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9-Nitrominocycline is used as a reagent in the preparation of tigecycline from minocycline hydrochloride. | [Biological Functions]
Minoxidil (Loniten) is an orally effective vasodilator. It
is more potent and longer acting than hydralazine and
does not accumulate significantly in patients with renal
insufficiency. It depends on in vivo metabolism by hepatic
enzymes to produce an active metabolite, minoxidil
sulfate. Minoxidil sulfate activates potassium channels,
resulting in hyperpolarization of vascular smooth
muscle and relaxation of the blood vessel. | [Metabolism]
Peak concentrations of minoxidil in the blood occur 1
hour after oral administration, although the therapeutic
effect may take 2 or more hours to manifest. This is
probably related to the time it takes to convert minoxidil
to minoxidil sulfate. The antihypertensive action after
an oral dose of minoxidil lasts 12 to 24 hours. The
long duration of action allows the drug to be administered
only once or twice a day, a regimen that may be
beneficial for compliance. Interestingly, the therapeutic
half-life is considerably longer than the plasma half-life.
This may be, as has been suggested for hydralazine, a result
either of accumulation of the drug and its active
metabolite in arterial walls or a longer plasma half-life
of the sulfated metabolite, or both.
The ultimate disposition of minoxidil depends primarily
on hepatic metabolism and only slightly on renal excretion
of unchanged drug. Because of this, pharmacological
activity is not cumulative in patients with renal failure. |
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