Types of Antidepressants
Selective serotonin reuptake inhibitors (SSRIs)
Selective serotonin reuptake inhibitors (SSRIs) are a family of
antidepressants considered to be the current standard of drug treatment. It is
thought that one cause of depression is an inadequate amount of
erotonin,
a chemical used in the brain to transmit signals between neurons. SSRIs are said
to work by preventing the reuptake of serotonin(5-HT) by the presynaptic neuron,
thus maintaining higher levels of 5-HT in the synapse. Recently, however, work
by two researchers has called into question the link between serotonin
deficiency and symptoms of depression, noting that the efficacy of SSRIs as
treatment does not in itself prove the link.
Recent research indicates that these drugs may interact with transcription
factors known as "lock
genes",
which may be important for the addictive properties of drugs of abuse, and
possibly in obesity.
Recent
randomized controlled trials in Archives of General Psychiatry showed that
up to one-third of effects of SSRI Treatment can be seen in first week. Early
effects also shown to have secondary effect of reducing absolute reduction in
HDRS score by 50%. Even more recent studies, published by the Archives of
General Psychiatry note that 25% of so-called clinical depression does not meet
a disease criteria and should be considered to be ordinary sadness and
adjustment to the difficulties in life.
This family of drugs includes
luoxetine
(Prozac),
paroxetine (Paxil),
escitalopram (Lexapro, Esipram),
italopram
(Celexa), and
ertraline
(Zoloft). These antidepressants typically have fewer adverse side effects than
the tricyclics or the MAOIs, although such effects as drowsiness, dry mouth,
nervousness, anxiety, insomnia, decreased appetite, and decreased ability to
function sexually may occur. Some side effects may decrease as a person adjusts
to the drug, but other side effects may be persistent. Though safer than first
generation antidepressants, SSRI's may not work as often, suggesting the role of
norepinephrine.
Serotonin-norepinephrine reuptake inhibitors (SNRIs)
Serotonin-norepinephrine reuptake inhibitors (SNRIs) such as
venlafaxine (Effexor) and
uloxetine
(Cymbalta) are a newer form of antidepressant that works on both norepinephrine
and 5-HT. They typically have similar side effects to the SSRIs, although there
may be a withdrawal syndrome on discontinuation that may necessitate dosage
tapering.
Noradrenergic and specific serotonergic
antidepressants (NASSAs)
Noradrenergic and specific serotonergic antidepressants (NASSAs) form a
newer class of antidepressants which purportedly work to increase norepinephrine
(oradrenaline)
and serotonin neurotransmission by blocking presynaptic alpha-2
adrenergic receptors while at the same time minimizing serotonin related
side-effects by blocking certain serotonin receptors. The only example of this
class in clinical use is
mirtazapine (Avanza, Zispin, Remeron).
Norepinephrine (noradrenaline) reuptake inhibitors
(NRIs)
Norepinephrine (noradrenaline) reuptake inhibitors (NRIs) such as
eboxetine
(Edronax) act via norepinephrine (also known as noradrenaline). NRIs are
thought to have a positive effect on concentration and motivation in particular.
Norepinephrine-dopamine reuptake inhibitors
Norepinephrine-dopamine reuptake inhibitors such as
upropion
(Wellbutrin, Zyban) inhibit the neuronal reuptake of
opamine
and
norepinephrine (noradrenaline).
Tricyclic antidepressants (TCAs)
Tricyclic antidepressants are the oldest and include such medications as
amitriptyline and
desipramine. Tricyclics block the reuptake of certain neurotransmitters such
as norepinephrine (noradrenaline) and serotonin. They are used less commonly now
due to the development of more selective and safer drugs. Several side effects
include increased
heart rate, drowsiness, dry mouth, constipation, urinary retention, blurred
vision, dizziness, confusion, and sexual dysfunction. Toxicity occurs at
approximately ten times normal dosages. However, tricyclic antidepressants are
still used because of their high potency, especially in severe cases of clinical
depression.
