In vivo imaging of serotonin transporter occupancy by means of SPECT and [123I]ADAM in healthy subjects administered different doses of escitalopram or citalopram

Background Escitalopram is a dual serotonin reuptake inhibitor (SSRI) approved for the treatment of depression and anxiety disorders. It is the S-enantiomer of citalopram, and is responsible for the serotonin reuptake activity, and thus for its pharmacological effects. Previous studies pointed out that clinically efficacious doses of other SSRIs produce an occupancy of the serotonin reuptake transporter (SERT) of about 80% or more. The novel radioligand [¹²³I]ADAM and single photon emission computer tomography (SPECT) were used to measure midbrain SERT occupancies for different doses of escitalopram and citalopram.Methods Twenty-five healthy subjects received a single dose of escitalopram [5 mg (n=5), 10 mg (n=5), and 20 mg (n=5)] or citalopram [(10 mg (n=5) and 20 mg (n=5)]. Midbrain SERT binding was measured with [¹²³I]ADAM and SPECT on two study days, once without study drug and once 6 h after single dose administration of the study drug. The ratio of midbrain-cerebellum/cerebellum was the outcome measure (V3”) for specific binding to SERT in midbrain. Subsequently, SERT occupancy levels were calculated using the untreated baseline level for each subject. An E _max model was used to describe the relationship between S-citalopram concentrations and SERT occupancy values. Additionally, four subjects received placebo to determine test–retest variability.Results Single doses of 5, 10, or 20 mg escitalopram led to a mean SERT occupancy of 60±6, 64±6, and 75±5%, respectively. SERT occupancies for subjects treated with single doses of 10 and 20 mg citalopram were 65±10 and 70±6%, respectively. A statistically significant difference was found between SERT occupancies after application of 10 and 20 mg escitalopram, but not for 10 and 20 mg citalopram. There was no statistically significant difference between the SERT occupancies of either 10 mg citalopram or 10 mg escitalopram, or between 20 mg citalopram and 20 mg escitalopram. E _max was slightly higher after administration of citalopram (84%) than escitalopram (79%). In the test–retest study, a mean SERT “occupancy” of 4% was found after administration of placebo, the intraclass correlation coefficient was 0.92, and the repeatability coefficient was 0.25.Conclusion SPECT and [¹²³I]ADAM were used to investigate SERT occupancies after single doses of escitalopram or citalopram. The test–retest study revealed good reproducibility of SERT quantification. Similar SERT occupancies were found after administration of equal doses (in respect to mg) of escitalopram and citalopram, giving indirect evidence for a fractional blockade of SERT by the inactive R-citalopram.     

Higher serotonin transporter occupancy after multiple dose administration of escitalopram compared to citalopram: an [123I]ADAM SPECT study

Objectives Previous studies have investigated the occupancy of the serotonin reuptake transporter (SERT) after clinical doses of citalopram and other selective serotonin reuptake inhibitors. In the present study, the occupancies of SERT after multiple doses of escitalopram and citalopram were compared using the radioligand [¹²³I]ADAM and single photon emission computed tomography (SPECT). Methods Fifteen healthy subjects received escitalopram 10 mg/day (n = 6) or citalopram 20 mg/day (n = 9) for a total of 10 days. SERT occupancies in midbrain were determined with SPECT and [¹²³I]ADAM at three different time points: at baseline (no medication) and at 6 and 54 h after last drug intake. Results At 6 h after the last dose, mean SERT occupancies were 81.5 ± 5.4% (mean±SD) for escitalopram and 64.0 ± 12.7% for citalopram (p < 0.01). At 54 h after the last dose, mean SERT occupancies were 63.3 ± 12.1% for escitalopram and 49.0 ± 11.7% for citalopram (p < 0.05). The plasma concentrations of the S-enantiomer were of the same magnitude in both substances. For both drugs, the elimination rate of the S-enantiomer in plasma was markedly higher than the occupancy decline rate in the midbrain. Conclusion The significantly higher occupancy of SERT after multiple doses of escitalopram compared to citalopram indicates an increased inhibition of SERT by escitalopram. The results can also be explained by an attenuating effect of R-citalopram on the occupancy of S-citalopram at the SERT.     

