A simple kinetic spectrophotometric method for the determination of isoxsuprine in dosage forms.

A simple and sensitive kinetic method was developed for the determination of isoxsuprine in pharmaceutical preparations. The method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permanganate at room temperature for a fixed time of 30 min. The absorbance of the coloured manganate ion was measured at 610 nm. Alternatively, the decrease in the absorbance of potassium permanganate after addition of the drug was measured at 525 nm. The absorbance-concentration plots in both procedures were rectilinear over the range of 0.5-4 microg ml(-1) (r = 0.9998) with a minimum detectability of 0.05 microg ml (-1) (1.48 x 10(-7) M). The different experimental parameters affecting the development and stability of the colours were carefully studied and optimized. The determination of isoxsuprine by the fixed concentration and rate constant methods is also feasible with the calibration equations obtained but the fixed time method has been found to be more applicable. Both procedures were applied to the determination of isoxsuprine in formulations. The results obtained were in good agreement with those obtained using a reference method. The proposed method was also adopted to detect isoxsuprine in spiked human plasma at its therapeutic level of concentration (0.4 microg ml(-1)). A proposal of the reaction pathway was postulated.

Fluorimetric determination of isoxsuprine hydrochloride in pharmaceuticals and biological fluids.

Two simple and highly sensitive fluorimetric methods have been developed for the determination of isoxsuprine hydrochloride in bulk, in dosage forms and in biological fluids. The first method involves the direct measurement of the native fluorescence of the drug in the concentration range 0.4-4.0 microg ml(-1), the second method is based on the oxidation of isoxsuprine HCl with cerium(IV) followed by fluorimetric measurement in the concentration range 0.02-0.2 microg ml(-1). The average % found were 99.9 +/- 0.78 and 100.0 +/- 0.62 for the two methods, respectively. The minimum detectability (3 S(B)) were 0.11 and 0.007 microg ml(-1) for the two methods, respectively. The methods results showed insignificant difference with those of the official method.

Determination of phenolic sympathomimetic drugs in pharmaceutical samples and biological fluids by flow-injection chemiluminescence.

A rapid and highly sensitive flow-injection chemiluminometric method was developed for determination of 3 sympathomimetic drugs, namely, etilefrine hydrochloride, isoxsuprine hydrochloride, and prenalterol hydrochloride. The method is based on chemiluminescence induced by oxidation of drugs with acidified potassium permanganate in the presence of formic acid as a carrier. The calibration graphs were linear over the concentration ranges 0.2-9, 0.2-12.5, and 0.025-1.25 microg/mL for the 3 compounds, respectively. The method was applied successfully in determining the drugs in dosage forms and in biological fluids. A proposal for the reaction pathway is suggested.

Voltammetric determination of isoxsuprine and fenoterol in dosage forms and biological fluids through nitrosation.

A simple and highly sensitive voltammetric method was developed for the determination of isoxsuprine HCl (I) and fenoterol HBr (II) in dosage forms and biological fluids. The method is based on treatment of the two compounds with nitrous acid followed by measuring the cathodic current produced by the resulting nitroso derivatives. The voltammetric behavior was studied adopting Direct Current (DCt), Differential Pulse (DPP) and Alternating Current (ACt) polarography. Both compounds produced well-defined, diffusion-controlled cathodic waves over the whole pH range in Britton-Robinson buffers (BRb). At pH 11 and pH 9, the values of diffusion-current constants (Id), were 9.4 +/- 0.3 and 7.7 +/- 0.4 for I and II, respectively. The current-concentration plots for I were rectilinear over the range of 0.6-12 microg/ml and 0.1-12 microg/ml in the DCt and DPP modes, respectively. As for II, the range was 1-20 microg/ml and 0.1-20 microg/ml in the DCt and DPP modes, respectively. The minimum detectability (S/N = 2) were 0.02 microg/ml (approximately 6 x 10(-8) M) and 0.01 microg/ml (approximately 2.6 x 10(-8) M) for I and II, respectively, adopting the DPP mode. The proposed method was applied to the determination of both compounds in dosage forms and the results obtained were in good agreement with those obtained using reference methods. The proposed method was further applied to the determination of isoxsuprine in spiked human urine and plasma. The percentage recoveries adopting the DPP mode were 98.84 +/- 1.18 and 99.26 +/- 0.97, respectively.

