How Does Spedra Work in the Body
Chemical Composition, Mechanism of Action & Metabolic Effects Explained
Key Takeaways: How Spedra Works
- Primary Action: Highly selective PDE5 enzyme inhibition (100-fold selectivity over PDE6)
- Chemical Effect: Increases cyclic guanosine monophosphate (cGMP) levels in penile tissue
- Physiological Result: Relaxes smooth muscle cells in penile arteries, boosting blood flow
- Fast Onset: Can work in as little as 15–30 minutes for some men
- Duration: Effects last up to 6 hours, with a half-life of 5–10 hours
- Requirement: Sexual stimulation is essential to trigger nitric oxide release
Spedra (avanafil) is a modern PDE5 inhibitor designed for rapid absorption and high selectivity. It enhances the body's natural response to sexual stimulation, helping men with erectile dysfunction achieve and maintain erections suitable for sexual activity. Below we explain the detailed science behind how it works.
Important Medical Advice
If you experience an erection lasting more than 4 hours (priapism), sudden vision loss, or chest pain while taking Spedra, seek immediate medical attention. Do not take Spedra with nitrate medications (e.g., glyceryl trinitrate) as this can cause dangerously low blood pressure.
Chemical Composition & Molecular Structure
Avanafil, the active ingredient in Spedra, is a pyrimidine derivative specifically engineered for potent and selective PDE5 inhibition.
Chemical Structure Details
(S)-2-(2-aminopyrimidin-4-yl)-4-(3-chloro-4-methoxybenzylamino)-2-isopropylbutanenitrile
This structure contains a pyrimidine ring and a chloro-methoxybenzyl group, conferring high selectivity for PDE5.
C23H26ClN7O3
23 carbon, 26 hydrogen, 1 chlorine, 7 nitrogen, and 3 oxygen atoms.
484.0 g/mol (free base)
The molecular weight influences its absorption and tissue distribution.
Key Pharmaceutical Properties
| Property | Value/Characteristic | Clinical Significance |
|---|---|---|
| Solubility | Poorly soluble in water, but formulation enhances absorption | Rapid dissolution in gastrointestinal tract |
| pKa | Approx. 4.5 (weak base) | Affects ionisation and permeability at physiological pH |
| Protein Binding | ~99% bound to plasma proteins | High binding influences drug interactions and distribution |
| Selectivity | PDE5 vs PDE6: ~100-fold | Minimal visual side effects compared to older PDE5 inhibitors |
🗒️ Pharmaceutical Insight: The unique chloro-methoxybenzyl group in avanafil contributes to its high lipophilicity and rapid tissue penetration, enabling fast onset of action.
Mechanism of Action: How Spedra Creates an Erection
Avanafil works by amplifying the natural erectile pathway through targeted PDE5 inhibition in penile tissue.
The Normal Erection Pathway
- Sexual Stimulation: Nerves release nitric oxide (NO) in penile tissue
- Enzyme Activation: NO activates guanylate cyclase enzyme
- cGMP Production: Guanylate cyclase produces cyclic GMP (cGMP)
- Smooth Muscle Relaxation: cGMP causes relaxation of penile arteries
- Increased Blood Flow: Blood enters corpora cavernosa, creating erection
- Natural Breakdown: PDE5 enzyme normally breaks down cGMP, ending erection
Spedra's Intervention
| Step | Normal Process | Spedra Effect |
|---|---|---|
| 1. NO Release | Sexual stimulation triggers nitric oxide release | Spedra doesn't affect this step – requires natural stimulation |
| 2. cGMP Production | Guanylate cyclase produces cGMP | Normal production continues unaffected |
| 3. PDE5 Action | PDE5 breaks down cGMP, limiting erection duration | Spedra blocks PDE5, preventing cGMP breakdown |
| 4. Result | Limited cGMP leads to weaker/shorter erections | Enhanced cGMP levels support stronger, longer-lasting erections |
🗒️ Physiological Insight: Avanafil has a higher selectivity for PDE5 than sildenafil, meaning fewer off-target effects (like facial flushing or visual disturbances) at therapeutic doses.
