My neighbor Maria learned the hard way that “water pills” aren’t interchangeable. After her pharmacy subbed furosemide for the torsemide she’d taken for years, her ankles ballooned by dinnertime and she gained six pounds of fluid overnight. Her cardiologist fixed it with a simple 2-to-1 ratio, but only after an ED trip. If you’re staring at a discharge sheet that says “change torsemide to furosemide,” here’s the math clinicians use–and the pocket trick they teach residents so nobody repeats Maria’s surprise.
Quick rule: 20 mg of torsemide ≈ 40 mg of furosemide. That 1:2 conversion works for most stable out-patients, but double it (1:4) if the person has advanced kidney disease or is already on big loop doses. Always give the furosemide twice daily; its half-life is shorter than a coffee break, so once-a-day dosing leaves 16 hours of rebound.
Real-life example: Mr. Alvarez takes 10 mg torsemide each morning for mild heart failure. His new HMO formulary only lists furosemide. Retail price: $4 instead of $78–nice for him, but only if the dose is right. Using the 1:2 ratio, he needs 20 mg furosemide, so the pharmacist dispenses 10 mg tablets and tells him “one tab twice a day, eight hours apart.” He weighs himself daily for a week; no new socks marks, no 3-lb jumps–conversion successful.
One last tip: take the first furosemide dose around 7 a.m. and the second no later than 3 p.m.; otherwise you’ll meet your bathroom floor at 2 a.m. And keep the same salt intake the first week–changing both drug and diet is like turning two steering wheels at once.
Torsemide to Furosemide Conversion: 7-Step Dose-Swap Formula That Saves Hours at the Bedside
Friday 3 a.m., six admissions still waiting, and the attending just asked why Mrs. K’s 20 mg of torsemide is “suddenly” 80 mg of furosemide. You could flip through three guideline PDFs, or you could run the seven-line card every ICU nurse keeps taped inside the badge wallet. Here it is, cleaned up for the chart and stripped of anything that wastes keystrokes.
Step-Line Card (laminate it, photograph it, never google again)
1. Check the gut. PO torsemide absorbs at 80 %, PO furosemide at 50 %. If the patient is swallowing pills, multiply the torsemide dose by 1.6 before you do anything else. Example: 20 mg PO torsemide → 32 mg PO furosemide.
2. Decide on the vein. IV torsemide is 1:1 with PO torsemide. IV furosemide is 2:1 with PO furosemide. So the same 20 mg IV torsemide becomes 40 mg IV furosemide–no calculator needed.
3. Halve if the albumin < 2.5 g/dL. Hypoalbuminemic patients hang on to loop diuretics like a sponge. Whatever number you got in step 1 or 2, cut it in half and plan to re-dose in 6 h instead of 12 h.
4. Add 20 % for CHF flair, subtract 20 % for CKD 4. A crashing ejection fraction needs more punch; scarred kidneys need less flood. These two cancel out surprisingly often, but write the adjustment once so the next shift does not repeat the math.
5. Split high doses. Anything above 80 mg PO furosemide (or 40 mg IV) given once will ride the ototoxicity elevator. Split to BID and stagger by 8 h so the night dose does not land at 2 a.m. when pharmacy is closed.
6. Match the timing of other meds. If the patient takes digoxin or lithium, give furosemide at least 2 h apart to avoid spike-induced toxicity. A simple “Hold ACE-I for 2 h post-dose” order prevents the BP crater.
7. Chart the ratio. Write “Conversion: torsemide 20 mg ≈ furosemide 64 mg PO (1:3.2)” in the progress note. Next week when coverage sees “diuresis inadequate,” they will escalate sensibly instead of doubling blindly.
Real-World Sanity Checks
“But my patient swears the yellow pills worked better.” They probably did–bioavailability swings 30 % between generics. If urine output drops > 30 % after the swap, bump the furosemide by 20 % and recheck in 8 h; 90 % of the time that nails it.
“Lasix drip after bolus?” Only if the 24-h total exceeds 240 mg PO equivalent. Below that, scheduled boluses waste less nursing time and fewer IV lines.
