Cialis (Tadalafil) and Viagra (Sildenafil)

Both Cialis (Tadalafil) and Viagra (Sildenafil) belong to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors, which enhance erectile function by increasing blood flow to the penis.

1. Nitric Oxide Release – Sexual stimulation triggers the release of nitric oxide (NO) in the corpus cavernosum (erectile tissue of the penis).
2. cGMP Production – NO activates the enzyme guanylate cyclase, increasing cyclic guanosine monophosphate (cGMP) levels. cGMP relaxes smooth muscle cells, allowing blood vessels to expand and increasing blood flow to the penis.
3. PDE5 Inhibition – Both drugs block the enzyme PDE5, which normally breaks down cGMP. This prolongs cGMP activity, sustaining smooth muscle relaxation and enhancing the erectile response.
4. Increased Blood Flow – The dilation of blood vessels improves blood circulation to the penis, facilitating and maintaining an erection.

• Cialis (Tadalafil) has a longer half-life (~17.5 hours), allowing effects to last up to 36 hours, making it suitable for both on-demand and daily use.
• Viagra (Sildenafil) has a shorter half-life (~4 hours), with effects lasting 4 to 6 hours, making it better for planned sexual activity.

Both require sexual stimulation to be effective and do not cause automatic erections.

Contraindications

Both Cialis (Tadalafil) and Viagra (Sildenafil) are contraindicated in the following cases:

1. Use with Nitrates – Concomitant use with nitrates (e.g., nitroglycerin, isosorbide mononitrate/dinitrate) can cause severe hypotension (dangerous drop in blood pressure).
2. Severe Cardiovascular Disease – Not recommended for patients with: 
   • Unstable angina
   • Recent heart attack (within the last 90 days)
   • Severe heart failure
   • Uncontrolled hypertension or hypotension

1. History of Stroke – Patients with a recent stroke (within the last 6 months) should avoid these medications.
2. Severe Liver or Kidney Disease – Use is contraindicated in severe hepatic impairment and end-stage renal disease requiring dialysis.
3. Retinal Disorders – Non-arteritic anterior ischemic optic neuropathy (NAION), a condition that can lead to vision loss, has been reported in some PDE5 inhibitor users.
4. Hypersensitivity – Contraindicated in individuals with a known allergy to tadalafil, sildenafil, or any inactive ingredients in the formulation.
5. Concurrent Use of Riociguat – A medication used for pulmonary hypertension that, when taken with PDE5 inhibitors, can cause severe hypotension.

Precautions

1. Hypotension Risk – Use cautiously in patients taking alpha-blockers (e.g., tamsulosin, doxazosin) due to the risk of low blood pressure.
2. Priapism (Prolonged Erection) – If an erection lasts more than 4 hours, immediate medical attention is required to prevent permanent damage.
3. Hearing or Vision Loss – Sudden hearing or vision loss has been reported; patients should discontinue use and seek medical help if this occurs.
4. Liver or Kidney Impairment – Dose adjustments may be needed in moderate kidney or liver dysfunction to prevent drug accumulation.
5. Alcohol Consumption – Excessive alcohol intake can increase the risk of side effects like dizziness, hypotension, and headache.
6. Bleeding Disorders – Use cautiously in individuals with bleeding disorders or those taking anticoagulants (e.g., warfarin) due to potential increased bleeding risk.
7. Elderly Patients – Older adults may be more sensitive to side effects such as dizziness and low blood pressure.

Common Side Effects

These side effects are usually mild and temporary:

• Headache
• Flushing (redness or warmth in the face, neck, or chest)
• Dizziness
• Nasal congestion or runny nose
• Indigestion or upset stomach
• Muscle or back pain (more common with Cialis)
• Mild vision disturbances (e.g., blurred vision, sensitivity to light, or color tinge, more common with Viagra)

Pregnancy

• Category: Both Cialis (Tadalafil) and Viagra (Sildenafil) are classified as FDA Pregnancy Category B (Viagra) and Category C (Cialis). This means that: 
  • Viagra: Animal studies have not shown direct harm to the fetus, but human data is limited.
  • Cialis: Animal studies have shown potential adverse effects, but there are no well-controlled studies in pregnant women.
• Use During Pregnancy: 
  • These medications are not typically prescribed for women, including those who are pregnant, as they are primarily used for erectile dysfunction and pulmonary arterial hypertension (PAH).
  • For PAH treatment in pregnant women, alternative options are generally preferred.

Breastfeeding

• Presence in Breast Milk: It is unknown whether sildenafil or tadalafil is excreted into human breast milk.
• Potential Risks: 
  • The effects of these drugs on breastfed infants are not well studied, so their safety cannot be confirmed.
  • Due to possible systemic effects on the infant (such as cardiovascular effects), breastfeeding while taking these medications is not recommended.
• Recommendation: 
  • Alternative medications should be considered if treatment is necessary.
  • If a woman requires these medications, she should consult a healthcare provider about discontinuing breastfeeding.

• Temperature: Store at 68°F to 77°F (20°C to 25°C).
• Protection: Keep away from heat, moisture, and direct light.
• Avoid Extreme Conditions: Do not store in bathrooms or areas with high humidity.
• Child Safety: Keep all medications out of reach of children.
• Disposal: 
• Do not flush unused medication or pour it down a drain.
• Dispose of properly according to local regulations or pharmacy take-back programs.
• Packaging: Keep in the original container with the lid tightly closed.