Biomedical subjects

Mark E Schmidt

Publications and source records attributed to Mark E Schmidt.

10 recordsLinked to original sources

PubMed2005

A comparison of brain and serum pharmacokinetics of R-fluoxetine and racemic fluoxetine: A 19-F MRS study.

Racemic fluoxetine consists of R- and S-fluoxetine, which are metabolized to R- and S-norfluoxetine, respectively. This study was designed to compare brain levels achieved with R-fluoxetine to those achieved with racemic fluoxetine in healthy subjects using fluorine-19 (19-F) magnetic resonance spectroscopy (MRS). In all, 13 healthy volunteers received study drug for 5 weeks using a dosing schedule designed to achieve steady state for 20 mg/day racemic fluoxetine, 80 mg/day R-fluoxetine, or 120 mg/day R-fluoxetine. The resulting brain drug levels were measured using 19-F MRS. At 5 weeks, the racemate, 80 and 120 mg/day R-fluoxetine groups had mean brain levels of 25.5, 34.9, and 41.4 microM, respectively. In the serum, R-norfluoxetine, which is thought to be an inactive metabolite, accounted for 17, 71, and 63% of the fluoxetine/norfluoxetine concentration, respectively. When the relative proportion of active to total species in serum are taken into account, the data suggest that doses of R-fluoxetine greater than 120 mg/day would be needed to achieve brain levels of active drug comparable to 20 mg/day of racemate. The 120 mg/day R-fluoxetine group experienced a mean increase in QTc interval of 44 ms, with one individual having an increase of 89 ms, which suggests that higher doses may not be tolerable. While these data support the use of MRS to aid in defining the therapeutic dose range for drug development, they also highlight the need for additional studies with concurrent animal models to establish the validity of using serum drug/metabolite ratios to interpret MRS determined brain drug levels.

Brain↗

PubMed2005

Functional imaging in drug discovery and development.

The use of in vivo imaging with radioisotope- and magnetic resonance-based methods is increasing for all stages of drug development. The primary role for these methods has, and continues to be, clinical diagnosis, although the technology itself is highly versatile and can be adapted to very different applications. Techniques may be developed to measure the drug target, tissue-specific drug disposition and action, and to pursue basic investigations of the pathophysiology of disease. The sensitivity, spatial resolution, temporal resolution and frequency of measurement with radioisotope and magnetic resonance imaging are significantly different. Whether the application is related to the drug target, action or disease response, must first be considered before selecting which functional imaging approach can be used.

Animals↗

PubMed2004

Chronic lithium administration enhances noradrenergic responses to intravenous administration of the alpha2 antagonist idazoxan in healthy volunteers.

The acute and chronic effects of lithium carbonate administration at therapeutic blood levels on peripheral noradrenergic activity and sympathetic responses to alpha2 adrenoceptor blockade were examined in 10 medically and psychiatrically healthy volunteers. Supine resting levels of plasma norepinephrine and the increases in norepinephrine following intravenous infusion of 200 microg/kg of idazoxan, a selective alpha2 adrenoceptor antagonist, were determined before lithium (Li+) administration and after 5 days and after 4 weeks of daily Li+ treatment. Chronic Li+ treatment significantly increased mean resting plasma norepinephrine levels by 53.6%. The noradrenergic responses to infusions of idazoxan were slightly enhanced after 5 days of Li+ administration and significantly increased following 4 weeks of Li+ treatment. The possibility that Li+ produces functional alpha2 subsensitivity causing enhanced peripheral noradrenergic activity in humans is supported by the findings of increased mean resting plasma norepinephrine and increased response to idazoxan following chronic Li+ administration. Alteration of regulatory mechanisms in the noradrenergic system may be relevant to understanding the clinical effects of Li+ in manic-depressive illness.

Adrenergic alpha-2 Receptor Antagonists↗

PubMed2004

The course of depressive illness in general practice.

