With the advent of monoamine oxidase inhibitors (MAOIs) and tricyclic antidepressants (TCAs) in the 1950s,
depression
treatment was revolutionized. These medicines target the monoamine
system, including the neurotransmitters serotonin, norepinephrine and
dopamine.
For decades, the dominant hypothesis of depression has been that low
levels of monoamines in the brain cause this debilitating disorder.
In the ‘80s, the selective serotonin reuptake inhibitor (SSRI)
fluoxetine (brand name: Prozac) heralded a new era of safer drugs which
also target the monoamine system. Since then, various SSRIs and
serotonin-norepinephrine reuptake inhibitors (or SNRIs) have been
developed as new antidepressants. While these drugs aren’t more
effective than older antidepressants, they are less toxic.
But SSRIs and SNRIs don’t work for everyone, so MAOIs and TCAs still are prescribed.
Two out of three patients with depression do not fully recover on an antidepressant medication according to findings from
STAR*D,
the largest clinical trial study of treatments for major depressive
disorder, funded by the National Institute of Mental Health. (One-third
of patients do have a remission of their depression symptoms.)
These results “are important because previously it was unclear just how effective (or ineffective)
antidepressant medications are in patients seeking treatment in real-world settings,” said
James Murrough,
M.D., board-certified psychiatrist and a research fellow at the Mount
Sinai School of Medicine Mood and Anxiety Disorders Program.
As Murrough explained,
depression treatment
can be thought of in thirds: “for one third of patients, symptoms
remit; another third don’t have as good of an outcome, experiencing
residual symptoms and waxing and waning course or chronic course and are
at risk for relapse whether they’re on or off medication; and then a
third don’t get much benefit at all.”
He added that around “10 to 20 percent have persistent clinically
significant symptoms that aren’t decreased by current treatment — these
are the patients that we are the most worried about.”
So there’s a real need to find treatments that work for these
patients. Since the 1950s and 1980s breakthroughs, researchers haven’t
discovered drugs that target chemical systems in the brain other than
the monoamine system.
“We haven’t been able to find any new systems, because we don’t understand the underlying biology of depression,” Murrough said.
But researchers are studying other mechanisms of depression and
various drugs have recently been approved to treat depression. Below,
you’ll learn about these drugs along with several chemical systems
research is exploring.
Recently Approved Drugs for Depression
Recently approved drugs for depression are generally “me-too” drugs. A
“me-too drug is a drug whose mechanism of action (what it does at the
molecular level in the brain) is not meaningfully different than its
predecessor,” Dr. Murrough said.
Prime examples of me-too drugs are desvenlafaxine (Pristiq), an SNRI,
and escitalopram (Lexapro), an SSRI, he said. Pristiq is simply
Effexor’s main metabolite. Lexapro is essentially a close relative
derivative of citalopram (Celexa). Interestingly, sales still
skyrocketed when Lexapro came out.
As Murrough said, there is value in some me-too drugs. Generally, all
drugs within the classes SSRIs and SNRIs are me-too drugs. But the side
effect profiles for each drug have slight differences, which can help
patients.
For instance, Prozac tends to be more activating, so a doctor may
prescribe it for patients with low energy, Murrough said. In contrast,
paroxetine (Paxil) makes people more tired, so it’s prescribed to
patients who have trouble sleeping, he said.
The drug Oleptro was approved this year for depression. It doesn’t
target new mechanisms, and it isn’t even a me-too drug, Murrough said.
It’s a reformulation of trazodone, an atypical antidepressant that’s
been used as a sleeping aid by psychiatrists and other doctors. Because
it’s so sedating, its earlier form would just put patients to sleep. “It
is unclear if the new formulation will offer any benefit for patients
over the original,” Murrough said.
These recently approved medicines “characterize the state of drugs in
psychiatry,” Murrough said, and speak to “what’s wrong with
antidepressant drug development today.” Novel treatments just aren’t on
the market.
Augmentation of Depression Drugs
Recently, the biggest development in
depression treatment
has been the use of augmenting agents, said David Marks, M.D.,
assistant professor at the Department of Psychiatry & Behavioral
Sciences at the Duke University Medical Center.
Specifically, some research has found that adding atypical
antipsychotic drugs, like aripiprazole (Abilify) and quetiapine
(Seroquel), to an antidepressant can boost its effectiveness.
Atypical antipsychotics are used to treat schizophrenia and bipolar
disorder. “Abilify has three strong studies that show how well it works
in patients that have partially responded to antidepressants,” Marks
said. According to Murrough, augmentation has become a common strategy
in depression treatment.
The Glutamate System and Depression
Researchers have looked at the role of the glutamate system in
depression. Glutamate is abundant in the brain and is one of the most
common neurotransmitters. It’s involved in memory, learning and
cognition.
Some research has implicated the dysfunction of the glutamate system
in medical conditions, such as Huntington’s chorea and epilepsy, and
psychological disorders, such as schizophrenia and anxiety disorders.
Recent research suggests that drugs targeting a specific type of
glutamate receptor in the brain — called the NMDA receptor — may have
antidepressant effects.
Studies have explored ketamine, an NMDA antagonist, in treating
treatment-resistant depression and acute suicidal ideation. Ketamine has
a long history in analgesia and anesthesiology.
Currently, when a person is at imminent risk for attempting suicide
or has attempted suicide, they’re admitted to a psychiatric hospital and
closely monitored. But, as Murrough explained, medically, there’s
nothing doctors can do to help with suicidal ideation or intense
depressed mood. Antidepressants typically four to six weeks to work.
Ketamine appears to have fast antidepressant effects — within hours
or a day. Thus, it may help protect patients from suicidal thinking or
acute dysphoria when they’re in the hospital. Unfortunately, its effects
only last seven to 10 days.
This research is “highly experimental, and probably less than 100
patients in the country have participated in controlled depression
studies of ketamine,” Murrough said. The patients in these studies
typically have treatment-resistant depression: They haven’t responded to
several antidepressants and have moderate to severe symptoms of
depression.
They’re admitted to the hospital and receive ketamine intravenously
from an anesthesiologist, while their vital signs are closely monitored.
Ketamine is a drug of abuse, known by such street names as “Special
K.” It induces trance-like or hallucination states. It also produces
mild to moderate cognitive side effects, like other anesthetics. People
report feeling “out of it,” intoxicated and disconnected in general.
These side effects actually “introduce a potential bias to the study
design” because participants know they’re getting the treatment (when
saline is given in the placebo condition), Murrough said.
To eliminate this bias, Murrough and his team are conducting the
first-ever study to compare ketamine to a different anesthetic — the
benzodiazepine midazolam (Versed) — which has similar transient effects
as ketamine, he said. The study is currently recruiting participants.
Murrough cautioned that ketamine isn’t meant to be a treatment
administrated at your doctor’s office. In a recent article in the
journal Nature Medicine, he said ketamine treatment may be “akin to
electroconvulsive shock treatment.”
Studying ketamine may reveal mechanisms underlying depression and
help to find drugs that can be prescribed as antidepressants to a wider
patient population.
Pharmaceutical companies have started exploring other NMDA receptor
antagonists for treatment-resistant depression. For instance, in July
2010, the pharmaceutical company Evotec Neurosciences began testing a
compound in a Phase II study, which evaluates the safety and efficacy of
a drug.
Source: http://psychcentral.com/lib/depression-new-medications-on-the-horizon/0005794