Levofloxacin
Fluoroquinolones · given by injection, ophthalmic, oral · on the market since 2010
What it's made of
Each functional group on the molecule does a specific, predictable job.
Carboxylic acid
What it does. At the pH of blood this group is ionised, which means the molecule is permanently charged. Charged molecules stick tightly to blood proteins, get filtered by the kidney, and are largely locked out of the brain.
What it opens up. Excellent for anything in the bloodstream, joints, or kidney. Effectively rules out brain targets unless a transporter carries it in.
Basic amine
What it does. Neutral enough to slip through membranes, then becomes charged inside the acidic compartments of the cell and gets trapped there. Concentrations inside cells can reach many times the blood level.
What it opens up. Diseases of the cell's internal recycling compartments, and a common reason a drug accumulates in lung, liver, and eye tissue far beyond what the blood level suggests.
Aromatic fluorine
What it does. The liver attacks rings at predictable positions. Fluorine is small enough not to disturb the shape but strong enough that the attack fails, so the molecule survives longer.
What it opens up. Mainly a durability upgrade, but it also nudges the molecule into being slightly greasier, which helps it enter the brain.
Quinolone core
What it does. Traps the enzyme that unwinds DNA mid-cut, converting a repair machine into a source of DNA breaks.
What it opens up. Bacterial by design, but the human equivalent enzyme is a known cancer target, so the frame recurs in oncology.
Where it can get to
Predicted from molecular weight, lipophilicity, polar surface area and hydrogen-bond donor count. A drug can only act where it distributes, so this constrains which conditions are addressable before any biology is considered. derived
What it binds — and whether we can reach it
Binding affinity is only meaningful against the plasma concentration reached at the approved dose. A target requiring higher concentrations cannot be engaged in a patient, whatever the in vitro potency. Most repurposing hypotheses fail at this step, and it is rarely checked before a trial is proposed. measured
| Target | Kind | Action | Affinity (pAct) | Can it be engaged? |
|---|---|---|---|---|
| SLC47A1 | Transporter | — | 4.75 | Not reachable |
| RCE1 | Enzyme | — | 4.39 | Not reachable |
| KCNH2 | Ion channel | — | 3.04 | Not reachable |
New uses, and who is already trying them
2 conditions are linked to targets this drug engages at a dose people already tolerate, but none has been checked against trial records yet. That is missing work, not a negative result — trial-record checking has been run on 110 of 1208 generics so far.
Why nobody will fund it
20 companies make this across 54 approved products. With that many manufacturers the price has fallen to production cost. A company funding a trial could not recover it — competitors could market the same molecule for the new indication immediately, without contributing.
A new route or dosage form qualifies for a 505(b)(2) application, which carries three years of exclusivity for that formulation. It is the only remaining route to exclusivity on a generic molecule.
What it would cost to find out
Derived, not quoted. Events needed is 4(zα+zβ)²/ln(HR)²; enrolment is that divided by the event rate and follow-up. The 1/ln(HR)² term dominates: halving the detectable effect size roughly quadruples enrolment. derived
Cost per person reached is the relevant metric for a non-commercial funder, since there is no revenue to set against the outlay.
Ask for ideas nobody has listed
Reasons from the functional groups and distribution above, excluding conditions already listed. Output is hypotheses for falsification, not findings. Not medical advice.
Who might pay for the trial
Trials of off-patent drugs are rarely funded by venture capital or pharma. They are paid for by government grants and disease foundations. Here is who has funded work on this molecule before, what federal mechanisms are open now, and which foundations fund trials in the disease areas it touches. measured
Open notices with an explicit mandate to fund work on approved or off-patent molecules.
Grants.gov lists US federal money. Many off-patent drug trials are supported by disease foundations and nonprofits. These are matched to the body systems this drug touches. assumed
Who manufactures it
Companies holding an approved abbreviated application for this molecule in the United States, from the FDA Orange Book. Supply already exists at scale, so a trial would not need a manufacturing programme — but any of these could also be a partner, or an objector.
Nothing on this page is medical advice. Candidate uses are unproven hypotheses derived from public data; established uses are listed for verification only. Figures carry their provenance inline — anything marked assumed or derived is not a measurement.
← Back to the full ledger