Transcript Dose

Dose :
is the quantitative amount administered or taken
by a patient for the produced medicinal effect.
may be expressed as:
 a single dose, the amount taken at one time;
 A daily dose; may be subdivided and taken in divided
doses, two or more times per day depending on the
characteristics of the drug and the illness.
 A total dose, the amount taken during the time-course of
therapy.
 The schedule of dosing {e.g., four times per day for 10
days) is referred to as the dosage regimen.
Doses
Interpreting Labels
Label Info
Meaning
25 mg/ml
This ratio tells the amount of medication
in each ml of solution
1:4
Ratios written this way always mean
grams per milliliter
30%
Amount of medication (in grams) in
every 100 ml of solution
40 mg = 2cc
Equation tells the amount of medication
in the given volume
U-100
Units per ml (100 units per ml in this
case)
20 mEq/ml
This ratio tells the number of milliequivalents per milliliter of solution
Commonly used abbreviations
English AND ROMAN NUMERALS
 English and Roman numerals are used interchangeably to
express quantity or degree of measure. Roman numbers are
formed by combining the following letters according to the
rules
English numbers
Roman numbers
½
Ss
1
I
5
V
10
X
50
L
100
C
500
D
1000
M
English AND ROMAN NUMERALS
 1- To repeat a Roman number doubles its value. I =1;
II=2
 2. To place a letter to the right of a Roman number
adds its value to that number. V=5; VI=6.
 3. To place a letter to the left of a Roman number
decreases the value of that number by the amount
of the number added. V=5; IV=4.
Systems of Measurement and
Conversion
 There are three primary systems
1 - the metric system,
 The metric system is widely used in dosage calculations. It uses
powers of the basic units of measure are the gram, liter, and
meter.
 A gram measures weight, a liter measures fluid, and a meter
measures length.
 The metric system also uses prefixes to describe how much of
the basic unit:
 Kilo =1000 times the basic unit.
 Centi =1/100 of the basic unit or 0.01.
 Milli = 1/1000 of the basic unit or 0.001.
 Micro =1/1,000,000 of the basic unit or 0.000001.
METRIC BASIC EQUIVALENTS
 1 Kg. = 1000 Gm.
 1 Gm. = 1000 mg.
 1 mg. = 1000 migrogram .
 1 ml. = 1 c.c.
 1 L. = 1000 c.c. or 1000 ml.
2- Apothecary system,
 is another method of expressing units of measure.
 It is an old system and is not used exclusively because it is not
standardized. That means that each measure is an approximate
amount,
 It is different from the metric system in the following ways:
1- It uses Roman numerals (ss = 1/2, i = 1, iv = 4, v = 5, ix =9, x =10)
 2. The unit is written before the amount (gr i, gr ss, gr iv)
 3. Fractions are written as common fractions (gr. 1/150). The only
exception is ½, which is written as is .
The basic units of measure that are
commonly used are the
1- grain,: measures weight and is written gr.
2- Ounce : measures liquid amounts and is written like a
cursive Ҙ but with an extra hump on top =
3- Dram: Used to measure smaller amounts of liquid
medicine. It is written just like a cursive Ҙ .
4- minim. Tiny amount of liquid medicine. A minim equals
a drop. It is written like a cursive ᶆ and sometimes it has a
long tail.
APOTHECARY BASIC EQUIVALENCES
 (60 minims) = 1 fluid dram
 (8 fluid drams) = I fluid ounce
 (16 fluid ounces) = 1 pint
 (2 pints) = 1 quart
 (4 quarts) = 1 gallon
3- the household system
 The Household Unit of Measure is the most commonly
recognized by laypeople. It includes
 1- drops, is written gtt
 teaspoons, is written tsp or t
 tablespoons, is written Tbsp, or T
 and cup is written C
HOUSEHOLD EQUIVALENTS
 60 drops (gtts.) = 1 teaspoon (t.)
 3 teaspoons = 1 Tablespoon (T.)
 2 Tablespoons = 1 ounce
 8 ounces = 1 cup (C.).
Conversion Between Systems:
 YOU MUST KNOW
 1- Known the unit of measure
 2- Known the equivalent unit of measure
 3- Desired unit of measure
 4- Unknown equivalent (X)
BASIC EQUIVALENCES
•
 Example: How many grams are there in 500mg?
 ( The known ratio is 1000 mg = 1 gm)
X = 500 ÷1000
X = 0.5 gm.
