Aminoglycoside nephrotoxicity in critically iii surgical patients

Renal effects of gentamicin in chronic bile duct ligated rats

Patients with advanced cirrhosis and rats with short-term bile duct ligation (BDL) are prone to develop nephrotoxicity from aminoglycosides. In this study, we characterized the renal response to gentamicin in rats with chronic BDL. BDL and sham-operated (SO) rats were given gentamicin (20 and 40 mg/kg/d) for 7 consecutive days, starting on the 18th postoperative day. Administration of gentamicin to SO group caused a decrease in cortical and medullary prostaglandin E(2)(PGE(2)) generation. However, mild reduction in creatinine clearance and an increase in fractional excretion of sodium occurred only in the BDL rats given the high gentamicin dose. This was accompanied by a reduction in cortical and medullary PGE(2) generation and a reduction in plasma nitric oxide production. In conclusion, gentamicin administration to rats with chronic BDL causes impairment of renal function. This happens only after the occurrence of simultaneous multiple insults to the renal protective mechanisms.

Assessment of the enzymuria resulting from gentamicin alone and combinations of gentamicin with various beta-lactam antibiotics

OBJECTIVE

To determine the propensity of beta-lactam antimicrobials to ameliorate or potentiate aminoglycoside-induced renal enzymuria.

DESIGN

Two open, randomized, double-blind, parallel-group studies were conducted in young, healthy, male volunteer subjects. Using a common protocol, 24-hour urine collections were analyzed for the renal tubular enzymes alanine aminopeptidase (AAP) and N-acetyl-beta-D-glucosaminidase (NAG), as well as for creatinine. Antimicrobial combinations studied included gentamicin plus placebo and gentamicin plus ticarcillin/clavulanate (protocol 1); and gentamicin plus placebo, gentamicin plus piperacillin, and gentamicin plus ceftazidime (protocol 2). The antimicrobial regimens were administered for 7 days. Eight subjects completed each treatment group.

RESULTS

There were no significant differences between treatment groups with regard to urine creatinine excretion or serum gentamicin concentrations in either protocol. Enzymuria (AAP [p = 0.039] and NAG [p = 0.337]) was decreased in the gentamicin plus ticarcillin/clavulanate treatment compared with that in the gentamicin plus placebo treatment. Increased enzymuria, as indicated by increased urine concentrations of AAP and NAG, was observed in the gentamicin plus ceftazidime treatment (p < 0.05) compared with the other two treatments.

CONCLUSIONS

Based on relative enzymuria, ticarcillin/clavulanate may be renal protective. Piperacillin neither potentiated nor ameliorated aminoglycoside-induced enzymuria. Since acute elevations in AAP and NAG reflect insults to the kidney, these studies suggest that ceftazidime may enhance aminoglycoside-induced renal injury. Piperacillin had no effect on enzymuria and would appear not to enhance or protect against aminoglycoside-induced renal injury.

Gentamicin-induced nephrotoxicosis in lambs

Lambs injected with gentamicin sulphate remained bright and continued to eat, but their plasma creatinine and urinary microprotein concentrations and activities of alkaline phosphatase, gamma glutamyltransferase, leucine aminopeptidase, and N-acetyl-beta-glucosaminidase were significantly increased. Urinary creatinine and specific gravity were significantly decreased. The kidneys of lambs killed shortly after the last treatment with gentamicin were pale and oedematous and microscopic changes included marked tubular necrosis and dilation. Mild tubular dilation was the only lesion in lambs killed later. Reduced enzyme activity was observed histochemically in cells of the convoluted tubules. The lambs showed little clinical evidence of gentamicin toxicity, but the urinary enzyme activity and protein content were sensitive and reliable markers of renal injury, in agreement with the pathological findings. The lesions were different from those reported in naturally occurring tubular nephrosis of lambs.

Gray-scale sonographic characterization of aminoglycoside-induced nephrotoxicosis in a canine model

RATIONALE AND OBJECTIVES

The diagnostic usefulness of gray-scale sonography was evaluated in a canine model of aminoglycoside-induced nephrotoxicosis.

METHODS

Sonography was performed before and during the onset and progression of nephrotoxicosis induced by administration of a toxic dosage of gentamicin. Subjective visualization of increased renal cortex echogenicity (IRCE) was objectified with digital image analysis methods. Results of both subjective and objective evaluation were correlated with clinicopathologic tests and renal cortex biopsy obtained concurrently.

RESULTS

Subjective visualization of IRCE was associated with significant nephrotoxicosis and was superior to serum creatinine elevation in nephrotoxicity detection. Objective detection of IRCE improved nephrotoxicity detection sensitivity to that of increased urine enzymuria.

CONCLUSIONS

Based on the above results, subjective visualization of IRCE in patients with aminoglycoside-induced nephrotoxicity may occur before azotemia and is suggestive of significant renal dysfunction; application of digital image analysis methods may lead to earlier sonographic recognition of nephrotoxicity.

