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

Preventing surgical site infections after bariatric surgery: value of perioperative antibiotic regimens

Bariatric surgery for obesity has emerged as an effective and commonly used treatment modality. This paper reviews the surgical site infections (SSIs) that occur post bariatric surgery and SSI prevention. The benefit of bariatric surgery resulting in profound weight loss brings with it consequences in the form of postoperative complications that can have profound effects on morbidity and mortality in these patients. This paper sets out to define different types of SSIs that occur following bariatric surgery and to discuss existing literature on the critical aspects of SSI prevention and the appropriate use of surgical antimicrobial prophylaxis for bariatric surgery.

Drug disposition in obesity and protein–energy malnutrition

Clinical response to medication can differ between patients. Among the known sources of variability is an individual's nutrition status. This review defines some pharmacokinetic terms, provides relevant body size metrics and describes the physiologic influences of protein–energy malnutrition and obesity on drug disposition. Weight-based drug dosing, which presumes a healthy BMI, can be problematic in the protein–energy malnourished or obese patient. The use of total body weight, lean body weight, or an adjusted body weight depends on the drug and how it is differently handled in malnutrition or obesity. Most of the recognized influences are seen in drug distribution and drug elimination as a result of altered body composition and function. Distribution characteristics of each drug are determined by several drug-related factors (e.g. tissue affinity) in combination with body-related factors (e.g. composition). Drug elimination occurs through metabolic and excretory pathways that can also vary with body composition. The current data are limited to select drugs that have been reported in small studies or case reports. In the meantime, a rational approach to evaluate the potential influences of malnutrition and obesity can be used clinically based on available information. Antimicrobials are discussed as a useful example of this approach. Further advancement in this field would require collaboration between experts in body composition and those in drug disposition. Until more data are available, routine monitoring by the clinician of the protein–energy malnourished or obese patient receiving weight-based drug regimens is necessary.

Use of vancomycin pharmacokinetic-pharmacodynamic properties in the treatment of MRSA infections

Vancomycin is a commonly used antimicrobial in patients with methicillin-resistant Staphylococcus aureus (MRSA) infections. Increasing vancomycin MIC values in MRSA clinical isolates makes the optimization of vancomycin dosing pivotal to its continued use. Unfortunately, limited data exist regarding the optimal pharmacokinetic-pharmacodynamic (PK-PD) goal to improve bacterial killing and clinical outcomes with vancomycin. The hallmark study in this area suggests that achieving an AUC to MIC ratio of over 400 improves the likelihood of achieving these outcomes. Challenges in the implementation of PK-PD-based dosing for vancomycin include current methodologies utilized in microbiology laboratories, as well as intra- and interpatient pharmacokinetic variability. Individualized dosing based on MIC and specific patient factors is important to achieve optimal outcomes from vancomycin therapy.

Development of teicoplanin dosage guidelines for patients treated within an outpatient parenteral antibiotic therapy (OPAT) programme

OBJECTIVES

The long elimination half-life of teicoplanin facilitates outpatient parenteral antibiotic therapy (OPAT) with thrice-weekly dosing. This study aimed to develop teicoplanin dosage guidelines for OPAT use from routine clinical data.

METHODS

Patients received 15-25 mg/kg/day for 3 days, then 15-25 mg/kg thrice weekly. Trough concentrations were measured weekly and doses adjusted to maintain 20-30 or 10-20 mg/L according to clinical condition. Concentration-time data were analysed using the pharmacokinetic package NONMEM and the final model was used to develop new dosage guidelines.

RESULTS

Data from 94 and 36 patients were used for model development and validation, respectively. Patient ages ranged from 15 to 94 years, weights from 43 to 146 kg and estimated CL(CR) from 9 to 195 mL/min. Teicoplanin concentrations (n = 670) ranged from 6.7 to 66.9 mg/L and a one-compartment model adequately described the data. The typical estimate of CL was 0.542 L/h and changed by 10.6% for every 10 mL/min difference from a CL(CR) of 66 mL/min. V was 1.62 L/kg. Dosage guidelines based on body weight and CL(CR) can be expected to lead to a significant improvement in the proportion of concentrations in the range 20-30 mg/L. Alternative doses aimed at lower target concentrations have also been developed.

