High-performance liquid chromatography–tandem mass spectrometry in the identification and determination of phase I and phase II drug metabolites

Applications of tandem mass spectrometry (MS/MS) techniques coupled with high-performance liquid chromatography (HPLC) in the identification and determination of phase I and phase II drug metabolites are reviewed with an emphasis on recent papers published predominantly within the last 6 years (2002–2007) reporting the employment of atmospheric pressure ionization techniques as the most promising approach for a sensitive detection, positive identification and quantitation of metabolites in complex biological matrices. This review is devoted to in vitro and in vivo drug biotransformation in humans and animals. The first step preceding an HPLC-MS bioanalysis consists in the choice of suitable sample preparation procedures (biomatrix sampling, homogenization, internal standard addition, deproteination, centrifugation, extraction). The subsequent step is the right optimization of chromatographic conditions providing the required separation selectivity, analysis time and also good compatibility with the MS detection. This is usually not accessible without the employment of the parent drug and synthesized or isolated chemical standards of expected phase I and sometimes also phase II metabolites. The incorporation of additional detectors (photodiode-array UV, fluorescence, polarimetric and others) between the HPLC and MS instruments can result in valuable analytical information supplementing MS results. The relation among the structural changes caused by metabolic reactions and corresponding shifts in the retention behavior in reversed-phase systems is discussed as supporting information for identification of the metabolite. The first and basic step in the interpretation of mass spectra is always the molecular weight (MW) determination based on the presence of protonated molecules [M+H]+ and sometimes adducts with ammonium or alkali-metal ions, observed in the positive-ion full-scan mass spectra. The MW determination can be confirmed by the [M-H]- ion for metabolites providing a signal in negative-ion mass spectra. MS/MS is a worthy tool for further structural characterization because of the occurrence of characteristic fragment ions, either MSn analysis for studying the fragmentation patterns using trap-based analyzers or high mass accuracy measurements for elemental composition determination using time of flight based or Fourier transform mass analyzers. The correlation between typical functional groups found in phase I and phase II drug metabolites and corresponding neutral losses is generalized and illustrated for selected examples. The choice of a suitable ionization technique and polarity mode in relation to the metabolite structure is discussed as well

Comparison of Adjacent Segment Degeneration After Nonrigid Fixation System and Posterior Lumbar Interbody Fusion for Single-Level Lumbar Disc Herniation: A New Method of MRI Analysis of Lumbar Nucleus Pulposus Volume

Purpose: To evaluate the influence of a nonrigid fixation system and posterior lumbar interbody fusion on adjacent intervertebral disc degeneration by using MRI analysis of lumbar nucleus pulposus volume for single-level lumbar disc herniation. Materials and Methods: We selected 112 patients who underwent nonrigid fixation (17 men and 44 women) or posterior lumbar interbody fusion (13 men and 38 women) for this retrospective study. Based on the T2-weighted magnetic resonance imaging (MRI) scans taken preoperatively, and 6, 12, and 24 months after surgery, the nucleus pulposus in the upper segments of the operated level was considered an ellipsoid, and their volumes were measured respectively and then compared between the two groups. Results: The posterior lumbar interbody fusion group had significantly lower lumbar nucleus pulposus volume than the nonrigid fixation group at 12 (4.04 ± 1.42 vs. 5.25 ± 1.47 mm3) and 24 months (4.16 ± 0.89 vs. 5.06 ± 1.23 mm3), and had the highest nucleus pulposus. Meanwhile, the h value in the posterior lumbar interbody fusion group was notably smaller than the preoperative level at 12 (0.46 ± 0.03 vs. 0.55 ± 0.05 mm) and 24 months (0.44 ± 0.03 vs. 0.55 ± 0.05 mm). Conclusions: MRI analysis of lumbar nucleus pulposus volume is a new and quantitative method of analysis, which is a considerable method and contributes to the detection of severe intervertebral disc degeneration. Based on this new method, nonrigid fixation demonstrates excellent outcomes on the adjacent segment in comparison with posterior lumbar interbody fusion

Survivorship analysis of 150 consecutive patients with DIAM™ implantation for surgery of lumbar spinal stenosis and disc herniation

Recently, the Device for Intervertebral Assisted Motion (DIAM™) has been introduced for surgery of degenerative lumbar disc diseases. The authors performed the current study to determine the survivorship of DIAM™ implantation for degenerative lumbar disc diseases and risk factors for reoperation. One hundred and fifty consecutive patients underwent laminectomy or discectomy with DIAM™ implantation for primary lumbar spinal stenosis or disc herniation. The characteristics of the 150 patients included the following: 84 males and 66 females; mean age at the time of surgery, 46.5 years; median value of follow-up, 23 months (range 1–48 months); 96 spinal stenosis and 54 disc herniations; and 146 one-level (115, L4–5; 31, L5–6) and 4 two-level (L4–5 and L5–6). In the current study, due to lumbosacral transitional vertebra (LSTV) L6 meant lumbarization of S1 and this had a prominent spinous process so that the DIAM™ was implanted at L5–6. Reoperations due to any reasons of the DIAM™ implantation level or adjacent levels were defined as a failure and used as the end point for determining survivorship. The cumulative reoperation rate and survival time were determined via Kaplan–Meier analysis. The log-rank test and Cox regression model were used to evaluate the effect of age, gender, diagnosis, location, and level of DIAM™ implantation on the reoperation rate. During a 4-year follow-up, seven patients (two males and five female) underwent reoperation at the DIAM™ implantation level, giving a reoperation rate of 4.7%. However, no patients underwent reoperation for adjacent level complications. The causes of reoperation were recurrent spinal stenosis (n = 3), recurrent disc herniation (n = 2), post-laminectomy spondylolisthesis (n = 1), and delayed deep wound infection (n = 1). The mean time between primary operation and reoperation was 13.4 months (range 2–29 months). Kaplan–Meier analysis predicted an 8% cumulative reoperation rate 4 years post-operatively. Survival time was predicted to be 45.6 ± 0.9 months (mean ± standard deviation). Based on the log-rank test, the reoperation rate was higher at L5–6 (p = 0.002) and two-level (p = 0.01) DIAM™ implantation compared with L4–5 and one-level DIAM™ implantation. However, gender (p = 0.16), age (p = 0.41), and diagnosis (p = 0.67) did not significantly affect the reoperation rate of DIAM™ implantation. Based on a Cox regression model, L5–6 [hazard ratio (HR), 10.3; 95% CI, 1.7–63.0; p = 0.01] and two-level (HR, 10.4; 95% CI, 1.2–90.2; p = 0.04) DIAM™ implantation were also significant variables associated with a higher reoperation rate. Survival time was significantly lower in L5–6 (47 vs. 22 months, p = 0.002) and two-level DIAM™ implantation (46 vs. 18 months, p = 0.01) compared with L4–5 and one-level DIAM™ implantation. The current results suggest that 8% of the patients who have a DIAM™ implantation for primary lumbar spinal stenosis or disc herniation are expected to undergo reoperation at the same level within 4 years after surgery. Based on the limited data set, DIAM™ implantation at L5–6 and two-level in patients with LSTV are significant risk factors for reoperation