Vitamin K: Nursing Drug Guide, Warfarin Reversal & IV Safety
Phytonadione restores vitamin K–dependent clotting factors when warfarin or deficiency drives a prolonged INR—but injectable labeling carries a boxed warning for fatal IV/IM anaphylaxis, coagulation is not instant, and excessive reversal can restore thrombotic risk. Injectable phytonadione prefers subcutaneous administration when feasible; urgent reversal protocols may specify oral or slow IV per bleeding severity—follow institutional anticoagulation guidance, never rush IV above 1 mg/min, and recheck INR after 6 to 8 hours.
Fatal hypersensitivity reactions, including anaphylaxis, have occurred during and immediately after intravenous and intramuscular injection of phytonadione injectable emulsion—despite dilution and on first and subsequent doses. Administer subcutaneously whenever feasible. Avoid IV and IM unless SC is not feasible and the serious risk is justified. When IV is unavoidable, inject very slowly, not exceeding 1 mg per minute, with continuous monitoring. Coagulant effects are not immediate—repeat INR and use the lowest effective dose when reversing warfarin.
📋 Contents
⚡ Quick facts
💡 Key takeaway
Before phytonadione, confirm indication, warfarin hold status, and route per institutional reversal protocol—injectable labeling prefers subcutaneous when feasible, but urgent bleeding may warrant oral or slow IV per pharmacy/prescriber. If IV is unavoidable, infuse no faster than 1 mg per minute and stay with the patient. Vitamin K does not normalize INR instantly—recheck in 6 to 8 hours and avoid oversized doses that restore thrombotic risk when anticoagulation must continue.
Most common brand names
Phytonadione (vitamin K1) is supplied as generic phytonadione tablets and historically as Mephyton (5 mg oral tablets per labeling). Parenteral products include generic phytonadione injectable emulsion and legacy names such as AquaMEPHYTON. Strengths and concentrations differ between oral tablets and injectable vials—verify milligrams, volume, and route on every order. Do not confuse phytonadione with multivitamin or dietary vitamin K supplements on the home medication list.
Why we give it — Indications
Phytonadione treats coagulation disorders from faulty formation of factors II, VII, IX, and X when caused by vitamin K deficiency or interference with vitamin K activity per injectable and oral labeling.
| Use | Detail |
|---|---|
| Anticoagulant-induced hypoprothrombinemia | Reversal of excessive effect from coumarin or indanedione derivatives such as warfarin when atrial fibrillation, deep vein thrombosis, or other indications require INR correction per labeling. |
| Vitamin K deficiency / malabsorption | Hypoprothrombinemia from obstructive jaundice, biliary fistula, sprue, celiac disease, intestinal resection, cystic fibrosis, regional enteritis, or antibacterial therapy per labeling. Oral route requires bile salts when bile flow is deficient. |
| Other drug-induced hypoprothrombinemia | When interference with vitamin K metabolism is documented (e.g., salicylates per labeling). Review MAR via medication reconciliation. |
| Neonatal vitamin K deficiency bleeding | Prophylaxis and treatment in neonates per injectable labeling (0.5 to 1 mg prophylaxis within one hour of birth; 1 mg treatment dose SC or IM). Institutional neonatal protocols may vary. |
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How it works
Phytonadione is a vitamin K replacement that promotes hepatic carboxylation of inactive precursors of clotting factors II, VII, IX, and X—the same pathway warfarin suppresses. In vitamin K–deficient or warfarin-antagonized patients, phytonadione restores production of functional clotting factors. It is not a direct clotting agent; severe bleeding may still require blood products per labeling. Phytonadione does not affect heparin anticoagulant action but may induce temporary resistance to warfarin, especially with larger doses.
Dosing overview
Dosing must be verified against current prescribing information, prescriber order, indication, and INR response. Use the lowest effective dose when correcting warfarin-associated hypoprothrombinemia—overzealous therapy may restore thromboembolic conditions per labeling.
Renal / hepatic adjustment: Not specified in the reviewed prescribing information for adult dose reduction. Repeated large doses are not warranted in liver disease if initial response is unsatisfactory per labeling.
Missed dose: Not specified in the reviewed prescribing information for adult oral or parenteral phytonadione—follow prescriber and anticoagulation protocol for repeat INR-based dosing.
