article · Pharmacopsychiatry
A clinical study examined how blood levels of the antidepressant paroxetine relate to treatment outcomes in forty-six depressed patients receiving a fixed daily dose of forty milligrams. After five weeks of therapy, twenty-nine individuals showed a positive response, whereas seventeen did not. Throughout the treatment period, patients who responded successfully maintained significantly lower serum drug concentrations compared to those who did not improve. Specific upper concentration thresholds were identified across weeks one to four, including twenty-two point seven nanograms per millilitre at week one and thirty-nine point one nanograms per millilitre at week four, above which therapeutic response became improbable. In contrast to conventional pharmacological expectations where higher drug levels are typically sought, higher paroxetine concentrations in the blood appear to be linked with treatment failure in patients with depression.
Prescribing antidepressants often relies on trial and error because drug levels in the blood do not clearly predict recovery. Discovering that excessively high paroxetine levels associate with poor response challenges conventional assumptions. Recognising clear upper thresholds can help clinicians understand why some patients fail standard dosing, potentially guiding better monitoring strategies to improve recovery rates in clinical depression.
These findings could inform therapeutic drug monitoring protocols or diagnostic testing services used by psychiatrists and clinical laboratories to identify patients unlikely to respond to standard paroxetine doses. The research represents early-stage clinical findings from a small cohort of forty-six patients, meaning further clinical validation is required before diagnostic cut-offs can be implemented into routine clinical or commercial practice.
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INTRODUCTION: There is no established relationship between the serum concentration of selective serotonin reuptake inhibitors (SSRIs) and clinical response in depressed patients. METHODS: We analyzed paroxetine concentrations in serum of 46 depressed patients during treatment with a fixed dosage of 40 mg paroxetine. RESULTS: After 5 weeks 29 patients responded to treatment, while 17 did not. Analysis of variance with repeated measures (ANOVA-rm) revealed a significant effect of "response" with responders having lower serum concentrations throughout the treatment period, when compared to non-responders. After 2, 3, and 4 weeks of treatment, we could define an upper threshold of paroxetine serum concentrations (week 1 : 22.7 ng/mL; week 2 : 43 ng/mL; week 3 : 53.4 ng/mL; week 4 : 39.1 ng/mL) above which response to treatment was unlikely. CONCLUSION: We conclude that -- in contrast to other pharmacological approaches -- high rather than low drug serum concentrations may be associated with non-response in paroxetine treatment of depressed patients.
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DOI: 10.1055/s-2005-864121
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