Why does 2.5 mg exist if the usual start is still 10 mg?
Selectivity is a fold, not a medal
Skip the internet habit of crowning the 'most selective' pill. The Levitra label's own in-vitro line is specific: more than 15-fold versus PDE6, more than 130-fold versus PDE1, more than 300-fold versus PDE11, and more than 1,000-fold versus PDE2, 3, 4, 7, 8, 9, and 10. Those are distances, not trophies.
PDE6 is the neighbour that still matters in a consulting room. A 15-fold gap is enough to call the drug PDE5-preferring and not enough to promise a colour-free evening. Tadalafil's gap versus PDE6 is wider in most bench comparisons. That is a counseling difference, not a reason to mock this card.
This review is a selectivity-and-hold file, not a second monograph and not a league table. Draw the QT line. Note why 2.5 mg is on the blister. Shelf-check food and the short four-to-five-hour clock. Bind 2.5 or 20 only after those marks.
Food and the short clock
Holds that outrank any fold number
- Class IA: quinidine, procainamide - avoid vardenafil.
- Class III: amiodarone, sotalol - avoid vardenafil.
- Congenital long QT - avoid vardenafil.
- Nitrates / NO donors - contraindicated; no safe home interval on this label.
- Riociguat - same shut door as the other PDE5 cards.
Fasted Tmax sits near 60 minutes (often 30 minutes to 2 hours). Absolute bioavailability is only about 15 percent, which is one reason small CYP3A4 changes move the needle. Terminal half-life of parent and the M1 metabolite is about 4 to 5 hours.
High-fat meals cut Cmax in the 18 to 50 percent band across label studies and can push Tmax later by about an hour. A ordinary 30-percent-fat meal left PK essentially alone. The tablet may be taken with or without food. Onset may simply arrive late after a heavy plate.
Nitrates and nitric-oxide donors remain contraindicated. The Levitra label does not even grant a tidy hour-count for when a nitrate becomes discussable. That unknown interval is a hold, not a puzzle to solve at home.
Alpha-blockers and other antihypertensives can still potentiate a fall in pressure even when the QT line is clean. Stabilize those first. Start at the low end if the list is crowded. A 20 mg leap on an unstable alpha-blocker is not 'using the high card.' It is skipping the shelf-check. The same caution applies to heavy alcohol on a short clock: two vasodilator ideas in one evening make a faint look like a plan.
The QT line before any milligram
Fifty-nine healthy men took therapeutic 10 mg, supratherapeutic 80 mg, and moxifloxacin 400 mg as an active control. QTc moved in a similar band. A later look at combining vardenafil with another QT-active drug showed an additive bump. That is why the label tells you to think before you prescribe into a long QT history.
Avoid the tablet if congenital QT prolongation is already on the chart, or if a Class IA drug (quinidine, procainamide) or a Class III drug (amiodarone, sotalol) is already in the pillbox. This is not a 'watch the first dose' courtesy. It is an avoid.
Potency at PDE5 does not cancel a QT caution. A 'stronger' erection card is not a safer heart card. If the question was which molecule looks cleanest on a long-QT chart, this one does not win by showing up.
Why 2.5 mg exists on this shelf
The US start for most men is 10 mg about an hour before sex, adjustable to 5 mg or 20 mg, once a day. The 2.5 mg tablet is not a 'gentle lifestyle' dose. It is the interaction floor.
Ritonavir is the loudest example: a single 2.5 mg, and not again inside 72 hours. Indinavir and high-dose ketoconazole or itraconazole pull the same low card into a 24-hour cap. Moderate inhibitors such as erythromycin often land at 5 mg in 24 hours. Those bands are why 2.5 mg is cut at all.
This site locks 2.5 or 20 as the two marks worth arguing on the slip: the CYP3A4 floor and the labeled ceiling. We are not telling a typical new start to skip 10 mg. We are telling readers why the small tablet is not a prize for 'sensitive types' and why it must not be ignored when a protease inhibitor is already in the box.
Geriatric starts sometimes drop to 5 mg on European sheets. That is a third mark, and it is not this site's lock. If a clinician writes 5 mg for age or a moderate inhibitor, that is ordinary titration. What we refuse is treating 2.5 mg as a souvenir or 20 mg as a personality. Floor and ceiling. Everything between is a clinic conversation, not a trophy chart.