Pharmacoeconomic evaluation of once-daily aminoglycoside treatment

A special topic in pharmacoeconomics concerns antimicrobial therapy. The cost of antimicrobial therapy and an economic evaluation of aminoglycoside antibiotics in the last 30 years are reviewed. Some innovative approaches have been found to be effective in the control of the use of aminoglycosides and those are: 1) selecting the appropriate aminoglycoside, 2) therapeutic drug monitoring and, 3) once-daily administration. The practical advantages of once-daily aminoglycoside dosing are discussed and the conclusion is that combination therapy continues to be a mainstay in several serious Gram-negative infections. Concerns about breakthrough infection with extended aminoglycoside dosing intervals can be resolved by combination with a betalactam antibiotic. The lower costs associated with once-daily aminoglycoside dosing are the consequence of a straightforward dosage calculation, a guaranteed peak serum concentration in the therapeutic range, potential reduction in treatment period, easier quality control of preparation and administration, decreased personnel time, and fewer assays. However, some practical considerations remain unanswered.

Aminoglycoside-associated nephrotoxicity in extrahepatic obstructive jaundice

Experimental data demonstrate that biliary obstruction increases renal sensitivity to gentamicin. In the present study the incidence of and risk factors for aminoglycoside nephrotoxicity were prospectively studied in patients with extrahepatic obstructive jaundice. Two hundred and thirty-seven hospitalized adult patients were classified into three groups. Group I consisted of 84 patients with extrahepatic obstructive jaundice, who received aminoglycoside (gentamicin or tobramycin). Group II consisted of 81 patients with extrahepatic obstructive jaundice, who received either antibiotics other than aminoglycoside or no antimicrobial therapy. Group III consisted of 72 noncholestatic patients receiving aminoglycosides for different disorders. Nephrotoxicity developed in 27 patients (32%) in group I vs 9 patients (11%) in group II and 4 patients (5.6%) in group III (p < 0.00001). In group I, a comparison of patients with and without nephrotoxicity revealed significantly higher values in the former for mean serum bilirubin concentration, initial steady-state trough aminoglycoside concentration and estimated half-life. Stepwise multivariate analysis with nephrotoxicity status as the dependent variable determined that the most significant variable for predicting nephrotoxicity was serum total bilirubin level. In extrahepatic cholestasis a high serum bilirubin level is a distinct factor predisposing to aminoglycoside nephrotoxicity.

The effect of verapamil on the nephrotoxic potential of gentamicin as measured by urinary enzyme excretion in healthy volunteers

The effects of verapamil on the nephrotoxic potential of multiple-dose gentamicin were studied in healthy adult male volunteers. Subjects received a gentamicin infusion every 8 hours for 19 doses. Gentamicin dosage was adjusted to maintain peak concentrations of 5.5 mg/L and trough concentrations of 0.5 mg/L. Verapamil was given as a sustained release preparation of 180 mg twice daily starting 2 days before the aminoglycoside, and continued for 4 days post-gentamicin therapy. Nephrotoxicity was assessed by measuring 24-hour urinary alanine aminopeptidase excretion (AAP). The urinary AAP results of six subjects given gentamicin with verapamil were compared with urinary AAP from nine subjects treated with gentamicin alone. These nine subjects were matched with the verapamil-treated subjects on the basis of gentamicin area-under-the-curve (AUC). After matching AUC, gentamicin exposure was virtually identical between the two groups with an average gentamicin AUC of 26.61 +/- 1.49 and 27.51 +/- 1.25 mg.hr/L for the gentamicin/ve-rapamil and gentamicin only groups respectively. Verapamil retarded the rise in mean daily AAP excretion on days 1 to 6 of gentamicin therapy, with a significant difference with respect to AAP urinary excretion (P < .05) observed on day 2. There was no significant difference in total cumulative AAP excretion or in the time to return to baseline AAP excretion. Therefore, verapamil was effective in reducing AAP excretion associated with gentamicin therapy.

Calculated empiric antimicrobial therapy for mixed surgical infections

In acute life-threatening surgical infections requiring immediate institution of antimicrobial therapy before bacteriological results are available, antibiotic treatment must be empiric. For best efficacy a more sophisticated form of empiric therapy is offered, termed calculated antibiotic therapy (CAT). Calculated antibiotic therapy requires consideration of a) typical bacterial spectrum; b) bacterial pathogenicity and synergism; c) antibacterial concentrations at the site of infection; d) toxicity and adverse effects; e) interaction with immune response; and f) results of properly conducted trials. Intraabdominal infections are used as an example here to assess the efficacy of clinically used cephalosporins and penicillins for determination of calculated antibiotic therapy. CAT identifies Escherichia coli and Bacteroides fragilis as the most important pathogens for intraabdominal infections and determines the most effective antibiotics at the tissue breakpoint, which is defined as the minimal concentration maintained for more than 90% of the dosage interval period at the infected tissues. At the tissue breakpoint calculated antibiotic therapy identifies cefotaxime-generation cephalosporins to be fully (100%) active against the most important aerobic pathogen E. coli and metronidazole as fully active against the important obligate anaerobe B. fragilis. Calculated antibiotic therapy becomes relatively important, since impeccably controlled clinical therapeutic trials as a foundation for therapy are rarely published.

