Heparin

Heparin is an injectable anticoagulant used across several products and routes to prevent and treat blood clots and related complications. The following uses are supported by the FDA product evidence:

• Prevention and treatment of venous thrombosis (blood clots in the veins) and pulmonary embolism (clots in the lungs)
• Prevention of post-surgical deep vein thrombosis and pulmonary embolism in patients undergoing major chest or abdominal surgery, or others at elevated risk
• Atrial fibrillation with embolization (irregular heartbeat causing clots to travel) — supported by Heparin Sodium Injection; Heparin Sodium in Sodium Chloride and Heparin Sodium in 5% Dextrose label this as thromboembolic complications associated with atrial fibrillation
• Treatment of disseminated intravascular coagulation (DIC) — a serious condition of widespread internal clotting
• Prevention of clotting during arterial and cardiac surgery
• Prevention and treatment of peripheral arterial embolism (clots in the arteries of the arms or legs)
• Anticoagulant use during blood transfusions, extracorporeal circulation (such as heart-lung bypass), and dialysis procedures

Heparin works by latching on to a natural blood protein called Antithrombin III and changing its shape, dramatically boosting its ability to block clotting factors — especially Factor Xa and thrombin (Factor IIa). These factors are key steps in the chain reaction your body uses to form a clot. Heparin also prevents the final hardening of a clot by blocking the fibrin-stabilizing factor. One important limit: heparin cannot dissolve clots that already exist — it stops new ones from forming and existing ones from worsening.

Resistance to heparin can occur in certain situations — including fever, active thrombosis, infection, heart attack, cancer, or antithrombin III deficiency — so close monitoring and possible dose adjustment are needed in those cases.

Heparin is always given by injection — never by mouth, since the gut cannot absorb it. Depending on the situation, it may be given as a continuous intravenous infusion, as intermittent intravenous injections every 4 to 6 hours, or as a deep subcutaneous (under-the-skin) injection every 8 to 12 hours using a different site each time.

• Intravenous doses work almost immediately after administration
• Doses are adjusted based on frequent blood clotting tests — your care team tracks this carefully
• Always follow the exact product, strength, and schedule your prescriber has ordered

The most important side effects to know about with heparin include:

• Bleeding — the most common and serious complication; can occur at virtually any site in the body
• Low platelet count (thrombocytopenia) — reported in up to 30% of patients
• Redness, pain, mild bruising, or skin breakdown at the injection site (more common with subcutaneous use)
• Generalized allergic reactions — chills, fever, hives; rarely, severe reactions including anaphylaxis
• Elevated liver enzymes (aminotransferase levels) — seen in a high percentage of patients
• High potassium levels (hyperkalemia) — especially in those with diabetes, kidney disease, or acidosis
• Hair loss (temporary and delayed)
• Osteoporosis with long-term high-dose use

Serious internal bleeding — including adrenal, ovarian, and retroperitoneal hemorrhage — can be hard to detect. Any unexplained drop in blood pressure or blood count should prompt urgent evaluation.

• Bleeding risk: Hemorrhage, including fatal events, can occur anywhere in the body. Risk is highest in patients over 60 (especially women), and in those with bleeding disorders, recent surgery, stomach ulcers, or liver disease.
• HIT and HITT: Heparin can trigger a rare but dangerous immune reaction (heparin-induced thrombocytopenia) where the body paradoxically forms more clots. This can happen during treatment or even weeks after stopping heparin. Platelet counts must be monitored regularly.
• Fatal medication errors: Heparin vials come in different strengths. Concentrated vials have been fatally confused with catheter lock flush products — always verify the correct vial before use.
• Benzyl alcohol toxicity: Heparin formulations containing the preservative benzyl alcohol must never be used in neonates or infants — it can cause a life-threatening condition called gasping syndrome and other serious reactions.
• Hyperkalemia: Heparin can suppress a hormone (aldosterone) that regulates potassium, causing dangerously high potassium levels — particularly in patients with diabetes, chronic kidney disease, or metabolic acidosis.
• Andexanet alfa interaction: Using heparin after andexanet alfa (used to reverse other blood thinners) can make heparin ineffective and lead to serious clotting events; avoid this combination.

