Assay of gentamicin in cerebrospinal fluid.

Abstract

CSF gentamicin level of 1-2 mg/l (range 0 2-2 9) after intramuscular administration of 1-5-2-5 mg/kg. The same authors measured 2-6 mg gentamicin/l (range 2.5-2.7) in CSF 24 hours after an intrathecal dose of 0 5 mg, and 15-8 mg/l (range 4 3-60) after an intraventricular dose of 0 5-1 mg. CSF levels of gentamicin up to 7 mg/l were obtained by Newman and Holt (1967) after 1-2 mg/kg per day intramuscularly and 0 2-1 mg/day intraventricularly.It is well documented that the action of gentamicin is particularly susceptible to changes in the salt concentration of the medium (Rubenis et al, 1963;Schoutens and Yourassowsky, 1972). When it is necessary to assay the drug in body fluids this is usually done against reference standards which are made up in the same fluid in order to minimize any discrepancies due to variation in the constituents of the medium. However, this principle appears to have been neglected in assays of gentamicin in CSF, probably due, at least in part, to the fact that pooled human CSF is not readily available in many laboratories.Received for publication 20 January 1976 Reported levels of gentamicin in the CSF are often the result of assays against reference standards made up in water (Newman and Holt, 1967). In other cases the assay method is not described in sufficient detail, and this applies particularly to assays performed by a reference laboratory.

Serum standards for the bioassay of aminoglycosides in cerebrospinal fluid.

“…The results of our studies indicate that this is valid for gentamicin as well as for four newer aminoglycosides and that the use of distilled water or electrolyte solutions may lead to considerable inaccuracies. The reasons for the lack of agreement of our results with those of Deacon (1976a) are unclear. Technical differences such as the use of a single assay plate for all samples in our study versus the use of several separate plates by Deacon (1976a) may be responsible.…”

“…The reasons for the lack of agreement of our results with those of Deacon (1976a) are unclear. Technical differences such as the use of a single assay plate for all samples in our study versus the use of several separate plates by Deacon (1976a) may be responsible. Shanson and Daniels (1975) reported that ionic content affected serum standards when the pH was altered from 7.5 to 6-7.…”

“…CSF 1, 2, and 3 and different pools of human serum were used for each of three experiments involving gentamicin (Table 1). The NaCl/CaCI2 solution was prepared as recommended by Deacon (1976a).…”

“…Although CSF would seem to be the best diluent for standards, it is often not available. A recent report described an alternative solution for CSF standards (Deacon, 1976a). We compared this artificial diluent (150 mmol NaCI/4 5 mmol CaCl2) with distilled water, human CSF, and pooled human serum.…”