Is there a reliable index of glomerular filtration rate in critically ill patients?

Assessment of renal function in critically ill patients is important for appropriate individualization of dosage regimens and nutrition, but is complicated by a high incidence of acute renal failure (ARF). The most common cause of ARF in intensive care unit (ICU) patients is hypoperfusion. Other causes of ARF include intrinsic injury, nephrotoxicity, and postrenal obstruction. ARF is associated with a decreased glomerular filtration rate (GFR), reduced or maintained urine output (nonoliguric renal failure), and alterations in other commonly obtained urinary indices. Twenty-four-hour or shorter urinary creatinine clearance studies may overpredict GFR as creatinine is both filtered and secreted. The use of serum creatinine in empiric predictive equations is impaired in ICU patients because of decreases in creatinine production due to immobilization and malnutrition or increases in creatinine production due to catabolic illnesses. Adjustment of empiric methods by employing lean body weight, ideal body weight, or corrected serum creatinine values has not been evaluated against uncorrected values in this population, but is routinely performed in clinical practice. Inulin and radiolabeled substances are not practical for routine clinical use and may overpredict GFR in ARF due to backleak of large molecular-weight substances through the tubules. Comparative clinical trials have shown essentially equivalent performance of empiric methods relative to 24-hour urinary creatinine clearance in adults. No studies have compared these methods to a reference method for determination of GFR. Until conclusive data become available, clinicians should cautiously compare results from at least two independent methods of assessment to estimate renal functional impairment in ICU patients.

Algorithm for assessing renal dysfunction risk in critically ill trauma patients receiving aminoglycosides

A recent retrospective study proposed that the following screening criteria be used in identifying critically ill trauma patients receiving aminoglycosides who are at significant risk to develop renal dysfunction: (1) post-admission shock, (2) minimum serum concentration more than 2 mg/L, and (3) diagnosis of septicemia. The major purpose of the present study was to validate these criteria and design a corresponding algorithm for clinical use. All patients admitted to a trauma intensive care unit and receiving an aminoglycosides was also studied. All patients studied over a 7-month period. A control group not receiving aminoglycosides was also studied. All patients were evaluated for the presence of renal dysfunction (i.e., serum creatinine increase greater than or equal to 0.5 mg/dL). Univariate and multivariate statistical analyses were used to compare potential associated risk factors. The overall renal dysfunction incidence was 10% in the treatment patients (n = 93) versus 5% in the control patients (n = 199) (p = 0.13). Sensitivity and specificity of the screening criteria were 67% and 92%, respectively. The predictive values of a positive and negative test relative to correctly labeling patients at high risk or low risk to develop renal dysfunction were 46% and 96%, respectively. Major risk factors associated with renal dysfunction in the treatment group were post-admission shock, minimum serum concentration more than 2 mg/L, and liver dysfunction. Use of three major risk factors has excellent predictive value in identifying severely traumatized patients at low risk for developing renal dysfunction while receiving aminoglycosides. The modest predictive value of a positive test results in conservative management of patients by avoidance of aminoglycosides, i.e., use of alternative antimicrobial agents.

Etappenlavage: advanced diffuse peritonitis managed by planned multiple laparotomies utilizing zippers, slide fastener, and Velcro analogue for temporary abdominal closure

Etappenlavage is defined as a series of planned multiple operative procedures performed at a 24-hour interval. It includes a commitment to reexplore the patient's abdomen at the initial corrective operation. This is a report of a prospective study of 117 patients treated by etappenlavage for severe advanced suppurative peritonitis in 2 institutions. Etappenlavage was performed in 15% of all patients with operations for peritonitis. In these patients, the abdominal infection had progressed to an advanced stage of severe functional impairment. A total of 669 laparotomies were performed and the abdomen closed temporarily utilizing retention sutures (n = 45), a simple zipper (n = 26), a slide fastener (n = 29), and Velcro analogue (n = 17). An average of 6.1 procedures were necessary to control the infection. In 57% of the patients, additional complications were recognized and repaired after the initial operation. Patients were artificially ventilated for an average of 17 days. The median duration of therapy was 33 (range, 3-183) days. Twenty-eight patients died between days 3 and 71 (median, 9) after initiation of therapy. In 88%, uncomplicated wound healing was observed after wounds were closed definitely. In the last 17 patients, no complications were attributable to the use of 2 adhesive sheets of polyamide plus nylon or perlon for temporary abdomimal closure (Velcro-like artificial burr). APACHE II scoring predicted a median mortality of 47%. The actual mortality was 25%. Overall, the mortality of advanced diffuse peritonitis was reduced from a predicted 34-93% (APACHE II/SIS scoring) to 24%. Velcro analogue (artificial burr) was the most practical device for temporary abdominal closure.

