Drug Knowledge

Nursing drug handbooks are the best references for the nurse who needs a variety of information specifically designed to help assess, manage, evaluate, and teach the patient/client. The following headings represent the kind of information found in a nursing handbook.

• Generic and trade names

• Classification and category

• Side and adverse effects

• Pregnancy category

• Dosage and route

• Action

• Indications

• Contraindications and precautions

• Interactions and incompatibilities

• Nursing implications

• Signs of effectiveness

• Patient/client teaching

Two long-standing Web sites that include drug information are the U.S. Food and Drug Administration (www.fda.gov) and Rx Med (www.rxmed.com). Nursing publishing companies include drug information on their Web sites. Lippincott Williams & Wilkins is www.nursingcenter.com.

Generic and Trade Names

The generic name, which is not capitalized, is the official name given to a drug. In the United States, a drug can only have one generic name. The letters USP (United States Pharmacopeia) following a generic name indicate that the drug meets government standards for purity and assay.

A trade name is the brand name under which a company manufactures a generic drug. While a drug has only one generic name, it may have several trade names. The trade name is capitalized and is sometimes followed by the symbol®, which stands for registered trademark, or ™, which stands for trademark.

EXAMPLE

Consumer groups have advocated that drugs be prescribed by generic name only so that the pharmacist may dispense the least expensive drug available in the market. The nurse should understand that generic drugs, because they are manufactured by different companies, are not exactly the same. Although the active ingredient in the drug meets standards of uniformity and purity, manufacturers use different fillers and dyes. These substances can cause adverse effects (e.g., severe nausea caused by the dye used in coloring).

Also, when a pharmacist dispenses the same drug with a different trade name, the patient/client may become confused and distressed about medication that appears unlike previous doses. While the active ingredient is the same, the medication size, shape, or color may vary according to trade name and manufacturer.

Drug Classification and Drug Category

Drug classification is a way to categorize drugs by the way they act against diseases or disorders, especially by their effect on a particular area of the body or on a particular condition. A diuretic, for instance, acts on the kidneys; an anticonvulsant prevents seizures. Because drug classifications are a quick reference to a drug’s therapeutic actions, uses, and adverse effects, they provide the administering nurse with a drug’s general indications, precautions, and nursing implications.

Category (as used in this text) refers to the way a drug works at the molecular, tissue, or body system level (e.g., beta-blocker, selective serotonin reuptake inhibitor (SSRI)).

EXAMPLE

Side Effects and Adverse Effects

Side effects are non therapeutic reactions to a drug. Because these reactions are transient, they may not require any nursing intervention. Side effects occur as a consequence of drug administration; often they are unrelated to the desired action of the drug.

Adverse effects are nontherapeutic effects that may be harmful to the patient/client and thus require lowering the dosage or discontinuing the drug. Because these effects can be life threatening, they may require medical intervention.

Idiosyncratic effects are effects from drugs that are not expected. Genetic predisposition is possibly a reason some individuals exhibit idiosyncratic effects. It may also be due to a hypersensitive immune reaction. Although each drug is tested extensively to determine side and adverse effects, occasionally an idiosyncratic effect will appear in an individual.

Drowsiness is a side effect that occurs with some antihistamines. A serious decrease in white blood cells (WBCs) is an adverse effect, resulting in lowered resistance to infection. The nurse must watch for these effects, know how to manage them, and, if necessary, teach the patient/client about them.

EXAMPLE

Pregnancy Category

The U.S. Food and Drug Administration (FDA) has established the following categories for pregnant women:

A: No risk to the fetus in any trimester

B: No adverse effect demonstrated in animals; no human studies available

C: Studies with animals have shown adverse reactions; no human studies are available; given only after risks to the fetus have been considered

D: Definite fetal risk exists; may be given despite risk to the fetus if needed for a life-threatening condition

X: Absolute fetal abnormality; not to be used anytime during pregnancy

A nurse administering a drug to any woman of childbearing age should know the pregnancy categories. If the drug has a category of D or X, the nurse should inform the woman of that category’s significance and determine whether there is any possibility of the woman being pregnant. If a woman has a confirmed pregnancy, the nurse should find out the pregnancy’s current gestational week. The nurse also should use this circumstance as an opportunity to educate the patient/client about the risks of any current medication (whether prescribed, over the counter (OTC), herbal, or nutritional supplement) and its known or potential effects on a fetus.

EXAMPLE

Dosage and Route

Information about the dosage and route of administration is crucial to protect against medication error. Most handbooks include, for each drug, appropriate dosage ranges for adults, the elderly, and children.

