Simultaneous determination of pentoxifylline, metabolites M1 (lisofylline), M4 and M5, and caffeine in plasma and dried blood spots for pharmacokinetic studies in preterm infants and neonates

From "wet" matrices to "dry" blood spot sampling strategy: a versatile LC-MS/MS assay for simultaneous monitoring caffeine and its three primary metabolites in preterm infants

OBJECTIVES

To update traditional "wet" matrices to dried blood spot (DBS) sampling, based on the liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) technique, and develop a method for simultaneous analyzing caffeine and its three primary metabolites (theobromine, paraxanthine, and theophylline), supporting routine therapeutic drug monitoring (TDM) for preterm infants.

METHODS

DBS samples were prepared by a two-step quantitative sampling method, i.e., volumetric sampling of a quantitative 10 μL volume of peripheral blood and an 8 mm diameter whole punch extraction by a methanol/water (80/20, v/v) mixture containing 125 mM formic acid. Four paired stable isotope labeled internal standards and a collision energy defect strategy were applied for the method optimization. The method was fully validated following international guidelines and industrial recommendations on DBS analysis. Cross validation with previously developed plasma method was also proceeded. The validated method was then implemented on the TDM for preterm infants.

RESULTS

The two-step quantitative sampling strategy and a high recovery extraction method were developed and optimized. The method validation results were all within the acceptable criteria. Satisfactory parallelism, concordance, and correlation were observed between DBS and plasma concentrations of the four analytes. The method was applied to provide routine TDM services to 20 preterm infants.

CONCLUSIONS

A versatile LC-MS/MS platform for simultaneous monitoring caffeine and its three primary metabolites was developed, fully validated, and successfully applied into the routine clinical TDM practices. Sampling method switching from "wet" matrices to "dry" DBS will facilitate and support the precision dosing of caffeine for preterm infants.

Determination of caffeine, paraxanthine, theophylline and theobromine in premature infants by HILIC-MS/MS

Aim: Caffeine is a central nervous system stimulant, used to treat apnea of prematurity. A hydrophilic interaction chromatography-tandem mass spectrometry (HILIC-MS/MS) approach was developed to detect caffeine, paraxanthine, theophylline and theobromine in premature infants. Method: Protein precipitation of plasma samples (10 μl) was carried out by treating with acetonitrile containing caffeine-¹³C₃. The separation was carried out on an ACQUITY HPLC^® BEH HILIC column. Caffeine and its metabolites were quantified by multiple reaction monitoring modes with positive electrospray ionization. Results: The established method had a good linear relationship in the range of 0.0600-60.0 μg/ml for caffeine, 0.0250-7.50 μg/ml for theobromine and 0.0150-4.50 μg/ml for paraxanthine and theophylline. Conclusion: A HILIC-MS/MS method was developed and validated to determine caffeine and its major metabolites in plasma of premature infants.

The use of dried blood spots for characterizing children's exposure to organic environmental chemicals

Biomonitoring is a commonly used tool for exposure assessment of organic environmental chemicals with urine and blood samples being the most commonly used matrices. However, for children's studies, blood samples are often difficult to obtain. Dried blood spots (DBS) represent a potential matrix for blood collection in children that may be used for biomonitoring. DBS are typically collected at birth to screen for several congenital disorders and diseases; many of the states that are required to collect DBS archive these spots for years. If the archived DBS can be accessed by environmental health researchers, they potentially could be analyzed to retrospectively assess exposure in these children. Furthermore, DBS can be collected prospectively in the field from children ranging in age from newborn to school-aged with little concern from parents and minimal risk to the child. Here, we review studies that have evaluated the measurement of organic environmental toxicants in both archived and prospectively collected DBS, and where available, the validation procedures that have been performed to ensure these measurements are comparable to traditional biomonitoring measurements. Among studies thus far, the amount of validation has varied considerably with no studies systematically evaluating all parameters from field collection, shipping and storage contamination and stability to laboratory analysis feasibility. These validation studies are requisite to ensure reliability of the measurement and comparability to more traditional matrices. Thus, we offer some recommendations for validation studies and other considerations before DBS should be adopted as a routine matrix for biomonitoring.

Barriers and Challenges in Performing Pharmacokinetic Studies to Inform Dosing in the Neonatal Population

A number of barriers and challenges must be overcome in order to conduct the pharmacokinetic studies that are urgently needed to inform the selection and dosing of medication in neonates. However, overcoming these barriers can be difficult. This review outlines the common barriers researchers are confronted with, including issues with ethics approval and consent, study design for pharmacokinetic studies and the ability to measure the drug concentrations in the blood samples obtained. Strategies to overcome these challenges are also proposed.

