Comparison of amikacin lung delivery between AKITA® and eFlow rapid® nebulizers in healthy controls and patients with CF: A randomized cross-over trial

INTRODUCTION

Nebulization plays a key role in the treatment of cystic fibrosis. The Favorite function couple to jet nebulizers (AKITA®) emerged recently. The aim of this study was to assess the efficiency of the lung delivery by the AKITA® by comparing the urinary concentration of amikacin after nebulization with the AKITA® and the eFlow rapid®, in healthy subjects and patients with CF (PwCF).

METHOD

The two samples (healthy subjects and PwCF) were randomized (cross-over 1:1) for two nebulizations (500 mg of amikacin diluted in 4 mL of normal saline solution), with the AKITA® and with the eFlow rapid®. The primary endpoint was the amount of urinary excretion of amikacin over 24 h. The constant of elimination (Ke) was calculated based on the maximal cumulative urinary amikacin excretion plotted over time.

RESULTS

The total amount of urinary amikacin excretion was greater when AKITA® was used in PwCF (11.7 mg (8.2-14.1) vs 6.1 mg (3.7-13.3); p = 0.02) but not different in healthy subjects (14.5 mg (11.7-18.5) vs 12.4 mg (8.0-17.1); p = 0.12). The duration of the nebulization was always shorter with eFlow rapid® than with AKITA® (PwCF: 6.5 ± 0.6 min vs 9.2 ± 1.8 min; p = 0.001 - Healthy: 4.7 ± 1.3 min vs 9.7 ± 1.6 min; p = 0.03). The constant of elimination was similar between the two modalities in CF subjects (0.153 (0.071-0.205) vs 0.149 (0.041-0.182); p = 0.26) and in healthy subjects (0.166 (0.130-0.218) vs 0.167 (0.119-0.210), p = 0.25).

CONCLUSION

the Favorite inhalation is better to deliver a specific amount of drug than a mesh nebulizer (eFlow rapid®) in PwCF but not in healthy subjects.

Specific fluorometric assay for direct determination of amikacin by molecularly imprinting polymer on high fluorescent g-C3N4 quantum dots

Here, a specific and reliable fluorometric method for the rapid determination of amikacin was developed based on the molecularly imprinting polymer (MIP) capped g-C₃N₄ quantum dots (QDs). g-C₃N₄ QDs were obtained by facile and one-spot ethanol-thermal treatment of bulk g-C₃N₄ powder and showed a high yield fluorescence emission under UV irradiation. The MIP layer was also created on the surface on QDs, via usual self-assembly process of 3-aminopropyl triethoxysilane (APTES) functional monomers and tetraethyl ortho-silicate (TEOS) cross linker in the presence of amikacin as template molecules. The synthesized MIP-QDs composite showed an improved tendency toward the amikacin molecules. In this state, amikacin molecules located adjacent to the g-C₃N₄ QDs caused a remarkable quenching effect on the fluorescence emission intensity of QDs. This effect has a linear relationship with amikacin concentration and so, formed the basis of a selective assay to recognize amikacin. Under optimized experimental conditions, a linear calibration graph was obtained as the quenched emission and amikacin concentration, in the range of 3-400 ng mL^-1 (4.4-585.1 nM) with a detection limit of 1.2 ng mL^-1 (1.8 nM). The high selectivity of MIP sites as well as individual fluorescence properties of g-C₃N₄ QDs offers a high specific and sensitive monitoring method for drug detection. The method was acceptably applied for the measurement of amikacin in biological samples.

Effect of continuous positive airway pressure combined to nebulization on lung deposition measured by urinary excretion of amikacin

Continuous positive airway pressure (CPAP) is frequently used in patients attending emergency units. Its combination with nebulization is sometimes necessary in those patients presenting with a CPAP dependency.

STUDY OBJECTIVE

To compare lung deposition of amikacin delivered by a classical jet nebulizer (SideStream; Medic-Aid; West Sussex, UK) used alone (SST) or coupled to a CPAP device (Boussignac; Vygon; Belgium).

METHOD

Amikacin (1g) was nebulized with both devices in six healthy subjects during 5 min on spontaneous breathing. A 1-week wash-out period between each nebulization was applied. Lung deposition was indirectly assessed by urinary monitoring of excreted amount of amikacin.

RESULTS

Total daily amount of amikacin excreted in the urine was significantly lower with CPAP than with SST (1.97% initial dose versus 4.88% initial dose, p<0.001) with a corresponding mean ratio CPAP/SST of 0.41. The residual amount of amikacin in the nebulizer was higher with CPAP than with SST (607 mg versus 541 mg) but the difference was not significant (p=0.35).

