Cialis

Executive Summary & Molecular Mechanism

This module explores the foundational pharmacology of Tadalafil, a potent, selective, and reversible inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). By preventing cGMP hydrolytic degradation in pelvic and pulmonary vasculature, Tadalafil sustains nitric oxide (NO)-mediated smooth muscle relaxation. Below, explore the underlying signaling cascade and Tadalafil's isoenzyme selectivity profile, which minimizes visual disturbances while explaining skeletal muscle side effects.

Elimination Half-Life

17.5 hrs

Vs 4 hrs for Sildenafil

Duration of Action

Up to 36 hrs

Unlocks once-daily option

Plasma Protein Binding

94%

Unaffected by renal status

PDE5 vs PDE6 Selectivity

>700x

Extremely low visual side-effects

The NO / cGMP Physiological Cascade

Click through the interactive steps below to understand how sexual arousal leads to smooth muscle relaxation and how Tadalafil intervenes.

Step 1 of 4

Phosphodiesterase (PDE) Isoenzyme Selectivity

Relative ratio of selectivity for PDE5 over other PDE family members (Higher = Safer off-target profile).

Clinical Insight: Tadalafil exhibits >700x selectivity over PDE6 (retinal, preventing blue-tint vision common with Sildenafil), but holds lower relative selectivity over PDE11 (skeletal muscle), explaining reported back pain and myalgia.

Pharmacokinetics & Clinical Dosing Regimens

Tadalafil's unique terminal elimination half-life of 17.5 hours enables both flexible "on-demand" dosing (active up to 36 hours) and once-daily low-dose therapy. Unlike short-acting PDE5 inhibitors, Tadalafil absorption is completely unaffected by food or high-fat meals. Below, compare plasma concentration curves over time and calculate tailored dosage adjustments for patients with hepatic or renal impairment.

Plasma Concentration Curve (36 Hours)

Simulated single-dose plasma drug exposure over time comparing Tadalafil 20mg vs Sildenafil 100mg.

*Tmax occurs between 0.5 to 6 hours (median 2 hrs). Half-life ~17.5 hours allows continuous therapeutic levels over 36 hours.

Interactive Patient Dosing Selector

Select clinical indication and organ dysfunction parameters to determine recommended dosing limits.

1. Select Clinical Indication

2. Select Organ Impairment Status

Food Interaction: None (Taken with or without food) Excretion: Feces (61%), Urine (36%)

Benign Prostatic Hyperplasia (BPH) & LUTS Efficacy

Tadalafil 5 mg once daily is the only PDE5 inhibitor approved for the treatment of lower urinary tract symptoms (LUTS) secondary to BPH. Efficacy is achieved through smooth muscle relaxation of the bladder neck and prostate, enhanced pelvic vascular perfusion, anti-inflammatory effects, and blunting of afferent sensory signaling. Below, review clinical trial data showing significant reductions in International Prostate Symptom Scores (IPSS).

IPSS Score Mean Change from Baseline (12 Weeks)

Comparison of Tadalafil 5mg once daily vs Placebo across total IPSS, storage, and voiding subscores.

*Statistically significant improvement vs placebo (p < 0.01). Tadalafil provides substantial subjective symptom relief and quality of life improvement.

Multifactorial Pelvic Mechanisms in BPH

Why PDE5 inhibition effectively alleviates voiding and storage urinary symptoms:

1. Direct Smooth Muscle Relaxation

High PDE5 expression in prostate stromal tissue and bladder neck; cGMP accumulation reduces tone and widens prostatic urethra.

2. Pelvic Perfusion & Tissue Oxygenation

Dilation of pelvic vasculature increases chronic perfusion to ischemia-prone bladder and prostate beds, halting tissue remodeling.

3. Local Anti-Inflammatory Effects

Downregulates pro-inflammatory cytokines in prostatic stroma, decreasing structural prostate overgrowth and fibrosis.

4. Afferent Sensory Modulation

Blunts hyperactive neural signaling from bladder stretch receptors, relieving overactive bladder storage symptoms like urgency and nocturia.

