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PharmaCALCULATIONS
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Pharmaceutical CALCULATIONS
Hello every one ...... The very first blog I would like to place in this April is on calculations.
Generally most of the students are confused while dealing with calculations. During my course of time till now, here are few calculations which I have come across. Before proceeding into the calculation the pre requisite step is to read the data thoroughly, understand the given information and select the required procedure for calculation.
I would like to touch up few important concepts in these calculations.
A) DOSAGE CALCULATIONS
B) ALCOHOL DILUTIONS
C) ISOTONICTY CALCULATIONS
D) PROOF SPIRIT CALCULATIONS
E) DOSAGE REPLACEMENT FACTOR
F) TEMPERATURE CONVERSION
A) DOSAGE CALCULATIONS^{1}
Based on Age
Young Rule (Children under 12 yrs of age)
Child's dose = Age (yrs)/ Age (yrs) +12 x Adult dose
Example: 1. Let us consider a drug whose dose is 350 mg, then the dose for a three year old child will be:
Sol: Child dose = 3/3+12x 325 = 65mg
Dillings formula
Dose for the child = Age in years/20 x Adult dose
Fried's Formula
Dose for the child = Age in months/150 x AD
Example 2:
Consider that the dose of a drug for adult is 100 mg then the dose for a 9 month old infant and a boy of 16 yrs age can be calculated as below:
Ans i) Fried's Rule 9/150x100 Dose = 6 mg
ii) Dillings formula: Dose = 16/20 x 100 = 80 mg
Based on Body Weight:
Clarks's Rule
Dose for the child = Weight of the child/ 150 x Adult dose
Example 3: If the adult dose of a drug is 10mg the dose for a 40 lb child will be:
Child's Dose = 40/150 x 100 = 2.67mg
Based On the Body Surface
Child's Dose = Body surface area of a child/Body surface area of Adult x Adult dose
Average body surface area for adult = 1.73 m2
Example 4: Let us see how to calculate the dose for child who has a body surface equal to 0.57 sq.m. when an average adult dose of a drug is 50 mg
Child dose (approx) = 0.57/1.73 x 50 = 16.5 mg.
B) ALCOHOL DILUTIONS ^{2 }
Alligation method
This method is used to find out the intermediate strength by mixing two preparations which are similar and having different strengths.
Example 5 Calculate the volume of 95% alcohol required to prepare 600 ml of 70% alcohol?
Volume required = 600ml
Percentage of alcohol required = 70
Percentage of alcohol used = 95
By allegation method Alcohol Water
95 0
70
700 9570 =25
To produce required % of alcohol, 70 parts of 95% alcohol and 25% of water mixed.
Quantity of 95% alcohol required = 600x70/95 = 442.10ml
Quantity of water required = 600 x 25/95= 157.90ml.
C) ISOTONICTY CALCULATIONS^{3}
Freezing point method or Cryoscopic method:
% w/v of adjusting substance needed = [0.52a]/b
a= Freezing point of the unadjusted solution
b=Freezing point of a 1% W/V solution of the adjusting sub.
Example 6:
Using croscopic method how will you prepare 1% solution of boric acid, isoosmotic with blood plasma. (Hints: freezing point of 1% w/v solution of boric acid is 0.288o C). The freezing point of 1% w/v solution of NaCl is  0.576 o C)
Solution: % w/v of NaCl required = [0.52 0.288]/0.576 = 0.402% w/v.
So, weigh 1 gm of Boric acid and transfer to a volumetric flask then weigh 0.4 g of NaCl and add it to the boric acid in flask. Then add small quantity of water, dissolve and make up the volume up to 100 ml. Now we will have an isoosmotic solution.
