6-1 PHARMACOLOGY

LEARNING OBJECTIVE: Recall the subsciences of pharmacology, drug standards, medication administration methods, and factors that affect dosage.

Pharmacology is the science that deals with the origin, nature, chemistry, effects, and uses of drugs. The subsciences of pharmacology and their specific areas of concentration are as follows:

The science of treating disease by any method that will relieve pain, cure disease, or prolong life is called therapeutics. Therapeutics does not deal solely with giving or taking medicine. This field also includes many other methods, such as radiological treatment, diathermy, and hydrotherapy.

DRUG STANDARDS

The texts dealing with pharmaceutical preparations include the United States Pharmacopeia and National Formulary (USP-NF), which provides standards for drugs of therapeutic usefulness and pharmaceutical necessity. Inclusion of drugs into this compendium is based on therapeutic effectiveness and popularity. The USP-NF provides tests for drug identity, quality, strength, and purity.

Drug Facts and Comparisons and the Physicians Desk Reference (PDR) have multiple indexes of commercially available drugs. Both are used as advertising outlets for various drug manufacturers. A comprehensive description of each pharmaceutical preparation (including composition, action and use, administration and dosage, precautions and side effects, dosage forms available, and the common (generic) drug names) is provided in both publications. These two publications are used as references for in-depth information on pharmaceutical products by healthcare providers and pharmacy personnel.

Remington: The Science and Practice of Pharmacy is probably the most widely used text/reference in American pharmacies. It contains all areas relevant to the art/science of pharmacy. The Pharmacological Basis of Therapeutics (Goodman and Gilman) is a textbook of pharmacology, toxicology, and therapeutics. This work is known as the 澱lue bible of pharmacology.

MEDICATION ADMINISTRATION

The quantity and frequency of a drug痴 administration to a patient depend on several factors, as does the method of that medication痴 administraュtion. This section will cover some of the factors affecting dosage calculations and methods of administration.

Dosage

The amount of medication to be administered is referred to as the dose. The study of dosage and the criteria that influence it is called posology. The doses given in the United States Pharmacopeia and National Formulary (USP-NF) are average therapeutic doses and are known as 砥sual adult doses. The following terms are used in connection with doses.

THERAPEUTIC DOSE.裕herapeutic dose is also referred to as the normal adult dose, the usual dose or average dose. It is the amount needed to produce the desired therapeutic effect. This therapeutic dose is calculated on an average adult of 24 years who weighs approximately 150 pounds.

DOSAGE RANGE.優osage range is a term that applies to the range between the minimum and maximum amounts of a given drug required to produce the desired effect. Many drugs (such as penicillin) require large initial doses that are later reduced to smaller amounts. Closely associated with 電osage range are the terms minimum dose (the least amount of drug required to produce a therapeutic effect), maximum dose (the largest amount of drug that can be given without reaching the toxic effect), and toxic dose (the least amount of drug that will produce symptoms of poisoning).

MINIMUM LETHAL DOSE .柚inimum lethal dose is the least amount of drug that can produce death.

Factors Affecting Dosage

The two primary factors that determine or influence the dosage of a medication are the age and weight of the patient.

AGE.輸ge is the most common factor that influences the amount of drug to be given. An infant requires a lower dose than an adult. Elderly patients may require a higher or lower dose than the average dose, depending upon the action of the drug and the condition of the patient.

The rule governing calculation of pediatric (child痴) doses, Young痴 Rule, is expressed as follows:

The age in years of the child is the numerator, and the age plus 12 is the denominator. This fraction is multiplied by the normal adult dose.

WEIGHT.悠n the calculation of dosages, weight has a more direct bearing on the dose than any other factor, especially in the calculation of pediatric doses. The rule governing calculation of pediatric doses based on weight is Clark痴 Rule, expressed as follows:

The child痴 weight in pounds is the numerator, and the average adult weight (150 pounds) is the denominator. This fraction is multiplied by the adult dose.

Example:

The adult dose of aspirin is 650 mg.
What is the dose for a child weighing 60 pounds?

OTHER FACTORS THAT INFLUENCE DOSAGE.涌ther factors that influence dosage include the following:

Methods of Administering Drugs

Drugs may be introduced into the body in several ways, each method serving a specific purpose.

ORAL.涌ral administration of medications is the most common method. Among the advantages of administering medication orally (as opposed to other methods) are the following:

Oral medication administration may be disadvantageous for the following reasons:

Other methods of administration closely associated with oral administration are sublingual and buccal. Sublingual drugs are administered by placing the medication under the tongue. The medication is then rapidly absorbed directly into the blood stream. An example of a sublingual drug is nitroglycerin sublingual tablets (for relief of angina pectoris).

Buccal drugs are administered by placing the medication between the cheek and gum. Buccal drugs, like sublingual drugs, are quickly absorbed directly into the blood stream. An example of a drug that may be given buccally is the anesthetic benzocaine.

PARENTERAL .猶arenteral medications are introduced by injection. All drugs used by this route must be pure, sterile, pyrogen-free (pyrogens are products of the growth of microorganisms), and in a liquid state. There are several methods of parenteral administration, including subcutaneous, intradermal, intramuscular, intravenous, and intrathecal or intraspinal.

Subcutaneous.裕he drug is injected just below the skin痴 cutaneous layers. Example: Insulin.

Intradermal.裕he drug is injected within the dermis layer of the skin. Example: Purified protein derivative (PPD).

Intramuscular.裕he drug is injected into the muscle. Example: Procaine penicillin G.

Intravenous.裕he drug is introduced directly into the vein. Example: Intravenous fluids.

Intrathecal or Intraspinal.裕he drug is introduced into the subarachnoid space of the spinal column. Example: Procaine hydrochloride.

INHALATION.悠nhalation is a means of introducing medications through the respiratory system in the form of a gas, vapor, or powder. Inhalation is divided into three major types: vaporization, gas inhalation, and nebulization.

Vaporization.遊aporization is the process by which a drug is changed from a liquid or solid to a gas or vapor by the use of heat (such as in steam inhalation).

Gas Inhalation.宥as inhalation is almost entirely restricted to anesthesia.

Nebulization.湧ebulization is the process by which a drug is converted into a fine spray by the use of compressed gas.

TOPICAL.裕opical drugs are applied to a surface area of the body. Topically applied drugs serve two purposes:

Examples of topical preparations are ointments, creams, lotions, and shampoos.

RECTAL.優rugs are administered rectally by inserting them into the rectum. The rectal method is preferred to the oral route when there is danger of vomiting or when the patient is unconscious, uncooperative, or mentally incapable. Examples of rectal preparations are suppositories and enemas.

VAGINAL.優rugs are inserted into the vagina to produce a local effect. Examples of vaginal preparations are suppositories, creams, and douches.