 Example: 20 mg is equal to how many grains?
 ( The known ratio is 60 mg = 1 gr)
 Use the above formula:
60 mg : 1gr :: 20 mg : X gr
60 X = 20
X = 20 ÷60
X = grain 1/3.
CALCULATION OF ORAL DOSAGES
 Oral dosage forms of medications include Tablets Capsules -
Liquids
 Only scored tablets are intended to be divided
 Enteric-coated tablets cannot be crushed
 Sustained-release capsules cannot be opened and mixed
with food or fluid.
Dosage Calculations
 Three-step approach:
 Convert:
All units of measurement must be in same system and all
units must be in same size
 If not, convert before proceeding
 Think
Estimate reasonable amount of drug to administer
 Calculate
Set up ratio between dosage on hand and desired dosage
Dosage on hand
Dosage desired
Amount on hand
Amount desired
Example
 Need 100 mg and have 50 mg per tablet
Want to give twice the equivalent of each tablet
 Dosage on hand
Dosage desired
Amount on hand
Amount desired
 Cross-multiply
50mg
100 mg
1 tablet
X TABLTE
50 X = 100
X = 2 tablets
Example2
 Order: Flagyl 0.75 g p.o. t.i.d. (three times per day)
Available: Flagyl 500 mg tablets How many tablets per
dose are needed?
 Step 1: Convert
 Units are same system, but size is different
 Equivalent: 1 g = 1,000 mg
 Set up ratio:

Dosage on hand
Dosage desired
Amount on hand
Amount desired
 Cross-multiply
1g
1000
X = 1,000 * 0.75
0.75 g
X mg
X = 750 mg
 How many 500 mg tablets should be required to
administer 750 mg?
 Cross-multiply
500 mg
1 tablet
 500 X =750
X = 1.5 tablet
750 mg
X tablets
Example
 Order: Codeine sulfate gr3/4 p.o. q. 4 h p.r.n. (take as
needed) • Available: Codeine sulfate 30 mg tablet
• Calculate one dose
 Step 1: Convert
 Approximate equivalent
gr i = 60 mg
 Set up ratio
gr 1
gr3/4
60 mg
X mg
X= 45 mg , Codeine ¾ gr =45 mg
 Step 2: Think
Estimate giving more than one tablet but less than two
tablets
 Step 3: Calculate
Order: Codeine 45 mg p.o. q. 4 h
• Available: Codeine 30 mg per tablet
 Set up ratio
30 mg
45 mg
1 tablet
X tablets
30 X =45 X= 1.5 tablets needed for each dose
Calculating Dosages for Oral Liquids
 Use same three steps
 • Doses calculated in mL
 Example 1:
– Order: Cefaclor 100 mg p.o. q.i.d. (four times per day)
– Available: Cefaclor 125 mg per 5 mL
 – Calculate one dose
125 mg
100 mg
5 mL
X mL
125 X= 500
, X= 4 mL Cefaclor needed per dose.
 Order :phenobarbital elixir 0.2 gm hs the drug available
in 20 mg/5ml
(Dose desired )
× drug form
Dose available
0.2gm
20mg/5ml
200mg
20mg/5ml
20mg :5 ml :: 200mg :X ml =50ml/dose
Parenteral medication
Three method
 1- A prefilled syringe labeled with a certain dosage in a
certain volume (ex: demerol 100mg in 1ml)
 2- A single or multiple-dose ampule labeled with a certain
dosage in certain volume (ex: epinephrine 1:1000 in 0.1
ml).
 3- A vial with a powder or crystals that must be mixed with
saline solution ,the drug my be measured in grains ,grams,
milligrams or unit .the amount of solution to be added
varies and must be calculated according to the instruction
with vial .generally intradermal and subcutaneous involve
very small amount of solution whereas IV need 50 ml or
more
 the equation is Drug available : dilution = Dose desired : X
 Order : digoxin 0.2 mg I.M drug a available as 0.5 mg /ml
Dose desired
X volume which dissolved it
Drug available
0.2mg
× 1ml
0.5mg
2/5 × 1 ml = 0.4ml
CALCULATION OF PARENTERAL DOSAGES
 Parenteral means injection of drugs into the tissue or fluids of the
body.
 Calculating Dose as Volume
the volume you want to administer =
Dosage desired
X volume which dissolved it
Amount available
Example :
A patient is prescribed 200mg of Furosemide I.V. The ampoules
available contain 250mg in 10mL. What volume containing the
drug do you need to administer?
