Renal excretion of vancomycinin in kidney disease

A Meta-Analysis on the Performance of Cystatin C- versus Creatinine-based eGFR Equations in Predicting Vancomycin Clearance

BACKGROUND

The objective of this study was to compare the performance of cystatin C- and creatinine-based estimated glomerular filtration rate (eGFR) equations in predicting the clearance of vancomycin.

METHODS

MEDLINE and Embase databases were searched from inception up to September 2019 to identify all studies that compared the predictive performance of cystatin C- and/or creatinine-based eGFR in predicting the clearance of vancomycin. The prediction errors (PEs) (the value of eGFR equations minus vancomycin clearance) were quantified for each equation and were pooled using a random-effects model. The root mean squared errors were also quantified to provide a metric for imprecision.

RESULTS

This meta-analysis included evaluations of seven different cystatin C- and creatinine-based eGFR equations in total from 26 studies and 1,234 patients. The mean PE (MPE) for cystatin C-based eGFR was 4.378 mL min^-1 (95% confidence interval [CI], -29.425, 38.181), while the creatinine-based eGFR provided an MPE of 27.617 mL min^-1 (95% CI, 8.675, 46.560) in predicting clearance of vancomycin. This indicates the presence of unbiased results in vancomycin clearance prediction by the cystatin C-based eGFR equations. Meanwhile, creatinine-based eGFR equations demonstrated a statistically significant positive bias in vancomycin clearance prediction.

CONCLUSION

Cystatin C-based eGFR equations are better than creatinine-based eGFR equations in predicting the clearance of vancomycin. This suggests that utilising cystatin C-based eGFR equations could result in better accuracy and precision to predict vancomycin pharmacokinetic parameters.

Vancomycin Resistance Is Overcome by Conjugation of Polycationic Peptides

Multidrug-resistant bacteria represent one of the biggest challenges facing modern medicine. The increasing prevalence of glycopeptide resistance compromises the efficacy of vancomycin, for a long time considered as the last resort for the treatment of resistant bacteria. To reestablish its activity, polycationic peptides were conjugated to vancomycin. By site-specific conjugation, derivatives that bear the peptide moiety at four different sites of the antibiotic were synthesized. The most potent compounds exhibited an approximately 1000-fold increased antimicrobial activity and were able to overcome the most important types of vancomycin resistance. Additional blocking experiments using d-Ala-d-Ala revealed a mode of action beyond inhibition of cell-wall formation. The antimicrobial potential of the lead candidate FU002 for bacterial infection treatments could be demonstrated in an in vivo study. Molecular imaging and biodistribution studies revealed that conjugation engenders superior pharmacokinetics.

Vancomycin-Induced Kidney Injury: Animal Models of Toxicodynamics, Mechanisms of Injury, Human Translation, and Potential Strategies for Prevention

Vancomycin is a recommended therapy in multiple national guidelines. Despite the common use, there is a poor understanding of the mechanistic drivers and potential modifiers of vancomycin-mediated kidney injury. In this review, historic and contemporary rates of vancomycin-induced kidney injury (VIKI) are described, and toxicodynamic models and mechanisms of toxicity from preclinical studies are reviewed. Aside from known clinical covariates that worsen VIKI, preclinical models have demonstrated that various factors impact VIKI, including dose, route of administration, and thresholds for pharmacokinetic parameters. The degree of acute kidney injury (AKI) is greatest with the intravenous route and higher doses that produce larger maximal concentrations and areas under the concentration curve. Troughs (i.e., minimum concentrations) have less of an impact. Mechanistically, preclinical studies have identified that VIKI is a result of drug accumulation in proximal tubule cells, which triggers cellular oxidative stress and apoptosis. Yet, there are several gaps in the knowledge that may represent viable targets to make vancomycin therapy less toxic. Potential strategies include prolonging infusions and lowering maximal concentrations, administration of antioxidants, administering agents that decrease cellular accumulation, and reformulating vancomycin to alter the renal clearance mechanism. Based on preclinical models and mechanisms of toxicity, we propose potential strategies to lessen VIKI.

