A Phase 1 Study To Assess the Pharmacokinetics of Intravenous Plazomicin in Adult Subjects with Varying Degrees of Renal Function

Plazomicin is an FDA-approved aminoglycoside for the treatment of complicated urinary tract infections. In this open-label study, 24 adults with normal renal function or mild, moderate, or severe renal impairment (n = 6 per group) received a single 7.5-mg/kg of body weight dose of plazomicin as a 30-min intravenous infusion. Total clearance declined with renal impairment, resulting in 1.98-fold and 4.42-fold higher plazomicin exposures, as measured by the area under the concentration-time curve from 0 h to infinity, in subjects with moderate and severe impairment, respectively, than in subjects with normal renal function. (This study has been registered at ClinicalTrials.gov under identifier NCT01462136.).

Distribution and serum concentration of sisomicin released from fibrin glue-sealed dacron graft in the rat and human

We investigated whether or not fibrin glue (FG) used as a sealant in vascular prostheses to prevent leakage might be useful as a carrier of antibiotics for the prevention of local graft infection. Sisomicin (SISO) was incorporated into fibrin glue (SISO-FG) and evaluated as to its safety and pharmacokinetics. SISO (1.75 mg) -FG Dacron grafts were implanted subcutaneously in the anterior abdominal region of Sprague-Dawley rats, and then the changes in SISO concentrations in the serum and in the tissue around the implantation sites were compared with those same sites in rats that had had intravenous injection of SISO (1.75 mg). The serum SISO concentrations were significantly lower in the SISO-FG Dacron graft group than they were in the intravenous injection group. However, until 4 h after implantation the SISO concentrations in the tissues around the implantation sites were significantly higher in the SISO-FG Dacron group than they were in the iv injection group, and the peak concentrations during that time were 5.8 times higher for the SISO-FG Dacron group than they were for the intravenous injection group. The ratio of the area under the tissue concentration time curve of SISO (AUC tissue) after implantation of the SISO-FG Dacron graft to that after intravenous injection of SISO was 13.08. Therefore, FG was considered to control the release of SISO into the serum and to maintain a high SISO concentration in the tissue around the implantation site. Clinically, SISO (45 mg) -FG was applied directly to the Dacron grafts implanted in 10 patients who underwent prosthetic vascular reconstruction. No graft infection was observed in any of the patients who received SISO-FG Dacron grafts. The mean serum concentration of SISO was 0.65+/-0.17 microg/mL after 1 h and 0.33+/- 0.21 microg/mL after 3 h. The results of these clinical applications are in close correlation with those of the animal experiment and suggest that FG is useful as a carrier of SISO, allowing its controlled release for the prevention of local infection.

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.

[Pharmacokinetic monitoring of aminoglycoside therapy: an optimal method of administration of individualized doses of gentamicin and sisomicin]

One of the most promising approaches to design the optimal schedule for TDM provides a single determination of a drug content in the blood specimen being collected at the "ideal" sampling time equaled to the inverse value of the elimination rate constant. Three versions of the one-point method when the specimen was collected at the "ideal" time point (3 h after a single i.m. drug administration), as well as at the times of "maximum" (1 h after injection) and "minimum" (6 h after injection) concentrations were compared by the retrospective analysis of the routine TDM data obtained with HPLC-techniques in 47 patients treated with gentamicin or sisomicin. As optimal individualized doses were considered ones calculated on the base of three subsequent determinations of the aminoglycoside concentrations, i.e. 1, 3 and 6 h after injection, and the estimation of individual clearance values (Cli). The optimal doses (DCl) were calculated according to equation DCl = Dp.Cli/Clp, where Dp and Clp are population values of the dose (1 mg/kg) and Cl 72.4 ml/(h.kg), respectively. The approximate values of the individual doses (D) were calculated according to equation D = Dp.Cp/Ci, where Ci is the individual drug serum concentration 1, 3 or 6 h after administration and Cp is the corresponded population value (4.8, 1.9 and 0.8 mg/l, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of the aminoglycoside antibiotics sisomicin and netilmicin in dried blood spots on filter discs, by high-performance liquid chromatography with pre-column derivatization and fluorimetric detection

A simple method for the determination of the aminoglycoside antibiotic sisomicin or its 1-N-ethyl derivative, netilmicin in whole blood, using dried blood spots (DBSs) on filter-paper punched discs has been developed. Sisomicin or netilmicin in the DBSs were recovered most effectively in 0.5 M Na2HPO4 using ultrasonication. The eluates from the DBSs were treated by ultrafiltration for deproteinization and subjected to pre-column fluorescent derivatization using o-phthalaldehyde and beta-mercaptopropionic acid in 0.05 M KH2PO4-borate buffer (pH 9.0), followed by determination by reversed-phase high-performance liquid chromatography. The detection limits of sisomicin and netilmicin in the DBSs on punched discs (10.1 microliters of whole blood) were 0.053 and 0.50 micrograms per ml of whole blood, respectively (signal-to-noise ratio greater than or equal to 2). The method permits a simple collection of blood at the microlitre level and should prove particularly useful for monitoring sisomicin and netilmicin in blood at therapeutic levels in geriatric and paediatric patients.

