Enzyme immunoassay discrimination of a new angiotensin-converting enzyme (ACE) inhibitor, cilazapril, and its active metabolite

LC-MS determination and bioavailability study of imidapril hydrochloride after the oral administration of imidapril tablets in human volunteers

The purpose of the present study was to develop a standard protocol for imidapril hydrochloride bioequivalence testing. For this reason, a specific LC-MS method was developed and validated for the determination of imidapril in human plasma. A solid-phase extraction cartridge, Sep-pak C18, was used to extract imidapril and ramipril (an internal standard) from deproteinized plasma. The compounds were separated using a XTerra MS C18 column (3.5 microm, 2.1 x 150 mm) and acetonitrile-0.1% formic acid (67:33, v/v) adjusted to pH 2.4 by 2 mmol/L ammonium formic acid, as mobile phase at 0.3 mL/min. Imidapril was detected as m/z 406 at a retention time of ca. 2.3 min, and ramipril as m/z 417 at ca. 3.6 min. The described method showed acceptable specificity, linearity from 0.5 to 100 ng/mL, precision (expressed as a relative standard deviation of less than 15%), accuracy, and stability. The plasma concentration-versus-time curves of eight healthy male volunteers administered a single dose of imidapril (10 mg), gave an AUC12hr of imidapril of 121.48 +/- 35.81 ng mL(-1) h, and Cmax and Tmax values of 32.59 +/- 9.76 ng/mL and 1.75 +/- 0.27 h. The developed method should be useful for the determination of imidapril in plasma with sufficient sensitivity and specificity in bioequivalence study.

Voltammetric determination of cilazapril in pharmaceutical formulations

A sensitive adsorptive stripping voltammetric method for the measurement of cilazapril in 0.04 M Britton-Robinson buffer (pH 9.0) solution was described. The method was based on the adsorptive accumulation of the drug at a hanging mercury drop electrode (HMDE), followed by differential pulse voltammetry. The response was evaluated with respect to pre-concentration time, pH effect, accumulation potential, accumulation time and scan rate. The peak potential was -0.60 V (vs. Ag/AgCl). The peak current was directly proportional to the concentration of cilazapril with a detection limit of 17.6 ng ml(-1) at an accumulation time of 10 s. The reduction process was irreversible and the wave showed adsorptive characteristics. The results were compared to those obtained using a HPLC procedure. A reversed-phase C18e column with aqueous phosphate buffer (pH 3.5; 0.125 M)-acetonitrile (67:33, v/v) mobile phase and benazapril as internal standard was used. UV detector was set at 254 nm. Results obtained in HPLC were comparable to those obtained by adsorptive stripping voltammetric method.

Capillary zone electrophoresis applied to the determination of the angiotensin-converting enzyme inhibitor cilazapril and its active metabolite in pharmaceuticals and urine

A capillary zone electrophoresis method has been developed for the quantitation of antihypertensive drug cilazapril and its active metabolite cilazaprilat in pharmaceuticals and urine. The separation of the compounds was performed in a fused-silica capillary filled with the running electrolyte, which consisted of a 60 mM borate buffer solution at pH 9.5. Under the optimized experimental conditions, the separation took less than 5 min. The analysis of urine samples required a previous solid-phase extraction step using C8 cartridges. The method was successfully applied to the determination of the drug and its metabolite in urine samples obtained from three hypertensive patients (detection limits of 115 ng ml(-1) for cilazaprilat and 125 ng ml(-1) for cilazapril) and to pharmaceutical dosage forms. The method was validated in terms of reproducibility, linearity and accuracy.

Determination of the antihypertensive drug cilazapril and its active metabolite cilazaprilat in pharmaceuticals and urine by solid-phase extraction and high-performance liquid chromatography with photometric detection

A liquid chromatographic method with photometric detection for the determination of cilazapril and its active metabolite and degradation product cilazaprilat in urine and pharmaceuticals has been developed. The chromatographic method consisted of a microBondapak C18 column maintained at 30+/-0.2 degrees C, using a mixture of methanol-10 mM phosphoric acid (50:50 v/v) as mobile phase at a flow-rate of 1.0 ml/min. Enalapril maleate was used as internal standard. The detection was performed at a wavelength of 206 nm. A study of the retention of cilazapril and cilazaprilat using solid-liquid extraction has been carried out in order to optimise the clean-up procedure for urine samples, which consisted of a solid-liquid extraction using C(R) cartridges. Recoveries greater than 85% are obtained for both compounds. The method was sensitive, precise and accurate enough to be applied to the determination of urine samples obtained from three hypertensive patients up to 24 h after intake of a therapeutic dose (detection limit of 70 ng/ml for cilazapril and cilazaprilat in urine). A comparison of the method developed using photometric and amperometric detection has been carried out.

