Prozac
Influence of the antidepressants desipramine and fluoxetine on tryptophan-2,3-dioxygenase in the presence of exogenous melatonin.

Walsh HA, Daya S.

University of Fort Hare, Alice, South Africa. walsh ufhcc.ufh.ac.za

The effects of desipramine and fluoxetine were examined on rat hepatic tryptophan-2,3-dioxygenase activity in the presence or absence of exogenous melatonin. Male Wistar rats were treated intraperitoneally over 8 days. The antidepressants were also administered individually and their impact on the enzyme noted. Desipramine reduced basal hepatic tryptophan-2,3-dioxygenase activity in the liver while fluoxetine had no observable effect. However, fluoxetine also prevented the hemin induced elevation in total enzyme activity. Exogenous melatonin (0.25mg/kg/day) for 8 days counteracted the inhibitory effects of both desipramine and fluoxetine at concentrations of 2.5mg/kg/day. Total enzyme activity was restored when melatonin was administered in combination with either drug. The experimental findings indicate that there is chemical antagonism at the surface of the enzyme between melatonin and the antidepressants that abolishes the observed inhibitory effects of the administered compounds.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9651108&dopt=Abstract fluoxetine Prozac



Prozac
Minimal interaction between fluoxetine and multiple-dose zolpidem in healthy women.

Allard S, Sainati S, Roth-Schechter B, MacIntyre J.

Lorex Pharmaceuticals, Chicago, IL 60680-5110, USA.

The objective was to evaluate possible pharmacokinetic and pharmacodynamic interactions for repeated nightly zolpidem dosing with fluoxetine. Twenty-nine healthy female volunteers (mean age, 25. 6 years) received zolpidem (10 mg) and fluoxetine (20 mg) in the following open design: zolpidem on night 1 followed by 1 washout day, a daily morning dose of fluoxetine on days 3 through 27, and a morning dose of fluoxetine plus an evening dose of zolpidem on days 28 through 32. Plasma levels of zolpidem, fluoxetine, and norfluoxetine were determined at the transitions from one regimen to the next. Morning psychomotor tests were performed on days 1, 2, 28, 29, and 33. Steady-state plasma concentrations of fluoxetine/norfluoxetine were reached by day 24 of fluoxetine dosing. No significant differences in any pharmacokinetic parameters for fluoxetine and norfluoxetine were observed between day 27 and day 32. There were no significant differences in AUC, maximal plasma concentration, or time to maximal concentration parameters for zolpidem plasma concentrations among nights 1, 28, and 32. There was a statistically significantly increased t1/2 for zolpidem on night 32, compared with night 28 (3.64 and 3.29 hr, respectively). There were no significant differences in the next-morning Digit Symbol Substitution Test performance at any time in the study. Both zolpidem and fluoxetine were well tolerated alone or during coadministration. These findings indicate the absence of clinically significant pharmacokinetic or pharmacodynamic interactions between fluoxetine and zolpidem (five consecutive doses) when the drugs are coadministered to healthy women. Therefore, based on these observations, short-term cotherapy with fluoxetine (20 mg) and zolpidem (10 mg) appears safe.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9660843&dopt=Abstract fluoxetine Prozac



Prozac
Vasopressin, oxytocin, corticotrophin-releasing factor, and sodium responses during fluoxetine administration in the rat.

Marar IE, Amico JA.

Department of Medicine, University of Pittsburgh School of Medicine, PA 15261, USA.

Hyponatremia has been observed in elderly patients treated with the selective serotonin reuptake inhibitor (SSRI) fluoxetine. The pathogenesis of this effect is not known, but enhanced release of vasopressin (VP) and its renal actions may be a possible mechanism. Excess secretion of VP in combination with large fluid intake is known to induce hyponatremia. We determine if chronic fluoxetine administration in association with liberal fluid intake will induce hyponatremia via enhanced release of VP. We used a previously described model in which fluid intake is forced by administering rats a nutritionally balanced liquid diet. Male Sprague-Dawley rats in groups of 10 were randomized to solid and liquid diets, and each diet group administered daily i.p. injections of fluoxetine (10 mg/kg) or saline for 10 d. Water was given ad libitum to all groups. Daily weight, fluid and food intake, and urine output were measured. On d 10, rats were killed by rapid guillotine decapitation 1-3 h after injection. Trunk blood was collected for measurements of plasma VP and oxytocin (OT) and serum sodium (Na), BUN, creatinine, and glucose. Pituitary glands were assayed for VP and OT content. VP mRNA in the paraventricular and supraoptic nuclei (PVN and SON) and corticotrophin-releasing factor (CRF) mRNA in the PVN were measured by in situ hybridization histochemistry. Fluid intake was significantly higher in groups maintained on liquid vs solid diet (p < 0.0001), as was urine output (p < 0.0001). Fluoxetine-treated rats gained significantly less weight than placebo-treated rats (p = 0.01), in keeping with fluoxetine's anorexigenic properties. However, no significant differences were found among the groups in Na, plasma VP or OT, pituitary VP or OT, or PVN CRF or VP mRNA levels. We conclude that administration of fluoxetine to laboratory rats in the dose and duration used in this study does not significantly affect hypothalamic expression, pituitary stores, or peripheral secretion of VP.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9666340&dopt=Abstract fluoxetine Prozac



