paroxetine, Paxil
Influence of the new 5-HT-uptake inhibitor paroxetine on hypermotility in rats produced by p-chloroamphetamine (PCA) and 4,alpha-dimethyl-7-tyramine (H 77/77).

Lassen JB.

Two different forms of hypermotility produced by the amphetamine derivatives PCA and H 77/77, 5 mg/kg of each, was studied in rats treated s.c. with the new 5-HT uptake inhibitor paroxetine. The substance inhibited the effect of PCA but did not influence that of H 77/77. The 5-HT-uptake inhibitors paroxetine, imipramine, and chlorimipramine were also administered p.o. at various times before PCA. The three substances inhibited PCA-induced hypermotility. Paroxetine 0.5-2 mg/kg, was active at intervals of 1-4 h and 4 mg/kg was active at 18-h interval. Imipramine and chlorimipramine 25-30 mg/kg showed PCA inhibition at treatment intervals of 1-2h, but 80-100 mg/kg or more was required to inhibit PCA at intervals of 4 and 18 h. Previous results have shown that PCA-induced hypermotility is antagonized by substances inhibiting 5-HT synthesis and uptake, whereas H 77/77-induced hypermotility is inhibited by substances blocking NA synthesis, uptake, and receptors. The previous and present results indicate that paroxetine is a selective 5-HT-uptake inhibitor. After oral administration paroxetine presumably produces a more potent and long-lasting 5-HT-uptake inhibition than imipramine and chlorimipramine.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=418448&dopt=Abstract paroxetine, Paxil, Paxil CR



paroxetine, Paxil
Size determination of binding polymers for [3H]imipramine and [3H]paroxetine in human platelet membranes.

Mellerup ET, Plenge P, Nielsen M.

Imipramine and paroxetine both inhibit the transport of serotonin in serotonergic neurons and in platelets; furthermore specific high affinity binding sites for [3H]imipramine and [3H]paroxetine are located in these two cell types, probably on the serotonin transport mechanism. However, previous studies indicated that the binding site for [3H]imipramine was different from the binding site for [3H]paroxetine. We now report that the polymers on which the two binding sites are located have different molecular weights.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6099278&dopt=Abstract paroxetine, Paxil, Paxil CR



paroxetine, Paxil
Paroxetine: pharmacokinetics and cardiovascular effects after oral and intravenous single doses in man.

Lund J, Thayssen P, Mengel H, Pedersen OL, Kristensen CB, Gram LF.

Paroxetine kinetics and cardiovascular effects were studied in 4 healthy male subjects after single oral doses of 45 mg and after slow intravenous infusion of 23-28 mg. The plasma concentration/time curves could be described by a two-compartment open model, but the estimates of the model parameters were relatively inaccurate after the oral test. Plasma half-lives were longer after oral (19.8 hrs. S.D. 1.3 hrs) than after intravenous test (12.3 hrs. S.D. 3.8 hrs). Different methods of calculation of the systemic availability resulted in different values, most probably due to dose dependent kinetics. This is possibly related to saturated elimination kinetics during the first pass metabolism. Systolic time interval measurements showed that paroxetine causes a shortening of the electromechanical systole (QS2 corrected for heart rate) indicating a positive inotropic effect of the compound. Paroxetine also caused a reduction in heart rate and a moderate rise in systolic and diastolic blood pressure. After the intravenous dose some subjects experienced nausea and one subject a quite pronounced anxiety.

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paroxetine, Paxil
An early clinical phase II evaluation of paroxetine, a new potent and selective 5HT-uptake inhibitor in patients with depressive illness.

Borup C, Meidahl B, Petersen IM, Vangtorp A, le Fevre Honore P.

Paroxetine, a new, potent and selective serotonin (5-HT) uptake inhibitor has been evaluated in an open study for its clinical effect as well as its effect on the 5-HT concentration in whole blood in 19 patients with depressive illness. Paroxetine was administered in daily doses of 20 to 60 mg. The global evaluation after six to eight weeks showed a marked improvement in 11 patients, a moderate improvement in four and no change in four patients. Assessment with the Hamilton Rating Scale for Depression in ten patients showed a reduction from a mean score of 22.7 to 6.6 in six weeks. Maximal reduction was, however, first seen in three of the patients after 8 to 12 weeks. No correlation between the antidepressant effect and plasma concentrations of paroxetine was found. The only side effects noted with paroxetine were that two patients complained of dry mouth in the beginning of the treatment and a further patient experienced a burning sensation together with periodical light headache. Generally laboratory examinations did not show any trend towards pathological values except in one patient, where a moderate leucopenia was observed. Crista puncture/biopsy showed, however, no specific bone marrow reaction. The 5-HT concentration in whole blood was reduced to about 0.02 micrograms/ml indicating a total depletion of 5-HT from the thrombocytes. The present study indicates that paroxetine possesses a good antidepressive effect in combination with a very low frequency of side effects.