Heparin interacts with several medications that affect clotting or platelet function — combining them raises the risk of serious bleeding or, in some cases, reduces heparin's effectiveness:

• NSAIDs (ibuprofen, aspirin, indomethacin, celecoxib) — interfere with platelet function and raise bleeding risk
• Antiplatelet drugs (thienopyridines, dipyridamole, abciximab, eptifibatide, tirofiban) — further impair clotting defenses in patients on heparin
• Warfarin and other oral anticoagulants — heparin can affect prothrombin time test results; blood draws must be timed carefully after the last heparin dose
• Andexanet alfa — binds to antithrombin III and blocks heparin's effect, risking dangerous clotting; avoid using heparin after andexanet alfa
• Antithrombin III (human) — dramatically amplifies heparin's blood-thinning effect; heparin dose must be reduced to prevent bleeding
• Digitalis, tetracyclines, nicotine, antihistamines, IV nitroglycerin — may partially reduce heparin's anticoagulant action
• Dextran and hydroxychloroquine — can interfere with platelet function and increase bleeding risk

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Do not use heparin if you have a personal history of HIT or HITT (heparin-induced platelet and clotting reaction)
• Do not use if you have a history of low platelet count related to pentosan polysulfate
• Do not use if you have a known allergy to heparin or pork products
• Do not use if you have uncontrollable active bleeding (except when caused by DIC)
• Tell your doctor if blood clotting tests cannot be reliably performed — full-dose heparin requires ongoing monitoring
• Use with caution if you have a history of allergy, since heparin is derived from animal tissue
• Older adults (over 60), especially women, have higher blood levels of heparin and a greater bleeding risk; lower doses may be appropriate
• In neonates and infants, only preservative-free heparin formulations should be used to avoid benzyl alcohol toxicity
• If pregnant, preservative-free heparin is recommended; animal studies showed increased early fetal loss at very high doses, though human studies have not shown increased birth defects
• If breastfeeding, heparin is unlikely to pass into breast milk or be absorbed by the infant, but benzyl alcohol from preserved formulations may enter milk — preservative-free is preferred
• Tell your care team about all other medications, especially other blood thinners, anti-inflammatory drugs, or heart medications

Too much heparin causes excessive bleeding. Early signs may include nosebleeds, blood in the urine, black or tarry stools, or easy bruising. If overdose occurs, the antidote is protamine sulfate, given slowly by intravenous infusion — it directly neutralizes heparin's effect. Protamine sulfate itself carries a risk of severe low blood pressure and anaphylaxis (life-threatening allergic reaction), so it is only given in settings equipped to handle emergencies.

At full therapeutic doses, heparin measurably prolongs several blood clotting tests — including activated clotting time, activated partial thromboplastin time (aPTT), prothrombin time, and whole blood clotting time. These tests are used to guide dosing. Low doses of heparin generally do not significantly affect these test results. Heparin does not typically change bleeding time (how quickly a skin wound stops bleeding).

Heparin cannot be absorbed through the gut, so it must always be injected. When given intravenously, its effect begins almost immediately. It binds extensively to proteins in the blood — including antithrombin, fibrinogens, and lipoproteins. The body clears heparin primarily through the liver and immune system cells; it does not break down through normal enzyme pathways. Its half-life (the time for the drug level to drop by half) ranges from about 30 minutes to 2 hours and depends on the dose given. Patients over 60 may have higher heparin blood levels and prolonged clotting test results compared to younger patients on the same dose.

Store at 20° to 25°C (68° to 77°F); excursions permitted between 15° and 30°C (59° and 86°F).