A Larger Dose of Vancomycin Is Required in Adult Neurosurgical Intensive Care Unit Patients Due to Augmented Clearance

BACKGROUND

The objective of this study was to explore the pharmacokinetics of vancomycin and determine an appropriate dosage regimen for vancomycin in adult neurosurgical intensive care unit (ICU) patients.

METHODS

First, a 20-month therapeutic drug monitoring database at a medical center was used to retrospectively analyze the pharmacokinetic parameters of vancomycin in adult neurosurgical patients. Significant covariates were selected through Pearson or Spearman correlation tests and multiple linear regressions. Pharmacokinetic models were built using significant covariates to predict vancomycin clearance. Second, a 12-month prospective cohort of neurosurgical ICU patients was recruited to validate the models. Urine and cerebrospinal fluid samples were collected, and vancomycin concentrations were determined using a high-performance liquid chromatography assay. The relation between the model-predicted and observed pharmacokinetic parameters was assessed by Pearson correlation.

RESULTS

In the retrospective cohort, 98 sets of peak/trough serum concentrations obtained from 73 patients were analyzed. These patients had a mean age of 54 ± 16 years, an estimated creatinine clearance (eClCr) of 83 ± 29 mL/min, a total vancomycin clearance (ClVan) of 101 ± 41 mL/min, and a volume of distribution (Vd) of 0.93 ± 0.27 L/kg. In a subgroup analysis, the ClVan of ICU patients was higher than the ClVan of non-ICU patients (1.57 ± 0.34-fold versus 1.16 ± 0.32-fold of eClCr, P < 0.05). Fifteen patients enrolled in the prospective cohort had an average age of 67 ± 12 years, an eClCr of 108 ± 44 mL/min, a ClVan of 112 ± 29 mL/min, and a Vd of 1.03 ± 0.55 L/kg.

CONCLUSIONS

Adult neurosurgical ICU patients have a significantly elevated ClVan. In this study, 2 dosing equations were derived to achieve optimal serum vancomycin concentrations for this special population.

Evaluation of the Safety of a Vancomycin Nomogram Used to Achieve Target Trough Concentrations

BACKGROUND

Dosing vancomycin to achieve target concentrations of 15 to 20 mg/L has been recommended for select infections. To date, few vancomycin nomograms designed to target these higher concentrations have been published, and only one has been published in North America. Based on the success of this nomogram in developing empiric vancomycin regimens that achieve higher target trough concentrations with low rates of nephrotoxicity, a vancomycin nomogram targeting concentrations of 15 to 20 mg/L was developed and implemented at Emory University Hospital and Emory University Hospital Midtown.

OBJECTIVE

To evaluate the impact of a vancomycin-dosing nomogram on the incidence of vancomycin- associated nephrotoxicity and the time to achieve targeted trough concentrations.

METHODS

A retrospective chart review of 200 patients who received vancomycin dosed to achieve target trough serum concentrations of 15 to 20 mg/L was performed.

RESULTS

After implementation of the vancomycin nomogram, no statistically significant difference in incidence of vancomycin-associated nephrotoxicity was found (14% vs 16%; P = .197). Fewer patients had an initial vancomycin trough concentration within target range (29.1% vs 21.7%; P < .001). Adherence to the nomogram was poor, with only 41% of patients being dosed per the nomogram's recommendations.

CONCLUSION

Based on our results, implementation of a vancomycin dosing nomogram had no impact on the incidence of nephrotoxicity, and significantly fewer patients had an initial vancomycin trough within the target range of 15 to 20 mg/L. The clinical utility of a vancomycin dosing nomogram is still to be determined.