Prozac
Evidence for linkage disequilibrium between serotonin transporter protein gene (SLC6A4) and obsessive compulsive disorder.

McDougle CJ, Epperson CN, Price LH, Gelernter J.

Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA.

Obsessive compulsive disorder (OCD) is characterized by recurrent and intrusive thoughts that are distressing (obsessions) and/or repetitive behaviors or mental acts that the person feels driven to perform (compulsions). OCD has a partly genetic basis. For treatment of OCD, potent serotonin reuptake inhibitor (SRI) drugs (clomipramine (Anafranil), fluvoxamine (Luvox), fluoxetine (Prozac), sertraline (Zoloft), and paroxetine (Paxil)), which act on the serotonin transporter protein, are uniquely efficacious. A polymorphism in the promoter region of the gene (SLC6A4) encoding this protein, was recently reported to affect protein expression and to be associated with measures of anxiety and depression and with autism (using a family-controlled transmission disequilibrium test (TDT) design). SLC6A4 therefore has strong a priori support for potentially influencing risk for OCD: the protein it encodes is a medication target; a polymorphism in the gene affects function; and that polymorphism has been shown to be associated with behavioral phenotypes. We used the TDT with a set of 34 European-American family trios, 30 unrelated and four drawn from an extended pedigree, to test for linkage disequilibrium between OCD and alleles at the SLC6A4 promoter polymorphic locus. Of 35 heterozygous parents, 24 transmitted the 'l' SLC6A4 allele and 11 transmitted the 's' allele (chi 2 TDT = 4.83; P < 0.03). Considering only the 13 SRI drug nonresponders, there were 13 heterozygous parents, of whom 10 transmitted the 'l' allele and three the 's' allele (chi 2 TDT = 3.77; P < 0.052). These data provide preliminary support for association and linkage disequilibrium between the SLC6A4 'l' allele and OCD.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9672904&dopt=Abstract fluoxetine Prozac



Prozac
Drug-nutrient interactions: inhibition of amino acid intestinal absorption by fluoxetine.

Urdaneta E, Idoate I, Larralde J.

Departamento de Fisiologia y Nutricion, Universidad de Navarra, Pamplona, Spain.

Fluoxetine is one of the most widely used antidepressants and nowadays it is also being used to manage obesity problems. In our laboratory we demonstrated that the drug inhibited sugar absorption (Monteiro et al. 1993). The aim of the present work was to determine the effect of fluoxetine on intestinal leucine absorption. Using a procedure of successive absorptions in vivo the drug diminished amino acid absorption by 30% (P < 0.001). Experiments in vitro in isolated jejunum also revealed a reduction in leucine uptake of 37% (P < 0.001). In both cases fluoxetine only affected mediated transport without altering diffusion. In a preparation enriched in basolateral membrane, fluoxetine inhibited the Na+,K(+)-ATPase (EC 3.6.1.37) activity (55%; P < 0.001) in a non-competitive manner with an inhibition constant (Ki) value of 0.92 mM. Leucine uptake by brush-border membrane vesicles was diminished by the drug (a reduction of 48% was observed at 30s, P < 0.001); only the apical Na(+)-dependent transport system of the amino acid was modified and the inhibition was non-competitive. Leucine uptake in the presence of lysine indicated that transporter B was involved. These results suggest that fluoxetine reduces leucine absorption by its action on the basolateral and apical membrane of the enterocyte; the nutritional status of the patients under drug treatment may be affected as neutral amino acid absorption is decreased.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9682663&dopt=Abstract fluoxetine Prozac



Prozac
Effect of fluoxetine on the plasma concentrations of clozapine and its major metabolites in patients with schizophrenia.