Tape the card above the Pyxis. Your future self–running on coffee number four–will thank you when the conversion takes 30 seconds instead of half an hour.
1:2? 1:4? Stop Guessing–Here’s the Evidence-Based Ratio for Torsemide to Furosemide Switch
I still remember the call from Mrs. Alvarez’ daughter: “Mom’s ankles disappeared again and the clinic said to double the furosemide, but it’s not working.” Same story, different week. The poor woman had been yo-yoing between 40 mg and 80 mg of furosemide for months while the scale kept climbing. When we finally swapped her to torsemide, the question landed on my desk like a hot potato: what dose? 1:2? 1:4? Ask three cardiologists, get four answers. So we cracked the journals instead of guessing.
The first paper that made me blink was a 1995 crossover trial in J Card Fail. Twelve stable HF patients took each diuretic for a week, 10 mg torsemide vs 40 mg furosemide. Net sodium loss was almost identical. Translation: 1:4 potency, at least when kidneys still behave. But real life is messier. A 2011 Mayo Clinic cohort followed 254 discharged patients who’d been switched in either direction. After propensity matching, the 1:2 group (torsemide 20 mg ↔ furosemide 40 mg) landed back in the hospital just as often, while the 1:4 group stayed dry longer. Their edema scores at 30 days: 1.4 vs 2.2 on the 4-point scale. A dry ankle beats a squishy one.
Then came the punch-in-the-gut study nobody quotes at morning report: a 2020 VA database review of 3,700 guys with EF <40 %. Doses were normalized to furosemide equivalents. Mortality at one year:
- torsemide 1:1 → HR 1.38 (yes, worse)
- torsemide 1:2 → HR 1.07 (meh)
- torsemide 1:4 → HR 0.82 (winner)
Same findings for readmissions. The 1:4 crowd also needed fewer potassium runs–probably because they weren’t chasing loops with bigger blasts.
Practical cheat-sheet we taped above the Pyxis:
| Furosemide (mg PO) | Torsemide (mg PO) |
|---|---|
| 20 | 5 |
| 40 | 10 |
| 80 | 20 |
| 160 | 40 |
IV ratios? Halve the torsemide number–its oral bioavailability hovers near 80 %, while furosemide stumbles in at 50 %. That’s why 20 mg IV torsemide ≈ 40 mg IV furosemide, but don’t try the reverse without a bathroom plan.
Special cases: if GFR <30 mL/min, stay at 1:4 but split the dose. Once-daily torsemide still beats b.i.d. furosemide in trough natriuresis trials, but the kidney’s sluggish tubules need a second whack later in the day. And for the cirrhotic with ascites? Stick to 1:4, add spironolactone, then watch ammonia–torsemide’s longer half-life can tip a sleepy liver into asterixis faster than you can spell it.
Back to Mrs. Alvarez. We moved her from furosemide 80 mg b.i.d. to torsemide 20 mg every morning. Ten days later she sent me a photo: ankles with actual bones. Weight down 6 lb, no 3 a.m. sprints to the toilet. One happy daughter, one evidence-based smile.
So the next time someone shrugs and says “somewhere between 1:2 and 1:4,” hand them the VA numbers. Start at 1:4, adjust by wet socks and bathroom scales–not by habit.
IV Push vs PO: Does the Conversion Factor Change When You Drop the Needle?
Monday, 07:14. The charge nurse slaps a new chart on the counter: “Mrs. K’s lungs are full again–double her furosemide, but she’s NPO after mid-night.” You reach for the conversion card taped above the Pyxis: Torsemide 20 mg PO ≈ Furosemide 80 mg PO. Easy. Then you pause. Nothing’s going by mouth today. Does the 1:4 ratio still hold when the drug hits a vein instead of the duodenum?
Short answer: no. The gut and the vasculature play by different rules.
What happens to the numbers
- PO torsemide is almost fully absorbed (80–90 %), and half of it sneaks past the liver untouched. Bioavailability ≈ 80 %.
- PO furosemide limps in: anywhere from 10 % to 90 % depending on whether the patient just left a bacon buffet or is in florid edema. Average we use: 50 %.
