[Determination of netilmicin in rat serum using high performance liquid chromatography and resonance Rayleigh scattering].

A method was developed for the direct determination of netilmicin in rat serum using high performance liquid chromatography and resonance Rayleigh scattering (RRS). The separation was carried out on a C18 column with the isocratic elution of the mixture of 20 mmol/L sodium acetate aqueous solution and methanol containing 0.22% trifluoroacetic acid (92:8, v/v). With the molecular recognition probe of pontamine sky blue, netilmicin formed an ion-association complex and enhanced the intensity of RRS. The RRS signal was detected by a commercial fluorescence detector at 365 nm of both excitation wavelength (lambda ex) and emission wavelength (lambda em). Under the optimized conditions, the limit of detection (LOD, S/N = 3) for the netilmicin was 0.7 mg/L. With the internal standard (IS) of tobramycin, a linear calibration curve ranged from 1.2 mg/L to 30 mg/L was obtained. The presented method can be used for the pharmacokinetics study of netilmicin in rat serum, and can be a new choice for the determination of aminoglycoside antibiotics in biological samples.

[Optimalisation of netilmicin dosage based on therapeutic drug monitoring during the first days of life in very preterm neonates (gestational age 23-32 weeks)]. / Optymalizacja dawkowania netylmycyny w oparciu o terapie monitorowana stezeniem antybiotyku w pierwszych dniach zycia u noworodków bardzo niedojrzalych (23-32 tygodnie ciazy).

AIM: The aim of this study was to optimalise netilmicin dosage in low and very low birthweight premature neonates, based on drug serum concentrations obtained during therapeutic drug monitoring (TDM). PATIENTS AND METHODS: Prospective study of 55 neonates born at gestational age 23-32 (GA) and birthweight between 480 g to 1780 g, with suspected intrauterine infection, in whom netilmicin serum concentration was monitored. Initially the antibiotic was administered every 24 hours (group I: n=16; mean GA=28+/-3 weeks). Peak level was measured 30 minutes after completion of infusion after the 2(nd) dose of the drug, and trough level was measured immediately before administration of the 3(rd) dose of the drug. Due to excessive trough levels, the dosing regimen was modified, prolonging the interval between doses to 48 hours. Such dosing regimen was used in neonates, enrolled in group II (n=39; mean GA=28+/-2 weeks). Pharmacokinetic parameters were evaluated in order to find correlations between them and neonatal maturity, birthweight and creatinine serum concentration. Serum netilmicin concentration was measured by fluorescence polarization immunoassay (FPIA), using TDx/FLx (Abbott Laboratories). Creatinine concentration was measured on the 3(rd) day of life using Cobas Integra 400. All children in the study underwent the first hearing examinations under 3 months of age. After excluding changes which could affect hearing ability, behavioural examination was conducted. If its result was inconclusive or abnormal, the child was referred for ABR (auditory brain stem response) examination. The children were followed-up until they were 2 years old. RESULTS: Netilmicin peak levels in both groups were within the recommended range (11.33+/-3.27 microg/mL in group I; 13.35+/-5.67 microg/mL in group II). Safe trough level was exceeded in 81.2% neonates in group I and 28.2% in group II. This was observed in the most immature neonates: born 23-27(th) GA, with mean birthweight 805+/-293 g, in whom trough level was on average 2.93 microg/mL and t(0.5) was 20.8 hours. Negative correlation was found between trough level and gestational age (r=-0.524; p<0.001) and birthweight (r= -0.293; p=0.030). Negative correlations was also found between t(0.5) and gestational age (r= -0.489; p<0.001) and birthweight (r=-0.320; p=0.016). No child was diagnosed with hearing impairment in group II and one case in group I. CONCLUSIONS: The results indicate that netilmicin dosage of 6 mg/kg every 48 h can ensure the desired trough and peak levels in premature neonates without the necessity of routine monitoring of antibiotic concentration. However, in very premature neonates (

Clinical pharmacokinetics of aminoglycosides in the neonate: a review.