Renal handling of beta 2-microglobulin in patients with cystic fibrosis

We evaluated the renal handling of beta 2-microglobulin (beta 2-M) and creatinine in healthy outpatients (n = 6), normal children hospitalized for infections treated with antibiotics (not including an aminoglycoside) (n = 4); outpatients with cystic fibrosis (CF; n = 12), and hospitalized patients with CF (n = 6) who received a 10- to 14-day course of antibiotic treatment that included an aminoglycoside. The serum beta 2-M concentrations in the normal outpatients (2020.1 +/- 276.6 micrograms/L) were significantly lower (p less than 0.05) than those observed for outpatients (2833.3 +/- 202.6 micrograms/L) or patients with CF (2861.8 +/- 340.5 micrograms/L. There were no significant differences found for creatinine clearance or fractional excretion of beta 2-M when subjects without CF were compared with those with the disease. Furthermore, no significant differences were observed in hospitalized patients with CF when creatinine clearance and fractional excretion of beta 2-M were compared between the initiation and conclusion of aminoglycoside treatment. Glomerular filtration and proximal tubular reabsorption of beta 2-M were not altered in patients with CF. These findings do not support a global defect in proximal renal tubular reabsorption as the underlying cause for altered aminoglycoside clearance in patients with CF.

Enhanced gentamicin nephrotoxicity after experimental biliary obstruction in rats

To explore whether bile duct ligation increased the risk for gentamicin nephrotoxicity, male Wistar rats were subjected to bile duct ligation or sham surgery and given either gentamicin 20 mg/kg or saline twice daily intraperitoneally for 8 days. Bile duct ligated and gentamicin injected rats elicited a decline in renal function and tubular cell necrosis after 8 days of treatment whereas equal dosage regimen in sham operated rats exhibited no evidence of renal dysfunction. In addition, though serum and kidney gentamicin levels were higher in bile duct ligated rats (1.84 +/- 0.11 micrograms/ml versus 0.20 +/- 0.03 microgram/ml, and 1453 +/- 164 micrograms/g versus 698 +/- 138 micrograms/g of cortex, respectively, P less than 0.05). The data indicate that complete biliary obstruction enhances renal sensitivity to gentamicin.

Antimicrobial therapy for pediatric patients

New antimicrobial agents are being introduced for clinical use at an increasingly rapid rate. This has required physicians continually to review relevant data and determine unique properties that might guide selection among any new antibiotics as well as older ones. Efficacy, potential toxicity, and comparative cost (in that order) generally guide selection. The present comprehensive review examines currently available antibiotics along with some under investigation, emphasizing these three basic areas of consideration.

Application of Bayesian estimation for the prediction of an appropriate dosage regimen of amikacin

A Bayesian approach was developed to determine an amikacin dosage regimen to achieve the desired plasma concentrations for each patient. Statistical characteristics of pharmacokinetic parameters were first evaluated in a group of patients (reference population), which when combined with three individual plasma concentrations of drug led to a Bayesian estimation of individual pharmacokinetic parameters. By using these parameters, an individual dosage regimen was then established to avoid residual and peak amikacin concentrations of up to 3 and 25 micrograms/mL, respectively. In a test group of 33 patients, adapted amikacin dosage regimens ranged from 4 to 43 mg/kg/d, with schedules requiring up to four infusions per day. Infusion time varied from 40 min to 4 h. These differences in drug administration protocol result from the wide interindividual variability of amikacin pharmacokinetic parameters. Performance of the developed methodology was evaluated by computing bias and precision of the estimated total body clearance and of the trough and peak amikacin concentrations that were reached after dosage regimen determinations.

Probability assessment approach to therapeutic drug monitoring: tobramycin

Pharmacokinetic monitoring is an important therapeutic goal of aminoglycoside therapy. The overall goal of this study was to identify specific patient groups that would derive the maximum benefit from therapeutic drug monitoring services. These groups are patient populations with high probabilities of achieving toxic or subtherapeutic concentrations. Out of a total population of 86 stable, noncritically ill patients, 27 toxic concentrations (trough greater than 2.0 micrograms/mL) occurred in 15 patients. In comparison to patients (n = 46) with therapeutic concentrations (trough less than 2.0 micrograms/mL, peak greater than 4.0 micrograms/mL), these patients were older (64 +/- 11 vs. 54 +/- 18 years; p less than 0.02) and had a higher percentage of females (66.7 vs. 37 percent; p less than 0.05). Those patients with subtherapeutic concentrations (43 concentrations in 25 patients) had higher estimated creatinine clearance values than those with therapeutic concentrations (94 +/- 45 vs. 74 +/- 27 mL/min; p less than 0.005). Probability assessment analysis of the data showed a sevenfold increase in toxic concentrations in patients above 50 years. Females over age 50 had 2.3 times the risk of developing toxic concentrations as males over age 50. In contrast, the development of low concentrations was not predicted by age or sex. Underdosage by greater than or equal to 30 percent was a reasonable predictor (75 percent) of low peak concentrations. Furthermore, toxic concentrations did not occur in patients who were underdosed, justifying dosage increases prior to obtaining serum concentrations in these patients. The group with the highest probability of attaining therapeutic concentrations was males receiving therapeutic doses who were under age 50 (85.5 percent).(ABSTRACT TRUNCATED AT 250 WORDS)

