Simultaneous determination of doxapram and 2-ketodoxapram in plasma of neonates by gas chromatography

Simultaneous Quantification and Pharmacokinetic Characterization of Doxapram and 2-Ketodoxapram in Porcine Plasma and Brain Tissue

Atrial fibrillation (AF) is an arrhythmia associated with an increased stroke risk and mortality rate. Current treatment options leave unmet needs in AF therapy. Recently, doxapram has been introduced as a possible new option for AF treatment in a porcine animal model. To better understand its pharmacokinetics, three German Landrace pigs were treated with intravenous doxapram (1 mg/kg). Plasma and brain tissue samples were collected. For the analysis of these samples, an ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) assay for the simultaneous measurement of doxapram and its active metabolite 2-ketodoxapram was developed and validated. The assay had a lower limit of quantification (LLOQ) of 10 pg/mL for plasma and 1 pg/sample for brain tissue. In pigs, doxapram pharmacokinetics were biphasic with a terminal elimination half-life (t_1/2) of 1.38 ± 0.22 h and a maximal plasma concentration (c_max) of 1780 ± 275 ng/mL. Its active metabolite 2-ketodoxapram had a t_1/2 of 2.42 ± 0.04 h and c_max of 32.3 ± 5.5 h after administration of doxapram. Protein binding was 95.5 ± 0.9% for doxapram and 98.4 ± 0.3% for 2-ketodoxapram with a brain-to-plasma ratio of 0.58 ± 0.24 for doxapram and 0.12 ± 0.02 for 2-ketodoxapram. In conclusion, the developed assay was successfully applied to the creation of pharmacokinetic data for doxapram, possibly improving the safety of its usage.

Simultaneous quantification of fentanyl, sufentanil, cefazolin, doxapram and keto-doxapram in plasma using liquid chromatography-tandem mass spectrometry

A simple and specific UPLC–MS/MS method was developed and validated for simultaneous quantification of fentanyl, sufentanil, cefazolin, doxapram and its active metabolite keto‐doxapram. The internal standard was fentanyl‐d5 for all analytes. Chromatographic separation was achieved with a reversed‐phase Acquity UPLC HSS T3 column with a run‐time of only 5.0 min per injected sample. Gradient elution was performed with a mobile phase consisting of ammonium acetate or formic acid in Milli‐Q ultrapure water or in methanol with a total flow rate of 0.4 mL min⁻¹. A plasma volume of only 50 μL was required to achieve adequate accuracy and precision. Calibration curves of all five analytes were linear. All analytes were stable for at least 48 h in the autosampler. The method was validated according to US Food and Drug Administration guidelines. This method allows quantification of fentanyl, sufentanil, cefazolin, doxapram and keto‐doxapram, which is useful for research as well as therapeutic drug monitoring, if applicable. The strength of this method is the combination of a small sample volume, a short run‐time, a deuterated internal standard, an easy sample preparation method and the ability to simultaneously quantify all analytes in one run.

Development and validation of an LC–MS/MS method for simultaneously determining doxapram and keto-doxapram in human serum

Aim: Doxapram, a respiratory stimulant, is used to treat apnea. A reliable method of determining doxapram in blood is required for monitoring purposes. Results: Doxapram, keto-doxapram (active metabolite) and propranolol (internal standard) were extracted from human serum by protein precipitation and plate filtration. Molecular ions were generated by electrospray ionization in positive ion mode, and the ions were analyzed using a triple-quadrupole mass spectrometer. The calibration curves were linear from 20 to 5000 ng/ml. The method was validated and the selectivity, reproducibility and stability met the acceptance criteria. Conclusion: An LC–MS/MS method was successfully developed for determining doxapram and keto-doxapram in human serum. The method can be used to monitor doxapram and keto-doxapram concentrations in blood.

Severe side effects and drug plasma concentrations in preterm infants treated with doxapram

A high-performance liquid chromatography method has been developed for simultaneous determination of doxapram and its metabolites including ketodoxapram, the main and only active metabolite. The aim of the study was to evaluate this microtechnique and to report the cases involving severe adverse effects to determine toxic plasma levels in neonates. The method was found to be selective, and showed a good baseline separation of doxapram and metabolites. Recovery, linearity, intraday/interday precision, and limit of detection determined in aqueous solutions and in spiked plasma were satisfactory. The assay is simple, rapid, and plasma-sparing, which represents a true advantage in managing neonates. Case analysis was performed in two consecutive periods: 124 preterm infants in the first period and 173 in the second period. Severe toxic effects were observed in 4 cases in the first period, with doxapram plus keto-doxapram levels 9 mg/L. In the second period, only one case was observed. High-range plasma concentrations were significantly less frequent in the second period than in the first one. The authors conclude that measuring doxapram plus keto-doxapram in plasma may be of interest to avoid severe toxic effects in preterm neonates treated with doxapram.

Urinary metabolites of doxapram in premature neonates

1. Urine samples from 20 premature neonates who received doxapram by i.v. infusion were analysed for drug metabolites by g.l.c-mass spectrometry. 2. In addition to doxapram, all urines contained at least one metabolite, but the known metabolite, 3-ketodoxapram, was detected in only 50% of the samples, and in some instances only in trace amounts. 3. Significant inter-individual differences in the metabolic pathways of doxapram were observed. 4. A total of six metabolites of doxapram were isolated three of which have not been observed previously in human or in dog. 5. Appropriate structures for the new metabolites have been deduced from their mass spectral fragmentation pathways, and are 1-ethyl-4-[2-(N-formyl-N-(2-hydroxy-ethyl)amino)ethyl]-3,3-diphenyl-2- pyrrolidinone (VII), 1-ethyl-4-[2-(4-morpholin-2-onyl)ethyl]-3,3-diphenyl-2-pyrro lidinone (IX) and 4-ethenyl-1-ethyl-3,3-diphenyl-2-pyrrolidinone (X).