Striatal dopamine transporter availability with [<Superscript>123</Superscript>I]β-CIT SPECT is unrelated to gender or menstrual cycle

Objectives The effect of gender and female menstrual cycle on human striatal dopamine transporters (DATs) was investigated with single-photon emission computed tomography (SPECT) using the ligand 2β-carbomethoxy-3β-(4-[¹²³I]iodophenyl)tropane.Methods Ten female subjects aged 18–40 years (25.3±7.3 years) were scanned twice during the early follicular and the mid-luteal phases to detect any hormone-mediated changes in DAT availability in the striatum or serotonin transporter (SERT) availability in brainstem–diencephalon. Plasma estradiol and progesterone levels were obtained at the time of SPECT and confirmed the expected increases from the follicular to the luteal phases. Finally, in a post hoc analysis of a previously published healthy-subject sample, striatal DAT availability was compared between 70 male and 52 female subjects who ranged in age from 18 to 88 years.Results In the ten menstrual cycle subjects, DAT availability (V₃″) in striatum and SERT availability in brainstem–diencephalon did not differ between follicular and luteal phases. Moreover, change in V₃″ for striatum or brainstem–diencephalon was uncorrelated with change in plasma estradiol or progesterone from the follicular to the luteal phase. In the larger healthy-subject sample, there was no significant effect of gender or the interaction of age and gender on striatal V₃″.Conclusions These findings suggest that in using DAT or SERT ligands in the study of neuropsychiatric disorders, matching of female subjects according to a menstrual cycle phase is unnecessary. Although the present investigation did not confirm previous reports of gender differences in striatal DAT availability, controlling for gender in such studies still seems advisable.     

Occupancy of brain serotonin transporters during treatment with paroxetine in patients with social phobia: a positron emission tomography study with 11C McN 5652

Abstract Rationale. Although selective serotonin reuptake inhibitors (SSRIs) are widely used in the treatment of anxiety and depressive disorders, the occupancy of the serotonin reuptake transporter (SERT) achieved in humans at typical clinical doses by these agents remains poorly characterized. Objective. The purpose of this study was to determine the occupancy of the SERT achieved in vivo by the SSRI paroxetine in social phobia patients at typical antianxiety doses. Methods. Measures of SERT availability were obtained with positron emission tomography and the SERT radiotracer [¹¹C](+)-McN 5652 in five patients with social phobia before and during treatment with paroxetine at usual therapeutic doses (20–40 mg per day). Results. Occupancy of the SERT by paroxetine was high in all subjects and in all regions measured after 3–6 months of continuous treatment. Conclusions. The results of this study in an anxiety disorder sample are consistent with previously reported results in a depressed sample and suggest that paroxetine at therapeutic doses achieves very high occupancy levels of the SERT. Electronic Publication     

Terbinafine increases the plasma concentration of paroxetine after a single oral administration of paroxetine in healthy subjects

Objective Paroxetine is believed to be a substrate of CYP2D6. However, no information was available indicating drug interaction between paroxetine and inhibitors of CYP2D6. The aim of this study was to examine the effects of terbinafine, a potent inhibitor of CYP2D6, on pharmacokinetics of paroxetine. Methods Two 6-day courses of either a daily 150-mg of terbinafine or a placebo, with at least a 4-week washout period, were conducted. Twelve volunteers took a single oral 20-mg dose of paroxetine on day 6 of both courses. Plasma concentrations of paroxetine were monitored up to 48 h after dosing. Results Compared with the placebo, terbinafine treatment significantly increased the peak plasma concentration (C_max) of paroxetine, by 1.9-fold (6.4 ± 2.4 versus 12.1 ± 2.9 ng/ml, p < 0.001), and the area under the plasma concentration-time curve from zero to 48 h [AUC (0–48)] of paroxetine by 2.5-fold (127 ± 67 vs 318 ± 102 ng/ml, p < 0.001). Elimination half-life differed significantly (15.3 ± 2.4 vs 22.7 ± 8.8 h, p < 0.05), although the magnitude of alteration (1.4-fold) was smaller than C_max or AUC. Conclusion The present study demonstrated that the metabolism of paroxetine after a single oral dose was inhibited by terbinafine, suggesting that inhibition of CYP2D6 activity may lead to a change in the pharmacokinetics of paroxetine. However, further study is required to confirm this phenomenon at steady state.     

