Although Viagra, Levitra, and Cialis all work by inhibition of PDE5, tadalafil’s distinguishing pharmacologic feature is its longer half-life (17.5 hours) compared with Viagra and Levitra (4-5 hours). This longer half-life results in a longer duration of action and is, in part, responsible for the Cialis nickname of the “weekend pill.” This longer half-life also is the basis of current investigation for tadalafil’s use in pulmonary arterial hypertension as a once-daily therapy. At present, sildenafil (trade name Revatio) is approved in various regions worldwide as a 3-times daily therapy for pulmonary arterial hypertension.

Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and corpus cavernosal smooth muscle. This response is mediated by the release of nitric oxide (NO) from nerve terminals and endothelial cells, which stimulates the synthesis of cGMP in smooth muscle cells. Cyclic GMP causes smooth muscle relaxation and increased blood flow into the corpus cavernosum. The inhibition of phosphodiesterase type 5 (PDE5) enhances erectile function by increasing the amount of cGMP. Tadalafil (as well as sildenafil and vardenafil) inhibits PDE5. Because sexual stimulation is required to initiate the local release of nitric oxide, the inhibition of PDE5 by tadalafil has no effect in the absence of sexual stimulation. A 20 mg dose of tadalafil is comparable to a 100 mg dose of sildenafil (Viagra). However, the recommended starting dose of Cialis in most patients is 10 mg, taken prior to anticipated sexual activity. The dose may be increased to 20 mg or decreased to 5 mg, based on individual efficacy and tolerability

Tadalafil is currently undergoing clinical trials for the treatment of pulmonary arterial hypertension. In patients with pulmonary arterial hypertension, it is believed that there is an imablance of the PDE5/NO system in the pulmonary vasculature that favors selective vasoconstriction of the pulmonary artery. Investigation of tadalafil in this disease assumes that PDE5 inhibition will result in pulmonary artery vasodilation, thus lowering pulmonary artery pressure and pulmonary vascular resistance. These physiologic changes may then reduce the workload of the right ventricle of the heart. Right heart failure is the main consequence of pulmonary arterial hypertension.

It is usually recommended to start with a dosage of 50 mg and then lower or raise the dosage as appropriate. The drug is sold in three dosages (25, 50, and 100 mg), all three costing about US$10 per pill. Name-brand Viagra sildenafil is not scored and a fairly hard coating makes it more difficult to accurately cut the pills in half, even with a pill cutter.

Viagra pills are blue and diamond-shaped with the words “Pfizer” on one side, and “VGR xx” (where xx stands for “25″, “50″ or “100″, the dose of that pill in milligrams) on the other.

Phase I clinical trials under the direction of Ian Osterloh suggested that the drug had little effect on angina, but that it could induce marked penile erections. Pfizer therefore decided to market it for erectile dysfunction, rather than for angina. The drug was patented in 1996, approved for use in erectile dysfunction by the Food and Drug Administration on March 27, 1998, becoming the first pill approved to treat erectile dysfunction in the United States, and offered for sale in the United States later that year. It soon became a great success: annual sales of Viagra in the period 1999–2001 exceeded $1 billion.

The British press portrayed Peter Dunn and Albert Wood as the inventors of the drug, a claim which Pfizer disputes. Their names are on the manufacturing patent application drug, but Pfizer claims this is only for convenience.

Even though sildenafil is available by prescription from a doctor, it was advertised directly to consumers on US TV (famously being endorsed by former United States Senator Bob Dole and football star Pelé). Numerous sites on the Internet offer Viagra for sale after an “online consultation”, a mere web questionnaire. The “Viagra” name has become so well known that many fake aphrodisiacs now call themselves “herbal Viagra” or are presented as blue tablets imitating the shape and colour of Pfizer’s product. Viagra is also informally known as “Vitamin V”, “the Blue Pill”, as well as various other nicknames.

In February 2007, it was announced that Boots the Chemist would trial over the counter sales of Viagra in stores in Manchester, England. Men aged between 30 and 65 would be eligible to buy four tablets after a consultation with a pharmacist.

