Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ATMEKSI vs CIALIS
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
ATMEKSI (atazanavir/cobicistat) is a fixed-dose combination of atazanavir, an HIV-1 protease inhibitor that inhibits viral protease, preventing cleavage of viral polyproteins and resulting in immature non-infectious virions, and cobicistat, a pharmacokinetic enhancer that inhibits CYP3A, increasing atazanavir exposure.
Phosphodiesterase-5 (PDE5) inhibitor; increases c GMP levels, causing smooth muscle relaxation and vasodilation in the corpus cavernosum, enhancing erectile function.
Treatment of HIV-1 infection in adults and pediatric patients weighing at least 35 kg,Off-label use as part of antiretroviral therapy in treatment-experienced patients with viral suppression
Treatment of erectile dysfunction,Treatment of benign prostatic hyperplasia,Treatment of pulmonary arterial hypertension (as Adcirca)
1.5 mg/kg IV every 4 weeks
Tadalafil 10 mg or 20 mg orally as needed at least 30 minutes before sexual activity; maximum dosing frequency once daily. Alternative: 2.5 mg or 5 mg once daily for daily use.
Terminal elimination half-life is 12 hours; renally impaired patients have prolonged half-life up to 24 hours.
The terminal elimination half-life of tadalafil is approximately 17.5 hours in healthy subjects, which supports once-daily dosing for erectile dysfunction and once-daily use for benign prostatic hyperplasia. This long half-life distinguishes it from other PDE5 inhibitors.
Atazanavir is metabolized by CYP3A4; cobicistat is metabolized by CYP3A and to a minor extent by CYP2D6.
Primarily hepatic via CYP3A4; minor pathways include CYP2C9 and glucuronidation.
Primarily renal (80% unchanged) and biliary/fecal (15% as metabolites).
Following oral administration, tadalafil is predominantly eliminated by hepatic metabolism. The metabolites are excreted mainly in feces (approximately 61% of the dose) and to a lesser extent in urine (approximately 36% of the dose). No unchanged parent drug is detected in urine.
95% bound to albumin and alpha-1-acid glycoprotein.
Tadalafil is 94% bound to plasma proteins, primarily to albumin. The protein binding is independent of drug concentration over a wide range.
2.0 L/kg, indicating extensive tissue distribution.
The apparent volume of distribution (Vd/F) is approximately 63 L (or roughly 0.9 L/kg for a 70 kg individual), indicating distribution into tissues beyond the vascular space, including the penis and other target organs.
Oral: 60-70% due to first-pass metabolism.
Absolute oral bioavailability of tadalafil has not been formally determined; however, the drug is well absorbed after oral administration, with peak plasma concentrations reached in 0.5 to 6 hours (median 2 hours). Food does not affect the extent of absorption (AUC), though it may delay the rate (Tmax) by about 1–2 hours.
GFR 15-29 m L/min: 1.0 mg/kg IV every 4 weeks; GFR <15 m L/min: not recommended
Cr Cl 30-50 m L/min: 5 mg once daily (max) for daily use; as-needed dosing: 10 mg not to exceed once every 48 hours. Cr Cl <30 m L/min: not recommended. Hemodialysis: not studied.
Child-Pugh A: no adjustment; Child-Pugh B: 1.0 mg/kg IV every 4 weeks; Child-Pugh C: not recommended
Child-Pugh A and B: no dose adjustment necessary for as-needed dosing; daily use: caution, start at 5 mg once daily. Child-Pugh C: not recommended.
Age 2-17 years: 1.5 mg/kg IV every 4 weeks; maximum 120 mg per dose
Not indicated for pediatric patients under 18 years.
No specific adjustment; monitor renal function and reduce dose if GFR <30 m L/min
No dose adjustment required solely based on age; consider renal function and concomitant medications.
None
None
Hepatotoxicity, especially in patients with pre-existing liver disease or elevated transaminases,Nephrolithiasis and cholelithiasis,Cardiac conduction abnormalities (PR interval prolongation),Risk of developing resistance if not used with other antiretrovirals,Renal impairment (cobicistat decreases estimated creatinine clearance)
Risk of hypotension with vasodilators or alpha-blockers,Contraindicated with nitrates due to severe hypotension risk,Patients with left ventricular outflow obstruction (e.g., aortic stenosis) should avoid use,Caution in patients with hypotension, severe hepatic impairment, or end-stage renal disease,Risk of priapism: advise immediate medical attention for erections lasting >4 hours,Decreased visual or hearing ability requiring discontinuation
Concomitant use with drugs highly dependent on CYP3A for clearance (e.g., alfuzosin, rifampin, ergot derivatives, St. John's wort, lovastatin, simvastatin, sildenafil for pulmonary arterial hypertension),Severe hepatic impairment (Child-Pugh Class B or C)
Concomitant use of nitrates (any form) or riociguat,Hypersensitivity to tadalafil,Concomitant use with alpha-blockers (except for BPH with appropriate dosing)
Avoid alcohol (may exacerbate CNS effects). Grapefruit juice may increase atomoxetine exposure; limit consumption. High-fat meals do not significantly affect absorption.