- IV furosemide skips the turnstile–100 % arrives at the nephron.
So the 1:4 PO ratio already folds in the gut lottery. Strip that away and the handicap disappears. Convert IV to IV and the spread tightens.
The real-world table we scribble on the glove box
| Torsemide PO | Furosemide PO | Furosemide IV |
|---|---|---|
| 5 mg | 20 mg | 10 mg |
| 10 mg | 40 mg | 20 mg |
| 20 mg | 80 mg | 40 mg |
| 50 mg | 200 mg | 100 mg |
Notice the IV column is exactly half the oral column. Once you drop the needle, cut the furosemide dose in half compared with the oral equipotent number. Torsemide doesn’t change; its bioavailability is already high, so 20 mg PO ≈ 20 mg IV.
Three traps that bite on the floor
- Albumin < 2 g/dL – Loop diuretics hitch-hike on albumin to the tubule. When it’s scarce, double the IV dose or run a drip; the conversion table becomes wishful thinking.
- CRRT in the wings – If the patient is about to go on continuous filtration, IV furosemide is money wasted. Torsemide still works–its hepatic clearance keeps it alive.
- Home dose creep – Mrs. K swore she takes “one little white water pill” at home. Pharmacy reconciliation shows 160 mg furosemide PO daily. That’s 80 mg IV, not 40. Always verify the home dose before trusting the ratio.
One-sentence cheat sheet
When the patient goes NPO, halve the furosemide dose if you’re jumping from PO to IV; keep torsemide flat; and recheck urine output at 6 h–because kidneys can’t read conversion cards.
Crunch the Numbers Live: Free Calculator That Spits Out Exact Furosemide Equivalents in 3 Clicks
Last Thursday, the ICU pharmacist slid a scrap of paper across the counter: “Torsemide 40 mg PO b.i.d. → furosemide IV push. How much?”
I opened the browser tab I keep pinned on every hospital workstation, tapped three boxes, and read the number aloud before he finished chewing his pen cap. Twenty milligrams. He blinked twice, muttered “no way,” then double-checked with the reference book. Same answer. We moved on. Patient peed, potassium stayed put, attending smiled. That’s the whole story.
The widget lives at loopconverter.com–no sign-up, no ads, no spinning wheels. First box: type the torsemide dose the patient is swallowing. Second box: pick the route you want for furosemide (PO, IV, or continuous drip). Third box: hit “Convert.” The screen flashes the milligram figure plus a one-line caveat about bioavailability. Copy it, paste it into the order entry, done. If you’re on your phone, the keypad pops automatically and the answer shows in 18-point green so you can read it under the bright hallway lights.
Behind the curtain, the math is boringly reliable: 20 mg oral torsemide ≈ 40 mg oral furosemide ≈ 20 mg IV furosemide. The tool just bakes in the 50 % oral absorption fudge factor and the 2:1 oral-to-IV ratio so you don’t have to run the same scribble on the back of a glove. It also spits out the 24-hour total if you punch in divided doses–handy when the day team wrote for torsemide twice daily and the night team wants one bolus drip.
Residents keep it in their WhatsApp group description, nurses slap the QR code on the med room door, and one attending laminated it to his badge reel. No grand claims: it won’t write the progress note or check the creatinine. It just answers the one question that used to stall hallway traffic. Try it during the next drip titration and you’ll hear the same surprised grunt I got–sounds like victory in hospital speak.
Hidden Trap: Why Heart-Failure Patients Sometimes Need a 50 % Bump After the Swap
Cardiology fellows learn the 1:2 ratio on day one–20 mg of torsemide equals 40 mg of furosemide. The textbooks print it in bold, the pharmacists repeat it, and the electronic order sets hard-code it. Yet three days after the “equivalent” switch, the same person who walked in dry at 1.8 kg suddenly gains two pounds, neck veins pop, and the night nurse pages you about orthopnea at 02:15. What happened? The loop-diuretic math ignores one rude fact: torsemide hangs around roughly seven hours; furosemide, barely two. When the drug clock runs out sooner than the kidneys expect, sodium re-absorption snaps back like a released spring. Unless you compensate for that gap, the patient re-absorbs every milliliter you just spent shifts peeing away.
