What are the dosage directions for sildenafil (Viagra)?

Sildenafil Dosing Directions

For Erectile Dysfunction (Viagra)

Start with sildenafil 50 mg taken orally approximately 1 hour before sexual activity, with a maximum frequency of once daily, and adjust the dose to 25 mg or 100 mg based on efficacy and tolerability. 1

Initial Dosing Strategy

• Standard starting dose: 50 mg taken approximately 1 hour before anticipated sexual activity, not more than once daily 1
• The medication is taken as needed (on-demand), not as a scheduled daily medication 1
• Peak plasma concentrations occur within 1 hour of administration, with an elimination half-life of 3-5 hours 1

Dose Adjustment

• Increase to 100 mg if the 50 mg dose provides insufficient efficacy and is well-tolerated 1, 2
• Decrease to 25 mg in elderly patients, those with hepatic or renal impairment, or patients taking CYP3A4 inhibitors (ritonavir, saquinavir, ketoconazole, erythromycin, cimetidine) 1
• Most patients in clinical trials ultimately required either 50 mg or 100 mg for optimal efficacy 1

Evidence Supporting 100 mg Starting Dose

While 50 mg is the standard recommendation, emerging evidence suggests potential benefits of initiating at 100 mg:

• Men starting at 100 mg reported significantly less anxiety about subsequent intercourse attempts (56% felt no anxiety) compared to those starting at 50 mg (39% felt no anxiety) 2
• The 100 mg starting dose showed improved treatment satisfaction and sexual experience compared to 50 mg, with no increase in adverse events 2
• However, FDA-approved labeling and established guidelines support 50 mg as the standard starting dose 1

Timing and Administration

• Take approximately 1 hour before sexual activity 1, 3
• Maximum frequency: once daily 1, 3
• Sexual stimulation is required for the medication to be effective 4

Critical Safety Considerations

Absolute contraindication with nitrates: Never combine sildenafil with any nitrate medication due to risk of life-threatening hypotension 5, 6, 3

• Nitrates include: nitroglycerin (all forms), isosorbide mononitrate/dinitrate, and recreational "poppers" (amyl nitrate/nitrite) 6
• Wait at least 24 hours after sildenafil use before administering nitrates in a medical emergency (under close medical supervision) 4

Common Adverse Effects

• Headache (most common), flushing, dyspepsia, nasal congestion, and abnormal vision 5, 1
• Most adverse effects are transient, mild to moderate in severity, and related to vasodilation 5
• Discontinuation rate due to adverse effects is approximately 3% 5

Optimizing Treatment Response

If initial treatment appears unsuccessful, evaluate for modifiable factors before declaring treatment failure 4:

• Hormonal abnormalities requiring correction 4
• Food or drug interactions that may reduce efficacy 4
• Inadequate sexual stimulation (patient education needed) 4
• Improper timing or frequency of dosing 4
• Heavy alcohol use interfering with response 4
• Relationship issues with partner 4

After re-education, counseling on proper administration, and titration to maximum dosing, some initial non-responders become successful responders 4

Special Populations

• Cardiovascular disease/hypertension: Sildenafil remains effective (71% treatment response vs 27% placebo) 7
• Diabetes: Effective but slightly lower response rate (63% vs 24% placebo) 7
• Spinal cord injury (T6-L5): 75% reported improved erections with 50 mg dose 8
• Age ≥65 years: Consider starting at 25 mg; efficacy maintained across all age groups 1, 7

Monitoring and Follow-Up

• Periodic follow-up should assess efficacy, side effects, and any significant changes in health status or medications 4
• This is typically done at the time of prescription renewal 4

---

For Pulmonary Arterial Hypertension (Revatio)

The FDA-approved dose for pulmonary arterial hypertension is 20 mg administered orally three times daily, with doses spaced 4-6 hours apart. 6

PAH-Specific Dosing

• Standard dose: 20 mg three times daily (TID) 6
• Administer doses 4-6 hours apart 6
• Higher doses (>20 mg TID) are not recommended as clinical trials showed no greater efficacy 6
• Do not confuse this indication with erectile dysfunction dosing—these are completely different regimens 6

Critical Warning for PAH Patients

• Do not combine sildenafil 20 mg TID (for PAH) with sildenafil 25-100 mg (for erectile dysfunction) or other PDE-5 inhibitors 6
• Absolute contraindication with riociguat due to hypotension risk 5