Monoamine oxidase inhibitor (MAOIs)
Monoamine oxidase inhibitors (MAOIs) such as
henelzine
(Nardil) may be used if other antidepressant medications are ineffective.
Because there are potentially fatal interactions between this class of
medication and certain foods (particularly those containing
yramine),
as well as certain drugs, classic MAOIs are rarely prescribed anymore. MAOIs
work by blocking the enzyme monoamine oxidase which breaks down the
neurotransmitters dopamine, serotonin, and norepinephrine (noradrenaline). MAOIs
can be as effective as tricyclic antidepressants, although they can have a
higher incidence of dangerous side effects (as a result of inhibition of
cytochrome P450 in the liver). A new generation of MAOIs has been introduced;
moclobemide (Manerix), known as a
reversible inhibitor of monoamine oxidase A (RIMA), acts in a more
short-lived and selective manner and does not require a special diet.
Additionally, (elegiline)
marketed as msam
in a transdermal form is not a classic MAOI in that at moderate dosages it tends
to effect MAO-B which does not require any dietary restrictions.
Augmenter drugs Some antidepressants have been found to work more effectively in some
patients when used in combination with another drug. Such "augmenter" drugs
include
tryptophan (Tryptan) and
uspirone
(Buspar).
Tranquillizers and
edatives,
typically the benzodiazepines, may be prescribed to ease anxiety and promote
sleep. Because of their high potential for fostering dependence, these
medications are intended only for short-term or occasional use. Medications
often are used not for their primary function but to exploit what are normally
side effects.
uetiapine
fumarate (Seroquel) is designed primarily to treat
schizophrenia and bipolar disorder, but a frequently reported side-effect is
omnolence.
Therefore, this drug can be used in place of an antianxiety agent such as
lonazepam
(Klonopin, Rivotril).
Antipsychotics such as
risperidone (Risperdal),
lanzapine
(Zyprexa), and
uetiapine
(Seroquel) are prescribed as mood stabilizers and are also effective in treating
anxiety. Their use as mood stabilizers is a recent phenomenon and is
controversial with some patients. Antipsychotics (typical or atypical) may also
be prescribed in an attempt to augment an antidepressant, to make antidepressant
blood concentration higher, or to relieve
psychotic or
aranoid
symptoms often accompanying clinical depression. However, they may have serious
side effects, particularly at high dosages, which may include blurred
vision, muscle spasms, restlessness,
tardive dyskinesia, and weight gain.
Antidepressants by their nature behave similarly to psychostimulants.
Antianxiety medications by their nature are depressants. Close medical
supervision is critical to proper treatment if a patient presents with both
illnesses because the medications tend to work against each other.
Psycho-stimulants are sometimes added to an antidepressant regimen if the
patient suffers from
nhedonia,
hypersomnia and/or excessive eating as well as low motivation. These
symptoms which are common in
atypical depression can be quickly resolved with the addition of low to
moderate dosages of amphetamine or methylphenidate (brand names
dderall
and
Ritalin, respectively) as these chemicals enhance motivation and social
behavior, as well as suppress appetite and sleep. These chemicals are also known
to restore sex drive. Extreme caution must be used however with certain
populations. Stimulants are known to trigger manic episodes in people suffering
from bipolar disorder. They are also easily abused as they are effective
substitutes for
Methamphetamine when used recreationally. Close supervision of those with
substance abuse disorders is urged. Emotionally labile patients should avoid
stimulants, as they exacerbate mood shifting.
Lithium remains the standard treatment for bipolar disorder and is often
used in conjunction with other medications, depending on whether mania or
depression is being treated. Lithium's potential side effects include thirst,
remors,
light-headedness, and
ausea or
iarrhea.
Some of the
anticonvulsants, such as
carbamazepine (Tegretol),
sodium valproate (Epilim), and
lamotrigine (Lamictal), are also used as mood stabilizers, particularly in
bipolar disorder.
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