NaCl Equivalent method:
Quantity of NaCl required to adjust tonicity = 0.9  (n x E) n = number of grams of unadjusted substance E = NaCl equivalent (quantity of NaCl i.e. equivalent to 1 gm of drug)
White Vincet method:
V = w x E x 111.1
Where V = volume of isotonic solution in ml that can be prepared by dissolving drug in water w = wt. of drug
E = NaCl equivalent
Molecular Concentration^{4}:
% w/v of adjusting substance required = 0.03M/N M= Gram molecular weight
N=Number of ions
Example 7:
How to prepare an isoosmotic solution using dextrose.
Molecular wt of dextrose=180
Dextrose is non ionizing substance so no ions.
W= 0.03 x M = 0.03 x 180 = 5.4 g/100ml
D) PROOF SPIRIT CALCULATIONS^{2 }
Any alcoholic solution which has 57.1% v/v alcohol is proof spirit.
Steps which are involved in calculating.
Firstly let us known how 1.753 is obtained. 57.1 Volume of ethyl alcohol = 100 Volume of P.S Volume of ethyl alcohol= 100/57.1= 1.753 volume of PS
Step1: The % strength of alcohol is to be multiplied with 1.753 and substract100 from the value obtained after multiplying.
Step2. If value obtained is + then it is over proof
Step3. If value obtained is  then it is under proof.
Example 8:
What is the proof strength for 95% v/v alcohol?
% strength of alcohol x1.753 100 = 95 x 1.753100 = 166.53100=
+66.53 o So 66.53 o OP
E) DOSAGE REPLACEMENT FACTOR^{5 }
Number of parts by weight of drug that replaces one part by weight of base.
Displacement factor= 100 (EG)/Gx + 1
E = Wt of pure suppositories
G = Wt of suppositories containing x % of drug
For preparation of suppositories in uniform and accurate weight this factor is used
TEMPERATURE CONVERSION^{6}
9C = 5F  160C
C = Degree centigrade
F = Degree Fahrenheit
REFERENCES
1. Remington the science and practice of pharmacy, 21st edition, volume1 pg no 116 [accessed date: 12th march, 2010]
2. Remington the science and practice of pharmacy, 21st edition, volume1 pg no 122123 [accessed date: 12th march, 2010]
3. Physical pharmacy and pharmaceutical sciences by Martin, Fourth edition, Pages182185 [accessed date: 13th march, 2010]
4. Dispensing Pharmacy by RM Mehta, 3rd edition, Page. No. 94 [accessed date: 13th march, 2010]
5. Theory and Practice of Pharmacy, 20th edition, Page No. 585 [accessed date: 14th march, 2010]
6. http://en.wikipedia.org/wiki/Temperature[accessed date: 14th march, 2010]
7. Image source: http://kunaljanu.files.wordpress.com/2009/02/ist2_1457667confusion1.jpg
"This blog does not contain any plagiarized material"
Regards
V.B.S. Aishwarya
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IV. ACE inhibitors+Antipsychotics
Comments
Tejaswi Padma
Fri, 04/16/2010  14:12
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hi aishwarya
Regards,
Tejaswi Redla
STUDENT'S CORNER N WALL POSTING EVENTS INCHARGE
,
http://www.pharmainfo.net/tejaswiredla
V.B.S.Aishwarya
Sun, 04/18/2010  17:02
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Dear Teja, Very happy to see
Regards
V.B.S.Aishwarya
Sirisha Pingali
Fri, 04/16/2010  15:45
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hi aishwarya.. good blog.
Sirisha Pingali
http://www.pharmainfo.net/sirisha
Viswanadha Institute of Pharmaceutical Sciences.
www.vnips.edu.in
V.B.S.Aishwarya
Sun, 04/18/2010  14:29
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Dear Sirisha, thanks a lot
Regards
V.B.S.Aishwarya
Prof. J. Vijaya...
Fri, 04/16/2010  17:20
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Hope you don't mind my joke!
http://www.pharmainfo.net/vijayaratna
www.drvijayaratna.in
V.B.S.Aishwarya
Sun, 04/18/2010  16:55
Permalink
Dear mam
Respected Mam,
First of all thanks for spending your time in giving comment to my blog. Always we will be waiting for comments from experienced teachers like you. Such comments will encourage, boost up, give proper guidance and more than let us know our mistakes such that we rectify them in further steps.