BACKGROUND: Sepsis is common in neonates and is a major cause of morbidity and mortality. Sixty percent of preterm neonates receive at least one antibiotic, and 43% of the antibiotics administered to these neonates are aminoglycosides. The clearance (Cl), serum half-life (t(1/2)), and volume of distribution (Vd) of aminoglycosides change during the neonatal life, and the pharmacokinetics of aminoglycosides need to be studied in neonates in order to optimise therapy with these drugs. OBJECTIVE: The aim of this work is to review the published data on the pharmacokinetics of aminoglycosides in order to provide a critical analysis of the literature that can be a useful tool in the hands of physicians. METHODS: The bibliographic search was performed electronically using PubMed, as the search engine, through July 11th, 2008. Firstly, a Medline search was performed with the keywords "pharmacokinetics of aminoglycosides in neonates" with the limit of "human". Other Medline searches were performed with the keywords "pharmacokinetics of ... in neonates" followed by the name of the aminoglycosides: amikacin, gentamicin, netilmicin and tobramycin. In addition, the book Neofax: A Manual of Drugs Used in Neonatal Care by Young and Mangum (Thomson Healthcare, 2007) was consulted. RESULTS: The aminoglycosides are mainly eliminated by the kidney, and their elimination rates are reduced at birth. As a consequence Cl is reduced and t(1/2) is prolonged in the neonate as compared to more mature infants. The high body-water content of the neonate results in a large Vd of aminoglycosides as these drugs are fairly water soluble. Postnatal development is an important factor in the maturation of the neonate, and as postnatal age proceeds, Cl of aminoglycosides increases. CONCLUSION: The maturation of the kidney governs the pharmacokinetics of aminoglycosides in the infant. Cl and t(1/2) are influenced by development, and this must be taken into consideration when planning a dosage regimen with aminoglycosides in the neonate. Aminoglycosides are fairly water soluble, and the larger water content of neonates yields a larger Vd in these patients.

[Determination of netilmicin in rat plasma by reversed-phase high performance liquid chromatography with fluorescence detection and pre-column derivatization].

A new, simple and sensitive method based on pre-column derivatization by reversed-phase high performance liquid chromatography (HPLC) is described for the separation and quantification of netilmicin in plasma, using 9-fluorenylmethyl chloroformate (FMOC-Cl) as the derivatization reagent. Its pharmacokinetics is also presented. The derivatization modes and chromatographic conditions were optimized. The separation was performed on an Agilent ZORBAX Eclipse XDB-C8 column (150 mm x 4.6 mm, 5 microm) with a mixture of water-acetonitrile (15:85, v/v) as mobile phase and the flow rate was 1.0 mL/min. The excitation wavelength was 265 nm and the emission wavelength was 315 nm. The linear range was 0.045-8.88 mg/L and the correlation coefficient (r) was 0.9993. The limit of detection (LOD) (S/N = 3) was about 0.01 mg/L, and the limit of quantification was 0.03 mg/L (3LOD) for netilmicin. The relative standard deviation was less than 3% for intra-day assay (n = 5) and 3.5% for inter-day assay (n = 5) and the relative recovery was in the range of 96.62%-100.84% (n = 3). The plasma volume of 30 microL was sufficient for the determination of netilmicin. The method provides a reliable bioanalytical methodology to carry out netilmicin pharmacokinetics in rat plasma.

Once-daily netilmicin for neutropenic pyrexia in paediatric oncology.

