Review of Pharmacology - 9E (2015)

Review of Pharmacology
Selective MAO-B inhibitors
Selegiline inhibits only MAO-B and is useful in Parkinsonism. It is available as a transdermal
patch for treatment of depression.
B. Atypical Antidepressants
Central Nervous System
Venlafaxine, milnacipran, levomilnacipran
and duloxetine
inhibit reu ptake of serotonin and
NA but lack anticholinergic and
a blocking properties. These
are also referred to as serotonin
and nor-adrenaline reuptake
inhibitors (SNRI).
Mirtazapine is also known as
nor-adrenergic and specific
serotonergic anti-depressant
(NSSA).
Bupropion is used for smoking
cessation.
Uses of anti-depressants
D - Depression
E - Enuresis (Imipramine)
P - Phobia
R - Recurrent panic attacks
E - Eating disorders (Bulimia)
S - Smoking cessation
(Bupropion)
S - Stress disorder (Post
traumatic)
I - Impulse disorder
(Kleptomania)
O - Obsessive compulsive
disorder
N - Neuropathic pain
These drugs may or may not increase monoaminergic levels and possess different antidepressant
mechanisms.
• Trazodone is a prominent α blocker and weak 5-HT 2
antagonist. It produces
sedation, priapism (prolonged and painful erection) and postural hypotension as
adverse effects.
• Mianserin acts by blocking presynaptic a 2
receptors but seizure augmenting and
bone marrow depressant actions restrict its use.
• Tianeptin and amineptine acts by enhancing the serotonin reuptake (action
opposite to SSRI).
• Venlafaxine, milnacipran, levo-milnacipran and duloxetine inhibit reuptake
of serotonin and NA but lack anticholinergic and a blocking properties. These
are also referred to as serotonin and nor-adrenaline reuptake inhibitors (SNRI).
Venlafaxine has faster onset of action. It has minimum drug-drug interactions.
• Mirtazapine: It inhibits presynaptic a 2
receptors and thus increases NA and 5-HT
release due to inhibition of auto- and hetero-receptors respectively. Although
it increases serotonin levels in synapse, there is selective activation of 5-HT 1
receptors due to antagonistic activity at 5-HT 2
and 5-HT 3
receptors. Therefore it is
also known as nor-adrenergic and specific serotonergic anti-depressant (NSSA).
It has minimal sexual side effects compared with SSRIs. It commonly causes
sedation, weight gain, lipid abnormalities and dizziness.
• Bupropion: It inhibits the uptake of NA and DA. It is metabolized to amphetamine
like compound and possesses excitatory property. It is used for smoking cessation
as sustained release formulation. It can precipitate seizures at high dose.
• Nafazodone: It blocks serotonin reuptake and antagonizes 5-HT 2
receptors. It
lacks antichelinergic effects (of TCAs) and agitation (seen with SSRI). It has very
short half life and is hepatotoxic.
• Atomoxetine: It is a selective inhibitor of NA reuptake and is useful for Attention
Deficit Hyperkinetic Disorder (efficacy similar to methylphenidate).
• Duloxetine (a mixed NA and 5HT reuptake inhibitor) is also useful in treating
chronic neuropathic pain e.g. in diabetic neuropathy and fibromyalgia.
Note:
• Most potent blocker of 5-HT reuptake – Paroxetine
• Least potent blocker of 5-HT reuptake – Bupropion
• Most potent blocker of NA reuptake – Desipramine
• Least potent blocker of NA reuptake – Mirtazapine
• Most selective inhibitor of 5-HT reuptake – Escitalopram
• Most selective inhibitor of DA reuptake – Bupropion
• Most selective inhibitor of NA reuptake – Oxaprotiline
• Maximum antimuscarinic activity – Amitriptyline
• Maximum antihistaminic activity – Nefazodone
• Maximum a 1
blocking activity – Doxepin
• Minimum antimuscarinic, a 1
blocking and antihistaminic activity – Venlafaxine
• Doxepin contains high antimuscarinic, antihistaminic and a-blocking (maximum) activities.
• Fluoxetine is longest acting and nefazodone is shortest acting antidepressant.
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