CONCLUSION

These data suggest that the amount of amikacin delivered to healthy lungs is 2.5-fold lower with CPAP than with SST for the same nebulization time and that the nebulization time when using CPAP should be increased to reach the same amount of drug delivered with a classical jet nebulizer.

Determination of amikacin in body fluid by high-performance liquid-chromatography with chemiluminescence detection

A simple and sensitive method was developed for the quantification of amikacin in human plasma and urine samples. The method involves centrifugation of body fluid plasma after dilution with an ethanol/sodium carbonate mixture, and then an aliquot of the supernatant is directly injected into the chromatograph. After separation on a reversed-phase C18 column (runtime 20 min), aminoglycoside is detected on the basis of its complex formation reaction with Cu(II), the catalyst of the luminol/hydrogen peroxide chemiluminescence system. Using a volume of 500 microl biological sample, linearity is established over the concentration range 0.15-2.0 microg/ml and the limit of detection (LOD) is ca. 50 microg/l in plasma or urine. The intra-day and inter-day precision (measured by relative standard deviation, R.S.D.%) are always less than 9%, and relative recoveries are found to be over 92%.

Comparison of Lung Deposition of Amikacin by Intrapulmonary Percussive Ventilation and Jet Nebulization by Urinary Monitoring

The intrapulmonary percussive ventilation (IPV), frequently coupled with a nebulizer, is increasingly used as a physiotherapy technique; however, its physiologic and clinical values have been poorly studied. The aim of this study was to compare lung deposition of amikacin by the nebulizer of the IPV device (Percussionaire; Percussionaire Corporation; Sandpoint, ID) and that of standard jet nebulization (SST; SideStream; Medic-Aid; West Sussex, UK). Amikacin was nebulized with both devices in a group of five healthy subjects during spontaneous breathing. The deposition of amikacin was measured by urinary monitoring. Drug output of both devices was measured. Respiratory frequency (RF) was significantly lower when comparing the IPV device with SST (8.2 +/- 1.6 breaths/min vs. 12.6 +/- 2.5 breaths/min, p < 0.05). The total daily amount of amikacin excreted in the urine was significantly lower with IPV than with SST (0.8% initial dose vs. 5.6% initial dose, p < 0.001). Elimination halflife was identical with both devices. Drug output was lower with IPV than with SST. The amount of amikacin delivered to the lung is sixfold lower with IPV than with SST, although a lower respiratory frequency was adopted by the subjects with the IPV. Therefore, the IPV seems unfavorable for the nebulization of antibiotics.

Pharmacokinetic interactions of ceftazidime, imipenem and aztreonam with amikacin in healthy volunteers

The common usage of extended spectrum beta-lactams co-administered with amikacin in everyday clinical practice for infections by multidrug-resistant isolates has created the need to search for pharmacokinetic interaction. Eighteen healthy volunteers were enrolled in the study; six were administered 1g of ceftazidime singly intravenously or combined with 0.5 g of amikacin; six received 0.5 g of imipenem singly or combined with 0.5 g of amikacin and six 1g of aztreonam singly or combined with 0.5 g of amikacin. Blood and urine samples were collected at regular time intervals and apparent serum levels were determined by a microbiological assay. Co-administration of ceftazidime and amikacin resulted in higher C(max) and AUC for amikacin than when administered alone. Co-administration of imipenem and amikacin resulted in higher C(max) for imipenem than when administered alone. The tested interactions did not affect plasma half-life (t(1/2)) and clearance rate of any antimicrobial compared with its single administration. All tested drugs were mainly eliminated by glomerular filtration. It is concluded that co-administration of ceftazidime, imipenem or aztreonam with amikacin in healthy volunteers might affect C(max) and AUC without influencing any other pharmacokinetic parameter. The probable clinical endpoint is that giving ceftazidime, imipenem or aztreonam with amikacin might result in a transient elevation of beta-lactam serum levels without further affecting the complete pharmacokinetic profile of each drug as obtained after administration of the drug alone.