Effects of receptor density on Nociceptin/OrphaninFQ peptide receptor desensitisation: studies using the ecdysone inducible expression system

Pretreatment of the G-protein coupled nociceptin receptor (NOP) with nociceptin/orphaninFQ (N/OFQ) produces desensitisation. The influences of receptor expression and genomic effects are largely unknown. We have used an ecdysone-inducible NOP expression system in a CHO line (CHO_INDhNOP) to examine the effects of N/OFQ pretreatment upon receptor density, GTPγ[³⁵S] binding, cAMP formation and NOP-mRNA. CHO_INDhNOP induced with 5 and 10 μM PonasteroneA (PonA) for 20 h produced NOP densities (B _max) of 194 and 473 fmol. mg^-1 protein, respectively. This was accompanied by decreased NOP mRNA. The lower B _max is typical of the central nervous system. Pretreatment with 1 μM N/OFQ significantly (p < 0.05) reduced B _max at 5 and 10 μM PonA to 100 and 196 fmol. mg^-1 protein, respectively. There was no change in binding affinity. Along with the reduction in B _max, potency and efficacy for N/OFQ-stimulated GTPγ[³⁵S] binding were also reduced (5 μM PonA: pEC₅₀-control = 8.55 ± 0.06, pretreated = 7.88 ± 0.07; E _max-control = 3.52 ± 0.43, pretreated = 2.48 ± 0.10; 10 μM PonA: pEC₅₀-control = 8.41 ± 0.18, pretreated = 7.76 ± 0.03; E _max-control = 5.07 ± 0.17, pretreated = 3.38 ± 0.19). For inhibition of cAMP formation, there was a reduction in potency (5 μM PonA: pEC₅₀-control = 9.78 ± 0.08, pretreated = 8.92 ± 0.13; 10 μM PonA: pEC₅₀-control = 9.99 ± 0.07, pretreated = 9.04 ± 0.14), but there was no reduction in efficacy. In addition, there were 39 and 31% reductions in NOP mRNA at 5 and 10 μM PonA, respectively, but these measurements were made following concurrent N/OFQ challenge and PonA induction. In CHO_INDhNOP, we have shown a reduction in cell surface receptor numbers and a reduction in functional coupling after N/OFQ pretreatment. This was observed at pseudo-physiological and supraphysiological receptor densities. Moreover, we also report a reduction in NOP mRNA, but further studies are needed which include ‘pulsing’ PonA and desensitizing following wash-out.     

Differences in platelet serotonin transporter sites between African-American tobacco smokers and non-smokers

Rationale. The serotonin transporter (5HTT) regulates the magnitude and duration of serotonergic neurotransmission. Although nicotine and other constituents of tobacco smoke may influence serotonin turnover among animals, few studies have examined whether smoking is associated with alteration in 5HTT in humans. Objective. We investigated whether tobacco smokers and non-smokers differed in platelet tritiated paroxetine binding, a measure of 5HTT sites, and whether severity of nicotine dependence (ND) was related to 5HTT measures. Methods. Tritiated paroxetine binding sites on platelets were assayed in 26 African-American smokers and 30 non-smokers. Severity of smoking was assessed using the Fagerstrom Test for Nicotine Dependence (FTND). Relationships between FTND scores and maximum number of transporter sites (B_max) and affinity constant (K_d) of paroxetine binding were determined. Results. B_max values showed a significant negative correlation with FTND scores (rho=−0.28, P<0.01). Notably, smokers with higher ND had significantly lower B_max compared to those with lower ND and non-smokers; the latter two groups did not differ in B_max (F=3.92, P<0.05). Smokers scored higher on impulsivity than non-smokers, however, behavioral variables did not influence the relationship of smoking with B_max. Age, gender and K_d values were not associated with smoking or B_max. Conclusions. Smoking, in particular higher nicotine dependence, appears to be correlated with decreased density of platelet 5HTT sites in African-Americans. The nature of the relationship and whether similar changes occur in the brain merit further investigation. Electronic Publication     

Synthesis and biological evaluation of 125I/123I‐labelled analogues of citalopram and escitalopram as potential radioligands for imaging of the serotonin transporter

