Bridging Therapy: How to Safely Switch Between Blood Thinners

Switching between blood thinners isn’t just a matter of stopping one pill and starting another. For patients on long-term anticoagulation, even a short break - like for surgery or a dental procedure - can be dangerous. Too little protection, and you risk a stroke or blood clot. Too much, and you could bleed uncontrollably. That’s where bridging therapy comes in. But here’s the catch: most people don’t need it anymore.

What Is Bridging Therapy, Really?

Bridging therapy means using a fast-acting injectable blood thinner - usually low molecular weight heparin (LMWH) like enoxaparin - while temporarily stopping a longer-acting one like warfarin. The goal is to fill the gap when your blood’s natural clotting ability is at its lowest. It’s not a routine step. It’s a targeted tool for very specific high-risk cases.

Think of it like this: warfarin takes days to wear off and days to build back up. If you stop it for a knee replacement, your body is unprotected for a week. LMWH works in hours and leaves in hours. So you start it a few days before surgery to keep things covered, then stop it 24 hours before the cut to reduce bleeding risk.

But here’s what changed in the last decade: studies proved bridging doesn’t help most people. The 2015 BRIDGE trial, which followed over 1,800 patients, found that those who got LMWH bridging had more major bleeding - 2.3% - compared to 1% in those who didn’t. And the stroke risk? Exactly the same. That’s not a win. It’s a loss.

Who Actually Needs Bridging?

Not everyone on blood thinners needs this. In fact, fewer than 1 in 10 do. Current guidelines from the American Heart Association and American College of Cardiology limit bridging to just two groups:

• People with mechanical heart valves in the mitral position
• Those who had a blood clot (like a DVT or pulmonary embolism) within the last 3 months

If you have atrial fibrillation with a CHA₂DS₂-VASc score of 5 or higher - say, you’re 75, had a stroke before, have high blood pressure and diabetes - you might think you’re high risk. But unless you have one of those two conditions above, bridging isn’t recommended. The bleeding risk outweighs the benefit.

Why? Because for most people with atrial fibrillation, the real danger isn’t clots during the break - it’s the bleeding from the bridge itself. The body doesn’t need constant full-strength anticoagulation. It just needs enough to prevent clots, and that’s often already covered by stopping warfarin a few days early and restarting it right after surgery.

Why DOACs Changed Everything

Direct oral anticoagulants - apixaban (Eliquis), rivaroxaban (Xarelto), dabigatran (Pradaxa), and edoxaban (Savaysa) - have made bridging almost obsolete. Why? Because they work fast and leave fast.

Warfarin has a half-life of 36 to 42 hours. That means it takes days to clear your system. DOACs? Half-lives range from 5 to 17 hours, depending on kidney function. Apixaban clears in about 12 hours. So if you’re on Eliquis and need a colonoscopy, you just skip your morning dose the day before. No injections. No bridging. No extra risk.

That’s why, as of 2023, DOACs make up 75% of all new anticoagulant prescriptions. Doctors aren’t switching patients to warfarin anymore unless there’s a specific reason - like a mechanical valve or severe kidney disease. The days of routine bridging are over.

How Bridging Works (If You Need It)

If your doctor says you’re one of the few who need bridging, here’s what to expect:

1. Stop warfarin 5-6 days before surgery. This lets your INR drop below 1.5 - the target to reduce bleeding risk.
2. Start LMWH 3 days before surgery. Typically, enoxaparin 1 mg/kg once daily or 0.5 mg/kg twice daily. This keeps your blood thin during the warfarin gap.
3. Stop LMWH 24 hours before surgery. For major procedures, you might stop it 36 hours before if there’s high bleeding risk.
4. Restart warfarin 12-24 hours after surgery. Often at 15-20% higher than your previous daily dose to get back to therapeutic levels faster.
5. Check INR in 3-4 days. Your doctor will adjust your warfarin dose based on the result.

Don’t skip the INR check. Too low, and you’re at risk for clots. Too high, and you’re at risk for bleeding. Timing matters. Miss the window, and you could end up in the ER.

What About Other Blood Thinners?

If you’re on fondaparinux (Arixtra), stop it 36-48 hours before surgery. Unfractionated heparin (UFH) - given by IV - can be stopped just 4-6 hours before. But UFH is rarely used outside hospitals because it needs constant monitoring.

For DOACs, the rules are simpler:

• Apixaban (Eliquis): Skip the dose the day before surgery. No bridging.
• Rivaroxaban (Xarelto): Skip the day before. If you have poor kidney function, skip two doses.
• Dabigatran (Pradaxa): Skip the day before. If your creatinine clearance is under 30 mL/min, skip two doses.

Transitioning from a DOAC to warfarin? That’s different. You don’t bridge. You start warfarin on the same day you stop the DOAC - and keep giving the injectable heparin for 5 days until your INR hits 2.0. It’s not bridging. It’s overlapping.

The Hidden Risks of Bridging

Even if you’re in the 10% who need it, bridging isn’t harmless. Here’s what you might not know:

• Bleeding risk jumps. The BRIDGE trial showed a 2.3% chance of major bleeding with bridging versus 1% without.
• It’s inconvenient. You need daily injections for 5-7 days. Many patients miss doses or give them wrong. Studies show 15-20% non-adherence.
• It’s expensive. A 7-day course of enoxaparin costs $300-$500 out-of-pocket in the U.S. - and insurance doesn’t always cover it.
• It’s confusing. Patients often don’t know when to stop, when to restart, or why they need two drugs. Miscommunication between surgeon and primary doctor is common.

One patient I spoke with - a 68-year-old woman with atrial fibrillation - was told she needed bridging for a hip replacement. She started injections, got a bruise from a missed dose, and bled for days after surgery. Her INR was fine. The problem? No one checked her kidney function. Her body couldn’t clear the LMWH fast enough.

What Should You Do?

If you’re on a blood thinner and have surgery coming up:

• Ask your doctor: “Am I in the 10% who need bridging?”
• Ask: “Is this a DOAC? If so, do I need to stop it?”
• Ask: “What’s my CHA₂DS₂-VASc score? What’s my HAS-BLED score?”
• Ask: “What happens if I just stop my pill and restart it after surgery?”

Don’t assume bridging is safer. It’s not. The default answer should be: “No, you don’t need it.” Only if you have a mechanical mitral valve or a clot in the last 3 months should it even be discussed.

What If You’re Switching from Warfarin to a DOAC?

This is common. Many patients are switched because DOACs are easier, safer, and don’t need blood tests. Here’s how to do it right:

1. Stop warfarin.
2. Wait until your INR is below 2.0.
3. Start the DOAC the next day.

No bridging. No overlap. No injections. Just stop one, start the other. The only exception? If your INR is still above 2.0 after 2 days, wait until it drops. Rushing this step can cause bleeding.

Same rule applies in reverse: if you’re switching from a DOAC to warfarin, start warfarin the same day you stop the DOAC. Add heparin for 5 days until your INR is therapeutic. But again - that’s not bridging. That’s overlap.

The Bottom Line

Bridging therapy isn’t outdated because it doesn’t work. It’s outdated because we now know it harms more people than it helps. For the vast majority of patients - especially those on DOACs - the safest move is to stop the blood thinner, do the procedure, and restart it.

Doctors used to bridge out of habit. Now, they should bridge out of necessity. If your doctor suggests it, ask why. Demand to see your risk scores. Push back if you’re not in the high-risk group. You’re not being difficult - you’re being smart.

The goal isn’t to keep your blood thin at all times. It’s to keep you alive - without bleeding, without clots, without unnecessary shots, without extra cost, without fear.