Cardiovascular Risk Assessment & Primary Care Guidelines

Erectile dysfunction is an early vascular sentinel marker for systemic endothelial disease and coronary heart disease. In New Zealand, Best Practice Advocacy Centre (BPAC NZ) guidelines mandate a 5-year cardiovascular disease (CVD) risk assessment prior to initiating PDE5 inhibitors. Use the interactive tool below to determine blood pressure intervention thresholds and check absolute cardiovascular contraindications.

NZ BPAC 5-Year CVD Risk Classifier

Select patient risk stratum to display blood pressure management thresholds before starting Tadalafil.

*Source: BPAC NZ Cardiovascular Primary Prevention Equations & Guidelines.

Absolute & Strict Safety Contraindications

Tadalafil MUST NOT be prescribed under the following clinical circumstances:

×

Concurrent Organic Nitrates:

Glyceryl trinitrate, isosorbide mononitrate, sodium nitroprusside, or amyl nitrite. Dual cGMP accumulation triggers catastrophic hypotension. Requires 48-hour washout minimum.

×

Guanylate Cyclase Stimulators:

Riociguat co-administration causes severe systemic vasodilation and syncope.

×

Recent Cardiac Events & Instability:

Myocardial infarction within past 90 days, unstable angina, NYHA Class II+ heart failure within 6 months, uncontrolled arrhythmias, or resting BP < 90/50 mmHg.

×

History of NAION:

Non-Arteritic Anterior Ischemic Optic Neuropathy history prohibits use due to risk of permanent optic nerve infarction.

Adverse Events & Alcohol Interaction Simulator

While Tadalafil is generally well tolerated, systemic vasodilation can produce side effects such as headache, dyspepsia, nasal congestion, back pain, and myalgia. Furthermore, concurrent consumption of ethanol (alcohol)—also a systemic vasodilator—creates a dose-dependent risk of orthostatic hypotension. Use the interactive simulator below to evaluate hemodynamic risk based on standard alcohol intake.

Alcohol Consumption Risk Simulator

Adjust the slider to simulate standard drinks consumed concurrently with Tadalafil.

Alcohol Intake: 2 Standard Drinks

0 (Sober) 2 (Moderate) 5+ (Binge / High Risk) 8+ (Severe)

*Note: High ethanol levels simultaneously blunt central nervous arousal, negating erectile benefit while maximizing hypotension risk.

Reported Adverse Event Incidence (≥ 2%)

Percentage of clinical trial patients experiencing common treatment-emergent side effects.

*Back pain and myalgia are attributed to PDE11 isoenzyme binding in skeletal muscle tissue.

New Zealand Regulatory Framework, Pharmac Funding & Access

In New Zealand, Tadalafil is classified by Medsafe as a Prescription-Only Medicine. Unlike Sildenafil (which can be supplied by accredited pharmacists), Tadalafil's 17.5-hour half-life requires doctor oversight. Pharmac funding is strictly restricted to Pulmonary Arterial Hypertension (PAH) under Special Authority criteria, leaving ED and BPH indications unfunded. Below, compare out-of-pocket costs and explore modern telehealth prescription pathways.

NZ Pharmaceutical Schedule & Retail Cost Breakdown

Compare pricing across branded (Cialis) vs generic (Cilatil, Tadalafil Sandoz) in NZ pharmacies.

Indication	Pharmac Subsidy Status	Formulation & Strength	Brand Options	Estimated NZ Retail Cost (NZD)

Telemedicine & Virtual Care Pathways in NZ

To overcome social stigma around ED and LUTS, New Zealand telehealth platforms (e.g., Practice Plus, The Doctors Online, info.health.nz) offer 24/7 virtual consultations with registered GPs.

Conducts structured virtual cardiovascular screening per BPAC guidelines.
Verifies absence of nitrate co-prescriptions.
Issues electronic prescriptions sent directly to community pharmacies.
Preserves patient confidentiality without requiring clinic waiting room visits.

Medsafe Warning: Adulterated Supplements

Medsafe routinely issues urgent public alerts regarding illicit OTC male enhancement supplements (e.g., "So Hard for Men", "Pulse8", "The Rock") sold online or in unverified health shops.

Frequently contain undeclared, high-dose active Tadalafil or Sildenafil.
Poses severe risk of fatal hypotensive collapse if consumed by patients on nitrates.
Bypasses clinical organ function screening and CVD risk evaluation.

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Tadalafil (Cialis) Clinical Explorer