Besides contraindications for a drug, the drug’s profile in the drug manual also provides the nurse with the pharmacologic response of the drug (see Chapter 2)—
how the drug works in the body. Knowing this, the nurse can assess the patient to determine if the patient’s body will be able to metabolize and eliminate the medication.
Here are the areas that the nurse needs to consider:
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AbsorptionThe patient must be able to absorb the medication. For example, PO medication is absorbed in the GI tract (stomach and small intestine). A patient with GI disturbances such as vomiting or diarrhea will not be able to absorb the medication.
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DistributionOnce absorbed, the medication must be distributed throughout the body.
In order for this to occur, some drugs must bind to protein, which carries drug particles through the veins and arteries. If the patient has low protein levels, some drug particles are unable to bind to the protein and the unbound drug par-ticles are free drug which can possibly result in a toxic effect.
For example, Dilantin binds to albumin. If the patient has a low albumin level, there will be less Dilantin bound to protein. The patient will be receiving the proper therapeutic dose but because much of it is not bound to protein, the serum levels of free drug will be too high—causing toxicity.
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MetabolismThe liver breaks down drugs so they can be excreted from the body. If the patient’s liver isn’t functioning properly, then the drug particles are not metabo-lized and cannot be excreted from the body. This results in a buildup of the drug and can possibly cause toxicity in the patient. It is important to remember that inadequate liver function is not always caused by liver disease. Age influences
liver function. For example, newborns have an immature liver while the elderly have decreased liver function.
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ExcretionThe kidney is the main organ that excretes medication although some med-ication is excreted in bile, feces, respiration, saliva, and sweat. The patient is unable to excrete drugs if these routes are not functioning properly. The nurse should be aware of the route in which the drug is excreted from the body and then determine if that route is fully functional before administering the medication to the patient.
In addition to the pharmacologic response of the drug, the nurse must also assess other aspects of the patient and the medication. These are:
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AgeThe very young and the elderly are more sensitive to drugs than the average adult because there is a decrease in gastric secretion resulting in poor absorption through the GI tract. The elderly are particularly sensitive to barbiturates and central nervous system depressants. Therefore, it is crit-ical that the nurse assess the patient’s age before administering medication and carefully monitor very young and elderly patients afterwards for adverse side effects.°
Body WeightThe prescriber might order medication given at the recommended dose.
However, the recommended dose is typically for a patient whose body weight is within the average range (70 kg for an adult). The medication might have a different effect if the patient’s body weight falls outside this range. For example, the recommended dose might be too strong for a very thin patient resulting in a toxic effect. Likewise, the recommended dose might be too low for an obese patient and never reach the therapeutic level. This is particularly important to assess when administering medications such as antineoplastics (anti-cancer drugs) where a low therapeutic level can have a non-therapeutic effect for the patient—resulting in an undesirable outcome. Using body weight to determine drug dose will avoid this problem.
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PharmacogeneticGenetic factors might have a serious influence on the response to a drug. Depending on the medication, a patient might have a genetically based adverse reaction to the drug. Therefore, in assessing the patient, the nurse must determine if parents, siblings, or other close relatives have had an adverse reaction to the medication.
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TimeMedication must be given to the patient at the most opportune time dur-ing the day to assure that the therapeutic effect is attained. Some drugs are effective only if taken with meals while other medication cannot be taken with meals. Likewise, certain drugs are more effective if taken at bedtime.°
Food-drug interactionCertain types of foods can adversely effect the drug’s therapeutic effect by increasing absorption, delaying absorption, and even preventing absorption of the medication. Furthermore, food may cause the patient to experience an adverse reaction as in the case with phenelzine sulfate (Nardil), which is an MAO monoamineoxidase inhibitor anti-depressant.
Nardil cannot be given with foods that use bacteria or molds in their prepa-ration or for preservation of those that contain tyramine, such as cheese, sour cream, beer, wine, figs, raisins, bananas, avocados, etc. The nurse must assess if the drug has a contraindication with food and educate the patient about this food-drug interaction.
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Drug-drug interactionThe nurse should be aware that the combination of drugs administered to the patient may have a negative effect. Some drugs when administered together might increase or decrease the therapeutic effectiveness of either or both medications by competing for the same receptor sites in the body.
Furthermore, a combination of some medications produce toxicity or a fatal condition such as anaphylaxis. Sometimes there is more than one provider prescribing medications. The prescribers should be notified before medica-tions are administered if there is a possibility of a drug-drug interaction.
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Drug History, Tolerance, and the Cumulative EffectContinued use of a medication might lessen the therapeutic effect of the drug because the patient’s body becomes tolerant of the medication. The nurse must assess the patient’s drug history and monitor the patient for signs and symptoms that the drug is having a therapeutic effect. One such example would be the absence of seizures if the patient is taking phenytoin (Dilantin), an antiseizure medication. Another concern is the drug buildup in the patient’s body. The patient may be unable to metabolize and excrete the medication as fast as new doses are administered. The result is a cumulative effect that can result in toxicity. The patient should be monitored for signs of drug build-up.
For example, ataxia (muscular incoordination), nystagmus (rhythmic oscilla-tion of eyes), and double vision are signs of toxic levels of Dilantin.