Netilmicin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Thylakoid-based green preparation of porous microneedles for antibiotic residues detection in food samples

BACKGROUND

Antibiotic residues in food chain have raised concerns regarding their toxicity and involvement in antimicrobial resistance. However, most existing antibiotic biosensors are primarily applicable to liquid food samples. Given the complex matrix characteristics of foods, there is an urgent need for the development of effective antibiotic detection platforms that exhibit high universality and flexibility. Porous microneedles (PMN) are microdevice structures with needle-like shapes and microscale pores throughout their composition, which facilitate rapid sampling. Consequently, the integration of PMN with biosensors holds significant promise for the detection of antibiotic residues in complex food samples.

RESULTS

In this study, hydrogel-forming PMN are fabricated by leveraging the oxygen-production capacity of thylakoid to generate bubbles and form porous structures. These PMN are then integrated with a fluorescence aptasensor for the quantification of the antibiotic netilmicin. The aptasensor consists of a netilmicin (NET) aptamer with stem loop and hairpin structure, which facilitated the binding of SYBR Green I to produce a fluorescent signal. In the presence of NET, the complete binding between NET and the aptamer results in a reduction of fluorescence intensity, thereby generating a detectable signal change for the detection of NET. Utilizing capillary action accelerate fluid extraction (2.9 times faster than nonporous microneedles) and a large specific surface area (5.1072 m2/g) conducive to aptasensor adsorb, the PMN achieve efficient capture and quantification of antibiotic with limits of detection and quantitation of 5.99 nM and 19.8 nM, respectively.

SIGNIFICANCE

Porous microneedles with tunable porosity and desirable mechanical properties are successfully fabricated. The integration of PMN with aptasensor enable the efficient detection of netilmicin in fish, milk and river water samples, demonstrating high recovery rates. The PMN represent potential tools for the convenient and rapid detection of antibiotic residues within complex food matrices, thereby enhancing food safety monitoring.

Development of Sٍٍensitive Spectrofluorimetric Methods for Determining Netilmicin Based on Selective Condensation Reactions of its Amine Moiety with each Acetylacetone/Formaldehyde and Ninhydrin/Phenylacetaldehyde Reagents

Netilmicin is an aminoglycoside antibiotic used to treat infections caused by a broad spectrum of Gram-negative and Gram-positive bacteria and is pharmaceutically formulated in ophthalmic dosage forms. In this study, two spectrofluorimetric approaches were designed and developed to switch-on the fluorescence activity of NTC. The first method, or Hantzsch (HNZ) method, was relied on measuring the generated fluorescence intensity upon the condensation of NTC with acetylacetone and formaldehyde (Hantzsch reaction) at λ_emis=483 nm/λ_excit=425.5 nm. While the second fluorometric method (NHD method) was relied on measuring the generated fluorescence intensity upon the condensation of NTC with ninhydrin/phenylacetaldehyde at λ_emis=482.2 nm/λ_excit=385.8 nm. The reaction conditions for the two approaches were well investigated and optimized. The selectivity study for the methods was investigated by determining NTC in the presence of the co-formulated drug (dexamethasone) and pharmaceutical excipients. The validation for two approaches was performed based on ICH guidelines, and ranges of linearity were 0.1-1.2 and 1.5-6.0 µg/mL, while LOD values were 0.039 and 0.207 µg/mL for the HNZ method and the NHD method, respectively. Finally, NTC has been determined in different ophthalmic preparations by the proposed approaches with adequate recovery values.

Amphiphilic aminoglycosides: Modifications that revive old natural product antibiotics

Widely-used Streptomyces-derived antibacterial aminoglycosides have encountered challenges because of antibiotic resistance and toxicity. Today, they are largely relegated to medicinal topical applications. However, chemical modification to amphiphilic aminoglycosides can revive their efficacy against bacterial pathogens and expand their targets to other pathogenic microbes and disorders associated with hyperactive connexin hemichannels. For example, amphiphilic versions of neomycin and neamine are not subject to resistance and have expanded antibacterial spectra, and amphiphilic kanamycins are effective antifungals and have promising therapeutic uses as connexin hemichannel inhibitors. With further research and discoveries aimed at improved formulations and delivery, amphiphilic aminoglycosides may achieve new horizons in pharmacopeia and agriculture for Streptomyces aminoglycosides beyond just serving as topical antibacterials.

