Development and Validation a UPLC-MS/MS Method for Quantification of Pentoxifylline in Beagle Plasma: Application for Pharmacokinetic Study of Food Effect.

Purpose: To develop an UPLC-MS/MS method for the quantitative analysis of pentoxifylline in beagle dog plasma and apply it to a pharmacokinetic study of food effect. Methods: Sample separation was achieved using a Kinetex Phenyl-Hexyl column (50 × 2.1 mm, 1.7 µm) with a gradient elution program in 5.5 min after a simple protein precipitation with methanol. Using the mobile phase that made up by 0.2% formic acid and 5mM ammonium formate water (A) and methanol (B). Quantitation was carried out using the positive ionization mode with multiple reaction monitoring (MRM). A randomized, single-dose, two-period crossover study was conducted in six fasted or fed beagles that received 400 mg pentoxifylline sustained-release tablets (Brand name: Shuanling™, CSPC Pharmaceutical Group). WinNonlin® software was used to calculate pharmacokinetic parameters. Results: The linear calibration range was 2-1000 ng/mL (r2> 0.99). Both intra- and inter-batch precision were less than 6.27%, and the accuracy ranged from 88.65% to 97.18%. Pentoxifylline was readily absorbed in fasted and fed dogs administered a dose of 400 mg (tmax:1.54h vs 1.83h). Compared to the fasted group, the AUC0→t and Cmax in the fed group increased by 1.71-fold and 1.30-fold, respectively. In the fasted group, the AUC0→t and Cmax values were 4684.08 h•ng/mL and 2402.33 ng/mL, respectively. In the fed group, these values were 8027.75 h•ng/mL and 3119.67 ng/mL. The difference in AUC0-t between the fed and fasted group was statistically significant. Conclusion: The novel optimized UPLC-MS/MS assay is an effective tool for the determination of pentoxifylline and has been successfully applied in pharmacokinetic studies of pentoxifylline in beagle dogs. The administration of pentoxifylline sustained-release tablets with food significantly increased the area under the time curve, and it is recommended that they should be administered during or shortly after feeding.

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.

Simultaneous estimation of lisofylline and pentoxifylline in rat plasma by high performance liquid chromatography-photodiode array detector and its application to pharmacokinetics in rat.

Lisofylline (LSF) is an anti-inflammatory and immunomodulatory agent with proven activity in serious infections associated with cancer chemotherapy, hyperoxia-induced acute lung injury, autoimmune disorders including type-1 diabetes (T1DM) and islet rejection after islet transplantation. It is also an active metabolite of another anti-inflammatory agent, Pentoxifylline (PTX). LSF bears immense therapeutic potential in multiple pharmacological activities and hence appropriate and accurate quantification of LSF is very important. Although a number of analytical methods for quantification of LSF and PTX have been reported for pharmacokinetics and metabolic studies, each of these have certain limitations in terms of large sample volume required, complex extraction procedure and/or use of highly sophisticated instruments like LC-MS/MS. The aim of current study is to develop a simple reversed-phase HPLC method in rat plasma for simultaneous determination of LSF and PTX with the major objective of ensuring minimum sample volume, ease of extraction, economy of analysis, selectivity and avoiding use of instruments like LC-MS/MS to ensure a widespread application of the method. A simple liquid-liquid extraction method using methylene chloride as extracting solvent was used for extracting LSF and PTX from rat plasma (200µL). Samples were then evaporated, reconstituted with mobile phase and injected into HPLC coupled with photo-diode detector (PDA). LSF, PTX and 3-isobutyl 1-methyl xanthine (IBMX, internal standard) were separated on Inertsil® ODS (C18) column (250×4.6mm, 5µm) with mobile phase consisting of A-methanol B-water (50:50v/v) run in isocratic mode at flow rate of 1mL/min for 15min and detection at 273nm. The method showed linearity in the concentration range of 50-5000ng/mL with LOD of 10ng/mL and LLOQ of 50ng/mL for both LSF and PTX. Weighted linear regression analysis was also performed on the calibration data. The mean absolute recoveries were found to be 80.47±3.44 and 80.89±3.73% for LSF and PTX respectively. The method was successfully applied for studying the pharmacokinetics of LSF and PTX after IV bolus administration at dose of 25mg/kg in Wistar rat. In conclusion, a simple, sensitive, accurate and precise reversed-phase HPLC-UV method was established for simultaneous determination of LSF and PTX in rat plasma.

