Gentamicin pharmacokinetics during hemodialysis

Development of a Semimechanistic Model to Describe the Pharmacokinetics of Gentamicin in Patients Receiving Hemodialysis

The aim of this study was to ascertain the most suitable dosing schedule for gentamicin in patients receiving hemodialysis. We developed a model to describe the concentration-time course of gentamicin in patients receiving hemodialysis. Using the model, an optimal dosing schedule was evaluated. Various dosing regimens were compared in their ability to achieve maximum concentration (C(max), > or = 8 mg/L) and area under the concentration time-curve (AUC > or = 70 mg x h/L and < or = 120 mg x h/L per 24 hours). The model was evaluated by comparing model predictions against real data collected retrospectively. Simulations from the model confirmed the benefits of predialysis dosing. The mean optimal dose was 230 mg administered immediately before dialysis. The model was found to have good predictive performance when simulated data were compared to data observed in real patients. In summary, a model was developed that describes gentamicin pharmacokinetics in patients receiving hemodialysis. Predialysis dosing provided a superior pharmacokinetic profile than did postdialysis dosing.

Influence of hemodialysis on gentamicin pharmacokinetics, removal during hemodialysis, and recommended dosing

BACKGROUND AND OBJECTIVES

Aminoglycoside antibiotics are commonly used in chronic kidney disease stage 5 patients. The purpose of this study was to characterize gentamicin pharmacokinetics, dialytic clearance, and removal by hemodialysis and to develop appropriate dosing strategies. Design Setting, Participants, and Measurements: Eight subjects receiving chronic, thrice-weekly hemodialysis with no measurable residual renal function received gentamicin after a hemodialysis session. Blood samples were collected serially, and serum concentrations of gentamicin were determined.

RESULTS

Median (range) systemic clearance, volume of distribution at steady state, and terminal elimination half-life were 3.89 ml/min (2.69-4.81 ml/min), 13.5 L (8.7-17.9 L), and 39.4 h (32.0-53.6 h), respectively. Median (range) dialytic clearance, estimated amount removed, and percent maximum rebound were 103.5 ml/min (87.2-132.7 ml/min), 39.6 mg (19.7-43.9 mg), and 38.7% (0%-71.8%), respectively. Gentamicin dialytic clearance was statistically significantly related to creatinine dialytic clearance (r(2) = 0.52, P = 0.04), although this relationship is not likely to be strong enough to serve as a surrogate for gentamicin monitoring. The pharmacokinetic model was used to simulate gentamicin serum concentrations over a one-wk period.

CONCLUSIONS

In clinical situations where gentamicin is used as the primary therapy in a patient receiving hemodialysis with a CAHP hemodialyzer, conventional doses after each dialysis session are not as efficient at achieving treatment targets as predialysis dosing with larger doses.

Gentamicin pharmacokinetics during slow daily home hemodialysis

BACKGROUND

Gentamicin is commonly used in hemodialysis patients. Gentamicin pharmacokinetics during traditional hemodialysis have been described. Slow daily home (SDH) hemodialysis (7 to 9 hours a day/6 days a week) use is increasing due to benefits observed with increased hemodialysis. We determined gentamicin pharmacokinetics for SDH hemodialysis patients.

METHODS

Eight patients (four male and four female) received a single intravenous dose of 0.6 mg/kg gentamicin post-hemodialysis. Blood samples were collected at 5, 10, 15, 30, and 60 minutes after dose. The next day patients underwent a typical SDH hemodialysis (high-flux F50NR dialyzer) session. Blood samples were taken at 0, 5, 15, 60, 120, 240, 360, 480 minutes during and 15, 30 and 60 minutes post-hemodialysis. Baseline and 24-hour urine samples were collected. Pharmacokinetic parameters were calculated assuming a one-compartment model.