What you WANT
What you have GOT
X what it is IN
200 mg
250 mg
× 10 mL = 8 mL
Drug Strengths & Stated Concentrations
 How much fluid is required (Volume) =
What you HAVE (mg)
CONCENTRATION (mg/mL)
 Example
A patient is prescribed 250mg of Aciclovir I.V. Aciclovir has to be
initially reconstituted with water for injection, then added to a bag
of compatible infusion fluid, giving a final concentration of
5mg/mL. How much infusion fluid should be used dilute the
reconstituted Aciclovir to achieve this final concentration?
What you HAVE (mg)
CONCENTRATION (mg/mL)
250 mg
5mg/mL
= 50 mL
ADVANCED DOSAGE CALCULATIONS:
 Include
 1- reconstitution of powered drugs,
 2- insulin administration
 3- calculating safe pediatric dosages of medications.
Reconstitution OF Powder Drugs
 A- On the drug label or the package insert will state the
diluents to be used and the exact amount to be added.
When adding a solution or diluents to the powder, you will
notice that the directions will state the volume and dose
after the solution has been added.
 B- Use the formula method:
Administration =
Dose × volume
Available
Example
A patient is to receive Penicillin 200mg IV every 6 hours.
The label on the vial reads: add 1.8 mL of sterile water
diluents. On the label it states, after reconstitution the vial
will contains 250 mg/mL( the dosage supply amount).
 200 mg X 1 mL = 0.8 mL
250 mg
You would prepare 0.8 mL to administer in the IV to your
patient
INSULIN ADMINISTRATION
 To determine the amount of the short-acting insulin to
administer, depending on label
Types of insulin dosg form
 The standardized measure called a unit.
 Is available in 10 ml vials and two strengths (U-100 units
per 1 ml
 U-500(500 units per 1 ml this five times stronger
than U-100
 If not insulin syringe available must be calculated
by formula by which tuberculin syringe
Number of minims to administrated =
Insulin desired
× 16 minims
Insulin available
insulin syringe
tuberculin syringe
CALCULATING SAFE PEDIATRIC DOSAGES
 Pediatric patients, which include both infants and
children, require special dosing that is adjusted for their
1- body weight. the most commonly used method is stated
as mg/kg
2- A number of formulas have been used throughout the
years to determine the best dose for pediatric patients
3- by Body Surface Area.
Pediatric Formulas
 Children need lower dosages of medication compared to adults.
Three formulas are used to help calculate a pediatric dosage
based on whatever information is available.
EXAMPLE
 An infant, 15 months old and, needs Streptomycin Sulfate,
which is usually administered to adults as 1 gm (1000 mg),
as a daily IM injection. What is the appropriate dosage for
the infant?
Pediatric Dose =
15 (Age in months) * 1000 mg (Adult Dose)
150
Pediatric Dose = 15
× 1000
150
 Pediatric Dose = 0.1 * 1000
 Pediatric Dose = 100 mg
 Now, let’s reexamine using Young’s Rule, which uses the
child’s age in years. The age of a 15-month-old could be
expressed as 1.25 years old, since he or she has lived for 12
months (1 year) _ 3 months (1/4 or 0.25 of a year).
 Pediatric Dose =
 1.25 (Age in years)
× 1000 mg (Adult Dose)
13.25 (Age of child + 12)
 Pediatric Dose = 1.25
* 1000
13.25
 Pediatric Dose = 0.094 * 1000
 Pediatric Dose = 94 mg
Calculating drip rates
1- Calculation the flow rates for IV fluid administration .
Two concepts must be understood
A- flow rates : measured in drops per minute
B- drops factor :number of drops per milliliter of liquid .this
different for different manufactures of IV infusion equipment
As general range between 10 and 15 drops per milliliter
Drop factor × Milliliters per minute = flow rate (drops/ minute
 1- EX :Order (N.S) IV infusion to run at a slow rate to keep
vein open, the rate is to be at 2 ml/minute .the IV infusion
set delivers 10 drops/ml. the goal is to determine the flow
rate in drops/minute
 10 (drop factor) × 2ml /min =20 drops/minute
 2- EX
Order 1000 ml normal saline to be administered in 5h (DF=15)
Total of fluid to give × drop factor
= flow rate (drops/miniute
Total time (minutes)
1000
× 15 = 1500ml = 50 drops /minute
300min
300min
Note
Drip flow regulation is controlled by tightening or releasing the roller
clamp (white plastic clamp) and counting the drops falling into the
drip chamber. For microdrip administration sets note that:
drops/minute = mls/hour
Calculating infusion rates for infusion
devices
 calculation of the volume to be delivered per hour
 calculation of the number of drops to be administered per hour
 calculation of the number of drops to be delivered in one minute.