Even I could remember your speech given in our college as Chief Guest on the occasion of Valedictory Function, National Pharmacy Week Celebrations 2008 which inspired us a lot and even today I have the hand out provided by you during the speech.
Coming to this blog, I thought of presenting the data right from basics to the end of significance. Of course all these are of basics, but I am interested to just warm up all the readers bringing them back to their early calculations which we have to follow even we go to our PG studies.
Mam, Shortly we will provide a blog justifying these day's blogs from our team . So please consider the case and spend time in giving your valuable comments to our blogs.
Thanking you once again for such funny joke. We enjoyed it!
Regards
V.B.S.Aishwarya
Prof. J. Vijaya...
Tue, 04/20/2010  04:50
Permalink
Calculations are needed.
http://www.pharmainfo.net/vijayaratna
www.drvijayaratna.in
Uma Pratyusha
Fri, 04/23/2010  16:44
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hiii
Regards
Uma Prathyusha
V.B.S.Aishwarya
Fri, 04/23/2010  17:17
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Dear .... There are two
Regards
V.B.S.Aishwarya
Jigard Patel
Fri, 04/16/2010  18:12
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nice brush up
V.B.S.Aishwarya
Sun, 04/18/2010  14:00
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hello Jigar, Thank you for
Regards
V.B.S.Aishwarya
Meghna Datta
Sat, 04/17/2010  07:18
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Topic chosen was really
V.B.S.Aishwarya
Sun, 04/18/2010  13:58
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dear , thanks a lot for your
Regards
V.B.S.Aishwarya
D Shravani
Sat, 04/17/2010  17:32
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Hi Aishwarya, Really i must
Regards,
Shravani
Team:"CHAR"MINAR
http://www.pharmainfo.net/dshravani
V.B.S.Aishwarya
Sun, 04/18/2010  13:57
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Hiii Shravani, Yeah you are
Regards
V.B.S.Aishwarya
TK Indira
Sun, 04/18/2010  12:36
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Dear Aishwarya,
T.K. Indira. http://www.pharmainfo.net/tkindira
 "Our greatest glory is not in never falling, but in rising every time we fall..." Team 'Char'minar.
V.B.S.Aishwarya
Sun, 04/18/2010  13:55
Permalink
thank you
Regards
V.B.S.Aishwarya
P.V.ABHIGNA
Mon, 04/19/2010  16:58
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application part
ABHIGNA.P.V.
V.B.S.Aishwarya
Fri, 04/23/2010  17:14
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Dear Abhigna, Yeah you are
Regards
V.B.S.Aishwarya
P.V.ABHIGNA
Fri, 04/23/2010  20:29
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thanks aishwarya
ABHIGNA.P.V.
Niklesh Rao V
Mon, 04/19/2010  19:47
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Dear Aishwarya, Useful info
Regards, Niklesh Rao V
V.B.S.Aishwarya
Fri, 04/23/2010  16:56
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Hello Niklesh,Very happy to
Regards
V.B.S.Aishwarya
kranthi kumar
Wed, 04/21/2010  13:55
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Good job.
Regards
Kranthi
http://www.pharmainfo.net/kranthikumar
V.B.S.Aishwarya
Fri, 04/23/2010  16:48
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Dear sir, Thank you for your
Regards
V.B.S.Aishwarya
Pratibha Singh
Wed, 11/10/2010  12:00
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thanks
pratibha singh
V.B.S.Aishwarya
Wed, 11/10/2010  15:25
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really very happy to know
Regards
V.B.S.Aishwarya
Hanumantha Rao
Wed, 04/20/2011  07:55
Permalink
Hi madam
Hanu
Avinash Robin
Fri, 09/02/2011  11:55
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Please clarify my doubt in proof spirit method.
robin