Compounding Facts and Information
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allowable % error in mass in compounding pharmacy practice (typically)
allowable % error in mass in manufacturing
+/- 6% (sometimes 3%)
Prescription Balance: Position of Drug
Double-pan Torsion Balance Class
- Class A (USP)
- Class III (NIST)
NIST name and former name
- Current: National Institute for Standards and Technology
- Former name: NBS (National Bureau of Statistics)
How to avoid getting drug stuck in crease of folded weighing paper?
Fold paper only at the corners.
Top-Loading balance features
- digital display
- SR = 1 mg
- Avoid errors of 5% or more (do not weigh < 20 mg)
Percentage Error Formula:
[(Qty. weighed - qty. desired)/(qty. desired)] x 100%
[(Error x 100%)/(qty. desired)]
if max potential error is +/- 5 mg in a total of 200 mg, what is the percentage of error?
[(205 - 200)/(200)]x100% = +/- 2.5%
Least Weighable Quantity factors
- 1. sensitivity requirement of the balance used.
- 2. potential error that may be allowed to incur in the weighing process.
A pharmacist weighs 40 mg on a Rx balance having an SR of 6 mg. What is the percentage of error?
6mg/40mg x 100% = +/- 15% error
National Standard sensitivity requirement of Class A/Class III balance.
A Class A Rx balance has a SR of 0.006 g. How would you weigh 0.015 g of Aspirin with a potential error not exceeding 5%, using lactose as the diluent?
- LWQ = (6mg/5) x 100% = 120 mg
- weigh 120 mg Aspirin
- [(15)/(120) = (120)/(x)] ==> x = 960
- add (960 - 120) 840 mg lactose to aspirin
- take 120 mg of this mixture (contains 15 mg aspirin and 105 mg lactose)
A balance has a SR of 0.001 g (1 mg). How would you weigh 5 mg of a drug with a potential error not exceeding 5% using lactose as the diluent?
- LWQ = (1mg/5%) x 100% = 20 mg
- weigh 20 mg of drug
- [(5 mg)/(20 mg) = (20 mg)/(x)] ==> x = 80
- add 60 mg of lactose to 20 mg drug
- now weigh out 20 mg of this mixture to obtain 5 mg of drug and 15 mg lactose
Electronic Prescription Balance Assumption
- SR = 1 mg
- Potential Error = 5%
- LWQ = 20 mg
Aspirin 4 mg
Acetaminophen 30 mg
Assume LWQ = 20 mg
- weigh 20 mg Aspirin
- [(4)/(20) = (20)/(x)] ==> x = 100
- add 80 mg diluent to aspirin
- weigh out 20 mg of this mix to obtain 4 mg aspirin needed
- now simply weigh and add 30 mg acetaminophen (it is over the lwq)
use of conical graduates
ONLY ONE for measuring AND mixing
How to be accurate with graduated prescription bottles
- QS the Rx bottle with exact-measured water and mark level on bottle with a line.
- Fill formulation to this line, not the pre-marked line.
this procedure is especially important for viscous compounds
How would you measure 1.5 mL of a liquid using a 10 mL graduate cylinder calibrated from 2 mL to 10 mL in 1 mL divisions?
- First try the least possible amount (2 mL in this case):
- [(1.5 mL)/(2) = (2)/(x)] ==> x = 2.6
- 2.6 mL cannot be measured with what you have.
- Now Try 3:
- [(1.5 mL)/(3) = (2)/(x)] ==> x = 4
- so measure 3 mL of drug and dilute with 1 mL of diluent.
- now extract 2 mL of this mixture (contains 1.5 mL drug)
How would you measure 0.75 mL of a liquid using a 10 mL graduate cylinder calibrated from 2 mL to 10 mL in 1 mL divisions?
- [(0.75 mL)/(2) = (2)/(x)] ==> x = 5.33 mL (not measurable)
- [(0.75 mL)/(2) = (3)/(x)] ==> x = 8 mL
- measure 2 mL of drug
- add 6 mL of diluent liquid
- extract 3 mL of this mixture to obtain 0.75 mL drug in 2.25 mL diluent liquid
How would you measure 0.25 mL of a liquid using a nongraduated medicine dropper calibrated to 20 drops/mL?
