9-Nitrominocycline is used as a reagent in the preparation of tigecycline from minocycline hydrochloride.
9-Nitrominocycline is a 9-substituted Minocycline (M344800) derivative used as antibacterial agent.
Minoxidil, an antihypertensive agent, produces arteriolar
vasodilation by an unknown mechanism. In limited
clinical studies, minoxidil increases penile rigidity
and has been used in the long-term treatment of organic
impotence.
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.
The hemodynamic effects of minoxidil are generally
similar to those of hydralazine, with the noteworthy exception
that a greater decrease in peripheral vascular
resistance and consequently a larger reduction in blood
pressure can be achieved with minoxidil. Minoxidil produces
no important changes in either renal blood flow
or glomerular filtration rate. It has little or no effect on
venous capacitance and does not inhibit the reflex activation
of the sympathetic nervous system. Orthostasis
and other side effects of sympathetic blockade are
therefore not a problem. As with hydralazine, there is a
significant increase in cardiac output that is secondary
to reflex increases in sympathetic activity, hyperreninemia,
and salt and water retention.These effects can substantially
reduce the effectiveness of minoxidil when it
is used alone.The addition of a -blocker and a diuretic
to the therapeutic regimen will preserve minoxidil’s antihypertensive
action while attenuating some of the undesirable
side effects.
The major indications for the use of minoxidil are
(1) severe hypertension that may be life threatening
and (2) hypertension that is resistant to milder forms of
therapy. Compromises in renal function do not prolong
either the plasma or the therapeutic half-life of minoxidil,
and therefore, it seems to be particularly important
for hypertensive patients with chronic renal failure.
Signs of toxicity common to vasodilator therapy in general
also occur with minoxidil; they are attributable to
vasodilation and reflex increases in sympathetic nerve
activity. These include headache, nasal congestion,
tachycardia, and palpitations. These effects do not have
great clinical importance, since minoxidil is almost always
administered in combination with a -blocker,
which antagonizes the indirect cardiac effects. A more
troublesome side effect, particularly in women, is the
growth of body hair, possibly due to a direct stimulation
of the growth and maturation of cells that form hair
shafts. Apparently, minoxidil activates a specific gene
that regulates hair shaft protein. In any case, this particular
side effect has been capitalized upon, and minoxidil
is now marketed as Rogaine for the treatment of
male pattern baldness.
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.