Determination of sisomicin in eluate from dried blood spot on filter paper disc for monitoring of blood level in rat, by reversed-phase high-performance liquid chromatography after pre-column fluorimetric derivatization

About 20 microliters of whole blood obtained by venipuncture from rat tail vein was spotted onto a filter paper and the blood spot was punched out (5 mm diameter). Sisomicin (SISO) in the dried blood spot (DBS) was extracted effectively into 0.5 M Na2HPO4 solution by ultrasonication and determined by reversed-phase high-performance liquid chromatography with pre-column derivatization using o-phthalaldehyde and beta-mercaptopropionic acid. This method could be used for the pre-clinical study of SISO blood levels of a number of mice or rats without killing. The results were identical with those for SISO in serum, if corrected for hematocrit values, and were used for the calculation of pharmacokinetic parameters for individual rats. The detection limit of SISO in DBS (10.1 microliters of whole blood) was 1.0 microgram per ml of whole blood.

Pre-column derivatization of sisomicin with o-phthalaldehyde-beta-mercaptopropionic acid and its application to sensitive high-performance liquid chromatographic determination with fluorimetric detection

The stability of the o-phthalaldehyde (OPA) derivatives of sisomicin obtained using beta-mercaptopropionic acid was investigated by reversed-phase high-performance liquid chromatography. One of the fluorescent derivatives of sisomicin was stable at least for 6 h in 50% methanol under the optimal conditions used (OPA concentration, pH and temperature). When plasma samples spiked with sisomicin were analysed, the response was linear in the calibration range 136-900 pg of sisomicin per injected volume (40 microliters). As little as 0.06 micrograms of sisomicin per 1 ml of plasma could be detected with signal-to-noise ratio greater than or equal to 2. For plasma samples spiked with 0.2 micrograms/ml sisomicin, the recovery was 97.1 +/- 6.6% (mean +/- S.D., n = 5) with a within-run coefficient of variation of 6.8% and a day-to-day coefficient of variation of 7.2%. The method was also applied to plasma samples from rabbit after a subcutaneous injection of 1 mg/kg sisomicin.

[Effectiveness of the new aminoglycoside sisomicin in surgery]

Antimicrobial activity of sisomicin against causative agents of wound infections was studied. It was shown that by its antimicrobial activity and the rate of bactericidal effect attainment sisomicin is superior to other aminoglycosides, such as gentamicin and tobramycin. Individual variability of the pharmacokinetics of sisomicin on its intravenous and intramuscular injection to patients with wound infections was observed. For prediction of the treatment efficacy it is suggested that the drug be used under the control of its blood levels in comparison to the MTC for the isolated causative agent.

[Kinetics of the antimicrobial effect in a dynamic system: the microcalorimetric recording method and choice of parameters for characterizing kinetic curves]

The kinetics of the in-vitro antimicrobial effect of sisomicin on E. coli, A 20363 was studied microcalorimetrically in a dynamic model simulating the pharmacokinetic profiles (intramuscular administration in a dose of 1 mg/kg) of the antibiotic obeying the one-compartmental model with first-order absorption. The microcalorimetric method was more accurate than the count of the colony forming units (CFU). Unlike the CFU method, it permits continuous recording of the process and unlike the turbidimetric method, it is more sensitive and selective. For quantitative characteristic of the curves of the antimicrobial effect kinetics it is suggested to use a new parameter, the effect duration (Td) which is determined by the difference in the moment of the antibiotic administration into the dynamic model (Tin) and the moment (Tout) when the rate of heat production or the number of the CFU or the optical density during the microbial secondary growth was the same as that at Tin. It was shown that the values of Td estimated in experiments with recording of the antimicrobial effect by different methods are similar. Evaluation of Td may be useful in predicting the optimal dosing intervals.

Serum concentration of sisomicin by intravenous infusion and its clinical response as a single agent

SISO in doses of 1.0 to 1.8 mg/kg was administered by a 30-minute intravenous infusion every 12 hours to 10 patients with infections, 9 of whom had underlying diseases including malignant diseases, diabetes mellitus, and diabetes insipidus with indwelling FOLEY catheter. The serum concentration of SISO was around 6.75 micrograms/ml in the end of infusion, and less than 1.0 micrograms/ml at 8 to 12 hours after infusion. SISO was given to the patients as a single agent for at least 3 to 5 days and all patients experienced an excellent to good response clinically, and causative organisms which showed a minimal inhibitory concentration of less than 1.56 micrograms/ml disappeared after the treatment associated with clinical improvement. There were no untoward effects noted in this study.

