dose calculation for drugs for veterinary

1. D C l l i i
D C l l i i
Dose Calculations in
Dose Calculations in
Veterinary Pharmacology
Veterinary Pharmacology
Veterinary Pharmacology
Veterinary Pharmacology

2. Drug Dose
Drug Dose
• The dose of a drug is the amount of drug administered at one
h h d d ff ( b l bl
time to achieve the desired effect (can be in ml, mg, g, tablets,
etc.)
• Loading dose: initial dose of drug given to get the drug
concentration up to the therapeutic range in a very short
period of time
• Maintenance dose: dose of drug that maintains or keeps the
drug in the therapeutic range
• Total daily dose: total amount of drug delivered in 24 hours

3. Drug Dosage
Drug Dosage
• The dosage of a drug is the amount of drug per
i l ’ b d i h
animals’ body weight or measure
– Examples include mg/kg or g/lb
• Dosage interval: how frequently the dosage is given
– Examples include BID or TID
• Dosage regimen: dosage interval and the dosage
together
Examples include
Examples include
– 30 mg/kg TID,
– 5 g/lb BID

4. Dose Calculations
Dose Calculations
• Must know correct amount of drug to administer to a
Must know correct amount of drug to administer to a
patient
• Must be in same system of measurement
y
• NB:
– drugs can be measured in ug, mg, g, gr, ml, l, units
g g, g, g, g , , ,
– drugs can be dispensed or administered in tablets, ml, l,
capsules

5. Dose Calculations
Dose Calculations
Metrology:
¾ is the study of weights and measures as applied to
¾ is the study of weights and measures as applied to
the preparation of drugs.
‰Two System
y
¾The metric system: kg, g, mg, ug; l, ml, ul
¾The apothecary system: ounce, drums, grains, minims
‰ The metric system preferred to The apothecary system
¾1kg= 1000g
¾1g= 1000mg
¾1mg 100ug ¾1l=1000ml
¾1mg=100ug
¾1ug=1000ng
¾1l=1000ml

6. Several conversion equivalents
Several conversion equivalents
¾1kg= 2 2 pounds
¾1kg= 2.2 pounds
¾1g= 15 grains
¾ l i i
¾1ml= 15 minims
¾20 drop= 1ml
¾1 tea spoonful= 5ml
¾1 coffee cup= 60ml
¾1 coffee cup 60ml

7. Solutions
Solutions
• Solutions are a homogeneous mixture of two or
more substances in which the molecules or atoms of
the substances are completely dispersed.
– The dissolving substance of a solution is referred to as the
solvent (liquid)
– The dissolved substance of a solution is referred to as the
solute (solid or particles)
solute (solid or particles)
– Substances that form solutions are called miscible
– Substances that do not form solutions are called
immiscible

8. Working with Solutions
Working with Solutions
• The amount of solute dissolved in solvent is known as the
concentration
• Concentrations may be expressed as
Concentrations may be expressed as
– parts (per some amount),
– weight per volume,
volume per volume and
– volume per volume, and
– weight per weight
• Usually reported out as percents or percent solution
• NB: a percent is the parts per the total times 100
NB: a percent is the parts per the total times 100

9. Rules of Thumb When Working with
l i
Solutions
• Parts:
– parts per million(PPM) means 1 mg of solute in a kg (or l)
of solvent (1:1000)
– 1ppm=1mg/kg or 1mg/l
d l d
• Liquid in liquid:
– the percent concentration is the volume per 100 volumes
of the total mixture (1 ml/100 ml)
S lid i lid
• Solids in solids:
– the percent concentration is the weight per 100 weights of
total mixture (60 mg/100 mg)
S lid i li id
• Solids in liquid:
– the percent concentration is the weight in grams per 100
volume parts in milliliters (dextrose 5% = 5 g/100ml)

10. Percent Concentration Calculations
Percent Concentration Calculations
• Pure drugs are substances that are 100% pure
• Stock solution is a relatively concentrated solution from which
more dilute solutions are made
• Ratio proportion method:
• Ratio‐proportion method:
– one method of determining the amount of pure drug needed to make
a solution
– Amount of drug/amount of finished solution = % of finished
– Amount of drug/amount of finished solution = % of finished
solution/100% (based on a pure drug)
• Remember that the amount of drug used to prepare a
solution is added to the total volume of the solvent
solution is added to the total volume of the solvent

11. Another Way to Determine Volume
Another Way to Determine Volume
Volume concentration method/dilution:
Volume concentration method/dilution:
• Vs = volume of the beginning or stock solution
• C = concentration of the beginning or stock solution
Cs = concentration of the beginning or stock solution
• Vd = volume of the final solution
• C = concentration of the final solution
• Cd = concentration of the final solution
Vs x Cs = Vd x Cd
Vs x Cs Vd x Cd

12. Drug Concentrations in Percents
Drug Concentrations in Percents
• Drug concentrations are sometimes listed in percents
g p
• Parts per total = parts (in g) per 100
• The front of the vial specifies the concentration
p
– (for example, 2% lidocaine=2g/100ml)
• Use X g/100 ml to determine dose
g/

13. Exercises
Exercises
1 The recommended dosage to be administered
1. The recommended dosage to be administered
to sheep is 10mg/kg of BW and the solution is
labelled 10% How many ml of the drug should
labelled 10%. How many ml of the drug should
be adm if the BW of the sheep is 60kg.
Ans. 6ml
10mg=1kg
10%=10g/100ml=
¾10,000mg=100ml
Xmg=60kg
ans= 600mg
¾10,000mg 100ml
600mg= xml
Ans = 6ml
Ans 6ml

14. 2. The general dose of atropine is 0.05mg/kg of BW
and the solution is labelled 0.1%. How many ml of
the drug should be adm if the wt of the animal is
50kg
50kg.
Ans: 2.5ml
0.05g=1kg
0.1g=100ml where 0.1%=0.1g/100ml
2.5mg=x
X= 50kg
¾2.5mg
g
Ans
Ans X=2.5ml
X=2.5ml

15. Exercise problems (assignment)
Exercise problems (assignment)
1. A solution of sodium hypochlorite contains 5% of activated
yp
chlorine. If we want to prepare a sol. of 1:10,000 how many
ml H2O we need to add to obtain this conc.?
2. The injectable B‐complex contains 1% of thiamine, 0.1% of
riboflavine, 17.6% Ca pantotenate. What is the conc.of each
, p
vitamin in mg/ml?
3. If we want to administer 1.5ml of Na phenobarbitone in the
dose of 15mg/kg BW to the rabbit that weighs 5kg. In what
conc you may dissolve the drug?
conc you may dissolve the drug?