Effect of saquinavir/ritonavir on P-glycoprotein activity in healthy volunteers using digoxin as a probe.

BACKGROUND: Saquinavir and ritonavir, both human immunodeficiency virus-1 protease inhibitors, also inhibit the adenosine triphosphate-dependent efflux pump P-glycoprotein (P-gp), which is located at a variety of anatomic sites, including the human intestine. P-gp plays an important role in the absorption, distribution and elimination of numerous drugs. This study investigated the inhibitory potential of multiple administrations of ritonavir-boosted saquinavir at the target therapeutic dose of 1,000 mg saquinavir/100 mg ritonavir twice daily on the pharmacokinetics of oral digoxin, a model P-gp substrate that is predominantly excreted as unchanged drug in the urine. METHODS: In an open-label, 1-sequence, 2-period crossover study, a single digoxin dose of 0.5 mg was administered orally on Day 1. From Days 11 through 26, participants received oral administration of saquinavir/ritonavir 1,000/100 mg twice daily. A second dose of digoxin was administered on Day 24. Blood and urine sampling for pharmacokinetic analyses of digoxin was performed at scheduled time points on Days 1 - 4 and Days 24 - 27. Serial blood samples were drawn to determine plasma levels of saquinavir and ritonavir on Days 21 - 24. Adverse event reports were collected. RESULTS: Of the 17 enrolled participants (9 males and 8 females) who received at least one dose of study medication, 16 completed the study. Two weeks of pretreatment with ritonavir and saquinavir resulted in a 1.27-fold increase in digoxin Cmax (90% confidence interval (1.05 - 1.54)) and a 1.49-fold increase in AUC0-72 (90% CI (1.32 - 1.69)). Renal clearance decreased by a factor 0.88 from 111 to 97.3 ml/min while digoxin half-life increased from 37.0 to 45.3 h. The unbound fraction of digoxin was almost unaffected. The changes in digoxin renal clearance and exposure (AUC0-72) following 2 weeks of treatment with saquinavir/ritonavir were found to be more pronounced among female participants compared with males. Plasma concentrations of saquinavir/ritonavir at trough and at 4 h postdose were within the expected ranges for each gender, with female participants showing higher concentrations than male participants. All three treatments were well tolerated, with no serious adverse events noted. Despite the higher digoxin exposure among females compared to males following saquinavir/ritonavir administration, overall safety profiles were similar. On electrocardiographic readings, a trend of a longer PR interval was noted with triple combination of agents. CONCLUSIONS: Pretreatment with saquinavir/ritonavir 1,000/100 mg twice daily increased digoxin exposure most likely via P-gp-inhibition. Given the relatively narrow therapeutic window of digoxin, caution should be exercised when these three drugs are administered together. It is recommended to reduce digoxin doses and to monitor digoxin serum concentrations.

An intervention program for ADHD in patients with substance use disorders: preliminary results of a field trial.

The comorbidity of attention deficit hyperactivity disorder (ADHD) is frequently not well recognized in substance abuse treatment institutions in The Netherlands. As a consequence, patients with substance use disorder (SUD) and ADHD often receive suboptimal treatment. To prevent every treatment center from having to invent its own diagnostic procedure and intervention for ADHD, a national working group was established. This group developed an intervention program for the screening, diagnosis, and treatment of ADHD in patients with SUD. This article describes the development and content of this intervention program. An important part of this development was testing the intervention program in two addiction treatment centers in The Netherlands. Systematic screening of ADHD was part of the test. A self-report questionnaire was used. Subjects with positive screening results were referred for the diagnostic procedure. Nine hundred twenty-eight screenings were performed: 207 screened positive, 115 came for further diagnostics, and 65 were ultimately diagnosed with ADHD.

Effects of social stress on behavior and corpus luteum in female golden hamsters (Mesocricetus auratus).