A simple tool for monitoring nebulized amikacin treatments based on a single urine assay

Aerosolized aminoglycosides have demonstrated their efficacy in the treatment of P. aeruginosa pneumonia in cystic fibrosis (CF) patients. There is wide interpatient variability in the deposited and systemic drug doses that depend on both the nebulization and inhalation conditions and result in a risk of inefficacy or toxicity. We have developed a tool to provide a simple method for individual dose monitoring by estimating the total quantity of amikacin excreted, which corresponds to the dose absorbed systemically. It is based on a single urine assay. Thirty-seven urinary pharmacokinetic time courses in healthy volunteers (groups A and B) or in CF patients (groups C and D) were used. The rules for extrapolating the total dose excreted on the basis of 6-, 8-, 10-, and 12-h urine samples, were determined from group A. The accuracy of these rules was then tested in the other three groups. The total amount excreted was poorly predictable, with a coefficient of variation (CV) of 36 and 30% in the healthy volunteers, and of 48 and 82% in the CF group, whereas the CV of the estimated amount, based on 8- to 12-h samples, was only 10-15% in the healthy volunteers and 4-8% in the CF patients. Collecting a single sample over an 8- to 12-h period requires overnight sampling. The very low circadian variations in renal function, ranging from -2% to +5%, demonstrated the absence of any significant bias resulting from overnight sampling. A single urine assay can therefore be proposed as a simple, noninvasive, low cost, and reliable method for the clinical monitoring of nebulized amikacin in CF patients. Further studies are needed before this method can be extended to aerosol treatments with other aminoglycosides.

Pharmacokinetics of amikacin in lactating goats

The pharmacokinetics of amikacin was studied in five lactating goats after single intravenous and intramuscular administrations of 7.5 mg kg-1 body weight. After intravenous injection, the plasma concentration-time curve of amikacin was characteristic of a two-compartment open model with a distribution half-life of 11.03 min and an elimination half-life of 114.81 min. The mean residence time was 142.96 min and the volume of the central compartment was 0.061 kg-1. Following intramuscular injection, amikacin was rapidly absorbed with an absorption half-life of 20.39 min. The peak plasma concentration was 34.48 micrograms ml-1 and was attained at 62.15 min. The elimination half-life of amikacin after intramuscular administration was 122.86 min and the corresponding mean residence time was 205.51 min. The systemic bioavailability of amikacin after intramuscular administration was 98.27%. Amikacin was not bound to plasma and milk proteins in vitro. Amikacin was detected only at low concentrations in the goat's milk 2-6 h after intravenous and intramuscular injections. Amikacin urine concentrations were much higher than those of plasma. Thus, amikacin is likely to be efficacious in the eradication of many Gram-negative urinary tract pathogens.

Pharmacokinetics and urinary excretion of amikacin in low-clearance unilamellar liposomes after a single or repeated intravenous administration in the rhesus monkey

Liposomal aminoglycosides have been shown to have activity against intracellular infections, such as those caused by Mycobacterium avium. Amikacin in small, low-clearance liposomes (MiKasome) also has curative and prophylactic efficacies against Pseudomonas aeruginosa and Klebsiella pneumoniae. To develop appropriate dosing regimens for low-clearance liposomal amikacin, we studied the pharmacokinetics of liposomal amikacin in plasma, the level of exposure of plasma to free amikacin, and urinary excretion of amikacin after the administration of single-dose (20 mg/kg of body weight) and repeated-dose (20 mg/kg eight times at 48-h intervals) regimens in rhesus monkeys. The clearance of liposomal amikacin (single-dose regimen, 0.023 +/- 0.003 ml min-1 kg-1; repeated-dose regimen, 0.014 +/- 0.001 ml min-1 kg-1) was over 100-fold lower than the creatinine clearance (an estimate of conventional amikacin clearance). Half-lives in plasma were longer than those reported for other amikacin formulations and declined during the elimination phase following administration of the last dose (from 81.7 +/- 27 to 30.5 +/- 5 h). Peak and trough (48 h) levels after repeated dosing reached 728 +/- 72 and 418 +/- 60 micrograms/ml, respectively. The levels in plasma remained > 180 micrograms/ml for 6 days after the administration of the last dose. The free amikacin concentration in plasma never exceeded 17.4 +/- 1 micrograms/ml and fell rapidly (half-life, 1.47 to 1.85 h) after the administration of each dose of liposomal amikacin. This and the low volume of distribution (45 ml/kg) indicate that the amikacin in plasma largely remained sequestered in long-circulating liposomes. Less than half the amikacin was recovered in the urine, suggesting that the level of renal exposure to filtered free amikacin was reduced, possibly as a result of intracellular uptake or the metabolism of liposomal amikacin. Thus, low-clearance liposomal amikacin could be administered at prolonged (2- to 7-day) intervals to achieve high levels of exposure to liposomal amikacin with minimal exposure to free amikacin.