RESULTS

Patients were 42.5 +/- 13.1 years old (mean +/- SD). Inter-, intra-, and post-hemodialysis collection periods were 17.0 +/- 2.1 hours, 8.1 +/- 0.4 hours, and 1.1 +/- 0.1 hours, respectively. Intra-, and interdialytic gentamicin half-lives were different (intradialytic, 3.7 +/- 0.8 hours; interdialytic, 20.4 +/- 4.7 hours; P < 0.0001). Hemodialysis clearance accounted for 70.5% gentamicin total clearance. Renal clearance correlated with glomerular filtration rate (GFR) (renal clearance=1.2 GFR; r2=0.98; P < 0.001). Mean peak and trough of hemodialysis concentrations were 1.8 +/- 0.6 microg/mL and 0.5 +/- 0.2 microg/mL, respectively. Post-hemodialysis rebound was 3.1 +/- 8.8% at 1 hour.

CONCLUSION

Pharmacokinetic model predicts 2.0 to 2.5 mg/kg dose gentamicin post-hemodialysis would provide peak (1 hour post-dose) and trough (end of SDH hemodialysis session) concentrations of 6.0 to 7.5 microg/mL and 0.7 to 0.8 microg/mL, respectively. This would provide adequate coverage for most gram-negative organisms in SDH hemodialysis patients.

Acute massive gentamicin intoxication in a patient with end-stage renal disease

A 65-year-old man with end-stage renal disease on continuous ambulatory peritoneal dialysis accidentally received an acute massive overdose of gentamicin as a treatment of peritonitis. The patient developed acute vestibular dysfunction and hearing loss following the overdose. His serum gentamicin had reached the extremely toxic level of 220 microg/mL. To remove the gentamicin, the patient received hemodialysis and hemoperfusion immediately. This was followed by two more courses of hemodialysis during the following 2 days. The gentamicin level was brought down to 10 microg/mL after the third hemodialysis. Moderate and persistent high-frequency hearing loss was documented with serial audiograms. The patient made a gradual but incomplete recovery from the vestibular dysfunction. The complications of gentamicin toxicity and its management are discussed with respect to our patient.

Gentamicin clearance during hemodialysis: a comparison of high-efficiency cuprammonium rayon and conventional cellulose ester hemodialyzers

The advent of high-efficiency hemodialyzers has afforded improved efficiency of urea clearance; however, increased clearance of other substances, particularly antibiotics, also may occur, necessitating changes in clinical practice. Accordingly, we compared the efficiency of gentamicin removal using two different hemodialyzers, a conventional saponified cellulose ester (CD 135) and a high-efficiency cuprammonium rayon dialyzer (TAF 175L), in eight hospitalized patients undergoing antibiotic therapy for suspected or proven gram-negative infection. The rate of dialysis, estimated as the ratio of dialyzer urea clearance (K) to urea distribution volume (V) (K/V urea), and the total elimination rate constant (k) of gentamicin were measured during 17 hemodialysis treatments. The K/V urea for the two dialyzers, TAF 175L and CD 135, was 0.390 +/- 0.024 hr-1 and 0.413 +/- 0.129 hr-1 (P = NS), respectively. The TAF 175L hemodialyzer was almost twice as efficient in removing gentamicin as the CD 135: TAF 175, k = 0.263 +/- 0.024 hr-1; CD 135, k = 0.132 +/- 0.027 hr-1 (P < 0.001). Moreover, the rate of dialysis (K/V urea) was correlated with k of gentamicin for the TAF 175L dialyzer (r2 = 0.50, P < 0.02) but not for the CD 135 dialyzer. We conclude that dialyzer characteristics and the rate of dialysis (K/V urea) should be taken into consideration when determining the dosage of gentamicin in patients on hemodialysis.

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.

Inactivation of amikacin and gentamicin by carbenicillin in patients with end-stage renal failure

Aminoglycosides are inactivated by carbenicillin in vitro and in patients with end-stage renal failure. In vitro, amikacin is inactivated to a lesser extent than is gentamicin. In five patients on chronic hemodialysis, serum levels of amikacin alone and after repeated intravenous carbenicillin infusions were determined. Analogous gentamicin studies were conducted with five different patients. Neither amikacin serum levels nor serum clearances were affected by carbenicillin. The mean gentamicin serum half-life was significantly lower in the presence of carbenicillin: 18.4 +/- 8.2 compared with 61.6 +/- 30.7 h. Serum clearance increased significantly. The inactivation of gentamicin by carbenicillin was both time related (greater than 12 h of exposure) and concentration dependent (molar carbenicillin/gentamicin ratios greater than or equal to 39:1). Amikacin would be preferable to gentamicin in patients with end-stage renal failure.