The consequences of group-keeping as a social stressor on the solitary-living golden hamster were studied. Two females at the same stage of the estrous cycle were kept together for 5 weeks. Behavioral observations showed that the dominance structures within groups were unstable. Intensity of aggression was highest at metestrous, whereas the greatest activity was observed during the estrous stage. After 1 week, the body masses of singly kept and group-kept hamsters were different. Five weeks after the onset of the experiment, the body mass of the singly kept hamsters had increased by 3.6%, and that of the group-kept hamsters by 25%. The plasma progesterone level of group-kept females was 60 to 70% higher than that of singly kept females. The absolute masses of the adrenal glands and the ovaries were higher in group-kept females. Nevertheless, the relative masses did not differ. Whereas a significant positive correlation between the weights of both organs and the body mass was observed in singly kept females, in group-kept females such a correlation was only observed between body and ovary weight. Number and size of corpora lutea were enlarged in group-kept individuals, and this seems to be responsible for elevated plasma progesterone titres. These results indicate social stress in group-kept female hamsters.

Founder events as determinants of within-island and among-island genetic structure of Daphnia metapopulations.

The genetic structure of metapopulations offers insights into the genetic consequences of local extinction and recolonization. We studied allozyme variation in rock pool metapopulations of two species of waterfleas (Daphnia) with the aim to understand how these dynamics influence genetic differentiation. We screened 138 populations of D. magna and 65 populations of D. longispina from an area in the archipelago of southern Finland. The pools from which they were sampled are separated by distances between 1.5 and 4710 m and located on a total of 38 islands. The genetic population structure of the two species was strikingly similar, consistent with their similar metapopulation ecology. The mean F(PT) value (differentiation among pools with respect to the total metapopulation) was 0.55 and a hierarchical analysis showed that genetic differentiation was strong (>0.25) among pools within islands as well as among whole islands. Within islands, pairwise genetic differentiation increased with geographic distance, indicating isolation by distance due to spatially limited dispersal. Previous studies have shown strong founder events occurring during colonization in our metapopulation. We suggest that the genetic population structure in the studied metapopulations is largely explained by three consequences of these founder events: (i) strong drift during colonization, (ii) local inbreeding, which results in hybrid vigour and increased effective migration rates after subsequent immigration, and (iii) effects of selection through hitchhiking of neutral genes with linked loci under selection.

The protease thrombin is an endogenous mediator of hippocampal neuroprotection against ischemia at low concentrations but causes degeneration at high concentrations.

We have considered the extracellular serine protease thrombin and its receptor as endogenous mediators of neuronal protection against brain ischemia. Exposure of gerbils to prior mild ischemic insults, here two relatively short-lasting occlusions (2 min) of both common carotid arteries applied at 1-day intervals 2 days before a severe occlusion (6 min), caused a robust ischemic tolerance of hippocampal CA1 neurons. This resistance was impaired if the specific thrombin inhibitor hirudin was injected intracerebroventricularly before each short-lasting insult. Thus, efficient native neuroprotective mechanisms exist and endogenous thrombin seems to be involved therein. In vitro experiments using organotypic slice cultures of rat hippocampus revealed that thrombin can have protective but also deleterious effects on hippocampal CA1 neurons. Low concentrations of thrombin (50 pM, 0.01 unit/ml) or of a synthetic thrombin receptor agonist (10 microM) induced significant neuroprotection against experimental ischemia. In contrast, 50 nM (10 units/ml) thrombin decreased further the reduced neuronal survival that follows the deprivation of oxygen and glucose, and 500 nM even caused neuronal cell death by itself. Degenerative thrombin actions also might be relevant in vivo, because hirudin increased the number of surviving neurons when applied before a 6-min occlusion. Among the thrombin concentrations tested, 50 pM induced intracellular Ca(2+) spikes in fura-2-loaded CA1 neurons whereas higher concentrations caused a sustained Ca(2+) elevation. Thus, distinct Ca(2+) signals may define whether or not thrombin initiates protection. Taken together, in vivo and in vitro data suggest that thrombin can determine neuronal cell death or survival after brain ischemia.