Selection and identification of a DNA aptamer for fluorescent detection of netilmicin

Netilmicin (NET) is an antibiotic widely used in healthcare and agriculture, but it can accumulate in the environment to threat human health. Netilmicin (NET) is an antibiotic used for veterinary purposes, for human therapy and for agricultural purposes. Therefore, there is a need to develop high-sensitive measuring methods to detect NET. Aptamer-based detecting methods are highly sensitive, inexpensive, and portable. In this study, we developed an aptamer-based fluorescence method to detect and quantify NET. NET was first conjugated to magnetic beads by amidation reaction and then NET-coated beads were used as the stationary phase to isolate aptamers by systematic evolution of ligands by exponential enrichment (SELEX) screening method. After ten rounds of SELEX screening, 32 aptamers with NET-binding affinity were obtained and the candidate aptamer APT-21 was finally chosen by comprehensively comparing their secondary structure characters and NET-binding affinity. APT-21 bound to NET with high affinity (Kd = 194.1 nmol/L) and high specificity that it displayed low cross-binding activities on 7 different structural analogs. We also developed a fluorometric assay using SYBR Green I (SG-I) and the APT-21. Key experimental parameters were optimized, including buffer system, SG-I and APT-21 reaction time, SG-I concentration, and aptamer concentration, to improve the detecting sensitivity. Our results suggest that the low limit of detection (LOD) of this method reached a low level of 1.95 nM and it also exhibited a good linear range up to 200 nM. Moreover, we successfully applied our method to detect the NET spiked in tap water and river water with good recoveries in the range from 97% to 111%. In conclusion, our current study isolated a NET-specific aptamer and developed an aptamer-based quantification method, which is promising to apply to detect NET in environmental samples.

Discovery and Development of Antibacterial Agents: Fortuitous and Designed

Today, antibacterial drug resistance has turned into a significant public health issue. Repeated intake, suboptimal and/or unnecessary use of antibiotics, and, additionally, the transfer of resistance genes are the critical elements that make microorganisms resistant to conventional antibiotics. A substantial number of antibacterials that were successfully utilized earlier for prophylaxis and therapeutic purposes have been rendered inadequate due to this phenomenon. Therefore, the exploration of new molecules has become a continuous endeavour. Many such molecules are at various stages of investigation. A surprisingly high number of new molecules are currently in the stage of phase 3 clinical trials. A few new agents have been commercialized in the last decade. These include solithromycin, plazomicin, lefamulin, omadacycline, eravacycline, delafloxacin, zabofloxacin, finafloxacin, nemonoxacin, gepotidacin, zoliflodacin, cefiderocol, BAL30072, avycaz, zerbaxa, vabomere, relebactam, tedizolid, cadazolid, sutezolid, triclosan and afabiacin. This article aims to review the investigational and recently approved antibacterials with a focus on their structure, mechanisms of action/resistance, and spectrum of activity. Delving deep, their success or otherwise in various phases of clinical trials is also discussed while attributing the same to various causal factors.

Ocular flora and their antibiotic susceptibility in patients having cataract surgery in Italy

PURPOSE

To characterize the ocular flora in a consecutive group of patients having cataract surgery and to determine the antibiotic susceptibility profile of isolates to several ophthalmic antibiotics.

SETTING

Hospital Di Stefano, Catania, Italy.

DESIGN

Observational case series.

METHODS

Conjunctival and eyelid cultures from patients were obtained 14 days before surgery and, if positive, repeated the day of the surgery. Antimicrobial susceptibility for aminoglycosides (netilmicin and tobramycin), fluoroquinolones (ofloxacin, levofloxacin, and moxifloxacin), chloramphenicol, and azithromycin was tested using the Kirby-Bauer disk diffusion method. Susceptibility was also tested for oxacillin, cefuroxime, and vancomycin. All positive patients received a 2-day preoperative course of 3 mg/mL netilmicin ophthalmic solution 4 times a day. The recovery rate of microorganisms after antibiotic treatment compared with baseline was calculated.

