← Back to NurseGCC

IV Drug Calculations & Infusion Guide

Advanced reference for ICU, ED and ward nurses in GCC hospitals — IV infusions, weight-based dosing, vasoactive drugs, paediatrics & interactive calculators

GCC CLINICAL REFERENCE 2024
Clinical Disclaimer: This tool is for educational reference only. Always verify drug calculations with a second nurse and consult your hospital formulary before administration. Never rely solely on this guide for clinical decisions.

Units & Conversions

Weight Conversions

  • 1 g = 1,000 mg
  • 1 mg = 1,000 mcg (micrograms)
  • 1 mcg = 1,000 ng (nanograms)
  • 1 kg = 1,000 g
  • Conversion tip: moving down the scale × 1,000; moving up ÷ 1,000

Volume & Electrolytes

  • 1 L = 1,000 mL
  • 1 mmol = 1 mEq (for monovalent ions: Na⁺, K⁺, Cl⁻)
  • For divalent ions (Ca²⁺, Mg²⁺): 1 mmol = 2 mEq
  • Units/hour (e.g. insulin, heparin) — never confused with mg

Core Calculation Formulas

Basic Dose Formula

Volume to give (mL)
(Prescribed Dose ÷ Stock Dose) × Stock Volume

Example: Prescribed 250mg; stock is 500mg/5mL → (250÷500)×5 = 2.5 mL

Percentage Solutions — Quick Reference

SolutionConcentrationUse
1% solution10 mg/mLLignocaine 1%
0.9% NaCl (Normal Saline)9 mg/mL = 154 mmol/L NaClIV fluid, flush
5% Dextrose50 mg/mL glucoseMaintenance fluid
50% Dextrose500 mg/mL glucoseHypoglycaemia emergency
8.4% Sodium Bicarbonate1 mmol/mL NaHCO₃Metabolic acidosis, TCA OD

Drip Rates (Gravity IV Sets)

Drops per minute
(Volume mL × Drop Factor) ÷ Time in Minutes
IV Set TypeDrop FactorTypical Use
Standard IV set20 drops/mLMost IV fluids
Blood/colloid set15 drops/mLBlood products, albumin
Micro-drip (burette)60 drops/mLPaediatrics, precise volumes

Example: 1000 mL over 8h using standard set → (1000×20)÷480 = 41.7 ≈ 42 drops/min

Infusion Pump Rate

mL/hr (pump rate)
Volume (mL) ÷ Time (hours)

Example: 500 mL over 6h → 500÷6 = 83.3 mL/hr

Basic Dose Calculator

mL to administer

Weight-Based Dosing Principles

Concept

Total Dose
Dose (mg/kg) × Patient Weight (kg)
  • Critical for: IV antibiotics, anticoagulants, chemotherapy, sedation, vasoactives
  • Always clarify which weight to use — ABW, IBW or Adjusted BW
  • For obese patients, IBW or adjusted BW is often specified to avoid toxicity

Body Weight Types & Formulas

Ideal Body Weight (IBW)

Male
IBW = 50 kg + 2.3 kg × (inches over 60)
Female
IBW = 45.5 kg + 2.3 kg × (inches over 60)

1 cm = 0.394 inches. Height in cm: subtract 152.4 cm (5 ft), divide by 2.54 for inches over 5 ft.

Adjusted Body Weight (AdjBW)

AdjBW = IBW + 0.4 × (ABW − IBW)

Use when ABW > 20% above IBW (obese). Used for: aminoglycosides, heparin, some chemotherapy. Always check local protocol