Onset, peak, duration, half-life
| Parameter | Value | Nursing relevance |
|---|---|---|
| Onset (IV) | Generally detectable within 1–2 hours per injectable labeling | Do not expect immediate hemostasis—continue bleeding precautions |
| Hemostasis (IV) | Hemorrhage often controlled within 3–6 hours per injectable labeling | Reassess bleeding; whole blood or components may still be needed if severe |
| INR improvement | May take 1–8 hours; normal INR often in 12–14 hours IV per injectable labeling | Schedule repeat INR 6–8 hours after dose per protocol |
| Onset (oral) | Generally 6–10 hours per Mephyton labeling | Oral route unsuitable when rapid reversal is required unless protocol allows |
| Half-life / elimination | Not specified in the reviewed prescribing information | Monitor INR trend rather than assuming single-dose cure |
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Before you give it — Safety check
Pretreatment checks
- Confirm indication (warfarin reversal vs deficiency vs neonatal prophylaxis) and latest INR with prescriber/pharmacy protocol
- Verify warfarin hold status, active bleeding assessment, and whether higher-level reversal (prothrombin complex concentrate, plasma) is indicated per institutional pathway
- Review allergy history and prior reactions to phytonadione or formulation components (polysorbate, propylene glycol in injectable emulsion per labeling)
- Confirm route: SC preferred for parenteral; question IV push orders that exceed 1 mg/min or IM route when SC is feasible
Contraindications
- Hypersensitivity to phytonadione or any component of the medication per injectable and oral labeling
Important interactions
| Drug / class | Effect | Nursing action |
|---|---|---|
| Warfarin / coumarin anticoagulants | Temporary resistance to prothrombin-depressing anticoagulants, especially with larger phytonadione doses per injectable labeling | Document dose given; plan repeat INR; anticipate higher warfarin dose or alternate anticoagulant when resuming |
| Heparin | Phytonadione does not affect heparin action per injectable labeling | Continue heparin per order while correcting vitamin K–dependent factors; do not confuse reversal agents |
| Antibiotics / malabsorption states | Underlying cause of hypoprothrombinemia may persist after vitamin K dose | Treat cause; repeat INR; ensure bile salts with oral dose when jaundice or malabsorption present per oral labeling |
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Administration
Oral (Mephyton / phytonadione tablets)
- Protect tablets from light; store in original carton per oral labeling
- When bile flow is deficient, oral vitamin K is not absorbed unless bile salts are given concurrently per oral labeling
- Avoid oral route when clinical disorder prevents absorption—use parenteral route per labeling
Parenteral (phytonadione injectable emulsion)
- Preferred route: subcutaneous whenever feasible per boxed warning
- IV: Only when SC not feasible; inject very slowly, not exceeding 1 mg per minute; monitor continuously for flushing, dyspnea, hypotension, chest pain, or cyanosis
- IM: Avoid unless SC not feasible—same boxed hypersensitivity warning as IV
- May dilute with 0.9% sodium chloride, 5% dextrose, or dextrose/saline; protect from light; start immediately after dilution; discard unused portions per injectable labeling
- Follow subcutaneous injection technique or IV infusion pump setup when programming slow IV rates
Preparation, compatibility, and stability
Inspect parenteral emulsion for particulate matter and discoloration before administration per injectable labeling. Dilute with compatible fluids listed in labeling; administer immediately after dilution. Protect from light at all times. Oral tablets: protect from light in closed original carton. Institutional protocols and product formulations may vary.
Expected therapeutic response
- Downward INR trend within 1 to 8 hours after parenteral dose (sooner action detectable IV than oral per labeling)
- Reduced active bleeding or stabilization of minor bleeding signs such as gum bleeding
- No infusion-related hypersensitivity during and after parenteral administration
- When anticoagulation must continue, INR returns toward—but not necessarily below—goal without overshooting into prothrombotic range per labeling warnings
Not working may look like: INR unchanged at 6–8 hours, ongoing bleeding, or failure to shorten prothrombin time after oral dose in 12–48 hours—notify prescriber/pharmacy for repeat dosing or alternate diagnosis per labeling.