Prospective trial of a novel nomogram to achieve updated vancomycin trough concentrations

Purpose. To determine if the use of a novel vancomycin nomogram predicts dosing regimens that achieve target trough concentrations equal to or more accurate than dosing regimens calculated using traditional pharmacokinetic calculations, evaluate the incidence of subtherapeutic and supratherapeutic troughs, and assess pharmacist's impressions of the nomogram. Methods. Prospective, open-label study in 473 patients who had a new order for vancomycin and were >18 years of age and ≤120 kg. Patients were randomized to the active group, dosed using the nomogram, or to the control group, dosed using traditional pharmacokinetic calculations already in place at our institution. Results. Patients dosed via nomogram were within the appropriate trough range in 44% of cases compared to 33% in the control group (P = 0.014). Vancomycin troughs less than 10 mcg/mL were significantly decreased with the use of nomogram (P = 0.032). Incidence of supratherapeutic troughs, greater than 20 mcg/mL, was not significantly different between groups (P = 0.706), and pharmacists agreed that the nomogram was easy to use and saved their time. Conclusions. A novel vancomycin nomogram was prospectively validated and found to be more effective than traditional pharmacokinetic dosing. The nomogram is being implemented as the standard dosing protocol at our institution.

Vancomycin

This review describes the use of vancomycin in neonates over the last three decades. Given the relation of late-onset neonatal septicaemia to outcome and the increase in coagulase-negative staphylococcal infection as causative organism, vancomycin remains an important antibacterial in the neonatal intensive care unit. The pharmacokinetic behaviour of vancomycin in neonates can be adequately described by a one- or two-compartment model and is mainly determined by postconceptional age and renal function. In neonates, a patent ductus arteriosus as well as treatment with indomethacin or extracorporeal membrane oxygenation (ECMO) leads to an increase in volume of distribution and a decrease in clearance. Microbiological studies in vitro have shown that an increase in vancomycin concentrations above the minimum inhibitory concentration does not result in more effective killing. The microbiological and clinical efficacy of vancomycin in neonates has only been studied explicitly in a restricted number of patients. There are no definitive data relating serum concentrations to effect in this patient group. Vancomycin-related nephrotoxicity and ototoxicity in neonates is rare, and no clear relation to serum concentrations has been demonstrated. Based on the pharmacokinetic profile of vancomycin in neonates, several administration regimens have been constructed. Recent guidelines have suggested that dosage can be independent of gestational age or postconceptional age in neonates without renal failure. In patients with renal failure, therapy can be adequately tailored by using a regimen based on serum creatinine. The usefulness of routine monitoring of peak serum concentrations is doubtful based on the current literature. Recent research demonstrates a shift towards taking only routine trough serum concentrations in order to optimise efficacy. Patients with renal failure and other special subpopulations, such as patients exposed to ECMO or indomethacin, need to be monitored more closely.

Clinical review: use of vancomycin in haemodialysis patients

Following intravenous administration, vancomycin is poorly metabolized and is mainly excreted unchanged in urine. Total body clearance is thus dependent on the kidney, and is correlated with glomerular filtration rate and creatinine clearance. Accumulation of vancomycin in patients with renal insufficiency may therefore occur, and this may lead to toxic side effects if dosage is not modified according to the degree of renal failure. Furthermore, vancomycin easily diffuses through dialysis membranes. The aim of the present review is to establish guidelines for handling this drug in such patients. We indicate how and when plasma concentrations of vancomycin should be determined in dialysis patients.

Study of the pharmacokinetics of vancomycin in patients with impaired liver function

Infections caused by methicillin-resistant Staphylococcus aureus pose a serious problem postoperatively. Patients with hepatic dysfunction can be considered to be more susceptible to infection. Since little is known about the effects of the severity of hepatic dysfunction on the pharmacokinetics of vancomycin, we studied the pharmacokinetics of vancomycin in preoperative patients with hepatic dysfunction, after the intravenous infusion of 500 mg. In patients with liver disease and normal renal function, an enhancement of renal clearance caused by a reduction in percent protein binding was canceled out by a reduction in non-renal clearance caused by liver dysfunction, resulting in liver disease having no effect on the total clearance of the drug. In patients with impaired liver and renal functions and/or obstructive jaundice, the unbound fraction of vancomycin increased, whereas the renal excretion of vancomycin was delayed. It should be noted that an excessive increase in blood vancomycin concentration may be brought about even with a conventional dose in patients with hepatic dysfunction.

