title: Pharmacokinetic modelling of interleukin-1 receptor antagonist in plasma and cerebrospinal fluid of patients following subarachnoid haemorrhage.
abstract: What is already known about this subject? The naturally occurring interlukin-1 receptor antagonist (IL-1RA) markedly protects rodents against ischaemic, excitotoxic and traumatic brain injury, suggesting it may be of therapeutic value. When administered intravenously to patients soon after stroke, IL-1RA is safe and reduces the peripheral inflammatory response. However, IL-1RA is a large protein (17 kDa), which may limit brain penetration, thereby limiting its potential utility in brain injury. What this study adds. The purpose of these experiments was to determine the pharmacokinetics of IL-1RA in cerebrospinal fluid (CSF) of patients, to allow modelling that would aid development of therapeutic regimens. Peripherally administered IL-1RA crosses slowly into and out of the CSF of patients with subarachnoid haemorrhage and, at steady state, CSF IL-1RA concentration (range 115-886 ng ml(-1)) was similar to that found to be neuroprotective in rats (range 91-232 ng ml(-1)), although there was considerable variability among patients. However, there is a large concentration gradient of IL-1RA between plasma and CSF. These CSF:plasma data are consistent with very low permeation of IL-1RA into the CSF and elimination kinetics from it controlled by the volumetric turnover of CSF.
  
  
  OBJECTIVE
  The naturally occurring interlukin-1 receptor antagonist (IL-1RA) markedly protects rodents against ischaemic, excitotoxic and traumatic brain injury, suggesting it may be of therapeutic value. The aim was to determine the pharmacokinetics of IL-1RA in cerebrospinal fluid (CSF) of patients, to allow modelling that would aid development of therapeutic regimens.
  
  
  METHODS
  When administered intravenously to patients soon after stroke, IL-1RA is safe and reduces the peripheral inflammatory response. However, IL-1RA is a large protein (17 kDa), which may limit brain penetration, thereby limiting its potential utility in brain injury. In seven patients with subarchnoid haemorrhage (SAH), IL-1RA was administered by intravenous bolus, then infusion for 24 h, and both blood and CSF, via external ventricular drains, were sampled during and after stopping the infusion.
  
  
  RESULTS
  Plasma steady-state concentrations were rapidly attained and maintained throughout the infusion, whereas CSF concentrations rose slowly towards a plateau during the 24-h infusion, reaching at best only 4% of that in plasma. Plasma kinetic parameters were within the literature range. Modelling of the combined data yielded rate constants entering and leaving the CSF of 0.0019 h(-1)[relative standard error (RSE) = 19%] and 0.1 h(-1) (RSE = 19%), respectively.
  
  
  CONCLUSIONS
  Peripherally administered IL-1RA crosses slowly into and out of the CSF of patients with SAH. However, there is a large concentration gradient of IL-1RA between plasma and CSF. These CSF:plasma data are consistent with very low permeation of IL-1RA into the CSF and elimination kinetics from it controlled by the volumetric turnover of CSF.
authors: Centre for Applied Pharmacokinetic Research, School of Pharmacy and Pharmaceutical Sciences, University of Manchester, UK. gueorguieva_ivelina@lilly.com
authors: Ivelina
authors: I
authors: Gueorguieva
authors: Simon R
authors: SR
authors: Clark
authors: Catherine J
authors: CJ
authors: McMahon
authors: Sylvia
authors: S
authors: Scarth
authors: Nancy J
authors: NJ
authors: Rothwell
authors: Pippa J
authors: PJ
authors: Tyrrell
authors: Pippa J
authors: PJ
authors: Tyrell
authors: Stephen J
authors: SJ
authors: Hopkins
authors: Malcolm
authors: M
authors: Rowland
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein / Q000097:blood / Q000134:cerebrospinal fluid / Q000493:pharmacokinetics*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D013345:Subarachnoid Hemorrhage / Q000097:blood* / Q000134:cerebrospinal fluid* / Q000188:drug therapy; D013997:Time Factors
chemical_list: D053590:Interleukin 1 Receptor Antagonist Protein