The half-life mismatch is only half the story. Oral furosemide is famously moody–absorption swings from 10 % to 90 % depending on gut edema, food, and whether the patient took it with the morning oatmeal or an hour later. Torsemide behaves more politely, soaking in at 80 % no matter the buffet. Swap 20 mg of torsemide for 40 mg of furosemide on paper and, in real blood levels, you may have cut the exposure by 60 %. The ventricle notices before you do.
Then there’s the aldosterone angle. Chronic torsemide use knocks the hormone down a peg; furosemide hardly touches it. Drop the torsemide, and aldosterone rebounds within 48 h, grabbing every distal sodium molecule it can find. The result is a stealth sodium claw-back that no 1:2 table predicts.
Real-world fix: most heart-failure teams quietly add 50 % more oral furosemide right after the switch–60 mg instead of 40 mg, or 80 mg if the baseline edema was stubborn–and then chase the response with daily weights and basic chemistries. If the urine output stays shy of 1.5 L by day two, they bump again instead of waiting for the third-pound overnight gift. IV doses bypass the gut roulette and are easier to titrate, but send the patient home on the same increased oral dose you landed on, not the textbook ratio.
Teach the patient the warning signs: shoes tight by supper, pillow count climbing, or a 2-lb morning jump. Those clues surface long before BNP creeps up. And document the starting weight in the discharge summary; the next provider will need it, because the “hidden” 50 % extra is often peeled away by well-meaning clinicians who still trust the 1:2 myth.
Renal Roller-Coaster: Adjusting the Ratio When eGFR Drops Below 30 mL/min
The 4:1 rule you learned in residency–four milligrams of furosemide for every one milligram of torsemide–starts to wobble once the eGFR dips under 30 mL/min. At that point the kidneys behave like a clogged storm drain: you can pour more water in, but nothing rushes out. Here’s how I retune the loop when the scaffold of nephrons is half-gone.
- Start with a 2:1 ratio. 20 mg of torsemide replaces 40 mg of furosemide instead of the textbook 80 mg. The reason? Organic-anion transporters on the basolateral side are sleepy, so furosemide lingers longer; torsemide still hops the shuttle, but fewer shuttles are running.
- Give it once, wait six hours. If the scale shows less than 500 mL net loss by hour six, double the torsemide dose the next day rather than redosing the same day. Below 30 mL/min the half-life of both drugs stretches to 4–6 h; stacking doses only spikes the ototoxicity curve.
- Add a thiazide on day three. Metolazone 2.5 mg with breakfast, or bendroflumethiazide 5 mg if your hospital still stocks it. The distal convoluted tubule is scarred but not dead, and the segmental synergy can pull off an extra 1–1.5 L without upping the loop dose.
- Check magnesium before you celebrate. A patient who’s +2 kg but trembling at 1.2 mmol/L Mg²⁺ will be back in ED within a week. Replace with magnesium glycinate 400 mg nightly; it absorbs better when phosphate is high, which it usually is in stage 4 CKD.
Last winter Mr. Alvarez, 68, eGFR 25 mL/min, came in with 3+ pitting to the knees. We gave torsemide 40 mg IV at 08:00. Eight hours later he’d lost 300 mL. Next morning we bumped to 80 mg and added metolazone 2.5 mg. By 18:00 the Foley bag read 2.1 L and his lungs were clear enough to lie flat. We stopped there; day-three labs showed K⁺ 3.8, Mg²⁺ 1.5, creatinine unchanged. Discharged on torsemide 30 mg po daily, metolazone every other day, and a stern handshake to weigh himself naked every sunrise.
If the urine still refuses to budge, don’t chase it with heroic boluses. Think mechanical: ultrasound for obstruction, duplex for renal-vein compression, or a quick call to interventional to rule out high-grade stenosis. Diuretics can’t squeeze a stone.
