Determination of molsidomine and its active metabolite in human plasma using liquid chromatography with tandem mass spectrometric detection

Examination of imprinting process with molsidomine as a template

Eight different functional monomers were used with ethylene glycol dimethacrylate as a cross-linker and molsidomine as a template to obtain molecularly imprinted polymers (MIPs). Non-covalent interactions between molsidomine and each functional monomer in DMSO prior to thermal bulk polymerization were utilized. On the basis of calculated imprinting factors, MIP prepared with N,N'-diallyltartaramide was chosen for further investigations. Examination of interactions in the prepolymerization complex between molsidomine and N,N'-diallyltartaramide was performed using the Job method. The absorbance of isomolar solutions reaching a maximum for the molar ratio of template to monomer equal to 1:4. Scatchard analysis was used for estimation of the dissociation constants and the maximum amounts of binding sites. The polymer based on N,N'-diallyltartaramide has two classes of heterogeneous binding sites characterized by two values of K(d) and two B(max): K(d)(1) = 1.17 mM(-1) and B(max)(1) = 0.8 mumol/mg for the higher affinity binding sites, and K(d)(2) = 200 microM(-1) and B(max)(2) = 2.05 mumol/mg for the lower affinity binding sites. Furthermore, effects of pH and organic solvent on binding properties of MIP and NIP were investigated, together with release of molsidomine from both MIP and NIP.

A pilot double-blind randomized placebo-controlled study of molsidomine 16 mg once-a-day in patients suffering from stable angina pectoris: correlation between efficacy and over time plasma concentrations

OBJECTIVES

A new once-a-day (o.a.d.) formulation of molsidomine (16 mg) was evaluated in patients with stable angina pectoris. The aims were to characterize its pharmacokinetics after a single dose, to demonstrate its clinical efficacy and safety versus placebo and to investigate correlations between pharmacokinetics and pharmacodynamics.

METHODS

Forty-two patients were recruited in a double-blind, crossover, randomized placebo-controlled trial. The pharmacokinetics of molsidomine and SIN-1, its active metabolite, were determined at specific time points (3, 6, 10, 14, 18, 22 and 24 h) after the administration of a single dose of molsidomine 16 mg o.a.d. in all patients distributed into seven groups. Twenty-eight of these 42 patients showed a positive baseline cycloergometric exercise test response during the run-in placebo period and were used to compare the efficacy of molsidomine to placebo. Relationships between plasma concentration in molsidomine or SIN-1 and ischemic threshold were assessed in 16 of the 28 patients with a positive exercise test at baseline. Indeed, the censored variable ischemia-limited tolerance to exercise could not be evaluated in those patients who did not show exercise-induced ischemia anymore under molsidomine 16 mg o.a.d. Pharmacokinetic-pharmacodynamic relationships were evaluated using regression models and correlation coefficients.

RESULTS

The highest average concentration in molsidomine and SIN-1 occurred after 6 h, then a plateau of 15-20 ng/ml molsidomine and 0.8-3.0 ng/ml SIN-1 was maintained for at least 8 h and the mean residual molsidomine concentration 24 h post-drug intake was around 8 ng/ml, still in the effective range of 5-10 ng/ml. A significant increase in total workload (+52 W min, P=0.009), total exercise time (+32 s, P=0.003) and time to angina (+25 s, P=0.016) was measured with molsidomine 16 mg o.a.d. relative to placebo. Using linear regression, significant correlation coefficients were determined between molsidomine plasma concentrations (but not SIN-1) and exercise test improvements (r=0.827, P<0.001 for the total workload; r=0.772, P<0.001 for the total exercise time; and r=0.566, P=0.028 for the time to 1 mm ST-segment depression).

CONCLUSION

The pharmacokinetics of molsidomine 16 mg in patients with stable angina pectoris is compatible with a o.a.d. dosage regimen. This o.a.d. formulation is effective and well-tolerated, providing a 24-h therapeutic control of myocardial ischemia. A positive and significant linear relationship between molsidomine plasma concentration and the increase in exercise tolerance was observed.

Quantitative analysis of N-acetylcysteine and its pharmacopeial impurities in a pharmaceutical formulation by liquid chromatography-UV detection-mass spectrometry

A new method for the simultaneous determination of N-acetylcysteine and its pharmacopeial impurities, cysteine, cystine, N,N'-diacetylcystine and N,S-diacetylcysteine in an effervescent tablet has been developed. The method is based on on-line LC-UV-MS using a pneumatically-assisted electrospray interface (ionspray). The stability of the thiol moieties of the analytes was ensured by the acidic pH of the LC mobile phase. Quantitation of N-acetylcysteine was performed with UV detection to avoid ion-source overloading effect due to its higher concentration, whereas the impurities could be easily separated and quantified in MS. The method was validated in terms of stability, linearity, precision and accuracy.