Quantitative analyses of CTP-499 and five major metabolites by core-structure analysis.

CTP-499 is a novel oral multi-subtype selective inhibitor of PDEs that is currently in clinical testing, in combination with angiotensin modulators, as a potentially first-in-class treatment for diabetic kidney disease. The compound was discovered and developed by using Concert's proprietary DCE Platform(®) in which deuterium was incorporated at select positions of 1-((S)-5-hydroxyhexyl)-3,7-dimethylxanthine (HDX). CTP-499 metabolizes to five major metabolites: C-21256, D-M2, D-M3, D-M4 and M5, of which all contains deuterium except M5. During in vivo metabolism, however, H/D exchange takes place. As a result, each analyte, except M5, has multiple molecular masses. To accurately quantify the analytes, we developed an LC-MS/MS method focusing on the core structures of the molecules, termed "core-structure analyses". The core-structure analyses method was then validated under GLP guidance in dog, rat and rabbit plasma, with a sample volume of 50 µL. Results demonstrated that this approach accurately quantifies each of the six analytes despite partial exchange of deuterium with hydrogen atoms in the in vivo samples. The validation parameters included accuracy, precision, sensitivity, stability, dilution integrity, hemolysis, matrix effect, selectivity, and recovery. Acceptable intra-run and inter-run assay precision (%CV ≤ 5.5%) and accuracy (90.1-106.7%) were achieved over a linear range of 10-5,000 ng/mL of each analyte. Various stability tests, including bench-top, freeze/thaw, stock solution, and long-term storage, were also performed. All stability results met acceptance criteria. The robustness of the methods was demonstrated by the incurred sample reproducibility (ISR) tests. After validation, the method was successfully used in support of multiple toxicological studies of CTP-499.

Pharmacokinetics of pentoxifylline and its main metabolites in patients with different degrees of heart failure following a single dose of a modified-release formulation.

Pentoxifylline (PTX) is extensively metabolized in the body, and all its 3 plasma metabolites (M1, M4, M5) are pharmacologically active. The authors evaluated the pharmacokinetics of PTX and its metabolites in 20 patients with chronic heart failure (CHF). Eleven had moderate and 9 severe CHF. The time courses of PTX, M1, M4, and M5 plasma levels were determined after oral administration of a sustained-release 600-mg tablet of PTX, and for each compound, AUC, maximal plasma concentration (C(max)), and time to C(max) (T(peak)) were calculated. Compared with patients with moderate CHF, those with severe CHF showed a significant delay in T(peak) of PTX (3.9 vs 1.6 hours) and M5 (5.6 vs 3.6 hours), a 59% significant increase in M5 AUC, and a 56% nonsignificant increase in PTX AUC. In the whole population, the AUCs of PTX, M4, and M5 were inversely correlated with markers of liver function, whereas the AUCs of M4 and M5 were inversely correlated with the creatinine clearance. In view of the kinetic features of slow-release formulations (flip-flop phenomenon), the delay in T(peak) of PTX in patients with severe CHF compared with moderate CHF should be ascribed to a reduced elimination rate.

Successful treatment of life-threatening pentoxifylline intoxication by high-flux hemodialysis.

High-flux hemodialysis is the method of choice for the treatment of many life threatening intoxications. Reports on intoxication with pentoxifylline are rare, and although pharmacokinetic properties of the drug suggest a potential role for hemodialysis, there are no published reports on extracorporeal treatment attempts. We report the first case of successful treatment of potentially life-threatening pentoxifylline intoxication by high-flux hemodialysis. Based on this single case, dialysis should be considered, especially in anuric patients with pentoxifylline intoxication.

[Influence of perftoran on pharmacokinetics of hydrophilic drugs].

Influence of perfluorocarbon blood substitute Perftoran on pharmacokinetics of cefazolin (20 mg/kg), cefotaxime (25 mg/kg), ciprofloxacin (4 mg/kg) and pentoxifylline (10 mg/kg) upon their intravenous introduction separately or immediately after Perftoran infusion (5 ml/kg) was investigated on rabbits. It was found that the presence of Perftoran accelerated the transfer from blood to tissues for Cefazolin and Cefotaxime, which have negative values of the distribution logarithm in octanol/water (logP = -0.4 and -1.4, respectively). With respect to pentoxifylline and ciprofloxacin, which are less hydrophilic, the effect of pharmacokinetic interference was either weaker or absent. Probably, the infusion of hydrophobic Perftoran nanoemulsion enhances the hydrophobicity of blood plasma, which is a prerequisite for the more intensive transfer of hydrophilic ligands from blood to tissues.