RESULTS

One hundred twenty consecutive patients were included in the study. Cultures were positive in 72.5% of patients; 131 isolates, mainly gram-positive, were identified. Staphylococcus epidermidis (58.0%) and Staphylococcus aureus (15.3%) were the most frequently isolated microorganisms. Methicillin-resistant staphylococci accounted for 3.8% of S epidermidis and 20.0% of S aureus. A high in vitro susceptibility (>90%) for all isolates, including multiresistant coagulase-negative Staphylococcus, was obtained for netilmicin, vancomycin, and cefuroxime. The recovery rate of isolates before surgery was reduced by 93.9% (P < .001).

CONCLUSIONS

Conjunctival and lid margin isolates were sensitive to netilmicin, vancomycin, and cefuroxime. Microorganisms were less susceptible to other ophthalmic antibiotics, with the exception of moxifloxacin. A 2-day preoperative course with topical netilmicin reduced most bacteria identified on the conjunctiva and eyelids.

FINANCIAL DISCLOSURE

Dr. Papa and Ms. Blanco are employees of Società Industria Farmaceutica Italiana SpA. Dr. Santocono has no financial or proprietary interest in any material or method mentioned.

A novel multi-parametric high content screening assay in ciPTEC-OAT1 to predict drug-induced nephrotoxicity during drug discovery

Drug-induced nephrotoxicity is a major concern in the clinic and hampers the use of available treatments as well as the development of innovative medicines. It is typically discovered late during drug development, which reflects a lack of in vitro nephrotoxicity assays available that can be employed readily in early drug discovery, to identify and hence steer away from the risk. Here, we report the development of a high content screening assay in ciPTEC-OAT1, a proximal tubular cell line that expresses several relevant renal transporters, using five fluorescent dyes to quantify cell health parameters. We used a validation set of 62 drugs, tested across a relevant concentration range compared to their exposure in humans, to develop a model that integrates multi-parametric data and drug exposure information, which identified most proximal tubular toxic drugs tested (sensitivity 75%) without any false positives (specificity 100%). Due to the relatively high throughput (straight-forward assay protocol, 96-well format, cost-effective) the assay is compatible with the needs in the early drug discovery setting to enable identification, quantification and subsequent mitigation of the risk for nephrotoxicity.

Netilmicin/dexamethasone fixed combination in the treatment of conjunctival inflammation

Purpose

To compare the efficacy and safety of 0.1% dexamethasone/0.3% netilmicin (Netildex), with that of 0.1% dexamethasone/0.3% tobramycin (Tobradex) in the treatment of external ocular inflammation requiring antibiotic therapy.

Methods

In this randomized, double-blind study, 139 subjects with conjunctival inflammation associated with signs of ocular infection were treated with Netildex (n = 71) or Tobradex (n = 68) four times daily for 6 days. The primary efficacy analysis was based on the percentage of patients with at least a 50% decrease in conjunctival hyperemia at the endpoint visit (Day 6 [± 1]) with respect to baseline (responder rate). An equivalence margin of 20% was set for this study. A follow-up visit was performed at Day 14 (± 1). Other efficacy parameters were: conjunctival edema, conjunctival discharge, lid hyperemia, lid edema, presence of ocular infection, and symptoms of ocular discomfort. Safety evaluations included intraocular pressure, visual acuity, and adverse events.

Results

At Day 6, a decrease of conjunctival hyperemia was observed in 87.3% and 90.9% of the patients treated with Netildex and Tobradex, respectively. The 95% confidence interval for the difference between groups (−15.3 ÷ 8.0) satisfied the equivalence hypothesis. Subjects treated with Netildex had a better control of lid hyperemia (P = 0.016), tearing (P = 0.001), burning (P = 0.007), and stinging (P = 0.004). No adverse reactions were observed during the study except one case of keratitis in the Tobradex group.

Conclusion

Netildex was as effective and safe as Tobradex in reducing signs and symptoms in patients with conjunctival inflammation when ocular infection was suspected.

A new eye gel containing sodium hyaluronate and xanthan gum for the management of post-traumatic corneal abrasions

PURPOSE

The aim of this study was to investigate the effects of an ophthalmic gel containing sodium hyaluronate and xanthan gum in addition to the antibiotic netilmicin in the management of traumatic corneal abrasions.