Development and validation of bioanalytical liquid chromatography-tandem mass spectrometry method for the estimation of pentoxifylline in human plasma: Application for a comparative pharmacokinetic study

A method for bioanalysis of pentoxifylline in human plasma was developed using liquid chromatography-tandem mass spectrometry, which is simple, specific, and sensitive. Pentoxifylline D5 was used as the internal standard. Employing only 100 µl of human plasma, processing was done with solid-phase extraction technique. The analyte and the internal standard were separated from endogenous components on Ace phenyl column using a mixture of 5 mM ammonium acetate buffer and high performance liquid chromatography grade acetonitrile (60:40, v/v) as mobile phase at a flow rate of 1 ml/min. The linearity of the method was in the range of 3-1200 ng/ml with r² > 0.99. Positive ion MRM mode was used for the detection of the analyte and the internal standard. The method was validated as per the US Food and Drug Administration guidelines and the results were within the acceptance limits. The proposed method was applied for comparative pharmacokinetic study of pentoxifylline after oral administration of 400 and 600 mg tablets to South Indian male subjects under fed conditions.

Physical compatibility of pentoxifylline and intravenous medications

OBJECTIVE

To investigate the physical and chemical compatibility of pentoxifylline (PTX) with a wide range of parenteral medications used in the neonatal intensive care setting.

DESIGN

PTX and drug solutions were combined in glass phials and inspected visually for physical incompatibility. The chemical compatibility was evaluated on the basis of PTX concentrations.

RESULTS

Precipitation, colour change or turbidity was not visible in any of the test mixtures, indicating no observed physical incompatibility or apparent risk of blockage in narrow-bore intravenous tubing. The PTX concentration was approximately 2.5% and 4.5% lower when combined with dopamine and amoxicillin, respectively. The PTX concentration ratios for all other combinations were in the range of 99%-102%.

CONCLUSION

In simulated Y-site conditions, physical compatibility testing of PTX and 30 parenteral medications revealed no evidence of precipitation. Based on PTX concentration tests, it could be prudent to avoid mixing PTX with dopamine or amoxicillin.

Analysis of Inflammatory Mediators in Newborn Dried Blood Spot Samples by Chip-Based Immunoaffinity Capillary Electrophoresis

A chip-based immunoaffinity capillary electrophoresis (ICE) system has been developed for measuring inflammatory mediators in dried blood samples routinely taken from newborn babies. A defined area of each dried blood spot was removed from the sample card and its contents eluted. The recovered eluates were injected into the chip and the analytes of interest isolated by the immunoaffinity disk within the chip. The captured analytes were labeled in-situ with a red light-emitting laser dye and electro-eluted into the chip separation channel. Electrophoretic separation of all of the analytes was achieved within 2.0 min with quantification of each peak being performed by online LIF detection and integration of each peak area. The degree of accuracy and precision achieved by the chip-based system is comparable to conventional immunoassays and the system is robust enough to be applied to the analysis of clinical samples.

Pentoxifylline Alone or in Combination with Gentamicin or Vancomycin Inhibits Live Microbe-Induced Proinflammatory Cytokine Production in Human Cord Blood and Cord Blood Monocytes In Vitro

Neonatal sepsis and its accompanying inflammatory response contribute to substantial morbidity and mortality. Pentoxifylline (PTX), a phosphodiesterase inhibitor which suppresses transcription and production of proinflammatory cytokines, is a candidate adjunctive therapy for newborn sepsis. We hypothesized that PTX decreases live microbe-induced inflammatory cytokine production in newborn blood. Cord blood was stimulated with live microorganisms commonly encountered in newborn sepsis (Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, or Candida albicans) and simultaneously treated with antimicrobial agents (gentamicin, vancomycin, or amphotericin B) and/or clinically relevant concentrations of PTX. Microbial colony counts were enumerated by plating, supernatant cytokines were measured by multiplex assay, intracellular cytokines and signaling molecules were measured by flow cytometry, and mRNA levels were measured by quantitative reverse transcription-PCR. PTX inhibited concentration-dependent E. coli-, S. aureus-, S. epidermidis-, and C. albicans-induced tumor necrosis factor (TNF) and E. coli-induced interleukin-1β (IL-1β) production in whole blood, with greater suppression of proinflammatory cytokines in combination with antimicrobial agents. Likewise, PTX suppressed E. coli-induced monocytic TNF and IL-1β, whereby combined PTX and gentamicin led to significantly greater reduction of TNF and IL-1β. The anti-inflammatory effect of PTX on microbe-induced proinflammatory cytokine production was accompanied by inhibition of TNF mRNA expression and was achieved without suppressing the production of the anti-inflammatory IL-10. Of note, microbial colony counts in newborn blood were not increased by PTX. Our findings demonstrated that PTX inhibited microbe-induced proinflammatory cytokine production, especially when combined with antimicrobial agents, without enhancing microbial proliferation in human cord blood in vitro, thus supporting its utility as candidate adjunctive agent for newborn sepsis.

