The first time I noticed selective action of a drug was when I took a high dose paracetamol tablet for an attack of migraine. It works if taken in time. I also suffer from backache, often with acute exacerbations, precipitated by playing tennis. Even for these acute backaches, I swallow a larger dose of paracetamol which works well. It happened once when I was going through an acute exacerbation of the backache during which time I also got an attack of migraine. So as usual I swallowed paracetamol very early during the attack and the attack was aborted. I was surprised that though the drug aborted migraine attack, there was no change at all in my backache, which usually responded to paracetamol.

Today, in allopathic medical practice, I am seeing the same scenario. Sildenafil has been used for erectile dysfunction and causes a good erection in selected subjects, if taken in an adequate dose along with sufficient sexual arousal. Interestingly, this drug never picked up in Indian market. There is still fear in the minds of the Indian public that the drug can affect the heart and cause a heart attack, though this is not true. In fact, recently the drug is being used in diseases of lungs, heart and in gastrointestinal practice as described below.

1. Lungs and Chest : Patients having pulmonary hypertension have responded very well to this drug. Though no cure takes place, the fact is that all these years we had very few drugs, which reduced pulmonary hypertension.
2. Heart : In patients, who have suffered myocardial infarction the drug is being used for ventricular remodelling and further results are awaited.
3. GI Practice: Gastroenterologists doing manometric studies of oesophageal sphincter have been using sildenafil to study the relaxation of the oesophageal sphincter.

Coming to the subject of selective action of drugs in the body in different circumstances, I had the good fortune of using sildenafil in four patients of pulmonary hypertension. Really speaking, being a private non-academic physician, I was not interested in seeing the degree of fall of pulmonary artery pressure, but I always used to ask these patients whether they experienced erection more often while taking this drug. The answer was always ‘no’. I have also asked doctors who use this drug while doing manometric studies of the oesophagus to ask their patients whether after use of this drug, the patient experiences unusual erection. The answer has always been ‘no’.

This confirms my impression that we have to delve much deeper while studying the pharmaco-dynamics of a drug. In the patients which I have described above, how did the drug sildenafil know that we were giving the drug for the chest condition or GI condition and not with the motive of causing erection?