Red flags — Stop and act
- During or after IV/IM/SC dose: flushing, diaphoresis, chest pain, shortness of breath, tachycardia, hypotension, cyanosis, weakness, dizziness—stop infusion/injection and escalate per anaphylaxis protocol
- Cardiorespiratory arrest or shock during parenteral administration per boxed warning
- Delayed rash, eczematous plaques, or scleroderma-like skin changes days to months after injection—discontinue and notify prescriber per labeling
- Continued major bleeding despite dose—may need blood products or higher-level reversal, not repeat large vitamin K alone
- New unilateral leg swelling, chest pain, or neurologic deficit after large reversal—possible thromboembolism when anticoagulation still indicated
Adverse effects
| Adverse effect | Frequency / severity | Nursing response |
|---|---|---|
| Fatal hypersensitivity / anaphylaxis | Reported with IV and IM; may occur on first dose per boxed warning | Stop drug; emergency escalation; document route and rate |
| Flushing, dyspnea, hypotension, tachycardia, cyanosis | Listed common reactions per injectable labeling | Stop infusion; monitor vitals; notify prescriber |
| Cutaneous reactions | Eczema, urticaria, scleroderma-like patches; onset 1 day to 1 year after parenteral use per labeling | Discontinue; medical management; document timing |
| Injection site pain/swelling | Reported per injectable labeling | Document; rotate SC sites; assess for infection |
| Hyperbilirubinemia (neonates) | Reported with parenteral use, rarely above recommended doses per oral labeling | Monitor bilirubin in neonates; follow NICU protocol |
| Thromboembolic risk after over-reversal | Warning when anticoagulation still indicated per labeling | Use lowest effective dose; monitor for clot symptoms |
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Overdose, toxicity, and antidote
Injectable labeling reports hemolysis, jaundice, and hyperbilirubinemia in newborns, particularly premature infants, with phytonadione overdose. Adult overdose-specific signs are not detailed in the reviewed prescribing information.
Antidote: No specific antidote is listed in the reviewed prescribing information; management is supportive. Contact poison control or medical toxicology services per facility protocol and local emergency guidance.
- Monitor INR and bleeding/thrombosis balance after excessive reversal doses
- Supportive care for hypersensitivity or hemolysis per clinical presentation
- Neonatal overdose: monitor for jaundice and hemolysis per NICU protocol
Look-alike / sound-alike and error prevention
- Vitamin K vs vitamin K antagonist (warfarin)—opposite effects; verify drug name and indication on MAR
- Phytonadione vs multivitamin / dietary vitamin K—reversal doses are prescription mg orders, not OTC supplement units
- Oral tablets vs injectable emulsion—route and mg strength confusion; injectable vials may be 1 mg/0.5 mL or other concentrations per product
- IV push vs slow infusion—rapid IV administration violates 1 mg/min maximum and increases anaphylaxis risk
- Duplicate reversal—vitamin K plus PCC/plasma without protocol—confirm orders with pharmacy
No specific look-alike/sound-alike pair beyond general vitamin naming was identified in the reviewed sources, but independent double-check remains mandatory for all reversal agents.
Practical bedside notes
| Topic | Bedside guidance |
|---|---|
| Route priority | SC first; IV only if SC not feasible; avoid IM when possible per boxed warning |
| IV rate | Never exceed 1 mg/min; use pump when available |
| INR timing | Recheck 6–8 h after parenteral dose; oral repeat in 12–48 h if inadequate per labeling |
| Light protection | Protect injectable and oral products from light per labeling |
| Commonly missed | IV push at full rate; duplicate warfarin dose still on MAR; assuming instant INR normalization |
| Ask pharmacy when | Unclear mg dose for INR level, need for PCC/plasma, warfarin restart timing, or neonatal dosing |
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High-risk populations
| Population | Considerations |
|---|---|
| Neonates / premature infants | Overdose risk with hemolysis and hyperbilirubinemia per injectable labeling; use prophylaxis doses per protocol |
| Patients requiring ongoing anticoagulation | Lowest effective reversal dose; INR monitoring; thromboembolism risk if over-treated per labeling |
| Malabsorption / cholestasis | Oral absorption requires bile; give bile salts with oral dose or use parenteral route per oral labeling |
| Pregnancy | Published data do not report clear harm; maternal vitamin K deficiency increases bleeding risk per injectable labeling—use preservative-free formulation when available |
| Lactation | Phytonadione present in breastmilk; preservative-free formulation preferred when available per injectable labeling |