Pfizer’s worldwide patents on sildenafil citrate will expire in 2011–2013. The UK patent held by Pfizer on the use of PDE5 inhibitors as treatment of impotence was invalidated in 2000 because of obviousness; this decision was upheld on appeal in 2002.

Anorgasmia (often related to delayed ejaculation in males) is a form of sexual dysfunction sometimes classified as a psychiatric disorder in which the patient cannot achieve orgasm, even with “adequate” stimulation. However, it can also be caused by medical problems such as diabetic neuropathy, multiple sclerosis, pelvic trauma, hormonal imbalances, total hysterectomy, spinal cord injury and cardiovascular disease. Anorgasmia is far more common in females than in males and is especially rare in younger men.

A common cause of anorgasmia, in both men and women, is the use of anti-depressants, particularly selective serotonin reuptake inhibitors. Though reporting of anorgasmia as a side-effect of selective serotonin reuptake inhibitors is not precise, it is estimated that 15-50% of users of such medications are affected by this condition. Some popular selective serotonin reuptake inhibitors are escitalopram, paroxetine, fluoxetine and sertraline. The chemical amantadine has been shown to cure selective serotonin reuptake inhibitor-induced anorgasmia in some, but not all, people.

Other sex researchers have defined premature ejaculation as occurring if the man ejaculates within two minutes or less of penetration; however, a survey by Alfred Kinsey in the 1950s demonstrated that three quarters of men ejaculated within two minutes of penetration in over half of their sexual encounters. Today, most sex therapists understand premature ejaculation as occurring when a lack of ejaculatory control interferes with sexual or emotional well-being in one or both partners.

Most men experience premature ejaculation at least once in their lives. Often adolescents and young men experience “premature” ejaculation during their first sexual encounters, but eventually learn ejaculatory control. Because there is great variability in both how long it takes men to ejaculate and how long both partners want sex to last, researchers have begun to form a quantitative definition of premature ejaculation. Current evidence supports an average intravaginal ejaculation latency time of six and a half minutes in 18-30 year olds. If the disorder is defined as an intravaginal ejaculation latency time percentile below 2.5, then premature ejaculation could be suggested by an intravaginal ejaculation latency time of less than about one and a half minutes. Nevertheless, it is well accepted that men with intravaginal ejaculation latency times below 1.5 minutes could be “happy” with their performance and do not report a lack of control and therefore do not suffer from Premature ejaculation. On the other hand, a man with 2 minutes intravaginal ejaculation latency time could present with perception of poor control over his ejaculation, distressed about his condition, has interpersonal difficulties and therefore be diagnosed with Premature ejaculation.

Sexual desire disorders or decreased libido can be caused by a decrease in normal estrogen (in women) or testosterone (in both men and women) production. Other causes may be aging, fatigue, pregnancy, medications (such as the SSRIs) or psychiatric conditions, such as depression and anxiety. Loss of libido from SSRIs usually reverses after SSRIs are discontinued, but in some cases it does not. This is known as PSSD.
Sexual arousal disorders were previously known as frigidity in women and impotence in men, though these have now been replaced with less judgmental terms. Impotence is now known as erectile dysfunction, and frigidity has been replaced with a number of terms describing specific problems with, for example, desire or arousal.

For both men and women, these conditions can manifest as an aversion to, and avoidance of, sexual contact with a partner. In men, there may be partial or complete failure to attain or maintain an erection, or a lack of sexual excitement and pleasure in sexual activity.

There may be medical causes to these disorders, such as decreased blood flow or lack of vaginal lubrication. Chronic disease can also contribute, as well as the nature of the relationship between the partners. As the success of sildenafil (Viagra) attests, most erectile disorders in men are primarily physical, not psychological conditions.

Orgasm disorders are a persistent delay or absence of orgasm following a normal sexual excitement phase. The disorder can occur in both women and men. Again, the SSRI antidepressants are frequent culprits — these can delay the achievement of orgasm or eliminate it entirely.

Sexual pain disorders affect women almost exclusively and are known as dyspareunia (painful intercourse) and vaginismus (an involuntary spasm of the muscles of the vaginal wall that interferes with intercourse). Dyspareunia may be caused by insufficient lubrication (vaginal dryness) in women.

