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  • Impact of a Pharmacist-Initiated Therapeutic Drug Monitoring Consult Service: DISCUSSION part 2

After discontinuation of the TDM service, the clinicians appeared to assume that determination of serum gentamicin concentration was appropriately timed with respect to dose administration. Thus, gentamicin dose adjustments were made in 12 instances in this patient group when an appreciation of the impact of the timing of the samples relative to the time of dose administration would have suggested no dose adjustment.The appropriateness of timing of dose adjustments differed between the 2 groups. Before discontinuation of the TDM service, all dose adjustments were made before the next scheduled dose. However, after discontinuation of the service, most dose adjustments were not made before the next scheduled dose, which would have increased the potential for suboptimal therapy or toxic effects. With prolonged gentamicin therapy, weekly monitoring of trough gentamicin concentration or serum creatinine was always suggested, although not always implemented, for patients treated before discontinuation of the TDM service. Pharmacists were able to suggest monitoring parameters through the hospital ordering system, but these orders required authorization by a physician before they could be implemented. After discontinuation of the TDM service, weekly monitoring of trough gentamicin concentration and serum creatinine was rarely ordered or carried out. This suggests a lack of understanding about the increased risk of nephrotoxicity with prolonged gentamicin therapy on the part of both physicians and nurses. Clearly, education regarding nurses’ compliance with orders for laboratory tests is also required.

This study was limited by its retrospective nature. The data extracted were not always complete. Exact dose times were not always available and, when necessary, standard dose times were assumed when calculating pharmacokinetic parameters. Also, documentation regarding the assessment of serum gentamicin concentrations was not always adequate for patients treated after discontinuation of the TDM service; therefore, explanations for decisions with respect to dose adjustment or lack thereof were not always available. Conclusions about secondary outcomes are limited by the small number of data points available for analysis.
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After elimination of the pharmacist-initiated TDM consult service, a TDM algorithm was put in place to allow continued triaging of responses to TDM questions (as in Table 2). Physicians were directed to call the Drug Information Service or the dispensary when pharmacist support was required for specific patients; if a full clinical consult was necessary, a TDM-certified pharmacist was available. Through this mechanism, 4 pairs of serum gentamicin determinations, included in the results for the second patient group, had full pharmacist consultation with documentation. Informal assistance by pharmacists in the Drug Information Service or the dispensary was not adequately documented, and it is therefore impossible to accurately determine the degree of pharmacy involvement in the decision-making process for patients treated after discontinuation of the formal TDM service. Furthermore, 17 pairs of serum gentamicin determinations in this group involved children with febrile neutropenia who were followed by the Haematology/Oncology Service. Physicians in this service have greater exposure to TDM, as well as limited TDM education as part of their orientation. In addition, the Haematology/Oncology team includes pharmacists who are often consulted informally regarding the care of children who are receiving care on other units (off-service). In previous studies, the impact of pharmacist-based TDM services has been evaluated after implementation of such services, but not after withdrawal of the service, as was done here. It is possible that the care provided by physicians and nurses after withdrawal of the pharmacist-initiated TDM service in this study was influenced by prior interaction with pharmacists. Continued pharmacy involvement after removal of the TDM service, as well as the education provided during the period when the pharmacist-initiated TDM service was available, may explain why the results in this investigation were not as dramatic as reported by other investigators.

Finally, the impact of a pharmacist-based TDM service on direct patient outcomes was beyond the scope of this retrospective study. However, pharmacist- based TDM services involving aminoglycosides have led to positive patient outcomes in other hospitals, including decreases in morbidity and mortality, length of drug therapy, and duration of hospital stay.
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In conclusion, the appropriate assessment of exceptional serum gentamicin concentrations decreased significantly after discontinuation of a pharmacist- initiated TDM consult service. Potential consequences may include increased potential for toxic effects, increased potential for suboptimal therapy, decreased quality of life, increased workload, and increased overall costs. Given these results, the Pharmacy Department will review strategies to improve TDM in nursing units without clinical pharmacy services by focusing on physician education and expanding clinical pharmacy services to all areas of the hospital.

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