CONCLUSIONS

New dosage guidelines have been developed to support thrice-weekly administration of teicoplanin in an OPAT setting.

Multicenter evaluation of vancomycin dosing: emphasis on obesity

BACKGROUND

There is a paucity of data available regarding the dosing of antimicrobials in obesity. However, data are available demonstrating that vancomycin should be dosed on the basis of actual body weight.

METHODS

This study was conducted at 2 tertiary care medical centers that did not have pharmacy-guided vancomycin dosing programs or other institutional vancomycin dosing policies or protocols. Patients who received vancomycin between July 1, 2003, and June 30, 2006, were stratified by body mass index and randomly selected from the computer-generated queries. Patients >or=18 years of age with a creatinine clearance of at least 60 mL/min who received vancomycin for at least 36 hours were included.

RESULTS

Data were collected on a random sampling of 421 patients, stratified by body mass index, who met the inclusion criteria. Most patients in each body mass index category received a fixed dose of vancomycin 2 g daily divided into 2 doses (underweight 82%, normal weight 90%, overweight 86%, and obese 91%). Adequate initial dosing (>or=10 mg/kg/dose) was achieved for 100% of underweight, 99% of normal weight, 93.9% of overweight, and 27.7% of obese patients (P < .0001). Ninety-seven percent of underweight, 46% of normal weight, 1% of overweight, and 0.6% of obese patients received >or=15 mg/kg/dose recommended by several Infectious Diseases Society of America guidelines. Pharmacists also failed to correct inadequate dosing because only 3.3% of patients receiving less than 10 mg/kg/dose had their regimen changed in the first 24 hours of therapy.

CONCLUSION

In this multicenter pilot study, obese patients routinely received inadequate empiric vancomycin using a lenient assessment of dosing. Greater efforts should be undertaken to ensure patients receive weight-based dosing because inadequate dosing can lead to subtherapeutic concentrations and potentially worse clinical outcomes.

Antimicrobial dosing considerations in obese adult patients

As obesity continues to increase in prevalence throughout the world, it becomes important to explore the effects that obesity has on antimicrobial disposition. Physiologic changes in obesity can alter both the volume of distribution and clearance of many commonly used antimicrobials. These changes often present challenges such as estimation of creatinine clearance to predict drug clearance. Although these physiologic changes are increasingly being characterized, few studies assessing alterations in tissue drug distribution and the effects of obesity on antimicrobial pharmacokinetics have been published. The available data are most plentiful for antibiotics that historically have included clinical therapeutic drug monitoring. These data suggest that dosing of vancomycin and aminoglycosides be based on total body weight and adjusted body weight, respectively. Obese patients may require larger doses of beta-lactams to achieve similar concentrations as those of patients who are not obese. Fluoroquinolone pharmacokinetics are variably altered by obesity, which prevents a uniform approach. Data on the pharmacokinetics of drugs that have activity against gram-positive organisms-quinupristin-dalfopristin, linezolid, and daptomycin-reveal that they are altered in the presence of obesity, but more data are needed to solidify dosing recommendations. Limited data are available on nonantibacterials. An understanding of the physiologic changes in obesity and the available literature on specific antibiotics is valuable in providing a framework for rational selection of dosages in this increasingly common population of obese patients.

Factors influencing caspofungin plasma concentrations in patients of a surgical intensive care unit

BACKGROUND

Co-morbidity, medical and surgical interventions often cause alterations to drug plasma concentrations and pharmacokinetic parameters in critically ill patients. In the present study, we investigated parameters influencing plasma caspofungin concentrations in patients of a surgical intensive care unit (SICU).

METHODS

In a monocentre open study, caspofungin trough concentrations (C(24)) were determined for a group of SICU patients. A linear-mixed model was then used to assess factors influencing caspofungin plasma concentrations.

RESULTS

A total of 40 SICU patients were enrolled. Age and body weight ranged from 22 to 76 years and 47 to 108 kg, respectively. All participants received a caspofungin loading dose of 70 mg and a maintenance dose of 50 mg/day. The median duration of therapy was 10 days. Caspofungin C(24) in SICU patients varied more than those determined for healthy subjects reported in previous studies (0.52-4.08 microg/mL versus 1.12-1.78 microg/mL). According to our model, caspofungin C(24) were predicted to be significantly higher in patients with body weight <75 kg (P=0.019) and patients with albumin concentration >23.6 g/L (P=0.030).

