Potentiation of gentamicin nephrotoxicity by metabolic acidosis

Impaired Renal Function Secondary to Gentamicin — Identifying the Special Risk Patient

Although gentamicin has been commercially available since 1969, reports concerning the incidence of nephrotoxicity from this drug and variables relating to this toxicity are still unclear and conflicting. In view of this, a prospective study of patients receiving gentamicin over a two month period was undertaken to determine the incidence of nephrotoxicity and to study the influence of several variables on the potential for developing gentamicin associated nephrotoxicity. The variables studied were patient's age; the total grams of gentamicin received; the total number of days the patient received gentamicin with a hemoglobin of less than 12 g%; sex; total days duration of therapy; hemoglobin prior to therapy; hematocrit prior to therapy; red blood cell count prior to therapy; albumin level prior to therapy; and if the patient received another potentially nephrotoxic drug concomitantly with gentamicin. Sixty patients in total were studied. However, in the “toxic” and “nontoxic” grouping process, seventeen patients were excluded from the study due to missing variables. Of the remaining sample, ten patients were classified as “toxic” and thirty-three were classified as “nontoxic.” Thus the incidence of nephrotoxicity was at least 10/60 or 16.7 percent. The data relating to the variables identified were analysed utilizing Chi-square, t-test, and multiple regression analyses. Two variables were found to be highly significant in relationship to the development of nephrotoxicity while receiving gentamicin therapy. These were (1) the albumin level prior to therapy (lower albumin level in the “toxic” group) and (2) the concomitant use of another potentially nephrotoxic drug. The mechanism behind the influence of albumin on gentamicin toxicity is unclear, but may be related to protein binding. The basis for nephrotoxicity relating to combined use of nephrotoxic drugs is probably additive or synergistic toxicity but this is also unclear.

Until larger prospective studies concerning gentamicin associated nephrotoxicity provide more meaningful information concerning the significance of the variables involved in this adverse reaction, caution is recommended when using this drug in the albumin deficient patient or in combination with nephrotoxic drugs. In addition, it is further recommended that in patients receiving gentamicin, renal function should be closely monitored and the dosage regimen determined accordingly.

Inhibition of tobramycin reabsorption in nephron segments by metabolic alkalosis

Chronic metabolic acidosis appears to potentiate aminoglycoside induced nephrotoxicity and renal cortical accumulation while some, but not all, studies show that bicarbonate loading reduces nephrotoxicity. The purpose of the present study was to determine if reabsorption of tobramycin in proximal and distal nephron segments in vivo is altered by systemic pH. To test this possibility on the single nephron level, 24 nl samples of [3H] tobramycin were micro-injected into proximal and distal nephron segments, and its recovery was compared to that of [14C] inulin in rats undergoing osmotic diuresis with NaHCO3 or Na2SO4 containing HCl. Results were obtained in 66 tubules in 20 rats. Although plasma and urine pH were altered as anticipated in bicarbonate-infused and acid-infused animals, urine and late proximal tubule flow rates were similar. When animals were acid infused, 24.8 +/- 1.90% of [3H] tobramycin injected into proximal nephrons was reabsorbed compared to 7.5 +/- 1.56% (P less than 0.001) when the animals were bicarbonate-infused. When [3H] tobramycin was injected into distal tubules, 5.9 +/- 0.75% was reabsorbed in acid-infused rats while virtually none of the injected tobramycin, 0.43 +/- 1.59%, was reabsorbed by the distal nephron of bicarbonate-loaded animals. Our results provide evidence that tobramycin reabsorption by both proximal and distal nephron segments is substantially reduced by bicarbonate-infusion.