Emotional factors affecting sex include both interpersonal problems (such as marital/relationship problems, or lack of trust and open communication between partners) and psychological problems within the individual (depression, sexual fears or guilt, past sexual trauma, sexual disorders and so on).

Physical factors include drugs (alcohol, nicotine, narcotics, stimulants, antihypertensives, antihistamines, and some psychotherapeutic drugs); injuries to the back, problems with an enlarged prostate gland, problems with blood supply, nerve damage (as in spinal cord injuries); or disease (diabetic neuropathy, multiple sclerosis, tumors, and, rarely, tertiary syphilis); failure of various organ systems (such as the heart and lungs); endocrine disorders (thyroid, pituitary, or adrenal gland problems); hormonal deficiencies (low testosterone, estrogen, or androgens); and some birth defects.

The causes of erectile dysfunction may be physiological or psychological. Physiologically, erection is a hydraulic mechanism based upon blood entering and being retained in the penis, and there are various ways in which this can be impeded, most of which are amenable to treatment. Psychological impotence is where erection or penetration fails due to thoughts or feelings (psychological reasons) rather than physical impossibility; this can often be helped. Notably in psychological impotence there is a very strong placebo effect.

Erectile dysfunction, tied closely as it is to cultural notions of potency, success and masculinity, can have devastating psychological consequences including feelings of shame, loss or inadequacy; often unnecessary since in most cases the matter can be helped. There is a strong culture of silence and inability to discuss the matter. In fact around 1 in 10 men will experience recurring impotence problems at some point in their lives.

Folk remedies have long been advocated, with some being advertised widely since the 1930s. The introduction of the first pharmacologically approved remedy for impotence, sildenafil (trade name Viagra), in the 1990s caused a wave of public attention, propelled in part by heavy advertising.

The Latin term impotentia coeundi describes simple inability to insert the penis into the vagina. It is now mostly replaced by more precise terms. The study of erectile dysfunction within medicine is covered by andrology, a sub-field within urology.

A statistically highly significant improvement in erectile function occurred in over 70 per cent of 1000 cases treated at a Harley street clinic with a variety of different forms of testosterone. This was particularly marked with the more powerful oral preparation, Restandol, which sometimes needed to be given in high but safe doses, and with the pellet implants.

Though this use of testosterone to help erection problems is controversial and not acknowledged by some authorities, which say it only increases frustration without giving back the means to perform, this is certainly not his experience in this large group of patients. The efficiency of testosterone in restoring potency is a common experience with doctors prepared to give it an adequate trial.

It was even recognised over 50 years ago in the article on the ‘male climacteric’ by Drs Heller and Myers in an article on”The Male Climacteric” in JAMA in 1944. They found that erectile function returned in nearly all of their testosterone deficient patients when they gave the hormone and went away again when they stopped.

Even though it is more difficult to restore function than desire, unless the source of the problems is obviously psychological or mechanical, it seems logical to investigate the testosterone balance of the patient, and restore it to normal as the first stage of treatment. Even if erections are not greatly improved by this alone, libido and confidence usually are. The most commonly used methods such as penile injections of prostaglandins, as in Caverject, then seem to work much better. Recent experience  has shown this to be particularly true when Viagra and Testosterone are combined to cure over 95% of impotence problems.

In chronic disease on the other hand susceptibility becomes gradually low because of long continued suffering and organic changes – hence they require low or medium potencies. Carelessness in selecting correct potency in such cases may lead to Dr. Kent’s 1st or 2nd observation which is undoubtedly not at all desirable to any homoeopathic physician. But in chronic diseases without gross organic changes, e. g. migraine, neuralgias, most of the paralysis, neurosis etc., high potencies act curatively if given in single or repeated doses as the case may be. Too low potencies in repeated doses even in organic chronic disease may lead to observation No. 10 while too high potencies in comparison to patient’s susceptibility leads to observation No.3 and the patient may have to pass through grievous suffering before amelioration or cure takes place. Difficult and incurable cases require medium and low potencies to start with. In my opinion 50-millesimal potency is best for this purpose. Even an incurable case may turn to curable stage after the use of few successive potencies in this scale.