OBJECTIVE: Depression is reported to be common in primary care settings and to have a high likelihood of relapse during the 4- to 6-month period following initial symptomatic improvement. However, most prospective studies of long-term treatment of depression have been conducted with patients selected for participation in placebo-controlled drug protocols or psychiatric clinics associated with tertiary referral centres. METHOD: We examined the treatment course and outcome of outpatients with major depressive episode treated in a primary care setting. The general practitioners were free to choose the treatment and its duration. Their only obligation was to assess the therapeutic outcome in terms of efficacy and safety and to perform a final evaluation at the end of the 6-month observation period or, if the patient was treated for a shorter period, at the end of the treatment. RESULTS: Of the 476 patients involved, 308 (64.7%) responded to treatment and remained well, 117 (24.6%) showed no response, and 51 (10.7%) had an early relapse after initial improvement. Among the studied demographic, clinical, and therapeutic factors, the history of recurrent depression was the only variable with a significant effect size in predicting the course of the illness. CONCLUSION: Patients with recurrent depression were at higher risk of relapse or nonresponse.

Adolescent↗

PubMed2004

Long-term treatment outcomes of depression with associated anxiety: efficacy of continuation treatment with fluoxetine.

BACKGROUND: Severity of anxiety does not appear to influence the antidepressant response to fluoxetine during acute treatment of major depressive disorder (MDD). We report a retrospective pooled analysis of 2 studies to assess the effect of associated anxiety on the efficacy of fluoxetine in the continuation treatment phase of MDD. METHOD: Patients whose MDD remitted (study 1) or responded (study 2) after approximately 12 to 13 weeks of open-label treatment with fluoxetine 20 mg daily were randomly assigned in double-blind fashion to placebo, continued treatment with fluoxetine 20 mg daily, or, in study 2 only, treatment with enteric-coated fluoxetine 90 mg once weekly, for at least 25 weeks. Both studies included male and female outpatients who met criteria for MDD as assessed by DSM-III-R (study 1) or DSM-IV (study 2). Patients were categorized into high anxiety (> or = 7) or low anxiety (< 7) subgroups based on baseline Hamilton Rating Scale for Depression (HAM-D) anxiety/somatization subfactor scores. Subgroups were compared by therapy for time from randomization to relapse and change in efficacy scores. RESULTS: No significant differences in time to relapse were observed between anxiety subgroups in either active treatment group. However, in patients switched to placebo for continuation treatment, the high anxiety subgroup had a significantly higher risk of relapse than those with low anxiety (risk ratio = 1.63, p =.013). Significant differences between anxiety groups were seen in change in HAM-D anxiety/somatization subfactor scores in the fluoxetine 20 mg and placebo treatment groups, and in change in HAM-D-17 scores in the placebo treatment group (p <.05). CONCLUSION: Although high baseline anxiety does not appear to impact the benefit of continuation therapy with fluoxetine, it does appear to predict increased risk of relapse in individuals who do not remain on antidepressant therapy for the duration of continuation treatment.

Adult↗

PubMed2003

Selective serotonin reuptake inhibitor discontinuation syndrome is associated with a rostral anterior cingulate choline metabolite decrease: a proton magnetic resonance spectroscopic imaging study.

The selective serotonin reuptake inhibitor (SSRI) discontinuation syndrome (DS) is an important potential complication of treatment for major depression. We hypothesized that SSRI treatment discontinuation, resulting in change in clinical state, would be associated with reduced rostral anterior cingulate choline (Cho) metabolite ratios. Individuals with a DSM-III-R diagnosis of unipolar major depression who had been stabilized on paroxetine (n = 13) or fluoxetine (n = 13) were study subjects. They were monitored for change in clinical state (mood ratings, discontinuation symptoms) and underwent proton magnetic resonance spectroscopic imaging of the rostral anterior cingulate 3 days after medication substitution with active SSRI and placebo.Placebo-day Cho/Cre (choline/total creatine) metabolite ratios were decreased in four paroxetine and two fluoxetine subjects meeting DS criteria, as compared with asymptomatic subjects (Mann-Whitney z = -2.31, p =.021). Discontinuation syndrome is associated with a rostral anterior cingulate Cho/Cre metabolite ratio decrease that may reflect dynamics of rostral anterior cingulate function.