Enzyme Inhibition: Targeting Phosphodiesterase Type 5
Avanafil's effectiveness stems from its competitive, reversible inhibition of PDE5, an enzyme concentrated in penile smooth muscle, lungs, and platelets.
Enzyme Inhibition Characteristics
Competitive Reversible Inhibition
Avanafil competes with cGMP for the catalytic site of PDE5, blocking cGMP hydrolysis.
IC50 ≈ 5.2 nM
Very high affinity for PDE5, meaning potent inhibition at low concentrations.
PDE5:PDE6 ≈ 100:1
100 times more selective for PDE5 than PDE6, virtually eliminating blue-tinted vision side effects.
Selectivity Across Phosphodiesterase Enzymes
| PDE Enzyme Type | Tissue Location | Avanafil Selectivity | Clinical Relevance |
|---|---|---|---|
| PDE5 | Penile tissue, lungs, blood vessels | High (Primary target) | Erectile dysfunction treatment |
| PDE6 | Retina (eye) | Very low (100x less than PDE5) | Minimal visual disturbances |
| PDE1 | Brain, heart | Very low | No significant cardiac effects |
| PDE11 | Testes, skeletal muscle | Negligible | Unlikely to affect fertility or muscle |
🗒️ Biochemical Insight: The high selectivity of avanafil for PDE5 means that at recommended doses (50–200 mg), side effects related to PDE6 inhibition (like chromatopsia) are extremely rare.
Metabolic Effects and Duration in the Body
Avanafil undergoes hepatic metabolism to form active and inactive metabolites, determining its duration of action.
Metabolic Pathway
Primary Metabolism
Location: Liver (mainly CYP3A4 enzyme)
Process: Oxidation and dealkylation
Result: Forms active metabolite M4 (approx. 3% potency of parent)
Secondary Metabolism
Enzymes: CYP2C9 minor role
Process: Further oxidation to inactive metabolites
Result: Water-soluble compounds for excretion
Elimination
Route: ~60% faeces, ~20% urine
Half-life: 5–10 hours (mean 6.7 hours)
Active Metabolite: M4 contributes minimally to overall effect
Timeline of Effects After 100mg Dose
- 0–30 minutes: Rapid absorption, detectable in blood within 15–20 minutes
- 30–45 minutes: Peak plasma concentration (fasting); optimal time for sexual activity
- 45 minutes – 6 hours: Therapeutic PDE5 inhibition maintained; gradual decline
- 6–12 hours: Residual effects possible but diminishing
- 12–24 hours: Complete elimination in most individuals
🗒️ Clinical Correlation: A high-fat meal can delay absorption by approximately 1 hour and reduce peak concentration by 24%, so taking Spedra on an empty stomach is recommended for fastest onset.
Absorption, Distribution & Elimination
Avanafil's pharmacokinetic profile supports its use as an on-demand treatment with rapid onset and predictable duration.
Pharmacokinetic Profile
Absorption
Bioavailability: ~30% oral absorption
Peak Time: 30–45 minutes (fasting)
Food Effect: High-fat meal delays Tmax by ~1h, reduces Cmax by 24%
Distribution
Volume of Distribution: 30–40 L
Protein Binding: 99% (mainly albumin)
Tissue Penetration: Rapid into penile tissue due to lipophilicity
Elimination
Half-life: 5–10 hours
Renal Excretion: 20% as metabolites
Fecal Excretion: 60% as metabolites
Special Population Considerations
| Population | Effect on Avanafil | Dosing Consideration |
|---|---|---|
| Elderly (≥65 years) | Modestly increased exposure | Start with 50mg, titrate as tolerated |
| Renal Impairment (severe) | Limited data, but no significant accumulation expected | Use with caution, starting dose 50mg |
| Hepatic Impairment (moderate) | Increased AUC (30–50%) | Max dose 50mg per day; avoid in severe impairment |
| CYP3A4 Inhibitors (e.g., ketoconazole) | Significantly increased exposure (up to 13-fold) | Contraindicated with strong CYP3A4 inhibitors; with moderate inhibitors (e.g., erythromycin), max 100mg every 2 days |
🗒️ Clinical Warning: Grapefruit juice (a moderate CYP3A4 inhibitor) should be avoided within 24 hours of taking Spedra, as it can increase avanafil levels and side effects.
