venlafaxine (Effexor)
Potentiation of the time-dependent, antidepressant-induced changes in the agonistic behaviour of resident rats by the 5-HT1A receptor antagonist, WAY-100635.

Mitchell PJ, Redfern PH.

School of Pharmacy and Pharmacology, University of Bath, UK.

Acute and chronic antidepressant drug treatments respectively decrease and increase the aggressive behaviour of resident rats during encounters with unfamiliar conspecifics. We have now examined the effect of the 5-hydroxytryptamine1A receptor antagonist, WAY-100635, on fluoxetine-, paroxetine- or venlafaxine-induced changes in aggression. WAY-100635 (0.1 mg/kg), which did not modify behaviour when given alone, potentiated the venlafaxine (5.54 mg/kg)-induced reduction in aggression after acute treatment and, during chronic treatment, accelerated the fluoxetine (0.34 mg/kg/day)-induced increase in aggression, from day 5 to day 2. A similar change in time course was seen with paroxetine (0.33 mg/kg/day), although the increase in aggression was smaller. Venlafaxine (5.54 mg/kg/day, alone or co-administered with WAY-100635) increased aggression by day 2. During chronic treatment, therefore, venlafaxine, at the dose used, had a more rapid onset of action than either fluoxetine or paroxetine, whereas the fluoxetine- and paroxetine-, but not the venlafaxine-, induced increase in aggression was accelerated by WAY-100635. These studies further support the hypothesis that selective blockade of the 5-hydroxytryptamine1A receptor augments the effects of antidepressant drugs in an animal model predictive of antidepressant activity, presumably by concomitant blockade of the somatodendritic 5-hydroxytryptamine1A autoreceptor-mediated negative feedback system of serotonergic neurones.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9832972&dopt=Abstract venlafaxine Effexor refs
Effexor, Effexor XR

venlafaxine (Effexor)
Effects of fluoxetine, phentermine, and venlafaxine on pulmonary arterial pressure and electrophysiology.

Reeve HL, Nelson DP, Archer SL, Weir EK.

Department of Physiology, University of Alberta, Edmonton, Canada T6G 2R7.

The anorexic agents dexfenfluramine and fenfluramine plus phentermine have been associated with outbreaks of pulmonary hypertension. The fenfluramines release serotonin and reduce serotonin reuptake in neurons. They also inhibit potassium current (IK), causing membrane potential depolarization in pulmonary arterial smooth muscle cells. The recent withdrawal of the fenfluramines has led to the use of fluoxetine and phentermine as an alternative anorexic combination. Because fluoxetine and venlafaxine reduce serotonin reuptake, we compared the effects of these agents with those of phentermine and dexfenfluramine on pulmonary arterial pressure, IK, and membrane potential. Fluoxetine, venlafaxine, and phentermine caused minimal increases in pulmonary arterial pressure at concentrations < 100 microM but did cause a dose-dependent inhibition of IK. The order of potency for inhibition of IK at +50 mV was fluoxetine > dexfenfluramine = venlafaxine > phentermine. Despite the inhibitory effect on IK at more positive membrane potentials, fluoxetine, venlafaxine, and phentermine, in contrast to dexfenfluramine, had minimal effects on the cell resting membrane potential (all at a concentration of 100 microM). However, application of 100 microM fluoxetine to cells that had been depolarized to -30 mV by current injection elicited a further depolarization of >18 mV. These results suggest that fluoxetine, venlafaxine, and phentermine do not inhibit IK at the resting membrane potential. Consequently, they may present less risk of inducing pulmonary hypertension than the fenfluramines, at least by mechanisms involving membrane depolarization.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9950882&dopt=Abstract venlafaxine Effexor refs
Effexor, Effexor XR

venlafaxine (Effexor)
Efficacy and safety of venlafaxine-ECT combination in treatment-resistant depression.

Gonzalez-Pinto A, Gutierrez M, Gonzalez N, Elizagarate E, Perez de Heredia JL, Mico JA.

