What is the appropriate dosing regimen for sildenafil (Viagra) and should it be taken as needed?

Sildenafil (Viagra) Dosing and Administration

Sildenafil should be taken as needed, starting at 50 mg approximately 1 hour before sexual activity, with a maximum frequency of once daily. 1, 2

Standard Dosing Protocol

• Starting dose: 50 mg taken approximately 1 hour before anticipated sexual activity 2, 3
• Maximum frequency: Once daily 2, 3
• Dose titration based on response:
  • If 50 mg is inadequate after an adequate trial, increase to 100 mg (maximum dose) 2, 4
  • If side effects are problematic, reduce to 25 mg 2, 3

Defining an Adequate Trial Before Dose Adjustment

Before declaring treatment failure or escalating the dose, patients must complete at least 5 separate attempts at the current dose with proper technique. 5, 2 This is critical because up to 30% of apparent non-responders become successful responders after addressing modifiable factors. 5

Key Modifiable Factors to Address:

• Sexual stimulation is mandatory – sildenafil enhances but does not replace natural arousal 2, 3
• Timing relative to meals – avoid taking with large or fatty meals, which delays absorption and reduces efficacy 6
• Alcohol consumption – heavy alcohol use impairs erectile function independent of medication 5, 2
• Hormonal status – check testosterone levels; men with testosterone deficiency respond less robustly to PDE5 inhibitors alone 5, 2
• Psychological factors – depression, anxiety, and relationship conflict significantly impact treatment response 5

Dose-Response Relationship

Sildenafil demonstrates dose-dependent efficacy: 50 mg is superior to 25 mg, though the incremental benefit of 100 mg over 50 mg is less pronounced. 7, 2 However, starting at 100 mg may provide additional benefits:

• 56% of men on 100 mg felt no anxiety about the next intercourse attempt compared with 39% on 50 mg 4
• Treatment satisfaction and sexual experience significantly favored 100 mg over 50 mg 4
• No increase in adverse events with the higher starting dose 4

Timing and Duration of Action

• Pharmacological activity begins 30-120 minutes after oral administration (average 60 minutes on empty stomach) 3, 8
• Peak efficacy occurs 1.5-2 hours after ingestion 6
• Duration of action may exceed 10 hours, though efficacy gradually declines after 2 hours 6
• Taking with meals does not significantly reduce efficacy – no significant loss of efficacy occurs when sildenafil is taken shortly before or with a meal 6

Special Population Dosing Adjustments

Start at 25 mg in the following situations: 2, 3

• Severe hepatic impairment
• Severe renal impairment (creatinine clearance <30 mL/min)
• Concurrent use of CYP3A4 inhibitors (ritonavir, saquinavir, ketoconazole, erythromycin, cimetidine)
• Age >65 years (consider lower starting dose)

Critical Safety Contraindications

Absolute contraindication: Concurrent nitrate use in any form (organic nitrates, nitroglycerin, isosorbide dinitrate) due to potentially fatal hypotension. 2, 9

Emergency nitrate protocol: If a patient on sildenafil requires emergency nitrate administration, wait at least 24 hours after sildenafil use before administering nitrates under close medical supervision. 5, 2

High-risk cardiovascular conditions requiring cardiac stabilization before treatment: 2, 9

• Unstable or refractory angina
• Uncontrolled hypertension
• Recent MI or stroke (within 2 weeks)
• Severe heart failure (NYHA class II or higher)
• High-risk arrhythmias

Expected Efficacy Outcomes

• 69% of men report successful sexual intercourse attempts versus 35.5% with placebo 7, 2
• 73-88% improvement in erections versus 26-32% with placebo 2
• Efficacy maintained across various etiologies including diabetes, cardiovascular disease, post-prostatectomy, and spinal cord injury, though response rates may be lower in these populations 2, 3

Common Adverse Effects

Transient and mild-to-moderate side effects include: 2, 3

• Headache
• Flushing
• Dyspepsia
• Nasal congestion
• Abnormal vision (blue-tinged vision)

When to Switch or Add Therapies

Consider switching to a different PDE5 inhibitor (tadalafil or vardenafil) only after: 5, 2

• Completing at least 5 attempts at maximum dose (100 mg)
• Addressing all modifiable factors
• Evaluating testosterone supplementation if levels are low (<300 ng/dL)

For hypogonadal men (testosterone <300 ng/dL), combining sildenafil with testosterone replacement therapy is more effective than either alone. 5, 2

Second-line therapies should be considered only after failure of at least two different PDE5 inhibitors at maximum dose with proper technique. 5