CONCLUSIONS

Our results show that body weight and albumin concentration influence caspofungin C(24) in SICU patients and should therefore be considered prognostic factors.

Population pharmacokinetic parameters of vancomycin in critically ill patients

BACKGROUND

Intensive care unit patients are a highly heterogeneous population. Accurate dosing for this population requires characterization of the appropriate pharmacokinetic parameters.

OBJECTIVE

To estimate population pharmacokinetic parameters of vancomycin (VAN) in adult critically ill patients and to establish the predictive performance of the resulting model.

PATIENTS AND METHOD

Fifty critically ill patients with suspected or documented infection with VAN-sensitive micro-organisms were included. Thirty patients and 234 serum concentration-time sets obtained during clinical routine monitoring were used to estimate the pharmacokinetic parameters (group A). An open bicompartimental model with intermittent intravenous administration was used to adjust the data. Data were evaluated using a nonlinear mixed effects model (nonmem software). Forty plasma concentration-time data sets from 20 patients were used for validation using the Bayesian method (group B).

RESULTS

There was a linear relationship between creatinine clearance (Cl(cr)) and VAN clearance (Cl(VAN)). The inclusion of the non-renal clearance (Cl(nr)) (intercept of Cl(VAN) vs. Cl(cr) relationship) improved the model significantly (Cl(nr) 17 mL/min). The volume of distribution seems to be larger than previously reported: volume of the central compartment (V(c)) was 0.41 L/kg and volume of the peripheral compartment was (V(p)), 1.32 L/kg. The mean error (bias) and mean absolute error (precision) for predicting subsequent peak concentrations were -2.16 and 9.28 mg/L and for trough concentrations, -0.22 and 3.87 mg/L respectively.

CONCLUSION

The use of population-specific pharmacokinetic parameters and Bayesian forecasting improves dosage-regimen design.

What is the best size descriptor to use for pharmacokinetic studies in the obese?

The prevalence of obesity in the western world is dramatically rising, with many of these individuals requiring therapeutic intervention for a variety of disease states. Despite the growing prevalence of obesity there is a paucity of information describing how doses should be adjusted, or indeed whether they need to be adjusted, in the clinical setting. This review is aimed at identifying which descriptors of body size provide the most information about the relationship between dose and concentration in the obese. The size descriptors, weight, lean body weight, ideal body weight, body surface area, body mass index, fat-free mass, percent ideal body weight, adjusted body weight and predicted normal body weight were considered as potential size descriptors. We conducted an extensive review of the literature to identify studies that have assessed the quantitative relationship between the parameters clearance (CL) and volume of distribution (V) and these descriptors of body size. Surprisingly few studies have addressed the relationship between obesity and CL or V in a quantitative manner. Despite the lack of studies there were consistent findings: (i) most studies found total body weight to be the best descriptor of V. A further analysis of the studies that have addressed V found that total body weight or another descriptor that incorporated fat mass was the preferred descriptor for drugs that have high lipophilicity; (ii) in contrast, CL was best described by lean body mass and no apparent relationship between lipophilicity or clearance mechanism and preference for body size descriptor was found. In conclusion, no single descriptor described the influence of body size on both CL and V equally well. For drugs that are dosed chronically, and therefore CL is of primary concern, dosing for obese patients should not be based on their total weight. If a weight-based dose individualization is required then we would suggest that chronic drug dosing in the obese subject should be based on lean body weight, at least until a more robust size descriptor becomes available.

Prophylactic use of vancomycin in adult cardiology and cardiac surgery

The recent appearance of Staphylococcus aureus and Staphylococcus epidermidis strains that have reduced susceptibility to vancomycin, and the spread of vancomycin-resistant enterococci, raise the specter of endovascular infections that will be difficult or impossible to cure with available drugs. We review issues concerning the prophylactic use of vancomycin in adult cardiology and cardiac surgery with special attention to dosing and indications. There is no indication for the routine use of prophylactic vancomycin in pacemaker implantations, cardiac catheterization, and transesophageal echocardiography. In institutions with a high incidence of methicillin-resistant S. aureus and S. epidermidis, vancomycin may be used for antibiotic prophylaxis in place of cephalosporins for pacemaker or defibrillator implantation. The strongest evidence in support of the prophylactic use of vancomycin is during cardiac surgeries, particularly valvular surgeries in institutions with a high prevalence of methicillin-resistant S. aureus and S. epidermidis. When vancomycin is used prior to open heart surgery, the dose should be 15 mg/kg rather than the standard 1 g dose that is often recommended in the literature and used by 85% of institutional pharmacists who responded to our survey. Cardiologists and cardiac surgeons should assume leadership roles in promoting its responsible use.