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paroxetine, Paxil
Imipramine binding site. Temperature dependence of the binding of 3H-labeled imipramine and 3H-labeled paroxetine to human platelet membrane.

Plenge P, Mellerup ET.

The characteristics of 3H-labeled imipramine and 3H-labeled paroxetine binding to human platelet membranes were determined at various temperatures between 0 and 37 degrees C. Both paroxetine and imipramine probably bind to the same molecular complex in the platelet membrane, but the binding characteristics are different for the two molecules. The dissociation constant (Kd) for imipramine increases from 0.3 nM to 7.0 nM with increasing incubation temperature in a continuous way, whereas Kd for paroxetine is almost constant, about 0.05 nM, between 0 and 19 degrees C, and first begins to increase from 0.06 nM to 0.16 nM between 20 and 37 degrees C. This suggests that the binding of paroxetine to the binding site induces a conformational change in the molecular complex of the binding site, whereas the binding of imipramine takes place without conformational changes in the binding site.

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paroxetine, Paxil
High affinity binding of [3H]paroxetine and [3H]imipramine to human platelet membranes.

Mellerup ET, Plenge P, Engelstoft M.

Paroxetine, one of the most potent and specific serotonin uptake inhibitors, was tritiated and used for binding studies with human platelet membranes. Specific, high affinity binding was demonstrated. The binding was compared with [3H]imipramine binding; it was found that the maximal binding (Bmax) was the same for [3H]paroxetine and [3H]imipramine, whereas the affinity was much higher for [3H]paroxetine (KD 0.08 nM and 0.56 nM for paroxetine and imipramine binding, respectively). IC50 was calculated for the inhibition of [3H]paroxetine and [3H]imipramine binding by a number of antidepressants; the corresponding Hill coefficients were also calculated.

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paroxetine, Paxil
Interactions of a non-selective monoamine oxidase inhibitor, phenelzine, with inhibitors of 5-hydroxytryptamine, dopamine or noradrenaline re-uptake.

Marley E, Wozniak KM.

Interactions of combined antidepressants which occur in man were reproduced in rats pretreated with phenelzine, features elicited including myoclonic phenomena, an augmented lower limb flexor reflex, muscle fasiculation and fatalities, particularly with combinations incorporating 5-hydroxytryptamine (5-HT) re-uptake inhibitors. Combinations of antidepressants included phenelzine with 5-HT re-uptake inhibitors (paroxetine, fluoxetine, clomipramine); with "mixed" re-uptake inhibitors affecting 5-HT and noradrenaline (imipramine, amitriptyline); with noradrenaline re-uptake inhibitors (desipramine, maprotiline, nisoxetine) and with dopamine re-uptake inhibitors (benztropine, nomifensine). Myoclonic phenomena such as forelimb flexor-extensor movements, head and body twitches, occurred in phenelzine pretreated rats after paroxetine, fluoxetine, clomipramine, imipramine, amitriptyline and desipramine. Wet dog shakes, the most intense phenomenon, were obtained only after paroxetine, fluoxetine, clomipramine and imipramine. Myoclonic features were prevented when pretreatment included p-chlorophenylalanine but were unaffected when this incorporated alpha-methyl-p-tyyrosine; there were attenuated by methysergide, cyproheptadine, clozapine or pimozide. The myoclonic phenomena were reproduced by combination of 5-hydroxytryptophan but not L-3,4-dihydroxyphenylalanine with clomipramine. Electrocortical changes observed included 2-4 Hz, 5-8 Hz, large amplitude potentials unrelated to the myoclonic incidents and unaffected by sensory stimulation. Following phenelzine, brain monoamine oxidase (MAO) A inhibition was 99% and that of MAO B, 88%; 5-HT concentration was significantly elevated in the cortex and hypothalamus, as was hypothalamic noradrenaline. Peak and basal tensions of a lower-limb flexor reflex were elevated in phenelzine pretreated spinal rats by fluoxetine, paroxetine, clomipramine and imipramine, effects attenuated by cyproheptadine. Forelimb flexor-extensor movements and body twitches were elicited by fluoxetine and paroxetine in phenelzine pretreated spinal rats in the presence of electrical stimulation of the central stump of a divided posterior tibial nerve. Pressor responses were observed in phenelzine pretreated spinal rats given 5-HT re-uptake inhibitors, "mixed" re-uptake inhibitors and those affecting noradrenaline re-uptake; ECG anomalies occurred in such rats given clomipramine.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6747915&dopt=Abstract paroxetine, Paxil, Paxil CR