Two novel radioligands for the serotonin transporter (SERT), [¹²⁵I]{3‐[5‐iodo‐1‐[4‐fluorophenyl)‐1,3‐dihydroisobenzofuran‐1‐yl]‐propyl}‐dimethylamine ([¹²⁵I]‐2) and S‐[¹²⁵I]{3‐[5‐iodo‐1‐(4‐fluorophenyl)‐1,3‐dihydroisobenzofuran‐1‐yl]‐propyl}‐dimethylamine ([¹²⁵I]‐(S)‐2) were synthesized in a Br/¹²⁵I exchange reaction. Binding experiments in rats yielded K_d values of 0.7 ± 0.06 and 0.52 ± 0.02 nM for [¹²⁵I]‐2 and [¹²⁵I]‐(S)‐2, respectively. One hour after intravenous injection of [¹²⁵I]‐2, 0.34% of the injected dose had accumulated in the brain. The highest hypothalamus‐to‐cerebellum ratio was reached 2 h after injection of [¹²⁵I]‐(S)‐2 and amounted to 2.4. Pre‐treatment experiments with paroxetine resulted in effective reduction of the target‐to‐cerebellum ratios. The corresponding iodine‐123 labelled compound S‐[¹²³I]{3‐[5‐Iodo‐1‐(4‐fluorophenyl)‐1,3‐dihydroisobenzofuran‐1‐yl]‐propyl}‐dimethylamine [¹²³I]‐S‐ 2 was investigated in a pig single photon emission computed tomography (SPECT) study. Between 60 and 110 min after IV injection, the midbrain‐to‐cerebellum ratio was 1.2. However, the uptake did not differ between high‐density and medium‐density regions questioning the feasibility of the radioligand in imaging cortical SERT distribution in vivo. These data suggest that the iodine‐labelled derivatives of citalopram and escitalopram are not superior to another SPECT tracer for the SERT, namely [¹²³I]ADAM. Copyright © 2010 John Wiley & Sons, Ltd.     

Seasonality-resilient individuals downregulate their cerebral 5-HT transporter binding in winter – A longitudinal combined 11C-DASB and 11C-SB207145 PET study

We have recently shown that the emergence and severity of seasonal affective disorder (SAD) symptoms in the winter is associated with an increase in cerebral serotonin (5-HT) transporter (SERT) binding. Intriguingly, we also found that individuals resilient to SAD downregulate their cerebral SERT binding in the winter. In the present paper, we provide an analysis of the SERT- and 5-HT dynamics as indexed by 5-HT₄ receptor (5-HT4R) binding related to successful stress coping. We included 46 ¹¹C-DASB positron emission tomography (PET) scans (N?=?23, 13 women, age: 26 ± 6 years) and 14 ¹¹C-SB207145 PET scans (7 participants, 3 women, age: 25 ± 3 years) from 23 SAD-resilient Danes. Data was collected longitudinally in summer and winter. We found that compared to the summer, raphe nuclei and global brain SERT binding decreased significantly in the winter (p_raphe = 0.003 and p_global?=?0.003) and the two measures were positively correlated across seasons (summer: R²?=?0.33, p?=?.004, winter: R² = 0.24, p?=?.018). A voxel-based analysis revealed prominent changes in SERT in clusters covering both angular gyri (0.0005 < p_corrected < 0.0016), prefrontal cortices (0.00087 < p_corrected < 0.0039) and the posterior temporal and adjacent occipital cortices (0.0001 < p_corrected < 0.0066). We did not observe changes in 5-HT4R binding, suggesting that 5-HT levels remained stable across seasons. We conclude that resilience to SAD is associated with a global downregulation of SERT levels in winter which serves to keep 5-HT levels across seasons.     

Acute hormonal changes after IV citalopram and treatment response in OCD

Rationale Serotonergic pharmacological challenges have failed to produce consensual results in patients with obsessive–compulsive disorder (OCD), suggesting a heterogeneous 5-hydroxytryptamine (5-HT) activity in this disorder. Objectives The aim of this study was to compare the neuroendocrine response to a serotonergic challenge in OCD patient responders (RP) and nonresponders (NR) to serotonin reuptake inhibitors treatment and healthy volunteers. Materials and methods Thirty OCD treatment NR, 30 RP, and 30 controls (CN) matched for sex and age were included. Each subject received 20 mg of intravenous citalopram. Prolactin, cortisol, and growth hormone plasma concentration were measured at times—20, 0, 20, 40, 60, 80, 100, 120, 140, and 160 min after the onset of citalopram infusion. Results Citalopram did not induce anxiety or OCD symptoms in patients. Citalopram was associated with stronger prolactin response in the CN group (maximal percentage variation [max%Δ] = 65.76 ± 105.1) than in NR (max%Δ = 17.41 ± 31.06) and RP groups (max%Δ = 15.87 ± 31.71; p = 0.032; Friedman χ ² = 6.87; df = 2). On the other hand, cortisol response did not differ between CN and RP groups and was blunted in the NR group (NR max%Δ = 20.98 ± 58.14 vs RP max%Δ = 47.69 ± 66.94; CN max%Δ = 63.58 ± 88.4; p = 0.015; Friedman χ ² = 8.60; df = 2). Conclusions Compared to CN, both treatment RP and NR patients showed blunted prolactin response to citalopram, but only NR patients showed an attenuated cortisol response, suggesting a more disrupted central serotonergic transmission in this group.     