Determinaçäo do limite de decisao do teste imunoenzimático ELISA na análise de isoxsuprina em controle antidopagem de cavalos de corrida / Determination of decision limit of immunoenzymatic test ELISA for the analysis of isoxsuprine in antidoping control of horseracing

O uso de ensaios imunoenzimáticos tipo Elisa (Enzyme Lynked Immunosorbent Assay), largamente utilizado em laboratórios de controle de dopagem, é aceito apenas como método de triagem, havendo portanto, a necessidade de uma técnica mais apurada para confirmação. Devido à grande sensibilidade da técnica ELISA em relação às análises por CG/EM, torna-se necessária a determinação de um valor, que na técnica ELISA corresponda à menor concentração detectável detectável no método de confirmação no método de confirmação, facilitando com isto a seleção das amostras suspeitas. O presente trabalho tem como objetivo definir este valor, à partir do qual a amostra será submetida à técnica de Cromatografia a Gás com Espectrometria de Massa (CG/EM). Este limite de decisão empregado na técnica Elisa, irá minimizar o custo operacional, pois apenas as amostras que apresentem valores acima deste limite serão submetidas ao método de confirmação.

Prolonged presence of isoxsuprine in equine serum after oral administration.

1. Isoxsuprine [1-(4-hydroxyphenyl)-2-(1-methyl-2-phenoxyethylamino)-1- propanol] serum concentrations after single- and multiple-dose administration to horse were investigated using immunoenzymatic ELISA, HPLC-UV and thermospray HPLC-MS methods. 2. Using HPLC-MS, isoxsuprine was detected up to 72 h after a single administration (1.2 mg/kg by gastric probe) and up to 96 h after the end of serial administration (1.2 mg/kg every 12 h for 7 days). 3. ELISA detected the drug up to 96 h after a single dose and up to 6 days after the end of prolonged administration. 4. Isoxsuprine is present in horse serum almost totally in conjugated form very likely as glucuronide. 5. It is concluded the administration of this drug must be suspended much earlier than previously presumed if race horse antidoping tests for the drug are to be negative.

Determination of isoxsuprine in human plasma by gas chromatography with electron capture detection.

A rapid and sensitive gas chromatographic method for the determination of the beta-adrenergic agent isoxsuprine in human plasma has been developed. The procedure involves the extraction of the drug with ether and an internal standard (propranolol) from plasma at alkaline pH, solvent evaporation, and the formation of a tri-trifluoroacetyl derivative by reaction with trifluoroacetic anhydride in ethyl acetate. Analyses were carried out by gas-liquid chromatography on a 3% OV-17 column using an electron capture detector. The minimum detectable amount of isoxsuprine was 0.5 ng/ml of plasma and the electron capture detector response was tested to be linear (r2 greater than 0.999) between 0.5 and 20 ng/ml. No interferences from endogenous substances were found. Precision of the method was found to be 9.9, and 6.1% coefficient of variation at 1 ng/ml and 10 ng/ml of plasma, respectively. Determination of isoxsuprine at the nanogram level in cord plasma samples from newborns at the time of the delivery was possible using the described procedure.

Risk:benefit considerations for the use of isoxsuprine in the treatment of premature labor.

Seventy patients treated with isoxsuprine for premature labor were studied. In patients with intact membranes prolongation of pregnancy for more than 7 days occurred in 77% of women with 50% cervical effacement or less and 3 cm dilatation or less at the initiation of therapy, and in none with more than 50% effacement and more than 3 cm dilatation. Cervical effacement was the primary factor in determining success. Cord isoxsuprine concentrations averaged 90% of maternal concentrations at delivery. Maternal and cord isoxsuprine concentrations at delivery were inversely correlated with the drug-free interval before delivery. An interval of more than 5 hours was necessary to attain a cord concentration of less than 2 ng/ml, a level not associated with neonatal problems. Drug-free intervals of 2 hours or less usually resulted in cord isoxsuprine values of more than 10 ng/ml, levels that are associated with severe neonatal problems. Seventy-seven percent of infants with cord isoxsuprine concentrations of more than 2 ng/ml and 91% with values of more than 10 ng/ml were delivered of mothers with more than 3 cm dilatation or more than 50% effacement at the initiation or reinstitution of intravenous therapy. Most severe neonatal problems are preventable if patients are selected carefully.

Isoxsuprine in the perinatal period. II. Relationships between neonatal symptoms, drug exposure, and drug concentration at the time of birth.

Forty preterm infants with maternal isoxsuprine exposure less than 24 hours delivery and 40 matched control infants were studied prospectively to determine the acute neonatal effects of maternal ISX exposure. The cord ISX concentration correlated inversely with the drug-free interval before delivery (P < 0.001). Cord ISX concentrations > 10 mg/ml were seen only with intravenous maternal therapy and a drug-discontinuance to delivery interval of two hours or less. The plasma half-life of ISX in neonates ranged from 1.7 to 8 hours; gestationally younger infants required a longer time for drug clearance. Ileus was 13 times more common in the ISX group and was not directly related to the cord ISX concentration. The incidence of hypotension and hypocalcemia rose directly with the cord ISX concentration, reaching 89% and 100%, respectively, when the cord ISX level exceeded 10 ng/ml. The incidence of respiratory distress syndrome was low in the ISX infants with low cord drug values, but increased to that of the control group when the cord ISX concentration reached > 10 ng/ml.