Hospital Santiago Apostol, Department of Psychiatry, Vitoria, Spain. agonzalez sscc.osakidetza.net

Thirteen patients with treatment-resistant major depression were given venlafaxine, at doses ranging from 150 mg to 375 mg, combined with ECT. Propofol was used as an anesthetic. Ten of 13 (76.9%) were considered responsive to combined ECT-venlafaxine treatment, and positive responses were not associated with venlafaxine doses. An asystole episode was observed in 4 patients; these patients had received significantly higher doses of venlafaxine (P<0.01). Treatment seems to be safe at venlafaxine doses <300 mg/day. At higher doses, with propofol used as anesthetic, the possibility of asystole cannot be ruled out. A possible additive effect of high-dose venlafaxine and propofol-blocking sodium channels are discussed.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11983797&dopt=Abstract venlafaxine Effexor refs
Effexor, Effexor XR

venlafaxine (Effexor)
The disposition of venlafaxine enantiomers in dogs, rats, and humans receiving venlafaxine.

Wang CP, Howell SR, Scatina J, Sisenwine SF.

Drug Metabolism Division, Wyeth-Ayerst Research, Princeton, New Jersey 08543.

A stereospecific high-performance liquid chromatographic (HPLC) method was developed for the quantitation of the enantiomers of venlafaxine, an antidepressant, in dog, rat, and human plasma. The procedure involves derivatization of venlafaxine with the chiral reagent, (+)-S-naproxen chloride, and a postderivatization procedure. The method was linear in the range of 50 to 5,000 ng of each enantiomer per ml of plasma. No interference by endogenous substances or known metabolites of venlafaxine occurred. Studies to characterize the disposition of the enantiomers of venlafaxine were conducted in dog, rat, and human, following oral administration of venlafaxine. The Cmax, area under the curve (AUC) and (S)/(R) concentration ratios of the (R)- and (S)-enantiomers were compared. In rats, the mean plasma ratio of (S)-venlafaxine to that of (R)-venlafaxine over 0.5 to 6.0 h varied from 2.97 to 8.50 with a mean value of 5.51 +/- 2.45. The Cmax, AUC0-infinity, and t 1/2 values of the (R)- and (S)-enantiomers in dogs were not significantly different from one another (P greater than 0.1). The mean ratios [(S)/(R)] of enantiomers of venlafaxine in human over a 2 to 6 h interval ranged from 1.33 to 1.35 with an overall ratio of 1.34 +/- 0.26 (n = 12). These ratios of the enantiomers [(S)/(R)] were not statistically different from unity (P greater than 0.1) indicating that the disposition of venlafaxine enantiomers in humans is not stereoselective and is more similar to that in dogs than that in rats.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1616828&dopt=Abstract venlafaxine Effexor refs
Effexor, Effexor XR

venlafaxine (Effexor)
Venlafaxine for treatment-resistant unipolar depression.

Nierenberg AA, Feighner JP, Rudolph R, Cole JO, Sullivan J.

Depression Research Program, Massachusetts General Hospital, Boston 02114.

The purpose of this study is to evaluate the novel antidepressant venlafaxine for the management of treatment-resistant unipolar depression. We gave unblinded venlafaxine to 84 consecutive outpatients and inpatients who met DSM-III-R criteria for major depression and who had failed to respond to at least three adequate trials of antidepressants from at least two different antidepressant classes or electroconvulsive therapy, plus at least one attempt at augmentation. Patients were evaluated after a drug free period at baseline and regular intervals with the 21-item Hamilton Rating Scale for Depression (HAM-D-21), Montgomery-Asberg Depression Rating Scale (MADRS), and the Clinical Global Impressions Scale Improvement item (CGI). Full response for each scale was defined as follows: HAM-D-21 score of 8 or lower, a MADRS score of 12 or lower, and CGI score of 1; partial responses was defined as a 50% decrease in the HAM-D and MADRS, with final scores greater than 8 and 12, respectively, and for the CGI, a score equal to 2. About a third of patients were considered to be either full or partial responders (32.9% by HAM-D-21, 30.0% by MADRS, and 40% by CGI) after 12 weeks of venlafaxine treatment. To date, about 46% of responders have sustained their response for at least 3 months after the acute response. Venlafaxine is effective for a significant, but small, minority of patients with rigorously defined triple-resistant depression; the improvement was maintained for about half of the responders for the first 3 months of maintenance therapy.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7884023&dopt=Abstract venlafaxine Effexor refs
Effexor, Effexor XR