AIM: To establish the safety and efficacy of single daily intravenous netilmicin 6 mg/kg with piperacillin 100 mg/kg every 8 h for empirical, first-line management of children with neutropenic pyrexia following cytotoxic chemotherapy. METHODS: Observational study of children admitted to a regional oncology unit from October 1999-April 2002. Primary outcome measure was temperature 72 h after commencing antibiotic therapy; secondary measures were mortality, nephrotoxicity, symptomatic ototoxicity and serum netilmicin levels. RESULTS: 280 episodes for 128 patients (median age 7.1 y) were documented, and 248 episodes were evaluated and compared with a previous cohort of 100 episodes for which the only difference was administration of netilmicin three times daily. Twenty-seven per cent of single-dose netilmicin episodes remained febrile at 72 h compared to 32% in the comparator group (difference -4.7%; 95 % CI: -6.8% to 16.2%; p = 0.41). No patients died and we were unable to find evidence of nephrotoxicity or ototoxicity. Eighty-nine per cent of "peak" serum netilmicin levels measured 30 min after infusion were 10 mg/l or greater, and 94% and 86% measured 12-16 h after the first and third dose, respectively, were 1 mg/l or less. Peak serum netilmicin level measurements and 12-16-h measurements after the first dose were abandoned after the first 180 episodes. CONCLUSIONS: Netilmicin can safely be given as a single daily dose to children with febrile neutropenia who do not have biochemical evidence of nephrotoxicity. Monitoring peak serum levels of netilmicin is unnecessary. Levels taken 12-16 h after the third dose are adequate to monitor therapy if used in conjunction with a therapeutic guideline detailing the response to abnormal serum creatinine and netilmicin levels.

Validation of a simplified netilmicin dosage regimen in infants.

The aim of this study was to validate a simplified high-dosage, extended-interval netilmicin dosage regimen for infants. A total of 129 infants receiving 163 treatment courses of netilmicin (6 mg kg every 24 or 36 h depending on gestational age (GA), postnatal age and postmenstrual age) was analysed. Serum netilmicin concentrations were monitored before (Cmin), 30 min (C0.5h) after and 7.5 h (C7.5h) after the third dose. In 110 patients during first week of life mean C0.5h was 10.5 mg/l. Mean C0.5h was significantly lower (9.0 mg/l) in 38 infants older than 1 week of age. 14 of 15 patients with Cmin levels > or = 2 mg/l receiving netilmicin every 36 h were < 28 weeks of gestation. In the first week of life significant correlations between GA and elimination half-life (p < 0.001) and between plasma creatinine and elevated Cmin (p < 0.002) were found, but no correlation between C0.5h and GA. In this high-dosage regimen a dosing interval of 48 h for GA < 29 weeks, 36 h for GA 29-36 weeks and 24 h for full term babies seems appropriate, during first week of life, to avoid the majority of elevated trough levels and still obtain maximal therapeutic efficacy.

Use of once-daily netilmicin to treat infants with suspected sepsis in a neonatal intensive care unit.

Once-daily administration of aminoglycoside antibiotics has become the most acceptable dosing schedule for the majority of patients. There are few published data on the impact of post-natal age on aminoglycoside concentrations in preterm infants receiving once-daily dosage regimens. Netilmicin was administered as a once-daily dose of 4 mg/kg. In 141 episodes of suspected sepsis in 123 babies, trough netilmicin concentrations ranged from undetectable to 4.0 mg/l. Netilmicin concentrations were above a level of 2 mg/l in 10.6% of episodes. Netilmicin concentrations decreased with increasing post-natal age and weight. Levels were higher in males compared to females. Increased creatinine concentrations were associated with higher netilmicin concentrations. This study emphasises the importance of post-natal age as a determinant of aminoglycoside concentrations with a once-daily dosing regimen in a neonatal intensive care population. Trough levels should be carefully monitored and consideration given to extending dosage intervals particularly when netilmicin is administered once daily to preterm infants in the first week of life.

Population pharmacokinetics of netilmicin in short-term prophylactic treatment.