Health impact of renal disease due to nephrotoxicity

Both acute and chronic renal failure are reported in the context of nephrotoxicity. This overview of some major nephrotoxins reflects both the magnitude and the cost of this preventable health problem. Aminoglycosides and other antibiotics, contrast media and nonsteroidal anti-inflammatory drugs are the best documented nephrotoxins related to acute renal failure. Analgesic nephropathy is the best known drug-induced chronic renal disease. The cost of renal failure due to nephrotoxicity is not easy to compute. Drug-induced acute renal failure costs more than 2750 ECU per patient, depending on whether dialysis is required or not, and chronic renal failure costs at least 128,000,000 ECU annually in the European Communities. Recent epidemiological evidence, however, indicates that the cost may be even higher.

Electrolyte composition of renal tubular cells in gentamicin nephrotoxicity

The effect of long-term gentamicin administration on sodium, potassium, chloride and phosphorus concentrations was studied in individual rat renal tubular cells using electron microprobe analysis. Histological damage was apparent only in proximal tubular cells. The extent of damage was only mild after 7 days of gentamicin administration (60 mg/kg body wt/day) but much more pronounced after 10 days. GFR showed a progressive decline during gentamicin treatment. In non-necrotic proximal tubular cells, sodium was increased from 14.6 +/- 0.3 (mean +/- SEM) in controls to 20.6 +/- 0.4 after 7 and 22.0 +/- 0.8 mmol/kg wet wt after 10 days of gentamicin administration. Chloride concentration was higher only after 10 days (20.6 +/- 0.6 vs. 17.3 +/- 0.2 mmol/kg wet wt). Both cell potassium and phosphorus concentrations were diminished by 6 and 15, and by 8 and 25 mmol/kg wet wt after 7 and 10 days of treatment, respectively. In contrast, no major alterations in distal tubular cell electrolyte concentrations could be observed after either 7 or 10 days of gentamicin administration. As in proximal tubular cells, distal tubular cell phosphorus concentrations were, however, lowered by gentamicin treatment. These results clearly indicate that gentamicin exerts its main effect on proximal tubular cells. Decreased potassium and increased sodium and chloride concentrations were observed in proximal tubular cells exhibiting only mild histological damage prior to the onset of advanced tissue injury. Necrotic cells, on the other hand, showed widely variable intracellular electrolyte concentration patterns.

Aminoglycoside antibiotics in clinical use

Aminoglycosides are among the most used antibiotics despite competitive pressure from newer beta-lactam agents. The activity profile, pharmacology, toxicity potential, and methods of toxicity prevention of aminoglycosides are well appreciated after three decades. Nephrotoxicity, ototoxicity, and the added costs of drug level monitoring limit wider usage, but great activity against highly antibiotic resistant gram negative bacteria often outweigh these disadvantages and will likely keep aminoglycosides available for the foreseeable future.

Acute renal failure

Acute renal failure (ARF) is common among critically ill patients and renal dysfunction is often associated with the multisystem organ failure syndrome. The mortality of ARF remains high but animal data indicate that prevention and early treatment may decrease the morbidity and mortality. This review defines ARF based on urine volume, laboratory parameters, and clinical presentation. The pathophysiology of prerenal, postrenal, and intrinsic ART are differentiated and diagnostic criteria provided. Preventive therapy, supportive care, and proposed treatments are outlined. Studies examining the prevention and treatment of ARF in animal models and trials in humans are evaluated. Mannitol 0.5-1 g/kg, furosemide 0.5-1 mg/kg initially, and dopamine 1-5 micrograms/kg/min are effective in preventing or decreasing the severity of ARF in animal models. In humans these drugs are effective at maintaining urine output in various clinical situations and converting oliguria to nonoliguria in some patients; however, increased survival has not been adequately proven as of yet. Dialysis and experimental therapy are briefly discussed.

Exponential intravenous infusions in toxicological studies: achieving identical serum drug concentration profiles in individuals with altered pharmacokinetic states

It is common practice in the clinical setting to adjust the dosage of a drug administered to a patient with altered pharmacokinetic characteristics, e.g., renal impairment, in such a way that the steady-state level of the drug is the same as that which would be observed in normal patients. This may also be done in experimental studies of the interaction of drug toxicity and a disease state. Dosage adjustment does alter average steady-state serum concentrations but the resulting concentration-time profiles of the normal and the diseased groups will be of entirely different shapes due to differences in elimination. In a toxicological study, this would lead to a confounding of the disease state and the difference in exposure. In this paper, model-independent deconvolution analysis is applied to derive the infusion schedule needed to achieve a constant serum concentration followed by a predetermined monoexponential decline in concentration. The resulting exponential infusion is applied to attain identical serum gentamicin concentration-time profiles in five pairs of subtotally nephrectomized and normal dogs during a 12-h infusion.

