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[Gentamycin distribution volume in a mechanically ventilated patient-- pharmacokinetic and clinical aspects]
H Seligmann1, S Nicola, S H Krimerman
1Clinical Pharmacology and Intensive Care Units, Bnai-Zion Medical Center, Technion, Haifa.
Abstract:
Mechanical ventilation (MV) of more than 32 hours may alter the gentamycin pharmacokinetic profile by increasing its volume of distribution (VD). As a result, the standard garamycin dosage regime has to be adjusted in order to obtain an adequate peak serum concentration, which is well correlated with the efficacy of garamycin therapy. Garamycin is a water-soluble drug with negligible binding to plasma albumin, so its VD approximates the volume of extra-cellular fluid, which may be expanded by MV. MV-related fluid retention is mediated via various homeostatic compensatory systems. They are activated to combat the decrease in cardiac output and central blood volume caused by MV, due to the increase in airway and intrathoracic pressure. These phenomena are more prominent during prolonged ventilation, PEEP or C-PAP ventilation, and in previously hypovolemic patients. Patients requiring MV for more than 32 hours had an average garamycin VD of 0.36 L/Kg compared with the mean VD of 0.25 L/Kg in normal adults. In the patient presented, a similar change in garamycin VD was seen, while conventional doses given during MV failed to reach suitable clinical peak levels.
Insights
Mechanical ventilation (MV) significantly increases the volume of distribution (VD) for gentamicin, a key antibiotic. Standard dosing requires adjustment during prolonged MV to ensure effective gentamicin therapy.
Area of Science:
- Pharmacology
- Critical Care Medicine
- Nephrology
Background:
- Mechanical ventilation (MV) is a life-saving intervention for respiratory failure.
- Gentamicin is a critical antibiotic for treating severe bacterial infections.
- Optimizing gentamicin dosing is crucial for efficacy and minimizing toxicity.
Observation:
- Prolonged MV (>32 hours) alters gentamicin pharmacokinetics, specifically increasing its volume of distribution (VD).
- MV-induced fluid retention, due to homeostatic responses to increased intrathoracic pressure, expands extracellular fluid volume.
- This expansion leads to a larger VD for water-soluble drugs like gentamicin.
Findings:
- Patients on MV for >32 hours exhibited an average gentamicin VD of 0.36 L/Kg, compared to 0.25 L/Kg in healthy adults.
- Conventional gentamicin doses failed to achieve therapeutic peak serum concentrations in a patient requiring prolonged MV.
- The increased VD necessitates higher gentamicin doses to reach effective peak serum levels.
Implications:
- Standard gentamicin dosing regimens are inadequate for patients requiring prolonged mechanical ventilation.
- Dosage adjustments are essential to achieve target gentamicin peak serum concentrations and ensure treatment efficacy.
- Further research into optimized gentamicin dosing strategies in critically ill patients on MV is warranted.