Effects of dietary electrolyte supplementation on gentamicin nephrotoxicity

The effects of electrolyte supplementation via drinking solutions on gentamicin-induced nephrotoxicity were studied in rats. Four groups of animals were injected with gentamicin, 120 mg/kg daily for 5 days and were studied 2-4 days after the last injection. Electrolyte supplements were begun before the gentamicin injections and were continued throughout the study. The drinking solutions were tap water, NaCl, NaCl + KCl, or NaHCO3 + KHCO3 + diamox. At the end of the study, blood urea nitrogen (BUN) and serum creatinine were markedly increased only in the group receiving tap water. Nevertheless, 24 hour creatinine clearance in awake rats and inulin clearance in anesthetized rats were found to be severely reduced in all gentamicin-treated animals. However, the rats receiving NaHCO3 + KHCO3 + diamox had significantly higher creatinine clearance than all other experimental groups. Proximal intratubular free-flow pressure, measured by micropuncture, and internal proximal diameters were significantly increased above normal controls in all groups, but were least abnormal in the rats receiving HCO3- and diamox. Semiquantitative histologic evaluation revealed significantly less tubular necrosis and cast formation in this group than in all the other experimental groups. The observations suggest that dietary sodium, potassium, and chloride supplements, even accompanied by large fluid intake, provide relatively little protection against gentamicin nephrotoxicity. In contrast, HCO3- and diamox supplements resulted in significant, albeit incomplete, protection of GFR and renal histology.

A controlled study of the nephrotoxicity of mezlocillin and gentamicin plus ampicillin in the neonate

The nephrotoxicity of the aminoglycoside gentamicin was evaluated in an open, controlled study of newborn infants randomly allocated to receive either combination drug therapy with gentamicin and ampicillin or single drug therapy with mezlocillin for treatment of presumed neonatal sepsis. There were no significant differences in initial clinical characteristics between the groups. Neonates receiving gentamicin, in contrast to those receiving mezlocillin, had significant nephrotoxicity manifested by a smaller postnatal fall in mean serum creatinine concentration (-9%, P NS vs -21%, P less than 0.005, respectively) and a diminished postnatal rise in mean creatinine clearance (+ 21%, P NS vs + 51%, P less than 0.01, respectively). In neonates with a fall in creatinine clearance, the mean decline was significantly greater in those receiving gentamicin (44% vs 20%, P less than 0.01). There was no relationship between the incidence of gentamicin nephrotoxicity and either peak or trough gentamicin levels. For treatment of presumed neonatal sepsis, gentamicin proved more nephrotoxic than mezlocillin.

Adverse drug reactions in the horse

Adverse drug reactions occasionally occur in the horse. The majority can be anticipated and avoided. The practicing veterinarian should understand the various types of adverse reactions as well as their mechanisms so that should such a reaction occur, the practitioner can promptly recognize the problem and institute corrective measures.

Modification of experimental aminoglycoside nephrotoxicity

Some of the factors that modify experimental aminoglycoside nephrotoxicity are reviewed. Maneuvers ready to be tested for effectiveness in the clinical use of these drugs are highlighted. The use of concomitant penicillins and changes in dosing strategy seem to be particularly exciting new leads toward elimination of clinical aminoglycoside nephrotoxicity.

Increased nephrotoxicity of gentamicin in pyelonephritic rats

Multiple factors may increase the nephrotoxic potential of aminoglycosides. We studied gentamicin susceptibility of kidneys infected with E. coli. Several parameters of renal function, histological changes on light and electron microscopy, and drug levels in renal parenchyma were compared in pyelonephritic and normal rats treated with low doses (10 mg/kg/Q8 hr for 3 days), or high doses (60 mg/kg/day for 14 days), of gentamicin. A significant increase (P less than 0.01) in beta-galactosidase and protein excreted in urine over a period of 17 days associated with severe changes in diuresis and osmolality was noted in the infected treated rats (low doses) compared with normal, treated, infected or control animals. Histological modifications compatible with gentamicin nephrotoxicity were more persistent in the infected treated animals. A significant decrease in 14C inulin (P less than 0.01) and 3H-PAH clearance and secretion (P less than 0.02) was observed in the infected treated rats receiving high doses of antibiotics. Cellular necrosis and tubular desquamation also were more severe in this group. Gentamicin levels in the cortex and medulla of infected animals were significantly higher than in the normals (P less than 0.01) and might have been responsible for the increased toxicity noted in the pyelonephritic animals. Infected kidneys appeared to be more susceptible to the nephrotoxic potential of gentamicin.