Antibiotic blood concentrations in patients successfully treated with tobramycin

Thirty-nine patients with severe Gram-negative infections were treated with parenteral tobramycin. Thirty-one (79%) were cured of their infection. Tobramycin was most effective in the therapy of patients with urinary tract infections, arthritis and skin and soft tissue infections and relatively less effective in patients with septicaemia, pneumonia, and osteomyelitis. The infection was cured more frequently in patients who achieved a high ratio between the peak serum concentration of tobramycin and the minimal inhibitory concentration of tobramycin against the pathogenic organism (so-called therapeutic ratio). The ratio was greater than 4.0 in 11 of 13 (85%) assays performed in 12 cured patients, whereas this ratio was achieved in only 3 of 10 (30%) instances in 5 patients in whom the therapy failed (P less than 0.05). The latter group also included a greater proportion of patients with an ultimately fatal illness, such as lung cancer and uraemia, compared to the former successfully treated group. Adverse effects of tobramycin on renal function were transitory. No significant effect of tobramycin on the hearing was observed.

Gentamicin extraction from an anuric patient by combined haemodialysis and charcoal haemoperfusion

A 39-year-old woman who developed acute renal failure following intra-abdominal sepsis was treated with gentamicin. Her serum concentrations reached potentially toxic levels. Combined haemoperfusion and haemodialysis removed approximately 70% of the given drug and the patient made a complete recovery.

Pharmacokinetics of netilmicin in the presence of normal or impaired renal function

A pharmacokinetic study of netilmicin was conducted in 12 healthy subjects and 24 subjects with chronic renal failure. After intramuscular administrations of 2 and 3 mg of netilmicin per kg in normal subjects, the mean peak serum concentrations were 5.46 and 8.83 mug/ml, respectively. After intravenous infusions of identical doses, the mean maximum serum levels, occurring at the end of the infusion, were 11.79 and 15.75 mug/ml, respectively. The pharmacokinetic data were very similar via the two routes of administration and for the two doses. The elimination half-life was 2.20 h, and 80 to 90% of the injected dose was recovered in urine during the first 24 h. After intramuscular administration of 2 mg/kg in subjects with chronic renal impairment, the elimination half-life increased to 29.48 h, and urinary elimination was inversely related to the degree of impairment. A study was conducted throughout hemodialysis sessions: serum concentrations decreased by 63.3%. The linear relationships between the elimination rate constant and creatinine clearance and the elimination half-life and serum creatinine allowed us to establish dosage schedules according to the degree of renal failure.

Drug administration in renal failure

Renal failure impairs urinary excretion of drugs and may also modify drug action by alternations in protein binding, distribution, biotransformation and, possibly, by retention of active metabolites. Dialysis adds another variable by altering the blood levels of those drugs soluble in plasma water and therefore available for diffusion or ultrafiltration. Renal insufficiency clearly modifies decisions about the choice and dose of a wide variety of drugs. Although data are accumulating at a rapid rate, available information about the use of drugs in patients with kidney disease is rather limited. The following is a summary of recent information on the use of a variety of drugs frequently utilized in patients with impaired renal function. The guidelines presented here are not absolute, but they are intended to be practical and reasonable, based on current information for adult patients of average size with kidney disease.