A population approach to the forecasting of amikacin plasma and urinary levels using a prescribed dosage regimen

We retrospectively analyzed amikacin pharmacokinetics in 19 critically ill patients who received amikacin intravenously. Fourteen subjects (577 serum amikacin concentrations, 167 urine measurements) were studied to obtain data for population modeling, while 5 patients (267 serum amikacin concentrations, 68 urine measurements) were studied for the assessment of predictive performance. The population analysis was performed using serum and urine amikacin measurements; the renal clearance of amikacin was expressed as a function of creatinine clearance. A two-compartment model was fitted to the population data by using NONMEM. The population characteristics of the pharmacokinetic parameters (fixed and random effects) were estimated using the FOCE method. The population pharmacokinetic parameters with the interindividual variability (CV%) were as follows: slope (0.254, 126%) and intercept (3 l/h, 59.6%) of the linear model which relate the amikacin renal clearance to the creatinine clearance, initial volume of distribution (17.1 l, 22.2%), intercompartment clearance (5.22 l/h, 104%), steady state volume of distribution (55.2 l, 64.1%) and urinary elimination (67.5%, 36.3%). The Bayesian approach developed in this study accurately predicts amikacin concentrations in serum and urine and allows for the estimation of amikacin pharmacokinetic parameters, minimizing the risk of bias in the prediction.

The disposition kinetics, urinary excretion and dosage regimen of amikacin in cross-bred bovine calves

The disposition kinetics, urinary excretion and dosage regimen of amikacin after a single intravenous administration of 10 mg/kg was investigated in six cross-bred bovine calves. At 1 min, the concentration of amikacin in the plasma was 116.9 +/- 3.16 micrograms/ml and the minimum therapeutic concentration was maintained for 8 h. The elimination half-life and volume of distribution were 3.09 +/- 0.27 h and 0.4 +/- 0.03 L/kg, respectively. The total body clearance (ClB) and T/P ratio were 0.09 +/- 0.002 L/kg/h and 4.98 +/- 0.41, respectively. Approximately 50% of the total dose of amikacin was recovered in the urine within 24 h after administration. Amikacin in concentrations ranging from 5 to 150 micrograms/ml bound to plasma proteins to the extent of 6.32% +/- 0.42%. A satisfactory intravenous dosage regimen of amikacin in bovine calves would be 13 mg/kg followed by 12 mg/kg at 12 h intervals.

Lack of pharmacokinetic interaction between cefepime and amikacin in humans

The interaction potential between cefepime and amikacin was investigated in a steady-state pharmacokinetic study in 16 healthy male subjects. Eight subjects (group A) received a first course of 2,000 mg of cefepime; this was followed by a second course of 2,000 mg of cefepime with 300 mg of amikacin and a third course of 2,000 mg of cefepime. Eight other subjects (group B) received a first course of 300 mg of amikacin, a second course of 300 mg of amikacin with 2,000 mg of cefepime, and a third course of 300 mg of amikacin. Each course consisted of four consecutive doses administered every 8 h as 30-min intravenous infusions. Serial plasma and urine samples, which were collected after administration of the fourth dose of each course, were assayed for cefepime and/or amikacin by validated high-performance liquid chromatographic assays. Trough levels of cefepime and amikacin indicated that these antibiotics attained a steady state prior to administration of the fourth dose of each course. Key pharmacokinetic parameters for each antibiotic were determined by noncompartmental methods. The peak concentrations of cefepime and amikacin in plasma when the drugs were given alone were about 160 and 27 micrograms/ml, respectively. Levels of each antibiotic in plasma declined, with an apparent half-life of approximately 2.2 h. Urinary recovery of cefepime and amikacin accounted for more than 85% of the administered dose of each antibiotic. Mean renal clearances for cefepime and amikacin ranged from 79 to 95 ml/min and suggested that glomerular filtration is the primary excretion mechanism. The results of the statistical analyses indicated that the pharmacokinetic parameters of cefepime following the concurrent administration of amikacin and following the discontinuation of the amikacin following the concurrent administration of cefepime and following the discontinuation of the cefepime therapy were not significantly altered. Cefepime and amikacin can be coadministered to patients with normal renal function by using the standard recommended dosing regimens.