AIMS: To characterize the population pharmacokinetics of netilmicin, an aminoglycoside antibiotic, in adult urology patients and to develop a covariate model for improved dose titration. METHODS: Data from 62 adult patients (55 male, seven female), undergoing urological surgery and treated with netilmicin for short-term prophylaxis, were evaluated retrospectively. The group had (median, range) ages 68, 31-92 years, weights 72, 43-106 kg and heights 167, 148-182 cm. No patient showed renal impairment before netilmicin treatment (serum creatinine

Evaluation of a netilmicin-loading dose in very low birthweight infants.

BACKGROUND: The bactericidal efficacy of aminoglycosides is directly related to maximum serum concentrations, particularly the initial one. Therefore, several groups have recommended an aminoglycoside loading dose. Our goal was to develop a simplified dosage regimen for preterm infants which would result in therapeutic maximum serum concentrations early in the course of therapy. METHODS: Open, noncomparative study during November 2000 to April 2001. The modified netilmicin-dosing protocol included a loading dose of 5 mg/kg in the first week of life, followed by a maintenance regimen of 3.5 mg/kg every 24 h. After the first week of life the corresponding doses were 6 (loading) and 5 mg/kg (maintenance). A peak level was measured 30 min after the second dose, and a trough level immediately before the third dose. RESULTS: Thirty-five very low birthweight infants (mean birthweight 876 +/- 170, range 536-1,385 g; mean gestational age 26 +/- 1.8, range 23-30 weeks) who had 46 episodes of netilmicin treatment were included in the analysis. Mean netilmicin peak and trough values were 15.9 +/- 3.7 (range 8.9-28.9) and 3.4 +/- 1.3 (range 1.0-7.8) micromol/l, respectively. Ninety-one percent of all peak levels were within the targeted range of > or =10 micromol/l. Eleven trough values (24%) were > or =4 micromol/l: in 7 instances netilmicin was administered within the first week of life, 5 of these patients had concomitant indomethacin treatment. Only 1 of the 35 neonates had a rise in serum creatinine of > or =0.5 mg/dl during netilmicin therapy. Hearing evaluations were performed in 25 of the 29 surviving infants at discharge home, all of which gave normal results. CONCLUSIONS: The new netilmicin-dosing protocol yielded therapeutic maximum serum concentrations in 91% of cases after the second dose. However, a significant number of very low birthweight infants had elevated trough levels, particularly when netilmicin was administered in the first week of life with concomitant indomethacin treatment. We speculate that a longer interval between the loading dose and the first maintenance dose would result in fewer elevated trough levels with a similarly high number of therapeutic peak levels.

[Pharmacokinetics of netilmicin in neonates]. / Farmakokinetyka nietylmycyny u noworodków przedwczesnie urodzonych.

