Tadalafil and Sildenafil Dosing for Erectile Dysfunction
Tadalafil (Cialis) Dosing
For as-needed use, start with tadalafil 10 mg taken prior to anticipated sexual activity, with dose adjustment to 20 mg or down to 5 mg based on tolerability rather than efficacy expectations, since tadalafil does NOT show dose-dependent improvement between these doses. 1, 2
As-Needed Dosing
- Starting dose: 10 mg taken prior to sexual activity 1
- May increase to 20 mg (maximum dose) or decrease to 5 mg based on individual tolerability 1
- Maximum dosing frequency is once per day 1
- Effective for up to 36 hours after dosing 1
- Sexual stimulation is required for effectiveness 2
Daily Dosing Option
- Starting dose: 2.5 mg once daily, taken at approximately the same time every day 1
- May increase to 5 mg once daily based on efficacy and tolerability 1
- This eliminates the need to time medication with sexual activity, providing spontaneity for couples 2
- Taken without regard to timing of sexual activity 1
Key Clinical Pearl
The choice between 10 mg and 20 mg should be based primarily on tolerability rather than expecting dramatically better efficacy at higher doses, as tadalafil does NOT show dose-dependent improvement in erectile function between 5 mg, 10 mg, and 20 mg doses. 2
Sildenafil (Viagra) Dosing
Start with sildenafil 50 mg taken approximately 1 hour before sexual activity, with dose titration to 100 mg if inadequate response or reduction to 25 mg for tolerability concerns or special populations. 3, 1, 4
Standard Dosing Protocol
- Starting dose: 50 mg taken approximately 1 hour before sexual activity 3, 4
- Maximum dose: 100 mg once daily 3, 4
- Minimum dose: 25 mg for elderly, hepatic/renal impairment, or drug interactions 3, 4
- Take no more than once daily 3, 4
- Sexual stimulation is mandatory for effectiveness 3
Dose Titration Strategy
- If 50 mg is inadequate, increase to 100 mg (maximum dose) 3
- Unlike tadalafil, sildenafil shows dose-related improvement in erectile function (50 mg superior to 25 mg) 2, 3
- At least 5 separate attempts at maximum dose before declaring treatment failure 2
Timing and Administration
- Take approximately 1 hour before sexual activity 3, 4
- Avoid taking with large meals, which delays absorption 3
- Effective within 30 to 120 minutes after oral dosing in fasting state 5
Special Populations and Dose Adjustments
Renal Impairment (Tadalafil)
- Creatinine clearance 30-50 mL/min: Start with 5 mg, maximum 10 mg once every 48 hours 1
- Creatinine clearance <30 mL/min or hemodialysis: Maximum 5 mg once every 72 hours 1
- Once-daily tadalafil NOT recommended for creatinine clearance <30 mL/min 1
Hepatic Impairment (Tadalafil)
- Mild or moderate (Child-Pugh Class A or B): Maximum 10 mg once per day 1
- Severe hepatic impairment: Generally not recommended 2
Special Populations (Sildenafil)
- Hepatic impairment: Start with 25 mg 3
- Renal impairment: Start with 25 mg 3
- CYP3A4 inhibitors (ritonavir, ketoconazole, erythromycin, cimetidine): Start with 25 mg 3, 4
- Elderly patients: Consider starting with 25 mg 4
Critical Safety Considerations
Absolute Contraindications
- Concurrent nitrate use is absolutely contraindicated due to severe hypotension risk 3, 2
- Wait 24 hours after sildenafil before administering nitrates in emergencies 3, 2
- Wait 48 hours after tadalafil before administering nitrates in emergencies 2
High-Risk Cardiovascular Conditions
- Unstable or refractory angina 3
- Uncontrolled hypertension 3
- Recent MI or stroke (within 2 weeks) 3
- Severe heart failure (NYHA class II or higher) 3
- These conditions require cardiac stabilization before treatment 3
Low-Risk Patients (Safe to Prescribe)
- Asymptomatic coronary artery disease with <3 risk factors 2
- Controlled hypertension 2
- Mild, stable angina 2
- Successful coronary revascularization 2
- Uncomplicated past MI 2
- Mild valvular disease 2
- CHF (NYHA class I) 2
Common Pitfalls and Treatment Failures
Before Declaring Treatment Failure
An adequate trial consists of at least 5 separate attempts at maximum dose before declaring treatment failure. 2, 3
Evaluate These Modifiable Factors:
- Sexual stimulation is mandatory for effectiveness 2, 3
- Proper timing of medication (1 hour before for sildenafil, up to 36 hours for tadalafil) 3, 1
- Avoid large meals with sildenafil 3
- Heavy alcohol use 2
- Hormonal abnormalities (check testosterone) 2
- Drug interactions 2
- Relationship issues with partner 2
Special Populations: Efficacy Expectations
Diabetes and Post-Prostatectomy
- Men with diabetes and post-prostatectomy patients have more severe ED at baseline and may respond less robustly to PDE5 inhibitors 2, 3
- However, treatment response remains significantly greater than placebo in these populations 6, 7
- In diabetic men, 56% achieved improved erections with sildenafil vs 10% with placebo 6
Testosterone Deficiency
- For men with both ED and testosterone deficiency, combining tadalafil with testosterone therapy is more effective than tadalafil alone 2
- Testosterone therapy alone is NOT effective monotherapy for ED 2
- Check total testosterone, free testosterone, and SHBG levels if response is suboptimal 2
Adverse Effects
Common Side Effects (Tadalafil)
- Dyspepsia 2
- Headache 2
- Back pain 2
- Nasal congestion 2
- Myalgia 2
- Lower rates of flushing compared to other PDE5 inhibitors 2