PDE6 sits next to the target
Levitra in-vitro selectivity as printed on the US label. Folds, not ranks.
| Comparator | Label fold vs that PDE |
|---|---|
| PDE6 (retina) | >15-fold |
| PDE1 | >130-fold |
| PDE11 | >300-fold |
| PDE2, 3, 4, 7, 8, 9, 10 | >1,000-fold |
Photoreceptor PDE6 is structurally close to PDE5. Drugs built to occupy the PDE5 catalytic site often lean on PDE6 as well. A retinal paper that treated 'PDE5-selective' inhibitors as PDE5/6 drugs put vardenafil among the more potent PDE6 hits on the bench. Label language stays milder - that >15-fold line - and that is the language we counsel from.
Clinically the neighbour shows up as a bluish wash, extra brightness, or brief blur while the drug is in the blood. It tracks dose and usually fades as the four-to-five-hour half-life clears. It is not a badge of 'the tablet is working.'
Sudden vision loss is a different file. Stop the tablet. Seek care. Do not wait to see if the blue tinge 'settles into' a dark field. If colour shift at 20 mg is the only complaint and the hold is clean, the conversation may be a lower mark or a different card - not a trophy debate.
Bench papers that call vardenafil a potent PDE6 hitter are useful context and are not a license to invent a percentage of men who will see blue. Counsel the mechanism. Record whether it happened. Do not turn a fold number into a prediction you cannot defend.
What this slip will not rank
Internet charts love a winner: 'most selective,' 'fastest,' 'strongest.' Those words collapse a fold versus PDE6, a Tmax, and a milligram ceiling into one personality. This folio will not play. A 15-fold PDE6 gap is a counseling note. A 20 mg ceiling is a labeled maximum. A 2.5 mg tablet is an interaction floor.
Comparing vardenafil's in-vitro IC50 with sildenafil's or tadalafil's does not tell you who sleeps better after a first dose. It tells you the bench liked a tight PDE5 fit. Patients live on holds, food, and a QT line. Rank those.
If someone wants a league table anyway, send them to the match file and watch it refuse a crown too. Two refusals are the point. This site's method is Draw, Note, Shelf-check, Bind - not Draw, Rank, Boast, Sell.
Why 20 is the high card, not the winner
Twenty milligrams is the labeled maximum for the film tablet, once a day. It exists because some men need more effect after a fair 10 mg trial, and because the dose-response does not stop at 10. It is a ceiling, not a personality.
Going to 20 mg also goes toward more flush, more headache, and more chance of a PDE6 colour note. If 10 mg already moved QTc in a thorough study, 20 mg is not the place to get casual about a borderline ECG or a new antiarrhythmic.
Do not treat 20 as a trophy versus a 25 mg sildenafil diamond or a 10 mg Cialis card. Those milligrams are not interchangeable currencies. The match file keeps them on one shelf without a crown.
Stamp the hold, skip the trophy
Draw the fold versus PDE6 and stop calling it a medal. Note the QT study and the antiarrhythmic avoid. Shelf-check CYP3A4 so you know whether 2.5 mg is the only legal mark. Bind 20 mg only as a ceiling after a fair mid-dose trial on a clean hold.
Selectivity counseling is: colour wash can happen, sudden vision loss is an emergency, and tadalafil may be quieter on PDE6 if that is the only gripe. Heart counseling is: this card does not get a pass because it is 'potent.'
If the real question is which of three cards fits a clock and a plate, leave this slip and open the match file. This page will not crown a winner.
Last Updated
Reader mail
Reader questions on this review
Answered by Dr. Ingrid Halvorsen, MD · Internal medicine & clinical pharmacology
The letters I keep from this slip are about trophies, blue vision, and whether 2.5 mg is a 'soft' tablet. I answer with folds, QT, and the interaction floor. Bring your own ECG and bottle list to someone who can see you.