 The following equation can be used :
gtt/m1
cc/hour x-------------- = gtt/min
Min/hour
 cc/ hour = volume / hour
 gtt = drop
 min = minute
 The prescriber ordered:intravenous Ancef 1 g IVPB q4h
 The package insert information is as follows: Add 50 mL sterile
water to the bag of Ancef 1 g and infuse in 30 min. The tubing
is labeled 20 drops per milliliter. Calculate the flow rate in
drops per minute for this antibiotic.
 The patient receives 50 mL in 30 minutes. You want to change
this flow rate from mL per minute to an equivalent flow rate in
drops per minute.
 Calculation of IV Drip Rate Using an
Electronic Pump
 Solve: The physician orders 1 L of D5 W
over 12 hours
 Formula mL/hour:
 Total Volume to infuse (mL) = mL/h
Time (h)
1 L = 1000 mL
1000 mL = 83 mL/hour
12
 1000 mL of D5W is to infuse at 125 mL/hour. How
many hours will it take for this liter of fluid to be
completed?
 Formula for Infusion Time
Total volume to infuse = Infusion time (h)
mL/h
1000 mL = 8 hours
125 mL/h
In summary, 1000 mL at 125 mL/hour will take 8 hours.
Calculating Dosage by Body Surface Area
 In some cases, body surface area (BSA) may be used
rather than weight in determining drug dosages. This
used to calculating dosages for
 children,
 those receiving cancer therapy,
 burn patients,
 and patients requiring critical care.
A patient’s BSA can be estimated by using
 formulas
 nomograms.
BSA Formulas
 BSA, which is measured in square meters (m2) can be
determined by using either of the following two mathematical
formulas
 Formula for metric units
Example
 Find the BSA of an adult who is 183 cm tall and weighs 92
kg. Because this example
Example
 What is the BSA of a man who is 4 feet 10 inches tall and
weighs 142 pounds? First you convert 4 feet 10 inches to 58
inches.
 Because the example has household units (pounds and
inches), we use the following formula:
5.1286
5.12
2- Nomograms
 BSA can also be approximated by using a chart called a
nomogram .
 The nomogram includes height, weight, and body
surface area. If a straight line is drawn on the nomogram
from the patient’s height (left column) to the patient’s
weight (right column), the line will cross the center column
at the approximate BSA of the patient.
 Examle
child weighing 15 kg and measuring 100 cm in height has a
BSA of 0.64 m2
In the example shown, a child weighing 15 kg
and measuring 100 cm in height has a BSA of
0.64 m2
Body surface area (BSA)
of Children
dose calculated as follows
 Dose for child =
BSA for child
× adult dose
1.73 m2 (average adult BSA)
 Examples:
If the adult dose of a drug is 75 mg, what would be the dose
for a child weighing 40 lb and measuring 32 in. in height? (Use
the body surface area method.)
 Answer.
 From the nomogram, the BSA = 0.60 m2
 0.60 (m2)
X 75 mg
=26 mg
 1.73 (m2),
 The nomogram in designed specifically for determining
the BSA of adults may be used in the same manner as the
one previously described. The adult dose is then calculated
as follows
Examples:
 If the usual adult dose of a drug is 120 mg, what would be
the dose based on BSA for a person measuring 6 ft tall and
weighing 200
 Answer
BSA (from the nomogram) = 2.13 m2
(2.13 m2
X 120 mg=147.75 mg or 148mg
1.73 m2)
Another BSA Equation
Example:
 Calculate the BSA for a patient measuring 165 cm
in height and weighing 65 kg
The nomogram in designed specifically for
determining the BSA of adults may be used in
the same manner as the one previously
described.
The adult dose is then calculated as follows
 Examples: If the usual adult dose of a drug is
120 mg,
 what would be the dose based on BSA for a
person measuring 6 ft tall and weighing 200
 Answer.
 BSA (from the nomogram) = 2.13 m2
 (2.13 m2/1.73 m2) X 120 mg=147.75 mg or 148
mg,