UNLABELLED: Our goal was to perform a pharmacokinetic analysis of netilmicin to develop the optimum dosage regimen of this antibiotic in premature neonates hospitalized in Neonate Intensive Care Unit of the Institute of Mother and Child in Warsaw. MATERIALS AND METHODS: The pharmacokinetics of netilmicin was studied in 80 neonates, divided for analysis into three groups according to gestational age: group I - 10 full-term neonates (b.w. 3225 +/-502 g); group II - 35 premature neonates between 29-32 weeks (b.w. 1134+/-311 g); and group III - 35 premature neonates between 23-28 weeks (b.w. 910 +/-243 g). The whole studied group of neonates was initially given i.v. netilmicin every 24 h, then the dosing interval for the safety reasons was prolonged to 48 h in the premature group. The neonates received netilmicin in the following doses: group I - mean dose 6.2 +/-0.42 mg/kg; group II - 5.911+/-0.529 mg/kg and group III - 6.014+/-0.313 mg/kg. Serum netilmicin concentrations were determined by fluorescence polarization immunoassay (FPIA) - TD(x)FL(x) (Abbott). RESULTS: The mean of pharmacokinetic parameters for groups I, II, and III were defined respectively: t(0.5) (h): 7.14+/-1.88, 12.68+/-4.26, 15.98+/-5.9; AUC0-( (microg x h/ml): 149+/-41, 303+/-100, 401+/-172; Cl/kg (l/h/kg): 0.748+/-0.24, 0.371+/-0.13, 0.289+/-0.1; MRT0-( (h): 6.3+/-2.8, 10.8+/-6.3, 15.5+/-9.3; V(dss) (l/kg): 0.75+/-0.24, 0.59+/-0.52, 0.44+/-0.19. The obtained mean netilmicin serum concentrations (microg/ml) were: once-a-day dosage: C(max) - 10.25+/-2.616 (group I), 12.2+/-2.65 (group II), 12.9+/-2.77 (group III); C(min) - 1.158+/-0.657 (group I), - 2.65+/-1.02 (group II), 3.23+/-1.42 (group III); once-a-48 h dosage: C(max) - 11.7+/-1.09 (group II), 13.9+/-6.53 (group III); C(min) - 1.09+/-0.64 (group II), 1.74+/-0.98 (group III). CONCLUSIONS: 1. All the calculated pharmacokinetic parameters in the premature neonate groups (group II and III) significantly differs from the parameters calculated for full-term neonates. 2. Significant correlations were obtained between birth weight, gestational age and all the calculated pharmacokinetic parameters in all the groups of neonates. 3. The obtained results indicated that the use of the dosing schedule of netilmicin with the dose intervals of 48 h in premature neonates should guarantee adequate peak and trough levels without the need of routine monitoring of each patient in the premature neonate group except the very low weight neonates. Detection of the specific sensitivity of lymphocytes T during the diagnosis of food allergy.

[Evaluation of Emit netilmicin and amikacin assays on Dimension RXL HM (Dade Behring) open channels]. / Adaptation des trousses Emit nétilmicine et amikacine sur canaux ouverts du Dimension RXL HM (Dade Behring).

The aim of this study was to evaluate and to validate an enzyme immunoassay in homogeneous phase for netilmicin and amikacin, adapted on the Dimension RXL HM (Dade Behring) machine. The results were compared with those obtained with automated polarization of fluorescence immunoassay using TDx FLx (Abbott). The protocol of the study and the analytical criteria were inspired by the protocol Valtec version 2002 recommended by the French Society of Clinical Biology (SFBC). The validation of this technique as adapted to the Dimension RXL HM has allowed its use for routine dosage adjustment of amikacin and netilmicin. The practicability is however the weak point of the adaptation of these techniques, even limiting as for their implementation.

Population pharmacokinetic analysis of netilmicin in neonates and infants with use of a nonparametric method.

BACKGROUND: Although the therapeutic and toxic effects of netilmicin are related to its plasma concentration, its pharmacokinetics in neonates and infants and the influence of clinical and biological variables have been only partially assessed. METHODS: Therapeutic drug monitoring data collected from 186 neonates and 95 infants receiving netilmicin were analyzed with a nonparametric population approach. The influence of gestational and postnatal age, weight, Apgar score, and creatinine and urea plasma concentrations on the pharmacokinetic parameters was assessed. The neonate and infant groups were each randomly divided into a learning sample and a validation sample. The population analysis was performed on each learning subgroup with the nonparametric maximum likelihood (NPML) method. In the validation group, the data were used to assess the concentration predictability. Because there is no specific netilmicin formulation for neonates and infants, an error model was proposed to account for errors attributable to dilution processes when preparing the infusion. RESULTS: In neonates, the covariates that reduced expected variance of plasma clearance by more than 10% were postnatal age, body weight, and plasma creatinine, as well as plasma urea and creatinine in infants. Body weight and sex played a significant role in explaining the variability of the volume of distribution. The accuracy of the concentration predictability assessed in the validation samples was satisfactory, and no significant bias was found. CONCLUSION: These findings help explain the large interindividual variability of the pharmacokinetics of netilmicin and the influence of the clinical and laboratory covariates in neonates and infants.