Incongruent Reduction of Serotonin Transporter Associated with Suicide Attempts in Patients with Major Depressive Disorder: A Positron Emission Tomography Study with 4-[18F]-ADAM

Background:

Much evidence supports the role of the serotonin transporter (SERT) in the pathophysiology and pharmacotherapy of major depressive disorder (MDD) and suicidal behaviors.

Methods:

In this study, we recruited 17 antidepressant-naïve patients with MDD and 17 age- and gender-matched healthy controls. SERT availability was measured in vivo with N,N-dimethyl-2-(2-amino-4-[¹⁸F]fluorophenylthio)benzylamine (4-[¹⁸F]-ADAM) positron emission tomography (PET) imaging. The 21-item Hamilton Depression Rating Scale (HDRS) and Beck Scale for Suicide Ideation were used to assess the severity of depression and the intent of suicide ideation prior to PET imaging. All subjects with MDD were in a current state of depression with HDRS scores ≧18. Subjects who attempted suicide within two weeks of the study onset were recruited in the depressed suicidal group (n = 8). Subjects with MDD who denied any prior suicide attempt were recruited into the depressed non-suicidal group (n = 9).

Results:

A significant reduction of SERT availability in the midbrain, thalamus, and striatum was noted in the MDD group relative to the control group (Bonferroni-adjusted p-value < 0.05). Moreover, this effect was more pronounced in the depressed suicidal group compared to the control group (Bonferroni-adjusted p-value < 0.01). Relative to both the depressed non-suicidal and control groups, the depressed suicidal group showed an increased prefrontal cortex (PFC)/midbrain SERT binding ratio (Bonferroni-adjusted p-value < 0.01).

Conclusions:

This study suggests an incongruent reduction of PFC SERT binding relative to the midbrain might discriminate between depressed suicide attempters and non-attempters in patients with MDD and may be involved in the pathophysiology of suicide behaviors.     

Quetiapine augmentation of paroxetine CR for the treatment of refractory generalized anxiety disorder: preliminary findings

Rationale More data are needed to guide “next step” strategies for patients with generalized anxiety disorder (GAD) remaining symptomatic despite initial pharmacotherapy. Objective This study prospectively examined the relative efficacy of quetiapine versus placebo augmentation for individuals with GAD remaining symptomatic with initial paroxetine CR pharmacotherapy. Materials and methods Adult outpatients with GAD were recruited from 2004 to 2007 at two academic centers. Phase 1 consisted of 10 weeks of open-label paroxetine CR flexibly dosed to a maximum of 62.5 mg/day. Those remaining symptomatic (Hamilton Anxiety Scale [HAM-A] ≥ 7) at week 10 were randomized to quetiapine or placebo augmentation flexibly dosed from 25 to 400 mg/day. Results For participants receiving paroxetine CR (n = 50), there was a significant reduction in HAM-A scores (baseline mean ± SD = 22.4 ± 4.2 to endpoint mean ± SD = 11.2 ± 6.9; paired t = 12.1, df = 49, t < 0.0001) with 40% (n = 20) achieving remission. Counter to our hypothesis, we did not find significant benefit for quetiapine augmentation of continued paroxetine CR (HAM-A reduction mean ± SD = 2.6 ± 5.8 points quetiapine, 0.3 ± 5.5 points placebo; t = 0.98, df = 20, p = n.s.) in the randomized sample (n = 22) with relatively minimal additional improvement overall in phase 2. Conclusions Although conclusions are considered preliminary based on the relatively small sample size, our data do not support the addition of quetiapine to continued paroxetine CR for individuals with GAD who remain symptomatic after 10 weeks of prospective antidepressant pharmacotherapy and suggest that further research examining strategies for GAD refractory to antidepressants is needed.     

