Vancomycin: report on treatment of patients with severe staphylococcal infections

Antibacterial natural products in medicinal chemistry--exodus or revival?

To create a drug, nature's blueprints often have to be improved through semisynthesis or total synthesis (chemical postevolution). Selected contributions from industrial and academic groups highlight the arduous but rewarding path from natural products to drugs. Principle modification types for natural products are discussed herein, such as decoration, substitution, and degradation. The biological, chemical, and socioeconomic environments of antibacterial research are dealt with in context. Natural products, many from soil organisms, have provided the majority of lead structures for marketed anti-infectives. Surprisingly, numerous "old" classes of antibacterial natural products have never been intensively explored by medicinal chemists. Nevertheless, research on antibacterial natural products is flagging. Apparently, the "old fashioned" natural products no longer fit into modern drug discovery. The handling of natural products is cumbersome, requiring nonstandardized workflows and extended timelines. Revisiting natural products with modern chemistry and target-finding tools from biology (reversed genomics) is one option for their revival.

Vancomycin administration in continuous ambulatory peritoneal dialysis: the risk of ototoxicity

A prospective study was undertaken in 16 patients with chronic renal failure on continuous ambulatory peritoneal dialysis, with 22 episodes of peritonitis treated with vancomycin, a known ototoxic agent. Twelve patients had one episode each, and four had recurrent peritonitis. Each treatment course consisted of two infusions of vancomycin (30 mg/kg body weight) in 2 L of peritoneal dialysate administered at 6-day intervals. Serum vancomycin analyzed by enzyme immunoassay showed a mean trough level of 11.00 microg/ml on day 6 and mean serum levels of 33.8 and 38.6 microg/ml about 12 hours after administration on days 1 and 7, respectively. Similar levels, well within the therapeutic range, were encountered with repeated vancomycin therapy for recurrent episodes of peritonitis, suggesting that no changes occurred in the pharmacokinetic profile of the drug. Pure-tone audiometry, electronystagmography, and clinical assessment performed during each course of treatment showed no evidence of ototoxicity even on repeated courses of vancomycin therapy. The results suggest that vancomycin therapy when given in appropriate concentrations as a single therapeutic agent is both effective and safe. We believe, however, that vancomycin administered in combination with an aminoglycoside may produce ototoxic effects that may be greatly aggravated, possibly because of synergism.

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.

An updated comparison of drug dosing methods. Part IV: Vancomycin

The resurgence of the use of and interest in vancomycin, in conjunction with the high degree of interpatient variability in its pharmacokinetic profile, has prompted the development of many and varied dosing methods. Several dosing nomograms have been proposed and evaluated, methods which are useful for initial dosing but do not allow for individualisation of dosage. Given these constraints, several investigators have attempted to apply conventional least-squares regression techniques and, more recently, Bayesian methodologies using either 1- or 2-compartment pharmacokinetic models. Comparative information evaluating algorithmic methods demonstrates that those of Moellering and Lake offer the least biased and most precise predictions of vancomycin dosage. Patient individualisation using conventional least-squares methodology offers some improvement over nomogram-based methods, both in predictive performance and in dosage adjustment once serum concentration data are available. Overall, the latest data indicate that regimens which incorporate Bayesian principles tend to give better results than nomogram-based or conventional least-squares dosing methods for this drug. Despite the advances in methods for dosing vancomycin, several questions remain to be answered. A lack of convincing evidence of a correlation between serum concentrations and therapeutic outcome has prompted debate over the need for serum concentration monitoring and, if it is needed, over which patient population would most benefit. Secondly, little comparative information is currently available as to the dosing of vancomycin in paediatric and neonatal patient populations. Several nomograms for initial dosing have been proposed, but only 2 have been subject to subsequent testing. Finally, information regarding cost-effectiveness and the quality of patient outcome is lacking from the current literature.

An experimental study of vancomycin-induced cochlear damage

Vancomycin has been successfully used clinically for many years. Although early reports found ototoxicity to be a side effect of this antibiotic, later studies could not confirm this. For this reason we have started an experimental study in an animal model on the ototoxic effects of vancomycin. We now report the results of this study. Fourteen healthy Mongolian gerbils were treated with intraperitoneal injections of vancomycin (80 mg/kg per day) for a 2-week period. Before and after treatment each animal's hearing was evaluated by evoked response audiometry. Post mortem the cochleae were investigated by scanning electron microscopy in Amsterdam and by microdissection with surface preparations (hair cell counting) in Stockholm. The results of this study show that there is no clear evidence for the existence of ototoxicity due to vancomycin in this dosage.