Sensitive high-performance liquid chromatographic assay for aminoglycosides in biological matrices enables the direct estimation of bacterial drug uptake.

Following the development of a sensitive high-performance liquid chromatographic (HPLC) assay for gentamicin in biological matrices, the utility of this assay for the determination of other clinically important aminoglycosides (neomycin, netilmicin and sisomicin) in bacterial culture media or plasma is demonstrated. The high sensitivity of the assay enables direct measurement of the aminoglycoside content of bacterial cells cultured in the presence of unlabelled drug.

Pharmacokinetics and tissue residues of netilmicin and vancomycin in chickens.

Following a single intravenous injection of 10 mg netilmicin or 30 mg vancomycin/kg b.w. to normal chickens, the tested drugs obeyed a two or three compartments open model, with half-lives of distribution of 0.30 and 0.20 hours, respectively. The elimination half-lives following intravenous injection were 0.41 and 4.85 hours, respectively. Following a single intramuscular injection of 10 mg netilmicin or 30 mg vancomycin/kg b.w. to normal chickens, the serum drug concentrations peaked 2 hours post-injection with half-lives of absorption equal to 0.63 and 0.56 hours, respectively. The mean systemic bioavailability of netilmicin and vancomycin following a single intramuscular administration in normal chickens was 27.29 and 43.61%, respectively. These values indicated a limited and moderate absorption for netilmicin and vancomycin from intramuscular site, respectively. During repeated intramuscular administrations of both antibiotics for five consecutive days in normal chickens, the serum drug concentrations peaked two hours post each dose. The drugs concentrations during multiple dosage regimens were significantly increased in 2nd, 3rd, 4th and 5th days in comparison to the 1st day. Netilmicin and vancomycin persisted in liver and kidney for 96 and 120 hours, respectively, after the last intramuscular administration. The withdrawal time of netilmicin and vancomycin could be considered as five and six days, respectively. The in-vitro protein binding percents of netilmicin and vancomycin were 7.45 and 5.81%, respectively.

Comparison of a fluorescence polarization immunoassay of netilmicin in plasma, peritoneal dialysate, and urine with a high-performance liquid chromatographic method.

The quantitative analysis of netilmicin in plasma, peritoneal dialysate, and urine using the fluorescence polarization immunoassay (FPIA) of the Abbott TDx system is compared with the modified high-performance liquid chromatography (HPLC) method of Peng et al., which was chosen as a reference. Using the least square method, we found that the results of the FPIA (y) correlated well with those obtained with HPLC (x). The three regression equations for the plasma, peritoneal dialysate, and urine samples, respectively, were y = 0.71x + 0.44 with r = 0.88 and n = 45; y = 0.94x + 1.22 with r = 0.93 and n = 95; and y = 0.92x + 0.70 with r = 0.93 and n = 61. The corresponding mean errors (FPIA-HPLC) with their 95% confidence intervals were -0.19 (-0.38 to -0.02), 0.69 (-0.42 to 1.81), and -0.13 (-1.13 to 0.87) microgram/ml. According to results of the Wilcoxon matched-pairs signed-ranks test, these errors did not represent a significant bias. The FPIA is thus suitable for analyzing netilmicin in the three biological fluids studied except when dialysate is contaminated with Amuchina. In this case, HPLC should be used.

Pharmacokinetics of once-a-day netilmicin (6 mg/kg) in neonates.

The pharmacokinetics of once a day netilmicin (6 mg/kg) was studied in 21 neonates. The babies were divided into three groups according to gestational age: group I aged > 36 weeks; group II between 34-36 weeks and group III < 34 weeks. Serum concentrations were variable between patients and the concentration 24 h after the first dose ranged from 0.8 to 3.8 mg/L with only two babies having concentrations of < 1 mg/L while seven had concentrations of > 2 mg/L. There were also large patient-to-patient variations in serum half-life, volume of distribution, area under the curve and relative plasma clearance such that these parameters could not be correlated to gestational age or weight. Absolute plasma clearance was correlated with both gestational age and weight. There was evidence of accumulation between the first and second dose for all three patient groups and for patients of gestational age < 34 weeks (group III) these observations were statistically significant. A netilmicin dosage of 4.5 mg/kg once a day may be more suitable for all neonates supported by assay of serum concentrations.