Effect of kolanut on the pharmacokinetics of the antimalarial drug halofantrine

Objective To study the effect of the concomitant consumption of kolanut, a caffeine-containing nut, on the pharmacokinetics of halofantrine. Methods A single dose of 500 mg halofantrine hydrochloride was orally administered either alone or concomitant with 12.5 g kolanut to 15 healthy male volunteers in a Latin-square randomized crossover design with a wash-out period of 6 weeks between treatments. Blood samples were collected and analyzed by HPLC for halofantrine and the active metabolite N-desbutylhalofantrine. Results Concomitant intake of kolanut with halofantrine significantly decreased C_max and AUC of both halofantrine and the metabolite desbutylhalofantrine, while no significant effect was observed for t _max and t _1/2 of the compounds. In the case of halofantrine, C_max decreased from 179 ± 119 to 98 ± 32 ng/ml, and the AUC was reduced from 17,450 ± 4,611 to 11,821 ± 4,069 ng·h/ml. C_max of desbutylhalofantrine decreased from 124 ± 41 to 62 ± 23 ng/ml and the AUC from 13,341 ± 4,749 to 7,359 ± 3,018 ng·h/ml when kolanut was co-administered. Conclusions Co-administration of halofantrine and kolanut caused a significant decrease in the plasma concentrations of halofantrine and the active metabolite desbutylhalofantrine probably during adsorption of the drug due to complex formation. This indicates that caution should be exerted when the drug is taken together with caffeine-containing nutrients.     

Unexpected effect of concomitantly administered curcumin on the pharmacokinetics of talinolol in healthy Chinese volunteers

Objective To investigate the effect of concomitantly administered curcumin on the pharmacokinetics of the β1 adrenoceptor blocker talinolol. Methods The study was conducted in a self-controlled, two-period experiment with a randomized, open-labeled design, using 12 healthy volunteers and a wash out period of 1 week between the administration of a single oral dose of 50 mg talinolol and the concomitant administration of curcumin (300 mg day⁻¹ for 6 days) and a single oral dose of 50 mg talinolol on the seventh day. Concentrations of talinolol were measured in plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry. Non-compartmental analysis was used to characterize talinolol plasma concentration-time profiles, all pharmacokinetic parameters were calculated using DAS (ver. 2.0) software, and comparisons of mean values were analyzed by the Wilcoxon signed rank test. Differences were considered to be significant at p < 0.05 (two-sided test). Results The consumption of curcumin for 6 days reduced the area under the curve (AUC) from predose to infinity () of talinolol from 1860.0 ± 377.9 to 1246.0 ± 328.2 ng.h mL⁻¹, the highest observed concentration values (C_max) were significantly decreased from 147.8 ± 63.8 to 106.4 ± 39.9 ng mL⁻¹, and the CL/F was increased from 27.9 ± 5.5 to 43.1 ± 13.4 L.h⁻¹ (p < 0.05). There was no significant difference in sampling time for C_max (t_max) and elimination half-life (t_1/2) values between the two periods (p > 0.05). The interindividual variability in AUC_0–60 and C_max of talinolol was comparable in two study periods; the coefficient of variance (CV) of AUC_0–60 and C_max was 26 and 40% after curcumin versus 21 and 43% after talinolol alone, respectively. Conclusion We suggest that the reduced bioavailability of talinolol is most probably due to the low intraluminal curcumin concentration, or possibly due to the upregulation of further ATP-binding cassette transporters, such as MRP2, in different tissues.     

[123I]β-CIT SPECT imaging of dopamine transporter availability after mazindol administration in human cocaine addicts

The in vivo potency of mazindol for binding to striatal dopamine transporters (DAT) was assessed by [¹²³I]β-CIT ([¹²³I]2β-carbomethoxy-3β-(4-iodophenyl)tropane) single photon emission computed tomography (SPECT). Cocaine-dependent subjects (n=12) underwent three SPECT scans; one before, between, and after subchronic (1 week) administration of 2mg/day and 4mg/day mazindol. For each scan, subjects were injected with [¹²³I]β-CIT and imaged 24h later under equilibrium conditions. Results showed a statistically significant main effect of mazindol dose (df=2, F=10.30, P<0.001, repeated measures ANOVA) in reducing the specific to non-displaceable equilibrium partition coefficient, V₃″ (a measure proportional to DAT binding potential). Regression analysis of the logit transformed data enabled estimation of the 50% displacement dose of mazindol (ED₅₀=30mg/ day). These data suggest that low doses of mazindol (i.e., 2–4mg) occupy a small percentage (i.e., <25%) of DAT in human cocaine abusers and that much higher, potentially intolerable doses (i.e., ≥30mg/day) may be required to antagonize significantly cocaine binding in vivo. Received: 14 November 1996/Final version: 17 December 1997     