- 20 gtt/1 mL = x gtt/0.25 mL
- x = 5 drops
Normal physiologic pH of human blood
pH of blood suggesting life-threatening situation.
<6.9 or >7.8
Two Buffer Systems
- 1. In the plasma.
- -Carbonic Acid/Bicarbonate buffer
- -Acid sodium salt of phosphoric acid/alkali sodium salt of phosphoric acid
- 2. In Erythrocytes:
- -Hemoglobin/oxyhemoglobin buffer
- -Acid potassium salt of phosphoric acid/alkali potassium salt of phosphoric acid
Total Extracellular Fluid
- Plasma (3L for average 70 kg adult)
- Interstitial-Lymph Fluid
- Dense CT and cartilage fluid
- Inaccessible bone water
mEq calculation Formula
mEq = (weight of solute in mg)/[(atomic weight)/(number of valence)]
Calculating millequivalents of a salt
mEq = (weight of solute in mg) / [(atomic weight)/ (number of valence x n)]
where n is the number of ions created by the salt
% weight by volume
grams solute / 100 mL solution
One Equivalent = ?
the amount of positive (or equal negative) charge equal to the amount of charge in one mole of H+ ions.
Preferred as the source of drug during extemporaneous compounding rather than the drug as pure powder.
Especially when a small amount of drug is needed (this allows us to avoid the aliquot method)
Advantages of Tablet Dosage Forms
- Patient prefers them (ease of administration, self-medication, and convenience in carrying the day's supply)
- Pharmacist prefers them (convenience in dispensing)
- Prescriber favors them (accuracy of dose and patient compliance)
- Manufacturer likes them (economy, packaging, production considerations)
Advantages of Tablet Dosage Forms
- Precision and accuracy of dose
- possibility of variable dosage strengths
- broad range of drug release
- masking of bitter taste
- durability and stability
- convenience of handling, identification, and administration
- less expensive than capsule forms
REQUIRED in a Tablet Dosage Form:
- Active Ingredient
Force required to pass the breaking test for tablets:
Other components to tablets:
- Lubricant, antiadherent, glidant
- flavoring agents
Classes of Tablets:
- Oral tablets for ingestion
- tablets used in the oral cavity
- tablets administered by other routes (e.g. implantation tablets, vaginal tablets, etc.)
- tablets used to prepare solutions
- active ingredient formulated with Citric acid monohydrate and/or Tartaric acid and sodium bicarbonate
- when dissolved in water, citric acid reacts with sodium bicarbonate to produce sodium citrate and CO2 (or sodium tartrate and CO2)
- liberation of CO2
- increases absorption by pre-dissolving formulation
Depot vs. Repository Sustained Release Products
- Depot = Long Term
- Repository = More Short Term
USP has only TWO classifications of tablets:
- 1. Immediate-Release Tablets (IRT) ("conventional tablet dosage form")
- 2. Modified-Release Tablets (MRT) (e.g. delayed release, extended release, etc.)
Oral Dosage Forms that SHOULD NOT be crushed:
- EC products
- ER products
- Unpleasant tasting products
- effervescent tablets
- SL tablets
- Misc. (dosage forms containing drugs that produce mucosa irritation; formulations with dyes; drugs that may stain teeth or mucosal tissue; potentially carcinogenic drugs; products manufactured to alter the release characteristics of the drug from the dosage form)
Daily water requirements in patients < 10 Kg
Daily water requirements in patients 10 - 20 kg
1,000 mL plus 50 mL/kg/day for weight over 10 kg
Daily water requirements in patients 20 - 80 kg
1500 mL plus 20 mL/kg/day for weight over 20 kg
Total body water birth to 11 days
Total body water 11 days to 6 months
Total body water 6 months to 2 years
Total body water 2 years to 7 years
Total body water 7 years to 16 years
Total body water 16 years through adulthood
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