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allowable % error in mass in compounding pharmacy practice (typically)
+/- 10%
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allowable % error in mass in manufacturing
+/- 6% (sometimes 3%)
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Prescription Balance: Position of Drug
Left pan
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Double-pan Torsion Balance Class
- Class A (USP)
- Class III (NIST)
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NIST name and former name
- Current: National Institute for Standards and Technology
- Former name: NBS (National Bureau of Statistics)
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How to avoid getting drug stuck in crease of folded weighing paper?
Fold paper only at the corners.
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Top-Loading balance features
- digital display
- SR = 1 mg
- Avoid errors of 5% or more (do not weigh < 20 mg)
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Percentage Error Formula:
[(Qty. weighed - qty. desired)/(qty. desired)] x 100%
[(Error x 100%)/(qty. desired)]
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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%
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Least Weighable Quantity factors
- 1. sensitivity requirement of the balance used.
- 2. potential error that may be allowed to incur in the weighing process.
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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
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National Standard sensitivity requirement of Class A/Class III balance.
6 mg
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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)
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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
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Electronic Prescription Balance Assumption
- SR = 1 mg
- Potential Error = 5%
- LWQ = 20 mg
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Rx
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)
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use of conical graduates
ONLY ONE for measuring AND mixing
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Graduated Cylinder
measuring only
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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
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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)
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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
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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
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Normal physiologic pH of human blood
7.4
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pH of blood suggesting life-threatening situation.
<6.9 or >7.8
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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
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Total Extracellular Fluid
- Plasma (3L for average 70 kg adult)
- Interstitial-Lymph Fluid
- Dense CT and cartilage fluid
- Inaccessible bone water
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mEq calculation Formula
mEq = (weight of solute in mg)/[(atomic weight)/(number of valence)]
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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
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% weight by volume
grams solute / 100 mL solution
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One Equivalent = ?
the amount of positive (or equal negative) charge equal to the amount of charge in one mole of H+ ions.
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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)
Tablets
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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)
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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
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REQUIRED in a Tablet Dosage Form:
- Active Ingredient
- Diluent
- Binder
- Disintegrants
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Force required to pass the breaking test for tablets:
5 Kg
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Other components to tablets:
- Lubricant, antiadherent, glidant
- colorants
- flavoring agents
- sweeteners
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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
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Effervescent Tablets
- 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
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Depot vs. Repository Sustained Release Products
- Depot = Long Term
- Repository = More Short Term
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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.)
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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)
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Daily water requirements in patients < 10 Kg
100 mL/Kg/day
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Daily water requirements in patients 10 - 20 kg
1,000 mL plus 50 mL/kg/day for weight over 10 kg
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Daily water requirements in patients 20 - 80 kg
1500 mL plus 20 mL/kg/day for weight over 20 kg
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Total body water birth to 11 days
77.6%
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Total body water 11 days to 6 months
72.2
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Total body water 6 months to 2 years
63.1%
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Total body water 2 years to 7 years
59.5
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Total body water 7 years to 16 years
58.4%
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Total body water 16 years through adulthood
58%
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