Dosing of medications in morbidly obese patients in the intensive care unit setting

OBJECTIVE

To derive recommendations for the dosing of commonly used medications in the morbidly obese patient in the ICU.

DATA SOURCES

Articles were obtained through computerized searches involving MEDLINE. The bibliographies of retrieved publications and textbooks were reviewed for additional references.

STUDY SELECTION

All studies involving the pharmacokinetics or pharmacodynamics of medications in obese subjects or patients.

DATA EXTRACTION

The emphasis was on studies involving morbidly obese patients but, in the absence of such data, investigations involving lesser forms of obesity were extracted.

DATA SYNTHESIS

There is a paucity of data upon which to make recommendations for dosing commonly used medications in the morbidly obese patient in the ICU, although recommendations were provided based on the available information.

CONCLUSIONS

There is clearly a need for more investigations involving dosing regimens of medications in the morbidly obese population. Until such studies are available, the clinician must try to derive the best dosing regimens for medications based on the limited pharmacokinetic data available for some agents and clinical judgement.

Management of the obese critically ill patient

The management of the morbidly obese critically ill patient is a challenging and formidable task. A better understanding of the pathophysiologic changes that occur with obesity and the complications unique to this group of patients may improve their outcome.

Effects of obesity on pharmacokinetics implications for drug therapy

Obesity is a worldwide problem, with major health, social and economic implications. The adaptation of drug dosages to obese patients is a subject of concern, particularly for drugs with a narrow therapeutic index. The main factors that affect the tissue distribution of drugs are body composition, regional blood flow and the affinity of the drug for plasma proteins and/or tissue components. Obese people have larger absolute lean body masses as well as fat masses than non-obese individuals of the same age, gender and height. However, the percentage of fat per kg of total bodyweight (TBW) is markedly increased, whereas that chrome P450 isoforms are altered, but no clear overview of drug hepatic metabolism in obesity is currently available. Pharmacokinetic studies provide differing data on renal function in obese patients. This review analyses recent publications on several classes of drugs: antibacterials, anticancer drugs, psychotropic drugs, anticonvulsants, general anaesthetics, opioid analgesics, neuromuscular blockers, beta-blockers and drugs commonly used in the management of obesity. Pharmacokinetic studies in obesity show that the behaviour of molecules with weak or moderate lipophilicity (e.g. lithium and vecuronium) is generally rather predictable, as these drugs are distributed mainly in lean tissues. The dosage of these drugs should be based on the ideal bodyweight (IBW). However, some of these drugs (e.g. antibacterials and some anticancer drugs) are partly distributed in adipose tissues, and their dosage is based on IBW plus a percentage of the patient's excess bodyweight. There is no systematic relationship between the degree of lipophilicity of markedly lipophilic drugs (e.g. remifentanil and some beta-blockers) and their distribution in obese individuals. The distribution of a drug between fat and lean tissues may influence its pharmacokinetics in obese patients. Thus, the loading dose should be adjusted to the TBW or IBW, according to data from studies carried out in obese individuals. Adjustment of the maintenance dosage depends on the observed modifications in clearance. Our present knowledge of the influence of obesity on drug pharmacokinetics is limited. Drugs with a small therapeutic index should be used prudently and the dosage adjusted with the help of drug plasma concentrations.