Rapid high-performance liquid chromatography-tandem mass spectrometry method for determination of pentoxifylline and its active metabolites M1 and M5 in human plasma and its application in bioavailability study.

A new rapid, sensitive and selective liquid chromatography coupled with mass spectrometry method was developed and validated for the simultaneous quantification of pentoxifylline (PTX) and two major active metabolites in human plasma (M1 and M5). After a deproteinization step, chromatographic separation of the selected analytes was performed on a RP-C18 column. The detection of target compounds was in multiple reaction monitoring mode using an ion trap mass spectrometer equipped with an electrospray ion source. The method was validated and proved to be linear, accurate and precise over the range 5.08-406.14, 10.08-806.40 and 20.15-1611.60 ng/mL in case of PTX, M1 and M5, respectively. The major advantages of this method are the small sample volume, simple sample processing technique, the high sensitivity and the very good selectivity guaranteed by the MS/MS (in case of PTX) or MS/MS/MS (in case of M1 and M5) detection. The validated method has been successfully applied to a bioequivalence study.

Pharmacokinetic-pharmacodynamic modeling of methylxanthine derivatives in mice challenged with high-dose lipopolysaccharide.

AIMS: Pentoxifylline and lisofylline are methylxanthine derivatives that exhibit anti-inflammatory activity both in vitro and in vivo. This study was designed to develop a pharmacokinetic-pharmacodynamic (PK/PD) model to describe the inhibitory effect of these compounds on TNF-alpha production in mice challenged with bacterial lipopolysaccharide (LPS). METHODS: Male CD-1 mice received increasing intravenous doses of either compound simultaneously with high-dose LPS. A 2-compartment model with Michaelis-Menten-type elimination was used to describe the drug concentration versus time data. Serum TNF-alpha levels were fitted to an indirect response model. RESULTS: Pentoxifylline and lisofylline reduced LPS-induced TNF-alpha serum concentrations in a dose-dependent manner. PK/PD analysis revealed an almost 2-fold higher estimate of K(m) for pentoxifylline in comparison to lisofylline. The production and elimination rates of TNF-alpha were: k(in) = 2,167 pg/ml * h(-1) and k(out) = 1.65 h(-1), respectively. The drug concentration causing 50% of TNF inhibition (IC(50)) was markedly lower for pentoxifylline (0.47 vs. 1.61 microg/ml). CONCLUSIONS: It seems that pentoxifylline is more potent than lisofylline in inhibiting TNF-alpha production in vivo. The proposed PK/PD model allowed a better understanding of the pharmacological properties of both methylxanthine derivatives and may be helpful in appropriate dosage selection for further studies.

Bioanalysis of pentoxifylline and related metabolites in plasma samples through LC-MS/MS.

Analytical aspects related to the assay of pentoxifylline (PTX), lisofylline (M1) and carboxypropyl dimethylxanthine (M5) metabolites are discussed through comparison of two alternative analytical methods based on liquid chromatography separation and atmospheric pressure electrospray ionization tandem mass spectrometry detection. One method is based on a 'pure' reversed-phase liquid chromatography mechanism, while the second one uses the additional polar interactions with embedded amide spacers linking octadecyl moieties to the silicagel surface (C-18 Aqua stationary phase). In both cases, elution is isocratic. Both methods are equally selective and allows separation of unknowns (four species associated to PTX, two species associated to M1) detected through specific mass transitions of the parent compounds and owning respective structural confirmation. Plasma concentration-time patterns of these compounds follow typical metabolic profiles. It has been advanced that in-vivo formation of conjugates of PTX and M1 is possible, such compounds being cleaved back to the parent ones within the ion source. The first method was associated with a sample preparation procedure based on plasma protein precipitation by strong organic acid addition. The second method used protein precipitation by addition of a water miscible organic solvent. Both analytical methods were fully validated and used to assess bioequivalence between a prolonged release generic formulation and the reference product, under multidose and single dose approaches.