In children and young adults there is generally no wear and tear of organs and tissues. As such they require high potencies for an early cure. But in old age the susceptibility becomes generally low because of wear and tear and senile degeneration, hence they generally require low or medium potencies.

Females in villages of our country are generally less exposed to worries, anxieties and complications of life. Hence their nervouse system generally is of quiet nature having a moderate degree of susceptibility requiring medium potencies. But irritable, highly strung males possess a high degree of susceptibility requiring generally high potencies. Persons engged in highly intellectual and mental work, e. g. doctors, lawyers, ministers etc. generally require high potencies because of their high profile and high susceptibility. On the other hand, persons engaged in physical labour without much of mental exertion generally require low or medium potencies because of their low susceptibility.

Disease begins in the dynamic plane and ultimately settles in organs or tissues. As such in all diseases we get functional symptoms to start with followed by secondary organic or pathological symptoms. Hence the more the disease is in the dynamic plane, the higher should be the potency and the more it is in the organic plane the lower should be the potency. This is why we may be able to abort many violent acute diseases in their beginning stage with repeated doses of high potencies. But the problem arises when we come across to types of susceptibility in a patient at the same time – the susceptibility of the patient as a whole being high while the susceptibility of his affected tissue is low, e. g. in tumour or chronic eczema etc. In such cases it is better to start with medium or low potencies and the moment reaction sets in, the potency should be changed to higher one. The growths or organic changes may not be reversible with the help of these high potencies but the disease processs will be cured. The end product of the disease may require surgical interference for their removal so as to avoid mechanical effects of the same.

Primary manifestation of psora, sycosis and syphilis require high potencies in repeated and large doses for an early and permanent cure but the secondary effects of these conditions require medium or low potencies to start with.

In mental diseases the susceptibility is generally very high, but high potencies are contra-indicated in such cases to start with because of the possibility of too violent an aggravation. I have seen a single dose of 30th potency to act curatively in such cases for months together. In diseases like bronchial asthma, organic heart diseases, diabetes mellitus, hypertension, cirrhosis of the liver, pre-tubercular and pre-cancerous states, piles, brain tumour, peptic ulcer etc. 50-millesimal potency give wonderful result.

From what has been stated so far, it is probably clear that no hard and fast rule is possible for the selection of potency. Susceptibility is the only guide in this respect. But to gauge the susceptibility of a patient, it requires thorough knowledge of the allied subjects of medicine including hygience, unbiased expeprience, attention in observing, freedom from prejudice and clear conception of the basic principles of homoeopathy including remedy response and second prescription.

Before I conclude I would like to cite few cured cases to substantiate my view that it is not only the selection of medicine but the accuracy of potency and doses that are the prerequisites in arriving at the highest ideal of cure.

A case of acute headache with all the symptoms of Belladonna did not respond at all to 30th or 200th potency, but magically cured with a single dose of Belladonna 10M.

A case of abdominal colic in a girl of 13/14 years of age, persisting for about 2 weeks with all symptoms of Colocynth did not respond to Colocynth 6 and 30 but cured completely with Colocynth 50M – four doses given at an interval of about half an hour.

Case of whooping cough with all symptoms of Drosera did not respond well to Drosera 30 but cured within 3 or 4 days by repeated doses of Drosera 1M and 10M.

Several obstinate skin diseases were cured within few weeks or months with repeated doses of 6th or 12th potency or with 50-millesimal potency when 200th or 1M potency produced only prolonged aggravation without being followed by amelioration or there was no remedy response at all.

Cases of Bell’s Palsy or hemiplegia with all symptoms of Causticum did not respond at all to Causticum 30 but cured within a very short time with repeated (deviated) doses of 1M or 10M potency.

Cases of piles with all symptoms of Acid Nitric or Thuja did not respond satisfactorily to the 200th or 1M but responded nicely to 50-millesimal potency of these drugs.

A case of ascites due to cirrhosis of the liver responded unexpectedly to China in 50-millesimal potency when no satisfactory result had been obtained by prescribing centesimal potency.

A case of neuralgic headache with symptoms of Chelidonium did not respond to 30th or 200th potency, but cured within 24 hours with 3 or 4 doses of Chelidonium CM given at intervals of 3/4 hours.