[Clinical evaluation of sisomicin following intravenous drip infusion in respiratory tract infections]

The efficacy, safety and utility of sisomicin (SISO) followed intravenous infusion were evaluated in 35 cases with various respiratory infections. For many cases, SISO was given at a daily dosage of 100 mg, and a single dose was infused over about 1 hour. Clinical efficacy was evaluable in 28 cases including pneumonia (14 cases), bronchitis (8 cases), bronchiectasis (4 cases), pulmonary suppuration (1 case) and pulmonary abscess plus pyothorax (1 case). Almost cases had diagnosis of serious infection associated with various diseases. Clinical efficacy was evaluated as "excellent" in 2 cases, "good" in 15 cases, "fair" in 5 cases and "poor" in 6 cases, and efficacy rate in total case was 60.7%. Efficacy rate stratified by disease was calculated as 57.1% in pneumonia, 87.5% in bronchitis, 50.0% in bronchiectasis. Responses against pulmonary suppuration or pulmonary abscess with pyothorax were little or not. Bacteriologically, organisms isolated from sputum cleared in 7 out of 15 evaluable cases, thus the responses rate was 46.7%. Adverse reaction probably due to treatment observed in 2 cases with hepatic dysfunction. Blood levels of SISO at the end of infusion were ranged from 2.1 to 6.4 micrograms/ml, and no tendency of accumulation in blood after repeated infusion was showed.

The single-dose pharmacokinetics of 5-epi-sisomicin (Sch 22591) in human volunteers

5-epi-sisomicin was given as a single 1 mg/kg intramuscular injection to six adult male volunteers. No adverse effects were observed and the pharmacology was very similar to that of sisomicin. The extended spectrum of 5-epi-sisomicin and its enhanced antipseudomonal activity prompt further clinical evaluation of this agent.

In vitro evaluation of ceftazidime (GR 20263), amikacin and sisomicin, in a model simulating serum pharmacokinetics of therapeutic doses

The activity of ceftazidime, amikacin and sisomicin was investigated in an in vitro model using varying concentrations of antibiotic which mimic the serum levels of patients after the intramuscular administration of a 500, 250 and 70 mg dose respectively. Using this test, during the time of the agar MIC value correlation, ceftazidime, amikacin and sisomicin proved to be active against strains sensitive to 16 micrograms/ml, 8 micrograms/ml and 4 micrograms/ml respectively. Using the above concentrations as the cut-off points in defining the sensitivity of the strains, ceftazidime revealed the same level of activity as amikacin (6 and 5 resistant strains respectively out of the 185 tested) and proved much more active than sisomicin (48 resistant strains).

Determination of sisomicin, netilmicin, astromicin and micronomicin in serum by high-performance liquid chromatography

A high-performance liquid chromatographic method for monitoring serum levels of the aminoglycoside antibiotics sisomicin, netilmicin, astromicin, and micronomicin, using an amino acid analysis system is described. The procedure involves sample preparation with a CM-Sephadex column, and quantitation using internal standards chosen from each of the other aminoglycosides. The aminoglycosides were separated by reversed-phase ion-pair chromatography on Zorbax C8 and ODS columns, and detected by the post-column derivatization technique. The calibration curves of serum concentration for sisomicin, netilmicin, astromicin, and micronomicin were linear over the ranges 0.32-22.8 micrograms/ml, 0.17-11.6 micrograms/ml, 0.1-6.3 micrograms/ml, and 1.0-30 micrograms/ml, respectively. The coefficients of variation were 2.5, 2.8, 3.1 and 1.9%, at the serum concentrations of 1.3, 1.45, 1.58 and 2.5 micrograms/ml, respectively (n = 6). Determination by the internal standard method using another aminoglycoside gives accurate and reproducible results. This method is applicable also to other aminoglycoside antibiotics.

[Pharmacokinetic prediction of the efficacy of using sisomicin in wound infections]

The pharmacokinetics of sisomicin in the blood, infection foci and urine of patients with wound infections was studied comparatively. Higher blood levels of the antibiotic after intravenous injection as compared to those after intramuscular injection provided its more intensive penetration into the tissues of the wound edges and bottom. After intravenous injection the sisomicin concentration in the tissues was sufficient for inhibition of the strains of Staphylococcus, E. coli and Ps. aeruginosa detected in the patients, while after intramuscular injection the antibiotic levels were sufficient only for inhibition of the first two causative agents. Comparison of the data on the sisomicin pharmacokinetics in the blood and tissues of the wounds provided the characteristics of the level of the drug penetration into the focus of the infection ("therapeutic availability"). Since the levels of sisomicin in the blood and infection foci were highly variable in different individuals. It is recommended that the antibiotic be used under the control of its concentrations in patients. It was shown that the data on the sisomicin renal excretion might be used for the purposes of the pharmacokinetic control.