High-performance liquid chromatographic assays for the quantification of amikacin in human plasma and urine

Amikacin, an aminoglycoside antibiotic, is frequently coadministered with penicillins and broad-spectrum cephalosporins to synergize the activity of these agents. Sensitive, selective and reproducible high-performance liquid chromatographic assays have been developed for the quantification of amikacin in plasma and urine collected from human subjects. The plasma method involves the ultrafiltration of plasma prior to derivatization. An aliquot of plasma ultrafiltrate or urine is mixed with dimethyl sulfoxide and tris(hydroxymethyl)aminoethane followed by derivatization of amikacin with 1-fluoro-2,4-dinitrobenzene at 58 degrees C for 30 min. The reaction mixture is then injected directly onto a reversed-phase C18 column preceded by a guard column. The column is eluted with a mobile phase containing acetonitrile and 2-methoxyethanol in 1% Tris buffer. Amikacin derivative is detected at 340 nm. The methods were applied for the analysis of amikacin in plasma and urine samples from volunteers receiving amikacin and cefepime, a fourth-generation cephalosporin, in a clinical pharmacokinetic drug interaction study.

Treatment of disseminated Mycobacterium avium complex infection of beige mice with liposome-encapsulated aminoglycosides

Free and liposome-encapsulated amikacin are active in vitro against intracellular Mycobacterium avium complex (MAC). To examine whether liposome-encapsulated aminoglycosides might kill intracellular MAC more effectively in vivo, beige mice were infected with MAC strain 101 (serotype 1) and after 1 week were treated intravenously every other day (5 doses total) with amikacin liposomes (0.2, 1, or 4 mg/dose), amikacin solution (0.2, 1, or 2 mg), gentamicin liposomes or gentamicin solution (0.2 or 1 mg), placebo liposomes (without aminoglycosides), or buffer. Amikacin and gentamicin liposomes significantly reduced bacterial counts in blood, liver, and spleen (98.5%, 92.7%, and 92.8%, respectively, for the 1-mg dose of amikacin and 92.8%, 99.7%, and 99.4% for gentamicin; 95.7%, 69.7%, and 89.1%, respectively, for the 0.2-mg dose of amikacin and 49.9%, 76.7%, and 89.1% for gentamicin) compared with placebo liposomes and buffer. Equivalent doses of free drug were not associated with significant decreases in viable bacteria. Thus, aminoglycoside liposomes improved bactericidal effects over conventional treatment in disseminated MAC infection, offering potential application in treating MAC infection in humans.

Serum bactericidal activity and postantibiotic effect in serum of patients with urinary tract infection receiving high-dose amikacin

Ten patients received a 30-min infusion of amikacin (30 mg/kg) on day 1 and 15 mg/kg on day 2. Mean serum creatinine was 1.1 +/- 0.3 (standard deviation) mg/dl before and 1.0 +/- 0.3 mg/dl 3 days after the second infusion. Mean serum amikacin concentrations before, at the end of infusion, and 1, 6, 12, and 24 h after 30 and 15 mg/kg were 0, 157, 79, 31, 16, 5, 5, 85, 51, 19, 12, and 5 mg/liter, respectively. Five strains each of Staphylococcus aureus, Staphylococcus epidermidis susceptible and resistant to oxacillin, Streptococcus (Enterococcus) faecalis, corynebacterium sp. strain JK, Listeria monocytogenes, Mycobacterium fortuitum (three strains), Klebsiella pneumoniae, Serratia marcescens, Acinetobacter calcoaceticus, and Pseudomonas aeruginosa were tested. Serum bactericidal activities (SBAs) were greater than or equal to 1:8 in greater than or equal to 80% of the sera 1 and 6 h after 30 mg/kg and in greater than or equal to 60% of the sera 1 and 6 h after 15 mg/kg against Staphylococcus aureus and Staphylococcus epidermidis susceptible to oxacillin, A. calcoaceticus, and K. pneumoniae. L. monocytogenes, Serratia marcescens, and P. aeruginosa had lower SBAs. Very low or no activity was observed against oxacillin-resistant staphylococci and Streptococcus faecalis. The study of the killing rate in serum confirmed these results. Postantibiotic effect was studied by incubating a strain from each species in serum samples obtained 1 and 6 h after both regimens for 0.5, 1, or 2 h. The duration of postantibiotic effect depended on the duration of contact and the concentration of amikacin for the following organisms: oxacillin-susceptible staphylococci, L. monocytogenes, P. aeruginosa, A. calcoaceticus, K. pneumoniae, and Serratia marcescens. M. fortuitum was killed after 30 min of contact. No postantibiotic effect was observed with Streptococcus faecalis, Corynebacterium sp. strain JK, or oxacillin-resistant staphylococci. Amikacin at 30 mg/kg provided high levels and SBAs against susceptible pathogens. Prolonged postantibiotic effects were observed. No signs of nephrotoxicity occurred.

