A radioimmunoassay for total captopril in human serum or plasma samples

Development and validation of a capillary electrophoresis method with laser-induced fluorescence detection for the determination of captopril in human urine and pharmaceutical preparations

This study describes the development of a CE method for the analysis of the antihypertensive drug captopril using LIF detection. The method is based on the derivatization of captopril with the fluorescent label 5-iodoacetamidofluorescein. The optimization of the electrophoretic electrolyte composition together with other variables, such as applied voltage and injection time, resulted in a solution of 20 mM phosphate buffer adjusted to pH 12.0. The calibration curve for the fluorescent captopril derivative was linear in the concentration range 3.5-6000 ng/mL with a detection limit of 0.5 ng/mL. Intra- and interday precision (at a concentration of about 100 times the LOD) were less than 0.86 and 1.16%, respectively, both expressed as RSD. The assay was successfully used for quantification of captopril in some marketed pharmaceutical preparations and urine samples.

Pharmacokinetics of glycine–proline–glutamate, the N-terminal tripeptide of insulin-like growth factor-1, in rats

Glycine-proline-glutamate (GPE) is the N-terminal tripeptide of insulin-like growth factor-1 and has been shown to be neuroprotective following ischemia-induced brain injury. The pharmacokinetics of GPE were studied in adult rats since GPE is a candidate for use in neuroprotection therapies. To measure plasma concentrations of GPE a novel radioimmunoassay was developed whereby GPE was initially derivatized with Bolton and Hunter reagent before use in a standard homologous assay against the Bolton and Hunter iodinated form. The derivatized GPE radioimmunoassay showed a 83% recovery of unlabeled GPE and complete parallel displacement with rat plasma. The simplicity and speed of the assay described here indicate an exciting new use for a previously described technology. The pharmacokinetic studies were conducted in adult rats using a single bolus intravenous injection of GPE at 30 or 100 mg/kg and showed that GPE was rapidly cleared from the circulation. In addition, evidence of the route of the metabolic degradation of GPE is presented. The findings presented here are the first description of the pharmacokinetics of GPE and suggest that, because of its very short half-life in plasma, continuous intravenous infusion of GPE may be the preferred route of administration for use in future neuroprotection therapies.

Direct separation of captopril diastereoisomers including their rotational isomers by RP-LC using a teicoplanin column

A direct reversed-phase liquid chromatography (LC) method has been developed for the separation and analysis of captopril and its 2R,2S diastereoisomer using a teicoplanin stationary phase. The proline containing diastereoisomers, which are known to form conformers in aqueous solution, were also separated from their rotational isomers. The influence of temperature, different organic modifiers and buffer type, concentration and pH were optimised to obtain a working resolution between the two diastereoisomers and their respective rotational isomers. The diastereoisomeric purity of several commercial captopril batches was subsequently evaluated using a 0.05% triethylammonium acetate (TEAA) buffer (pH 3.8) run at 1.0 ml/min with mobile phase reservoir and column temperature controlled at 0 degrees C. Throughout the study online UV diode array and mass spectrometry detection was carried out simultaneously to confirm that peaks eluting from the teicoplanin column were in fact captopril and not its readily converted disulphide dimer. Additionally, as a result of the greater detection sensitivity of mass spectrometry, it also facilitated a more accurate optimisation study where trace amounts of the rotational isomers were found to be present in the baseline at temperatures higher than optimum.

Sensitive high-performance liquid chromatographic method for determination of captopril in plasma

A rapid, simple and sensitive high-performance liquid chromatographic method for the determination of captopril in plasma has been developed. Captopril is derivatized with a new reagent, 2-bromo-2'-acetonaphthone to form a product that showed ultraviolet-absorbing properties. For plasma samples, the protein was removed with 6% perchloric acid and the derivatized captopril was extracted with diethyl ether. The chromatographic separation was performed on an analytical mu bondapak NH2 column (300 x 3.9 mm, i.d.) with an isocratic mobile phase consisting of n-hexane-2-propanol-methanol-acetic acid (68:15:15:2). Using ultraviolet detection at 246 nm, the quantification limit for captopril in plasma was 10 ng/ml. The calibration curve was linear over the concentration range 12.5-500 ng/ml. The average recovery was 95% for plasma. The inter-day and intra-day assay coefficients of variation were found to be less than 12%.