The combined action of azlocillin and sisomicin in a model simulating the in vivo serum kinetics

The in vivo serum kinetics of azlocillin and sisomicin were simulated in a new in vitro test model. A strong synergistic effect against Pseudomonas aeruginosa resulted when both compounds were administered simultaneously and eliminated according to their individual half-life values, even when the decreasing drug concentrations exceeded the MICs for only a short period of time. When applied at intervals, neither pretreatment with azlocillin nor with sisomicin blocked the antibacterial activity of the combination partner.

[Build up of a given concentration of tobramycin and sisomycin in the blood of young children by the intravenous infusion of the antibiotics according to a calculated regimen]

Three regimens for intravenous infusion of tobramycin and sisomicin in doses of 1.33 and 1 mg/kg, respectively were analysed theoretically with the use of the constants of a two-compartmental model characterizing the tobramycin pharmacokinetics in adults. The regimen implied administration of the antibiotics by means of a 12-hour infusion. The second regimen consisted of a jet injection of the initial dose simultaneously with the beginning of the maintenance infusion. The third regimen consisted of a rapid initial infusion followed by a slow maintenance infusion. It was shown that maintenance of the drug concentration at the required levels, i.e. 2-8 microgram/ml for tobramycin and 2-61 microgram/ml for sisomicin was most safely provided by the regimen of the subsequent infusions. This regimen was tried clinically in the treatment of 17 children aged 2 months to 2.5 years with severe forms of acute pneumonia. The rate of the 25-minute initial infusion of tobramycin was 22.2 microgram/kg . min and that of the subsequent 2.7-hour maintenance infusion was 4.85 microgram/kg . min, the total dose being 1.33 mg/kg. The rate of the 20-minute initial infusion of sisomicin was 21.7 microgram/kg . min and that of the subsequent 2.4-hour maintenance infusion was 3.88 microgram/kg . min, the total dose being 1 mg/kg. It was shown that the levels of both the antibiotics in the blood serum of the patients were within the required ranges.

[Pharmacokinetics of a cefotetan and an aminoglycoside preparation in combined administration. 2. Absorption and exercise of cefotetan and sisomicin in dogs when the two are given together]

Cefotetan (20 mg/kg i.v.) and sisomicin (10 mg/kg i.m.) were administered alone or in combination to Beagle dogs. The mean plasma concentrations of cefotetan administered in combination with sisomicin at the above dosages were 98.0 microgram/ml at 5 minutes, 45.7 microgram/ml at 30 minutes and 3.46 microgram/ml at 4 hours. These plasma concentrations of cefotetan were similar to those of cefotetan administered alone to the corresponding dogs. The calculated plasma half-lives (T 1/2 beta) of cefotetan were 53.9 minutes in combination with sisomicin and 57.4 minutes alone. The excretion of cefotetan in dog urine were 52.4% and 50.2% of the dose after administration in combination with sisomicin and alone, respectively, during 24 hours. The results indicate that there were no significant differences in the pharmacokinetics of cefotetan alone or in combination with sisomicin in dogs. The maximum concentrations of sisomicin in dogs administered in combination with cefotetan were 20.2 microgram/ml at 30 minutes after dosing. The concentrations of 11.7 microgram/ml at 2 hours and 3.13 microgram/ml at 4 hours of administration were maintained in plasma. The calculated plasma half-lives of sisomicin were 68.8 minutes in combination with cefotetan and 86.4 minutes alone. The urinary rcoveries of sisomicin were 79.3% and 76.1% in combination with cefotetan and alone, respectively, during 24 hours. There were no significant differences in the pharmacokinetics of sisomicin alone and in combination with cefotetan in dogs.

[Elaboration of the procedures for the pharmacokinetic interpretation of aminoglycoside nephrotoxicity: the experimental evaluation of the safety of repeated gentamycin administration]

Nephrotoxicity and pharmacokinetics of gentamicin were studied on rats treated with the antibiotic for 30 days in doses of 6.25, 12.5 and 25 mg/kg administered daily. The pharmacokinetics of gentamicin and the time course of changes in the urea nitrogen levels of the blood serum were studied after the 1st, 5th, 8th and 30th injection. The analysis of the respective curves was used for calculation of the average integral values of the concentrations of the antibiotic (C) and urea nitrogen (E). After that the average integral values of these parameters ((CAVG and EAVG respectively) within the whole treatment couse with the use of every dose were calculated in the same way by using the curves of the dynamics of C and E changing. Comparison of the diagrams of E dependence on C for gentamicin and sisomycin showed that nephrotoxicity of sisomycin was 1.48 times higher than that of gentamicin.