Therapeutic drug monitoring of vancomycin in a morbidly obese patient

The authors describe the therapeutic drug monitoring of vancomycin in a man who is morbidly obese. Because serum vancomycin concentration (SVC) monitoring continues to be deemphasized, nomogram use will likely increase. However, vancomycin dosing nomograms have not been studied in patients who are morbidly obese. Furthermore, in nomograms that incorporate body weight, it is unclear whether ideal or total body weight (IBW and TBW, respectively) should be used to dose the morbidly obese. Therefore, the authors retrospectively evaluated four nomograms (Moellering, Matzke, Lake-Peterson, and Rodvold) and an individualized method in the simulated vancomycin dosing of their patient. Total body weight was more accurate than IBW in selecting a vancomycin dose when using the individualized method and in all nomograms except the Matzke nomogram. The Rodvold nomogram and the individualized method yielded the most appropriate doses. All nomograms suggested dosing intervals that were unacceptably short; the individualized method suggested an appropriately longer interval. Thus, if nomograms or the individualized method are used to empirically dose vancomycin, TBW--not IBW--should be used. Because these nomograms yielded inappropriately short dosing intervals in the patient, it is likely that patients who are morbidly obese represent a unique population in which at least one set of SVCs are necessary to select an appropriate dosing regimen.

In-vivo clearance study of vancomycin in rats

The renal handling of vancomycin in rats and the effects of various drugs (probenecid, cimetidine and quinidine) on urinary excretion of the antibiotic were investigated by in-vivo clearance. The vancomycin-to-inulin excretion ratio (ER) was greater than unity at various infusion rates of vancomycin. Quinidine, co-administered with vancomycin, significantly decreased the total, renal and net secretory clearance of the antibiotic. Cimetidine also decreased, though not significantly, the secretory clearance of vancomycin by about 20%, but probenecid did not. These results suggested that vancomycin is secreted in renal tubules in rats, and that quinidine decreases the total clearance of vancomycin partly by inhibiting its tubular secretion in the kidney.

Effect of obesity on vancomycin pharmacokinetic parameters as determined by using a Bayesian forecasting technique

Few data exist concerning the effect of obesity on the pharmacokinetic parameters of vancomycin. The purpose of this investigation was to assess the effect of obesity on vancomycin pharmacokinetic parameters in 95 nonobese and 135 obese adult patients (age range, 18 to 92 years) receiving vancomycin. All subjects had normal renal function as defined by a creatinine concentration in serum of < or = 1.5 mg/dl (mean estimated creatinine clearance +/- 1 standard deviation, 76 +/- 34; range, 23 to 215 ml/min). Vancomycin concentrations in serum were determined by the fluorescence polarization immunoassay. All data for vancomycin concentration in serum versus time for each course of therapy were fitted by using a two-compartment Bayesian forecasting program. Subjects were stratified into nine groups on the basis of the percent difference between actual body weight (ABW) and lean body weight (LBW) (> -10%, -10 to 0%, > 0 to 10%, > 10 to 20%, > 20 to 30%, > 30 to 40%, > 40 to 50%, > 50 to 60%, > 60%). Analysis of variance with post hoc Scheffe's testing revealed that statistically significant differences occurred in terminal disposition half-life (t1/2 beta) between the extremes of modestly obese (group 4) and morbidly obese (group 9, P < 0.05) patients. Similar analysis with distribution volume (V) identified significant differences in patients at or near their LBW (groups 2 to 4) and patients who were morbidly obese (groups 8 and 9, P < 0.05). Multiple regression models for the pharmacokinetic parameters V, t1/2beta, and vancomycin total body clearance were developed to assess the joint predictive power of LBW, ABW, and percent over LBW, controlling for the effects of age, initial creatinine concentration in serum, initial creatinine clearance, and gender. In the final model for V, both ABW and percent over LBW were independent and significant predictors. For total body clearance, only ABW was significant and predictive. Percent over LBW was a significant and independent predictor of t1/2beta. LBW is not predictive of these pharmacokinetic parameters and should not be used for initial dosing. On the basis of these data, ABW appears to be superior to LBW for calculating initial dose requirements for vancomycin.

