If I want one tablet to cover Friday and Saturday, which of the three is that?
Tadalafil and the 36-hour window
Label splits that actually change a pick
| Measure | Tadalafil | Sildenafil | Vardenafil 20 mg |
|---|---|---|---|
| Terminal t½ | 17.5 h | About 4 h | About 4-5 h |
| Useful span | Up to 36 h as needed | Hours; 4-5 h data | Short, on-demand |
| Usual start | 10 mg PRN or 2.5 mg daily | 50 mg | 10 mg; 20 mg is the cap |
| Food | No regard | High-fat: Tmax +60 min, Cmax -29% | High-fat: Cmax -18% to -50% |
| Daily ED label | Yes (2.5 to 5 mg) | No | No |
| BPH label | 5 mg daily | No | No |
| QT lead caution | Not the class story | Small QTc in a shared study | Labelled QT / Class I A, III |
| Nitrates | Banned | Banned | Banned |
As-needed tadalafil starts at 10 mg. A 20 mg step exists. Daily ED starts at 2.5 mg and may rise to 5 mg. Only this INN has that daily ED label among the three.
Mean terminal half-life is 17.5 hours. The as-needed label showed improved erectile function versus placebo up to 36 hours after a dose.
Food does not pick the tadalafil clock. Cialis may be taken without regard to food. That is the first practical split from sildenafil 50 mg and from vardenafil 20 mg after a fatty meal.
Only tadalafil carries a 5 mg daily urinary indication for BPH, or for ED plus BPH. Prostate symptoms often pick this INN before duration talk starts.
The nitrate wait, if a nitrate is later forced in an emergency, is at least 48 hours after the last tadalafil dose. The long half-life is why that wait is longer than a short tablet's day.
Tadalafil Tmax after a single dose sits between 30 minutes and 6 hours, median 2 hours. The long window is a fade, not a faster start. Men who want a 25-minute RigiScan story are looking at sildenafil's fasted file, not at 36 hours.
Daily 2.5 mg reaches steady state in 5 days at about 1.6-fold a single dose. That plateau is the only approved daily ED option among these three.
How to choose 2.5 mg daily versus a 10 mg hit is a separate note: picking tadalafil. This page only needs the 36-hour fact.
What the 20 mg vardenafil trials actually moved
| Setting | Vardenafil 20 mg result | Placebo |
|---|---|---|
| NA general ED, SEP2 | 80% | 52% |
| NA general ED, SEP3 | 65% | 32% |
| Diabetes, SEP3 | 54% | 23% |
| Post-prostatectomy, SEP3 | 34% | 10% |
Four main fixed-dose trials enrolled 2431 men. Doses were 5, 10, and 20 mg. Two trials were general ED. One was diabetes. One was after radical prostatectomy.
North American general ED (n=762): SEP2 at 3 months was 80% on 20 mg versus 52% on placebo. SEP3 was 65% versus 32%. EF domain on 20 mg was 21 versus 15 on placebo.
Diabetes trial (n=439): SEP3 was 54% on 20 mg versus 23% on placebo. After prostatectomy (n=427): SEP3 was 34% on 20 mg versus 10% on placebo. The molecule works in harder groups. The absolute rates drop, as expected.
Those cuts beat placebo. They do not make 20 mg a longer tablet than tadalafil. Duration is still the 4-to-5-hour half-life.
Age 65 or more: consider a 5 mg vardenafil start (Cmax about +34%, AUC about +52%). Moderate hepatic impairment: start 5 mg, do not exceed 10 mg. Severe hepatic impairment was not studied.
Treadmill studies in men with stable exertional angina found vardenafil 10 mg and 20 mg did not shorten total exercise time versus placebo. That is not a nitrate waiver. It is a selected, stable-angina file.
Mean baseline EF domain across the four main vardenafil trials was 11.8 on a 0 to 30 scale. These were not mildly bothered volunteers. They were men with established ED.
Side-effect signatures that are not the duration story
Headache and flushing sit on all three labels. They do not pick a winner.
Tadalafil's more typical extra is back pain or myalgia. In pharmacology trials it often started 12 to 24 hours after a dose and settled within 48 hours. Daily 2.5 or 5 mg can repeat that ache. A 10 mg hit leaves days off.
