Antidepressants - Venlafaxine Withdrawal

Neuroleptic Nightmare
by Malcolm Hulatt

General Comment On Drug Half-Life

If the frequency of taking a capsule/tablet (say 12 hours) is much shorter than the drug half life (say 24 hours), the capsule/tablet may be eliminated at something like three times the period of the half-life to reduce the average drug level slowly. The residual drug from the other capsules/tablets sustains the background level. If the frequency of elimination of a capsule/tablet is more than five times the half life, it will fall temporarily but then build back to its previous level.

For short half-life drugs taken twice or three times per day the drug reduction needs to be achieved in fractions of tablets with a consolidation period in between. The concentration in the body does not float down but reduces more rapidly according to the intake. Therefore the reduction here will need to be in small increments as the body levels fall so quickly. The greater the dependency the longer the consolidation will be needed between step changes in dosage and the smaller the size of the reduction acceptable. A given drug will have an inherent half-life range in the body. To achieve a longer half-life various techniques may be adopted. It is possible to have coatings on capsules/particles within capsules where the inner ones dissolve later and therefore release their drug more slowly.

Some drug particles are coated to slow down dissolution in the body. Double and triple coatings will give slower dissolution rates. However this technique can only be applied for as long as it takes the drug to pass through the body. If a longer half-life is required, a chemical intermediary can be used. Here the entire dose will be released into the blood stream but part of it will be in the form of a related drug which breaks down into the required drug over a period of several days. This can allow longer half lives to be achieved.

Antidepressant Half Life Information

Drug Generic Name Company Type Max mg/day Half life (hrs)
Anafranil Clomipramine Novartis TCAD 250 21 (19-37)
Asendis Amoxapine Wyeth TCAD 300 No Info

Cipramil

 

Lundbeck

SSRI

60

36 (28 - 42)

Edronax

 

Pharmacia

SNRI

12 8

Efexor

Venlafaxine

Wyeth

SSNRI

375 5 (5 to 11)

Faverin

 

Solvay

SSRI

300 21

Lentizol

Amitriptyline hyd.

Pfizer

  200 15 (10-28)

Lustral

Sertraline

Pfizer

SSRI

200 26 (22 to 33)

Prothiaden

Dothiepin hyd

Knoll

TCAD

150 19 to 33

Prozac

Fluoxetine

Dista

SSRI

  7 to 9 DAYS

Seroxat

Paroxetine

GSK

SSRI

50 21 to 26

Sinequan

Doxepin

Pfizer

TCAD

100 x 3 p.d 28 to 52

Surmontil

Trimipramine

Futuna

TCAD

300 24

Tofranil

Imipramine

Novartis

TCAD

200 19

Triptafen

Phenothiazine

Goldshield

TCAD

4 tabs daily 30

Zispin

Mirtazapine

Organon

N&S enhancer

45 20 to 40