citalopram Celexa
The effects of selective serotonin reuptake inhibitors and their metabolites on S-mephenytoin 4'-hydroxylase activity in human liver microsomes.

Kobayashi K, Yamamoto T, Chiba K, Tani M, Ishizaki T, Kuroiwa Y.

Department of Clinical Pharmacy, Showa University, Tokyo, Japan.

The inhibitory effects of four selective serotonin reuptake inhibitors (SSRIs), fluoxetine, sertraline, paroxetine and citalopram, and three metabolites (norfluoxetine, demethylcitalopram and didemethylcitalopram), on S-mephenytoin 4'-hydroxylation activities in human liver microsomes were studied. The 4'-hydroxylation of S-mephenytoin, a representative substrate toward CYP2C19, was competitively inhibited by all the SSRIs and their metabolites studied. The mean Ki values of fluoxetine, norfluoxetine, sertraline, paroxetine, citalopram, demethylcitalopram and didemethylcitalopram were 5.2, 1.1, 2.0, 7.5, 87.3, 55.8 and 7.7 microM, respectively. The findings suggest that some SSRIs and their metabolites with a low Ki value (e.g., fluoxetine, norfluoxetine) may reduce the clearance of drugs metabolized by this isoform of P450, thereby resulting in a possible drug-drug interaction, when administered simultaneously. In addition, SSRIs and their metabolites examined herein may be substrates toward CYP2C19.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8703653&dopt=Abstract citalopram Celexa



citalopram Celexa
Effects of acute and repeated administration of citalopram on extracellular levels of serotonin in rat brain.

Moret C, Briley M.

Centre de Recherche Pierre Fabre, Castres, France.

The effects of acute (2 days) and repeated (21 days) administration (50 mg/kg in the diet) of the selective serotonin (5-HT, 5-hydroxytryptamine) reuptake inhibitor, citalopram, on extracellular levels of 5-HT and their modulation by terminal autoreceptors in the hypothalamus of freely moving rats were compared in vivo by microdialysis. When studied without washout, extracellular levels of 5-HT were increased by both acute and repeated citalopram administration. In rats treated repeatedly, extracellular 5-HT levels were 43% (but not significantly) greater than in those treated acutely. Extracellular levels of 5-HT in control and citalopram-treated rats were similar when measured after 24 h washout. The enhancing effect of non-selective serotonergic autoreceptor antagonists, methiothepin (100 microM) or 1-(1-naphthyl)piperazine (NP) (10 microM), administered through the microdialysis probe, after 24 h washout, was similar in both control and chronically treated groups. These results suggest that repeated administration of citalopram followed by a washout of 24 h does not lead to desensitization of the terminal autoreceptor as measured in vivo in contrast to the effects we have shown previously in vitro. In rats treated chronically with citalopram without washout, methiothepin had a greater maximal effect on 5-HT outflow in comparison to rats receiving acute citalopram treatment. This finding suggests that a 5-HT autoreceptor antagonist or a combination of such a drug with a 5-HT uptake inhibitor would produce a greater increase of extracellular levels of 5-HT in hyposerotonergic states such as depression.

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citalopram Celexa
The effect of age and concomitant treatment with other psychoactive drugs on serum concentrations of citalopram measured with a nonenantioselective method.

Leinonen E, Lepola U, Koponen H, Kinnunen I.

Kuopio Psychiatric Research Clinic, Kuopio, Finland.