[Toxicological studies on isepamicin (HAPA-B). VII. Chronic intramuscular test in the rat]

Chronic toxicity in the rat of isepamicin (HAPA-B), a new aminoglycoside antibiotic, was examined in comparison with amikacin (AMK). Daily doses of 3.125, 6.25, 25 and 100 mg/kg of HAPA-B or 25 and 100 mg/kg of AMK were injected intramuscularly for 6 months, and recovery test was carried out for 2 months after discontinuing the drug. No animal died and there were no changes in general symptoms except for hemorrhage of injection sites of both drugs. Decreases in body weight gain and food consumption were observed in 100 mg/kg dose group of either drug. Water consumption was markedly increased in males of the AMK 100 mg/kg dose group during administration and recovery periods. Decreases in erythrocytes, hematocrit and hemoglobin were observed in 100 mg/kg dose group of either drug. These decreases seemed to be due to renal injury. An increase in the number of platelets was also observed. This was likely caused by the hemorrhage at injection sites. These changes persisted into the recovery period. Elevation of BUN was observed in the 100 mg/kg dose group of either drug. Its value in the AMK 100 mg/kg dose group was markedly higher than that in the HAPA-B 100 mg/kg dose group and did not decrease back to the normal values even during the recovery period. An increase of urine volume and a decrease of urine specific gravity were observed in males in the 100 mg/kg group of either drug. Furthermore, NAG was elevated in a dose-dependent manner from 25 mg/kg with both drugs. The weight of kidney increased dose-relatedly and significantly in groups administered with 25 mg/kg or more of either drug and weight of caecum increased dose-relatedly and significantly in groups administered with 6.25 mg/kg or more of HAPA-B or 25 mg/kg or more of AMK. Discoloration and enlargement of the kidney occurred in a dose-dependent manner as observed by necropsy. Eosinophilic granular degeneration, swelling, fatty degeneration, necrosis, calcification in the epithelial cells of the proximal convoluted tubuli, and thickenings of Bowman'S capsule and tubular basement membrane were observed at 25 and 100 mg/kg dose groups of either drug. In recovery periods, after the necrosis disappeared, calcification and regeneration were observed in epithelial cells. Electron microscopic findings showed an increase in the number of large lysosomes containing myeloid bodies in the epithelial cells of the proximal convolute tubuli with either drug.(ABSTRACT TRUNCATED AT 400 WORDS)

Renal disposition of gentamicin, dibekacin, tobramycin, netilmicin, and amikacin in humans

The tubular disposition of five aminoglycosides was studied in humans to establish a possible relationship between tubular reabsorption and the nephrotoxicity that has been described in the literature. Thirty-three healthy male volunteers received a continuous intravenous infusion of isotonic saline with inulin, followed 1 h later by inulin plus gentamicin, dibekacin, tobramycin, netilmicin, or amikacin (1 mg/kg per h) or amikacin (4 mg/kg per h) over a period of 2 h. Brain-stem-evoked response audiometry was performed both before and at the end of each infusion. The latency of wave V remained constant whichever antibiotic was considered. The glomerular filtration rate did not vary significantly during the infusion of each drug. The percent fractional excretion was 79 +/- 6, 81 +/- 22, 85 +/- 5, and 99 +/- 9 for gentamicin, dibekacin, tobramycin, and netilmicin, respectively, and 83 +/- 4 and 124 +/- 13 for amikacin at concentrations of 1 and 4 mg/kg per h, respectively. Net balance and renal clearance were similar for the five aminoglycosides when administered at a rate of 1 mg/kg per h. With gentamicin only, fractional excretion was correlated with the urinary flow rate. We can conclude that (i) gentamicin, generally considered the most nephrotoxic agent, had the highest degree of net reabsorption; (ii) netilmicin exhibited a net zero tubular balance; (iii) amikacin had different patterns of tubular disposition according to the dose, i.e., reabsorption at 1 mg/kg per h and secretion at 4 mg/kg per h, raising the hypothesis of a saturable process of reabsorption; and (iv) these differences in tubular reabsorption could account at least in part for the known different nephrotoxic potentials of these five aminoglycosides in humans.

