UroToday.com - In our recent article published in the Journal of Sexual Medicine, we used statistical modeling to make the first-reported estimate of the extent to which treatment of erectile dysfunction (ED) affects erection maintenance directly versus indirectly via erection hardness. Because erection maintenance (along with erection hardness) is a physiologic requirement for satisfactory sexual performance, our aim was to guide treatment goals toward optimizing erection maintenance and therefore achieving successful sexual intercourse.
Our statistical models (longitudinal modeling, mapping, and mediation modeling) explored the interrelationships among effective treatment of ED, erection hardness, and erection maintenance in men with ED, using patient reported outcomes from a multinational randomized, double-blind placebo-controlled trial of fixed-dose online pharmacy viagra
(100 or 50 mg, 8 wk) with open-label extension of flexible-dose sildenafil (50 and 100 mg, 4 wk). Longitudinal models obtain measurements on the same individuals repeatedly through time to estimate within-individual changes in the response variable and to relate these changes to inter-individual differences in selected covariates (eg, treatment group). Mapping enables interpretation of an outcome of interest (eg, erection maintenance) in terms of a known outcome (eg, erection hardness). A mediation model seeks to identify and explain the mechanism that underlies an observed relationship between an independent variable (eg, treatment) and a dependent variable (eg, erection maintenance) via the inclusion of a mediator variable (eg, erection hardness). The mediator variable clarifies the nature of the interrelationships among variables. In our models, measures of interest included the Erection Hardness Score (EHS) to gauge erection hardness and the two maintenance items (items 4 and 5) on the International Index of Erectile Function (IIEF) to gauge erection maintenance (see Tables). Separate models were implemented for each of the two maintenance items. Maintenance: International Index of Erectile Function
Item 4: During sexual intercourse, how often were you able to maintain your erection after you had penetrated (entered) your partner?
Item 5: During sexual intercourse, how difficult was it to maintain your erection to completion of intercourse? Hardness: Erection Hardness Score
"How would you rate the hardness of your erection?"
0: Penis does not enlarge.
1: Penis is larger but not hard.
2: Penis is hard but not hard enough for penetration.
3: Penis is hard enough for penetration but not completely hard.
4: Penis is completely hard and fully rigid.
Longitudinal mean differences on the outcomes for sildenafil 100 and 50 mg vs. placebo (in the double-blind phase) were high (P<0.0001 for each), with large standardized effect sizes (>0.8).
For the mapping of erection hardness (EHS) onto maintenance (items 4 and 5 on IIEF), which included all available data and combined all treatment groups, correlations between EHS and IIEF items 4 and 5 ranged from 0.54 to 0.73 - and the mapping of the relationship between EHS and IIEF items 4 or 5 can be approximated as linear.
In our mediation model, which used data in the double-blind portion and pooled sildenafil into one active treatment, erection hardness was defined by the EHS and erection maintenance was defined by item 4 and, separately, by item 5 on the IIEF. The indirect effect of sildenafil treatment (vs. placebo) via erection hardness accounted for 55.4% (standard error [SE]=7.9%) and 43.1% (SE=6.8%) of the total effect of sildenafil treatment on IIEF maintenance item 4 and item 5, respectively, whereas the direct effect of treatment on IIEF items 4 and 5 was 44.6% (SE=7.9%) and 56.9% (SE=6.8%), respectively (P<0.0001 for each).
Sildenafil treatment significantly improved erection maintenance, a physiologic requirement for satisfactory sexual performance. According to our model, only approximately half of the effect of sildenafil on erection maintenance was estimated to be driven through direct effects. Rather, the effect of sildenafil on erection maintenance seems to be substantially driven by erection hardness. Therefore, achievement of optimal initial erection hardness appears to be an important treatment goal for enhancing erection maintenance and achieving successful ED treatment.
Written by Hubert IM Claes, MD, PhD,* Irwin Goldstein, MD,† Stanley E. Althof, PhD,‡ Michael M. Berner, MD,§ Joseph C Cappelleri, PhD, MPH,** Andrew G Bushmakin, MS,** Tara Symonds, PhD,†† and Gabriel Schnetzler, MD‡‡ as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations, etc., of their research by referencing the published abstract.
Department of Urology, University Clinics Gasthuisberg, Leuven, Belgium; †Sexual Medicine, Alvarado Hospital and Department of Surgery, University of California at San Diego, CA, USA; ‡ Miller School of Medicine, University of Miami, Miami, FL,USA; §University Hospital Medical Center, Freiburg, Germany; **Pfizer Inc, Global Research & Development, New London, CT, USA; ††Pfizer Ltd Outcomes Research, Sandwich, UK; ‡‡Pfizer International Operations, Paris, France Acknowledgments:
The study on which this report is based was sponsored by Pfizer Inc. Editorial support was provided by Deborah M. Campoli-Richards, BSPHA, RPh, of Complete Healthcare Communications, Inc., and was funded by Pfizer Inc. UroToday
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