Toxicology Antidote Dosing Calculator
Antidote dosing for common poisonings: acetaminophen/NAC, opioid/naloxone, benzodiazepine/flumazenil, organophosphate/atropine, digoxin/DigiFab.
About this calculator
This calculator reproduces the weight-based dosing math for five well-established toxicology antidotes. For acetaminophen overdose, it uses the classic three-bag intravenous N-acetylcysteine protocol that Prescott and colleagues first described in 1979: a 150 mg/kg loading dose, then 50 mg/kg over the next infusion, then 100 mg/kg over the final infusion, totaling 300 mg/kg over 21 hours. For opioid overdose, naloxone starts at 0.4 mg with escalation toward 2 mg if the initial dose doesn't restore adequate breathing. For benzodiazepine reversal, flumazenil starts at 0.2 mg with repeat dosing toward a cumulative ceiling commonly cited around 3 mg for overdose reversal (a different, lower ceiling of 1 mg applies to reversing procedural sedation, which this calculator does not model).
For organophosphate poisoning, atropine is dosed to effect (titrated until secretions dry, with no true ceiling) alongside pralidoxime at a WHO-cited 30 mg/kg loading dose -- because this calculator's Loading Dose and Maintenance/Repeat Dose fields are shared, generic labels reused across all five antidotes, it's worth being explicit that in the organophosphate branch specifically they hold two DIFFERENT drugs: Loading Dose reports the atropine initial dose (a fixed 2 mg, not weight-based), while Maintenance/Repeat Dose reports pralidoxime's weight-based loading dose (~30 mg/kg), not a repeat atropine dose. For digoxin toxicity, this calculator reports the fixed empiric dose of 10 vials of digoxin-specific antibody fragments used for severe acute poisoning when a specific serum digoxin level isn't yet available -- it does not compute the weight-and-level-based formula used once a level is known. Every dose here is a starting point for a clinician to verify against current poison control guidance and the patient's actual clinical status, not a substitute for it.
Medical Disclaimer
This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.
This tool estimates a starting point only and is not a validated clinical decision-support system. It does not account for every patient-specific factor (organ function, drug interactions, allergies, comorbidities, or current clinical status). Any dose, rate, or setting must be independently verified by the treating clinician and pharmacist or respiratory therapist against current institutional protocols, product labeling, and the patient's full clinical picture before being administered or applied.
Inputs
Results
Loading Dose (mg)
10,500
Figures current as of 1979. Source: Prescott LF, Illingworth RN, Critchley JA, Stewart MJ, Adam RD, Proudfoot AT. Intravenous N-acetylcysteine: the treatment of choice for paracetamol poisoning. BMJ. 1979;2(6198):1097-1100.
How to Use This Calculator
- Enter Patient Weight (kg).
- Select the Toxin Type from the dropdown (acetaminophen, opioid, benzodiazepine, organophosphate, or digoxin).
- Review Loading Dose (mg), Maintenance/Repeat Dose (mg), and Treatment Duration (hours).
- Check Maximum Total Dose (mg) to avoid antidote toxicity.
- Note Route of Administration (IV, PO, IM, or IV+IM) for the selected antidote.
How the result changes with Patient Weight
| Patient Weight | Loading Dose (mg) |
|---|---|
| 35 | 5,250 |
| 53 | 7,950 |
| 105 | 15,750 |
| 175 | 26,250 |
What each input means
- Patient Weight
- Patient weight in kilograms.
- Toxin Type
- The suspected toxin, which determines which antidote protocol is calculated.
What each result means
- Loading Dose (mg)
- Initial antidote dose. For DigiFab, this is in mg (÷40 for vials).
- Maintenance / Repeat Dose (mg)
- Subsequent dose or second infusion rate. Context depends on antidote.
- Treatment Duration (hours)
- Expected duration of antidote therapy or observation period.