Spina E, Avenoso A, Facciola G, Fabrazzo M, Monteleone P, Maj M, Perucca E, Caputi AP.

Institute of Pharmacology, University of Messina, Italy.

The effect of fluoxetine on the plasma concentrations of clozapine and its major metabolites was studied in 10 schizophrenic patients with residual negative symptoms. Patients stabilized on clozapine therapy (200-450 mg/day) received additional fluoxetine (20 mg/day) for eight consecutive weeks. During fluoxetine administration, mean plasma concentrations of clozapine, norclozapine and clozapine N-oxide increased significantly by 58%, 36% and 38%, respectively. There was no difference in negative symptomatology, as measured by the Scale for Assessment of Negative Symptoms, and the drug combination was generally well tolerated. The concomitant elevation in plasma levels of clozapine and its major metabolites suggests that fluoxetine inhibits the metabolism of clozapine by affecting pathways other than N-demethylation and N-oxidation. Close monitoring of clinical response and, possibly, plasma clozapine levels is recommended whenever fluoxetine is given to patients stabilized on clozapine therapy.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9690983&dopt=Abstract fluoxetine Prozac



Prozac
Chronic fluoxetine microdialysis into the medullary raphe nuclei of the rat, but not systemic administration, increases the ventilatory response to CO2.

Taylor NC, Li A, Green A, Kinney HC, Nattie EE.

Department of Physiology, Dartmouth Medical Center, Borwell Bldg., Lebanon, NH 03756-000, USA. Natalie.C.Taylor dartmouth.edu

In conscious rats, focal CO2 stimulation of the medullary raphe increases ventilation, whereas interference with serotonergic function here decreases the ventilatory response to systemic hypercapnia. We sought to determine whether repeated administration of a selective serotonin reuptake inhibitor in this region would increase the ventilatory response to hypercapnia in unanesthetized rats. In rats instrumented with electroencephalogram-electromyogram electrodes, 250 or 500 microM fluoxetine or artificial cerebrospinal fluid (aCSF) was microdialyzed into the medullary raphe for 30 min daily over 15 days. To compare focal and systemic treatment, two additional groups of rats received 10 mg x kg(-1) x day(-1) fluoxetine or vehicle systemically. Ventilation was measured in normocapnia and in 7% CO2 before treatment (day 0), acutely (days 1 or 3), on day 7, and on day 15. There was no change in normocapnic ventilation in any treatment group. Rats that received 250 microM fluoxetine microdialysis showed a significant 13% increase in ventilation in wakefulness during hypercapnia on day 7, due to an increase in tidal volume. In rats microdialyzed with 500 microM fluoxetine, there were 16 and 32% increases in minute ventilation during hypercapnia in wakefulness and sleep on day 7, and 20 and 28% increases on day 15, respectively, again due to increased tidal volume. There was no change in the ventilatory response to CO2 in rats microdialyzed with aCSF or in systemically treated rats. Chronic fluoxetine treatment in the medullary raphe increases the ventilatory response to hypercapnia in an unanesthetized rat model, an effect that may be due to facilitation of chemosensitive serotonergic neurons.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15273241&dopt=Abstract fluoxetine Prozac



Prozac
Determination of fluoxetine and norfluoxetine concentrations in cadaveric allograft skin.

Neudeck BL, Taddonio TE, Garner WL, Welage LS.

University of Michigan College of Pharmacy, Ann Arbor 48109-1065, USA.

Fluoxetine hydrochloride is the sixth most prescribed drug in the United States and is administered to treat major depression. A cadaveric skin donation was obtained from a 46-year-old woman who died as a result of a fluoxetine overdose. Due to the potential penetration of the drug and its major metabolite, norfluoxetine, into skin, the safety of using the skin as an allograft was questioned. Our evaluation showed that mean concentrations in skin were 2304+/-175 and 1353+/-102 ng/g of skin, respectively. The skin:plasma ratio was 0.41. Clinically, the amount of fluoxetine that can be transferred to an allograft recipient depends on many factors. Based on penetration of drug and metabolite into skin, one would have to evaluate carefully the risk:benefit ratio of using allografts from a donor who died from a fluoxetine overdose.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9692660&dopt=Abstract fluoxetine Prozac