Michiel de Vries

Occupancy of agonist drugs at the 5-HT1A receptor

Drugs acting on the 5-HT1A receptor are used in the treatment of depression, generalized anxiety disorder, and schizophrenia. This study investigated 5-HT1A receptor occupancy by the 5-HT1A agonist drugs flesinoxan (a highly selective probe for the 5-HT1A receptor) and ziprasidone (a novel atypical antipsychotic drug). Using a within-subject design, 14 healthy volunteers each received two positron emission tomography scans using the selective 5-HT1A antagonist radiotracer [11C]WAY-100635. One scan constituted a baseline, while the other followed either 1 mg flesinoxan or 40 mg ziprasidone orally. In addition, rats were pretreated with intravenous flesinoxan at doses ranging from 0.001 to 5 mg/kg then [11C]WAY-100635 binding measured ex vivo. Cerebral cortical and hippocampal regions of interest, and cerebellar reference regions were sampled to estimate 5-HT1A receptor occupancy (inferred from reductions in specific radioligand binding). In man, occupancy was not significant despite volunteers experiencing side effects consistent with central serotonergic activity. The mean cerebral cortex occupancy (±1 SD) for flesinoxan was 8.7% (±13%), and for ziprasidone 4.6% (±17%). However, in rats, flesinoxan achieved significant and dose-related occupancy (17–57%) at 0.25 mg/kg and above. We conclude that 5-HT1A receptor agonists produce detectable occupancy only at higher doses that would produce unacceptable levels of side effects in man, although lower doses are sufficient to produce pharmacological effects. The development of agonist radiotracers may increase the sensitivity of detecting agonist binding, as 5-HT1A antagonists bind equally to low- and high-affinity receptor states, while agonists bind preferentially to the high-affinity state.

Relationship of estradiol levels to breakthrough bleeding during continuous combined hormone replacement therapy.

OBJECTIVE To determine whether serum estradiol and dydrogesterone concentrations are associated with the occurrence of breakthrough bleeding. METHODS In a prospective, double-blind study, 194 postmenopausal women were allocated randomly to receive one of four doses of dydrogesterone (2.5 mg, 5 mg, 10 mg, 15 mg) continuously combined with 2 mg of micronized 17beta-estradiol. All medication was taken orally for a total of 168 days. Vaginal bleeding was recorded on a daily basis. Serum estradiol (E2) and dihydrodydrogesterone (the main metabolite of dydrogesterone) trough levels were measured at day 85 and at the end of the study (day 168). Bleeding pattern analysis was done according to the reference period method. RESULTS One hundred fifty-two of 177 women who completed the study supplied valid data on drug compliance, smoking habits, bleeding episodes, and serum hormone concentrations, which were used to assess the impact of serum E2 and dihydrodydrogesterone concentrations on the occurrence of breakthrough bleeding. Logistic regression analysis identified only the serum E2 concentration as having an independent, statistically significant effect (P = .003) on the occurrence of breakthrough bleeding; no such effect was associated with dihydrodydrogesterone levels (P = .118). The relative risk for the occurrence of breakthrough bleeding was 2.7 (95% confidence interval [CI] 1.454, 5.609) for serum E2 concentrations greater than 40 pg/mL. CONCLUSION The occurrence of breakthrough bleeding during continuous combined hormone replacement therapy with estradiol and dydrogesterone in postmenopausal women was related to serum estradiol levels and not to dydrogesterone levels. Further studies are needed to test the hypothesis that estrogen is a major factor in the incidence of bleeding during postmenopausal hormone replacement therapy.

Comparison of 5 methods of QT interval measurements on electrocardiograms from a thorough QT/QTc study: effect on assay sensitivity and categorical outliers

INTRODUCTION We studied moxifloxacin-induced QT prolongation and proportion of categorical QTc outliers when 5 methods of QT measurement were used to analyze electrocardiograms (ECGs) from a thorough QT study. METHODS QT interval was measured by the threshold, tangent, superimposed median beat, automated global median beat, and longest QT methods in a central ECG laboratory in 2730 digital ECGs from 39 subjects during placebo and moxifloxacin treatment. RESULTS All 5 methods were able to demonstrate statistically significant moxifloxacin-induced QTcF prolongation. However, lower bound of 95% 1-sided confidence interval of QTcF prolongation did not exceed 5 milliseconds with the longest QT method. More QTcF outliers were observed with the longest QT and tangent methods, whereas the other 3 methods were comparable. QTcF values greater than 500 milliseconds were observed only with moxifloxacin by the tangent method, and with moxifloxacin and placebo by the longest QT method. CONCLUSION The method of QT measurement must be considered when interpreting individual thorough QT/QTc studies.