Comparison of venous and capillary blood sampling for the clinical determination of tobramycin serum concentrations

Tobramycin concentrations have been determined in serum from capillary, venous and arterial blood samples taken from 16 patients during and after surgery. In 73 paired samples the concentrations in capillary samples were not significantly different from those measured in venous samples. The small concentration differences were neither dependent upon sampling time nor core-peripheral temperature differences. In 26 paired samples, concentrations in capillary samples were not significantly different from those determined in arterial samples. We conclude that concentrations in capillary samples are precise and unbiased estimators of venous concentrations and may be used in the adjustment of tobramycin dosage regimens.

Reduction of the drug-induced nephrotoxicity by ATP-MgCl2. II. Effects on gentamicin-treated isolated perfused kidneys

Drug-induced nephrotoxicity (NT) has become an increasingly significant clinical problem. An in vitro model of drug-induced NT was therefore developed using gentamicin and the effects of ATP-MgCl2 on reduction or prevention of NT were determined. To study this, non-pulsatile perfusion in isolated rat kidneys was maintained at 100 mm Hg during 2 hr of perfusion at 37 degrees C. The oxygenated Krebs-HCO3 perfusate contained 7.5 g/dl albumin as colloid, glucose, creatinine, amino acids, trace amounts of [3H]inulin and 125I-lysozyme, and either 0, 0.4, 0.8, or 1.2 mg/ml of gentamicin. In some studies, 2 mM ATP-MgCl2 was added with 0.8 mg/ml of gentamicin at 0 and 60 min of perfusion. During each 10-min clearance period, glomerular filtration rates, sodium absorption, water absorption, and fractional clearance of TCA-precipitable lysozyme were measured. The results indicate that renal perfusate flow, glomerular filtration rate, urinary flow and tubular absorption of protein (a sensitive indicator of tubular function), sodium, and water were affected by gentamicin in a dose-dependent manner. An isolated kidney preparation can therefore be used to study gentamicin-induced NT. Higher in vitro perfusate concentrations of the drug were needed, however, to acutely mimic the in vivo cumulative effects. Nonetheless, renal perfusate flow, glomerular filtration rate, and the depression in protein reabsorption which occurred with gentamicin treatment were markedly improved by simultaneous treatment with ATP-MgCl2. Thus, ATP-MgCl2 may be useful in reducing drug-induced nephrotoxicity.

Complexation versus hemodialysis to reduce elevated aminoglycoside serum concentrations

Seven patients with acutely elevated aminoglycoside serum concentrations were studied comparing the effect of hemodialysis (n = 3) with removal by complexation using ticarcillin or carbenicillin (n = 4). Aminoglycoside serum half-life before intervention averaged 96 hours for the dialysis group and 67 hours for the complexation group. Ticarcillin was used for a minimum of 48 hours, while hemodialysis removal was estimated over 48 hours, which included two 4-hour dialysis periods. Aminoglycoside serum half-life was reduced to an average of 11 hours with hemodialysis, while with complexation using ticarcillin, it was reduced to 12 hours. During the 48-hour comparison period, complexation removed approximately 50% more aminoglycoside than did hemodialysis, primarily because the improved removal technique was sustained over the entire time. Complexation appears to be as effective as continuous hemodialysis in lowering excessive aminoglycoside serum concentrations. Complexation with ticarcillin can be more rapidly initiated, is less expensive and there is a low risk of adverse reactions. This method provides continued treatment of infections in patients with elevated serum concentrations and/or nephrotoxicity who require cessation of aminoglycoside therapy.

Specificity of renal tubular damage criteria for aminoglycoside nephrotoxicity in critically ill patients

Two populations of critical care patients were studied using indices of renal tubular damage (beta 2-microglobulin, enzymes, casts) and indices of glomerular filtration (creatinine, creatinine clearance). The purpose of these studies had been initially to elucidate the type of renal failure typical of the critically ill patient treated with aminoglycoside gentamicin or tobramycin, then to determine its frequency. The second study population included a control group of patients given the nonnephrotoxic cephalosporin moxalactam, in order to assess the specificity of the renal tubular damage criteria for aminoglycoside nephrotoxicity versus other types of renal injury in critical care patients. Creatinine rise occurred in approximately 30 per cent of each tobramycin-treated group and in only 12 per cent in the moxalactam control patients (P less than 0.05). Thus, the data indicate that aminoglycosides are associated with an approximate doubling of the renal damage in those older, critically ill patients. Renal tubular damage criteria appear specific for the aminoglycoside effect, but a substantial percentage of the renal damage in this population is not associated with detectable alterations in renal tubular status.

