and Muhammad M Hammami

A rapid liquid chromatographic tandem mass spectrometry (LC-MS/MS) assay for the measurement of metoclopramide level in human plasma was developed and validated. One ml plasma samples containing metoclopramide and 0.25 µg of loratadine as internal standard (IS) were extracted with 5 ml tert-butyl methyl ether and reconstituted in 80 µl of acetonitrile. Analysis was performed on reversed phase Atlantis dC18 column using a mobile phase of 0.4% formic acid (pH=3.0 ± 0.05) and acetonitrile (20:80, v:v) delivered at a flow rate of 0.25 ml/minute. Analytes were quantified multiple reaction monitoring in positive ion mode with transition mass to charge ratio (m/z) of 299.8→226.9 and 383.4→337.2 for metoclopramide and IS, respectively. Retention times of metoclopramide and IS were around 1.4 and 2.1 minutes, respectively. No significant matrix effect was observed on metoclopramide and IS peaks. Detection limit of metoclopramide in plasma was 0.3 ng/ml. Relationship between metoclopramide level and peak area ratio of metoclopramide / IS was linear (R2 ³ 0.9964) in the range of 0.5–100 ng/ml and inter-day coefficient of variations (CV) and absolute bias were ≤ 12.0% and ≤ 6.0%, respectively. Mean extraction recoveries for metoclopramide and the IS were 91% and 88%, respectively. The method was applied to assess stability of metoclopramide under various conditions generally encountered in the clinical laboratory. Stability of metoclopramide was ≥ 94% and ≥ 95% after 24 hours at room temperature or 48 hours at -20 ºC, respectively, in processed samples and 100% and ≥ 99% after 24 hours at room temperature or 12 weeks at -20 ºC, respectively, in unprocessed samples.

A rapid liquid chromatographic tandem mass spectrometry (LC-MS/MS) assay for the measurement of loratadine level in human plasma was developed and validated. One ml plasma samples containing loratadine and 0.18 µg of metoclopramide as (internal standard, IS) were extracted with 5 ml tert-butyl methyl ether and reconstituted with 80 µl of acetonitrile. Analysis was performed using a reversed phase Atlantis dC18 column and a mobile phase consisting of 0.4% formic acid and acetonitrile (20:80, v:v) and delivered at a flow rate of 0.25 ml/min. The eluents were monitored using electrospray ionization in the positive ion mode with transition mass to charge ratio (m/z) at 383.4→337.2 and 299.8→226.9 for loratadine and IS, respectively. The retention times of the IS and loratadine were around 1.53 and 2.33 min, respectively. Mean matrix effect was measured as -11.4% for loratadine and -14.4% for the IS. Detection limit of loratadine in plasma was 0.3 ng/ml. The relationship between loratadine concentration in plasma and the peak area ratio of loratadine / IS was linear (R2 ³ 0.9945) in the range of 0.5–100 ng/ml, and the intra- and inter-day coefficient of variations (CV) were ≤ 11.3%. Mean extraction recoveries for loratadine and the IS were 87% and 91% respectively, whereas accuracy (relative recovery) ranged from 99% to 111% quality control samples and from 93% to 105%  using back- calculated concentrations. The method was applied to assess the stability of loratadine under various conditions generally encountered in the clinical laboratory. Stability for processed samples (24 hours at room temperature, 48 hours -20 ºC) and unprocessed samples (24 hours at room temperature, 12 weeks -20 ºC) was ≥ 94%. Key words: Loratadine, Metoclopramide, Human plasma, HPLC