Paroxetine (Paxil)

Question 1

Brands

Answer 1

Paxil
Paxil CR (Control Released)

Question 2

Class

Answer 2

SSRI

Question 3

MOA

Answer 3

SSRI - Serotonin 1A receptors
Mildly anticholinergic
Mild NE reuptake blockade

Question 4

Uses

Answer 4

• MDD
• OCD
• Panic disorder
• Social anxiety disorder
• PTSD
• GAD
• PMDD
• Vasomotor symptoms (Brisdelle)

Question 5

Onset of action

Answer 5

• 2-4 weeks to start for depression
• 8 weeks to start fro anxiety, may take 6 months
• Relief of insomnia and anxiety early after starting

Question 6

If it works

Answer 6

• 1st episode - use till 1 year after symptoms stop

* 2nd or more - use indefinitely

Question 7

S/Es

Answer 7

Same as Sertraline

Specific to paroxetine - constipation, dry mouth, sedation due to anticholinergic action

Question 8

Dosing

Answer 8

• Range
• Depression - 20 to 50 mg (20 - 62.5 mg CR)
• Vasomotor symptoms - 7.5 mg at bedtime
• Forms
• Tablet 10, 20, 30, 40 mg
• Control released tablet 12.5, 25 mg
• Liquid 10 mg/5 ml - 250 ml bottle

Question 9

Dosing for Depression

Answer 9

Start at 20 mg (25 mg CR) once daily, usually bedtime
wait a few weeks and assess
Can inc by 10 mg (12.5 mg CR) every week
Max 50 mg/day (62.5 mg CR)

Question 10

Dosing for Panic Disorder

Answer 10

Start at 10 (12.5 CR) once daily
Wait a few weeks and assess
Increase by 10 (12.5 CR) every week
Max 60 (75 CR)

Question 11

Dosing for Social anxiety disorder

Answer 11

20 to start, inc by 10 weekly, max 60

Question 12

Dosing trick in Paroxetine

Answer 12

Increase by 10 mg every week instead of doubling or tripling because PAROXETINE INHIBITS ITS OWN METABOLISM and thus plasma conc is doubled when oral dose is increased by 50%.
If oral dose is doubled, plasma conc will inc 2-7 times. Don’t do that.

Question 13

Advantage of CR over regular

Answer 13

Lower S/Es like nausea, sedation, sexual dysfunction, withdrawal symptoms

Question 14

Tapering paroxetine

Answer 14

• Reduce dose by 50% for 3 days, then another 50% for 3 days, then stop.
• Withdrawal symptoms are MUCH MORE SEVERE with Paroxetine compared to other SSRIs since it inhibits its own metabolism (nausea, dizziness, stomach cramps, sweating, tingling, dysesthesias)

*For pts with severe problems on discontinuation, taper over many months, eg reduce dose by 1% every 3 days, by crushing tablet and dissolving in 100 ml juice and throwing away 1 ml and drinking the rest.
3-7 days later, throw away 2 ml and so on.
This helps in biological tapering, and also behavioral desensitization.
(not for CR)

*For some pts, you might want to add another long half life SSRI like FLUOXETINE before tapering paroxetine. First continue fluoxetine, taper paroxetine and stop it, then taper fluoxetine and stop it.

Question 15

OD symptoms

Answer 15

• Rarely lethal in monotherapy OD

* Vomiting, sedation, arrhythmia, dilated pupils, dry mouth

Question 16

Half life

Answer 16

24 hours

Inactive metabolites

Question 17

CYP action

Answer 17

Inhibits 2D6

Question 18

Drug interactions

Answer 18

Same as Sertraline

Specific to Paroxetine-

• increases theophylline levels
• increase anticholinergic effects of procyclidine

Question 19

C/I

Answer 19

Don’t use with

• MAOIs
• Pimozine (cardiac arrhythmia)
• Thioridazine (cardiac arrhythmia)
• Tamoxifen

Allergy

Question 20

Renal, Hepatic, Cardiac, Age groups

Answer 20

• Lower dose in renal and hepatic (Start at 10, Max 40)
• Lower dose in elderly (Start at 10, Max 40)
• Rest is same as sertraline

Question 21

Advantages

Answer 21

• Anxiety disorders
• Insomnia
• Mixed anxiety/depression

Question 22

Disadvantages

Answer 22

• Hypersomnia pts
• Alzheimer/cognitive disorder pt
• Pt with psychomotor retardation, fatigue, low energy

Question 23

Target symptoms

Answer 23

• depressed mood
• anxiety
• sleep disturbance, esp insomnia
• panic attacks, avoidant behavior, hyperarousal, re-experiencing

Question 24

Of note for Paroxetine

Answer 24

• Preferred drug in pts with depression+anxiety (and insomnia)
• Mild anticholinergic action - rapid anxiolytic and hypnotic action
• Less activating than other SSRIs
• More chances of withdrawal effects
• Dosing not linear as it inhibits its own metabolism