Sildenafil is the tablet more often tied to colour-tinge or brightness change, a PDE6-adjacent effect in the retina. Transient cyanopsia showed up in a small vardenafil retinal study too (two men on 20 mg).
Those visual stories are not a licence to ignore sudden vision loss. Sudden monocular or binocular loss is a stop-and-seek-care event on every PDE5 label, including NAION talk.
Vardenafil's extra is the QT file, not a unique headache rate. If the man already takes a QT-prolonging antibiotic or an antiarrhythmic, that file outranks colour-tinge gossip.
None of these signatures lift the nitrate ban. A milder flush is not a safer overlap with nitroglycerin.
Tadalafil excretion is mostly metabolites in faeces (about 61%) and urine (about 36%). Sildenafil is likewise a hepatic story. Vardenafil leaves mostly in faeces (about 91% to 95%). Those paths do not change the shared nitrate ban.
Do not combine two PDE5 tablets to stitch duration. That is two vasodilators, one nitrate problem, and no labelled regimen.
Sildenafil and the short curve
Sildenafil 50 mg about 1 hour before sex is the usual start. The half-life of parent and metabolite is about 4 hours. That is the four-hour number in the title.
Fasted Tmax median is 60 minutes. A high-fat meal delays Tmax 60 minutes and cuts Cmax about 29%. The short curve plus a late dinner is a common 'weak Viagra' story.
UK SmPC RigiScan data: median onset 25 minutes when fasted in responders, and a stimulated response still at 4 to 5 hours. That is not a 36-hour window.
Sildenafil bioavailability averages 41%. Vardenafil's is about 15%. Those absorption gaps are not potency rankings. They are why milligram numbers are not interchangeable across INNs.
The 50 mg hour is wasted more often by a late swallow than by 'the wrong brand'. Read the timing note before you swap to 20 mg vardenafil for speed.
There is no US once-daily ED regimen for sildenafil citrate in the Viagra label. Once per day is a maximum, not a plateau strategy.
The clock, the meal, and the 25 mg special starts live in the 50 mg timing note. Here the only job is to set sildenafil as the short, food-sensitive tablet.
Vardenafil 20 mg and the QT study
For most patients the vardenafil start is 10 mg about 60 minutes before sex. The dose may rise to 20 mg or fall to 5 mg. Once per day is the maximum. This site locks discussion on the 20 mg cap.
After a 20 mg tablet, Tmax is usually 30 minutes to 2 hours, median 60 minutes, fasted. Absolute bioavailability is about 15%. Half-life of parent and primary metabolite is about 4 to 5 hours.
High-fat meals cut Cmax 18% to 50% in two food studies. Levitra may be taken with or without food, but 20 mg after a heavy plate is a smaller peak.
The QT file is why vardenafil is not 'sildenafil with another brand'. In 59 men aged 45 to 60, vardenafil 10 mg and 80 mg were compared with placebo and with moxifloxacin 400 mg.
Therapeutic and supratherapeutic vardenafil doses and moxifloxacin produced similar QTc increases. Clinical impact is stated as unknown.
A later study of 44 volunteers found vardenafil 10 mg plus gatifloxacin 400 mg additive on QTcF (about 9 msec from baseline). Class I A drugs (quinidine, procainamide) and Class III drugs (amiodarone, sotalol), or congenital QT prolongation, are the labelled caution set.
Single 20 mg doses lowered supine pressure by a mean 7 mmHg systolic and 8 mmHg diastolic versus placebo, with heart rate up about 4 beats per minute.
Nitroglycerin 0.4 mg after vardenafil 20 mg still changed pressure at 1 and 4 hours. Extra heart-rate effects were seen out to 8 hours. At 24 hours those extra pressure effects were not detected. The contraindication with nitrates remains. A 24-hour lab gap is not a home nitrate plan.
How a prescriber actually picks
Start with the nitrate list and the QT list. Then pick duration. Food pattern and prostate symptoms break remaining ties.
Tadalafil if the couple needs 36 hours or a 2.5-to-5 mg daily plateau, or if BPH is on the same script. Sildenafil 50 mg if a short, cheap, well-studied evening tablet is enough and meals can be managed.
Vardenafil 20 mg if that is the tablet in hand and the QT medicines are absent. It is not the long option. It is not the food-proof option.
Labels: Cialis, Viagra, Levitra. A clinician still signs the pick.