We measured citalopram and desmethylcitalopram concentrations in serum from 169 psychiatric patients, who were treated with common therapeutic drug doses. Altogether 202 serum samples were assayed by a nonenantioselective high-performance liquid chromatography (HPLC) method. The results indicate that the kinetic variability (maximum concentration/minimum concentration) in dose- and weight-related serum citalopram (10.6-fold) and desmethylcitalopram (7.2-fold) is large even during monotherapy. Log serum citalopram (r = 0.36, p < 0.05) and desmethylcitalopram (r = 0.51, p < 0.01) concentrations of individual patients increased significantly with increasing drug doses. Dose- and weight-related (calculated as mg/kg dose basis) log serum citalopram (r = 0.29) but not desmethylcitalopram (r = 0.06) concentrations increased with aging (p < 0.001). No sex-related differences were found. Nineteen patients (19 samples) had concomitant treatment with neuroleptics, 84 patients (101 samples) with benzodiazepines, and 18 patients (28 samples) with tricyclic antidepressants. The concentrations in these patients were compared with those of 48 nonsmoking patients (54 samples) without any concomitant psychotropic drug treatment. None of the single neuroleptics alone had a significant effect on dose- and weight-related serum citalopram or desmethylcitalopram concentrations. However, citalopram concentrations increased by 121% (338 +/- 165 vs. 747 +/- 505, mean +/- SD; p < 0.01) and desmethylcitalopram by 85% (124 +/- 53 vs. 229 +/- 138; p < 0.05) when neuroleptics were pooled. Among single benzodiazepines, only alprazolam increased serum citalopram (338 +/- 165 vs. 391 +/- 267; p < 0.01) and desmethylcitalopram (124 +/- 53 vs. 186 +/- 175; p < 0.01) concentrations. When all the benzodiazepines were pooled, they still increased the serum concentration of the parent drug by 23% (338 +/- 165 vs. 414 +/- 303; p < 0.05) and those of the metabolite by 47% (124 +/- 53 vs. 182 +/- 163; p < 0.01). In patients who were simultaneously treated with clomipramine, serum citalopram (338 +/- 165 vs. 655 +/- 409; p < 0.001) and desmethylcitalopram (124 +/- 53 vs. 435 +/- 347; p < 0.001) concentrations were consistently higher than those of the controls. Even when the tricyclic antidepressants were pooled, they increased citalopram concentrations by 44% (338 +/- 165 vs. 486 +/- 312; p < 0.001) and desmethylcitalopram concentrations by 111% (124 +/- 53 vs. 261 +/- 260; p < 0.001). The results suggest that interindividual variability in serum citalopram concentrations is pronounced and that increased serum citalopram levels are related to advancing age and concomitant treatment with other psychotropic drugs. The citalopram dose should therefore ideally be individualized by therapeutic drug monitoring.

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citalopram Celexa
Protective effects of maternal buspirone treatment on serotonin reuptake sites in ethanol-exposed offspring.

Kim JA, Druse MJ.

Neuroscience Program, Loyola University Chicago, Stritch School of Medicine, Maywood, IL 60153, USA.

Previous work in this laboratory demonstrated that in utero ethanol exposure is associated with abnormal development of the serotonergic system. Specific abnormalities included deficiencies of serotonin (5-HT) and its metabolites, and cortical 5-HT reuptake sites. The concentration of 5-HT1A receptors was also altered. The serotonin deficit was detected in the fetal ethanol-exposed brain, at an age when 5-HT would normally function as an essential trophic factor. Thus, it was hypothesized that the early 5-HT ethanol-associated deficit of an essential trophic factor (e.g. 5-HT) could contribute to subsequent developmental abnormalities in serotonergic neurons. In the present investigation we used quantitative autoradiography (QAR) to more fully characterize the developmental abnormalities in 5-HT reuptake sites in developing offspring of ethanol-fed rats. In addition, we attempted to overcome the potential negative impact of the ethanol-associated deficit of fetal 5-HT, by administering a 5-HT1A agonist, buspirone, to pregnant rats. These investigations demonstrated that postnatal (PN) 19 and/or 35 day ethanol-exposed offspring had a significant decrease in [3H]citalopram binding to 5-HT reuptake sites in the frontal cortex, parietal cortex, lateral hypothalamus, substantia nigra, medial septum, and striatum. In contrast, [3H]citalopram binding was increased in the dorsal raphe on PN5 and in the median raphe on PN19. No significant ethanol-associated changes were detected in the hippocampus CA3 region or in the amygdala. When [3H]citalopram binding was compared in the offspring of saline- and buspirone-treated dams, it appeared that maternal treatment with buspirone prevented or reversed most of the ethanol-associated developmental abnormalities in 5-HT reuptake sites. Buspirone prevented the decline in binding of [3H]citalopram in the frontal cortex, lateral hypothalamus, substantia nigra and medial septum. Similarly, buspirone treatment prevented the ethanol-associated increase in binding in the dorsal and median raphe. Additional experiments are needed to elucidate the impact of maternal buspirone treatment on the development of other neurotransmitter systems in offspring.

