The present invention relates to the treatment of impotence, and, more particularly, to the reversible pharmaceutical treatment of impotence using prostaglandin PGE.sub.2. 
In excess of about 10 million men in the United States alone exhibit sufficient erectile dysfunction that they can be characterized as effectively impotent.  Impotence in the human male can arise from a variety of psychological and physiological etiologies.  For example, long term diabetes, damage to the spinal cord, multiple sclerosis, or nerve damage resulting for example from lower abdomen or prostate surgery, and advancing age can result in impotence.  For differing reasons, each of the foregoing result in an inability to pressurize the corpora cavernosa, which can result in turn from either an insufficient arterial inflow on the supple side, or an insufficient increase in the venous output resistance to blood flow. 
A wide variety of mechanical means have been provided, in an effort to overcome erectile dysfunction.  For example, U.S. Pat.  No.  4,596,242 to Fischell discloses a surgically implantable hydraulic system, having a fluid reservoir and pressure generator, a patient manipulable valve, a pressure reservoir and a distensible member responsive to actuation of the valve.  A variety of other prior art mechanical implants and other devices for this purpose are described in the Background of the Invention section of the U.S. Pat.  No.  4,596,242. 
In addition to the mechanical efforts to overcome erectile dysfunction, pharmaceutical approaches have been tried as well.  For example, prostaglandin E1 has been observed to produce erection in some cases, but only by direct percutaneous injection into the penis. 
Notwithstanding the foregoing, there remains a need for an improved treatment of erectile dysfunction.  Surgical implantation and/or repeated injections range from disfavored to medically disadvantageous, and do not, as a whole, provide a satisfactory solution to the problem.  From a patient usability standpoint, erectile dysfunction would most advantageously be treated on a self-administration basis, without the need of surgical intervention or repeated injections of a pharmaceutical agent.  This problem has been addressed by the use of PGE.sub.2 as claimed in my U.S. application Ser.  No.  08/090,483.  However, some patients on using urethral placement of PGE.sub.2 materials have experienced urethral burning and aching within the genital area.  Therefore, there is a need for a PGE.sub.2 formulation which avoids these negative sensations but does not interfere with the effectiveness of the PGE.sub.2 for treatment of impotence.