Influence of dose in the urinary excretion of amikacin

The urinary excretion kinetics of amikacin was studied in 28 healthy volunteers who received doses of 125, 250 and 500 mg of the antibiotic. The average percentages of the dose excreted were 67.67, 79.4 and 68.65% for each dose, respectively. The elimination constant (Ke), the urinary excretion constant (Ku) and the extra-renal excretion constant (Knr) had similar values for the three groups studied. The average value obtained for Knr showed the existence of a moderate extra-renal excretion of amikacin. A linear relationship was observed between the maximum excretion rate (Vmax) and the dose administered (D), according to the equation: Vmax (mg/h) = 3.714 + 0.207 X D (mg); r = 1.000 This relationship reveals the linear kinetics of renal excretion in the dose range studied. In view of the high urinary concentrations obtained, it is concluded that amikacin doses of 4 mg/kg/day should ensure therapeutic urinary concentrations sufficient to combat most amikacin-susceptible organisms.

[Amikacin concentration in the severely obstructed urinary tract]

Urinary amikacin concentration was determined in 9 patients with severely unilateral ureteral obstruction. Serum levels were within the normal range. The average concentration of amikacin in the urine from obstructed urinary tract was 118.9 mcg/ml 6 hours after 100 mg amikacin iv infusion. Urine concentration from the normal kidney was 155.9 mcg/ml at the first 2 hours after intravenous infusion, 98.8 at the second 2 hours 83.3 at the third 2 hours. Urinary amikacin excretion from severely obstructed urinary tract was about one third of the total excretion from a normal system. In summary, the urinary level in severely obstructed urinary tract after iv infusion of 100 mg amikacin may be enough prophylactically. But at the onset of infection in severely obstructed urinary tract, the administration of at least 200 mg amikacin intravenously is required.

Urine concentrations of gentamicin, tobramycin, amikacin, and kanamycin after subcutaneous administration to healthy adult dogs

Gentamicin, tobramycin, amikacin, and kanamycin were given subcutaneously in separate trials to healthy adult dogs of both sexes. Daily dosage levels were as follows: gentamicin, 6.6 mg/kg of body weight; tobramycin, 3 mg/kg; amikacin, 15 mg/kg; and kanamycin, 11 mg/kg. Gentamicin, tobramycin, and amikacin were given in divided doses of 8-hour intervals for 5 consecutive 8-hour periods, whereas kanamycin was given in divided doses at 12-hour intervals for 4 consecutive 12-hour periods. Mean 8-hour urine concentrations +/- 1 SD were gentamicin, 107 +/- 33 microgram/ml, tobramycin, 66 +/- 39 microgram/ml; and amikacin, 342 +/- 153 microgram/ml. Mean urine concentrations (+/- 1 SD) for kanamycin were 473 +/- 306 microgram/ml in urine collected between 0 and 6 hours after dosing and 63 +/- 47 microgram/ml in urine collected 6 to 12 hours after dosing.

Prediction of creatinine clearance from serum creatinine concentration based on lean body mass

An equation for predicting endogenous creatinine clearance (CrCl) in adults and children (with both stable and unstable renal function) from serum creatinine concentration is presented. The predictions are compared with four other available estimating methods, bases on values in 110 subjects with renal impairment of widely differing degrees. In patients with stable and with unstable renal function the corelaion between measured and predicted CrCl was better with the new equation. In patients with rapid changing renal function the new equation resulted in accurate predictions CrCl within a few hours after the change, as opposed to several with the other methods. The elimination rate constant of the aminoglycoside antibiotic amikacin correlated more precisely with CrCl values estimated from the new equation that with those measured doing 24 hr or with the other prediction methods.

Management of amikacin overdose

A woman with subarachnoid hemorrhage inadvertently received 18 g of amikacin over a 4-hr period, 20 times the recommended total daily dose. Intravenous fluids were administered to expedite renal excretion of the amikacin, and a peritoneal dialysis was performed to augment drug elimination. Drug levels were measured sequentially in serum, urine, and peritoneal dialysate. Renal clearance of the drug was increased compared to clearance following a standard dose and the drug was rapidly excreted in the urine. Amikacin was not detected in the peritoneal dialysate. There were no apparent toxic effects from the overdose. A patient with normal renal function who receives a potentially toxic dose of amikacin can be appropriately managed by careful hydration and maintenance of a generous diuresis.

[Delayed elimination of aminoglycoside antibiotics: importance for clinical use]

In 7 patients the elimination of amikacin (4), tobramycin (1) and gentamicin (2) in serum and urine was measured over several days after cessation of therapy. All three aminoglycosides showed multicompartmental pharmacokinetics with a terminal half life ranging between 46 and 150 hours. Using computer simulations, it is shown that slow drug accumulation in the body is to be expected during multiple dose therapy. Therefore, the indiscriminate use of these drugs should be avoided and the duration of therapy kept as short as possible.

