Venlafaxine assessment

As with venlafaxine, a double-blind continuation study has been done with nefazodone (see Jable 7-21). Patients who responded to nefazodone, imipramine, or placebo in the acute phase were offered the option of remaining on double-blind treatment for 1 year ( 272). Those patients who chose to participate were then followed up monthly to assess whether efficacy persisted. The relapse rate was 22% on placebo versus 10% on nefazodone and 7% on imipramine. The absolute difference in relapse rates between nefazodone and placebo was similar to that of venlafaxine versus placebo (i.e., 12% to 14%). Thus, maintenance treatment with nefazodone, as with venlafaxine and the SSRIs, reduced the risk of relapse when compared with placebo even when the comparison group had initially responded to placebo and remained on placebo for the maintenance period. 

SSRIs and venlafaxine can cause of variety of sexual dysfunctions including delayed ejaculation, anorgasmia, and decreased libido ( Table 7-24). For two reasons, the adverse effect of these medications on sexual function was underestimated during the early clinical trials. First, such trials rely on spontaneous reporting by participants. Second, these adverse effects appear to take several weeks to develop. These adverse effects develop in approximately 30% to 40% of patients on adequate doses of SSRIs and venlafaxine. Although all manufacturers of these medications endeavor to suggest that their product is less likely to cause these effects, there is no compelling evidence to indicate that is true. Comparisons of rates across studies are not fair comparisons because they may differ based on how these problems were assessed. 

Grunder G, Wetzel H, Schloer R, et al. Subchronic antidepressant treatment with venlafaxine or imipramine and effects on blood pressure assessment by automatic 24 hour monitoring. Pharmacopsychiatry 1993 26 155. 

Initially, plasma and oral fluid specimens from patients (n = 21) on different antidepressant treatment were collected twice to assess if any of the studied analytes was likely to show a good correlation. The best results were obtained for venlafaxine (%CV for plasma/oral fluid concentrations ratio (f OF/PL) <21%). Therefore, the study was extended for this antidepressant by analysis of oral fluid and plasma specimens from five patients on venlafaxine treatment collected on four occasions. Daily doses of venlafaxine retard formulations were 75 mg for two patients, and 150 mg for the remaining participants. Collection of oral fluid (direct spitting into polypropylene tubes) and plasma (heparinized tubes) specimens was performed, when possible, before the next dose to ensure the drug was in the elimination phase. The dose and the time of collection was the same on the four different occasions for each patient. For the analysis, oral fluid and plasma specimens were centrifuged at 14 x 103 rpm, and 0.2 mL of the supernatant were extracted. In addition, correlation between the concentrations in the plasmatic free fraction and in oral fluid was also evaluated. Plasmatic proteins were eliminated by filtering 0.5 mL of plasma samples using Microcon filter devices Ultracel YM-3 (Millipore Corp., Billerica, MA, USA). 

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