Pharmacology, CH 8

comparisons between two things

statement saying those two ratios are equal

rule prescribing how to calculate a dosage

dimensional analysis
method based on the premise that any number can be multiplied by one without changing its value

fraction method
uses two equivalent proportions to find the answer

drug dose calculation:step 1:
conversion of numbers to the same unit of measurement

drug dose calculation: step 2:
using the preferred method, write the problem on paper; check again to confirm that your calculations are correct

4 methods by which to calculate drug dosages for nonparenteral (oral) route of administration:
1. ratio and proportion method
2. formulation method
3. dimensional analysis
4. fractions


drug quantities can be in:
tablets, capsules, milliliters, or another unit, and each label has its own equivalents

sample drug label should include 8 things:
1. brand name (trade)
2. generic name
3: drug strength
4 drug form, route of administration if other than oral, total amount of medication in the container, directions for reconstitution if necessary
5. manufacturer
6. National Drug Code (NDC)
7. expiration date
8. lot number

Ratio and proportion method:
uses ratios, which are comparisons between two objects (numbers in this case) like 4 pieces of pepperoni pizza and 3 pieces of cheese pizza are 4:3::8:6 or 4/3 = 8/6. Medication order is for 400 mg. Available medication is 300 mg in 1mL. 300 mg/1mL = 400 mg/?mL

Formulation method:
involves stacking units that are the same and multiplying by the unit requested.

desired dose:
equals the dosage that has been ordered or ordered dose

available dose
the dosage on hand

D = ? H = ? Q = ?
D = desired Dose
H = on hand or available amount in ordered units
Q = quantity in units given

dimensional analysis:
uses the ordered amount of a drug to multiply with two equal quantities in different dimensions (units of measurement) to derive the answer

dimensional analysis steps:
step 1: write the units of the dose ordered
step 2: write the units that are on the label and the unit that you plan to give the patient
Mg (ordered) x ____ mL
_______________________ = mL (desired)
Mg for label (ordered)

conversion factor:
formula to change from one unit of measurement to another

fraction method:
dosage on hand desired dose
________________ = _______________
dosage unit dose given

special calculations include:
pediatric and geriatric patients; their bodies are either immature (pediatric) or weakened by the aging process (geriatric)

body surface area, patient’s weight or body surface to calculate for the correct dosage; convert patient’s weight from pounds to kilos and then multiply that number by number of milligrams to determine the daily dosage

infants and children

in pediatric population ____ is used to calculate dosages:

in children, total body water content is ____ in a child than an adult

medication is absorbed differently in children and at a ___ rate
different; children’s bodies cannot handle an adult dosage

geriatric patients need medications:
calculated very carefully because of high risk for toxicity resulting from their aging body systems, particularly renal (kidneys) hepatic (liver) and circulatory systems

physician may drug geriatric patient:
on an individual basis, after evaluating organ function and body weight; each medication might have a slightly different reaction, and must be assessed after each medication is begun or changes to doses implemented

complicated health of many elderly patients:
patients may be seeing a multitude of practitioners, each of whom treats a different health issue, as well as self medicating with vitamins and herbal medications

body surface area (define)
ratio of height to weight or total surface area of the human body; method most commonly used in children or administered chemotherapy to adults when dosage accuracy is critical

powdered medics occasionally must be converted to liquid form to be administered

after adding sterile water or saline solution;
use the conversion ratio on the drug label to calculate the dosage

amount of fluid, used to reconstitute the formula adds to the powder’s volume, so the final solution (powder and fluid) may be greater than the volume of the diluent

intravenous or IV

dimensional analysis is best way:
to calculate an IV drip rate because this method uses ratios as conversion factors and reduces the possibility of errors

laws related to IV therapy:
vary from state to state

you must know how IV dosages are calculated so
you can double-check other health-care workers calculations

electronic regulator pumps:
machines that deliver and monitor IV fluids at a set rate; these pumps alert health care professionals if a problem arises and allow them to perform other tasks; usually like 1000 mL/2 hours or 400 mL/8 hours

IV tubing:
specific to the type of pump, run through an electronic regulator

IV formula:
Total mL ordered
__________________________ = mL/hour (round 2 whole#)
Total time ordered in hours

If IV rate doesn’t come out correctly, like it’s taking 2 hours instead of 1,
report it to your supervisor of flow rate is not constant and correct. DO NOT change the flow rate because the change may cause the fluid or medication to be infused to quickly.

when there is leakage of IV fluid or medication into the surrounding tissue; you can cause damage by increasing the flow rate

Manual IV sets
use gravity to infuse a solution at a set rate; this means you need to know the drop factor

drop factor =
drops per milliliter (gtt/mL; how many drips are in 1 mL)and is stated on the package of the IV tubing (the drop factor is built into electronic pumps because the tubing matches the pump)

IV tubing has either ___ or ___ chamber
microdrip or macrodrip chamber

micro drip is:
60 gtt/mL

macrodrip is:
either 10 0r 15 gtt/mL, again as stated on the tubing practice

the health care professional who starts the IV infusion establishes the rate by:
hanging the bag or bottle at a certain height and adjusting the number od drops per minute with the roller clamp

IV set must not:
be moved (gravity changes how fast the drops fall) or adjusted; doing so could change the drip rate

formula for the IV flow rate is:
Total volume (V)
to be infused (mL) Drop factor (D) (gtt) Rate Flow
___________________________ x _______________ = _______
Total time in minutes mL min

simple formula for IV flow rate:
___ x D = R

fluid balance in pediatric and geriatric patients:
fluid balance is vital for life. Pediatric and geriatric patients can easily suffer from dehydration, overhydration, or electrolyte imbalances because of differences in their kidneys

fluid output is determined by measuring:
in mL either urine or emesis (vomit) caught in a special container that includes the unit of measure


fluids that have a diuretic effect on kidneys:
coffee, caffeinated sodas, and beer; they increase urination. These count as hydration, but are not best choices when intake and output are important to the patient’s health

physician’s order for fluid intake restrictions:
usually in milliliters mL

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