Determination of the enantiomers of 3-tert.-butylamino-1,2-propanediol by high-performance liquid chromatography using mass spectrometric detection

The chiral synthesis of beta-blockers such as (S)-timolol requires a sensitive analytical method for the enantioseparation of its intermediate, 3-tert.-butylamino-1,2-propanediol, in the ng/ml range. The method developed is based on on-line normal-phase LC-MS-MS using a chiral stationary phase and an atmospheric pressure chemical ionization (APCI) interface. The MS detection of 3-tert.-butylamino-1,2-propanediol was first optimized with a pneumatically-assisted electrospray interface (ionspray). The APCI interface was then selected for LC-MS-MS because of the incompatibility of electrospray with n-hexane. The method was validated for both enantiomers in the 25-500 ng/ml concentration range.

Enantiomeric determination of tramadol and its main metabolite O-desmethyltramadol in human plasma by liquid chromatography-tandem mass spectrometry

Pharmacokinetic studies require sensitive analytical methods to allow the determination of low concentrations of drugs and metabolites. When drugs present an asymmetric center, the enantiomeric determination of the compounds of interest should be performed. The method developed is based on on-line LC-MS-MS using atmospheric pressure chemical ionization as an interface determination of enantiomers of tramadol (T) and its active metabolite O-desmethyltramadol (ODT) in human plasma. This determination is preceded by an off-line solid-phase extraction (SPE) on disposable extraction cartridges (DECs), performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with ethyl silica (50 mg) was first conditioned with methanol and water. The washing step was performed with water and the analytes were finally eluted by dispensing methanol. The collected eluate was then evaporated to dryness before being dissolved in the LC mobile phase and injected into the LC system. The enantiomeric separation of tramadol and ODT was achieved on a Chiralpak AD column containing amylose tris-(3,5-dimethylphenylcarbamate) as chiral selector. The mobile phase was isohexane-ethanol-diethylamine (97:3:0.1, v/v). The LC system was then coupled to a tandem mass spectrometry system with an APCI interface in the positive ion mode. The chromatographed analytes were detected in the selected reaction monitoring mode. The MS-MS ion transitions monitored were 264-->58 for tramadol, 250-->58 for ODT, and 278-->58 for ethyltramadol, used as internal standard. The method was validated. The recoveries were around 90% for both T and ODT. The method was found to be linear for each enantiomer of both compounds (r2>0.999). The mean RSD values for repeatability and intermediate precision were 3.5 and 6.4% for T enantiomers and 5.0 and 5.6% for ODT enantiomers, respectively. Moreover, the method was found to be selective towards other metabolites, N-desmethyltramadol and N,O-desmethyltramadol (NODT). The method developed was successfully used to investigate plasma concentration of enantiomers of T and ODT in a pharmacokinetic study.

Automating solid-phase extraction: current aspects and future prospects

This paper reviews current trends and techniques in automated solid-phase extraction. The area has shown a dramatic growth the number of manuscripts published over the last 10 years, including applications in environmental science, food science, clinical chemistry, pharmaceutical bioanalysis, forensics, analytical biochemistry and organic synthesis. This dramatic increase of more that 100% per year can be attributed to the commercial availability of higher throughput 96-well workstations and extraction plates that allow numerous samples to be processed simultaneously. These so-called parallel-processing workstations represent the highest throughput systems currently available. The advantages and limitations of other types of systems, including discrete column systems and on-line solid-phase extraction are also discussed. Discussions of how automated solid-phase extractions can be developed, generic approaches to automated solid-phase extraction, and three noteworthy examples of automated extractions are given. The last part of the review suggests possible near- and long-term directions of automated solid-phase extraction.

Simultaneous determination of nifedipine and dehydronifedipine in human plasma by liquid chromatography-tandem mass spectrometry

Quantitative analysis of therapeutic compounds and their metabolites in biological matrix (such as plasma, serum or urine) nowadays requires sensitive and selective methods to allow the determination of concentrations in the ng/ml range. A new on-line LC-MS-MS method using atmospheric pressure chemical ionisation (APCI) as interface for the simultaneous determination of nifedipine (NIF) and its metabolite in human plasma, dehydronifedipine (DNIF) has been developed. The compounds were extracted from plasma using solid-phase extraction (SPE) on disposable extraction cartridges (DECs). The SPE operations were performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with phenyl modified silica was first conditioned with methanol and water. The washing step was performed with water. Finally, the analytes were successively eluted with methanol and water. The liquid chromatographic (LC) separation of NIF and DNIF was achieved on a RP-18 stationary phase (4 microm). The mobile phase consisted of methanol-50 mM ammonium acetate solution (50:50, v/v). The LC was then coupled to tandem mass spectrometry with an APCI interface in the positive ion mode. The method developed was validated. The absolute recoveries evaluated over the whole concentration range were 95+/-2% and 95+/-4% for NIF and DNIF, respectively. The method was found to be linear in the 0.5-100 ng/ml concentration range for the two analytes (r2 = 0.999 for both NIF and DNIF). The mean R.S.D. values for repeatability and intermediate precision were 2.9 and 3.0% for NIF and 2.2-4.7% for the metabolite. The method developed was successfully used to investigate the plasma concentration of NIF and DNIF in the pharmacokinetic studies.