The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [422]
The use and monitoring of vancomycin have increased due to the emergence of meticillin-resistant Staphylococcus aureus (MRSA) but the emergence of vancomycin-resistant MRSA has further complicated its clinical use (Jones 2006).
Determination of serum blood levels of vancomycin depends on the frequency of administration. If given intermittently (usually twice-daily doses), trough levels should be taken at set times, immediately before the administration of the next bolus dose (Jones 2006). The use of the continuous infusion of vancomycin also occurs in clinical practice and it is suggested that this is a less toxic mode of administration (Hadaway and Chamallas 2003). If given intermittently, the trough level should be between 5 and 15 mg/L, whilst continuous infusions aim to maintain serum concentrations at between 15 and 25 mg/L.
Evidence-based approaches
Rationale
The main criterion for monitoring serum drug concentration is to ensure that there is enough drug given for efficacy whilst avoiding concentrations associated with a significant risk of toxicity (Catchpole and Hastings 1995).
Indications
Accurate and timely monitoring of microbial assay levels is indicated in patients receiving intravenous aminoglycoside or glycopeptide antibiotics:
to ensure optimum therapeutic range
to minimize high serum levels which may cause adverse side-effects of the drugs (particular caution should be exercised in patients who have renal impairment).
Contraindications
The samples should not be taken if there has been insufficient time lapse between dose administration and sample collection.
Principles of care
The initial dosage regimen should be appropriate for the clinical condition being treated, the patient’s clinical characteristics (age, weight, renal function and so on) and concomitant drug therapy (Thomson 2004). The timing of the sample and interpretation of the results of analysis need consideration in relation to the dose given and the timing of previous dose administration.
Serum samples can be taken at two different times: the peak or the trough. A peak sample is collected at the drug’s highest therapeutic concentration within the dosing period. The postdose peak level timing will vary depending on the drug; ordinarily this is 1 hour after the completion of an infusion, although in the case of vancomycin, which has a slow distribution phase, it is recommended that the sample is taken at least 1–2 hours after the infusion ends (Tobin et al. 2002).
Trough levels are measured just prior to the administration of the next dose, that is, at the lowest concentration in the dosing period (Tobin et al. 2002). Therefore, trough levels are more commonly used because the level is more representative of how the different variables such as drug absorption and renal function affect the concentration within a predetermined timeframe. The results can then be used to adjust dosages to achieve the optimal response with the minimal toxicity.
Abnormally elevated serum levels may be obtained if the samples are taken from a CVAD through which the drug has been administered. This is more likely when residual drugs remain in the catheter if it has not been flushed correctly following administration of the drug or the first 5–10 mL of blood has not been discarded (Himberger and Himberger 2001). If a multilumen CVAD is in situ, a different lumen from the one used to administer the drug should be used to obtain the blood specimen.
Procedure guideline 11.3 Blood sampling: antimicrobial drug assay
Essential equipment
Appropriate blood sample bottles
Vacuum-assisted collection system
Gloves
Apron
Appropriate documentation/forms
Preprocedure
Action Rationale
1 Discuss indication for procedure with patient. To ensure the patient understands the procedure and gives valid