Avoid high-fat meals prior to dosing as they may delay absorption and reduce peak plasma concentration. Avoid large quantities of grapefruit juice (more than 1 liter per day) as it may increase tadalafil exposure via CYP3A4 inhibition.
First trimester: Limited human data; animal studies show no teratogenicity at therapeutic doses. Second and third trimesters: No known fetal risks. Avoid use during organogenesis unless benefit outweighs risk.
FDA Pregnancy Category B. Animal studies show no evidence of teratogenicity or embryotoxicity. No adequate, well-controlled studies in pregnant women. Risk cannot be ruled out; use only if clearly needed.
Not recommended during breastfeeding. M/P ratio unknown. Excreted in animal milk; potential for serious adverse reactions in nursing infants.
Excretion in human milk unknown. Not recommended for use in nursing mothers. M/P ratio not determined.
No dose adjustment required in pregnancy. Pharmacokinetic profile unchanged.
No specific dose adjustments studied in pregnancy. Use lowest effective dose if necessary, with caution for increased plasma volume and renal clearance potentially altering pharmacokinetics.
ATMEKSI (atomoxetine) is a selective norepinephrine reuptake inhibitor (NRI) indicated for ADHD. It has a slower onset of action (2-4 weeks) compared to stimulants. Monitor for hepatotoxicity and suicidal ideation, especially in children and adolescents. Use cautiously with hepatic impairment (reduce dose) and CYP2D6 poor metabolizers (need lower dose). Avoid concurrent MAOIs. May cause orthostatic hypotension and urinary retention.
Tadalafil (Cialis) has a 17.5-hour half-life allowing once-daily dosing for ED or daily for BPH/LUTS. Avoid use with nitrates; may cause prolonged erection. Onset of action is 30-60 minutes, and effect may last up to 36 hours. Use with caution in patients with left ventricular outflow obstruction or severe hepatic impairment.
Take ATMEKSI exactly as prescribed; do not change dose without consulting your doctor.,It may take 2-4 weeks to notice improvement in symptoms.,Avoid alcohol and grapefruit juice as they may affect drug levels.,Report any signs of liver problems (yellowing of skin/eyes, dark urine, abdominal pain) or suicidal thoughts immediately.,May cause dizziness or fainting, especially when standing up; rise slowly.,Do not stop abruptly without medical advice.
Do not take tadalafil if you take any form of nitrate medication (e.g., nitroglycerin) for chest pain.,Seek immediate medical help if you have an erection lasting more than 4 hours.,Avoid alcohol consumption as it may increase the risk of dizziness and low blood pressure.,Take tadalafil at least 30 minutes before sexual activity; effect can last up to 36 hours.,For daily use, take at the same time each day without regard to timing of sexual activity.,Grapefruit and grapefruit juice may increase tadalafil levels; avoid large amounts.,Inform your doctor of all medications you take, especially alpha-blockers, antihypertensives, and antifungal or antibiotic drugs.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ATMEKSI vs CIALIS, answered by our medical review team.
ATMEKSI is a PDE5 Inhibitor that works by ATMEKSI (atazanavir/cobicistat) is a fixed-dose combination of atazanavir, an HIV-1 protease inhibitor that inhibits viral protease, preventing cleavage of viral polyproteins and resulting in immature non-infectious virions, and cobicistat, a pharmacokinetic enhancer that inhibits CYP3A, increasing atazanavir exposure.. CIALIS is a PDE5 Inhibitor that works by Phosphodiesterase-5 (PDE5) inhibitor; increases c GMP levels, causing smooth muscle relaxation and vasodilation in the corpus cavernosum, enhancing erectile function.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ATMEKSI and CIALIS depend on the specific clinical indication. These are both PDE5 Inhibitor agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ATMEKSI is: 1.5 mg/kg IV every 4 weeks. The standard adult dose of CIALIS is: Tadalafil 10 mg or 20 mg orally as needed at least 30 minutes before sexual activity; maximum dosing frequency once daily. Alternative: 2.5 mg or 5 mg once daily for daily use.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between ATMEKSI and CIALIS in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. ATMEKSI is classified as Category C. First trimester: Limited human data; animal studies show no teratogenicity at therapeutic doses. Second and third trimesters: No known fetal risks. Avoid use during organogenesis u. CIALIS is classified as Category C. FDA Pregnancy Category B. Animal studies show no evidence of teratogenicity or embryotoxicity. No adequate, well-controlled studies in pregnant women. Risk cannot be ruled out; use. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.