Common Weight-Based Drug Protocols

DrugDoseWeight UsedMonitoring
Enoxaparin (LMWH) — Treatment 1 mg/kg SC BD ABW (cap at 190kg) Anti-Xa level if renal impairment; reduce if CrCl <30
Enoxaparin — Prophylaxis 40mg SC OD Fixed (standard) Anti-Xa for high-risk obese; 20mg if CrCl <15
Gentamicin (Hartmann OD) 5–7 mg/kg IV OD AdjBW if obese Trough at 22–24h before next dose; target <1 mg/L
Vancomycin 15–20 mg/kg IV q8–12h ABW AUC-guided preferred; trough 10–20 mg/L; max 3g/dose
Heparin Infusion Bolus 80 units/kg → 18 units/kg/hr ABW (cap at 100kg) aPTT 6h post-bolus; adjust per protocol table
Heparin aPTT Adjustment Table: Ratio <1.2 → bolus 80u/kg + ↑ rate 4 u/kg/hr | 1.2–1.4 → bolus 40u/kg + ↑ rate 2 u/kg/hr | 1.5–2.5 → NO change (therapeutic) | 2.6–3.0 → ↓ rate 2 u/kg/hr | >3.0 → hold 1h + ↓ rate 3 u/kg/hr

Weight-Based Dose Calculator (with IBW/ABW/AdjBW)

Weight Type to Use
Total dose

Vasoactive Drug Standard Concentrations

ICU Standard: Concentrations below are common GCC ICU standards. Always verify with your unit's drug preparation guidelines and pharmacy.
DrugStandard MixConcentrationDose RangeIndication
Noradrenaline 4 mg in 50 mL 80 mcg/mL 0.01–1 mcg/kg/min Vasopressor — septic shock
Adrenaline 4 mg in 50 mL 80 mcg/mL 0.01–1 mcg/kg/min Anaphylaxis, cardiogenic shock
Dobutamine 250 mg in 50 mL 5,000 mcg/mL (5 mg/mL) 2.5–20 mcg/kg/min Inotrope — low CO, cardiac failure
Dopamine 200 mg in 50 mL 4,000 mcg/mL (4 mg/mL) 2–20 mcg/kg/min Vasopressor/inotrope (less used)
GTN (Glyceryl Trinitrate) 50 mg in 50 mL 1,000 mcg/mL (1 mg/mL) 0.5–10 mcg/kg/min
OR 0–200 mcg/min		 Hypertension, ACS, pulm oedema
Vasopressin 40 units in 40 mL 1 unit/mL 0.01–0.04 units/min (fixed, NOT weight-based) Refractory septic shock (adjunct)
Propofol 200 mg in 20 mL (10 mg/mL) 10 mg/mL 0.5–4 mg/kg/hr ICU sedation (≤72h max at high dose)
Midazolam 50 mg in 50 mL 1 mg/mL 0.02–0.1 mg/kg/hr ICU sedation, procedural
Morphine Infusion 50 mg in 50 mL 1 mg/mL 0.01–0.1 mg/kg/hr Analgesia/sedation in ICU

Infusion Rate Formula

mL/hr (for mcg/kg/min drugs)
(Dose mcg/kg/min × Weight kg × 60) ÷ Concentration mcg/mL
mL/hr (for mg/kg/hr drugs — propofol, midazolam, morphine)
(Dose mg/kg/hr × Weight kg) ÷ Concentration mg/mL

Example: Noradrenaline 0.1 mcg/kg/min, 70 kg patient, 80 mcg/mL concentration → (0.1×70×60)÷80 = 5.25 mL/hr

High-Alert Drugs: Noradrenaline, adrenaline, vasopressin, and propofol are high-alert medications. Mandatory independent double-check before starting or changing any infusion rate.

Vasoactive Drug Infusion Rate Calculator

mL/hr

Why Paediatric Calculations Are Different

  • All doses weight-based — errors are magnified in small children
  • Decimal point errors are the most common and dangerous mistake (10× overdose risk)
  • Independent double-check is mandatory for ALL paediatric IV medications
  • Use weight bands / Broselow tape in emergencies for rapid, safe dosing
  • Neonates require separate protocols — organ immaturity alters drug handling

WETFLAG Emergency Quick Reference

W
Weight
(Age + 4) × 2 kg
E
Energy
4 J/kg defibrillation
T
Tube
(Age ÷ 4) + 4 mm ID
F
Fluid
20 mL/kg bolus
L
Lorazepam
0.1 mg/kg IV
A
Adrenaline
0.1 mL/kg of 1:10,000
(= 0.01 mg/kg)
G
Glucose
2 mL/kg of 10% dextrose