Effect of Number of Replicate Electrocardiograms Recorded at Each Time Point in a Thorough QT Study on Sample Size and Study Cost

In a “thorough QT/QTc” (TQT) study, several replicate electrocardiograms (ECGs) are recorded at each time point to reduce within‐subject variability. This decreases the sample size but increases the cost of ECG analysis. To determine the most cost‐effective number of ECG replicates, the authors retrospectively analyzed data from the placebo and moxifloxacin arms of a TQT study with crossover design. Six replicate ECGs were recorded at 7 time points on day −1 (baseline day), day 1, and day 3 in 124 normal healthy volunteers who were randomized to receive moxifloxacin or placebo on day 1 and the other treatment on day 3. QT interval was corrected for heart rate by the Fridericia (QTcF) and individual subject‐specific (QTcI) formulas. Within‐subject and between‐subject standard deviations for QTcF obtained by repeated‐measures analysis of covariance were 9.5 and 13.3 milliseconds with 1 replicate; 7.8 and 12.7 milliseconds with 2 replicates; 7.3 and 12.3 milliseconds with 3 replicates; 6.9 and 12.2 milliseconds with 4 replicates; 6.8 and 11.9 milliseconds with 5 replicates; and 6.6 and 11.8 milliseconds with 6 replicates. Within‐ and between‐subject variance with QTcI also declined with increasing replicates. Sample size benefit based on these estimates was negligible beyond 4 replicates. The study cost was least with 3 or 4 replicates, depending on per‐ECG and per‐subject costs.

The effect of washing and the absence of interindividual transfer of estradiol gel

AimThe primary objective of this study was to evaluate the extent of interindividual transfer and subsequent exposure to estradiol, estrone and estrone sulfate in non-treated postmenopausal women after repeated daily direct skin-to-skin contact with postmenopausal women treated with estradiol gel. The secondary objective was to evaluate the effect on serum estradiol, estrone and estrone sulfate concentrations of washing the application site 1 hour after estradiol gel was applied.MethodsThis was a single-center, randomized, open-label, crossover, multiple-dose study. A total of 48 healthy, postmenopausal women were assigned to either the treated (application of 1.25g of transdermal estradiol gel 0.06%) or non-treated (secondary exposure) group in matched pairs. The study comprised two treatment periods each of 14 days, separated by a washout period of 14 days. Those randomized to the treated group received estradiol gel every day in both treatment periods, but in a crossover design were further randomized to thoroughly wash (or not wash) the application site 1 hour after gel administration for the duration of one of the treatment periods. To determine the extent of transfer of estradiol gel to non-treated women, a 15-minute direct skin-to-skin contact test was conducted daily 1 hour after gel application to the treated test partner (with or without washing of the application site). Serum estradiol, estrone and estrone sulfate concentrations were measured over a 24-hour period at baseline and on day 14 of each study period to determine the extent of transfer of estradiol gel and subsequent absorption in the non-treated group, and the extent of absorption of estradiol and the effect of washing (compared with not washing) the application site after gel administration in the treated group.ResultsIn the non-treated group, mean pharmacokinetic parameters for estradiol, estrone and estrone sulfate after 14 days of daily direct skin-to-skin contact with the women treated with estradiol gel were not statistically different from baseline. In the treated group, washing the application site 1 hour after gel administration reduced the serum concentrations of estradiol, estrone, and estrone sulfate throughout the 24-hour blood sampling interval. These reductions were small but statistically significant.ConclusionInterindividual transfer of estradiol gel 1 hour after application from treated to non-treated individuals and subsequent absorption of estradiol, as determined by the area under the serum concentration-time curve and maximum serum concentration of estradiol, estrone and estrone sulfate, was not statistically significant and clinically unimportant. Washing of the application site at 1 hour after daily transdermal administration of the gel reduced the extent of absorption of estradiol in treated individuals.