Bioanalysis of captopril: two sensitive high-performance liquid chromatographic methods with pre- or postcolumn fluorescent labeling

This study describes the development and comparison of two HPLC methods for the analysis of the antihypertensive drug captopril. The first method is based on a precolumn derivatization of captopril with the fluorescent label monobromobimane (MBB). The second method is based on a postcolumn reaction with the fluorescent reagent o-phthaldialdehyde (OPA). Since the disulfide metabolites of captopril can be reconverted to the active drug in vivo, the bioanalysis of captopril should involve both the determination of its free thiol form (free captopril) and the total amount of free thiol and reducible disulfides (total captopril). For total captopril analysis, disulfides were reduced with tributylphosphine (TBP) prior to protein precipitation. Since the reducing agent interfered with the MBB derivatization reaction, this method was not suitable for total captopril analysis. Both methods were validated for the bioanalysis of free captopril in human plasma. After removal of plasma proteins, samples were analyzed without an additional extraction procedure. The limit of quantitation in plasma was 12.5 ng/ml for the MBB method (limit of detection 30 pg) and 25 ng/ml for the OPA method (limit of detection 50 pg). The OPA method was also validated for total captopril analysis in human plasma and urine. The limit of quantitation was 25 ng/ml in plasma and 250 ng/ml in urine (limit of detection 50 pg). We conclude that for the analysis of free captopril the precolumn MBB method is superior to the OPA method since only the derivatization reaction has to be carried out immediately. The postcolumn OPA method is especially suitable for the analysis of total captopril since reducing reagents and high concentrations of endogenous thiols do not interfere with the derivatization reaction.

Determination of captopril in human blood by an enzyme-linked immunosorbent assay

An immunoassay for the quantitation of the angiotensin-converting enzyme inhibitor, captopril in human plasma is described. Antisera very specific for captopril were produced by immunization with captopril conjugated to bovine serum albumin or porcine thyroglobulin via the drug's thiol group. The antibodies were used to develop an enzyme-linked immunosorbent assay (ELISA) with a detection limit of 0.3 ng mL-1 and intra- and inter-assay coefficients of variation of 7 and 12%, respectively. Apart from stabilizing captopril by the addition of N-ethyl maleimide, the assay was used to detect the drug in human plasma without further extraction or purification. Our immunoassay provides a very sensitive and rapid (four hours) alternative for the study of captopril pharmacokinetics.

Application of 2-halopyridinium salts as ultraviolet derivatization reagents and solid-phase extraction for determination of captopril in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic method was developed for the determination of captopril in human plasma. 1-Benzyl-2-chloropyridinium bromide (BCPB) was used as a precolumn derivatizing reagent. The mercapto group of captopril was arylated by the reagent to generate a stable UV-sensitive product. The derivative was solid-phase extracted (SPE), separated on a C18 column using reversed-phase ion-paring chromatography and monitored by a spectrophotometric detector at 314 nm. The method enabled sensitive determination of captopril and its disulphides in human plasma in patients after oral administration. Disulphides of captopril with captopril itself and with endogenous thiol compounds are reduced with triphenylphosphine to form captopril, followed by derivatization with the same reagent. The quantification limit was 10 ng/ml. Calibration curves were prepared for human plasma samples spiked with captopril and captopril disulphide. The calibration curves were linear in the range of 10 to 500 ng/ml for captopril and 10 to 1000 ng/ml for captopril disulphide.

Antihypertensive effects of captopril without adverse effects on glucose tolerance in hyperinsulinemic rhesus monkeys

The rhesus monkey (Macaca mulatta), which has been found to develop spontaneous obesity, non-insulin dependent diabetes mellitus (NIDDM; Type 2), and hypertension, was used to evaluate the potential blood pressure-lowering effects of captopril as well as the specific effects, if any, on the prediabetic state. Intravenous and oral glucose tolerance testing was carried out with oral captopril dosing. Results showed that captopril significantly decreased both systolic and diastolic blood pressure in all monkeys and significantly decreased fasting plasma glucose levels. Based on these preliminary studies in monkeys, we conclude that captopril exerted antihypertensive effects without adverse effects on glucose metabolism.