Enhancement of oral bioavailability of pentoxifylline by solid lipid nanoparticles.

Pentoxifylline (PTX) is a highly water-soluble, hemorheologic drug that undergoes first-pass effect with 20% bioavailability. The solid lipid nanoparticles (SLNs) of PTX were prepared to enhance its oral bioavailability by homogenization, followed by the sonification method. Seven different variables, each at two levels, were studied: lipid type, surfactant type and concentration, speed of homogenizer, acetone:dichloromethane (DCM) ratio, lecithin:lipid ratio, and sonication time. The mean particle size and size distribution, drug entrapment efficiency (EE%), zeta potential, and drug release of the SLNs were investigated. A pharmacokinetic study was conducted in male Wistar rats after oral administration of 10 mg kg(-1) PTX in the form of free drug or SLNs. The z-average particle size, zeta potential, and EE% of the SLNs were at least 250 nm, -30.2 mV, and 70%, respectively. Among the studied factors, the lipid type, surfactant type, and percentage had a significant effect on the particle size. Zeta potential was more affected by lipid type, acetone:DCM ratio, and sonication time. Speed of homogenizer and acetone:DCM ratio had a significant effect on the EE%. The optimized SLN was prepared by 80 mg of cetyl alcohol, 10 mg of lecithin, acetone:DCM ratio (1:2), 30-second sonication, 3% Tween 20, and a mixing rate of 800 rpm. In vitro drug release lasted for about 5 hours. It was found that the relative bioavailability of PTX in SLNs was significantly increased, compared to that of the PTX solution. SLNs offer a promising approach to improve the oral bioavailability of PTX that is affected by a high first-pass effect.

Validation of an HPLC method for determination of pentoxifylline in human plasma and its application to pharmacokinetic study.

An HPLC method suitable for routine determination of pentoxifylline in human plasma has been adapted and validated. Sample preparation was done by solid-phase extraction. Chloramphenicol was used as the internal standard. The linear range was from 15-400 ng/mL (r2 = 0.9994), with a limit of quantitation of 15 ng/mL. The limit of detection was found to be 5 ng/mL. The intra- and interday accuracy ranged from 98.0 to 110.2% and the coefficient of variation was not more than 8.8% for both intra- and interday precision. The absolute recoveries of pentoxifylline and chloramphenicol from human plasma were >97%. The method was validated with excellent specificity, accuracy, precision, recovery, and stability. The pharmacokinetic study of a generic pentoxifylline 400 mg tablet in healthy Thai male volunteers after a single dose administration was determined by this developed assay.

Pharmacokinetic comparisons of tail-bleeding with cannula- or retro-orbital bleeding techniques in rats using six marketed drugs.

INTRODUCTION: The evaluation of drug disposition properties of chemical entities in drug discovery research typically involves the conduct of pharmacokinetic studies in rodents that requires blood sampling over several time points, preferably without disrupting the physiological status of the animals. Several blood withdrawal methods have been employed throughout the industry, yet these methods have not been comprehensively evaluated with regard to their effects on pharmacokinetic profiles of the drug investigated to recommend best practices. METHODS: In this paper, the pharmacokinetics of six marketed drugs from four distinct therapeutic classes were compared using tail-vein, femoral-artery cannula-, and retro-orbital sinus bleeding techniques. The marketed drugs used in these studies were pentoxifylline, gemfibrozil, glipizide, methotrexate, clonidine, and fluoxetine. RESULTS: Following oral administration, peak plasma concentration (C(max)), and area under the curve (AUC(0-24)) values for all compounds were not significantly different with the tail-vein method when compared to cannula- or retro-orbital sinus bleeding, except for fluoxetine and gemfibrozil for which minor, but statistically significant differences were observed. The effect of arterial versus venous tail-bleeding on the pharmacokinetics of pentoxifylline indicated no statistical differences in either C(max) or AUC(0-24) values. However, for fluoxetine, higher exposures were observed with tail arterial than venous sampling (2-fold with respect to C(max) and 1.7-fold with respect to AUC(0-24), p<0.05). DISCUSSION: The observed differences with fluoxetine may be due to its pharmacological effects on thermoregulatory responses that influence tail blood flow, a hypothesis that remains to be tested. Based on these observations, we recommend the tail-bleeding technique for pharmacology or toxicology exposure and F% studies, particularly in early discovery work. Retro-orbital bleeding is controversial and is no longer considered a humane method. Cannula-bleeding, especially coupled with automated blood-collection techniques, has become the most efficient way for pharmaceutical industry to perform rat bioavailability studies.