Because strong CYP3A4 inhibitors turn a 10 mg swallow into a much larger exposure. Ritonavir is the textbook: one 2.5 mg, then nothing again for 72 hours. Other strong inhibitors pull 2.5 mg into a 24-hour cap. The small tablet is an interaction card, not a personality dose and not a starter for a healthy man on no other drugs. If your list is clean, your prescriber will likely still open at 10 mg. If a protease inhibitor is already there, ignoring 2.5 mg is how people get loud vasodilator effects they then blame on 'Levitra being strong.'
Congenital long QT in the family file - is any Levitra card allowed?
The label says people with congenital QT prolongation should avoid vardenafil. That avoid is not graded by milligram. 2.5 mg is not a loophole. If ED still needs a drug, the conversation moves to a different molecule and a cardiology look, not to a half tablet of this one. I would rather you leave this slip blank than 'try a tiny bit.' QT risk is not a titration exercise at home.
Amiodarone is already in the box. Which hold wins?
The antiarrhythmic hold wins. Amiodarone is Class III. The label groups it with sotalol and tells you to avoid Levitra. Same sentence covers Class IA drugs such as quinidine and procainamide. Do not bargain with 2.5 mg. Do not assume an 'old' amiodarone prescription is inactive because the dermatologist wrote it years ago - check whether it is still being taken. If the antiarrhythmic stays, this card leaves the shelf.
Blue tinge after 20 mg - is that PDE6 or something I should fear?
A fading blue or bright wash while the drug is on board is the PDE6 neighbour, dose-linked, usually gone as the 4-to-5-hour half-life clears. Fear the other visual event: sudden loss in one or both eyes. That is stop-and-urgent-care, not 'wait for the blue to pass.' If the wash is merely annoying at 20 mg, ask about a lower mark or a card with a wider PDE6 gap. Do not keep climbing to prove a trophy.
High-fat lunch then 20 mg - delay, or a wasted tablet?
Delay and a softer peak, not a wasted tablet. Label food studies put the Cmax cut in the 18 to 50 percent range after a high-fat meal and can push Tmax later by about an hour. A ordinary mid-fat meal barely moved PK. If the lunch was a heavy plate, swallow earlier or accept a later onset. Do not add a second 20 mg because the first felt late. Once a day is the ceiling regardless of lunch.
Why shouldn't I treat 20 mg as the winner card on a forum chart?
Because 20 mg is a maximum, not a score. Forums collapse three different milligram locks into one 'strongest pill' cartoon. This shelf's Cialis lock is 10 mg PRN. The Viagra lock is 25 mg as a first diamond. Levitra's interesting marks here are 2.5 and 20. Those numbers do not compete. A man who needs 20 mg after a fair 10 mg trial is not 'winning.' He is on the labeled ceiling. A man who needs 2.5 mg because of ritonavir is not 'losing.' He is on the interaction floor.
Is ritonavir the only reason anyone ever sees 2.5 mg?
It is the loudest reason, not the only one. Other strong CYP3A4 inhibitors - certain azoles, other protease inhibitors - also pull the dose down, sometimes to 2.5 mg in 24 hours rather than 72. A clinician may also pick 2.5 mg when several smaller risks stack and they want the floor. What 2.5 mg is not: a starter souvenir for a man with a clean list who wants 'just a taste.' That man still belongs on the usual 10 mg conversation unless something else on the chart says otherwise.
Class IA quinidine - same rule as Class III, or a softer look?
Same avoid. The label lists Class IA and Class III together. Quinidine and procainamide are not a 'discuss' - they are in the avoid sentence with amiodarone and sotalol. If quinidine is historical and long stopped, the current list may be clean. If it is current, Levitra is the wrong card. Do not parse IA versus III as a loophole.
Does better PDE5 potency mean a safer tablet than the others?
No. Potency at the target tells you you can occupy PDE5 at a smaller milligram. It does not erase PDE6 neighbour effects, the QT study, the unknown nitrate interval, or a 15 percent bioavailability that makes CYP3A4 collisions punchy. Safer is a clean hold and a milligram that matches the list. The three-card file compares clocks and holds without handing out medals. I will not crown this molecule because a bench IC50 looks prettier.
These replies are teaching, not a treatment plan for the person who asked. Take your own history, labs and medicine list to a prescriber who can see all three.