Adult↗

PubMed2003

Cerebral blood volume and clinical changes on the third day of placebo substitution for SSRI treatment.

BACKGROUND: Interruptions in SSRI treatment have been associated with adverse effects that can resemble depressive illness. We hypothesized that brain regions implicated in depression, with extensive serotonergic innervation, would exhibit changes in activity associated with emergence of symptoms following drug discontinuation. METHODS: Subjects meeting DSM-IV criteria for remitted major depression on 20 mg/day of either fluoxetine or paroxetine were recruited into this 6-week study. During weeks 2 and 6, subjects underwent a 3-day period in which either active drug or placebo was substituted for their medication under double-blind conditions. Cerebral blood volume (CBV) maps were obtained via dynamic susceptibility magnetic resonance imaging at the end of each double-blind period. RESULTS: In the paroxetine group, change in CBV in left medial superior frontal region and left caudate nucleus correlated significantly with change in Discontinuation Emergent Symptom Scale and Hamilton Depression Rating Scale (HDRS; R2 = 0.66, p =.0007; R2 = 0.51, p =.006; and R2 = 0.43, p =.015; R2 = 0.32, p =.043, respectively). CONCLUSIONS: These data demonstrate that changes in regional CBV of left prefrontal cortex and left caudate nucleus correlate with the emergence of discontinuation symptoms and increased HDRS after interruption of paroxetine treatment.

Adult↗

PubMed2003

Evaluation of [3H]LY341495 for labeling group II metabotropic glutamate receptors in vivo.

New glutamatergic drugs are being developed as potential therapies for neurodegenerative disorders, anxiety disorders, and psychoses. The development of effective mGluR radiotracers would provide essential tools with which to probe these sites in living humans, providing critical information about certain disease processes involving the glutamaterigic system and its regulation in humans. As a first step towards this goal, the tritiated form of the high affinity group II metabotropic glutamate receptor (mGluR) antagonist LY341495 [K(D) (mGluR(2)) = 1.67 +/- 0.20 nM, K(D) (mGluR(3)) = 0.75 +/- 0.43 nM] was evaluated to determine its potential to label mGluRs in vivo. Dissection analysis of the regional brain distribution over time of [(3)H]LY341495 in male rats revealed low brain uptake and no significant demonstrable saturable binding of this tracer. A group II mGluR tracer possessing higher affinity than [(3)H]LY341495 and an absence of carboxylic acid groups is likely required for in vivo PET imaging purposes.

Amino Acids↗

PubMedDate not supplied

Treatment approaches to major depressive disorder relapse. Part 1: dose increase.

