Date of Award

1-1-2000

Thesis Type

Masters

Document Type

Thesis

Divisions

Institute for Advanced Studies

Department

-

Institution

Universiti Malaya

Abstract

Captopril is a highly specific competitive inhibitor of the angiotensin-convening enzyme (ACE). This enzyme converts angiotensin I, a relatively inactive decapeptide, to angiotensin II , a potent endogenous vasoconstrictor substance. Captopril is widely used for the treatment of hypertension and congestive heart failure. This drug, which contains a sulphydryl group binds readily to albumin and to other plasma proteins. Captopril is unstable in blood and plasma ex vivo because of the reactivity of sulphydryl group which results in oxidation and rapid formation of disulphides. Therefore a fixative or a stabiliser must be added to each blood sample immediately following collection. In this assay, N-e1hylmaleimide (NEM) was used as a stabilizer in the collection lubes, prior to a rapid extraction technique by solid phase extraction (SPE). An enhanced and sensitive Gas Chromatography-Mass Spectrometry (GCMS) assay was developed for the quantitation of captopril. A commercially available internal standard, thiosalicylic acid (TSA) was used to minimise error in quantitation by GCMS. To enhance the volatility and gas chromatography elution properties, both captopril and TSA were derivatized to ester products by using pentafluorobenzyl bromide. Captopril and TSA are quantitated as their bis-pentafluorobenzyl derivatives. The assay was linear from 1 to 160 ng/ml with mean recoveries of 104% and 99% for captopril and TSA, respectively, when the assay was carried out at 1. 5, 75 and I SO ng/ml captopril . At the three concentrations of captopril mentioned, the coefficient of variation (CV) for inter- assay precision was 7.4, 9.5. and 4.4% respectively while accuracy was 6.1, 7.4, and 5.7%, respectively. Four sets of bioequivalence studies were conducted for four generic captopril products with three products containing 25 mg captopril and one product containing 12.5 mg captopril. Bioequivalence studies were carried out in accordance with the Malaysian guideline on Good Clinical Practice (GCP) (adopted from ICH) which incorporates the Declaration of Helsinki as well as being accordance with standard operating procedures (SOP). All the generic products were found to be bioequivalent with the reference products based on statistical assessment of three parameters, namely T-. C-. and AUC. The ratio test over reference (T/R) for T-. C--. and AUC were very close to I with the values ranging from 0.9 to I .4, 0.9 to I. I and 1.0 to I.I for T C _ and AUC, respectively. The mean values for T-. C-. and AUC for 25 mg dose of brand leader and generic products was very similar. The values were 0.7, 117.1 and 212.6 for brand leader and 0.7, 120.5 and 212.6 for generic products. This is the same with 12.5 mg dose, where the mean value for T--. c_ and AUC were 0.8, 55.6 and I 15.7 for Brand leader, while the generic products were 0.8, 48.9, and 106.4, respectively. A standard two-stage analysis of pharmacokine1ic parameters obtained from the equivalence studies carried out, indicated that the clearance (CL), half-life (t,,,) and elimination rate constant (K) in the 66 subjects studied, were within the range obtained from published data.

Initial

snms

Additional Information

Dissertation (M.A) -- Institute for Advanced Studies, Universiti Malaya, 2001.

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