PATIENTS AND METHODS

PATIENTS WITH TRAUMATIC CORNEAL ABRASIONS WERE RANDOMLY TREATED AS FOLLOWS: Group A (n = 20) with an occlusive patching for 12 hours plus one drop of an eye gel containing 0.15% sodium hyaluronate, 1% xanthan gum and 0.3% netilmicin qid for 5 days; and Group B (n = 20) with an occlusive patching for 2-3 days plus one application of 0.3% netilmicin ophthalmic ointment qid for 5 days. All patients were evaluated after the third and seventh day by slit-lamp examination, fluorescein staining, and corneal defect photograph in order to assess corneal re-epithelialization. Conjunctival hyperaemia, lid oedema, subjective symptoms of discomfort, and conjunctival swabs were also evaluated.

RESULTS

No statistically significant difference was observed between the groups in terms of the extent of corneal healing after 3 days of treatment. Both treatments were also highly effective in decreasing the erosion score and the conjunctival hyperemia (P < 0.0001, P < 0.005, respectively) without any significant difference between the two types of treatment. Subjective symptoms of discomfort and conjunctival swabs were also evaluated.

CONCLUSION

In the management of traumatic corneal abrasions, the administration of an eye gel containing sodium hyaluronate and xanthan gum is able to reduce the length of occlusive patching. In addition, the presence of netilmicin guarantees good antibiotic prophylaxis during the wound repair process.

Comparative study of the disposition of levofloxacin, netilmicin and cefepime in the isolated rat lung

An experimental model of artificially perfused and mechanically ventilated lung has been applied to compare the kinetic behaviour of levofloxacin, cefepime and netilmicin in this body tissue. The study has been performed to explore the usefulness of the isolated lung technique in the pharmacokinetic field, particularly to study the disposition of antibiotics in pulmonary tissue. The lung was perfused with Krebs-Henseleit medium containing 3% bovine albumin at a flow rate of 5 mL min−1. It was ventilated at 60 respirations/min with a 2-mL tidal volume of air previously humidified and warmed to 37°C. The concentrations of the above antibiotics were determined by HPLC techniques and the outflow curves were analysed by stochastic, as well as by model-dependent, methods. The results show pharmacokinetic differences among these antibiotics, which are in accordance with previously reported data, levofloxacin being the drug with the highest distribution coefficient in this tissue (1.25 ± 0.14 vs 0.39 ± 0.07 and 0.41 ± 0.06 mL g−1 for netilmicin and cefepime, respectively). Accordingly, the isolated lung of the rat, under the experimental conditions used here, constitutes an alternative model to be incorporated to pharmacokinetic studies with a great potential use for those drugs that show a pharmacological or toxicological action depending on the kinetic profile in the lung tissue.

Dexamethasone-netilmicin: a new ophthalmic steroid-antibiotic combination. Efficacy and safety after cataract surgery

PURPOSE

The purpose of this study was to evaluate both efficacy and safety of a new ophthalmic steroid-antibiotic fixed combination containing dexamethasone and netilmicin in the postsurgical management of cataract surgery.

METHODS

In total, 223 patients were randomly treated with dexamethasone 1 mg/ml plus netilmicin 3 mg/ml (n=148), or dexamethasone 1 mg/ml plus tobramycin 3 mg/ml (n=75, TOBRADEX) four times in a day for 7+/-1 days starting immediately after surgery. Efficacy (anterior chamber (AC) inflammation, conjunctival hyperaemia, corneal and lid oedema, ocular infection, pain, photophobia and tearing) and safety (burning, stinging, blurred vision, intraocular pressure, and visual acuity) were analysed in the operated eye after 1 and 7+/-1 days. A follow-up visit was performed at day 14+/-2. The extent of AC inflammation, measured by slit-lamp according to a standard scoring system, was used as primary efficacy parameter.

RESULTS

At the primary end point (day 7) both fixed combinations were equally effective in reducing postoperative inflammation. The safety profile of the dexamethasone/netilmicin combination was excellent with no evidence of poor local tolerance or adverse reaction.

CONCLUSIONS

A new fixed combination of dexamethasone and netilmicin was effective and safe in controlling ocular inflammation after cataract surgery.