OBJECTIVE: Although continuing antidepressant treatment after patients have responded to medication has been shown to greatly reduce the risk of relapse, this risk is not eliminated. A number of theories have been proposed to account for this apparent loss of efficacy. A common initial approach to managing relapse is to increase the dose of antidepressant. We prospectively evaluated the likelihood of response to increasing the fluoxetine doses in patients relapsing during a long-term efficacy study of two fluoxetine dosing regimens. METHOD: Patients meeting the DSM-IV criteria for major depressive disorder with modified HAMD17 scores > or =18 and CGI-severity scores > or =4 were treated for 13 weeks with open-label 20 mg/day fluoxetine in a multicenter US study. Responders (n = 501) were randomized to 20 mg fluoxetine daily, placebo, or 90 mg enteric-coated fluoxetine weekly for 25 weeks of double-blind continuation treatment. If the patients relapsed during the continuation phase, they were offered a 25-week optional rescue treatment phase during which the study medication dose was increased as follows: (1) patients on placebo had treatment with fluoxetine 20 mg/day reinitiated, (2) patients on fluoxetine 20 mg/day had their dose increased to 40 mg/day, and (3) patients on a 90-mg weekly dose had their dose increased to 90 mg twice a week. The results of the rescue phase for the latter two groups who relapsed while on continuation treatment with fluoxetine are reported. Response was defined as a 50% reduction in the modified HAMD17 score since time of relapse and a CGI-severity score < or =2. Additional efficacy analyses included HAMD and CGI-severity changes from baseline to endpoint. Safety measures included assessment of treatment-emergent adverse events, vital signs, and laboratory measures. RESULTS: Overall, patients relapsing during the continuation treatment responded to an increased dose (57% of the 40-mg-daily group and 72% of the enteric-coated 90-mg-twice-weekly group). Mean modified HAMD17 scores decreased from a mean of approximately 20 to below 8 and were maintained for up to 6 months in the responders. Thirty-five percent of patients either did not respond or initially responded but again relapsed after augmentation of medication. CONCLUSIONS: The patients relapsing after initially responding to fluoxetine can benefit from an increase in fluoxetine dose. These results also generally support increasing dose as a first-line treatment strategy for a patient who has relapsed while taking a previously effective dose of an antidepressant. Increasing enteric-coated fluoxetine 90 mg once weekly to twice weekly appeared to be as well-tolerated and effective in restoring response as increasing a daily fluoxetine dose from 20 to 40 mg.

Adult↗

PubMedDate not supplied

Treatment approaches to major depressive disorder relapse. Part 2: reinitiation of antidepressant treatment.

BACKGROUND: Anecdotal reports concerning mood disorder patients suggest restarting drug treatment in patients who prematurely discontinue it may be associated with a diminished chance of response upon rechallenge. We evaluated the likelihood of response to reinitiation of fluoxetine treatment in patients relapsing after switching to placebo during a long-term efficacy study of two different dosing regimens of fluoxetine. METHOD: Patients who met the DSM-IV major depressive disorder criteria with modified HAMD17 scores > or =18 and CGI-Severity scores > or =4 were treated with open-label 20 mg/day fluoxetine for 13 weeks in a multicenter US study. Responders (n = 501) were randomized to placebo, 20 mg fluoxetine daily, or 90 mg enteric-coated fluoxetine weekly for 25 weeks of double-blind continuation treatment. Patients relapsing during the continuation phase were offered 25 weeks of double-blind rescue treatment during which the study medication dose was increased as follows: (1) patients on placebo had treatment with fluoxetine 20 mg/ day reinitiated; (2) patients on fluoxetine 20 mg/day had their dose increased to 40 mg/day, and (3) patients on a 90-mg weekly dose had their dose increased to 90 mg twice a week. Only the results of the rescue phase for the group who relapsed while on continuation treatment with placebo are reported here. Analyses included percentage of responders (50% reduction of modified HAMD17 and CGI-Severity < or =2) and assessments of change from baseline to endpoint (HAMD, CGI-Severity). Safety measures included assessment of vital signs, laboratory measures, and treatment-emergent adverse events. RESULTS: Of 122 patients assigned to placebo, 57 (47%) relapsed during continuation treatment. Fifty-five (96%) of these elected to enter double-blind rescue treatment. Overall, patients who relapsed upon switching to placebo responded well to reinitiation of fluoxetine (62%). The mean modified HAMD17 score decreased from 20 to less than 9 and was maintained for up to 6 months. Thirty-eight percent of patients either did not respond or initially responded but again relapsed after reinitiation of medication. CONCLUSION: This study suggests that patients who, after an initial response to fluoxetine, relapse upon switching to placebo have a relatively high probability of responding to the reinitiation of fluoxetine treatment. These results challenge the view that the efficacy of an agent prematurely discontinued is diminished when such an agent is restarted. They also generally support reinitiation of the same antidepressant as a 'first-line' treatment strategy in patients who relapsed after stopping a previously effective antidepressant.

Adolescent↗