Simplified dosing and monitoring of vancomycin for the burn care clinician

Vancomycin has excellent activity against Gram-positive bacteria and is often selected for use in the infected burn patient. Because of multiple-compartment pharmacokinetics, vancomycin serum concentrations can decrease dramatically in a short time period following the end of an intravenous infusion. This accounts for the widely divergent recommendations for serum vancomycin peak concentrations, e.g. from 15 mg/l up to 80 mg/l, when the time for blood sampling following the end of intravenous infusion is different. It is in general not necessary to monitor vancomycin peak concentrations, not only because its toxic potential is overrated but also because potential toxicity and therapeutic efficacy are correlated with trough concentrations. Post-distribution 'peak' concentrations are generally only useful for determining the optimal dosing interval for patients with impaired renal function. A dosing and monitoring paradigm for vancomycin therapy in burned adults has been devised for burn care clinicians. It provides suggested dose and dosing intervals based on body weight and creatinine clearance, with specific recommendations for regimen modification based upon the results of trough serum concentration determinations.

Protein binding of vancomycin in a patient with immunoglobulin A myeloma

Atypical vancomycin pharmacokinetics were observed in an immunoglobulin A myeloma patient. Drug concentrations in serum were extremely elevated, the elimination half-life was prolonged despite normal renal function, and the vancomycin therapy was ineffective. Extensive binding of vancomycin, presumably by high concentrations of an aberrant immunoglobulin A protein, may have accounted for these observations.

Application of a Bayesian method to monitor and adjust vancomycin dosage regimens

A Bayesian method for monitoring vancomycin concentrations and adjusting regimens in patients with unstable renal function by using a two-compartment population model was evaluated with a personal computer. The population model was derived from data from 12 cardiac outpatients who received single doses of vancomycin. The performance of the method was then tested in 27 acutely ill patients who received multiple doses of vancomycin. Significant renal impairment was observed in 15 patients. Renal function changed in 15 patients. The vancomycin concentrations in the patients with changing renal function were not at steady state during the observation times. Two concentrations in serum (peak and then trough, or trough and then peak) were fitted along with the population model to individualize the parameter values for each patient. All the subsequent concentrations in serum for each patient were then predicted by using the parameter values for each patient. Future concentrations of 118 serum samples were predicted. The mean absolute prediction error was 3.6 +/- 4.5 micrograms/ml, and the mean prediction error was -0.7 +/- 5.3 micrograms/ml. These results confirm that a two-compartment pharmacokinetic model can be sufficiently individualized with the knowledge of just two concentrations of drug in patient serum; it is possible to predict closely subsequent concentrations in serum, and dosing regimens for individual patients can be well adjusted to achieve the chosen therapeutic goals.

Simulation of vancomycin peak and trough concentrations using five dosing methods in 37 patients

Five methods of dosing vancomycin (Matzke, Moellering, Nielsen, Lake-Peterson, and manufacturer's) were simulated in 37 patients. Ten serum samples were obtained after a 1-hour intravenous infusion of 6.2-20 mg/kg total body weight. A preinfusion serum sample was obtained from patients not studied on the first dose. Initial estimates of pharmacokinetic values were made using nonlinear iterative least squares regression and serum concentration-time data. These data were fitted to a two-compartment, open-infusion model. Simulations of the peak and trough serum concentrations at steady state for each patient were determined by multiple-dose simulated pharmacokinetics and each patient's pharmacokinetic values using the regimen suggested by each of the five methods. Steady-state serum concentrations, predicted systemic clearance by each method (except Lake-Peterson), and the daily dose for each patient recommended by each method were determined. All the methods underpredicted actual drug clearance, with the Nielsen method having the lowest prediction. The Matzke method recommended the largest dosage. Using each of the methods, only 3-16% of patients would have achieved recommended peak and trough serum concentrations. In the simulation model used, no method performed satisfactorily in attaining the desired vancomycin peak and trough concentrations. We suggest that the Lake-Peterson method could be used initially, provided that monitoring is also performed to adjust the dosage regimen further.

