Changing SSRI's-Blood Plasma test

April 21, 2011

Sorry it took a while to get back to you on this.

When we were trying Fluvoxamine, and it didn't seem to be working, the pdoc

ordered a plasma level test. The drew blood and it had to be mailed off to a lab

capable of doing the test. A week or so later, we had the result. I can't tell

you the units of measurement, but DS's reading was below the expected range. In

other words, we were told that the plasma level of Fluvoxamine was expected to

be between 78 and 920 with a mean of 510, given what his dosage was at that time

(I believe his dose was 150, or we had just increased to 200 at the time the

blood was drawn.) DS's reading was less than 10. We stayed on and gradually

increased to 250. He still was not getting better. The test was done again and

his plasma level was only 35. The pdoc concluded that he was either not

absorbing it or was metabolizing too fast. He remarked that fluvoxamine has a

very wide range of readings that can be effective (i.e. one person's level could

be 78 and another's could be 920 on the same dose). However, given how long he

had been on it and how low his plasma reading was, pdoc concluded this was not

his med.

So, we switched to Prozac. For Prozac, pdoc says there is a narrower range and

lots of data to support it. One would expect a plasma range of 250-500 for

effectiveness against OCD. DS started on 10 of Prozac and slowly worked up to

50. The test was done twice over this time period. Once he got to 50mg, his

plasma level was in the high 600's. We cut back to 40 mg and indeed, he does

seem a little better. DS also augments- -SSRI alone does not work for him.

Pdoc feels that in his experience, there is a window of effectiveness against

OCD, and that too high a dose can be evidenced by trembling and agitation, or by

too much indifference, or just by not working as well vs. the OCD thoughts.

Sometimes it is hard to tell whether the dose is too low or too high- -you just

have to try it. But with Prozac, having so much data available, you can be

pretty sure that if the plasma level is between 250 and 500, that's the best

level to treat OCD. (Depression would require a lower level.)

The only thing I will say is that even though DS's level is between 250 and 500,

he still has alot of OCD thoughts. Maybe this is due to the metabolite issue

raised by another poster- -Lexapro was better for him, but for whatever reason,

stopped working well.

Hope this helps.

WorriedMom

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