Nephrotoxicity, high frequency ototoxicity, efficacy and serum kinetics of once versus thrice daily dosing of netilmicin in patients with serious infections.

The effect of dosing regimen on nephrotoxicity, high frequency ototoxicity, efficacy and serum kinetics was studied in a prospective, randomised clinical study. Therapy was started with total daily doses of 6 mg/kg given once (od) or thrice (tid) daily to 56 and 57 patients, respectively. Subsequent doses were adjusted according to serum levels. No major differences in toxicity or efficacy were noticed between od and tid regimens: clinical failures occurred in two and two patients, four and five patients suffered from a decrease of > or = 20 dB at least unilaterally at one frequency between 8 and 18 kHz, six and seven patients had a > 25 mumol/L or > 25% increase in serum creatinine, respectively. Serum creatinine or creatinine clearance did not change significantly during either therapy. Major differences between the two study groups were limited to pharmacokinetic parameters. Od dosing resulted in higher peak (mean of 21.6 vs 7.2 mg/L) and lower trough levels (0.5 vs 1.4 mg/L). Half-lives of netilmicin determined between 1 and 8 h increased significantly during therapy with tid (from a mean of 2.75 to a mean of 3.33 h, P < 0.01) but not significantly with od (rise from 2.8 to 3.03 h). Much longer half-lives were determined between 8 and 24 h in the od group (mean of 5.7 h, P < 0.01). In conclusion, only minimal differences in toxicity and efficacy were observed. Their clinical relevance appears to be minimal.

Incorporation, release and in-vitro antibacterial activity of liposomal aminoglycosides against Pseudomonas aeruginosa.

Amikacin, netilmicin and tobramycin were incorporated into either anionic or cationic liposomes prepared by sonication. The influence of lipid constituents (charges) on encapsulation efficiency was determined after lysis of vesicles by 0.2% (v/v) Triton X-100. The in-vitro activities of the liposomal aminoglycosides were evaluated against Pseudomonas aeruginosa by agar dilution and compared with free antibiotics. Normal human pooled sera, incubated at 37 degrees C, were supplemented with anionic or cationic liposomes containing known fixed concentrations of amikacin, netilmicin or tobramycin. At various time intervals (0-48 h), samples were taken and antibiotic concentrations determined by the enzyme multiplied immunoassay technique (EMIT). The encapsulation efficiency of cationic liposomes (amikacin 17.1 +/- 1.55%, netilmicin: 5.63 +/- 1.13%, tobramycin 6.7 +/- 0.5%) was approximately 30% higher than that of anionic liposomes (amikacin 12.3 +/- 0.95%, netilmicin 4.0 +/- 0.06%, tobramycin 5.13 +/- 0.18%). Anionic and cationic liposomes in human serum still retained 79.13 +/- 4.04% and 82.71 +/- 2.6% of amikacin, 50.67 +/- 1.8% and 38.6 +/- 0.8% of netilmicin, and 89.09 +/- 1.0% and 88.93 +/- 0.4% of tobramycin, respectively, after 48 h of incubation at 37 degrees C under 5% CO2. The MICs of amikacin (2, 16 and 2 mg/L), netilmicin (2, 1 and 4 mg/L) and tobramycin (1, 2 and 4 mg/L) in free, anionic or cationic liposomal formulations, respectively, were relatively comparable except for anionic liposomal amikacin for which the MIC was increased eight-fold. Empty cationic or anionic liposomes had no effect on bacterial growth. Cationic liposomes containing aminoglycosides should be evaluated further for the treatment of pseudomonal infection.