Section 2: Calculations

Question 1

Objectives:

Answer 1

2.1 Given a patient exposed to an amount of a gel, liquid or cream in specific concentrations, calculate
the ingested dose on an amount per weight dosage.
2.2 Given an exposure including a patient who has taken an unknown amount of a substance,
determine the amount of substance that would need to be ingested to reach a defined toxic dose.
2.3 Given an exposure including a patient who has taken a known amount of a solid substance,
calculate the amount ingested on an amount per weight dosage.
2.4 Convert units of measurement for common exposures.
2.5 Following are various formulas or pieces of information that may be useful for clinical practice and
testing.

Question 2

How to calculate maximum dose of lidocaine

Answer 2

Max dose in mg/kg * (wt in kg/10) * (1/percent of anesthetic) = ml lidocaine
o Max lido with epi = 7mg/kg
o Max lido without epi = 4mg/kg
o Max bupivacaine with or without epi = 2mg/kg

Question 3

How to calculate Digifab dosing

Answer 3

# vials = [ (dig level in ng/ml) * (wt in kg) ] / 100\
  If # of vials is not an even number, round up

*Note: For ingestions of plants with cardiac glycosides, start with 10 vials

Question 4

How to calculate Anion Gap

Answer 4

AG = Na – Cl – CO2

Normal gap is 8-12

Question 5

How to calculate Osmol Gap

Answer 5

• 2 (Na) + (glucose/18) + (BUN/2.8) + (Etoh/4.6) = calculated Osm
• Osmol Gap = measured Osm – calculated Osm
• Of note: measured osmol must be drawn at the same time as metabolic panel for accuracy

Question 6

How to calculate Sodium Chloride ingestion

Answer 6

• Volume of salt ingested (ml) * 1.19 = gm NaCl
• 0.5-1g/kg NaCl is considered toxic in most pts
• Local referral = 300mg/kg NaCl

Question 7

How to calculate estimated Toxic Alcohol levels

Answer 7

• OG * 6.2 = estimated EG level mg/dL

- OG * 3.2 = estimated methanol level mg/dL

Question 8

How to calculate estimated Blood Alcohol Concentration

Answer 8

(amt ingested in mL * % of product * sp gravity) / (Vd * pt wt in kg) = Peak BAL mg/dL

Rule of thumb:

• 1ml/kg of 100% Ethanol (200 proof) = BAL ~ 150 mg/dL
• 1ml/kg of 100% methanol, isopropanol, ethylene glycol = BAL ~ 130 mg/dL

Question 9

Ethanol

Answer 9

Sp Gravity: 0.79 g/mL

Vol Distribution: 0.53 L/kg

Question 10

Methanol

Answer 10

Sp Gravity: 0.79 g/mL

Vol Distribution: 0.60 L/kg

Question 11

Ethylene Glycol

Answer 11

Sp Gravity: 1.110 g/mL

Vol Distribution: 0.83 L/kg

Question 12

Isopropyl Alcohol

Answer 12

Sp Gravity: 0.785 g/mL

Vol Distribution: 0.60 L/kg

Question 13

How to calculate elemental iron Ingestion

Answer 13

o Ferrous Fumarate is 33% elemental iron
o Ferrous Sulfate is 22% elemental iron
o Ferrous Gluconate is 11% elemental iron

Question 14

Quick Trick: take mg of iron product and divide it by the trick# for an estimate of elemental iron content

Answer 14

Trick Numbers:
Fumarate 3
Sulfate 5
Gluconate 9

Question 15

How to calculate elemental fluoride Ingestion

Answer 15

o Divide milligrams of ingested fluoride product by mg # in below table to obtain equivalent of elemental fluoride

Product: >>  mg # >>   mg equivalent elemental F
Sodium Fluoride (45.2%): >>  2.2  >>  1
Stannous Fluoride (24.3%): >>  4.1  >>  1
Sodium Monoflurophosphate (MFP): >>  7.6  >>  1

Question 16

How to calculate ASA equivalent / salicylate ingestion from a cream or ointment

Answer 16

Hint: % = #g salicylate per 100g carrier
% salicylate compound / 100g product = X grams salicylate compound / #grams ingested
Then convert g to mg ingested

(mg of salicylate ingested * ACF) = mg/kg ASA equivalent

Question 17

Bismuth subsalicylate

Answer 17

Aspirin Conversion Factor (ACF) = 0.4957

Question 18

Methyl salicylate

Answer 18

Aspirin Conversion Factor (ACF) = 1.3978

Question 19

*for ASA equivalent to Salicylate compound:

Answer 19

divide by ACF

Question 20

*for salicylate compound to ASA equivalent:

Answer 20

multiply by ACF

Question 21

How to calculate an Aspirin Equivalent Dose (AED)

Answer 21

o Liquid non-ASA salicylate (NAS) products
- Express all % as decimal. Ex 100% = 1.0
 -Multiply ml of product by % = ml pure NAS
 -Find ACF and Sp.G.
 -(ml pure NAS) * (Sp. G) * (ACF) * (1,000) / pt weight in kg = mg/kg AED
 -Max product tolerated (per local protocol). For national: calculate on 300mg/kg

1. [ (wt in kg) * (150mg/kg ASA) ] / 1,000 = g ASA tolerated
2. [ (g ASA tolerated / ACF) / (Sp. G) ] / % NAS = ml product tolerated

Question 22

Semisolid or solid NAS product

Answer 22

 -Express all % as a decimal
 -Find ACF
 -Grams of product taken * % NAS = grams NAS
 -(grams of NAS) * (ACF) * (1,000) / pt weight in kg = mg/kg/ AED
 -Max product tolerated (per local protocol). For national: calculate on 300mg/kg

1. [ (wt in kg) * (150mg/kg ASA) ] / 1,000 = g ASA tolerated
2. (g ASA tolerated / ACF) / % NAS = g product tolerated

Question 23

Other:

Answer 23

1. mEq = (mg * valence) / atomic, molecular, or formula weight
2. mg = (mEq * atomic, molecular, or formula weight) / valence
3. Molar or M = 1g molecular weight / L solution
4. Normal or N = 1 g equivalent (ion count) wt / L solution
5. Percentage preparations
   o % w/v = g/dL 7
   o % v/v = 1ml/100ml
   o % w/w = 1g /100g

Question 24

 Ratio Strength

Answer 24

All % are ratio strengths of parts per hundred
- Ex 5% = 5:100 or 1:20

For solids in liquids, 1:1,000 = 1g:1,000ml
For liquids in liquids, 1:1,000 = 1ml:1,000ml

Question 25

Density and Specific Gravity

Answer 25

Density = mass/volume = g/ml

Sp Gravity = wt of product in grams / wt of equivalent amount of water in grams
*Remember water is 1g/ml

Question 26

Anion Gap

Answer 26

Na - (Cl+HCO3)

*or Na - Cl - CO2

Question 27

Osmolal Gap

Answer 27

Measured - Calculated

Question 28

Calculated Osmolality

Answer 28

2 (Na) + Glucose/18 + BUN/2.8 + etoh/4.6

Question 29

To determine estimated ethanol blood level

Answer 29

(%etoh) x (ml ingested) x (0.79) / (wt) x (0.053) = mg%