Captopril enhances aminoglycoside nephrotoxicity in potassium-depleted rats

We demonstrated that potassium depletion significantly increased gentamicin nephrotoxicity in Sprague-Dawley rats (100 mg X kg-1 X day-1). To determine whether this enhanced toxicity was mediated by renin secretion, we evaluated the effect of a converting enzyme inhibitor in this model. When we administered the combination of captopril (100 mg X kg-1 X day-1) and gentamicin in potassium-depleted rats, we observed a surprising and significant adverse effect of this combination on the clearances of inulin (CIn) and PAH (CPAH) and renal blood flow (RBF). Pretreatment with indomethacin significantly improved CIn and CPAH, and potassium repletion abolished this effect entirely. In potassium-depleted animals that received both gentamicin and captopril, the intra-arterial administration of imidazole, a thromboxane synthetase inhibitor, significantly reduced urinary TXB2 excretion and significantly improved RBF and CIn in vivo. In the same group of animals, administration of the kallikrein antagonist aprotinin also significantly increased both RBF and CIn. To measure total renal thromboxane B2 production (TXB2), we perfused kidneys ex vivo with cell-free perfusate. Three groups of animals were studied: potassium-repleted control animals, potassium-depleted control animals, and potassium-depleted animals treated with gentamicin alone, captopril alone, or the combination of gentamicin and captopril. We measured TXB2 in renal venous effluent by radioimmunoassay. Ex vivo perfused kidneys from potassium-depleted control animals produced significantly more TXB2 than potassium-repleted controls. Kidneys from potassium-depleted animals that received both gentamicin and captopril produced significantly greater amounts of TXB2 than did kidneys from potassium-depleted animals treated with captopril alone, gentamicin alone, or control potassium-depleted kidneys. The administration of imidazole ex vivo at a rate equivalent to in vivo administration (10 microM/min) reduced TXB2 production by potassium-depleted kidneys that received the combination of gentamicin and captopril to that of potassium-repleted control kidneys. These results suggest that the deleterious effect of captopril in potassium-depleted rats that received gentamicin is due at least in part to kinin-stimulated renal TXB2 production.

Therapeutic initiatives for the avoidance of aminoglycoside toxicity

Aminoglycosides continue to be indispensable in the management of serious and life-threatening aerobic gram-negative infections. On an annual basis in the United States, they are used in the management of four million patients. Despite their clinical utility, they continue to manifest a high profile of toxic side effects such as nephrotoxicity and ototoxicity with the rare occurrence of neuromuscular toxicity. Animal experimental models have been invaluable in elucidating the pathophysiologic mechanisms by which aminoglycosides damage the kidney and the inner ear. However, it is from clinical therapeutic experience and prospective clinical trials that we have been able to solidly define the risk factors that accentuate the development of aminoglycoside-related toxicity. The clinical toxicity of these agents can be kept to a minimum by ensuring the use of an appropriate dose, for periods of time not exceeding nine to ten days, in a well-hydrated, normokalemic patient. Special subpopulation groups such as the elderly, the obese, those with preexisting renal disease, or patients who need the concurrent use of other nephrotoxins, require special care in the monitoring of their aminoglycoside therapy to ensure a safe and effective clinical outcome.

Effect of some simple manoeuvres on the course of acute renal failure after gentamycin treatment in rats

For a period of 5 days, Wistar rats received Gentamycin (G), 100 mg/kg b.w./day i.m. Three days after the last injection, the rats were sacrificed and the plasma concentrations of urea (PU) and creatinine (PCr) were determined. Both values were significantly higher than in the control rats receiving vehicle only. The increase was substantially greater in females than in males. The rats drinking isotonic NaCl solution instead of water 7 days prior to G showed near normal PU and PCr values; drinking of NaHCO3 had a similar protective effect. Isotonic sucrose solution was without any influence. The rats drinking Ca gluconate or NH4Cl solutions had similar or higher PU and PCr values as rats drinking water, but their body weight and overall condition markedly deteriorated. Brattleboro rats with diabetes insipidus exhibited a very similar course as Wistar rats; there was also no significant difference between the former and their heterozygous non-insipidic litter mates.

