruppen nicht signifikant Vunterschiedlich (experimentelle Gruppe 35,4 mg/kg pro Tag, 11,6 SD; Kontrollgruppe 31,1 mg/kg pro Tag, SD 6,6). Der mittlere Plasma VPA-Spiegel war signifikant niedriger in der experimentellen Gruppe (63,0 Μg/ml, SD 21,8) als in der Kontrollgruppe (99,3 Μg/m1, SD 23,3), p < 0.01. Das VerhÄltnis VPA-Spiegel: Dosis (LDR) war in der experimentellen Gruppe ebenfalls reduziert (1,92, SD 0,75) gegenuber der Kontrollgruppe (3,26, SD 0,65), p < 0.01. Innerhalb der experimentellen Gruppe waren die VPA-Spiegel und die VPA/LDR bei Patienten, die entweder Phenytoin oder Phenobarbital bekamen, signifikant erniedrigt. Die mittlere VPA-Dosis war nicht signifikant unterschiedlich in der experimentellen und in der Kontrollgruppe. Diese Daten lassen vermuten, daß andere Antiepileptika signifikanterweise den Steady-state-Spiegel im Hinblick auf die verabfolgte Dosis VPA Ändern.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66058/1/j.1528-1157.1981.tb06154.x.pd

Collusion through Joint R&D: An Empirical Assessment

This paper tests whether upstream R&D cooperation leads to downstream collusion. We consider an oligopolistic setting where firms enter in research joint ventures (RJVs) to lower production costs or coordinate on collusion in the product market. We show that a sufficient condition for identifying collusive behavior is a decline in the market share of RJV-participating firms, which is also necessary and sufficient for a decrease in consumer welfare. Using information from the US National Cooperation Research Act, we estimate a market share equation correcting for the endogeneity of RJV participation and R&D expenditures. We find robust evidence that large networks between direct competitors – created through firms being members in several RJVs at the same time – are conducive to collusive outcomes in the product market which reduce consumer welfare. By contrast, RJVs among non-competitors are efficiency enhancing

Pharmacokinetic parameters estimated from intravenous data by uniform methods and some of their uses

This article summarizes phamacokinetic parameters of 20 different drugs. The parameters were estimated by uniform methods for an n- compartment open mammillary model in which elimination was assumed to occur only from the central compartment. For various reasons, some of the reported parameters differ appreciably from those reported in the original articles. Some uses of the parameters are discussed .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45070/1/10928_2005_Article_BF01066219.pd