| Prior parenteral vitamin K reaction | High risk for repeat hypersensitivity—clarify route and alternative plan with prescriber/pharmacy |
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Monitoring and documentation
Monitor
- INR / prothrombin time before and after dose (6–8 h parenteral; 12–48 h oral per labeling)
- Active bleeding: gums, GI tract (blood in stool), urine, skin (easy bruising)
- Vitals during and after IV administration: BP, HR, RR, SpO2, perfusion
- Signs of thromboembolism if anticoagulation still clinically required—e.g. stroke symptoms or leg swelling
- Skin for delayed cutaneous reactions after parenteral doses
Document
- Indication, dose, route, rate (mg/min for IV), site, and lot when required by policy
- Pre- and post-dose INR values and prescriber/pharmacy notifications
- Warfarin hold status and planned restart instructions
- Hypersensitivity symptoms, interventions, and patient response
Patient teaching
- Vitamin K works over hours—not minutes—continue bleeding precautions until INR improves per provider guidance
- Report flushing, trouble breathing, chest tightness, dizziness, or rash during or after injection immediately
- When on warfarin, do not take extra vitamin K supplements or change diet drastically without prescriber advice
- Understand warfarin may need dose adjustment after reversal—follow anticoagulation clinic instructions
- Report new leg swelling, severe headache, chest pain, or sudden weakness—possible clot or bleeding
The Hold Rule
Do not give and contact the prescriber/pharmacist when:
- Known hypersensitivity to phytonadione or formulation components
- IV ordered as rapid push or faster than 1 mg/min when IV route is used
- IM route ordered without clear justification—clarify route with pharmacy/prescriber because IM and IV carry boxed hypersensitivity risk, and IM also adds injection-site bleeding concern in anticoagulated patients
- Unclear indication, wrong patient, or duplicate reversal agents without protocol approval
- Active anaphylaxis during administration—stop immediately
- Dose appears excessive for INR level without pharmacy verification when anticoagulation must continue
- Oral route ordered but malabsorption or absent bile flow prevents absorption—needs parenteral route or bile salts per labeling
Hold parameters may vary by institutional protocol. Follow prescriber orders, pharmacy guidance, and facility policy.
Clinical practice integration and workflow
Vitamin K sits at the intersection of bleeding rescue and route-specific hypersensitivity risk. Injectable phytonadione labeling prefers subcutaneous administration whenever feasible because IV and IM routes carry boxed hypersensitivity risk. However, urgent warfarin reversal protocols may specify oral or slow IV vitamin K depending on bleeding severity and need for rapid INR correction. Follow the institutional anticoagulation/reversal protocol and pharmacy guidance; when IV is used, never exceed 1 mg/min and plan INR reassessment before declaring success.
1. Check-before-you-give protocol
- Right patient, indication, mg dose, route, and warfarin hold status
- Latest INR and bleeding assessment documented
- Pharmacy protocol reviewed for dose matching INR and bleeding severity
- IV pump or syringe pump available if IV route confirmed—never IV bolus at full rate
2. High-alert and safety badge
Parenteral reversal agent — boxed IV/IM hypersensitivity warningNot on all institutional high-alert lists, but injectable phytonadione carries an FDA boxed warning and fatal anaphylaxis reports. Use independent verification of route, rate, and dose.
3. Clinical workflow: hold and question rules
- If prescriber orders IV push phytonadione, pause and consult pharmacy—labeling requires ≤1 mg/min
- After dose, schedule INR redraw before warfarin restart; document communication with anticoagulation service
- If INR falls but bleeding continues, escalate for blood products or PCC per massive-transfusion protocol—not automatic repeat vitamin K
4. Critical teach-back questions
- “How fast should IV vitamin K be given?” (Never faster than 1 mg per minute; SC preferred when possible.)
- “When will your INR be rechecked?” (Patient should expect repeat labs hours after dose—not same-hour clearance.)
5. Care coordination
Pharmacist: Dose selection from INR/bleeding matrix, route clarification, warfarin restart planning, interaction with PCC/plasma orders
Prescriber / anticoagulation team: Indication for reversal, thrombosis risk when anticoagulation must continue, and timing of warfarin re-initiation
🧠 Quick mental checklist
- What is the indication and latest INR?
- Is warfarin held and bleeding actively assessed?
- Can this be given subcutaneously instead of IV or IM?
- If IV, is rate limited to 1 mg/min with monitoring?
- When is repeat INR ordered, and who plans warfarin restart?