A microcomputer program for tobramycin consult services, based on the two-compartment pharmacokinetic model

A microcomputer program has been developed to provide assistance to tobramycin clinical pharmacokinetic consult services. Written for the Apple II Plus computer with 64 K memory, one-disk drive, and a dot matrix graphics printer, this software is user-oriented and simple to operate. The program disk contains complete documentation and referenced instructions. Major sections provide empiric dosing recommendations based on population data and allow determination of dosage from measured serum concentrations. The program keeps a record of previous regimens, allows for the entry of the user's own recommendation, and provides complete flexibility for up to 15 dosage and interval changes. In addition to its dosing information and file management capabilities, the program simulates serum concentration profiles based on user-selected one-compartment, two-compartment, or two-compartment prenephrotoxic models. The program prints a consult sheet with concentration vs. time simulation, patient demographic data, and user-entered recommendations and comments. The program provides extensive disk storage capabilities for patient files, with immediate access to facilitate updating and dosing regimen changes as they occur. In addition to providing improvements in empiric dosing capabilities, pharmacokinetic modeling, and data handling, this computer software has been designed to incorporate pharmacokinetic data derived from important subpopulations into the empiric dosing algorithms. This unique aspect enables the program to provide improved empiric dosing regimens for patients who do not fall under the guidelines for any of the conventional aminoglycoside dosing nomograms.

Aminoglycoside pharmacokinetics on a microcomputer

The authors describe the use of a microcomputer to evaluate an existing dosage regimen and to determine a new regimen and steady-state peak and trough levels for four aminoglycoside antibiotics--amikacin, gentamicin, kanamycin, and tobramycin. The microcomputer program is based on a one-compartment open pharmacokinetic model for the aminoglycosides. It accounts for patients' sex, age, height, obesity, and ascitic compartment. The program is divided into seven subprograms for each of the four aminoglycosides: (1) steady-state peak and trough levels are predicted, based on serum creatinine for a given dosage regimen; (2) a dosage regimen that conforms to 6, 8, 12, 16, or 24 hours is ascertained, based on serum creatinine; (3) a dosage regimen is determined, on the basis of serum creatinine, for desired steady-state peak and trough levels; (4) a dosage regimen that conforms to 6, 8, 12, 16, or 24 hours is ascertained for given aminoglycoside serum levels; (5) a dosage regimen for desired peak and trough levels is ascertained for given aminoglycoside serum levels; (6) a dosage regimen that conforms to 6, 8, 12, 16, or 24 hours is ascertained from data collected using Sawchuk's and Zaske's method; and (7) a dosage regimen, estimated for desired peak and trough levels, is estimated from data collected using Sawchuk's and Zaske's method.

Treatment of pseudomonal endocarditis with high-dose aminoglycosides

High-dose aminoglycoside therapy (6–8 mg/kg/d) in an intravenous drug abuser with Pseudomonas aeruginosa endocarditis is described. The dose of tobramycin was adjusted to achieve peak serum concentrations of 15–20 μg/ml and trough concentrations of 〈 2 μg/ml. Significant drug-induced toxicities were not observed. Treatment of P. aeruginosa endocarditis with high-dose aminoglycosides may be appropriate and beneficial in selected patients.

Clinical and pathophysiologic aspects of aminoglycoside nephrotoxicity

Aminoglycoside antibiotics continue to be a mainstay of therapy in the clinical management of gram negative infections, but a major factor in the clinical use of aminoglycosides is their nephrotoxicity. With gram negative organisms accounting for the majority of hospital acquired infections, the occurrence of aminoglycoside induced acute renal failure has become commonplace. Presently at least 10% of all cases of acute renal failure can be attributed to these antibiotics. This article will cover the renal handling of the aminoglycosides, the pathogenetic mechanisms of nephrotoxicity, and the clinical aspects of aminoglycoside induced acute renal failure with particular emphasis on recent data which have increased our understanding of the interaction of aminoglycosides with the renal tubular cell and the effects of this interaction on cellular function and integrity.

The pharmacology of ototoxic drugs

This article briefly reviews the nature of the toxic effects of drugs on the inner ear and the incidence of ototoxic side effects in man. There follows a more detailed discussion of the most important groups of ototoxic drugs which are identified as the aminoglycoside antibiotics, the "loop" diuretics, quinine and chloroquine, the salicylates and some antitumour drugs. Attention is drawn to the synergistic interaction between aminoglycoside antibiotics and "loop" diuretics and the predisposition to ototoxicity if the drugs are given to subjects with renal impairment. The comparative ototoxicological potential of individual aminoglycosides is discussed and their toxic effects on the kidney and the neuromuscular junction summarized. The importance of an understanding of the pharmacokinetics of aminoglycosides both in relation to toxicity and the rational control of therapy is emphasized.