- Maximum Total Dose (mg)
- Maximum recommended total dose. 0 = no fixed maximum (titrate to effect).
- Route (1=IV, 2=PO, 3=IM, 4=IV+IM)
- Recommended administration route.
- Antidote Selected (1-5)
- Echo of selected toxin/antidote pair.
How this is calculated
Worked example, using the default values
- Identify Input ParametersPatient Weight (kg) = 70, Toxin Type = 1 = 2 input(s) provided
- Calculate Loading DoseLoading Dose10500 = 10500
- Calculate Maintenance / Repeat DoseMaintenance / Repeat Dose3500 = 3500
- Calculate Treatment DurationTreatment Duration21 = 21
Figures and sources
- Three-bag IV N-acetylcysteine protocol for acetaminophen overdose (1979) — Prescott LF, Illingworth RN, Critchley JA, Stewart MJ, Adam RD, Proudfoot AT. Intravenous N-acetylcysteine: the treatment of choice for paracetamol poisoning. BMJ. 1979;2(6198):1097-1100.
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the acetaminophen antidote take 21 hours to complete?
The standard intravenous N-acetylcysteine protocol delivers three sequential infusions -- 150 mg/kg over roughly the first hour, 50 mg/kg over the next four hours, and 100 mg/kg over the final sixteen hours -- adding up to 300 mg/kg total and 21 hours of infusion time. This staged approach was designed to front-load the highest concentration early, when glutathione replenishment matters most, while spreading the remaining dose out to reduce the risk of anaphylactoid reactions from infusing it all at once.
Does naloxone dosing change based on patient weight?
No -- unlike the acetaminophen, pralidoxime, and digoxin antidotes in this calculator, naloxone dosing for opioid overdose reversal is not weight-based. It's dosed in fixed increments (commonly starting at 0.4 mg and escalating toward 2 mg) regardless of the patient's size, titrated instead to the desired clinical effect: restoring adequate spontaneous breathing without provoking severe, abrupt opioid withdrawal.
Why is there no maximum total dose listed for atropine in organophosphate poisoning?
Unlike most antidotes on this calculator, atropine for organophosphate or nerve agent poisoning is dosed to a clinical endpoint -- drying of pulmonary secretions and reversal of bronchospasm -- rather than to a fixed ceiling, because severe poisoning can require very large cumulative doses that a single maximum number wouldn't safely capture. Pralidoxime, by contrast, does use a defined weight-based loading dose in this calculator -- reported in the Maintenance/Repeat Dose field, not the Loading Dose field, since Loading Dose is occupied by atropine's fixed 2 mg initial dose in this branch. The two fields hold two different drugs for organophosphate poisoning specifically.
Is the DigiFab dose here based on the patient's measured digoxin level?
No -- this calculator reports the fixed empiric dose (10 vials) used for severe, life-threatening acute digoxin toxicity when a specific serum digoxin level either isn't available yet or the ingestion is unknown. When a reliable serum level and ingested amount are known, dosing is instead typically calculated directly from those values using a separate weight-and-level-based formula that this calculator does not compute.
Related Calculators
The questions that sit next to this one — chosen by subject, including calculators filed under a different category.
Trauma Score Calculator
Revised Trauma Score (RTS) from GCS, systolic blood pressure, and respiratory rate with survival probability estimate.
Emergency MedicineTriage Score Calculator
Emergency Severity Index (ESI) triage level from acuity assessment and resource needs.
Forensic ScienceToxicology Dose Back-Calculator
Back-calculate an ingested dose from blood concentration using volume of distribution and elimination kinetics. Estimate peak concentration and elimination time.
Emergency MedicineBlood Transfusion Calculator
Calculate packed RBC units needed from current and target hemoglobin with estimated blood volume.
Marine BiologyAquatic Toxicology Calculator
Estimate LC50 from two dose-response data points using probit approximation. Calculate toxic units, PNEC, and environmental risk quotient.
More in Medical & Clinical.