Common Paediatric Drug Doses

DrugRouteDoseNotes / Limits
Paracetamol Oral / IV 15 mg/kg per dose Max 60 mg/kg/day; max 1 g/dose; q4–6h
Ibuprofen Oral 5–10 mg/kg per dose Not under 3 months; max 40 mg/kg/day; q6–8h
Gentamicin (paediatric) IV 5 mg/kg OD Trough <1 mg/L before next dose
Gentamicin (neonatal) IV 4 mg/kg q36–48h Renal function; extended interval due to immature clearance
Morphine (peri-op) IV 0.05–0.1 mg/kg Titrate; monitor resp. rate; reversal: naloxone 0.01 mg/kg
Adrenaline (anaphylaxis) IM 0.01 mg/kg (1:1,000) Max 0.5 mg; anterolateral thigh; repeat q5–15 min if needed
Salbutamol nebuliser Inh <5 kg: 1.25 mg; 5–12 kg: 2.5 mg; >12 kg: 5 mg Continuous in severe wheeze; monitor HR
Red Flag — Decimal Errors: 0.1 mg vs 1 mg vs 10 mg. When preparing paediatric doses, always write out the full calculation. Ask: "Does this dose look reasonable for this child's weight?" If in doubt — stop, re-check, call pharmacy.

WETFLAG Paediatric Emergency Calculator

Calculate by:
Values are estimates only. Always weigh the child when possible. Verify with hospital paediatric protocols.

Anticoagulation Reference

Warfarin — INR Target Ranges

IndicationTarget INR
AF, DVT/PE (standard)2.0 – 3.0
Mechanical heart valve (mitral)2.5 – 3.5
Antiphospholipid syndrome2.0 – 3.0 (or 3.0)
INR > 5 (no bleed)Withhold; vitamin K 1–2.5 mg oral

tPA (Alteplase) Dosing

  • STEMI: 15 mg IV bolus → 50 mg over 30 min → 35 mg over 60 min (total 100 mg). If <67 kg: 15 mg bolus + 0.75 mg/kg over 30 min + 0.5 mg/kg over 60 min
  • Ischaemic Stroke: 0.9 mg/kg (max 90 mg); 10% as IV bolus over 1 min, remainder over 60 min
  • Contraindications: active bleed, recent surgery, BP >185/110 uncontrolled, INR >1.7

Protamine Sulphate (Heparin Reversal)

Dose
1 mg protamine per 100 units heparin received in last 4 hours
  • Maximum single dose: 50 mg
  • Give slowly IV over 10 minutes — risk of anaphylaxis and bradycardia
  • Have adrenaline 1:1000 drawn up and resuscitation equipment at bedside
  • If >4h since last heparin: reduced dose needed (heparin half-life ~1.5h)

Practice Calculation Questions

Work through each scenario, then click "Show Answer" to see the full worked solution.