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citalopram Celexa
The 5-HT1A receptor antagonist (S)-UH-301 augments the increase in extracellular concentrations of 5-HT in the frontal cortex produced by both acute and chronic treatment with citalopram.

Arborelius L, Nomikos GG, Hertel P, Salmi P, Grillner P, Hook BB, Hacksell U, Svensson TH.

Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.

In a recent study, utilizing single cell recording techniques, we have shown that administration of 5-HT1A receptor antagonists, e.g. (S)-UH-301, to rats concomitantly treated, acute or chronically, with the selective serotonin reuptake inhibitor (SSRI) citalopram significantly increases the activity of 5-hydroxytryptamine (5-HT) containing neurons in the dorsal raphe nucleus (DRN). Here we report correlative experiments using microdialysis in freely moving animals to measure extracellular levels of 5-HT and its metabolite 5-hydroxyindole acetic acid (5-HIAA) in the frontal cortex, a major projection area for DRN-5-HT neurons. Acute administration of (S)-UH-301 (2.5 mg/kg s.c.) or citalopram (2.0 mg/kg s.c.) increased 5-HT concentrations with a maximum of about 70% and 185%, respectively, above baseline. However, when (S)-UH-301 was administered 30 min before citalopram the maximal increase in 5-HT levels was approximately 400%. In rats chronically treated with citalopram (20 mg/kg/day i.p. for 14 days) basal 5-HT concentrations in the frontal cortex were significantly increased and 5-HIAA concentrations were decreased when measured 10-12 h, but not 18-20 h, after the last injection of citalopram, as compared to basal 5-HT and 5-HIAA concentrations in chronic saline-treated rats. When (S)-UH-301 (2.5 mg/kg s.c.) was administered 12 h, but not 20 h, after the last dose of citalopram it produced a significantly larger increase in extracellular concentrations of 5-HT than in control rats. However, in rats pretreated with a single, very high dose of citalopram, 20 mg/kg i.p., administration of (S)-UH-301 at 12 h after citalopram did not increase 5-HT levels. The augmentation by (S)-UH-301 of the increase in brain 5-HT output produced by acute administration of citalopram is probably due to antagonism of the citalopram induced feedback inhibition of 5-HT cells in the DRN, as previously suggested. However, the capacity of (S)-UH-301 to further increase the already elevated extracellular concentrations of 5-HT in brain in animals maintained on a chronic citalopram regimen, in which significant tolerance to the initial feedback inhibition of DRN-5-HT cells and developed, represents a novel finding. Generally, the reduced feedback inhibition of 5-HT neurons obtained with chronic citalopram treatment, and the associated elevation of brain 5-HT concentrations, may be related to functional desensitization of somatodendritic 5-HT1A autoreceptors in the DRN. This phenomenon may also largely explain the larger increase in 5-HT output produced by (S)-UH-301 in chronic citalopram treated animals as compared to its effect in control animals. Yet, a contributory factor may be a slight, remaining feedback inhibition of the 5-HT cells caused by residual citalopram at 12, but not 20 h after its last administration. Previous clinical studies suggest that addition of a 5-HT1A receptor antagonist to an SSRI in the treatment of depression may accelerate the onset of clinical effects. Moreover, in therapy-resistant cases maintained on SSRI treatment, addition of a 5-HT1A receptor antagonist may improve clinical efficacy. Since the therapeutic effect of SSRIs in depression has been found to be critically linked to the availability of 5-HT in brain, our experiments results support, in principle, both of the above clinically based notions.

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citalopram Celexa
Chronic treatment with citalopram induces noradrenaline receptor hypoactivity. A microdialysis study.

Petersen B, Mork A.

Department of Pharmacology, University of Copenhagen, Denmark.

