1. Chapter one Pharma Calculation(1).ppt

Pharma calculation

1. Pharmaceutical calculations
By: Abera J (B.Pharm., MSc in Clinical Pharmacy).
1

2. Introduction
•Pharmaceuticalcalculation,
–istheareaofstudythatappliesthebasic
principlesofmathematicstothepreparationand
safeandeffectiveuseofpharmaceuticals.
•Pharmaceuticalcalculation,
–Encompasses calculationofamounts of
componentsbeingaddedtoacompoundedtotal
parenteralnutritiontothedropsperminuterateon
thelabelofanintravenousbag.
2

3. Introduction…
•Pharmacytechnicianrequiresavarietyofskills
andabilities,
–Themostimportantistheabilitytocarryout
importantmathematiccalculations.
•Thegoalofthismoduleistoprovideabasicreview
ofthemanytypesofpharmacycalculationsthat
pharmacytechniciansarerequiredtobeequipped
with.
3

4. Measurement of weight and volume
Pharmaceuticalmeasurementofweightand
volumeisanimportantpartofpharmacypractice.
Theknowledgeandapplicationofpharmaceutical
pharmaceuticalandclinicalapplicationsare
essentialforthepracticeofpharmacy.
The measurement systems include:
i.Metric systems
ii.Apothecary systems
iii.Household Systems 4

5. Manypharmaceuticalcalculationshavebeensimplified
bytheshiftfromapothecarytometricsystemof
measurements.
Inthehouseholdsystemofmeasurement,the
patientsusehouseholdmeasuringdevicessuchas;
teaspoon,tablespoon,teacup,wineglass.etc.
thoughthissystemisinaccurate,duetoincreased
homecaredeliverysystemarewidelyused.
Therefore,onlymetricsystemwillbediscussed
here.
Measurement of weight and volume…
5

6. 6

7. Volume measurement
The literis the metric unit of volume.
The table of metric volume follows:
7

8. Volume measurement….
Common instrumentsforthepharmaceutical
measurementofvolume;
Rangefrommicropipets,andburettesusedin
analyticprocedurestolarge,industrial-size
calibratedvessels
Examplesofcommoncontainersformeasuringvolume
are:
GraduatedMeasuringCylinders-5ml,10ml,50ml
Conicalmeasures-100ml,200ml,250ml,500ml
Beakers-100ml,200ml,300ml
8

9. Volume measurement…
Animportantfactorintheaccuracyofan
instrumentusedformeasuringvolumeisthe
surfaceareaoftheliquidinit.
Accuracyincreaseasthesurfacearea
increases.
However,adecreaseinsurfaceareadecreases
theconvenienceoftransferringaliquidtoand
fromtheequipment.
Therefore,accuracyandconvenienceshould
becompromised.
9

10. Measure of Weight
•The unit of weight in the metric system is
the gram(g). The table of metric weights
follows:
10

11. Measure of Weight…
Theselectionofbalanceandscaleforweight
measurementsdependsonthetaskathand,
Rangesfromhighlysensitiveelectronicanalytic
balances and prescriptionbalances in
extemporaneouscompoundingprocedurestolarge-
capacityscalesintheindustrialmanufacturing
andproductionofpharmaceuticalproducts.
11

12. Measure of Weight…
Weightisameasureofthegravitional
forceactingonabody,
itisdirectlyproportionaltothebody’smass.
Weightismeasuredbymeansofabalance.
Indispensing(hospitalandcommunity
pharmacies),thetypeofbalanceusedis
calledPrescriptionbalance.
12

13. There are two main types of prescription
balances:
1)ClassAPrescriptionBalance
Hasasensitivityrequirementof6mgwith
noloadandwithaloadof10goneachpan
Themaximumamountthatcanbeweighed
onthisbalanceis120g.E.g.Torison
prescriptionbalance
2)ClassBPrescriptionBalance
Hasasensitivityrequirementof30mg. 13

14. Prescription balances
Theirmajorpurposebeingthesame(i.e.
weighing),balancesaredifferentiatedfromeach
otherbythefollowingparameters:
1.Sensitivity
2.SensitivityRequirements
3.Capacity
14

15. Prescription balances…
Sensitivity
Isthesmallestweightthatmakesaperceptiblechangeinthe
pointerofabalancewhichindicatestheequilibriumposition.
SensitivityRequirements(SR)
Theminimumweightrequiredtomovethepointerbyone
divisiononthescale.
SRforclassAprescriptionBalanceis6mgwhilethatof
classBprescriptionbalanceis30mg.
N.B.Thesmallertheweightrequiredtomovethe
indicatoronedivision,themoresensitiveisthebalance.
15

16. Prescription balances…
Capacity
Isthemaximumweight,whichabalancecan
weigh.
ThecapacityofmostclassAandclassB
prescriptionbalanceis120g
16

17. Prescription balances…
17

18. Example
1.Ifachlorpheniraminemaleatetabletweighs
0.26gm,one-fourthofthesametabletweighshow
manymilligrams?Sincetheanswerisrequiredin
milligrams,converttheweightofthetabletinto
milligramsfirst.
0.26g=0.26x1000=260mg
1/4x260mg=65mg
Answer:65mg
18

19. Example…
2. Add 1.25g, 35mg and 80µg, and express the
results in milligrams.
Convert all the units into the same denomination
and then perform the computation.
1.25g=1250mg, and 80µg = 0.08mg
Therefore, 1250mg+0.08mg+35mg=1285.08mg
Answer=1285.08mg
19

20. Example…
3.Incalibratingamedicinaldropper,2mlofa
pediatricsolutionresultedin48drops.Ifitis
desiredtoadminister0.08mLofthemedicationto
ababy.approximatelyhowmanydropsshouldbe
given?
48drops/2mL=Xdrops.0.08mL
X=1.922or2drops
Answer=2drops
20