Pharmacokinetics and pharmacodynamics of a premixed formulation of soluble and protamine-retarded insulin aspart

Objective: With the aim to obtain a premixed rapid-acting insulin with a serum insulin profile more closely resembling the endogenous meal-stimulated serum insulin profiles, a 30/70 (rapid/intermediate-acting) premixed suspension of the rapid-acting insulin analogue insulin aspart (BIAsp30) was compared with a similar premixed suspension of biphasic human insulin 30/70 (BHI30) after a single subcutaneous injection. Methods: The study had a randomised, double-blind, two-period crossover design. Twenty-four healthy male subjects received a single subcutaneous dose of either 0.2 U · kg⁻¹ bodyweight of BIAsp30 or BHI30 on two study days. Results: BIAsp30 was absorbed faster than BHI30, as reflected in the area under the insulin concentration-time curve from 0 to 90 min after dosing [AUC_{(0–90 min)}]. This was significantly larger for BIAsp30 than for BHI30 (1403 ± 372 versus 752 ± 191 mU · l⁻¹ · min⁻¹ [mean ± SD]; P < 0.0001). Furthermore, the time to maximum serum insulin concentration (t_max) of BIAsp30 was approximately half the t_max of BHI30 (60 [45–70] versus 110 [90–180] min [median, interquartile range]; P=0.0001) and the maximum insulin concentration (C_max) was significantly higher for BIAsp30 than for BHI30 (23.4 ± 5.3 versus 15.5 ± 3.7 mU · l⁻¹ [mean ± SD]; P < 0.0001). The serum glucose profiles showed a significantly earlier onset of the glucose-lowering effect following BIAsp30 than following BHI30. Conclusions: The improved absorption properties of soluble insulin aspart in its premixed formulation provide a basis for a more efficient meal-related glucose control and immediate pre-meal delivery when compared with a similar human premixed insulin in the treatment of diabetes mellitus. Received: 22 November 1999 / Accepted in revised form: 7 April 2000     

Pharmacological evidence for altered src kinase regulation of <Emphasis Type="Italic">I</Emphasis><Subscript>Ca,L</Subscript> in patients with chronic atrial fibrillation

A reduction in l-type Ca²⁺ current (I _Ca,L) contributes to electrical remodeling in chronic atrial fibrillation (AF). Whether the decrease in I _Ca,L is solely due to a reduction in channel proteins remains controversial. Protein tyrosine kinases (PTK) have been described as potent modulators of I _Ca,L in cardiomyocytes. We studied α_1C l-type Ca²⁺ channel subunit expression and the regulation of I _Ca,L by PTK in chronic AF using PTK inhibitors: genistein, a nonselective inhibitor of PTK, and 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo-3,4-d-pyrimidine (PP1), a selective inhibitor of src kinases. Furthermore, type-1 and type-2A protein phosphatase activity was measured with phosphorylase as substrate in whole-cell lysates derived from atrial tissue of AF patients. Right atrial appendages were obtained from patients undergoing open-heart surgery. Protein levels of α_1C l-type Ca²⁺ channel subunit were determined using Western blot analysis and normalized to the protein amounts of calsequestrin as internal control. The protein concentrations of α_1C did not differ between AF and sinus rhythm (SR; α_1C/calsequestrin: 1.0 ± 0.1 and 1.2 ± 0.2, respectively, n = 8 patients). In cardiomyocytes from patients in SR (n = 20 patients), genistein and PP1 both evoked similar increases in I _Ca,L from 3.0 ± 0.3 to 6.1 ± 0.8 pA/pF and from 2.8 ± 0.4 to 6.1 ± 0.6 pA/pF, respectively. In cells from AF patients (n = 10 patients), basal I _Ca,L was significantly lower. In this case, genistein lead to the same relative increase in I _Ca,L as in SR cells (from 1.46 ± 0.30 to 3.2 ± 1.0 pA/pF), whereas no increase was elicited by PP1 suggesting impaired regulation of I _Ca,L by src kinases in AF. Total and type 1 and type 2A-related phosphatase activities were higher in tissue from patients with chronic AF compared to SR (4.8 ± 0.4, 2.1 ± 0.2, and 2.7 ± 0.4 nmol/mg/min and 3.6 ± 0.4, 1.3 ± 0.2, and 2.4 ± 0.3 nmol/mg/min, respectively, n = 7 patients per group). Downregulation of I _Ca,L in AF is not due to a reduction in l-type Ca²⁺ channel protein expression. Indirect evidence for an impaired src kinase regulation of I _Ca,L together with an increased phosphatase activity suggests that a complex alteration in the kinase/phosphatase balance leads to I _Ca,L dysregulation in chronic AF.     

