Stability-Indicating Chromatographic Methods for the Investigation of Ritodrine Hydrochloride Stability and Characterization of the Oxidative Degradation Product.

Two simple and sensitive chromatographic methods were developed and validated for quantitative determination of ritodrine hydrochloride in presence of its oxidative degradation product. The first method depends on densitomeric determination of thin-layer chromatograms of the intact drug in presence of its oxidative degradate. Excellent separation was achieved at 220 nm using a mobile phase of dichloromethane-methanol-glacial acetic acid (15 : 5 : 0.25, v/v/v). The second was an HPLC method, in which efficient separation was carried out on C18 column (150 × 4.6 × 5 µm) using a mobile phase consisting of water: acetonitrile (70,30, v/v) at a flow rate of 1 mL min-1 and UV detection at 220 nm. Beer's law was obeyed in the range of 0.025-0.3 µg/spot and 5-40 µg mL-1 of the intact drug using the two methods, respectively. The proposed methods were validated according to International Conference on Harmonization guidelines and successfully applied for the determination of ritodrine hydrochloride in bulk powder, laboratory prepared mixtures and pharmaceutical dosage form with good accuracy and precision. The results obtained were compared with those of the reported method and were found to be in good agreement.

Spectrofluorimetric determination of certain adrenergic agonist drugs in their pure forms and pharmaceutical formulations: Content uniformity test application.

A new, simple, sensitive and rapid spectrofluorimetric method has been developed for determination of certain adrenergic agonists such as isoxsuprine hydrochloride, ritodrine hydrochloride and etilefrine hydrochloride in their pure forms and pharmaceutical dosage forms. The method depends on micellar enhancement of the native fluorescence of investigated drugs by using 2% w/v sodium dodecyl sulfate (SDS) as an anionic surfactant. The enhanced fluorescence intensity of investigated drugs was measured at 305 nm after excitation at 278 nm. The interaction of studied drugs with SDS was studied, and the enhanced fluorescence intensity was exploited to develop an assay method for the determination of investigated drugs. The relative fluorescence intensity-concentration plots were rectilinear over the range 0.15-3.00 µg ml-1 , with low quantification limits of 0.132, 0.123 and 0.118 µg mL-1 for isoxsuprine, ritodrine and etilefrine, respectively. The proposed method was successfully applied for determination of studied drugs in their pharmaceutical formulations. Moreover, the high sensitivity of the proposed method allows performing the content uniformity testing of the studied drugs in their tablets by using the official United States Pharmacopeia (USP) guidelines. Statistical comparisons of the results with those of the reported methods revealed excellent agreement and indicated no significant difference in accuracy and precision.

Preparation and evaluation of ritodrine buccal tablets for rational therapeutic use.

Ritodrine hydrochloride (RD-HCl) tablets containing alginate (AL) and lactose (LC) with or without microcrystalline cellulose (MC) as excipients were produced as a buccal dosage form. The RD-HCl (2 mg) tablets with AL/LC but no MC swelled and dissolved gradually in the in vitro dissolution test. The tablet showing the fastest dissolution and highest drug release rate, called Tablet A1, was selected as a tablet to show rapid and prolonged absorption. However, in the in vivo buccal absorption test using rats, it could not give a plasma concentration over the human minimal effective level (15 ng/mL). The modified tablet containing AL, LC, MC and RD-HCl (4 mg), named Tablet B/MC, showed better hardness and faster drug release. Tablet B/MC gave a plasma concentration over the human effective level within 15 min, and the plasma concentration was maintained at >15 ng/mL over 4 h. Moreover, the deconvolution analyses demonstrated that a prolonged high absorption rate could be achieved in vivo best with Tablet B/MC. Tablet B/MC improved the pharmacokinetic profile in comparison with Tablet A1 and the solution dosage form. The RD-HCl buccal tablets with AL, LC and MC as excipients are suggested to be possibly useful for the treatment of premature labor.

In vitro evaluation of the genotoxicity of ritodrine and verapamil in human lymphocytes.

The aim of this study was to investigate the genotoxic effects of ritodrine and verapamil on human peripheral lymphocytes in vitro using micronucleus (MN) test. Also, fluorescence in situ hybridization (FISH) with a centromeric probe was performed to determine the origin of the induced MN. Cells were treated with 8.4 × 10(-6) M - 25.2 × 10(-4) M concentrations for ritodrine and 0.56 - 11 × 10(-5) M concentrations for verapamil, separately and combined. The MN frequencies showed increase after all treatments, but the difference between treated cells and untreated controls were found to be statistically significant only in the concentration range from 8.4 × 10(-5) M - 4.5 × 10(-4) M for ritodrine, 1.1 - 3.3 × 10(-5) M for verapamil, and in combined treatment with concentrations 8.4 × 10(-5) M + 1.1 × 10(-5) M for ritodrine and verapamil. The highest tested concentrations of both medicaments showed cytotoxic effect. Both medicaments decreased the nuclear division index (NDI) in tested concentrations. The results of FISH analysis suggest that verapamil, separately or combined with ritodrine, shows to a larger extent aneugenic than clastogenic effect.