EXAMPLE

Action

Action explains how the drug works—that is, what medical experts know or believe about how the drug acts to produce a therapeutic effect. This knowledge helps the nurse understand whether a drug should be taken with food or between meals, with other drugs or alone, orally, topically, or parenterally (IM, subcutaneous, or IV).

The nurse who knows drug action can better assess, manage, and evaluate drug therapy. For example, if a particular drug is metabolized in the liver and kidney, then the nurse can apply this knowledge. Because patients/clients with liver or kidney disease may not be able to metabolize or excrete certain drugs, this particular drug could accumulate in the body and possibly cause adverse effects.

EXAMPLE

Indications

Indications give the reasons for using the drug. This information helps the nurse watch not only for expected effects and therapeutic response but also for any side effects and adverse effects. One of the most common questions patients/clients ask nurses is “Why am I getting this drug?” With a good understanding of indications, the nurse can answer the patient/client’s question, describing the drug’s expected effects.

Often a drug can be used for an indication “off label”—that is, for an indication other than the one(s) “labeled,” or approved, by the FDA. The drug may be widely known to be effective in “off-label” conditions because of its side effects (e.g., Benadryl—generic diphenhydramine—causes sleep); or research studies may have proven the drug effective for that particular indication, but the drug hasn’t yet been licensed as a treatment for it (e.g., Wellbutrin (bupropion)—helps a patient/client stop smoking).

The nurse should become familiar with the typical off-label uses of particular drugs. If a medication order requests a drug for an indication other than the one for which it is labeled and approved, or other than off-label uses with which the nurse is familiar, the nurse should question the medication order.

EXAMPLE

Contraindications and Precautions

The terms contraindications and precautions refer to conditions in which a drug should be either given with caution or not given at all. For instance, patients/clients who have exhibited a previous reaction to penicillin should be cautioned against taking that drug again; if a patient/client has poor kidney function, certain antibiotics must be administered with caution. Because the nurse has a responsibility to safeguard the patient/client and carry out effective nursing care, a knowledge of contraindications and precautions is important—especially in relation to patients/clients with glaucoma, renal disease, or liver disease and patients/clients who are very young or very old.

EXAMPLE

Interactions and Incompatibilities

When more than one drug is administered at a time, unexpected or nontherapeutic responses may occur. Some interactions are desirable: for example, Narcan (naloxone) is a narcotic antagonist that reverses the effects of a morphine overdose. Other interactions, however, are undesirable: aspirin, for instance, should avoid being taken with an oral anticoagulant because that combination may increase the possibility of an adverse effect (e.g., increased bleeding). The nurse must carefully consider some drug–herbal interactions as well.

Some drugs are incompatible and thus should not be mixed. Knowledge of incompatibilities is especially important when medications are combined for injection in IV administration. Chemical incompatibility usually produces a visible sign such as precipitation or color change. Physical incompatibility, however, may not give a visible sign, so the nurse should never combine drugs without checking a suitable reference, such as a drug compatibility chart. The nurse can also contact a pharmacist regarding incompatibilities.

A good rule of thumb: When in doubt, do not mix.

Interactions also may occur between drugs and certain foods. Here are some common examples. The calcium present in dairy products interferes with the absorption of tetracycline. Foods high in vitamin B₆ can decrease the effect of an antiparkinsonian drug. Foods high in tyramine, such as wine and cheese, can precipitate a hypertensive crisis in patients/clients taking MAO inhibitors. Grapefruit juice interferes with the absorption of multiple drugs.

Additionally, cigarette smoke—which can increase the liver’s metabolism of drugs—may decrease drug effectiveness. People exposed even to secondhand cigarette smoke may require higher doses of medication.

EXAMPLE

Nursing Implications

To administer a drug safely and to assess, manage, and teach the patient/client, the nurse needs a knowledge of implications: whether the drug should be taken with or without food, what specific vital signs to monitor, and what lab values may be affected by the drug or may need to be ordered to check the drug’s effectiveness or toxicity.

EXAMPLE

Signs of Effectiveness

Few drug references actually list this heading, yet the nurse is expected to evaluate the drug regimen and to record and report observations. Knowledge of the drug’s class, its action, and its use helps the nurse understand the expected therapeutic outcomes.

Ampicillin sodium, for instance, is a broad-spectrum antibiotic that is used for urinary, respiratory, and other infections. Signs of effectiveness might include these: normal temperature; the laboratory report of the WBC count, indicating a normal result; clear urine, no pain on urination, and no WBCs in urine; decreased pus in an infected wound; wound healing; a patient/client showing alertness, interest in surroundings, and improved appetite.