Dissolution tests of benazepril-HCl and hydrochlorothiazide in commercial tablets: comparison of spectroscopic and high performance liquid chromatography methods

Simple, rapid and reliable spectroscopic methods (absorbance ratio and Vierordt) were compared with HPLC for quantitative determination in dissolution tests of benazepril-HCl (BNZ) and hydrochlorothiazide (HCT) in commercial tablets. A 249 nm wavelength was chosen as the isosbestic point in the absorbance ratio method, and the absorbance ratios A236/A249 nm for BNZ and A269/A249 nm for HCT were used for calculation of regression equations. For the Vierordt method, A1(1) values (%1.1 cm) obtained at 236 and 269 nm for both substances were used for quantitative analyses of BNZ and HCT. In the HPLC method, simultaneous determination of BNZ and HCT from dissolution medium was achieved using the mobile phase containing phosphate buffer (0.01 M, pH 6.2) and acetonitrile (65:35) on a Supelcocil LC-18 (4.6 x 250, 5.6 mm) reversed phase column. Dissolution tests of commercial tablets were carried out according to USP XXII paddle method in 0.1 N HCl at 50 rpm at 37 +/- 0.5 degrees C. Comparison of the dissolution data from the HPLC and two spectroscopic methods indicated that spectroscopic and HPLC methods were in good correlation with each other. Therefore, it was concluded that both spectroscopic methods as well as HPLC can be used in routine analyses of BNZ and HCT in dissolution tests of commercial tablets.

Determination of imidapril and imidaprilat in human plasma by high-performance liquid chromatography-electrospray ionization tandem mass spectrometry

A sensitive and specific assay of imidapril and its active metabolite, imidaprilat, in human plasma has been developed. This method is based on rapid isolation and high-performance liquid chromatography (HPLC)-electrospray ionization (ESI)-tandem mass spectrometry (MS-MS). Imidapril and imidaprilat were isolated from human plasma using OASIS HLB (solid-phase extraction cartridge), after deproteinization. The eluent from the cartridge was evaporated to dryness, and the residue was reconstituted in mobile phase and injected into the HPLC-ESI-MS-MS system. Each compound was separated on a semi-micro ODS column in acetonitrile-0.05% (v/v) formic acid (1:3, v/v). The selected ion monitoring using precursor-->product ion combinations of m/z 406-->234 and 378-->206, was used for determination of imidapril and imidaprilat, respectively. The linearity was confirmed in the concentration range of 0.2 to 50 ng/ml in human plasma, and the precision of this assay, expressed as a relative standard deviation, was less than 13.2% over the entire concentration range with adequate assay accuracy. The HPLC-ESI-MS-MS method correlates well with the radioimmunoassay method, therefore, it is useful for the determination of imidapril and imidaprilat with sufficient sensitivity and specificity in clinical studies.

Quantitative determination of the angiotensin-converting enzyme inhibitor cilazapril and its active metabolite cilazaprilat in pharmaceuticals and urine by high-performance liquid chromatography with amperometric detection

A rapid and simple high-performance liquid chromatographic method with amperometric detection has been developed for the quantitation of cilazapril and its active metabolite and degradation product cilazaprilat in urine and tablets. The chromatographic system consisted of a microBondapak C18 column, using a mixture of methanol-5 mM phosphoric acid (50:50, v/v) as mobile phase, which was pumped at a flow-rate of 1.0 ml/min. The column was kept at a constant temperature of (40+/-0.2) degrees C. Detection was performed using a glassy carbon electrode at a potential of 1350 mV. Sample preparation for urine consisted of a solid-phase extraction using C8 cartridges. This procedure allowed recoveries greater than 85% for both compounds. The method proved to be accurate, precise and sensitive enough to be applied to pharmacokinetic studies and it has been applied to urine samples obtained from four hypertensive patients (detection limit of 50 ng/ml for cilazapril and 40 ng/ml for cilazaprilat in urine). Results were in good agreement with pharmacokinetic data.

Evaluation of cilazapril versus captopril in patients with mild to moderate essential hypertension

OBJECTIVE

Cilazapril, a long-acting angiotensin converting enzyme (ACE) inhibitor, was evaluated against captopril for safety and efficacy in the treatment of mild to moderate essential hypertension.

