All equations and Conversions (from RxPrep Formula Sheet)

1 tsp = ? mL

5 mL

1 tbsp = ? mL

15 mL

1 fl oz = ? mL

30 mL (29.5 ml/fl oz)

1 cup = ___ oz

8 oz

1 pint = ? oz = ? mL

16 oz, 473 mL (2 cups)

1 quart = ? pints

2 pints (32 oz, 4 cups)

1 gallon = ? quarts

4 quarts (3840 mL)

1 kg = ? lbs

2.2 lbs

1 oz = ? g

28.4 g

1 pound = ? g

454 g

1 grain = ? mg

65 mg (64.8 mg exact)

K+, Na+, monovalent ions: 1 mEq = ? mmol

1 mEq = 1 mmol (for monovalent ions)

Ca++, divalent ions: 1 mEq = ? mmol

1 mEq = 0.5 mmol (for divalent ions)

Weight in volume (%w/v)

X g/100 mL

volume in volume (% v/v)

X mL/100 mL

weight in weight (% w/w)

X g/100 g

NS w/v

0.9 g/100 mL

Ration strength -> % strength

% strength = 100/ratio strength

Ex: 1:2500 to % strength

% strength = 100/2500= 0.04%

% strength -> ratio strength

Ratio strength = 100 / % strength

Ex: 0.04% to ratio strength

ratio strength = 100/0.04 = 2500, so 1:2500

PPM to percentage strength

Move decimal left 4 places

Ex: 2.2 PPM = 0.00022%

Percent strength to PPM

Move the decimal right 4 places

Ex: 0.00022% = 2.2 PPM

Specific gravity equation

SG = g/mL

When to use C1V1 vs alligation

C1V1: use with 2 concentrations

Alligation: use with 3 concentrations

1 gallon = ? mL (approx)

3840 mL

1 quart = ? mL

960 mL

1 pint = ? mL

480 mL

1 cup = ? mL

240 mL

Osmolarity

the concentration of a solution expressed as the total number of solute particles per liter.

Osmolality

A measure of the number of particles per kilogram of water

How many particles does sodium acetate disassociate into?

2

How many particles does magnesium sulfate disassociate into?

2

How many particles does calcium chloride disassociate into?

3

How many particles does sodium citrate disassociate into?

4

Osmolarity Equation (mOsmol/L)

mOsmol/L = (weight (g/L)/MW (g/mol)) x # particles x 1000

1) add up the number of disassociation particles

2) Calculate # of g in 1L

3) use MW to solve the problem

Always normalize to 1 L (miliosmoles don't do this)

If there are multiple things in solution, solve for the mOsmol of each separately then add together at the end (see page 143, #53 of book for example)

E value equation

E = 58.5 (i) / MW of drug (1.8)

*multiply the E-value of a number times the amount of that product to see the amount of sodium chloride represented from that product

(1) calc how much NaCl will come from the sodium product (NS, 1/2NS)

(2) calc how much product you will need then multiply it times the E value; this gives you the sodium equivalent of the product

(3) subtract product equivalent to NaCl from amt NaCl needed for isotonicity

Dissociation (i) factors (based on # of dissociation ions)

1 ion: i = 1

2 ions: i = 1.8

3 ions: i = 2.6

4 ions: i = 3.4

5 ions: i = 4.2

Mol equation

mols = g/MW

mmol equation

mmol = mg/MW

mEq equation

mEq = (mg x valence)/MW

or

mEq = mmol x valence

(so basically the equation for mmol but multiplied by valence)

Valence is the charge associated, so KCl has a valence of 1 b/c K and Cl only have 1 charge. Ca (Ca++) has a valence of 2 because it has a 2+ charge

Molecules with a valence of 2

Ca carbonate

Ca chloride

Ferrous sulfate

Magnesium sulfate

(these are a lot of the same drugs that chelate)

KCl mEq to percent strength conversion

KCl 10% = 20 mEq/15 mL

After how many days of being unable to absorb enteral nutrition is parenteral nutrition considered?

> 5 days of inadequate absorption

2-in-1 vs 3-in-1 TPN

2-in-1: Dextrose and protein

3-in-1: Dextrose, protein, and lipid

Estimated BEE

15-25 mg/kg (adults)

Dextrose monohydrate provides _____ kcal/g

3.4 kcal/g

Amino acid solutions provide _____ kcal/g

4 kcal/g

10% lipid emulsion provides ___ kcal/ml

1.1 kcal/mL

20% lipid emulsion provides ___ kcal/ml

2 kcal/mL

30% lipid emulsion provides ___ kcal/mL

3 kcal/mL

Enteral dextrose and protein provide ____ kcal/g

4 kcal/g

Enteral lipids provide ____ kcal/g

9 kcal/g

1 gram of Nitogen = ____ g of protein

1 g Nitrogen = 6.25 g protein

(e.g. for every 6.25 g of protein given to a patient, it will be broken down into 1 g of Nitrogen)

Calculate the number of grams of protein given then divide by 6.25 to find g of N

Non-protein to nitrogen ratio

First calculate g of Nitrogen (1 g N = 6.25 g protein)

Then divide total non-protein calories by g of N

Equation for fluid needs

Fluids needed = 1500 mL + 20mL (# kg over 20 kg)

Estimate using 30-40 mL/kg/day

Total Energy Expenditure (TEE) equation

BEE x activity factor x stress factor

Aminosyn, FreAmine, Clinisol

Amino acid solutions for TPN

What filter do lipids require?