Therapeutic update on glycopeptide and lipopeptide antibiotics

Glycopeptide antibiotics in the form of vancomycin have been available for almost 30 years. In the past, vancomycin usually was reserved as an alternative agent to treat staphylococcal and streptococcal infection in patients with a penicillin allergy or hemodialysis shunt infection. With the increasing frequency of both methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis, now it is often used as a first-line agent. Over a 10-year period, vancomycin sales have increased by almost $1 hundred million. Several new glycopeptide and lipopeptide antibiotics are in various stages of evaluation. While vancomycin resistance to date is a rare phenomenon, these drugs represent a potentially more potent and safer antibiotic alternative to vancomycin. Teicoplanin and daptomycin are two of these investigational agents.

Vancomycin pharmacokinetics in patients with various degrees of renal function

The influence of age, protein binding, and renal function on the pharmacokinetics of intravenous vancomycin was evaluated in 37 adult patients with various degrees of renal function. Patients were categorized into three groups based on measured creatinine clearance (CLCR): groups 1, 2, and 3 had 24-h CLCRs of greater than 70, 40 to 70, and 10 to 39 ml/min per 1.73 m2, respectively. After 1 h of intravenous infusion, concentrations of vancomycin in serum declined in a biexponential manner in all patients. Diminished renal function in groups 2 and 3 was accompanied by a lower total body vancomycin clearance (CL) (52.6 and 31.3, respectively, versus 98.4 ml/min per 1.73 m2) and a lower renal vancomycin clearance (CLR) (48.2 and 19.8, respectively, versus 88.0 ml/min per 1.73 m2) than in group 1. No significant differences in apparent distribution volume of the central compartment or apparent distribution volume at steady state were observed. Mean serum protein binding of vancomycin was 30% and was not significantly affected by renal function. Stepwise multiple linear regression analysis revealed that CLCR was the strongest predictor of vancomycin CL (r = 0.77, P less than 0.001) and vancomycin CLR (r = 0.87, P less than 0.001). Age did not significantly improve these correlations once CLCR was included. The relationship of vancomycin CL and CLCR was utilized to develop the following equation to dose vancomycin in the majority of renally impaired patients: dose (milligrams per kilogram per 24 h) = 0.227CLCR + 5.67, where CLCR is standardized to milliliters per minute per 70 kg. The practical dosing intervals that the calculated dose can be divided into and administered include 8, 12, 24, and 48 h based on the CLCR of the patient.

Vancomycin serum protein binding determination by ultrafiltration

Sixty-two serum concentrations were obtained from 12 infected patients enrolled in a vancomycin pharmacokinetic study. Both unbound and total serum vancomycin concentrations were measured using ultrafiltration and a commercial fluorescent polarization immunoassay. Ultrafiltrates were obtained by centrifugation at 1000 X g for ten minutes at room temperature and their assay indicated a range in protein binding from 7.9 to 71 percent. The mean protein binding (mean +/- SD) was 41.95 +/- 14.15 percent. No measurable adsorption of vancomycin onto the ultrafiltration membrane was noted. Orthogonal regression of unbound versus total vancomycin concentrations was described by the equation y = 0.597x-0.362 with a correlation coefficient of 0.948.

Monitoring vancomycin therapy

Vancomycin is an effective and widely used antistaphylococcal antibiotic. Despite several decades of use, however, our knowledge of the toxicologic and pharmacokinetic properties of vancomycin remains incomplete. This review summarizes current information regarding the adverse reactions and pharmacokinetics of vancomycin. Although there have been reports of side effects with vancomycin, these effects tend to be infrequent, easily managed, and reversible. Several methods for adjustment of vancomycin therapy have been recommended. The relationship between serum concentrations of vancomycin and the occurrence of ototoxicity or nephrotoxicity has not been well established. However, because of large interpatient variations in pharmacokinetic parameters, it seems preferable to individualize vancomycin therapy based on serum concentration data.