Pharmacokinetics of intranasal and intratracheal pentoxifylline in rabbits.

STUDY OBJECTIVE: To evaluate the disposition of pentoxifylline and its metabolite, lisofylline, in New Zealand rabbits after two alternative routes of administration, intranasal and intratracheal. DESIGN: Pharmacokinetics study in an animal model. SETTING: University-affiliated animal care facility. SUBJECTS: Twenty New Zealand white rabbits divided into four groups of five rabbits each: group 1 did not receive study drug (control group), and groups 2, 3, and 4 evaluated intravenous, intranasal, and intratracheal routes of administration, respectively. INTERVENTION: Each rabbit in groups 2-4 received pentoxifylline as a single 20-mg/kg dose by their respective route of administration. MEASUREMENTS AND MAIN RESULTS: Blood samples were collected over a 24-hour period and were analyzed by using high-performance liquid chromatography-tandem mass spectrometry. The pharmacokinetic parameters evaluated were area under the concentration-time curve from time zero extrapolated to infinity (AUC(0-infinity)), maximum concentration (Cmax), time to maximum concentration (Tmax), elimination rate constant (k(el)), and half-life (t1/2). Median pentoxifylline pharmacokinetic parameters after intravenous administration were AUC(0-infinity) 5420 ng x hr/ml, Cmax 16,727 ng/ml, Tmax 5 minutes, k(el) 0.036 minute(-1), and t1/2 19 minutes. Median pharmacokinetic parameters after intranasal and intratracheal administration, respectively, were AUC(0-infinity) 4224 and 6824 ng x hr/ml, Cmax 11,181 and 16,758 ng/ml, Tmax 5 and 5 minutes, k(el) 0.028 and 0.032 minute(-1), and t1/2 25 and 22 minutes. The metabolite, lisofylline, displayed a similar disposition after the three different routes of administration. CONCLUSION: The pharmacokinetic profiles after intranasal and intratracheal administration of pentoxifylline appear similar to those after intravenous administration. These data provide support for development of pentoxifylline intranasal and intratracheal dosage formulations that would be suitable for use in premature neonates.

Pharmacokinetics of pentoxifylline and its 5-hydroxyhexyl metabolite after oral and intravenous administration of pentoxifylline to healthy adult horses.

OBJECTIVE: To determine serum pharmacokinetics of pentoxifylline and its 5-hydroxyhexyl metabolite in horses after administration of a single IV dose and after single and multiple oral doses. ANIMALS: 8 healthy adult horses. PROCEDURES: A crossover study design was used with a washout period of 6 days between treatments. Treatments were IV administration of a single dose of pentoxifylline (8.5 mg/kg) and oral administration of generic sustained-release pentoxifylline (10 mg/kg, q 12 h, for 8 days). Blood samples were collected 0, 1, 3, 6, 12, 20, 30, and 45 minutes and 1, 2, 4, 6, 8, and 12 hours after IV administration. For oral administration, blood samples were collected 0, 0.25, 0.5, 0.75, 1, 2, 4, 8, and 12 hours after the first dose and 0, 0.25, 0.5, 0.75, 1, 2, 4, 8, 12, and 24 hours after the last dose. RESULTS: Elimination of pentoxifylline was rapid after IV administration. After oral administration, pentoxifylline was rapidly absorbed and variably eliminated. Higher serum concentrations of pentoxifylline and apparent bioavailability were observed after oral administration of the first dose, compared with values after administration of the last dose on day 8 of treatment. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, oral administration of 10 mg of pentoxifylline/kg results in serum concentrations equivalent to those observed for therapeutic doses of pentoxifylline in humans. Twice daily administration appears to be appropriate. However, serum concentrations of pentoxifylline appear to decrease with repeated dosing; thus, practitioners may consider increasing the dosage if clinical response diminishes with repeated administration.

Nebulized pentoxifylline for prevention of bronchopulmonary dysplasia in very low birth weight infants: a pilot clinical study.