Effects of hepatic function on vancomycin pharmacokinetics in patients with cancer

Vancomycin is widely used in the prophylaxis and treatment of infections in neutropenic patients with cancer. The objective of this study was to analyze liver damage effects on vancomycin pharmacokinetics and determine the necessity for liver function evaluation when selecting vancomycin dosing schedules in these patients. A population pharmacokinetic analysis was performed using the global two-stage method. To this purpose serum vancomycin concentrations from 154 cancer patients were measured and individual vancomycin pharmacokinetic parameters were estimated by the Sawchuk and Zaske method. Mean and standard deviation of the vancomycin pharmacokinetic parameters were estimated for various subgroups of patients classified according to the degree of liver damage. Then a multiple linear regression analysis was performed to select the best predictive models for vancomycin clearance (Clvan) and steady state distribution volume (V). Results revealed that Clvan is not influenced by liver failure. Differences in V between patients with and without hepatic failure were initially observed, but these disappeared when patients with ascites were excluded. In conclusion, vancomycin dosing schedule does not need to be modified for patients with liver failure, with the exception of patients with ascites.

Dosage adjustments for antibacterials in obese patients: applying clinical pharmacokinetics

Obesity is associated with physiological changes that can alter the pharmacokinetic parameters of many drugs. Vancomycin and the aminoglycosides are the only antibacterials that have been extensively investigated in the obese population. The apparent volume of distribution (Vd) and total body clearance of vancomycin are increased in obese patients and have a better correlation with total bodyweight (TBW) than with ideal bodyweight (IBW). The Vd of aminoglycosides is increased in obesity and can be estimated from an adjusted bodyweight that accounts for a fraction of the excess bodyweight (TBW - IBW). These observed changes in pharmacokinetic parameters of vancomycin and aminoglycosides in obese patients may necessitate a deviation from the commonly recommended dosages administered to non-obese individuals. There are limited data regarding the pharmacokinetics of other antibacterial classes in obese patients. The available information for cephalosporins suggests that dosages may need to be increased in obese patients in order to obtain similar serum and tissue concentrations as in non-obese patients. Additional pharmacokinetic studies of other antibacterial classes are required in this special patient population.

Pharmacodynamics, pharmacokinetics, and therapeutic drug monitoring of glycopeptides

The glycopeptide antibacterial drugs, vancomycin and teicoplanin, are widely used in hospitals for therapy of severe or multiresistant infection that has a positive results on Gram's stain test. Although vancomycin resistance is common in some hospital-acquired Enterococcus sp and resistance to teicoplanin occurs among Staphylococci sp glycopeptides remain the cornerstone of therapy for infection due to methicillin-resistant Staphylococcus aureus (MRSA), coagulase-negative Staphylococcus organisms, and infection related to implanted devices. Therapeutic drug monitoring (TDM) of these agents remains controversial, but advances in our understanding of their pharmacodynamics and further clinical studies are helping clarify the situation. In the future, a more rational approach to monitoring will probably result in less intensive monitoring of vancomycin but more intensive monitoring of teicoplanin.

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.

Population pharmacokinetics of vancomycin in Japanese adult patients

Population pharmacokinetic parameters of vancomycin (VCM) in Japanese adult patients infected with methicillin-resistant Staphylococcus aureus (MRSA) were estimated using 1253 items of serum concentration data from 190 patients obtained in routine drug monitoring. The two-compartment linear model was adopted, and VCM clearance (CL) was correlated with the creatinine clearance (CLcr), which was observed or estimated by the Cockcroft-Gault equation. The population pharmacokinetic analysis program NONMEM with first-order conditional estimation method was used. The results showed VCM clearance to be linearly correlated with CLcr (CL [ml/min] = 0.797 x CLcr) when the estimated CLcr was <85 ml/min, but no linear relationship at higher than this level because of the lack of accuracy in the CLcr estimates. The interindividual variability of CL was 38.5%; K12 and K21 were 0.525 hr(-1) and 0.213 hr(-1), respectively. The distribution volume at steady state (V[SS]) was 60.71, with no significant dependence on the actual body weight. The interindividual variability of Vss was 25.4%. The calculated half-life (t1/2,beta) in a typical patient with CLcr of 85 ml/minute was 12.8 hours. Residual variability was 23.7%. These results were compared to those of healthy volunteers, and guidelines for dosage adjustment in VCM therapy are discussed.