Vancomycin: an update

Vancomycin is a narrow-spectrum glycopeptide antibiotic with potent antistaphylococcal activity. It is primarily active against gram-positive organisms. Bacterial resistance rarely develops due to its numerous modes of action. The toxic potential of vancomycin is less significant than previously thought. "Red neck syndrome" seems to be the most common side effect and appears to be caused by rapid intravenous infusion. It is characterized by erythema at the base of the neck and the upper back; hypotensive episodes may also occur. Nephrotoxicity and ototoxicity are rare. Relationships between toxicities and serum concentrations have not been established. The disposition of vancomycin after intravenous administration proceeds biphasically--rapid distribution followed by elimination. The drug is excreted primarily unchanged in the urine by glomerular filtration. Vancomycin clearance is reduced and elimination half-life is prolonged in patients with renal insufficiency. Various methods have been published to aid in dosing the drug in these patients. Vancomycin is the drug of choice in the treatment of methicillin-resistant staphylococcal infections. It is also useful in the treatment of gram-positive endocarditis and has been used as alternative therapy in the treatment of prophylaxis of gram-positive infections in penicillin-allergic patients. Oral vancomycin is the preferred therapy in antibiotic-associated colitis.

Individualized adjustment of vancomycin dosage: comparison with two dosage nomograms

An individualized method of vancomycin dosage adjustment using steady-state serum concentrations was assessed in 50 patients (86 sets of vancomycin serum concentrations). The predictive accuracy of this method was compared with that of two published nomograms (Moellering, Matzke). Peak and trough serum concentrations predicted from previously drawn vancomycin serum concentrations (individualized method) using a one-compartment pharmacokinetic model were compared with measured steady-state peak and trough serum concentrations. Predicted peak and trough serum concentrations were also generated for both the Moellering and Matzke nomograms by using the elimination rate constant derived from each of the respective nomograms and the fixed volume of distribution (0.9 L/kg) assumed by the nomograms, and the actual administered vancomycin dose and dosage interval. These predicted concentrations were also compared with the measured peak and trough concentrations. Statistical measures of bias and precision indicated that the individualized method of dosage adjustment more closely predicted vancomycin serum concentrations following a dosage change than did either of the nomograms. Overall, the Moellering nomogram was the least accurate of the three methods in predicting vancomycin serum concentrations, and this nomogram should not be used to titrate vancomycin dosages in a clinical setting. Adjustment of vancomycin dosages should be individualized based on pharmacokinetic data derived from measured serum concentrations. In situations where quantitative analysis of vancomycin concentrations is not available, the Matzke nomogram appears to be a reasonable method of adjusting vancomycin dosages.

A simplified dosing method for initiating vancomycin therapy

Vancomycin dosing regimens should be individualized for each patient. The routine use of standard doses 500 mg every 6 hours or 1.0 g every 12 hours regardless of patients' age, weight or kidney function is no longer appropriate. A simplified method for initiating vancomycin therapy was developed and evaluated prospectively in 30 patients. Average doses of 8.3 +/- 0.6 mg/kg lean body weight (rounded to the nearest 50 mg) were administered to patients with varying degrees of renal function (estimated creatinine clearances 19-113 ml/min). The dosing interval was predicted by the patient's estimated creatinine clearance. Our simplified schedule resulted in desired serum levels and required no modification in 25 of 30 patients. Only slight dosage changes were needed in the remaining five patients. Mean peak and trough serum concentrations of vancomycin were 26.9 +/- 5.8 micrograms/ml (range 18.8-39.7 micrograms/ml) and 7.7 +/- 2.0 micrograms/ml (range 4.5-11.8 micrograms/ml) respectively. Our regimen is practical and simple and requires limited patient information.

