24 June 2004

The ED Market Today

I came home last night from a festive dinner celebration of the first anniversary of Lilly and Icos' Cialis at the EDSA Shangrila Hotel. Cialis is tadalafil, an erectile dysfunction (ED) medication that is currently competing with market leader Viagra (sidenafil citrate) made by Pfizer. In the Philippine market, there are 3 erectile dysfunction medications, the two just mentioned, and Bayer HealthCare and GSK's Levitra or vardenafil HCl.

Known as impotence two decades ago, erectile dysfunction (ED) is a medical condition wherein a man cannot get an erection to have sex or cannot keep an erection long enough to finish having sex (what is termed successful sexual intercourse). Current data says that 50% of men over 40 has some form of ED, and roughly this translates to more than 50 million males worldwide, although many cases may be temporary. Local data on Filipino males is still vague and sketchy, as being labeled "impotent" carries a dreadful stigma in our macho culture. Local urologists, however, will tell you that more and more Filipino males are coming out with this problem. Proof of this is the more than P500 million sales of Viagra locally since its introduction on April 1998 and noted urologist Dr. Eduardo Gatchalian's comment a year ago that,
"Maybe in the field of human relations, Viagra should be given the Nobel Prize." [INQ7.net]
Psychiatrist Ma. Luz Casimiro-Querubin of the University of the Philippines, said that:
"Sex is very important in marriage. The relationship of husbands and wives through the years will change. Lovemaking, in fact, becomes difficult after several years. Wives sometimes look at it as a chore. The reality is that marital relationships will develop according to certain interpersonal dynamics. Sexual relationship moves in cadence and in accordance with how that relationship improves or suffers through the years." [INQ7.net]
There are various causes of ED and, in some cases, unexpected. Alcoholism, chronic kidney and liver problems, heart disease and diabetes are some of the more common causes. A fractured pelvis, spinal injury or nerve damage from an operation on the prostate gland or rectum can also permanently damage erectile tissue and cause ED. Of course, not to be forgotten are the psychogenic causes: a recent divorce, sexual assault or marital discord.

The "fils," that is how I like to call the ED medications, because they have similar endings (sildenafil, tadalafil, and vardenafil) are all phospodiesterase-5 or PDE-5 inhibitors. Phospho...wwhat??? Don't be alarmed. I'm not getting technical here. I just want you to understand what happens when you have ED. In our bodies, there is a nitric oxide system (NOS) that causes relaxation of smooth muscle in blood vessel walls, ie, vasodilation, in various organ systems, including the muscles of the penis. A mediator termed cGMP, facilitates the NOS pathway. PDE-5 catalyzes the degradation of cGMP, and prevents erection from happening. When males get sexually excited, the normal reaction is to increase blood flow to the penis. The NOS promotes this process and results in an erection. What Viagra, Cialis, and Levitra accomplishes is to inhibit PDE from destroying cGMP, and thereby lengthen and promote penile erection.

Courtesy of USRF

This is also where the drug interaction and side-effects explanation come in. In patients taking heart medications like nitrates, or alpha-blockers, combination with any of the "fils," can cause a sudden blood pressure drop which can be fatal. Side effects like headache and muscle pain are due to overlapping PDE specificity of the "fils." You see, there are many PDE's in the body. There's PDE-1, PDE-2, so forth and so on, in charge with different organ systems. PDE-5 is for the penis. Viagra, unlike Cialis and Levitra, exhibit overlaps in its PDE specificity and hence, the observable side-effects.

In summary, all 3 "fils" have about 70% efficacy. Side effects are almost similar, except that blue discoloration of vision (overlap with PDE-6 in the retina) is seen only with Viagra (<0.5%) and muscle aches only with Cialis (~5%). Vasodilatory side effects (headaches, nasal congestion, flushing) are common with all, but are mild, and only rarely cause men to drop out of clinical trials (2-3% quit rate). All 3 will carry a contra-indication in men using organic nitrates. Otherwise, the long half-life of Cialis of about 17.5 hours is noteworthy, earning this drug the nickname "weekender Cialis" as a single dose taken on Friday would still be exerting an effect Sunday (or even Monday). [USRF report]

Guys, whatever your choice is, don't self-medicate. Don't also fall for those Internet scams that offer unbelievably low discounted prices of medicines that can be bought without a prescription! The most popular of these is Viagra and other erectile dysfunction drugs, weight loss medicines and drugs that "enlarge" whatever part of your anatomy. See your physician so you can get an accurate evaluation and a proper prescription.

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