METHODS

One hundred thirty-two patients were randomly assigned to receive cilazapril, 2.5 mg once daily; 62 patients were randomly assigned to receive captopril, 25 mg twice daily. If necessary, dosage was increased to 5.0 mg cilazapril, once daily or 50 mg captopril, twice daily. Adjunctive hydrochlorothiazide (12.5 mg once daily) was later added to this higher dosage, if required.

RESULTS

After eight weeks of monotherapy, sitting diastolic blood pressure (SDBP) had decreased 7.5 mm Hg from baseline for cilazapril-treated patients, versus 5.6 mm Hg for captopril-treated patients. These decreases were 7.6 mm Hg and 6.8 mm Hg for cilazapril and captopril, respectively, at Week 12. At Week 8, 36.5% of patients receiving cilazapril had achieved a SDBP of 90 mm Hg or less, versus 26.0% of captopril-treated patients. The overall responder rate at Week 8 was 47.1% for cilazapril and 34.0% for captopril. None of these differences between the two treatment groups were statistically significant. Both drugs alone or in combination with hydrochlorothiazide were well tolerated during the 12-week treatment period.

CONCLUSION

The results of this study indicate that cilazapril, alone or with adjunctive hydrochlorothiazide, is effective and well tolerated as treatment for mild to moderate hypertension.

Cilazapril. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in cardiovascular disease

Cilazapril is an orally active angiotensin converting enzyme (ACE) inhibitor which lowers peripheral vascular resistance without affecting heart rate. Like enalapril and ramipril it is a prodrug, and is hydrolysed after absorption to cilazaprilat, which has a long terminal phase elimination half-life permitting once daily administration. Given once daily at doses between 2.5 and 5 mg, cilazapril reduces arterial blood pressure in patients with mild to moderate essential and renal hypertension. Patients who do not respond adequately to cilazapril monotherapy usually respond with the addition of a diuretic such as hydrochlorothiazide. Preliminary data suggest that cilazapril is of comparable antihypertensive efficacy to usual therapeutic dosages of hydrochlorothiazide, slow release propranolol, nitrendipine, captopril and enalapril. In small studies cilazapril has produced sustained beneficial haemodynamic effects in patients with congestive heart failure. Cilazapril has been well tolerated and exhibits tolerability typical of ACE inhibitors as a class, including their lack of detrimental effect on glucose or lipid metabolism. Cilazapril should provide an effective alternative in the treatment of hypertension and, if preliminary data are confirmed, in congestive heart failure.

Dose-finding study of cilazapril (Inhibace) in patients with uncomplicated essential hypertension

Cilazapril, an angiotensin converting enzyme (ACE) inhibitor with a long half-life, effectively reduced sitting diastolic blood pressure in patients with uncomplicated essential hypertension at dosages of 2.5, 5.0, and 10.0 mg/day, evaluated in a double-blind, placebo-controlled study. After a four-week placebo run-in period, 235 patients received either cilazapril or placebo for four weeks. At the end of the treatment period, significant decreases from baseline in sitting diastolic blood pressure were seen in all four groups (mean decreases of 3.3 mm Hg with placebo and 6.4, 9.2 and 8.3 mm Hg with 2.5, 5.0 and 10.0 mg cilazapril, respectively). The cilazapril groups had significantly greater blood pressure reductions than did the placebo group (p less than or equal to 0.02). The 5.0 mg cilazapril dose was significantly more effective than the 2.5 mg dose (p less than 0.03). The response rate was notably greater in the cilazapril treatment groups than in the placebo group (placebo, 27.5%; 2.5 mg cilazapril, 42.9%; 5.0 mg cilazapril 62.5%; 10.0 mg cilazapril, 50.0%). Cilazapril was well tolerated at all three dosages.