Effect of ofloxacin and netilmicin on human corneal and conjunctival cells in vitro

The purpose of this study was to compare the cytotoxic effects of the fluoroquinolone ofloxacin with that of the aminoglycoside netilmicin. Human corneal epithelial cells (HCE-T) and human conjunctival epithelial cells (Wong-Kilbourne derivative of Chang conjunctiva) were exposed to antibiotics (0.08-5.0 mg/mL) for 4 or 24 hours. Cell proliferation and viability were assessed with the MTT assay, neutral red uptake, and bromo deoxy uridine incorporation. In both cell lines, ofloxacin inhibited cell proliferation and viability. These effects were time and dose dependent. Concentrations of ofloxacin ranging from 0.4 to 2.4 mg/mL (0.04% to 0.24%) produced a 50% inhibition of proliferation and viability. In contrast, netilmicin induced no toxic effect. The differences between ofloxacin and netilmicin were highly statistically significant (p < 0.001). This finding is particularly relevant in deciding the optimal antibiotic to be applied in clinical situations in which the epithelium is compromised.

In vitro toxicity of netilmicin and ofloxacin on corneal epithelial cells

PURPOSE

To evaluate the in vitro cytotoxic effect of the aminoglycoside antibiotic netilmicin on rabbit corneal epithelial cells (SIRC) compared with ofloxacin, a commonly used fluoroquinolone ocular antibiotic.

METHODS

SIRC cell cultures were incubated for 8 to 72 h in the presence and absence of netilmicin (1.5, 3, and 6 mg/mL) and equal concentrations of ofloxacin. Cell viability in treated and untreated SIRC cells was measured by both neutral red and MTT colorimetric assays at 8, 24, and 72 h, whereas changes in cell morphology were examined at 8, 24, 48, and 72 hours by the use of phase-contrast microscopy.

RESULTS

Netilmicin, at all tested concentrations, failed to alter SIRC cell viability or morphology. In contrast, all concentrations of ofloxacin caused statistically significant dose- and time-dependent reductions in cell viability even after 8 h. After 72 h there was complete loss of cell viability. Morphologic examination of SIRC cells after 8 h of incubation with ofloxacin revealed that the fluoroquinolone antibiotic, at all concentrations, produced large numbers of dead cells, compromised intercellular contacts, and altered general morphology. After 48 h the cell monolayer was observed to be completely destroyed.

CONCLUSION

Netilmicin, at the concentrations used, is an antibiotic devoid of obvious cellular toxicity and may also be considered as a suitable first-choice drug in the treatment of those pathologies that compromise the integrity of the ocular surface.

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 </=1.9 mg dl-1). Netilmicin (100 mg) was administered as a maximum of four successive intravenous infusions of 30 min, at 8-h intervals. A total of five blood samples were collected from each patient. Prior to analysis, the dataset was divided into 'index' (n = 44) and 'validation' (n = 18) groups at random. The time courses of netilmicin concentrations from all subjects were analysed using a mixed effects, population, nonlinear modelling package (WinNonMix). For covariate model development, a stepwise procedure was used with backward elimination followed by forward inclusion based on age, sex, weight, height, creatinine clearance and type of surgery. The final covariate model parameters from the index group were used to simulate concentrations in the validation group and the bias and precision were compared with the observations.

RESULTS

A bi-compartmental open model with a proportional residual error best described the data. The population parameters for central and peripheral volumes of distribution were (typical population value [interindividual CV%]) Vc = 14.5 l [56%] and Vp = 10.2 l [not estimated], and the systemic and intercompartmental clearances were CL = 3.9 l h-1[42%] and CLQ = 10.1 l h-1[not estimated], respectively. The final population covariate relationships were based on sex (SEX) and creatinine clearance (CrCL): (Vc, l) = 18.9 - 5.9 x SEX [29%] and (CL, l h-1) = 0.06 x CrCL [33%]. Compared with the observations in the validation group, this model showed a bias (95% confidence interval) of -0.028 (-0.28, 0.25) and precision of 1.22 (0.78, 1.34).

CONCLUSION

Bi-compartmental pharmacokinetic parameters of netilmicin have been estimated from clinical data in urological surgery patients using a population approach. A given single dose results in large variability in plasma concentrations and thus the population covariate final model can be used for direct estimation of initial dosing in patients.

Treatment of acute bacterial conjunctivitis with topical netilmicin

PURPOSE

This study compares the clinical and microbiologic value of topical netilmicin with that of gentamicin in the treatment of acute bacterial conjunctivitis.

