3.3 Antimicrobial Administration Considerations

The administration of antimicrobial drug therapy involves special considerations to ensure that the therapeutic drug effect is achieved while also maintaining patient safety and minimizing complications.

Let’s consider variables that impact antimicrobial administration, such as half-life, life span considerations, liver and kidney function, dose dependency/time dependency, route, and drug interactions.

Half-Life

Many antimicrobial medications are administered to ensure a certain therapeutic level of medication remains in the bloodstream, which may require interval or repeated dosing throughout the day. Recall from Chapter 1 that half-life is the rate at which 50% of a drug is eliminated from the plasma. Half-life can vary significantly among antimicrobial drugs. Some antibiotics, such as penicillin, have a short half-life of only a few hours and must be administered multiple times a day, whereas other antibiotics, such as levofloxacin, have long half-lives and can be administered as a single dose every 24 hours.

Although a longer half-life can be considered an advantage for a prescribed antibiotic when it comes to convenient dosing intervals, medications with longer half-lives that cause side effects will also exert these side effects over a longer period of time. 

Life Span Considerations

Many antibiotic dosages are calculated based on the client’s age and weight. Age and weight are especially important when calculating pediatric dosages, resulting in common medication errors when these calculations are inaccurate. The size and development of the internal organs in infants and children also impact how the body absorbs, distributes, metabolizes, and excretes medications.

In older adults, metabolism of antibiotics by the liver may significantly decline in the older adult. As a result, dosages should be adjusted according to the client’s liver function and their anticipated metabolic rate. First-pass metabolism also decreases with aging, so older adults may have higher “free” circulating drug concentrations and thus be at higher risk for side effects and toxicities.

Liver and Kidney Function

Many antimicrobial medications require tailored dosing based on the client’s liver and kidney function. For more information about the effects of liver and kidney function on metabolizing and excreting medications, review Chapter 1.

Peak and trough blood levels are monitored for some antibiotics to determine how a client’s body is responding to an antimicrobial. Dosing is then tailored to the individual based on peak and trough levels. This is especially important for older adults or those with known liver and/or kidney impairment. Individuals with diminished liver and kidney function are prone to developing toxic levels of medications because of their reduced ability to metabolize or clear medications from the body. For more information about peak and trough levels, review the “Efficacy, Dose-Response, Onset, Peak, and Duration” section in Chapter 1.^[1]

Dose Dependency/Time Dependency

The goal of antimicrobial therapy is to select an optimal dosage that will result in clinical cure, while reducing potential side effects and adverse effects. Many medications are dose dependent, meaning there is a more significant killing of the bacteria with increasing levels of the antibiotic. For example, fluroquinolones are dose-dependent medications with higher dosages of antibiotic killing more bacteria.

Other medications are time dependent. Time-dependent medications have optimal bacterial-killing effect at lower doses over a longer period of time. Time-dependent antimicrobials exert their effect by binding to the microorganism for an extensive length of time. Penicillin is an example of a time-dependent medication where duration of the bacteria’s exposure to the medication has the greatest effect.^[2]

Route

When administering antimicrobials to clients, nurses must consider the route of drug administration. Many of us may have been prescribed oral antibiotics and have simply filled our prescription and completed the drug therapy within the comfort of our own homes. However, there are many types of infections that do not respond well to oral antimicrobial therapy and require intravenous or intramuscular injections. Clients requiring intravenous or intramuscular injections may require additional considerations regarding hospitalization, home health nursing, or travel to the hospital/clinic for their therapy. For more information about considerations regarding routes of administration, refer to Chapter 1 on absorption.

Drug Interactions

Interactions between drugs may be beneficial or harmful. For example, when treating specific infections, two antibacterial drugs may be administered together to create a greater effect than the efficacy of either medication alone, referred to as synergistic interaction . An example of a synergistic drug combinations is trimethoprim and sulfamethoxazole (Bactrim). Individually, these two drugs provide only bacteriostatic inhibition of bacterial growth, but combined, the drugs are bactericidal.^[3]

In contrast to synergistic drug interactions providing a benefit to the client, antagonistic interactions produce harmful effects. Antagonistic interactions may occur between two antimicrobials or between an antimicrobial and medication used to treat other conditions. For example, antacids taken with antibiotics can delay and reduce the absorption of the antibiotic. Potential harmful effects vary depending on the drugs involved, but antagonistic interactions cause diminished drug activity, decreased therapeutic levels due to elevated metabolism and elimination, or increased potential for toxicity due to decreased metabolism and elimination.