Influence of biochemical parameters of liver function on vancomycin pharmacokinetics

The influence of biochemical parameters of hepatic function on vancomycin pharmacokinetics was retrospectively evaluated in 76 adult patients (age 18 to 81 years), from biochemistry data gathered during routine therapeutic drug monitoring. All subjects had normal serum creatinine levels. Vancomycin concentrations were determined by fluorescence polarization immunoassay in 101 paired serum samples. All data for vancomycin concentration versus time were fitted to a one-compartment model using the bayesian approach. Bilirubin, transaminases (n = 101), gamma-glutamyl transferase (n = 97), alkaline phosphatase (n = 95), albumin (n = 92) and lactate dehydrogenase (n = 42) were determined. No strong correlation was seen between any of the pharmacokinetic and biochemistry parameters studied. In patients with hyperbilirubinaemia, the mean Vss and t1/2 were increased (Vss: 0.75 +/- 0.31 versus 0.92 +/- 0.42 1.kg-1, p = 0.020; t1/2 5.93 +/- 3.30 versus 7.48 +/- 4.44 hr, p = 0.049). When liver function was evaluated according to hepatic profile (normal, mildly altered and severely altered), no significant differences were observed in vancomycin pharmacokinetics among the groups. In conclusion, vancomycin pharmacokinetics are only weakly influenced by the biochemistry parameters of liver function.

Changes in vancomycin pharmacokinetics during treatment

Using data gathered in routine monitoring, the pharmacokinetics of vancomycin during the first 10 days of treatment were compared with the pharmacokinetics after 10 days of treatment in 46 adult patients with normal renal function, ages 17-85 years old (mean +/- SD: 50.8 +/- 17.5). The mean time from initiation of treatment to the first sample determination was 5.5 days, and the mean time to the second determination was 13.4 days. Statistical differences between the two periods were observed for all pharmacokinetic parameters, except for the steady-state distribution volume. After 10 days of treatment, the mean +/- SD of the vancomycin clearance and elimination rate constant decreased from 1.31 +/- 0.82 to 1.13 +/- 0.72 ml/kg/min (p = 0.0044) and from 0.13 +/- 0.08 to 0.10 +/- 0.06 h-1 (p = 0.091), respectively. The half-life (t1/2) increased from 8.01 +/- 6.82 to 10.02 +/- 8.00 h (p = 0.012). The median percentage of the increment of t1/2 was 9.4%. The increase in t1/2 was > 50% in 12 patients and > 100% in nine cases. No association was found between the increment of t1/2 and the cumulative vancomycin dose. Frequent monitoring of serum vancomycin seems indicated, given the risk of decreased elimination during prolonged treatment.

Pharmacokinetic optimisation of vancomycin therapy

Renewed interest in vancomycin over the past decade has led to an abundance of data concerning the pharmacokinetics of vancomycin, and its dosage selection and concentration-response relationships. No definitive data exist that correlate vancomycin serum concentrations with clinical outcomes. However, inconsistencies in sampling times for peak serum concentrations and differences in infusion times make interpreting vancomycin serum concentrations difficult. Furthermore, the evidence implicating vancomycin as a cause of oto- or nephrotoxicity is circumstantial, and these adverse effects may occur only in high-risk populations. Owing to the variability in its dose-serum concentration relationship and multicompartmental pharmacokinetics, several methodologies have been developed for instituting and adjusting vancomycin dosages. Nomograms rely on a fixed volume of distribution and the relationship between vancomycin clearance and creatinine clearance. Since both of these factors may be altered in certain populations, dosage methodologies (both traditional and Bayesian) that use population- or patient-specific pharmacokinetic data perform better than standard nomograms for initiating vancomycin therapy. Controversy still exists as to whether a 1- or a 2-compartment model is more appropriate for making dosage adjustments; however, steady-state rather than non-steady-state vancomycin serum concentrations should be used for dosage adjustments. Certain pathophysiological states such as age, bodyweight and renal function contribute to altered pharmacokinetics and may alter the design of the dosage regimen. Since no definitive relationship exists between vancomycin serum concentrations and either clinical outcome or adverse effects, considerable controversy surrounds the utility of monitoring serum vancomycin concentrations. Therefore, routine vancomycin serum concentration monitoring may be warranted only in specific populations, such as patients receiving concurrent aminoglycoside therapy or those receiving higher than usual dosages of vancomycin, patients undergoing haemodialysis and patients with rapidly changing renal function.