METHODS

A double-blind, randomized, prospective, controlled study was performed in 209 patients. One to two drop(s) of either antibiotic was applied to the affected eye(s) four times a day for up to 10 days. Patients were examined at the time of diagnosis and after 3, 5, and 10 days. Clinical efficacy was measured as the cumulative sum score (CSS) of the key signs and symptoms of acute bacterial ocular infection. Sensitivity/resistance was evaluated using the disk diffusion method.

RESULTS

Drug efficacy assessment was restricted only to patients with positive baseline culture results (n = 121). Of the isolated organisms, 96.9% were sensitive to netilmicin, whereas only 75.0% were sensitive to gentamicin (p = 0.00001). Netilmicin provided a broad-spectrum coverage comparable with that of ciprofloxacin, ofloxacin, and norfloxacin. Netilmicin also was more effective than gentamicin in eradicating infections (p = 0.001 at day 5 and p = 0.037 at day 10) and in ameliorating the CSS (p = 0.037 at day 3, p = 0.001 at both day 5 and day 10). Only minor adverse events occurred in patients treated with either netilmicin or gentamicin.

CONCLUSIONS

This study demonstrates that netilmicin is a safe and effective antibiotic that can be used as first-line therapy for the treatment of acute bacterial conjunctivitis.

Residence time of netilmicin in tears

PURPOSE

To determine the concentration of netilmicin in tears after eye drop administration.

METHODS

A clinical study was carried out on 32 healthy volunteers. Subjects were divided into four groups and underwent tear collection at 5, 10, 20, and 60-minutes after drug administration, respectively. Tear samples were collected through capillary suction from the inferior conjunctival "cul-de-sac" and analyzed by high-pressure liquid chromatography (HPLC).

RESULTS

Netilmicin concentration in tears decreased after a first order kinetics, a best-fit curve was drawn and the minimum inhibitory concentration (MIC90) intersection for the most common ocular pathogens was calculated.

CONCLUSIONS

The extrapolation of the curve shows that the concentration of netilmicin on the ocular surface can be effective against microorganisms more than 120 minutes after eye drop instillation.

Pharmacokinetics and metabolism of 14C-isepamicin in humans following intravenous administration

Twelve healthy adult male volunteers received 1 g (base equivalent) of 14C-isepamicin (131 microCi) as an intravenous bolus over 5 min. The areas under the plasma concentration-time curves at infinity for isepamicin (196 micrograms*h/ml) and total radioactivity (164 micrograms*h/ml) were similar, indicating no biotransformation of isepamicin. The disappearance of isepamicin from plasma followed a triexponential decline, with half-lives of 0.17, 2.12, and 34 h for the alpha, beta, and gamma phases, respectively. However, the contribution of the gamma phase to the total area under the concentration-time curve was only 2.6%. There were no detectable metabolites in plasma and urine, confirming that isepamicin was not biotransformed. The cumulative levels of isepamicin and total radioactivity excretion in urine from 0 to 120 h were 97.3 and 92.1% of the dose, respectively, indicating that the drug was excreted mainly as unchanged isepamicin in urine.

In vitro postantibiotic effect and postantibiotic leukocyte enhancement of tobramycin

The occurrence of a postantibiotic effect (PAE) and postantibiotic leukocyte enhancement (PALE) of tobramycin, a natural aminoglycoside clinically used since the early 1970s, has been investigated in comparison to gentamicin on recent clinical isolates of Staphylococcus aureus (both methicillin-susceptible and -resistant strains) and of Gram-negative fermenting and non-fermenting rods. A concentration-dependent PAE was observed with both antibiotics, regardless of the bacterial species used, with some variability based on their intrinsic resistance. Tobramycin, at concentrations equal to or higher than the minimum inhibitory concentration (MIC), exhibited a rather long PAE (ranging from 1.9 to 10.9 h) which was often significantly longer than that observed with gentamicin (ranging from 1.0 to 7.5h). Moreover, pre-exposure to tobramycin led to enhanced polymorphonuclear leukocyte phagocytosis and killing with a 2- to 27-fold increase in activity compared to controls. These results suggest that tobramycin might be conveniently used with once-daily dosing for the treatment of infections due to sensitive pathogens.