Introduction
Cialis (tadalafil) is a phosphodiesterase type 5 (PDE5) inhibitor manufactured by Eli Lilly and Company. It is primarily prescribed for the treatment of erectile dysfunction (ED) and benign prostatic hyperplasia (BPH). First approved by the FDA in 2003, Cialis has become a widely used medication for sexual health and urological conditions.
Mechanism of Action
Tadalafil works by selectively inhibiting phosphodiesterase type 5 (PDE5), an enzyme that breaks down cyclic guanosine monophosphate (cGMP). During sexual stimulation, nitric oxide is released, which activates guanylate cyclase to produce cGMP. Increased cGMP levels cause smooth muscle relaxation in the corpus cavernosum, allowing increased blood flow and facilitating erection. For BPH, tadalafil improves urinary symptoms through smooth muscle relaxation in the prostate and bladder.
Indications
- Erectile dysfunction (ED)
- Benign prostatic hyperplasia (BPH) with or without ED
- Pulmonary arterial hypertension (PAH) (under the brand name Adcirca)
Dosage and Administration
For ED:- On-demand: 10 mg taken at least 30 minutes before sexual activity (may be increased to 20 mg or decreased to 5 mg based on efficacy/tolerability)
- Once-daily: 2.5 mg or 5 mg taken at approximately the same time each day
- 5 mg once daily
- Renal impairment: CrCl 30-50 mL/min: max 10 mg daily; CrCl <30 mL/min: max 5 mg daily
- Hepatic impairment: Mild to moderate: max 10 mg daily; Severe: not recommended
- Elderly: Consider lower starting doses
- Concomitant medications: Reduced doses required with certain CYP3A4 inhibitors
Pharmacokinetics
- Absorption: Rapid absorption with median Tmax of 2 hours; bioavailability approximately 36%
- Distribution: Volume of distribution 63 L; 94% protein bound
- Metabolism: Primarily hepatic via CYP3A4
- Elimination: Mean half-life 17.5 hours; primarily fecal excretion (61%) with minor renal excretion (36%)
Contraindications
- Concomitant use of organic nitrates or nitric oxide donors
- Hypersensitivity to tadalafil or any component of the formulation
- History of non-arteritic anterior ischemic optic neuropathy (NAION)
Warnings and Precautions
- Cardiovascular effects: Use with caution in patients with cardiovascular disease; not recommended in unstable angina, recent MI, or uncontrolled hypertension
- Prolonged erection: Priapism (erection >4 hours) requires immediate medical attention
- Effects on vision: Sudden vision loss (NAION) reported
- Hearing loss: Sudden decrease or loss of hearing reported
- Alpha-blocker use: Potential hypotension; separate administration by至少 4 hours
- Pulmonary hypertension: Adcirca formulation specifically indicated for PAH
Drug Interactions
- Nitrates: Contraindicated combination (severe hypotension)
- Alpha-blockers: Increased hypotensive effects
- CYP3A4 inhibitors: Ketoconazole, ritonavir, erythromycin (reduce tadalafil dose)
- Antihypertensics: Potentiated hypotensive effects
- Alcohol: May increase hypotensive effects
Adverse Effects
Common (≥2%):- Headache (15%)
- Dyspepsia (10%)
- Back pain (6%)
- Myalgia (5%)
- Nasal congestion (4%)
- Flushing (3%)
- Cardiovascular events (MI, stroke)
- Priapism
- Sudden hearing loss
- Vision loss (NAION)
- Hypotension
Monitoring Parameters
- Efficacy: Improvement in erectile function or urinary symptoms
- Cardiovascular status: Blood pressure, especially with concomitant antihypertensives
- Visual changes: Regular ophthalmologic exams in at-risk patients
- Adverse effects: Musculoskeletal pain, gastrointestinal symptoms
Patient Education
- Take as directed: On-demand dosing requires sexual stimulation
- Timing: Allow sufficient time for medication to work (30 minutes to 2 hours)
- Avoid: Grapefruit juice may increase concentrations
- Seek immediate care: For erections lasting >4 hours or sudden vision/hearing changes
- Disclosure: Inform all healthcare providers of Cialis use
- Storage: Room temperature (59-86°F) in original container
References
1. FDA Prescribing Information: Cialis (tadalafil). Revised 2023. 2. Hatzimouratidis K, et al. EAU Guidelines on EDI. Eur Urol. 2021. 3. Porst H, et al. J Sex Med. 2013;10(1):162-170. 4. Brock GB, et al. Eur Urol. 2002;42(6):608-615. 5. McVary KT, et al. J Urol. 2007;177(4):1401-1407. 6. Giuliano F, et al. Int J Impot Res. 2010;22(5):287-295.