[Rapid microbiological method of determining the gentamicin, sisomicin and kanamycin concentrations in patients' serum]

A modification of the microbiological agar-diffusion method for rapid determination of gentamicin, sisomycin and kanamycin levels in the blood serum of patients is described. The decrease in the time for determination of the antibiotic levels in the serum specimens with the modified method was provided by the use of a higher inoculation dose of the test microbe, higher levels of the incubation temperature and an enriched nutrient medium. The assay time was decreased from 18 to 3--4 hours as compared to the routine agar-diffusion method.

[Pharmacokinetic analysis of the nephrotoxic effect of sisomycin]

The kinetics of the urea nitrogen in serum was studied on anesthetized cats with constant concentrations of sisomycin in the blood. A correlation between the nephrotoxic effect of sisomycin and its concentration in the blood serum was found. High nephrotoxicity of sisomycin as compared to that of gentamicin, kanamycin or streptomycin under conditions of their equal levels in the blood was revealed on the basis of the above correlation. Still, when the antibiotic concentrations in the blood serum were maintained at the respective therapeutic levels, the nephrotoxic effects of sisomycin and gentamicin were almost equal. The above correlation was used for calculation of the maximum value of the sisomycin safe concentration in blood serum. The safe concentration of gentamicin in blood serum is 8 micrograms/ml, while that of sisomycin in 6 micrograms/ml. This approach may be used in estimation of safe concentrations for new aminoglycosides.

[Pharmacokinetic validation of the nephrotoxic action of sisomycin. The relationship between nephrotoxicity and sisomycin concentration in the blood serum of rats]

The kinetics of urine nitrogen in the blood serum and morphological changes in the kidneys after a single and repeated intramuscular administrations of the antibiotic in doses of 12.5 and 25 mg/kg a day were studied in Wistar rats. When sisomycin was administered in a dose of 12.5 mg/kg, the increase in the urine nitrogen level after 1--30 injections was reversible, whereas at a dose of 25 mg/kg it became irreversible already after the 5th injection. Maximum deviations in the urine nitrogen level observed within 3--6 hours after each injection of sisomicin were recorded after the 5th injection of the drug in a dose of 12.5 mg/kg and even after the 1st injection of the drug in a dose of 25 mg/kg. The deviations increased up to the 5th and 16th injection of sisomycin in doses of 12.5 and 25 mg/kg respectively. Later the deviations were less pronounced. Regardless of the dose, adipose degeneration in renal tubules was registered after 8--16 injections of the drug. By the 30th and 16th days of the drug administration in doses of 12.5 and 25 mg/kg respectively, the above changes also decreased. On the whole, pronounced functional and morphological changes in the kidneys correlated with the antibiotic dose. Relationship between the time from the beginning of sisomycin administration and the moment when the average integral concentration of the urine nitrogen increased to the upper limit of normal and the logarithm of the average integral concentration of the antibiotic in the serum was found. The safety of the clinical schemes for the use of sisomicin was estimated with the help of this relationship with respect to its nephrotoxic effect.

Data on sisomicin effect: human pharmacokinetic and bacteriological studies

Antibiotic sensitivity of bacteria cultured from 1020 pulmonological, medical and surgical cases was determined. Inhibitory effect on the bacterial growth was observed most frequently with sisomicin among the antibiotics of aminoglycoside type. Sisomicin levels were studied in the serum and lung tissue in 20 cases of pulmonary operations. Fifty to ninety minutes subsequent to an intramuscular administration of 1 mg sisomicin per 1 kg body weight, the serum levels amounted to 4.0 mcg/ml, whereas the apparently healthy, the inflamed and tumourous parts of the removed lung tissue contained 2.2, 1.2 and 0.2 mcg/g. The serum level remained unchanged even after 110-150 min, when the lung tissue levels were 3.0, 1.5 and 2.1 mcg/g. The sisomicin concentrations found in the lung tissue are of bactericid effect only against a part of the bacteria studied. This fact emphasizes the importance of exact indication and use of doses of sisomicin.