Pharmacokinetics of amikacin during hemodialysis and peritoneal dialysis

The pharmacokinetics of amikacin were examined in six bilaterally nephrectomized patients undergoing hemodialysis and in four patients with a minimal residual renal function undergoing peritoneal dialysis. The mean elimination half-life before the dialysis was 86.5 h in the anephric patients and 44.3 h in the patients with minimal residual kidney function. The results from the anephric patients suggest that some extrarenal elimination of amikacin may occur. The mean volume of distribution was about 25% of the total body weight. This is in accordance with values reported from subjects with normal renal function. During hemodialysis the half-life decreased to less than 10% (5.6 h) of the pretreatment value. The effectiveness of peritoneal dialysis was less as the half-life decreased to only about 30% (17.9 h) of the pretreatment value. During the dialyses a significant correlation between the half-life of amikacin and the decrease in blood urea and serum creatinine was demonstrated. The pharmacokinetic data were used to make dosage regimen recommendations for the treatment of patients undergoing intermittent hemodialysis or peritoneal dialysis.

Treatment of idiopathic membranous nephropathy

In a retrospective study of the effect of treatment in biopsy-proved idiopathic membranous nephropathy, 91 adults and 12 children were followed for periods up to 29 years after clinical onset (mean, 6.5 years). Forty-four were treated with corticosteroids, 15 with corticosteroids and immunosuppressants; 44 had no treatment and served as a control group. Clinical cure and improvement were significantly greater in the treated than in the nontreated group (P less than 0.01). The recurrence rate, occurrence of renal failure and probability of death were significantly greater in the nontreated group, although some of these patients eventually showed improvement. Prognosis was better in patients who responded to therapy. These data strongly suggest that steroid therapy is beneficial in patients with membranous nephropathy.

Inactivation of gentamicin by penicillins in patients with renal failure

Kinetics of gentamicin inactivation by carbenicillin and ticarcillin were studied in vitro and in 17 patients with renal failure. In vitro, the half-life of carbenicillin in human serum at 37 C is longer (19.2 +/- 0.7 h) than ticarcillin (7.2 +/- 0.6 h). Thus, incubation of gentamicin with equal concentrations of ticarcillin or carbenicillin results in greater inactivation of aminoglycoside activity by the latter. If concentrations of the two penicillins are held equal by repetitive addition, rates of gentamicin inactivation are the same. The serum half-life of gentamicin in patients serving as their own controls was significantly reduced by administration of either penicillin. After carbenicillin, the half-life decreased from 46 +/- 8 h to 22 +/- 3 h (P < 0.02). The constant for inactivation of gentamicin (k(i)) by carbenicillin was 0.02 h(-1). The results indicate that gentamicin requirements are underestimated by methods currently employed to calculate dosage for patients with renal failure who receive carbenicillin concurrently. Adjustment of gentamicin dosage in such cases by application of the k(i) for gentamicin is suggested.

Pharmacokinetics of gentamicin during peritoneal dialysis in children

The pharmacokinetics of gentamicin were examined on two occasions using intravenous and intraperitoneal routes in five children undergoing intermittent peritoneal dialysis for chronic renal failure. Serum, urine and dialysis fluid (DF) were assayed microbiologically for gentamicin and the data were subjected to computer analysis using equations evolved for a two-compartment model which considered the bi-directional flux of the drug. Following i.v. injection of 1 mg/kg of gentamicin, the apparent volume of distribution averaged 23% (range, 13 to 36%) of body wt (similar to normal), the mean half-life was 21 hr (range 9 to 37 hr; normal, 2 hr) and the peritoneal clearance averaged 4.0 ml/min/m2 (range, 1.2 to 7.0 ml/min/m2). During peritoneal administration of gentamicin (15 mg/liter of DF, 0.7 liters/m2 administered in each cycle over 9 to 12 cycles), serum concentrations increased towards extrapolated steady-state levels which averaged 42% (range, 25 to 68%) of DF concentrations. The mean renal clearance of gentamicin was only 1.6 ml/min/m2 while total body clearance ranged from 2.3 to 8.0 ml/min/m2 mostly occurring by a variable degree of dialysance. Peritoneal clearances and half-lives of gentamicin were similar in each patient following either treatment mode. The appreciable variability in gentamicin pharmacokinetics among adolescent patients with renal insufficiency necessitates dosage adjustments based on measurements of serum concentrations.