Role of tubular obstruction in acute renal failure due to gentamicin

Gentamicin sulfate was administered by intraperitoneal injection to male Sprague-Dawley rats in a dose of 100 to 120 mg/kg/day for 4 to 5 days to induce severe nephrotoxicity. In comparison to controls, inulin clearance was markedly decreased (2.87 +/- 0.31 vs. 8.65 +/- 0.31 ml/min/kg, P less than 0.001) as was urinary osmolality (462 +/- 36 vs. 1196 +/- 46, P less than 0.001). Surface tubules appeared heterogeneous. Some were plugged by whitish debris, whereas others were markedly dilated (I.D. = 41.5 +/- 2 mu). All other tubules were moderately dilated (I.D. = 28.8 vs. 20 mu). The microinfusion of tubules with cellular debris with an isotonic "equilibrium" solution resulted in a rise in intratubular pressure to as high as 60 to 80 mm Hg, compared with 13 to 15 mm Hg in normal rats. In better functioning nephrons, free-flow pressure (FFP) was increased significantly (16.0 +/- 0.5 vs. 10.2 +/- 0.1 mm Hg, P less than 0.001). Paired measurements of single nephron glomerular filtration rate (SNGFR) in these nephrons, made while monitoring intratubular pressure (ITP), revealed a rise in SNGFR when ITP was lowered from the initially high level to 10 mm Hg. Comparable changes in SNGFR were induced in normal rats by varying ITP from 10 to 15 mm Hg. The data suggest that in severe gentamicin nephrotoxicity, many cortical nephrons may be contributing very little to excretory function, presumably because of intratubular obstruction. The less impaired nephrons have reduced SNGFR, due in part to increased free-flow pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal uptake and nephrotoxicity of gentamicin during urinary alkalinization in rats

1. Effect of urine pH on accumulation of gentamicin in the renal cortex of rats was studied following constant intravenous infusion, and single or repeated i.v. injections with gentamicin. 2. The cortical uptake of gentamicin was moderately inhibited by urinary alkalinization due to sodium bicarbonate treatment, but was unaffected by acidification with ammonium chloride. The altered urinary pH had no effect on urinary excretion of gentamicin. 3. An alkaline urine induced by acetazolamide injections failed to influence cortical accumulation of gentamicin. This effect may be ascribed to 'acidification' of the proximal tubular fluid after carbonic anhydrase inhibition, even though the final urine was alkaline. 4. Nephrotoxicity resulting from chronic treatment of gentamicin was ameliorated by concomitant sodium bicarbonate administration. 5. In conclusion, the intratubular pH of the proximal tubule is a factor which influences the cortical uptake of gentamicin, probably by means of changing the cationic nature of the molecule and, therefore, reduced binding with the luminal membrane.

Mechanisms of the defect in glomerular ultrafiltration associated with gentamicin administration

Micropuncture studies were performed in three groups of Munich-Wistar rats: eight normal hydropenic controls (group I) and two groups (eight rats each) which were treated with gentamicin in doses of either 4 or 40 mg/kg/day for ten days (groups II and III, respectively). Following gentamicin administration, values for single nephron (SN) GFR were reduced markedly, from the control mean of 31 +/- 0.7 (SEM) nl/min to 22.4 +/- 1.5 and 20.5 +/- 0.9 for groups II and III, respectively. Declines in whole kidney GFR paralleled these falls in SNGFR. The primary cause of the reduction in SNGFR was a marked decline in glomerular capillary ultrafiltration coefficient, Kf, in both gentamicin treatment groups. None of the other determinants of glomerular ultrafiltration were significantly affected in the low dose group (group II). In the high dose group (group III), however, mean values for initial glomerular plasma flow rate and mean transglomerular hydraulic pressure difference were significantly lower than in the control group, accounting for the somewhat greater decline in SNGFR observed in group III. Electron microscopic examination of kidney tissue from rats treated with both doses of gentamicin revealed no obvious abnormalities of the glomerular capillary wall, whereas the previously described morphologic aberrations of proximal convoluted tubule cells were readily demonstrable.

In vitro uptake of gentamicin by rat renal cortical tissue

The mechanism of gentamicin uptake in vitro by renal cortical slices of rat kidney was investigated. The cortical-slice-uptake ratio of gentamicin concentration in 1.0 g of tissue water to that of 1.0 ml of incubation medium (SW/M) was 1.44 +/- 0.04. The uptake of gentamicin was inhibited by 2 x 10(-5) M dinitrophenol (SW/M = 1.03 +/- 0.04) and by anoxia (SW/M = 1.01 +/- 0.04). The results indicate that aerobic phosphorylation is required to transport gentamicin into the cells. The uptake of p-aminohippurate and tetraethylammonium chloride by renal cortical slices was not affected by gentamicin.