Clinical Efficacy for Erectile Dysfunction
Clinical studies demonstrate that avanafil is effective across a broad range of men with erectile dysfunction, including those with diabetes and after prostatectomy.
Efficacy Data from Clinical Studies
| ED Type/Cause | Spedra Efficacy Rate (100–200mg) | Study Details |
|---|---|---|
| General ED population | 70–80% successful intercourse attempts | Pooled analysis of phase III trials |
| Diabetes-related ED | 65–75% improvement | Significant over placebo, even with poor glycaemic control |
| Post-prostatectomy ED | 50–60% response rate | Best results in nerve-sparing surgery |
| Severe ED (IIEF score <11) | ~60% success | 200mg dose most effective |
Optimal Use Guidelines Based on Mechanism
- Timing: Take 30 minutes before sexual activity; can be taken as early as 15 minutes before for some men
- Dose: Start with 100mg, adjust to 50mg (if side effects) or 200mg (if insufficient response)
- Food: Avoid high-fat meals near dosing time for fastest effect
- Stimulation: Sexual arousal essential – Spedra does not work without it
- Frequency: Maximum once daily; when used with moderate CYP3A4 inhibitors, allow 48 hours between doses
- Contraindications: Strictly avoid nitrates, strong CYP3A4 inhibitors (e.g., ketoconazole, HIV protease inhibitors)
🗒️ Prescribing Insight: Avanafil's rapid onset and high selectivity make it a good choice for men who want spontaneity and minimal side effects. Always review concomitant medications for potential interactions.
Spedra Mechanism FAQs
How quickly does Spedra start working?
Spedra can start working in as little as 15–30 minutes for some men. Maximum effectiveness is usually reached within 30–45 minutes when taken on an empty stomach.
Does Spedra work without sexual stimulation?
No, Spedra only works if you are sexually aroused. It enhances the natural response to stimulation but does not cause automatic erections.
Can I take Spedra with food?
Yes, but a high-fat meal may delay absorption by about an hour and slightly reduce effectiveness. For fastest results, take it on an empty stomach.
Why does Spedra cause fewer visual side effects?
Spedra is about 100 times more selective for PDE5 than PDE6 (the enzyme in the retina), so it rarely causes the blue-tinted vision associated with other PDE5 inhibitors.
How long do the effects of Spedra last?
The effects of Spedra typically last up to 6 hours, although individual response may vary. The half-life is 5–10 hours, so some benefit may persist longer.
Need Treatment for Erectile Dysfunction?
If you're experiencing erectile dysfunction and want to know if Spedra could be right for you, speak with a UK-registered doctor through a confidential online consultation.
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Medical Content Manager
Nabeel is a co-founder, and medical content manager of Chemist Doctor. He works closely with our medical team to ensure the information is accurate and up-to-date.
Medical Doctor
Dr. Feroz is a GMC-registered doctor and a medical reviewer at Chemist Doctor. He oversees acute condition and urgent care guidance.
Medical Director
Usman is a co-founder, and medical director of Chemist Doctor. He leads the organisation's strategic vision, bridging clinical and operational priorities.
Review Date: 14 February 2026
Next Review: 14 August 2026
Published on: 14 February 2026
Last Updated: 14 February 2026