Determination of captopril in pharmaceutical samples by flow injection analysis

A flow injection spectrophotometric method for the determination of captopril involving measurement of the absorbance of the captopril complex with palladium(II) in a 0.12 M HCl medium at 400 nm is presented. The calibration graph was linear over the range 2 x 10(-5)-6 x 10(-4) M. The sampling frequency was 90 h-1 with sample injections of 70 microliters. The proposed method was applied to the determination of captopril in pharmaceutical samples.

A specific radioimmunoassay for the measurement of gadoteridol, a contrast agent for magnetic resonance imaging in biological fluids

Gadoteridol, a nonionic gadolinium chelate, is currently being evaluated for contrast-enhanced magnetic resonance imaging. A radioimmunoassay (RIA) has been developed for the measurement of gadoteridol in biological fluids. The RIA has a range of 0 to 25 micrograms/mL and has the sensitivity to detect 0.05 microgram/mL of gadoteridol. Satisfactory zero binding and sensitivity were obtained after an overnight incubation at 4 degrees C. Separation of the antibody-bound and free radiolabel was achieved with 12.5% polyethylene glycol. A quantitative recovery of the exogenous analyte was obtained at all concentrations of gadoteridol tested. Linearity in both serum and urine was satisfactory. Intraassay coefficients of variation were 6.4 and 2.8% for the low and medium controls, respectively. Interassay coefficients of variation were 5.4, 3.8, and 12.2% for the low, medium, and high controls, respectively. Cross reactivities of the ligand 5 and the calcium salt 6 were 37 and 29%, respectively. Clinical samples from the ascending dosage studies were analyzed by the gadoteridol RIA. The results obtained from the serum specimens demonstrated an excellent linear proportionality between drug concentration in blood and administered dosage of gadoteridol. Cumulative urinary excretion data showed that 94% of the drug was excreted in the urine within 24 h.

Pharmacokinetics and biological effects of captopril and hydrochlorothiazide after acute and chronic administration either alone or in combination in hypertensive patients

The pharmacokinetics of free unchanged captopril, total captopril and hydrochlorothiazide (HCTZ) were investigated in three groups of patients with moderate essential hypertension and normal renal function on the first and on the 45th days of an oral treatment with either captopril (50 mg once daily, n = 7) or HCTZ (25 mg once daily, n = 10) or their combination captopril 50 mg + HCTZ 25 mg once daily, n = 8. Simultaneously, the effects of the three treatments on plasma converting enzyme activity (PCEA) and plasma renin activity (PRA) were measured. Elimination half-lives of total captopril after acute (7.8 +/- 2.3 h) or chronic (7.0 +/- 0.5 h) captopril dosing were similar to those of HCTZ after acute (6.5 +/- 1.0 h) or chronic (8.0 +/- 2.5 h) HCTZ dosing. Elimination half-life of free unchanged captopril was 0.81 +/- 0.09 h after acute and 0.96 +/- 0.03 h after chronic captopril dosing. Addition of HCTZ to captopril induced no major change in free and total captopril pharmacokinetic parameters, in PCEA inhibition and in PRA increase (as they were determined after captopril alone) on acute as well as on chronic treatment. Addition of captopril to HCTZ induced no major change in HCTZ pharmacokinetic parameters and in PRA increase compared with those determined after HCTZ alone. Chronic treatment with captopril + HCTZ resulted, like chronic captopril treatment, in no accumulation of captopril, in no significant modification of free and total captopril pharmacokinetic parameters and of PCEA inhibition (as determined after acute administration) but led to a significant enhancement of the acutely induced increase in PRA. Chronic treatment with captopril + HCTZ resulted, like chronic HCTZ treatment, in no accumulation of HCTZ, in no significant modification of HCTZ pharmacokinetic parameters (as determined after acute administration) but also led to a significant enhancement of the acutely induced increase in PRA. Thus, the longer duration of the antihypertensive action of captopril + HCTZ as compared to that of captopril cannot be ascribed to a pharmacokinetic or biological interaction between captopril and HCTZ.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.