# 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

70-0 95-70 =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 = [0.52-a]/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, iso-osmotic 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 iso-osmotic 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 iso-osmotic 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 1.753-100 = 166.53-100=

+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 (E-G)/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 122-123 [accessed date: 12th march, 2010]

3. Physical pharmacy and pharmaceutical sciences by Martin, Fourth edition, Pages-182-185 [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_1457667-confusion-1.jpg

"This blog does not contain any plagiarized material"

Regards

V.B.S. Aishwarya

BLOGGING BEE's

## Comments

Tejaswi Padma

Fri, 04/16/2010 - 14:12

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## hi aishwarya

Regards,

Tejaswi RedlaSTUDENT'S CORNER N WALL POSTING EVENTS IN-CHARGE

,

http://www.pharmainfo.net/tejaswi-redla

V.B.S.Aishwarya

Sun, 04/18/2010 - 17:02

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## Dear Teja, Very happy to see

Regards

V.B.S.AishwaryaSirisha 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.AishwaryaProf. 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

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## 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 collegeas Chief Guest on the occasion of Valedictory Function,National Pharmacy Week Celebrations 2008which inspired us a lot and even today I have thehand outprovided 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.AishwaryaProf. J. Vijaya...

Tue, 04/20/2010 - 04:50

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## 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 PratyushaEvent co-ordinator.

V.B.S.Aishwarya

Fri, 04/23/2010 - 17:17

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## Dear .... There are two

Regards

V.B.S.Aishwaryajigardpatel

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.AishwaryaMeghna 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.AishwaryaD 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.AishwaryaIndu Roy

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

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## thank you

Regards

V.B.S.AishwaryaP.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.AishwaryaP.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.Aishwaryakranthi 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.AishwaryaPratibha 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.AishwaryaHanumantha Rao

Wed, 04/20/2011 - 07:55

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## Hi madam

Hanu

Avinash Robin

Fri, 09/02/2011 - 11:55

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## Please clarify my doubt in proof spirit method.

robin