Pharmacokinetics of vancomycin in patients with various degrees of renal function

The pharmacokinetics of vancomycin were characterized in 56 patients with different degrees of renal function after an intravenous dose of 18.4 +/- 4.7 mg kg-1 (mean +/- standard deviation). Seven subjects had a creatinine clearance (CLCR) of greater than 60 ml min-1 (group I), 13 had a CLCR of 10 to 60 ml min-1 (group II), and 36 had a CLCR of less than 10 ml min-1 (group III). Serial serum samples (range, 3 to 8) were collected during the 168 h after drug administration. The serum concentration-time profile in all patients demonstrated monoexponential decay. The mean half-lives were 9.1, 32.3, and 146.7 h in groups I, II, and III, respectively. A significant decline in serum clearance (CLS) was also noted (62.7 to 28.3 to 4.87 ml min-1 in groups I, II, and III, respectively). The steady-state volume of distribution varied from 0.72 to 0.90 liter kg-1. There was no significant relationship between the steady-state volume of distribution and CLCR. The observed relationship between CLS and CLCR (CLS = 3.66 + 0.689 CLCR; r = 0.8807) can be utilized to devise dosage schedules for patients with any degree of renal impairment. This relationship was utilized to develop a nomogram for initial and maintenance dosing of vancomycin.

Effects of hepatic function on vancomycin clinical pharmacology

Using a recently developed radioimmunoassay, we performed 15 vancomycin pharmacology studies in cancer patients with infections. Vancomycin (500 mg) was infused intravenously for 30 min every 6 h for up to 7 days. The plasma disappearance curve was biphasic, with an initial half-life of less than 30 min. The second half-life (t1/2 beta), not dose related, varied from 1.4 to 231 h among the patients. In six studies of patients with normal hepatic functions, the t1/2 beta was 2.6 h; the rate of total clearance was 162 ml/min. In contrast, nine studies of patients with impaired liver function had a much longer t1/2 beta (37 h) and a decrease in the rate of total clearance to 48 ml/min. These factors resulted in an increase in the value of area under the concentration-time curve from 59 to 3,434 micrograms X h/ml. These results have demonstrated the importance of the effects of liver function on vancomycin disposition. The vancomycin dose and schedule should be adjusted for patients with liver impairment.

Vancomycin

While vancomycin is thus not as nephrotoxic as once feared, its use by the parenteral route should be avoided if possible when other nephrotoxic drugs are being given. Used properly, vancomycin appears efficacious and can be given with safety to infants, children, and adults. Vancomycin is incompatible with many other drugs in intravenous solutions, especially chloramphenicol, adrenocorticosteroids, and methicillin.

Vancomycin therapy for serious staphylococcal infections in chronic hemodialysis patients

Vancomycin therapy during 7 episodes of serious staphylococcal infections in chronic hemodialysis patients was monitored by a sensitive bioassay technique. One gm of vancomycin was given during dialysis at a mean dosage interval of 7 days for a mean duration of 48 days. Serum peak and trough vancomycin levels were monitored during therapy. Accumulation of vancomycin occurred in 1 patient on prolonged therapy; progressive rising through levels required a reduction in vancomycin dosage. Pre and post-dialysis vancomycin levels in one patient were unchanged. Vancomycin was effective in eradication of all staphylococcal infections and bacteremias. Three A-V shunt infections required surgical revision; 2 A-V fistula infections were salvaged with vancomycin therapy alone. We conclude that 1 gm vancomycin every 7 days is an effective regimen for serious staphylococcal infections in chronic hemodialysis patients. Monitoring of vancomycin levels insures maintenance of adequate levels and prevents toxic accumulation.

Bacteremia after renal transplantation

Of 291 patients who received renal allotransplants in 1964-74, 94 patients developed 121 bacteremic episodes within the first 6 months after transplantation. The death rate was 38%. The bacteremic episodes occurred mainly during the first 2-3 months after transplantation. In 65% of the episodes bacteremia was secondary to urinary tract infections. The bacteria fourn were most often gram-negative rods such as Escherichia coli, Klebsiella and Proteus. Predisposing factors were ureteral complications such as leakage or necrosis of the ureter, leucopenia, immunosuppression, and source of the kidney. The frequency of bacteremia was the same in patients with infectious and non-infectious primary renal disease.