principles of pharmacy and pharmaceutical calculations

1. Lecture 4
Laith Al-Asadi

2. Calculation of doses
 The dose of a drug is the quantitative amount
administered or taken by a patient for the intended
medicinal effect.
 The dose may be expressed into many forms
- a single dose, the amount taken at one time
- a daily dose
- a total dose, the amount taken during the course of
therapy.
- A daily dose may be subdivided and taken in divided
doses, two or more times per day depending on the
characteristics of the drug and the illness.
- The schedule of dosing (e.g., four times per day for 10
days) is referred to as the dosage regimen.

3. Calculation of doses
 Quantitatively, drug doses vary greatly among drug
substances; some drugs have small doses, other drugs
have relatively large doses.
 The dose of a drug is based on its biochemical and
pharmacologic activity, its physical and chemical
properties, the dosage form used, the route of
administration, and various patient factors.
 The dose of a drug for a particular patient may be
determined in part on the basis of the patient’s age,
weight, body surface area, general physical health, liver
and kidney function (for drug metabolism and
elimination), and the severity of the illness being
treated.

4. Drug dose
 The usual adult dose of a drug is the amount that ordinarily
produces the medicinal effect intended in the adult
patient.
 The usual pediatric dose is similarly defined for the infant
or child patient.
 The usual dosage range for a drug indicates the
quantitative range or amounts of the drug that may be
prescribed within the guidelines of usual medical practice.
 Drug use and dose information is provided in the package
labeling and inserts that accompany manufacturers’
pharmaceutical products.

5. Drug dose
 The median effective dose of a drug is the amount that
produces the desired intensity of effect in 50% of the
individuals tested.
 The median toxic dose of a drug is the amount that
produces toxic effects in 50% of the individuals tested.
 Drugs intended to produce systemic effects must be
absorbed or placed directly into the circulation and
distributed in adequate concentrations to the body’s
cellular sites of action.

7. Drug dose
 minimum effective concentration (MEC): An average
blood serum concentration of a drug can be measured, and
the minimum concentration determined that can be
expected to produce the drug’s desired effects
 minimum toxic concentration (MTC) : The base
level of blood serum concentration that produces dose-
related toxic effects
 a larger-than-usual initial dose may be required to achieve
the desired blood drug level. This dose is referred to as the
priming or loading dose.
 maintenance doses: similar in amount to usual doses, are
then administered according to the dosage regimen to
sustain the desired drug blood levels or drug effects.

8. Drug dose
 Monotherapy: is the primary drug treatment.
 Adjunctive therapy: is additional to or supportive of a
different primary treatment.
 Prophylactic doses: administered to protect the
patient from contracting a specific disease.
 Therapeutic doses: administered to counter a disease
after exposure

9. Types of dosage forms
 Most pharmaceutical products are prepared on a large scale
within the pharmaceutical manufacturing industry for
distribution to institutional and community pharmacies.
These prefabricated products and dosage units are used
in filling prescriptions and medication orders in the
pharmacy.
 On a smaller scale, many community and hospital
pharmacists fill prescriptions and medication orders
requiring compounding—that is, the fabrication of a
pharmaceutical product from individual ingredients,
carefully weighed, measured, and mixed.
 Pharmaceutical products may be prepared to contain one
or more therapeutic agents. Products containing more than
one therapeutic agent are termed combination products.

10. Routes of Drug Administration
 Drugs are administered by a variety of dosage forms
and routes of administration

11. Dosage forms contents
 Dosage forms contain pharmaceutical
ingredients, which provide the physical
features, stability requirements, and aesthetic
characteristics desired for optimal therapeutic
effects.
 Included in the array of pharmaceutical
ingredients are solvents, vehicles, preservatives,
stabilizers, solubilizers, binders, fillers,
disintegrants, flavorants, colorants, and others.

12. Teaspoon and Tablespoon
 In calculating doses, pharmacists and physicians
accept a capacity of 5 mL for the teaspoonful and 15
mL for the tablespoonful. It should be noted that the
capacities of household teaspoons may vary from 3 to
7 mL and those of tablespoons may vary from 15 to 22
mL.

14. Teaspoon and Tablespoon
 According to the United States Pharmacopeia, ‘‘For
household purposes, an American Standard Teaspoon
has been established by the American National
Standards Institute as containing 4.93 ± 0.24 mL.
 In view of the almost universal practice of using
teaspoons ordinarily available in the household for the
administration of medicine, the teaspoon may be
regarded as representing 5 mL.
 Preparations intended for administration by teaspoon
should be formulated on the basis of dosage in 5-mL
units

15. Drops
 The Drop as a Unit of Measure : the drop (abbreviated gtt)
is used as a measure for small volumes of liquid
medications.
 A drop does not represent a definite quantity, because
drops of different liquids vary greatly.
 In an attempt to standardize the drop as a unit of volume,
the United States Pharmacopeia defines the official
medicine dropper as being constricted at the delivery end
to a round opening with an external diameter of about 3
mm.
 The dropper, when held vertically, delivers water in drops,
each of which weighs between 45 and 55 mg. Accordingly,
the official dropper is calibrated to deliver approximately
20 drops of water per milliliter

16. Drops
 It should be kept in mind, that few medicinal liquids
have the same surface and flow characteristics as
water, and therefore the size of drops varies materially
from one liquid to another.
 A dropper may be calibrated by counting the drops of a
liquid as they fall into a graduate until a measurable
volume is obtained. The number of drops per unit
volume is then established (e.g., 20 drops/mL).