21. Example…
4.Whatisaminimumamountthatcanbeweighed
onaclassAprescriptionbalancewithapotential
errorofnotmorethan10%
%Error=100*6mg/Q
Q=100*6/10=60mg
Answer=60mg
21

22. Density, specific gravity and specific
volume
•Density(d)ismassperunitvolumeofa
substance.
•Itisusuallyexpressedasgramspercubic
centimeter(g/cc).
•Densitymaybecalculatedbydividingmassby
volume,thatis:
22

23. Example
•What is the density of hydrochloric acid
weighing 20mL and 40g?
23
Density…

24. Specific Gravity
•Specificgravity(spgr)isaratio,expresseddecimally,
oftheweightofasubstancetotheweightofanequal
volumeofasubstancechosenasastandard,both
substancesatthesametemperatureorthe
temperatureofeachbeingknown.
•Specificgravitymaybecalculatedbydividingthe
weightofagivensubstancebytheweightofanequal
volumeofwater
24

25. Specific Gravity…
Becausesubstancesexpandorcontractatdifferent
rateswhentheirtemperatureschange,accuratework
necessitatesallowingcarefullyforvariationsinthespecific
gravityofasubstance.
IntheUSP,thestandardtemperatureforspecific
gravitiesis25°C,exceptforthatofalcohol,whichis
15.56°Cbygovernmentregulation.
25

26. Specific Gravity…
The density of a substance:
is a concrete number (1.8 g/mL in the example),
varies with the units of measure used
Specific gravity:
A ratio between like quantities is an abstract
number (1.8 in the example).
Has no dimension and is therefore a constant
value for each substance (when measured under
controlled conditions).
The specific gravity of water is always 1.
26

27. Specific Gravity…
•Substancesthathaveaspecificgravityof
lessthan1arelighterthanwater
•Substancesthathaveaspecificgravity
greaterthan1areheavierthanwater
27

28. Specific Gravity…
Example2
If52.5mLofoilweighs48.8g,whatisthe
specificgravityoftheoil?
Answer
52.5mLofwaterweighs52.5gm.
Therefore,specificgravityoftheoil=
48.8/52.5=0.929
28

29. Specific Gravity…
Example-3:If54.96mLofanoilweighs52.78g,
whatisthespecificgravityoftheoil?
54.96mLofwaterweighs54.96g
29

30. Specific Gravity…
Example-4:Ifaliterofacoughsyrupweighs
1285g,whatisitsspecificgravity?
•1000mlofwaterweighs1000g
Specificgravityofcoughsyrup=1285g/1000g
=
=1.285
30

31. Calculating the specific gravity of liquids
•Apycnometerisaspecialglassbottleusedto
determinespecificgravity.
•Tocalculatethespecificgravityofaliquidbymeans
ofaspecificgravitybottle,thecontainerisfilledand
weighedfirstwithwaterandthenwiththeliquid.
•Bysubtractingtheweightoftheemptycontainer
fromthetwoweights,wehavetheweightsofequal
volumes,eventhoughwemaynotknowthevolumes
exactly.
31

32. Calculating the specific gravity of
liquids…
32

33. Calculating the specific gravity of
liquids…
Exampe-2:A50mLpycnometerisfoundtoweigh120g
whenempty,171gwhenfilledwithwater,and160g
whenfilledwithanunknownliquid.Calculatethe
specificgravityoftheunknownliquid.
33

34. Calculating the specific gravity of solids using
displacement methods
Tocalculatethespecificgravityofasolidheavierthan
andinsolubleinwater,simplydividetheweightofthe
solidinairbytheweightofwaterthatitdisplaces
whenimmersedinit.
Theweightofwaterdisplaced(apparentlossofweightin
water)isequaltotheweightofanequalvolumeofwater.
34

35. Calculating the specific gravity of solids
using displacement methods…
35

36. Calculating the specific gravity of solids using
displacement methods….
Example-2: A glass weighs 12.64 g in air, 8.57 g when
immersed in water,and 9.12 g when immersed in an oil.
Calculate the specific gravity of the oil
36

37. Specific Volume
Specificvolume,inpharmaceuticalpractice,is
usuallydefinedasanabstractnumber
representingtheratio,expresseddecimally,ofthe
volumeofanequalweightofanothersubstance
takenasastandard,bothhavingthesame
temperature.
Wateristhestandardforliquidsandsolids.
Itmaybecalculatedbydividingthevolumeofa
givenmassbythevolumeofanequalweightof
water.
37

38. Specific Volume…
38

39. Specific Volume…
Becausespecificgravityandspecificvolumeare
reciprocals,
asubstancethatisheavierthanwaterwillhaveahigher
specificgravityandalowerspecificvolume,
whereasasubstancethatislighterthanwaterwillhavea
lowerspecificgravityandahigherspecificvolume.
Itfollows,therefore,thatwemaydeterminethespecific
volumeofasubstancebydividing1byitsspecific
gravity,andwemaydeterminethespecificgravityof
asubstancebydividing1byitsspecificvolume.
39

40. Specific Volume…
40

41. Use of Specific Gravity in Calculations of Weight and
Volume
Theweightsofequalvolumesandthevolumesofequal
weightsofliquidsareproportionaltotheirspecific
gravities.
Tocalculate,therefore,theweightofagivenvolumeor
thevolumeofagivenweightofaliquid,itsspecific
gravitymustbeknown.
Whenspecificgravityisusedasafactorinacalculation,
theresultshouldcontainnomoresignificantfiguresthan
thenumberinthefactor.
41

42. 42

43. THANK YOU.
43