Effects of maturation and size on population pharmacokinetics of pentoxifylline and its metabolites in very preterm infants with suspected late-onset sepsis or necrotizing enterocolitis: a pilot study incorporating clinical outcomes

AIMS

Infection-induced inflammation is associated with adverse long-term outcomes in preterm infants. Pentoxifylline (PTX) is a candidate for adjunct immunomodulatory therapy in preterm infants with late-onset sepsis (LOS) and necrotizing enterocolitis (NEC), but pharmacokinetic data in this population are extremely limited. This study aims to characterize the pharmacokinetic properties of intravenous PTX and its metabolites in preterm infants.

METHOD

An open label pilot clinical study of intravenous PTX as an adjunct therapy in preterm infants (gestation <32 weeks) with suspected LOS or NEC was undertaken. PTX was infused for 12 h for two days (60 mg kg^-1 per 12 h), and in infants with confirmed diagnosis of LOS or NEC, for 6 h for another 4 days (30 mg kg^-1 per 6 h). Plasma concentrations of PTX and its principal metabolites from collected blood samples were measured using a validated LCMS assay. NONMEM was used to analyse the data using population pharmacokinetic modelling.

RESULTS

The preterm infants (n = 26) had a median (range) gestation of 24.8 weeks (23.3-30.4) and birthweight of 689 g (370-1285). PTX was well tolerated and without treatment-limiting adverse effects. Changes in size (weight) and maturation were successfully modelled for PTX and metabolites. After allometric scaling, clearance increased with postmenstrual age, increasing by approximately 30% per week for PTX and M1 (lisofylline) and simulations of current dosing demonstrated a six-fold difference in exposure between 24 and 35 weeks postmenstrual age.

CONCLUSIONS

The developed model can be used to explore dosing strategies based on size and maturation for preterm infants.

Pentoxifylline, dexamethasone and azithromycin demonstrate distinct age-dependent and synergistic inhibition of TLR- and inflammasome-mediated cytokine production in human newborn and adult blood in vitro

Introduction

Neonatal inflammation, mediated in part through Toll-like receptor (TLR) and inflammasome signaling, contributes to adverse outcomes including organ injury. Pentoxifylline (PTX), a phosphodiesterase inhibitor which potently suppresses cytokine production in newborn cord blood, is a candidate neonatal anti-inflammatory agent. We hypothesized that combinations of PTX with other anti-inflammatory agents, the steroid dexamethasone (DEX) or the macrolide azithromycin (AZI), may exert broader, more profound and/or synergistic anti-inflammatory activity towards neonatal TLR- and inflammasome-mediated cytokine production.

Methods

Whole newborn and adult blood was treated with PTX (50–200 μM), DEX (10⁻¹⁰–10⁻⁷ M), or AZI (2.5–20 μM), alone or combined, and cultured with lipopolysaccharide (LPS) (TLR4 agonist), R848 (TLR7/8 agonist) or LPS/adenosine triphosphate (ATP) (inflammasome induction). Supernatant and intracellular cytokines, signaling molecules and mRNA were measured by multiplex assay, flow cytometry and real-time PCR. Drug interactions were assessed based on Loewe's additivity.

Results

PTX, DEX and AZI inhibited TLR- and/or inflammasome-mediated cytokine production in newborn and adult blood, whether added before, simultaneously or after TLR stimulation. PTX preferentially inhibited pro-inflammatory cytokines especially TNF. DEX inhibited IL-10 in newborn, and TNF, IL-1β, IL-6 and interferon-α in newborn and adult blood. AZI inhibited R848-induced TNF, IL-1β, IL-6 and IL-10, and LPS-induced IL-1β and IL-10. (PTX+DEX) synergistically decreased LPS- and LPS/ATP-induced TNF, IL-1β, and IL-6, and R848-induced IL-1β and interferon-α, while (PTX+AZI) synergistically decreased induction of TNF, IL-1β, and IL-6. Synergistic inhibition of TNF production by (PTX+DEX) was especially pronounced in newborn vs. adult blood and was accompanied by reduction of TNF mRNA and enhancement of IL10 mRNA.

Conclusions

Age, agent, and specific drug-drug combinations exert distinct anti-inflammatory effects towards TLR- and/or inflammasome-mediated cytokine production in human newborn blood in vitro. Synergistic combinations of PTX, DEX and AZI may offer benefit for prevention and/or treatment of neonatal inflammatory conditions while potentially limiting drug exposure and toxicity.