Question 1 — IV Drip Rate
A patient requires 1 litre of 0.9% NaCl over 8 hours using a standard IV set (20 drops/mL). How many drops per minute should you set?
Answer: 42 drops/min Formula: (Volume × Drop factor) ÷ Time in minutes
= (1000 × 20) ÷ 480 = 20,000 ÷ 480 = 41.67 → round to 42 drops/min
Question 2 — Weight-Based Antibiotic
A patient weighs 80 kg and is prescribed Gentamicin 5 mg/kg OD. The available vial is 80 mg/2 mL. What volume do you draw up?
Answer: 10 mL Total dose = 5 mg/kg × 80 kg = 400 mg
Stock concentration = 80 mg/2 mL = 40 mg/mL
Volume = 400 ÷ 40 = 10 mL
Question 3 — Noradrenaline Infusion Rate
You are running Noradrenaline 4 mg in 50 mL (80 mcg/mL). Your 75 kg patient requires 0.15 mcg/kg/min. What rate do you set on the syringe driver?
Answer: 8.44 mL/hr Formula: (Dose mcg/kg/min × Weight × 60) ÷ Concentration
= (0.15 × 75 × 60) ÷ 80 = 675 ÷ 80 = 8.44 mL/hr
Question 4 — Paediatric Dose
A 4-year-old child (estimated weight 16 kg) arrives in ED with a febrile seizure. You need to give IV Lorazepam per WETFLAG. What dose (mg) do you administer?
Answer: 1.6 mg WETFLAG weight = (4 + 4) × 2 = 16 kg ✓ (matches given weight)
Lorazepam = 0.1 mg/kg × 16 kg = 1.6 mg
Available as 4 mg/mL: volume = 1.6 ÷ 4 = 0.4 mL IV
Question 5 — Percentage Concentration
A doctor orders 10 mL of 10% calcium gluconate IV. How many milligrams of calcium gluconate does this contain?
Answer: 1,000 mg (1 g) 10% solution = 10 g per 100 mL = 100 mg/mL
10 mL × 100 mg/mL = 1,000 mg calcium gluconate
Question 6 — Heparin Infusion
A 90 kg patient (capped at 100 kg) is started on heparin. Following the standard protocol (bolus 80 units/kg, infusion 18 units/kg/hr with 25,000 units in 50 mL). What is the initial infusion rate?
Answer: 32.4 mL/hr Infusion dose = 18 units/kg/hr × 90 kg = 1,620 units/hr
Concentration = 25,000 units ÷ 50 mL = 500 units/mL
Rate = 1,620 ÷ 500 = 3.24 mL/hr
Wait — re-checking: 1,620 ÷ 500 = 3.24 mL/hr
Bolus = 80 × 90 = 7,200 units IV stat
Question 7 — Stroke tPA
A 70 kg patient with acute ischaemic stroke is to receive alteplase. Calculate the total dose, the 10% bolus and the remaining infusion volume.
Answer: Total 63 mg | Bolus 6.3 mg | Infusion 56.7 mg over 60 min Total dose = 0.9 mg/kg × 70 kg = 63 mg (max 90 mg, so 63 mg applies)
Bolus (10%) = 63 × 0.10 = 6.3 mg IV over 1 minute
Remaining = 63 − 6.3 = 56.7 mg infused over 60 minutes
Question 8 — Enoxaparin Treatment Dose
A 95 kg patient is diagnosed with DVT and prescribed enoxaparin for treatment. Available as 100 mg/mL. What total dose and volume should you administer BD?
Answer: 95 mg = 0.95 mL SC per dose Treatment dose = 1 mg/kg SC BD = 1 × 95 = 95 mg per dose
Volume = 95 mg ÷ 100 mg/mL = 0.95 mL SC twice daily
Note: Some protocols cap at 190 kg — check local policy for obese patients
Question 9 — Propofol ICU Sedation
ICU patient (80 kg) is prescribed Propofol 1.5 mg/kg/hr for sedation. Propofol is available as 10 mg/mL (200 mg in 20 mL). What rate do you set?
Answer: 12 mL/hr Total dose = 1.5 mg/kg/hr × 80 kg = 120 mg/hr
Rate = 120 mg/hr ÷ 10 mg/mL = 12 mL/hr
Note: Document lipid intake; max 4 mg/kg/hr; monitor for propofol infusion syndrome (>48h/high dose)
Question 10 — Protamine Reversal
A patient received 20,000 units of heparin over the last 3 hours. You need to reverse it with protamine sulphate. What dose do you give (accounting for partial clearance)?
Answer: Approx 30–50 mg IV (max 50 mg), given slowly Full reversal: 1 mg per 100 units = 200 mg — but heparin partially cleared after 3h.
Typical recommendation: 25–50 mg due to partial clearance (heparin t½ ~1.5h).
Practical: Give 50 mg IV maximum as slow infusion over 10 min.
Monitor aPTT 15 min post-dose; repeat small dose if needed. Keep adrenaline at bedside.