Vitamin K NCLEX practice questions
Practice NCLEX-style clinical judgment practice for vitamin K (phytonadione) using a tabbed inpatient reversal case (MAR, labs, vitals, nursing notes), then priority action, cue recognition (SATA), INR trend interpretation, matrix urgency sorting, reversal-dose judgment, and route cloze—recognise cues → analyse → prioritise → act → evaluate outcomes.
Select a tab to view MAR, labs, vitals, and nursing note details for this case.
- Warfarin 5 mg PO daily — held today per pharmacy protocol
- Phytonadione 10 mg IV push now × 1 (new order)
- Acetaminophen 650 mg PRN pain
- INR: 2.6 (1 week ago) → 8.2 today (goal 2–3)
- Hemoglobin 13.1 → 12.4 g/dL
- Platelets 198,000/mm³
- BP 118/72 mmHg; HR 98/min; RR 18/min; SpO2 97% on room air
- Non-valvular atrial fibrillation; age 71
- Reports lightheadedness with prior antibiotic course
- 0900: Gum bleeding when brushing × 2 days
- 1030: Nurse drew phytonadione in syringe for IV push over 30 seconds
- 1100: Pharmacy note on chart—“Prefer SC if feasible; IV ≤1 mg/min”
Answer key & rationale
Frequently asked questions
Why does phytonadione injectable emulsion carry a boxed warning for IV and IM routes?
Labeling reports fatal hypersensitivity reactions including anaphylaxis during and immediately after intravenous and intramuscular injection despite dilution and on first dose. Administer subcutaneously whenever feasible; avoid IV and IM unless subcutaneous is not feasible and the serious risk is justified. When IV is unavoidable, inject very slowly, not exceeding 1 mg per minute.
How long until vitamin K improves INR after warfarin-associated hypoprothrombinemia?
Injectable labeling states coagulant effects are not immediate; INR improvement may take 1 to 8 hours, with IV action generally detectable within 1 to 2 hours and hemorrhage often controlled within 3 to 6 hours. Oral Mephyton generally exerts effect within 6 to 10 hours. Repeat INR per protocol—do not assume instant normalization.
When should a nurse hold vitamin K and call the prescriber or pharmacist?
Hold for known hypersensitivity, IV push faster than 1 mg per minute, IM route when SC is feasible, unclear indication or duplicate reversal orders, active anaphylaxis during administration, or doses that appear excessive for the INR level without pharmacy approval when anticoagulation must continue.
Does vitamin K interact with heparin or warfarin?
Injectable labeling states phytonadione does not affect heparin anticoagulant action. It may induce temporary resistance to warfarin and other prothrombin-depressing anticoagulants, especially with larger doses—higher warfarin doses or alternate strategies may be needed when resuming therapy.
What is the usual adult dose for warfarin reversal?
For anticoagulant-induced hypoprothrombinemia, injectable labeling recommends 2.5 mg to 10 mg or more SC, IM, or IV, with up to 25 to 50 mg as a single dose in select cases. Oral Mephyton recommends 2.5 to 10 mg or up to 25 mg initially, rarely 50 mg. Use the lowest effective dose and follow INR response.
Is there an antidote for vitamin K overdose?
No specific antidote is listed in the reviewed prescribing information for adult overdose. Injectable labeling notes hemolysis, jaundice, and hyperbilirubinemia in neonates with phytonadione overdose. Management is supportive; contact poison control or medical toxicology services per facility protocol and local emergency guidance.
References
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U.S. National Library of Medicine. PHYTONADIONE injectable emulsion — Full prescribing information. DailyMed.https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e0b0c8f1-75be-4f25-898a-7b97b608c615
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U.S. National Library of Medicine. MEPHYTON (phytonadione) tablets — Prescribing information. DailyMed.https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=eb8d7fd3-4c7c-43e7-be09-98a446b905ef
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Drugs and Lactation Database (LactMed). Phytonadione. Bethesda (MD): National Institute of Child Health and Human Development.https://www.ncbi.nlm.nih.gov/books/NBK501922/
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U.S. National Library of Medicine. MedlinePlus — Phytonadione.https://medlineplus.gov/druginfo/meds/a606008.html
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U.S. Food and Drug Administration. Structured Product Labeling resources.https://www.fda.gov/industry/fda-data-standards-advisory-board/structured-product-labeling-resources
Review and transparency
This medication guide is written and reviewed using NurseOnShift editorial and clinical review standards.
Educational use only. This content does not replace clinical judgment, prescriber orders, pharmacist guidance, product labeling, or institutional protocols.