Real-World Case Walk-Through: 60 mg Torsemide → Lasix Dose Tweaked in 24 h Without Re-Admission
Cardiology floor, 7 a.m. report: Mrs. G, 72, lands back on the bed she left only two weeks ago. Bilateral pitting to the knees, 6-lb weight jump, BNP 1 180. Home recipe was torsemide 60 mg daily plus a potassium tab she kept forgetting. Overnight nurse charted two 40 mg IV furosemide pushes that barely nudged the scale. Attending scribbles “convert and titrate” on the margin of the chart. That’s where the 24-hour clock starts.
Step one: yank the PO torsemide. Oral bioavailability is good, but gut edema blunts it on arrival. We swap to IV furosemide at 2× the oral number–call it 80 mg IV q8h. Kidney list from last admission says GFR 38 mL/min, so we run a mini-bolus: 40 mg slow IV push, then 40 mg in 50 mL saline over 60 min. Urine output jumps from 30 mL/h to 180 mL/h by noon; the aide actually pages me, worried the Foley bag will overflow.
Step two: add 25 g albumin because albumin cuff reading is 2.1 g/dL. We give it right before the second furosemide bolus; the intensivist swears the oncotic drag pulls fluid back into the vasculature. Within three hours the BP climbs from 88/52 to 102/60 without a pressor, and she can breathe on 2 L nasal cannula instead of the non-rebreather she arrived with.
Step three: spot-check electrolytes at 4 p.m. K 3.0, Mg 1.4. We slam 40 mEq KCl and 2 g MgSO4 into the secondary port. The pharmacist pre-mixed the bags; no one waits for the pharmacy robot. By 8 p.m. the cumulative output is 3.2 L negative; lungs sound like popcorn instead of bathwater.
Morning math: how we landed on the new PO dose
Day-1 total furosemide: 240 mg IV. Convert to oral using 2:1 ratio (IV:PO) for furosemide → 480 mg PO furosemide equivalent. Torsemide is roughly twice as potent, so 60 mg torsemide = 120 mg furosemide. She needed four times her home dose to break the clog. We plan discharge on furosemide 80 mg PO twice daily (160 mg total) and tell her to weigh herself naked every sunrise. If the scale creeps up 2 lb, she adds 40 mg at lunch that same day–no phone tag, no ED. First follow-up in clinic at 72 h: weight down 5 lb, no orthostatics, creatinine unchanged. Zero readmission at 30 days.
Key take-away: the magic wasn’t the calculator; it was the nurse with the stopwatch charting urine every hour and the aide who refused to let the bag kink. Conversion formulas sit in books–real-life diuresis happens at the bedside, one tweaked Lasix dose at a time.
Pharmacy Insider Cheat-Sheet: Printable Wallet Card With Torsemide–Furosemide + Bumetanide Conversions
Your preceptor snaps, “What’s the IV bumetanide dose if he’s on 160 mg furosemide?” The attending’s tapping her foot, the Pyxis line is backing up, and your brain just blue-screens. Fold this card, laminate it with clear tape, and shove it behind your ID badge–problem solved before the drip chamber fills.
| Loop Agent | Oral Dose (mg) | IV Dose (mg) | Relative Potency vs Furosemide | Typical Adult Ceiling |
|---|---|---|---|---|
| Furosemide | 40 | 20 | 1× | PO 600 mg / IV 200 mg daily |
| Torsemide | 20 | 10 | 2× | PO 200 mg / IV 100 mg daily |
| Bumetanide | 1 | 0.5 | 40× | PO 10 mg / IV 5 mg daily |
Quick swap trick: 80 mg oral furosemide ≈ 40 mg oral torsemide ≈ 2 mg oral bumetanide. Halve everything for IV.
Real-world speed: Torsemide hits peak diuresis in 60 min, bumetanide 30 min, furosemide 60–120 min. If the floor nurse pages “only 200 mL since 6 a.m.,” check the agent and the clock before up-titrating.
Renal fail curveball: GFR <30 mL/min bumps furosemide to a 4× dog dose; switch to bumetanide or torsemide and you can usually stay on the card’s ratio.
Printer settings: landscape, 3×5 inch index card, narrow margins. Cut along the dashed line, fold in half, tape shut–fits a scrub pocket like a nicotine patch, minus the jitters.