EXAMPLE

Teaching the Patient/Client

The patient/client has a right to know the drug’s name and dose, why the drug is ordered, and what effects to expect or watch for. A patient/client who will be taking a drug at home also needs specific information. Making sure that patients/clients are knowledgeable about their drugs is a professional responsibility shared by three people: the physician or healthcare provider, the nurse, and the pharmacist.

Pharmacokinetics

When a drug is taken orally, the villi of the small intestine absorb it, and the bloodstream distributes it to the cells. The body metabolizes the drug to a greater or lesser extent and then excretes it. When a drug is given parenterally, it bypasses the gastrointestinal system, entering the circulation more quickly—or, in the case of the IV route, immediately. The general term pharmacokinetics includes these drug activities: absorption, distribution, metabolism or biotransformation, and excretion.

Absorption

Effective absorption of an oral drug depends on several conditions: the degree of stomach acidity, the time required for the stomach to empty, whether food is present, the amount of contact with villi in the small intestine, and the flow of blood to the villi.

Other circumstances, too, may affect a drug’s absorption. Enteric-coated (EC) tablets, for instance, are not meant to dissolve in the acidic stomach; they ordinarily pass through the stomach to the duodenum. When a patient/client receives an antacid along with an EC tablet, the pH of the stomach rises, perhaps causing the tablet to dissolve prematurely—which either can make the drug less potent or can irritate the gastric lining. Timed-release EC capsules that dissolve prematurely can deliver a huge dose of the drug, producing adverse effects.

Here’s another example: laxatives increase gastrointestinal movement and decrease the time a drug is in contact with the villi of the small intestine, where most absorption occurs. Food in the stomach, however, can impair absorption. In particular, foods that contain calcium, such as milk and cheese, form a complex with some drugs and inhibit absorption. Penicillin is a good example of a drug that should be taken on an empty stomach.

Distribution

Distribution describes the drug’s movement through body fluids—chiefly the bloodstream—to the cells. Drugs do not travel freely in the blood; instead, most travel attached to plasma proteins, especially albumin. If a drug is not attached to a plasma protein, it can attach to other cells and affect them in various ways.

When the bloodstream contains more than one drug, the drugs may compete for binding with protein sites. One drug may displace another, leaving the displaced drug free to interact with the cells, and its effect on the cells will be more pronounced. Aspirin is a common drug that displaces others; it should not be given with oral anticoagulants, which are 99% bound to albumin. Because aspirin displaces the anticoagulant, it leaves the anticoagulant free to act at the cellular level, sometimes causing the toxic effect of bleeding.

Metabolism or Biotransformation

Metabolism or biotransformation refers to the chemical change of a drug into a form that can be excreted. Most metabolism or biotransformation occurs in the liver. First-pass effect occurs with medications taken by mouth (enteral route). After ingestion, the drug is absorbed by the gastrointestinal system and then first passes through the liver, where some of the drug may be metabolized. Thus, the drug may not be as effective as it continues through the pharmacokinetic phases. The parenteral route (subcutaneous, IM, IV) bypasses the first-pass effect, so more of the drug is available to the body tissues and cells. Here, too, one drug can interfere with the effects of another. Barbiturates increase the liver’s enzyme activity. Since this activity makes the body metabolize the drugs more rapidly, it reduces their effect. Conversely, Tylenol (acetaminophen) blocks the breakdown of penicillin in the liver, thereby increasing the effect of the drug.

Excretion

The major organ of excretion—the process by which the body removes a drug—is the kidney. Drug interactions may also occur at this point. The drug probenecid, for example, inhibits the excretion of penicillin and increases its length of action. Lasix (furosemide), a diuretic, blocks the excretion of aspirin and can cause aspirin to produce adverse effects.

Drug interactions at the excretion stage are not necessarily harmful. For instance, narcotic antagonists are used intentionally to reverse the adverse effects of general anesthetics. This reversal action is termed antagonism. The term synergism, on the other hand, describes what happens when a second drug increases the intensity or prolongs the effect of a first drug. A narcotic and a minor tranquilizer together, for example, produce more pain relief than the narcotic alone. The nurse administering medications needs to be aware of possible interactions and must carefully evaluate the patient/client’s response.

To minimize adverse interactions, the nurse should closely review the patient/client’s drug profile, administer as low a dose as possible, know the actions and the side and adverse effects of the drugs administered, and monitor the patient/client. Continued monitoring is important, because some drug interactions may take several weeks to develop.

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