Grapefruit juice has no effect on quinine pharmacokinetics

Objective: As quinine is mainly metabolised by human liver CYP3A4 and grapefruit juice inhibits CYP3A4, the effect of grapefruit juice on the pharmacokinetics of quinine following a single oral dose of 600 mg quinine sulphate was investigated. Methods: The study was carried out in ten healthy volunteers using a randomised cross-over design. Subjects were studied on three occasions, with a washout period of 2 weeks. During each period, subjects received a pretreatment of 200 ml orange juice (control), full-strength grapefruit juice or half-strength grapefruit juice twice daily for 5 days. On day 6, the subjects were given a single oral dose of 600 mg quinine sulphate with 200 ml of one of the juices. Plasma and urine samples for measurement of quinine and its major metabolite, 3-hydroxyquinine, were collected over a 48-h period and analysed by means of a high-performance liquid chromatography method. Results: The intake of grapefruit juice did not significantly alter the oral pharmacokinetics of quinine. There were no significant differences among the three treatment periods with regard to pharmacokinetic parameters of quinine, including the peak plasma drug concentration (C_max), the time to reach C_max (t_max), the terminal elimination half-life (t_1/2), the area under the concentration–time curve and the apparent oral clearance. The pharmacokinetics of the 3-hydroxyquinine metabolite were slightly changed when volunteers received grapefruit juice. The mean C_max of the metabolite (0.25 ± 0.09 mg l⁻¹, mean ± SD) while subjects received full-strength grapefruit juice was significantly less than during the control period (0.31 ± 0.06 mg l⁻¹, P < 0.05) and during the intake of half-strength grapefruit juice (0.31 ± 0.07 mg l⁻¹, P < 0.05). Conclusion: These results suggest that there is no significant interaction between the parent compound quinine and grapefruit juice, so it is not necessary to advise patients against ingesting grapefruit juice at the same time that they take quinine. Since quinine is a low clearance drug with a relatively high oral bioavailability, and is primarily metabolised by human liver CYP3A4, the lack of effect of grapefruit juice on quinine pharmacokinetics supports the view that the site of CYP inhibition by grapefruit juice is mainly in the gut. Received: 2 November 1998 / Accepted in revised form: 18 February 1999     

Absorption of effervescent paracetamol tablets relative to ordinary paracetamol tablets in healthy volunteers

Objectives: The aim of this study was to compare the rate of absorption between ordinary paracetamol tablets and effervescent paracetamol tablets. Methods: Twenty healthy volunteers participated in an open randomised crossover study and were given a 1000-mg dose of either ordinary paracetamol tablets (2 × 500 mg Panodil tablets, SmithKline Beecham) or effervescent paracetamol tablets (2 × 500 mg Pinex Brusetablett, Alpharma AS) with a 3-week washout period in between. Blood samples were collected for 3 h. Maximum serum concentration (C_max) and the time to maximum serum concentration (t_max) were recorded and the area under the concentration versus time curve (AUC) was calculated. Results: The mean t_max was significantly shorter when paracetamol effervescent tablets were taken (27 min) rather than ordinary paracetamol tablets (45 min) (P=0.004). There was no significant difference between the mean C_max of 143 μmol/l with effervescent tablets and that of 131 μmol/l with ordinary tablets. The mean AUC_0–3 h was significantly higher with paracetamol effervescent tablets (223.8 μmol · h · l⁻¹) than with ordinary tablets (198.2 μmol · h · l⁻¹; P=0.003). After 15 min, 17 (85%) subjects in the effervescent group had a serum concentration of 70 μmol/l (lower therapeutic serum concentration) or higher relative to only 2 (10%) subjects in the ordinary tablet group (P=0.001). Conclusion: Paracetamol effervescent tablets are absorbed significantly faster than ordinary paracetamol. Thus, effervescent tablets might offer significantly faster pain relief when paracetamol is used. Received: 4 October 1999 ;/ Accepted in revised form: 15 February 2000