Abstract
OBJECTIVE To establish the relationship between dried blood spot (DBS) and serum concentrations of tamoxifen and endoxifen in order to allow the use of DBS sampling, a simple and patient-friendly alternative to venous sampling, in clinical practice. The antiestrogenic effect of tamoxifen is suggested to be mainly attributable to its metabolite endoxifen, and a minimum therapeutic threshold for endoxifen in serum has been proposed. DESIGN AND METHODS Paired DBS and serum samples were obtained from 50 patients using tamoxifen and analysed using HPLC-MS/MS. Serum concentrations were calculated from DBS concentrations using the formula: calculated serum concentration = DB S concentration/Id-haematocrit] + [blood cell/serum ratio) x haematocrit). The blood cell/serum ratio was determined ex vivo by incubating a batch of whole blood spiked with both analytes and imputed as a fixed value. The average haematocrit for female adults was imputed as a fixed value. Calculated and analysed serum concentrations were compared using weighted Deming regression. RESULTS Weighted Deming regression analysis comparing 44 matching pairs of DBS and serum samples showed a proportional bias for both analytes. Serum concentrations were calculated using [Tam]s.cals = [Tam)DBS/0.779 and [End)s.cal(; = [End]DBS/0.663. Calculated serum concentrations were within 20% of analysed serum concentrations in 84 and 100% of patient samples for tamoxifen and endoxifen, respectively. CONCLUSION DBS concentrations of tamoxifen and endoxifen were equal to serum concentrations after correction for haematocrit and blood cell/serum ratio. DBS sampling can be used in clinical practice.
| Translated title of the contribution | Use of dried blood spots for the determination of serum concentrations of tamoxifen and endoxifen |
|---|---|
| Original language | Dutch |
| Pages (from-to) | 24-30 |
| Number of pages | 7 |
| Journal | Pharmaceutisch Weekblad |
| Volume | 151 |
| Issue number | 7 |
| Publication status | Published - 19 Feb 2016 |