Theophylline dosing and pharmacokinetics for renal protection in neonates with hypoxic-ischemic encephalopathy undergoing therapeutic hypothermia.

BACKGROUND: Theophylline, a non-selective adenosine receptor antagonist, improves renal perfusion in the setting of hypoxia-ischemia and may offer therapeutic benefit in neonates with hypoxic-ischemic encephalopathy (HIE) undergoing hypothermia. We evaluated the pharmacokinetics and dose-exposure relationships of theophylline in this population to guide dosing strategies. METHODS: A population pharmacokinetic analysis was performed in 22 neonates with HIE undergoing hypothermia who were part of a prospective study or retrospective chart review. Aminophylline (intravenous salt form of theophylline) was given per institutional standard of care for low urine output and/or rising serum creatinine (5 mg/kg intravenous (i.v.) load then 1.8 mg/kg i.v. q6h). The ability of different dosing regimens to achieve target concentrations (4-10 mg/L) associated with clinical response was examined. RESULTS: Birth weight was a significant predictor of theophylline clearance and volume of distribution (p < 0.05). The median half-life was 39.5 h (range 27.2-50.4). An aminophylline loading dose of 7 mg/kg followed by 1.6 mg/kg q12h was predicted to achieve target concentrations in 84% of simulated neonates. CONCLUSIONS: In neonates with HIE undergoing hypothermia, theophylline clearance was low with a 50% longer half-life compared to full-term normothermic neonates without HIE. Dosing strategies need to consider the unique pharmacokinetic needs of this population. IMPACT: Theophylline is a potential renal-protective therapy in neonates with HIE undergoing therapeutic hypothermia; however, the pharmacokinetics and dose needs in this population are not known. Theophylline clearance was low in neonates with HIE undergoing therapeutic hypothermia with a 50% longer half-life compared to full-term normothermic neonates without HIE. As theophylline is advanced in clinical development, dosing strategies will need to consider the unique pharmacokinetic needs of neonates with HIE undergoing therapeutic hypothermia.

HPLC-atmospheric pressure chemical ionization MS/MS for quantification of 15-F2t-isoprostane in human urine and plasma.

BACKGROUND: Quantification of F(2)-Isoprostanes is considered a reliable index of the oxidative stress status in vivo and is valuable in the diagnosis and monitoring of a variety of diseases. Because of complex and lengthy sample preparation procedures, current chromatography/mass spectrometry and immunoassays are impractical for measuring larger numbers of samples. Thus, we developed and validated a semiautomated high-throughput HPLC tandem mass spectrometry assay for the quantification of F(2)-Isoprostane F(2t) in human urine and plasma. METHODS: After protein precipitation (500 microL methanol/zinc sulfate added to 500 microL plasma), samples were injected into the HPLC system and extracted online. The extracts were then back-flushed onto the analytical column and detected with an atmospheric pressure chemical ionization-triple quadrupole mass spectrometer monitoring the deprotonated molecular ions [M-H](-) of 15-F(2t)-IsoP (m/z = 353-->193) and the internal standard 15-F(2t)-IsoP-d(4) (m/z = 357-->197). RESULTS: In human urine, the assay was linear from 0.025 to 80 microg/L and in human plasma from 0.0025 to 80 microg/L (r(2)>0.99). Interday accuracy and precision for concentrations above the lower limit of quantification were <10%. Concentrations of 15-F(2t)-IsoP in urine of 16 healthy individuals ranged from 55-348 ng/g creatinine. In 16 plasma samples from healthy individuals, free 15-F(2t)-IsoP was detectable in all samples and concentrations were 3-25 ng/L. CONCLUSIONS: Our assay meets all predefined method performance criteria, allows for analysis of >80 samples/day, and has sufficient sensitivity for quantifying 15-F(2t)-IsoP concentrations in plasma and urine from healthy individuals. It is, thus, suitable for clinical routine monitoring and the analysis of samples from larger clinical trials.