Pharmacology Of Desipramine

Indication	For relief of symptoms in various depressive syndromes, especially endogenous depression. It has also been used to manage chronic peripheral neuropathic pain, as a second line agent for the management of anxiety disorders (e.g. panic disorder, generalized anxiety disorder), and as a second or third line agent in the ADHD management.
Pharmacodynamics	Desipramine, a secondary amine tricyclic antidepressant, is structurally related to both the skeletal muscle relaxant cyclobenzaprine and the thioxanthene antipsychotics such as thiothixene. It is the active metabolite of imipramine, a tertiary amine TCA. The acute effects of desipramine include inhibition of noradrenaline re-uptake at noradrenergic nerve endings and inhibition of serotonin (5-hydroxy tryptamine, 5HT) re-uptake at the serotoninergic nerve endings in the central nervous system. Desipramine exhibits greater noradrenergic re-uptake inhibition compared to the tertiary amine TCA imipramine. In addition to inhibiting neurotransmitter re-uptake, desipramine down-regulates beta-adrenergic receptors in the cerebral cortex and sensitizes serotonergic receptors with chronic use. The overall effect is increased serotonergic transmission. Antidepressant effects are typically observed 2 - 4 weeks following the onset of therapy though some patients may require up to 8 weeks of therapy prior to symptom improvement. Patients experiencing more severe depressive episodes may respond quicker than those with mild depressive symptoms.
Mechanism of action	Desipramine is a tricyclic antidepressant (TCA) that selectively blocks reuptake of norepinephrine (noradrenaline) from the neuronal synapse. It also inhibits serotonin reuptake, but to a lesser extent compared to tertiary amine TCAs such as imipramine. Inhibition of neurotransmitter reuptake increases stimulation of the post-synaptic neuron. Chronic use of desipramine also leads to down-regulation of beta-adrenergic receptors in the cerebral cortex and sensitization of serotonergic receptors. An overall increase in serotonergic transmission likely confers desipramine its antidepressant effects. Desipramine also possesses minor anticholinergic activity, through its affinity for muscarinic receptors. TCAs are believed to act by restoring normal levels of neurotransmitters via synaptic reuptake inhibition and by increasing serotonergic neurotransmission via serotonergic receptor sensitization in the central nervous system.
Absorption	Desipramine hydrochloride is rapidly and almost completely absorbed from the gastrointestinal tract. It undergoes extensive first-pass metabolism. Peak plasma concentrations are attained 4 - 6 hours following oral administration.
Volume of distribution	Not Available
Protein binding	73-92% bound to plasma proteins
Metabolism	Desipramine is extensively metabolized in the liver by CYP2D6 (major) and CYP1A2 (minor) to 2-hydroxydesipramine, an active metabolite. 2-hydroxydesipramine is thought to retain some amine reuptake inhibition and may possess cardiac depressant activity. The 2-hydroxylation metabolic pathway of desipramine is under genetic control.
Route of elimination	Desipramine is metabolized in the liver, and approximately 70% is excreted in the urine.
Half life	7-60+ hours; 70% eliminated renally
Clearance	Not Available
Toxicity	Male mice: LD50 = 290 mg/kg, female rats: LD50 = 320 mg/kg. Antagonism of the histamine H1 and α1 receptors can lead to sedation and hypotension. Antimuscarinic activity confers anticholinergic side effects such as blurred vision, dry mouth, constipation and urine retention may occur. Cardiotoxicity may occur with high doses of desipramine. Cardiovascular side effects in postural hypotension, tachycardia, hypertension, ECG changes and congestive heart failure. Psychotoxic effects include impaired memory and delirium. Induction of hypomanic or manic episodes may occur in patients with a history of bipolar disorder. Withdrawal symptoms include GI disturbances (e.g. nausea, vomiting, abdominal pain, diarrhea), anxiety, insomnia, nervousness, headache and malaise.