[Pharmacokinetic basis of the nephrotoxic action of sisomycin. The pharmacokinetics of sisomycin in single and multiple administrations to rats]

The pharmacokinetics of sisomicin was studied on Wistar rats. The antibiotic was used in single or repeated doses of 12.5 and 25 mg/kg. The kinetic data of the antibiotic titration in blood serum within 1 and 24 hours of intramuscular administration of the drug were formalized with the use of a linear two-compartment model. The average values of the elimination constant and the constants of sisomycin transfer from the central compartment into the peripheral one were 0.64, 0.34 and 0.13 hours-1 respectively. The value of the apparent distribution volume in the central compartment was 0.38 ml/kg and that of the stationary and kinetic distribution volumes was 1.37 and 3.06 1/kg respectively. The value of the general clearance was 0.24 1/(kg.hour) and that of the sisomicin half-life was 8.7 hours. Comparison of the antibiotic levels estimated with a model and actually measured in the blood after repeated administrations revealed the drug cumulation. When the antibiotic was used in a dose of 25 mg/kg daily, its cumulation was observed earlier (by the 5th--8th day) than on its use in a dose of 12.5 mg/kg (by the 30th day). Irrespective of the dose, sisomicin cumulation was accompanied by prolongation of the antibiotic half-life in the rats.

[Pharmacokinetic investigations on sisomicin in children (author's transl)]

Sisomicin is an aminoglycoside effective against gramnegative germs. The sensitiveness of coli, proteus, pseudomonas and klebsiella ranges from 0,1 to 0,4 mcg/ml. Germs with inhibition-values of up to 1 mcg/ml are certainly Sisomicin-sensitive. The side-effects of Sisomicin resemble those of other aminoglycosides, as for instance lesions of the VIIth cranial nerve and the kidney. Since aminoglycosides have a relatively small therapeutic range between toxicity and effective minimal-concentration, investigations are important especially in children. 66 children of different age groups received Sisomicin in doses of 3 mg/kg, 2 mg/kg and 1 mg/kg, and examined pharmacokineticly. Serum-levels were measured after 30 min 1, 2, and 4h, in some cases also after 6 and 8 h. In a separate group we determined the values after 5, 10, 15, 20, 30 and 40 min. The urinary output was controlled and the content of Sisomicin in meconium determined. Based on these results we recommend an individual, Sisomicin dosage for each age group. Clinically the Sisomicin proved to be well tolerated and effective antibioticum.

Nitroblue tetrazolium (NBT) reduction by bacteria employed for rapid determination of antibiotic concentrations in serum

The ability of bacteria to reduce nitroblue tetrazolium (NBT) to formazan, and the inhibition of this process by antibiotics, have been utilized in a method to determine antibiotic concentrations in serum. Escherichia coli, growing in the presence of increasing but subinhibitory concentrations of antibiotics, produces diminished amounts of formazan. This is photometrically quantified and the optical density obtained with the sample is compared with those obtained with know concentrations. Levels of aminoglycosides below 1 microgram/ml can be measured in the presence of other antibiotics also, and the assay can be carried out in three hours. Good correlation was obtained when 49 serum samples containing varying concentrations of sisomicin were tested simultaneously by the NBT assay and a disc diffusion method.

Ionic binding of aminoglycosides to human serum albumin in the absence of divalent cations. IV. Effect of structure, ph and concentration

The binding of sisomicin and streptomycin to human serum albumin was studied in the absence of divalent cations by means of the dialysis method. Hydrophobic bonds between albumin and sisomicin or streptomycin can be excluded by nuclear magnetic resonance measurements. The presence of hydrogen bonds is made unlikely according to the result that the binding of the aminoglycosides decreases with increasing number of OH groups in the aminoglycoside molecule. The pH dependence of protein binding suggests that ionic bonds are involved in the binding of aminoglycosides. On the basis of the concentration dependence of the albumin binding of sisomicin and streptomycin we determined the binding affinities delta F degrees, the binding constants K1, and the maximum number n of aminoglycoside molecules that can be bound by a molecule of albumin in the absence of Ca++ ions. The results were as follows: Sisomicin: delta F degrees = -4189 cal/mole, K1 = 900 1/mole, n = 12; Streptomycin: delta F degrees = 3512 cal/mole, K1 = 300 1/mole, n = 17.