OBJECTIVE: To evaluate the effectiveness of nebulized pentoxifylline (PTXF) compared to intravenous dexamethasone (DX) or placebo (nebulized distilled water) for the prevention of bronchopulmonary dysplasia (BPD). METHODS: One hundred and fifty very low birth weight infants were randomly assigned to three groups. Entry criteria were the need for oxygen administration on the fourth day of life, irrespective of whether ventilatory support was required. PTXF was administered with a nebulizer every 6 hours on three consecutive days (a single course) in a dose of 20 mg/kg when infants were breathing spontaneously or 10 mg/kg when they needed ventilatory support. DX was given every 12 hours on three consecutive days in a dose of 0.25 mg/kg. Nebulized distilled water was administered with the schedule of inhalation as in the PTXF group. When the need for ventilatory support or oxygen dependency persisted, the course of both drugs and placebo administration was repeated every seven days until the diagnosis of BPD was established. RESULTS: Both PTXF and DX reduced the incidence of disease when compared with placebo. The respective data obtained for the PTXF-group versus the placebo group were as follows: difference in risk, 27%; OR: 0.32; CI: 0.11-0.94; p = 0.039; whereas the results for the DX-group versus the placebo group were: difference in risk, - 23%; OR: 0.39; CI: 0.14-1.14; p = 0.07. CONCLUSION: Our data show that nebulized PTXF reduces the risk of BPD and may be a potential alternative to steroids in the prevention of this disease.

Interconversion and tissue distribution of pentoxifylline and lisofylline in mice.

The aim of this study was to assess the interconversion pharmacokinetics and tissue distribution of pentoxifylline and the active (R)-enantiomer of its metabolite M1, lisofylline in male CD-1 mice. Both compounds were administered intravenously at a dose of 50 mg/kg on two separate occasions. Serum and tissues were collected at different time points following drug administration. In addition, the (S)-enantiomer of M1 was administered to a group of mice and serum samples were obtained. Analyte concentrations were measured by chiral HPLC. All serum concentration versus time data were fitted simultaneously to a pharmacokinetic model incorporating interconversion processes of parent drug and metabolites. The estimated conversion clearance of (-)-(R)-M1 to pentoxifylline (CL21) was six times greater than that for the reverse process (CL12). The interconversion of pentoxifylline and (+)-(S)-M1 was faster as reflected by the values of conversion clearances CL13 and CL31 which were approximately 16 and 7 times greater in comparison with the corresponding clearances for the interconversion of pentoxifylline and (-)-(R)-M1. When fitting pharmacokinetic data of both parent compounds to a one-compartment model, the values of elimination clearances assessed were close to those obtained on the basis of the interconversion model. After administration of pentoxifylline, tissue-to-serum AUC ratios ranged from 0.1 for liver and lungs to 0.32 for brain tissue. Serum levels of its metabolite, (-)-(R)-M1 were very low, whereas its tissue levels exceeded serum concentrations. The highest value of metabolite-to-parent AUC ratio (4.98) was observed in lungs. When (-)-(R)-M1 was given as a parent drug, tissue-to-serum AUC ratios in liver, kidney, and lungs were very close and ranged from 0.64 to 0.72. At the same time, levels of its metabolite, pentoxifylline were relatively low both in serum and all tissues studied. In consequence, metabolite-to-parent AUC ratios did not exceed the value of 0.27. In conclusion, reversible metabolism plays a modest role in the disposition of pentoxifylline and (-)-(R)-M1. It seems that pentoxifylline has less favourable pharmacokinetic properties than (-)-(R)-M1 due to lower concentrations attained in target organs. High levels of (-)-(R)-M1 observed after pentoxifylline administration in certain tissues such as liver or lungs suggest that pentoxifylline may constitute an effective prodrug for (-)-(R)-M1 in these organs.

A placebo-controlled study of retinal blood flow changes by pentoxifylline and metabolites in humans.