To investigate whether chronic citalopram administration influences the cyclic AMP (cAMP) synthesis in vivo, microdialysis was used to assess citalopram-induced alterations in extracellular concentrations of cAMP in the dorsal hippocampus of freely moving rats. Citalopram administration for 4 weeks (40 mg/kg p.o. daily) did not affect the baseline levels of cAMP but decreased the noradrenaline-induced enhancement of cAMP levels. No change in forskolin-induced enhancement of cAMP levels was observed. Citalopram in situ did not exert any effect on the cAMP levels. These data support the hypothesis that chronic administration of antidepressants alters the function of noradrenergic receptors.

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citalopram Celexa
Regional distribution of the 5-HT innervation in the brain of normal and lurcher mice as revealed by [3H]citalopram quantitative autoradiography.

Strazielle C, Lalonde R, Riopel L, Botez MI, Reader TA.

Department de physiologie, Faculte de medecine, Universite de Montreal, Canada.

The neurological cerebellar mutant lurcher is characterized by a primary degeneration of Purkinje cells as well as retrograde secondary partial degeneration of cerebellar granule cells and inferior olivary neurons. Since serotonin (5-HT) has been implicated in the modulation of excitatory amino acid systems of the cerebellum, the 5-HT innervation of the normal and lurcher mice was examined by quantifying uptake sites using [3H]citalopram autoradiography, and by biochemical assays of the indoles 5-HT, 5-hydroxy-L-tryptophan and 5-hydroxyindole-3-acetic acid using high-performance liquid chromatography. Comparable results were found between [3H]citalopram binding and 5-HT tissue concentrations in different brain regions. The highest [3H]citaslopram labelling was observed in defined structures of the mesencephalic and upper pontine regions, in limbic strutures, in hypothalamus and in discrete thalamic divisions, while the lowest labelling of uptake sites was documented in cerebellum and brainstem reticular formation. In lurcher mutants, the histology confirmed cell degeneration and the reduction in width, leading to 65%, 45% and 25% atrophies of total cerebellum, deep nuclei and inferior olivary nucleus, respectively. The [3H]citalopram labelling corrected for surface loss was 45% and 20% higher to cerebellar deep nuclei and red nucleus, respectively, but remained unchanged in the cerebellar cortex and inferior olivary nucleus. Moreover, higher labelling was found in nucleus raphe dorsalis, ventral tegmental area, inferior colliculus, locus coeruleus, pontine central grey and anterior thalamic nuclei, areas known to be part of cerebellar afferent and efferent systems. The present results indicate that in such pathological conditions as described for the lurcher mutant, the 5-HT system may modulate motor function not only at the level of the cerebellum, but also in other forebrain structures functionally related to the motor system.

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citalopram Celexa
5-HT1A autoreceptors and the mode of action of selective serotonin reuptake inhibitors (SSRI).

Hjorth S, Auerbach SB.

Department of Pharmacology, University of Goteborg, Sweden.

The clinical efficacy of antidepressant drugs that block serotonin (5-HT) reuptake may be restrained in the short term by the indirect activation of autoreceptors. In vivo microdialysis in rat hippocampus was used to study the putative release-inhibitory properties of the SSRI citalopram and paroxetine. With 5-HT reuptake first blocked by local 'reverse-dialysis' infusion of citalopram (1 microM) into the hippocampus, acute systemic administration of citalopram or paroxetine resulted in a marked decrease in hippocampal 5-HT overflow. This presumably reflected the inhibition of 5-HT neuronal discharge and release, subsequent to reuptake blockade in the raphe nuclei and thus, activation of somatodendritic autoreceptors. In support of this hypothesis, pretreatment with (+/-)-pindolol or (+)-WAY100135, to block 5-HT1A autoreceptors, abolished the decrease in extracellular 5-HT produced by acute systemic injection of the reuptake blockers. The results suggest that the clinical efficacy of antidepressants that block 5-HT reuptake could be enhanced by co-administration of a 5-HT1A autoreceptor antagonist.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8788519&dopt=Abstract citalopram Celexa