1.2 micron filter

What are some medications that provide fat calories when infused?

Propofol

Clevidipine

Formulations of sodium that can be added to a TPN

Sodium Chloride

Sodium Acetate

Sodium Phosphate

What formulation of sodium should be added if a patient is acidotic?

Sodium acetate (converted to bicarb and can help)

Formualations of K that can be used in TPN

KCl

KPO4

K acetate

How to reduce risk of percipitation with Ca and Ph

1) use Calcium gluconate instead of CaCl (less reactive, lower risk of percipitation due to lower dissociation constant with Ca gluconate)

2) Add phosphorus first after dextrose and amino acids, then add everything else except Ca, agitate, and then add Ca to give it the largest volume to disperse in

3) Keep refrigerated until use (keeps dissociation of ions low)

4) Keep total Ca and Ph below 45 mEq/mL

What type of insulin is given in TPN?

Regular insulin

How to prevent drug and enteral feeding interactions

Hold feeding one hour before and 2 hours after the drug is administered

How long should enteral tube feeds be separated from warfarin?

Hold feeding for 1 hour before and 1 hour after administration of warfarin

How do levothyroxine, quinolones and tetracyclines interact with enteral tube feeds?

Chelate, seperate administration

What formulations of ciprofloxacin are and are not used for enteral tube feeding?

Cipro oral solution is NOT used because it adheres to the tube

Use IR tablets crushed and mixed in water instead

Flush line with water before and after administration

How should phenytoin be separated from enteral tube feeds?

Seperate feeds by 2 hours before and 2 hours after phenytoin

BMI equation

BMI = weight (kg) / height (m^2)

OR

BMI = (weight (lbs)/height (inches^2)) x 703

BMI classifications

underweight: <18.5

normal: 18.5-24.9

overweight: 25-29.9

obese: >30

IBW equation for women

IBW = 45.5 + 2.3 * (inches over 5 feet)

IBW equation for men

IBW = 50 + 2.3 * (inches over 5 feet)

Adjusted Body Weight Equation

AdjBW= IBW + 0.4 (TBW-IBW)

If a patient's TBW < IBW what dosing weight should be used?

TBW (for all medications)

If a patient's TBW is about equal to IBW (< 120% of IBW), which dosing weight should be used?

TBW for most medications

What medications only use IBW for dosing, unless TBW is < IBW?

Aminophylline

Theophylline

Acyclovir

Levothyroxine

(most narrow therapeutic index drugs use IBW for dosing to minimize risk of toxicity in normal weight and obese patients)

What dosing weight is used for LMWH, UFH and vacomycin if TWB is ≥ 120% IBW?

TBW (basically, always use TBW for these)

What dosing weight is used for aminoglycosides if TBW is ≥ 120% IBW?

AdjBW

CrCl equation

CrCl (mL/min) = (140 - age)(weight) / ([SCr](72))

x 0.85 if female

When calculating CrCl, if TBW < IBW, what weight should be used?

TBW

When calculating CrCl, if TBW is about equal to IBW, what weight should be used?

IBW

When calculating CrCl, if someone is overweight or obese (TBW > IBW) what weight should be used?

Depends on BMI:

BMI < 25: use IBW

BMI > 25: use AdjBW

pH < 7.35

acidosis

pH > 7.45

alkalosis

What BUN:SCr ratio indicates dehydration?

> 20:1

pCO2 range

35-45 mmHg

HCO3 range

22-26 mEq/L

Anion gap equation

AG = Na - Cl - HCO3

Causes of gap acidosis (CUTE DIMPLES)

Cyanide

Uremia

Toluene

Ethanol

Diabetic ketoacidosis

Isoniazid

Methanol

Propylene Glycol

Lactic acidosis

Ethylene Glycol

Salicylates

What does it mean when pH = pKa

It means that 50% of the drug is ionized and 50% of the drug is nonionized.

pH > pKa

More of the acid is ionized

pH < pKa

More of the acid is un-ionized

Differences in characteristics of an ionized vs. non-ionized drug

Ionized: more soluble but cannot cross lipid membranes

Non-ionzied: not soluble but can cross membranes to reach receptor site

Are most drugs weak acids or weak bases?

Weak acids

Weak acid formula

pH = pKa + log (salt/acid)

Weak base formula

pH = pKa + log (base/salt)

(flip the fraction from weak acid formula)

How much elemental calcium is in calcium carbonate?

40%

How much elemental calcium is in calcium citrate?

21%

How should calcium carbonate be taken?

Take with food (acid dependent absoprtion)

How should calcium citrate be taken?

With or without food (acid independent absorption)