Transitioning from Cialis (Tadalafil) to Viagra (Sildenafil)
When transitioning from Cialis (tadalafil) to Viagra (sildenafil), patients should discontinue Cialis for at least 24-48 hours before starting Viagra to avoid potential drug interactions and ensure safety.
Pharmacological Differences
- Tadalafil (Cialis) has a significantly longer half-life of 17.5 hours compared to sildenafil (Viagra) with a half-life of approximately 4 hours 1
- Due to tadalafil's longer duration of action, patients should wait at least 24-48 hours after their last tadalafil dose before initiating sildenafil therapy 1
- Sildenafil typically begins working within 30-60 minutes of oral administration and remains effective for approximately 4-5 hours 2, 3
Dosing Recommendations
- Start with sildenafil 50 mg for most patients when transitioning from tadalafil 2
- Consider a lower initial dose (25 mg) for elderly patients, those with hepatic or renal impairment, or patients taking medications that may interact with PDE5 inhibitors 2, 4
- Dose adjustments can be made based on efficacy and tolerability, with improvement in erectile function related to higher dose (50 mg vs. 25 mg), though less additional benefit when increasing from 50 mg to 100 mg 2
Administration Guidelines
- Sildenafil should be taken approximately 30-60 minutes before anticipated sexual activity 2, 3
- While sildenafil is traditionally recommended on an empty stomach, research shows no significant loss of efficacy when taken with food, though absorption may be delayed 3
- Some patients may benefit from sublingual administration (crushing the pill under the tongue), which can reduce onset time to approximately 29 minutes 5
Safety Considerations
- PDE5 inhibitors should never be used concomitantly with nitrate medications due to risk of severe hypotension 1
- Patients on sildenafil should avoid taking nitroglycerin for at least 24 hours after sildenafil use 1
- Common adverse effects include headache (8.8%), dyspepsia (4.2%), nasopharyngitis (2.8%), and flushing (4.7%) 2, 6
- The incidence of serious adverse events is less than 2% for PDE5 inhibitors 2
Efficacy Expectations
- High-quality evidence shows that sildenafil significantly improves erections (73-88% improvement) compared to placebo (26-32%) 7, 2
- The weighted mean percentage of successful sexual intercourse attempts is 69% for sildenafil versus 35.5% for placebo 7
- Sildenafil is effective for erectile dysfunction of various etiologies, including diabetes, depression, cardiovascular disease, and prostate cancer 7
Cardiovascular Considerations
- For patients with cardiovascular disease, assess risk before transitioning between PDE5 inhibitors 1
- Low-risk patients can generally resume sexual activity and use PDE5 inhibitors safely 1
- Indeterminate-risk patients may require additional cardiovascular evaluation before using sildenafil 1
- High-risk patients should defer sexual activity until their cardiac condition is stabilized 1