AIM: To investigate the possible effects of pentoxifylline metabolites on retinal blood flow in humans. METHODS: A randomized, placebo-controlled, four-period cross-over study that was observer blinded and partly blinded for the eight participants. On one occasion a placebo was given as an intravenous (i.v.) infusion over 100 min. On the other three occasions pentoxifylline was administered as i.v. infusions over 100 min at a rate of 3 mg min(-1). Before two of the pentoxifylline infusions the subjects were pretreated with either ciprofloxacin or rifampicin. Retinal blood flow was measured by scanning laser doppler flowmetry (SLDF) in a selected area of the central temporal retina before, during and until 5 h after the end of infusion. Blood samples for concentration analyses of pentoxifyllin, R-M1, S-M1, M4 and M5 were taken serially and areas under the curves (AUCs) were calculated. Linear mixed models were used for the statistical analyses. RESULTS: Mean AUCs (ng h ml(-1)) were significantly increased for pentoxifylline (1964 vs. 1453) and S-M1 (5804 vs. 4227), but not R-M1 when pentoxifylline was co-administered with ciprofloxacin. The mean AUC for M5 was significantly reduced when subjects were pretreated with rifampicin (2041 vs. 3080). Pentoxifylline with and without pretreatment with rifampicin significantly increased retinal blood flow assessed as mean flow, pulsation (i.e. 1-systole/diastole), and diastolic flow (but not during systole), compared with placebo. The increases over placebo were more pronounced on diastolic flow, 9.7% (95% confidence interval 4.2, 15.5) than on mean flow, 4.6% (1.1, 8.3) after pentoxifylline administration. With pentoxifylline after rifampicin pretreatment the corresponding differences were 11.7% (5.8, 17.9) and 5.1% (1.4, 7.8) over placebo, respectively. After co-administration of pentoxifylline and ciprofloxacin we saw only a nonsignificant trend towards increased flow during diastole, but a significant decrease in pulsation. When AUCs for pentoxifylline and its metabolites were used as regressor variables to retinal mean flow we found that pentoxifylline, R-M1 and M5 had coefficients with a positive sign indicating that they enhanced the retinal blood flow. In contrast, S-M1 and M4 had coefficients with negative sign and thus appeared to decrease the blood flow in subjects treated with pentoxifylline. CONCLUSION: The R-M1 and M5 metabolites of pentoxifylline contributed significantly to the effects of pentoxifylline on retinal blood flow.

Pharmacokinetics and oral bioavailability of pentoxyfylline in broiler chickens.

The pharmacokinetic properties of pentoxyfylline and its metabolites were determined in healthy chickens after single intravenous and oral dosage of 100 mg/kg pentoxyfylline. Plasma concentrations of pentoxyfylline and its metabolites were determined by a validated high-performance liquid chromatographic method. After intravenous (i.v.) and oral (p.o.) administration, the plasma concentration-time curves were best described by a one-compartment open model. The mean elimination half-life (t(1/2el)) of pentoxyfylline was 1.05 h, total body clearance 1.90 L/h x kg, volume of distribution 2.40 L/kg and the mean residence time was 2.73 h, after i.v. administration. After oral dosing, mean maximal plasma concentration of pentoxyfylline was 4.01 microg/mL and the interval from p.o. administration until maximum concentration was 1.15 h. The mean oral bioavailability was found to be 28.2%. Metabolites I, IV and V were present in chicken plasma after both i.v. and p.o. administration, with metabolite V being the most dominant.

Use of liquid chromatography-tandem mass spectrometry for the analysis of pentoxifylline and lisofylline in plasma.

A method was developed for the quantitation of pentoxifylline [1-(5-oxohexyl)-3,7-dimethylxanthine] and a primary active metabolite, lisofylline [1-(5-hydroxyhexyl)-3,7-dimethylxanthine], using high-performance liquid chromatography (HPLC)-tandem mass spectrometry. This method was developed in order to overcome problems encountered with HPLC-ultraviolet detection. The operating parameters of the electrospray interface (PE SCIEX, TurboIon Spray) and lens voltages of the triple-quadrupole detector (PE SCIEX 365) were optimized in positive ion mode to obtain the best sensitivity of the analytes. Collision-induced dissociation was used to produce fragment ions, and multiple reaction monitoring was used to quantitate pentoxifylline (m/z 279/181) and lisofylline (m/z 263/181). Dichloromethane was used to extract the drug, metabolite, and the internal standard (3-isobutyl-1-methylxanthine) from plasma. A reverse-phase C8(2) 150 x 1.0 mm HPLC column was used to resolve all three compounds in less than 6 min. Calibration curves were generated using peak area and were linear from 1 to 1000 ng/mL (R(2) > 0.99). The small sample volume, ease of extraction, and sensitivity provide advantages over more conventional methods of quantitation.