The aminoglycosides

Aminoglycosides remain the cornerstone of prophylaxis and therapy against the majority of aerobic gram-negative organisms responsible for serious sepsis in the hospital. Gentamicin, tobramycin, amikacin are all equally efficacious against susceptible organisms and differ only in their patterns of resistance and pharmacokinetic profiles. The ototoxic and nephrotoxic potential of gentamicin, tobramycin, and amikacin is comparable. Amikacin appears to be preferred for general use at present because of its low resistance potential and superior pharmacokinetic profile (high and predictable serum peaks, wide toxic-therapeutic ratio, high "kill ratio," and q 12 h dosing). In spite of the introduction of the third generation cephalosporins, which are highly active against a variety of aerobic gram-negative organisms, the aminoglycosides will continue to play an important role in the treatment of gram-negative infections. Indeed, the expected usefulness of aminoglycosides may be prolonged by the introduction of the third generation cephalosporins since these drugs will probably be used in combination with aminoglycosides to extend spectrum and to take advantage of possible synergy.

Reappraisal of guidelines for pharmacokinetic monitoring of aminoglycosides

The rationale for pharmacokinetic monitoring of aminoglycosides is critically reviewed. Retrospective studies suggest that for optimal antibacterial effect, peak serum gentamicin concentrations should exceed 5 micrograms/ml, despite the fact that these concentrations are indirect measures of the concentration of drug at the site of infection. When quantitative results of antimicrobial susceptibility are known (e.g. MIC or MBC), limited data suggest that for most infections, the peak serum aminoglycoside concentration should exceed the minimum inhibitory concentration by four-fold. However, the optimal duration for which the serum concentration should exceed the MIC or MBC during each dosing interval and the detrimental effect of prolonged subinhibitory drug concentrations have not been evaluated. Furthermore, the immunological competence of the host and the pathogenicity of the infecting organism are important factors in achieving antibacterial response. Using serum creatinine as an indirect and relatively late indicator of nephrotoxicity, nadir gentamicin concentrations greater than 2 micrograms/ml may predispose patients to develop nephrotoxicity. In addition, recent information indicates that patients who accumulate excessive amounts of aminoglycosides in their tissues may be at higher risk for developing nephrotoxicity; these patients may be identified based on the extent of accumulation in their nadir concentrations with continuous dosing. The aminoglycosides diffuse into the inner ear fluids slowly and diffuse out with a half-life of decline in inner ear fluid concentrations slower than that in serum. High transient peak serum concentrations probably do not contribute significantly to the risk of ototoxicity. However, there is evidence from early clinical trials, studies using continuous infusions of aminoglycosides, and animal studies indicating that elevated nadir serum concentrations relate to the development of ototoxicity. There is considerable interpatient variability in the peak serum concentration, even when identical dosages based on body weight or surface area are administered. Similarly, the half-life for decline in serum concentrations is highly variable from patient to patient, even in patients with stable normal renal function. Absorption after intramuscular administration is reliable in most patients, although critically ill patients may experience erratic absorption. The distribution of aminoglycosides is altered in obese patients because of differences in extracellular fluid content between fat and other tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

The clinical pharmacist and research

The question of whether or not clinical pharmacists are capable of performing meaningful research is addressed by reviewing the qualifications necessary for anyone to pursue an independent research career and by examining the current education and training of most clinical pharmacists. The types of research which appear to be best suited for clinical pharmacists include preclinical or clinical evaluations of basic science principles potentially affecting the therapeutic use of drugs in man, or the evaluation of clinical characteristics which alter the response to drugs in routine clinical use. It is concluded that clinical pharmacists with the appropriate postgraduate training and/or experience are capable of conducting meaningful research, and this is documented by current literature citations.

Dibekacin intrarenal distribution characteristics and renal cortical elution kinetics. Comparison with gentamicin and tobramycin

Dibekacin (3',4-dideoxykanamycin B) is a new semisynthetic aminoglycoside developed in Japan and one which has found wide clinical acceptance in that country. The antibacterial activity of this compound indicates that it is relatively similar to gentamicin. Since it appears that the intrarenal distributional characteristics and renal cortical kinetics of aminoglycosides provide some predictive information concerning the clinical incidence of nephrotoxicity, we designed a series of pharmacokinetic studies in healthy mongrel dogs which would define such kinetic information for dibekacin and would contrast the results with similar studies for gentamicin and tobramycin. The renal cortical kinetics of dibekacin, as developed in these studies, show that in a canine model the behavior of dibekacin is similar to that of gentamicin and significantly different from tobramycin. Dibekacin and gentamicin show reproducibly higher renal cortical tissue concentrations than tobramycin in both the acute infusion studies and multiple dosing studies. The results suggest that dibekacin may possess the same inherent nephrotoxic potential as that of gentamicin. In order to show any difference in clinical toxicity between gentamicin and dibekacin, a very extensive randomized, double-blind, prospective clinical trial of efficacy and toxicity will be needed.