The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [421]
Postprocedural considerations
Immediate care
Blood cultures should be dispatched to the laboratory for immediate process. If cultures cannot be processed immediately they should be incubated at 37°C in order for bacterial growth to begin and to prevent deterioration in pathogenic micro-organism yield (Higgins 2007).
Ongoing care
Decisions on commencing, changing or adding antimicrobial therapy may need to be considered depending upon the patient’s condition and history. Drug-resistant micro-organisms have highlighted the need for prudent control of antibiotic prescribing and usage. It is estimated that up to 40% of patients with moderate to severe infections are given unnecessary or inappropriate antibiotics to treat the in vitro susceptibility of the pathogen that is subsequently cultured (Johannes 2008). Decisions regarding appropriate choice of empirical therapy as well as the duration and dosage should be made in conjunction with advice from the microbiology team (Tacconelli 2009).
Antimicrobial drug assay
Definition
Therapeutic drug monitoring of blood serum ensures that there are sufficient levels of particular antimicrobial drugs to be therapeutically effective, whilst avoiding potentially toxic excess that may lead to adverse side-effects (Thomson 2004).
Related theory
The majority of drugs used in clinical practice have a wide therapeutic window; that is, the difference between the therapeutic and toxic level is substantial, and quantitative analysis of serum levels is unnecessary. However, there are certain drugs that require monitoring of serum concentration levels due to their narrow therapeutic range where toxicity is associated with persistently high concentrations, whilst therapeutic failure can result from low concentrations (Thomson 2004).
Examples of drugs that need monitoring in clinical practice include lithium, digoxin, theophylline, phenytoin, ciclosporin and certain antibiotics (Higgins 2007). This section will focus on aminoglycoside antibiotics, such as gentamicin and amikacin, and glycopeptide antibiotics such as vancomycin as these are the most commonly monitored antimicrobial assays.
These drugs are excreted almost entirely by glomerular filtration and are potentially nephrotoxic and ototoxic. When aminoglycosides or glycopeptides are used as single modes of treatment renal toxicity is estimated to be 5–10%, although this can increase to as much as 30% if both are used synergistically (Pannu and Nadim 2008).
Nephrotoxicity involves the proximal tubules that are capable of regeneration; therefore adverse effects may be reversible over time (Hadaway and Chamallas 2003).
Ototoxicity causes damage within the neuroepithelial cells of the inner ear, which can cause cochlear damage and/or vestibular impairment. These cells cannot be regenerated so the effects are irreversible (Hammett-Stabler and Johns 1998). Ototoxicity occurs in 0.5–3% of patients and is usually associated with very high serum concentrations of the drugs (Sha 2005).
Aminoglycoside antibiotics
Aminoglycosides such as gentamicin and amikacin are potent antibiotics, which are mainly used against aerobic, Gram-negative bacteria and are often used synergistically against certain Gram-positive organisms (Hammet-Stabler and Johns 1998). Single daily dosing of aminoglycosides is possible because of their rapid ‘concentration-dependent’ action, which increases both the rate and extent of bacterial cell death (Owens and Shorr 2009). The timing of serum sampling will be determined by the patient’s clinical manifestations, particularly renal function. For gentamicin the trough levels should be <1 mg/L (18 hours post dose) and <0.5 mg/L (24 hours post dose). For amikacin the trough level should be <5 mg/L.
Glycopeptide antibiotics
Vancomycin is the glycopeptide antibiotic most widely used for the treatment of serious infections caused by Gram-positive pathogens (Jones