Viagra is a household name for erectile dysfunction medication. The active ingredient in the drug is actually Sildenafil Citrate, some just called it Sildenafil. Despite its popularity of treating erectile dysfunction, in its initial phase, the medication was intended to be an anti-hypertensive drugs. This is because the drug is mainly responsible to inhibit phosphodiesterase type-5 (PDE-5) and increase cyclic guanosine monophosphate (cGMP). Ultimately, it results in relaxation of pulmonary circulation and smooth muscles lining them. 

What type of condition requires Sildenafil?

The MIMS (Monthly Index of Medical Specialities) guideline in Malaysia, stated that active ingredients of Sildenafil are safe and licensed to treat for two conditions. These conditions are erectile dysfunction and pulmonary arterial hypertension. Though special precautions are required for those who have kidney disease, liver disease, pregnant women, breastfeeding mothers and individuals who are on certain medications. Such medications are alpha-blockers, ritonavir and drugs that cause CYP3A4 inhibition. CYP3A4 inhibiting drugs include:

  • Macrolide antibiotics
  • Anti-HIV medications
  • Calcium channel blockers
  • Steroids
  • Antidepressants
  • Herbals or traditional medications

Dosage and prescription of Sildenafil to this group of people should be monitored closely.

What is the safe dosage and how to take Sildenafil?

In general, erectile dysfunction medications can be taken with or without food. However, heavy and fatty meals can actually reduce the efficacy of Sildenafil. This is because the drugs are metabolised in the liver similar to fatty food. Eating excessive fatty food can and may interrupt the metabolization. Not to mention, excessive meal before sex is never commended. 

The medication comes in oral and intravenous form. The most common form in pharmacies is the oral or tablet form. The dosage for Sildenafil tablets depends highly on the targeted effect. Such as adult patients with pulmonary arterial hypertension, 5-20mg, thrice daily via oral tablet is sufficient. While children of pulmonary arterial hypertension are based on their weight.

Besides that, higher doses are given to treat erectile dysfunction. This is only applicable for adults. The recommended doses are 50mg taken 1 hour prior to coitus and patients may adjust the dose depending on how their body responds to the medication. Keep in mind that the maximum safe dosage of Sildenafil is 100mg daily.

While in the subject of dosage, overdosage of the drugs can be a real concern. This is because there is no antidote to counteract Sildenafil overdose. The most common features of overdose are severe hypotension, fainting and prolonged erection lasting more than 4 hours. Since hypotension is the main distress, the best method of care for Sildenafil overdose is symptomatic treatment for the condition.  

What are the side effects of Sildenafil?

There are some adverse side effects that can occur due to taking this medication. These effects include:

  • Visual disturbances (photophobia, eye pain, redness, etc)
  • Gastrointestinal problems (vomiting, diarrhoea, etc)
  • Priapism (painful erection)
  • Fluid retention
  • Headache
  • Dyspepsia
  • UTI
  • Haematuria 
  • Hypotension
  • Cough
  • Rhinitis
  • Seizures
  • Hypersensitivity reactions (rare)

Furthermore, the more serious and possibly fatal reactions are cardiovascular problems. This includes arrhythmia, unstable angina, myocardial infarct and tachycardia. 

Who are the people that cannot take this medication? 

Based on the list of Sildenafil side effects, individuals that should never take this drug are:

  • Known hypotensive individuals
  • Cardiovascular disease patients
  • Liver disease patients
  • History of recent myocardial infarction or stroke
  • History of visual loss due to non-arteritic anterior ischaemic optic neuropathy in 1 eye
  • Patient who are on nitrates or nicorandil based drugs

Though hypertensive patient who are on anti-hypertensive is not included in the list above, they should always be wary of taking Sildenafil. This is because they will be more likely to experience severe hypotension as the medication itself causes pulmonary vessels relaxation. 


Please refer to a doctor before taking 100mg Sildenafil to confirm that it is suitable for you.

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