Serum levels and urinary concentrations of kanamicin, bekanamicin and amikacin (BB-K8) in diabetic children and a control group

Serum levels of kanamicin, bekanamicin, and amikacin were studied, after a single intramuscular dose of each antibiotic, in three groups of diabetic children, with their respective normal controls, paired by age, weight and sex. Lower serum levels were observed with kanamicin and bekanamicin in diabetic children compared to their controls. The difference in low serum levels was less noticeable with amikacin.

Pharmacokinetics of amikacin in patients with normal or impaired renal function: radioenzymatic acetylation assay

The acetylating radioenzymatic assay was used for determination of levels of amikacin in serum and urine. Because of an inhibitor present in various amounts in urine, assay of amikacin in urine by this method requires added internal standards and thus is less precise than the assay in serum. Determination of the rate of plasma clearance, half-life, and volume of distribution of amikacin in 10 patients with normal renal function, four patients undergoing dialysis, and five patients with end-stage renal diseases have shown a relation of half-life (t1/2 in hr) to rate of clearance of serum creatinine (Cer) of t1/2 = 3 X Cer, the same relation as found for kanamycin and gentamicin. The apparent steady-state volume of distribution of amikacin in patients with diminished renal function is slightly, but not significantly, larger than that in normal patients; the values were 0.28 +/- 0.10 and 0.21 +/- 0.10, respectively. In normal patients, 87% of the drug is excreted by the kidney.

Clinical pharmacology of amikacin and kanamycin

During and after a 4-hr intravenous infusion of amikacin and kanamycin in a cross-over study in healthy adult male volunteers, average concentrations of drug in serum were similar, with half-lives of approximately 2 hr. Apparent volumes of distribution at the steady state averaged 30% of body weight, and the rate of renal clearance was less than the rate of creatinine clearance (83 vs. 120 ml/min), a finding that indicates tubular reabsorption. The rate of serum clearance was greater than the rate of renal clearance (100 vs 83 ml/min). Urinary excretion in 24 hr averaged 94% of the dose, and there was no binding of serum proteins. In another cross-over study, volunteers received single intramuscular injections of these antibiotics. Peak concentrations of drug in serum after 45 min to 2 hr averaged 19.9 and 19.0 mug/ml for amikacin and kanamycin, respectively. Serum half-lives between 4 and 8 hr after administration of drug were 2 hr, and an average of 94% of the dose was recovered in the urine in 24 hr. Thus, the pharmacologic properties of amikacin and kanamycin were virtually identical.

Pharmacokinetics of amikacin in patients with impaired renal function

Pharmacokinetic parameters were determined after a single intramuscular injection of 7.5 mg of amikacin/kg to 10 volunteers with impaired renal function (creatinine clearance rate, 2.2-65ml/min per 1.73 m2) and to six volunteers with normal renal function. The mean peak concentrations of amikacin in sera of the two groups did not differ significantly from each other and exceeded by two to five times the reported in vitro minimal inhibitory concentrations for the majority of Pseudomonas aeruginosa and Enterobacteriaceae strains. There was a significant linear relation between the elimination rate constant of amikacin and the rate of creatinine clearance; there was a significant nonlinear relation between the half-life of amikacin and the serum creatinine concentration. Knowledge of these relations may aid in adjustment of the dosage of amikacin in patients with impaired renal function, especially when such information is used in conjunction with serum assays of amikacin.

Pharmacokinetics of amikacin in patients with renal insufficiency: relation of half-life and creatinine clearance

The half-life of amikacin after a single intramuscular injection was determined in patients with severe renal failure who received 3.75 mg of drug/kg and in patients with various degrees of renal function who received 7.5 mg of drug/kg. The relation of the half-life of amikacin to levels of serum creatinine is practically identical to that of kanamycin. However, although concentrations of serum creatinine remained practically unchanged, rates of creatinine clearance may by considerably decreased in older subjects. This decrease may result in overestimation of the rate of glomerular filtration and subsequent overdosage. Therefore, the half-life of amikacin should be derived from values of rates of creatinine clearance or be predicted with use of a nomogram. The calculated half-life values may be used for development of appropriate dosage schedules for patients with various degrees of renal function. Such schedules would ensure therapeutic levels of drug and avoid potentially toxic accumulation of antibiotic.