Stereoselective analysis of ritodrine diastereomers in human serum using HPLC.

A sensitive and selective method has been developed for the determination of ritodrine diastereomers in human serum using high-performance liquid chromatography with a chiral stationary phase column and a fluorescence detector. No interfering peaks from endogenous substances were observed. The method showed good reproducibility and accuracy, and the standard curve was linear up to 100 ng/mL with a correlation coefficient of 0.999. Limit of detection (signal-to-noise = 3) and quantitation (signal-to-noise = 10) were found to be 2 and 5 ng/mL, respectively. This method is suitable for chiral pharmacological and pharmacokinetic studies as well as the therapeutic drug monitoring of ritodrine diastereomers for which no information currently exists.

Simultaneous determination of ritodrine and isoxsuprine using coupling technique of synchronous fluorimetry and H-point standard addition method.

Simultaneous determination of two structurally related ss(2) adrenergic receptor agonists namely, Ritodrine HCl (RTH) and Isoxsuprine HCl (ISP) was performed using coupling technique of synchronous fluorimetry and H-point standard addition method. Under optimum conditions, linear determination ranges were 1.48 - 14.80 x 10(-6) mol L(-1) and 1.54 - 15.44 x 10(-6) mol L(-1) for ISP and RTH respectively. RTH and ISP could be determined simultaneously without interference from each other when their concentration ratio varies from 5:1 to 1:5 in the mixed sample. The proposed method was applied to the determination of RTH and ISP in synthetic mixture of pharmaceutical samples, the accuracy and precision of the results were satisfactory.

Effects of alcohols on CE enantioseparation of basic drugs with native gamma-CD as chiral selector.

The effects of alcohol on the CE enantioseparation of selected basic drugs with gamma-CD as the chiral selector was investigated. The enantioseparation behavior of the analytes with gamma-CD in the absence and presence of different alcohols specifically methanol, ethanol, 2-propanol (IPA), and 2-methyl-2-propanol (TBA), the relationship of enantiomeric resolution (R(s)) values with either hydrophobicity or bulkiness of the alcohols, as well as the effect of these alcohols on interaction of the analytes with gamma-CD were studied. Results showed that hydrophobicity and/or bulkiness of alcohols have an influence on the enantioresolution of most of the analytes based on the relatively high correlation coefficients (R) obtained between R(s) versus log P and between R(s) versus ovality (i.e., parameter to indicate bulkiness of a molecule). Comparison of the values of the average binding constants obtained for each enantiomeric pair in the presence and absence of 5% IPA showed that alcohols can increase, decrease, or give a minimal effect on the analyte-gamma-CD interaction depending on the analyte. Furthermore, the significant enhancement in the enantioresolution of both propranolol and pindolol in the presence of either IPA or TBA led to the baseline enantioresolution of both drugs using 35 mM gamma-CD.

A highly sensitive assay for ritodrine in human serum by hydrophilic interaction chromatography-tandem mass spectrometry.

We developed a sensitive assay for ritodrine (RTD), a beta2-adrenergic agonist, in human serum. This method was based upon the selective and sensitive technique by a tandem mass spectrometry (MS/MS) using a hydrophilic interaction chromatography (HILIC) technique. This method involved a mixed-mode cation-exchange solid-phase extraction of RTD and isoxsuprine, the internal standard (IS), from serum with Waters Oasis MCX cartridges. The detection was made using a Micromass Quattromicro API LC-MS/MS system with electrospray ionization source in positive ion mode. The separation of the analytes was achieved within 4 min on a silica column with a mobile phase of ammonium acetate (10 mM, pH 4.5) and acetonitrile (10:90, v/v). Multiple reaction monitoring was utilized by monitoring 288.2-->121.1 for RTD, 302.2-->107.0 for IS. The calibration curve for RTD was linear over a range of 0.5-1000 ng/mL. When 50 microL serum was used for extraction, the lower limit of quantification was 0.39 ng/mL (97.5 fg on-column). The percent coefficient of validation for accuracy and precision (inter- and intra-day) was less than 9.8% and the recovery was ranged from 83.5 to 94.7% for RTD. This method enabled us to successfully determine RTD in maternal and fetal sera.

Inhibitory effects of various beverages on ritodrine sulfation by recombinant human sulfotransferase isoforms SULT1A1 and SULT1A3.

