Clozapine levels are most affected by which of the following factors?
Smoking can have a significant effect on clozapine levels.
Smoking can have a significant effect on clozapine levels.
Clozapine (levels)
The average clozapine dose in the UK is 450 mg/day.
A 'therapeutic range' has not been established. It is generally accepted that a level of 350 µg/L is necessary to achieve a therapeutic response. Levels greater than 500 µg/L should be treated with caution as there is a risk of seizures.
Lower doses may be required in non-smokers, the elderly, females, and in patients using enzyme inhibitors (e.g. SSRI's).
Treatment should of course be guided by clinical response (treat the patient not the level).
| Plasma level | Action |
|---|---|
| <350 µg/L | If response good then no action. If response poor increase dose to get a level of 350 µg/L |
| 350 - 500 µg/L | If response good then no action If response poor then increase dose to get level >500 µg/L and consider prophylactic anticonvulsant when dose get beyond 500µg/L |
| 500 - 1000 µg/L | If response good then try to reduce dose to within 350 - 500 µg/L. If patient can't tolerate lower dose then consider prophylactic anticonvulsant. If poor response then consider prophylactic anticonvulsant and consider augmentation |
| >1000 µg/L | If response good then add anticonvulsant. If well tolerated then continue, if not then attempt dose reduction to get level of <1000 µg/L. If response poor then add anticonvulsant and attempt augmentation. Consider abandoning clozapine |
Above table adapted from Maudsley Guidelines 12th Edition.