Clinical pharmacokinetics of the newer ACE inhibitors. A review

The orally active angiotensin-converting inhibitors (ACE inhibitors) such as captopril and enalapril represent a significant therapeutic advance in the treatment of hypertension and congestive heart failure. Enalapril differs from captopril in several respects. It is a prodrug converted by hepatic esterolysis to the active (but more poorly absorbed) diacid, enalaprilat. Enalaprilat is more potent than captopril, more slowly eliminated and does not possess a sulfhydryl (SH) group. Enalapril was rapidly followed by a number of newer ACE inhibitors, the majority of which are similar to enalapril in that they are prodrugs, converted by hepatic esterolysis to a major active but poorly absorbed diacid metabolite. In one case (delapril) there are 2 active metabolites; in another (alacepril) the prodrug is converted in vivo to captopril. Lisinopril is an exception in that it is an enalaprilat-like diacid but with acceptable oral bioavailability, so that the prodrug route is not employed. The newer ACE inhibitors are at widely different stages of development, and it is not yet clear how many will reach regular clinical use. Of these newer drugs, lisinopril is the longest established and is the subject of the widest published literature. For a number there is as yet little published pharmacokinetic information. A variety of assay methods have been employed to characterise the pharmacokinetics of the ACE inhibitors, including enzymatic techniques, radioimmunoassay and chromatography. The peak plasma concentrations of the prodrugs are generally observed at around 1 hour and those of the diacid metabolites at about 2 to 4 hours. However, there is considerable variation within and between drugs, with benazepril and benazeprilat reaching peak concentrations early and enalapril and enalaprilat typical of later times to peak. Absorption of the active diacids is generally poor, and moderate (typically 30 to 70%) for the prodrugs. The bioavailability of lisinopril is about 25%. It is difficult to talk meaningfully about half-lives of the active drugs. The declines in their plasma concentrations are polyphasic and, if analytical sensitivity allows, active drug may be found at 48 hours or more following administration. This may reflect binding to ACE in plasma. Half-lives of accumulation are of the order of 12 hours; protein binding varies from little (lisinopril) to 90% (benazeprilat). Elimination is mostly renal but there may be biliary elimination for some, such as benazeprilat and fosinopril. The half-lives of the prodrugs are short. Impaired renal function decreases the elimination rate of the diacids.(ABSTRACT TRUNCATED AT 400 WORDS)

Antihypertensive effects and pharmacokinetics of single and consecutive doses of cilazapril in hypertensive patients with normal or impaired renal function

1. A 1.25 mg dose of cilazapril, a new angiotensin-converting enzyme (ACE) inhibitor, was administered orally to two groups of hypertensive patients, five with normal renal function (NRF) and seven with impaired renal function (IRF), once daily for 5 or 8 consecutive days. Blood pressure, heart rate and serum ACE activity were measured up to 24 h following the initial and the last dose. Plasma level profiles of cilazapril and its active diacid were also evaluated on the first and the last day of treatment. 2. Cilazapril induced significant falls in both systolic and diastolic blood pressures without increasing heart rate. The antihypertensive effect was evident within 1 h after drug administration and was sustained for up to 24 h, particularly after consecutive dosing. 3. Serum ACE activity was markedly suppressed over 24 h. The recovery of ACE activity was delayed in the IRF group when compared with the NRF group. 4. Plasma concentrations of the active diacid in the IRF group were higher than in the NRF group with significant differences in the peak concentrations and area under the plasma concentration-time curve (AUC). The plasma concentration profile for the parent drug was similar for both the NRF and IRF groups. 5. A significant inverse correlation was found between the creatinine clearance and the AUC for the diacid. 6. Cilazapril is a potent ACE inhibitor with a prolonged duration of antihypertensive effect and is a useful agent for controlling blood pressure in hypertensives either with NRF or IRF. In patients with severe renal impairment the dose of cilazapril should be reduced.

Glycolamide esters as biolabile prodrugs of carboxylic acid agents: synthesis, stability, bioconversion, and physicochemical properties

Benzoic acid esters of various substituted 2-hydroxyacetamides (glycolamides) were found to be hydrolyzed extremely rapidly in human plasma solutions, the half-lives of hydrolysis being less than 5 s in 50% plasma solutions for some N,N-disubstituted glycolamide esters. The rapid rate of hydrolysis could be largely attributed to cholinesterase (also called pseudocholinesterase) present in plasma. From a study of a variety of substituted glycolamide esters and structurally related esters, the most prominent structural requirement needed for a rapid rate of hydrolysis was found to be the glycolamide ester structure combined with the presence of two substituents on the amide nitrogen atom. A structural similarity of such esters with benzoylcholine, a good substrate for cholinesterase, was put forward. Esters of N,N-disubstituted glycolamides are suggested to be a useful biolabile prodrug type for several carboxylic acid agents. The esters combine a high susceptibility to undergo enzymatic hydrolysis in plasma with a high stability in aqueous solution. Furthermore, as demonstrated with the benzoic acid model esters, it is feasible to obtain ester derivatives with almost any desired water solubility or lipophilicity with retainment of marked lability to enzymatic hydrolysis.