Gas-liquid chromatographic method for the assay of aminoglycoside antibiotics in serum

A gas-liquid chromatographic (GLC) method is presented for the rapid analysis of gentamicin, tobramycin, netilmicin, and amikacin from human serum. This procedure may have application to all aminoglycoside drugs. The three isomers of gentamicin are resolved as two bands, while tobramycin, netilmicin, and amikacin appear in this system as single bands. Normal serum constituents do not interfere with chromatograms. Thus far, no assay interference has been found in cases where other drugs and antibiotics were administered concurrently with aminoglycoside therapy. Dose-response data demonstrating linear recovery are included for all four aminoglycosides as well as a comparison of the GLC method with the microbiological method for the assay of gentamicin and amikacin. Quantitation is based upon the relative response of the antibiotics to a fixed amount of the internal standards, either kanamycin A or paromomycin B. These standards are clearly resolved as symmetrical peaks from the antibiotics of assay interest. Isothermal chromatographic analysis time is less than 8 min, while total assay time per single serum specimen is approximately 50 min. Preparation of serum includes: precipitation, evaporative drying of the supernatant, a two-stage derivatization (N-trimethylsilylimidazole, N-heptafluorobutyrylimidazole), and a single hexane extraction with a water wash. The methodology described may be applied to the analysis of other compounds (e.g., saccharides, amino-saccharides, amino acids, etc.) which do not rapidly partition into an organic phase.

High-pressure liquid chromatographic assay of netilmicin in plasma

A high-pressure liquid chromatographic method for the quantitative determination of netilmicin in plasma was developed. The procedures involve acetonitrile protein precipitation, methylene chloride extraction, and dansylation to form the fluorescent dansyl derivative of netilmicin, which is extracted into ethyl acetate and chromatographed on a reverse-phase column with aqueous acetonitrile as the mobile phase. A good linear relationship between peak height measurements and netilmicin concentrations was found. This method is sensitive and reproducible; a netilmicin concentration as low as 0.5 mug/ml can be measured with only 0.1 ml of plasma sample. The results of assays of plasma or serum samples by this high-pressure liquid chromatographic method correlate well with those obtained by microbiological assays.

Pharmacokinetic study of netilmicin

Netilmicin at a dose of 2 mg/kg was infused intravenously into 10 healthy volunteers. A peak serum concentration of 16.56 mug/ml was obtained at the end of the infusion. Thirty-nine percent of the infused dose was excreted in the urine during the first 8 h after infusion. The pharmacokinetic parameters of netilmicin were derived by analyzing the elimination data according to a two-compartment model.

[Investigation of the c. s. fluid levels of two newer antibiotics; cefazolin and sisomicin (author's transl)]

In ten patients continuous estimations of the C.S.F. and serum levels were performed after the administration of a Cephalosporin derivative (Cefazolin - 4 cases) and a new alpha-amino-glycoside antibiotic (Sisomicin - 6 cases). After the evaluation of the results some doubts must be cast on the value of both these antibiotics for the treatment of meningitis or for per-operative chemo-prophylaxis in neurosurgical procedures. The values found were compared with those well-known in the literature, regarding the cephalosporins and the alpha-amino-glycoside Gentamycin.

125I radioimmunoassay of netilmicin

We report a radioimmunoassay for the new semisynthetic aminoglycoside netilmicin with a sensitivity of 480 pg per tube and a correlation coefficient of 0.94 between this radioimmunoassay and a microbioassay for measurement of netilmicin in serum.

Persistence of sisomicin and gentamicin in renal cortex and medulla compared with other organs and serum of rats

Aminoglycoside antibiotics seem to accumulate and persist in the kidney. For a better understanding of this problem, groups of six rats received a single 4 mg/kg i.p. injection of sisomicin and were sacrificed repeatedly from 30 min to 28 days later. Sisomicin concentrations (bioassay) decreased rapidly in the serum, lung and other tissues. There was only a trace at six hours. The situation was totally different for the kidney. Concentrations in the cortex increased up to six hours with a maximum of 99 mug/g, 11 times higher than the peak value in the serum then decreased very slowly to 56, 18, and 7 mug/g, 2, 14 and 28 days, respecitvely, after injection. The concentrations in the medulla were lower than in the cortex but also showed an accumulation and persistence. Similar results were observed with gentamicin. In another experiment, daily injections of sisomicin or gentamicin during seven days demonstrated that the concentrations of both antibiotics six hours after the last injection were nearly three times higher in the cortex and twice as high in the medulla than after a single injection. These data explain why the nephrotoxicity of sisomicin or gentamicin involves chiefly the cortex, increases with the length of the treatment and can persist for several weeks after the last injection. Therapeutic implications need further studies.

Biological activity of netilmicin, a broad-spectrum semisynthetic aminoglycoside antibiotic

Netilmicin (Sch 20569) is a new broad-spectrum semisynthetic aminoglycoside derived from sisomicin. Netilmicin was compared to gentamicin, tobramycin, and amikacin in a variety of in vitro test systems as well as in mouse protection tests. Netilmicin was found to be similar in activity to gentamicin against aminoglycoside-susceptible strains in both in vitro and in vivo tests. Netilmicin was also active against many aminoglycoside-resistant strains of gram-negative bacteria, particularly those known to possess adenylating enzymes (ANT 2') or those with a similar resistance pattern. Netilmicin was found to be markedly less toxic than gentamicin in chronic studies in cats, although gentamicin appeared less toxic in acute toxicity tests in mice. The concentrations of netilmicin and gentamicin in serum were compared in dogs after intramuscular dosing, and the pharmacokinetics including peak concentrations in serum were found to be similar.

