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Xenobiotica
the fate of foreign compounds in biological systems
Volume 15, 1985 - Issue 11
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Original Article

Metabolism and pharmacokinetics of the dihydropyridine calcium antagonist, ryosidine, in man

, , , , , , & show all
Pages 965-977 | Received 07 Dec 1984, Accepted 08 May 1985, Published online: 30 Sep 2009
 

Abstract

1. The metabolic fate of [14C]ryosidine (ryodipine) has been investigated after oral administration to human subjects (by capsule), and to rats and dogs (in solution). The excretion patterns of 14C were similar for all three species: about 50% dose was excreted in urine, mainly in 24 h, but a proportion was excreted slowly, particularly by humans. Absorption in man appeared to be less than in the animal species, probably as a result of the capsule dosage form used.

1 μg equiv./ml at four hours and declined biphasically thereafter (mean terminal t1/2 = 28 h). Unchanged ryosidine was only detected in plasma from two to six hours (mean t1/2 = 80 min), and never accounted for more than 5% of the plasma 14C. The extent of binding of ryosidine to the plasma proteins (in vitro) was similar (>90%) to that of total 14C (in vivo; mainly metabolites).

2. Mean concentrations of total 14C in human plasma reached a peak value of 0·4

3. Less than 0·5% of the dose to human subjects was excreted via the kidneys as unchanged ryosidine, whereas the bulk of the extractable faecal 14C was in the form of unchanged drug and presumably represented unabsorbed material. The principal routes of biotransformaiion of ryosidine in all three species involved oxidative aromatization of the 1,4-dihydropyridine ring, followed by ester hydrolysis, O-dealkylation, hydroxylation of an α-methyl group (and lactonization) and some glucuronidation, although quantitative inter-species differences were apparent.

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