Flumazenil : It is a BZD analogue which has little intrinsic activity (practically no effect on normal subjects), but competes with BZD agonists as well as inverse agonists for the BZD receptor and reverses their depressant or stimulant effects respectively.
BENZODIAZEPINE ANTAGONIST
It is a BZD analogue
which has little intrinsic activity
(practically no effect on normal subjects), but competes with BZD agonists as
well as inverse agonists for the BZD receptor and reverses their depressant or
stimulant effects respectively.
Flumazenil abolishes the hypnogenic, psychomotor, cognitive and
EEG effects of BZDs. At higher doses it has some week BZD agonist like as well
as inverse agonist like activity in animal models, but these are of no clinical
significance.
Flumazenil is absorbed orally; oral bioavailability is ~16%, but
it is not used orally. On i.v. injection, action of flumazenil starts in
seconds and lasts for 1–2 hr; elimination t½ is 1 hr, due to rapid metabolism.
Uses
Patients anaesthetized/sedated with a BZD wakeup, get oriented
and regain motor control within 1 min of an i.v. injection of 0.3–1 mg of
flumazenil. Resedation generally occurs after 1–2 hr (more with diazepam than
with midazolam): supplemental doses of flumazenil may be given. It allows early
discharge of patients after diagnostic procedures and facilitates post-anaesthetic
management.
Majority of patients
of BZD overdose require only
supportive measures like patent airway, maintenance of BP, cardiac and renal
function, etc. In addition, flumazenil 0.2 mg/min may be injected i.v. till the
patient regains consciousness. Practically all patients intoxicated with a BZD
alone respond within 5 min. However, reversal of respiratory depression is
incomplete. Flumazenil blocks the hypnotic effect of zolpidem-like non-BZDs as
well. In mixed CNS depressant poisoning, whatever sedation is not abolished by
5 mg of flumazenil should be taken to be due to a non-BZD/non-Zolpidem-like
depressant. It thus helps in differential diagnosis of such patients.
Flumazenil is safe and
well tolerated.
Agitation, discomfort, tearfulness, anxiety, coldness and
withdrawal seizures are the occasional side effects.
It is N-acetyl-5methoxy
tryptamine, the principal hormone
of the pineal gland which is secreted at night and has been found to play an
important role in entraining (synchronizing) the sleep-wakefulness cycle with
the circadian rhythm. Though high doses (80 mg) of melatonin can induce sleep,
low doses (2–10 mg) do not depress the CNS, but probably increase the propensity
of falling asleep. Started before the flight it has been shown to reduce jetlag
symptoms and to hasten re-entrainment with daynight cycle of the new place in
intercontinental travellers. Beneficial effects in shift workers and in individuals
with delayed sleep phase syndrome have also been reported. It has improved
sleep quality in elderly insomniacs and has helped weaning off regular BZD
users of their hypnotic. However, melatonin is not a dependable hypnotic; has
little effect on latency and duration of sleep, especially in nonelderly
insomniacs. Though it is unlikely to have the disadvantages of conventional
hypnotics, its long-term safety is not known. Lowering of seizure threshold at
night has been related to melatonin peak and psychiatric changes due to melatonin
are apprehended. Use may therefore be restricted to treatment of jetlag, shift
workers and elderly hypnotic dependent insomniacs.
Since melatonin
secretion declines with age, it has been argued that melatonin supplementation
might retard ageing. Though there is no proof of benefit melatonin (2–5 mg/day)
is being consumed as a health food in USA and some other countries. It has also
been tried in cluster headache. In India it is marketed as a remedy for
disturbed biorhythms and degenerative diseases.
MELOSET 3 mg tab, ZYTONIN,
ETERNEX melatonin 3 mg + pyridoxine 10 mg tab; one tab at evening daily.
It is a melatonin
receptor agonist introduced in some countries as a
novel hypnotic for sleep onset insomnia, that does not produce the usual BZD-like
side effects.
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