01Can 20 mg stay on the script with those inhibitors?
No. The inhibitor rows write 2.5 mg or 5 mg. Twenty milligrams is the ordinary maximum after a 10 mg start in men who are not on those drugs. This site's 20 mg lock does not override CYP3A4.
Age 65 consider-start of 5 mg does not raise a ritonavir cap. The two rows stack.
02Does daily grapefruit act like ritonavir?
Grapefruit can raise CYP3A4-substrate exposure. The insert does not print a grapefruit milligram table the way it prints ritonavir 49-fold. Tell the prescriber about a daily grapefruit habit before anyone prices ten 20 mg tablets.
A shop questionnaire that never asks about grapefruit or ritonavir is incomplete. That is a history gap, not a second labelled 2.5 mg row.
03How does ketoconazole split between 2.5 and 5 mg?
Ketoconazole 200 mg once daily with Levitra 5 mg produced a 10-fold AUC rise and a 4-fold Cmax rise. The cap at that ketoconazole dose is 5 mg in 24 hours.
Ketoconazole 400 mg daily may raise exposure further, so the cap becomes a single 2.5 mg Levitra dose in 24 hours. Itraconazole follows the same 200 versus 400 split.
05Which other drugs share the 2.5 mg in 24 hours row?
Indinavir, saquinavir, atazanavir, and clarithromycin sit with ketoconazole 400 mg on the 2.5 mg in 24 hours list. Indinavir 800 mg three times daily with Levitra 10 mg raised AUC 16-fold and Cmax 7-fold and doubled half-life.
Erythromycin sits on the moderate row with ketoconazole 200 mg: no more than 5 mg in 24 hours. Do not treat every antibiotic as the same cap.
06What if an alpha-blocker and a strong inhibitor are both there?
On a stable alpha-blocker, Levitra starts at 5 mg, or 2.5 mg when certain CYP3A4 inhibitors are also used. The alpha-gap probe holds the standing-pressure story.
Do not open at 20 mg because the vault lock is 20. The chart, not the SERP, picks the milligram.