PURPOSE: Ritodrine is known to undergo extensive presystemic sulfation in the intestinal mucosa, and its bioavailability is as low as 30%. Accordingly, inhibition of intestinal sulfation may lead to an increase in the bioavailability of ritodrine. In this study, we aimed to investigate the activities of ritodrine sulfation by SULT1A1, which is expressed predominantly in the liver, and SULT1A3, which is expressed predominantly in the intestine, as well as the inhibitory effects of beverages on their activities. METHODS: We investigated ritodrine sulfation by using recombinant human sulfotransferase (SULT) 1A1 and SULT1A3 in an in vitro study. Next, we investigated the inhibitory effects of grapefruit juice, orange juice, green tea, and black tea on ritodrine sulfation. RESULTS: Sulfation of ritodrine by SULT1A3 was much higher than that by SULT1A1, suggesting that the bioavailability of ritodrine may be limited by intestinal SULT1A3. The ritodrine sulfation activities of SULT1A1 and SULT1A3 were significantly inhibited by all beverages examined at a concentration of 10%. Green tea and black tea exhibited potent inhibition; even at a concentration of 5%, they both inhibited SULT1A1 by 100% and SULT1A3 by >or=95%. CONCLUSION: Our results suggest that concomitant ingestion of beverages such as green tea and black tea may increase the bioavailability of orally administered ritodrine, and perhaps other beta2-agonists, and lead to an increase in the clinical effects or adverse reactions.

Spectrophotometric methods for the determination of ritodrine hydrochloride and its application to pharmaceutical preparations.

Two simple and sensitive spectrophotometric methods are described for the determination of ritodrine hydrochloride (RTH) in both pure and dosage forms. The methods are based on the interaction of diazotised p-nitroaniline (DPNA) and sulphanilic acid (DSNA) with RTH in an alkaline medium. The resulting azo dyes are measured at 480 nm (for the DPNA method) and at 440 nm (for the DSNA method) and are stable for more than 1 h. The optimum reaction conditions and other analytical parameters are evaluated. A study of the effect of commonly associated excipients and additives do not interfere with the determinations. Statistical analysis of results indicates that the methods are precise and accurate.

Drug action of ritodrine on the sarcoplasmic reticulum Ca(2+)-ATPase from skeletal muscle.

Ritodrine inhibits the steady-state Ca(2+)-ATPase activity of isolated sarcoplasmic reticulum vesicles in a dose-dependent manner. The observed K0.5 value for inhibition (approximately 3 mM) gives proof of a low-affinity interaction. Ritodrine also interferes with the steady-state Ca2+ transport ability decreasing the maximal rate without modification of the Ca2+ or ATP affinity for the enzyme. This is consistent with an absence of competition for the transport and the catalytic sites. Analysis of the catalytic and transport cycle shows that: (i) ritodrine inhibits the phosphorylation partial reaction. This is supported by pre-steady-state kinetic experiments of Ca2+ transport and also by the temperature dependence of the phosphoenzyme level. (ii) At high ritodrine concentrations the dephosphorylation step becomes rate-limiting. This is suggested by the biphasic profile (V-shape) of phosphoenzyme accumulation at different ritodrine concentrations. This was also confirmed by chase experiments of radioactive phosphoenzyme decomposition at steady state. These data reveal a complex pattern of inhibition involving two sites for interaction with low and high ritodrine concentrations. It is envisaged that ritodrine does not exert any direct effect on the smooth muscle sarcoplasmic reticulum Ca(2+)-ATPase when used in the treatment of preterm birth.

Fetal and neonatal excretion of free and conjugated ritodrine.

The ability of the human fetus and neonate to conjugate and excrete ritodrine, a beta 2-sympathomimetic drug, was investigated. Free and conjugated ritodrine concentrations in the plasma, amniotic fluid and urine were measured in 11 mother-infant pairs, to whom intravenous ritodrine had been administered before elective cesarean section at term. Ritodrine was determined by HPLC with electrochemical detection. At delivery, conjugated ritodrine values were significantly higher than those for the free form in maternal and fetal plasma. There were significant positive correlations between the concentrations in the maternal and umbilical vein plasma for both free and conjugated ritodrine. In the amniotic fluid, the total ritodrine concentrations were much higher than those in the fetal plasma, the conjugated form accounting for 90.2% of the total. Furthermore, the percentages of conjugated ritodrine in the amniotic fluid and neonatal urine were significantly higher than the percentage in the maternal urine on the day of birth. In the neonatal urine, the concentrations of free and conjugated ritodrine decreased rapidly after birth as did those in the maternal urine, on day 3 postpartum being less than 2% of the values on the day of parturition. These results indicate that the fetus at term is capable of forming conjugated metabolites of ritodrine and of excreting free and conjugated ritodrine in its urine.