New ED still starts at the work-up. Duration and QT are the second conversation, after nitrates and fitness for sex.
A 20 mg vardenafil tablet is a cap, not a duration upgrade. If the need is Saturday after a Friday dose, that is still tadalafil.
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Answered by Dr. Elena Marchetti, MD · Infectious diseases & clinical pharmacology
These replies stay on 36 hours versus about 4 hours, and on the vardenafil 20 mg QT note. They are comparison teaching, not a brand prescription.
Tadalafil. The as-needed label showed a response versus placebo out to 36 hours. Half-life is 17.5 hours. Sildenafil's half-life is about 4 hours. Vardenafil's is about 4 to 5 hours. Neither short tablet is a weekend tablet. A Friday sildenafil 50 mg is gone as a planning tool by Saturday afternoon. A Friday vardenafil 20 mg is the same short math. Do not take two different PDE5 tablets to stitch a weekend. That stacks vasodilation and the nitrate problem. If Friday-Saturday is the real need, the discussion is tadalafil 10 mg as needed, or 2.5 mg daily if sex is frequent and kidneys allow. Food will not steal tadalafil the way a high-fat meal steals sildenafil peak. Nitrates still ban tadalafil, and the emergency nitrate wait after tadalafil is at least 48 hours. Duration is the split. It is not a safety loophole.
He is on amiodarone. Someone offered vardenafil 20 mg because 'it is stronger.'
Stop on the QT line. Vardenafil's label asks clinicians to think about known QT prolongation and about drugs that prolong QT. Class III agents include amiodarone and sotalol. Class I A agents include quinidine and procainamide. Congenital QT is in the same caution. 'Stronger' is not a labelled claim for 20 mg versus sildenafil 50 mg or tadalafil 10 mg. The 20 mg tablet is the vardenafil cap after a 10 mg start. In the thorough QT study, vardenafil 10 mg and 80 mg moved QTc in the same neighbourhood as moxifloxacin 400 mg. Impact is called unknown, which is exactly why we do not shrug. Offer the prescriber the amiodarone first, then ask which PDE5 is even allowed. Nitrates would already have ended the conversation. If amiodarone stays, vardenafil 20 mg is the wrong 'upgrade'. A different INN may still be banned for other reasons. That is a chart review, not a pharmacy-counter swap.
Do the diabetes and prostatectomy vardenafil numbers mean 20 mg beats tadalafil there?
They mean 20 mg beat placebo in those harder groups. Diabetes: SEP3 54% versus 23%. After radical prostatectomy: SEP3 34% versus 10%. Those are vardenafil-versus-placebo cuts, not vardenafil-versus-tadalafil cuts. Tadalafil and sildenafil also have diabetes and post-prostatectomy files of their own. Crossing one drug's placebo gap with another drug's duration is how people invent a winner. For a man with diabetes I still start with nitrates, QT drugs, meals, and whether he needs 36 hours or a daily 2.5 mg. The lower absolute SEP3 after prostatectomy is expected. Nerves were cut. A 20 mg tablet cannot rewrite that anatomy. If 20 mg is the tablet he already tolerates, keep the meal light and keep the once-daily cap. If he needs a long window, that is tadalafil, with the 48-hour nitrate wait in mind. Compare endpoints only when the trial compared those drugs head to head.
High-fat dinners are the household pattern. Which tablet even cares?
Sildenafil and vardenafil care. Tadalafil much less. Sildenafil 50 mg: high-fat meal delays Tmax 60 minutes and cuts Cmax about 29%. Vardenafil 20 mg: high-fat meals cut Cmax 18% to 50% in the food studies. Cialis may be taken without regard to food. If Friday dinner is the immovable ritual, tadalafil is the tablet that does not need an empty-stomach hour. That still is not a nitrate waiver and still is not a QT waiver. Vardenafil 20 mg after the roast is a smaller peak on a short half-life. That is a poor match. Sildenafil can work if the 50 mg is taken before the heavy course. Many households will not do that. Then duration plus food points to tadalafil 10 mg as needed, or 2.5 mg daily if frequency is high. Do not mix two PDE5 tablets at the same dinner. Pick one INN with a clinician who has the cardiac list.
Treat every answer here as general teaching, not a decision made for the individual who wrote in. What is right for you turns on your history, your bloods and the rest of your medicine list — and that is a conversation for a prescriber who can see all of it at once.