[Enzymatic quick determination of aminoglycoside antibiotics in serum]

The therapeutic range of aminoglycoside antibiotics is relatively narrow; therefore short-term controls of serum concentrations can be recommended, particularly for high-dosage therapy and for renal insufficiency. For the aminoglycosides Amicacin, Gentamycin, Sisomicin and Tobramycin an enzymatic quick-determination test within 2 hrs is being described, which is based on the pH-deviation of a medium containing urea by hydrolytic activity of proteus mirabilis-bacteriae. In more than 180 measurements of patients' sera as well as of sera with known concentrations the method was tried out and compared with the conventional agar diffusion procedure. In strict compliance with the methodical directions, reproducable results could be achieved at any time within the range of1.0-30.0mug/ml; the number of faults in the quick-determination test was with +/- 8.4% about the same as in the agar diffusion test. In comparison with other microbiological or biochemical quick-procedures, the simplicity of the described method must be emphasized, thus it can be performed, too, in non-bacteriological laboratories.

[Pharmacokinetics and clinical observations of sisomicin, a newly developed aminoglycoside derivative (author's transl)]

In a randomized study of 12 healthy subjects the pharmacokinetics of gentamicin, sisomicin and tobramycin were determined after a one-hour infusion of each drug (1.0 mg/kg body-weight) four weeks apart. There were no pharmacokinetic differences of therapeutic significance between the three drugs. The mean serum concentrations at the end of infusion were 3.85 mug/ml for gentamicin and 4.66 mug/ml for sisomicin, falling to 0.12 and 0.26 mug/ml, respectively, after eight hours. The biological half-life varied between 96 and 122 min and the apparent volumes of distribution corresponded closely tothe size of the extracellular space. The antibacterial effectiveness, tolerance and modes of application were studied in 24 patients, most of them with urinary infection, at a dosage of 1.0 mg per kg body-weight two to three times daily. Good clinical results were achieved in 15, satisfactory ones in three, and in 16 the causative bacteria were eradicated. Sisomicin was well tolerated, except for minor and reversible renal (2 patients), hepatic (3 patients), and hearing (1 patient) disturbances.

Assay of aminoglycoside antibiotics in clinical specimens

Optimal therapeutic use of aminoglycoside antibiotics requires monitoring of levels in serum. Three methods have been developed for clinical use; one yields a specific 14C-labeled product, and two are microbiologic methods in which different indicator strains are used to measure the diffusion of drug into agar. These methods were compared in assays with 200 sera from patients receiving gentamicin or sisomicin. Some specimens also contained either a beta-lactam antibiotic or clindamycin. In the presence of penicillin or cephalosporin, the level of aminoglycoside measured was accurate if the specimens were treated with beta-lactamase. The presence of clindamycin invalidated the results when Bacillus subtilis was used as the indicator strain, but not with the other microbiologic method or the enzymatic method. Under proper circumstances, the results obtained by the various methods were comparable, according to statistical analysis. The enzymatic procedure is the most specific and rapid method, but materials for agar well diffusion methods are more readily available and more economical. The procedures are practical, and their use is recommended in patients being treated with aminoglycoside antibiotics.

Treatment with sisomicin of complicated urinary tract infections in patients with varying degrees of renal function impairment, pharmacokinetics and dosage adjustment

The efficacy, tolerance and pharmacokinetics of the new aminoglycoside antibiotic sisomicin, have been studied in 29 elderly male patients with varying degrees of renal function impairment and suffering from complicated urinary tract infections. The antibiotic was equally effective in patients with normal and impaired renal function and a cure (negative urine culture at one week follow-up) of 56% was obtained. There was little apparent toxicity with the dosage regimens used, although serum creatinine values were statistically but not clinically significantly increased in some patients following treatment. Serum half-lives of sisomicin were prolonged in cases of impaired renal function but accumulation of antibiotic could be prevented by varying dosing intervals between 8 and 24 hours based on serum creatinine values. There was good correlation between serum creatinine and sisomicin serum half-life values and a practical method is described for dose adjustment based on the relationship between serum half-lives and serum creatinine concentrations.

Improved acetylating radioenzymatic assay of amikacin, tobramycin, and sisomicin in serum

The acetylating radioenzymatic assay of aminoglycosides was modified by using [(3)H]acetyl coenzyme A as cosubstrate. This modification reduces the cost of the method by at least one-half without sacrificing rapidity or accuracy.