Vancomycin ototoxicity and nephrotoxicity. A review

Vancomycin has been in clinical use as a potent antistaphylococcal antibiotic for over 30 years. Most reports of ototoxicity and nephrotoxicity have been associated with early, relatively impure, formulations of vancomycin. This paper reviews the literature concerning vancomycin ototoxocity and nephrotoxicity and the evidence for their correlation with the therapeutic serum concentration range. There have been 28 reports of vancomycin-associated ototoxicity published in the medical literature since 1958. It remains unclear whether any diminution in hearing is permanent or reversible. Few patients in the literature had follow-up audiometry and the hearing impairment tends to be at higher frequencies. Several authors reported peak serum vancomycin concentrations, but the exact time these were drawn with respect to the last dose is mostly unclear. In other reports, the 'peak' concentrations noted 3 to 6 hours after the last dose are probably indicative of much higher concentrations because of vancomycin's rapid phase of distribution. More than half the 57 cases of reported nephrotoxicity due to vancomycin occurred within the first 6 years of the drug's use. Many of these patients also had pre-existing renal dysfunction or were concomitantly receiving other nephrotoxic agents. It is unclear whether the coadministration of aminoglycosides produces a synergistic toxicity. The exact incidence of nephrotoxicity is uncertain, but is probably less with the current, relatively pure, product. The correlation of nephrotoxicity with certain serum vancomycin concentrations remains to be clarified. Other aspects also require clarification, such as when to draw samples to determine peak serum concentrations and whether or not routine measurements are necessary at all. In the absence of better guidelines, efforts should be made to tailor individual patient's regimens to produce peak and trough serum vancomycin concentrations to within the widely accepted ranges of 30 to 40 and 5 to 10 mg/L, respectively. In addition, the concomitant use of other potentially nephrotoxic and ototoxic agents should be avoided.

Evaluation of a new vancomycin dosing method

Thirty-one patients who were prescribed vancomycin therapy at our institution since January 1, 1986, were dosed using the guidelines as described by Lake and Peterson. Peak and trough vancomycin serum concentrations were measured at steady state: 24 (77%) peak serum concentrations were within the range of 20-30 mg/L, and 24 (77%) trough serum concentrations were within the range of 5-10 mg/L. We have found that the method of Lake and Peterson is satisfactory for initiating vancomycin therapy in most patients. Some, however, may not achieve optimal serum concentrations using these guidelines alone, and their regimens may have to be adjusted based upon actual serum concentration data.

Clinical pharmacokinetics of vancomycin

Vancomycin utilisation has increased dramatically in the last 10 years due to the increasing clinical significance of infections with methicillin-resistant staphylococci. Recent studies have focused on characterising the disposition of vancomycin in patients and assessing the relationship between serum concentrations and therapeutic as well as adverse effects. Although vancomycin is not appreciably absorbed from the intact gastrointestinal tract, several recent case reports have documented the attainment of therapeutic and potentially toxic vancomycin serum concentrations following oral administration to patients with pseudomembranous colitis. The disposition of parenterally administered vancomycin has been best characterised by a triexponential model. The half-life of the initial phase (t1/2 pi) is approximately 7 minutes, that of the second phase (t1/2 alpha) is approximately 0.5 to 1 hour, while the terminal elimination half-life (t1/2 beta) ranges from 3 to 9 hours in subjects with normal renal function. The volume of the central compartment (Vc) in adults is approximately 0.15 L/kg while the steady-state volume of distribution (Vdss) ranges from 0.39 to 0.97 L/kg. More than 80% of a vancomycin dose is excreted unchanged in the urine within 24 hours after administration, and the concentration of vancomycin in liver tissue and bile has been reported to be at or below detection limits. Vancomycin renal clearance approximates 0.5 to 0.8 of simultaneously determined creatinine or 125I-iothalamate clearances, suggesting that the primary route of renal excretion is glomerular filtration. Recently, non-renal factors such as hepatic conjugation have been proposed as an important route of vancomycin elimination. However, these data are difficult to reconcile with other studies showing minimal non-renal clearance of vancomycin in subjects with end-stage renal disease. As yet, the disposition of vancomycin in patients with hepatic disease has not been adequately defined. Only limited data are available regarding the concentrations of vancomycin in biological fluids other than plasma. The penetration of vancomycin into cerebrospinal fluid (CSF) in patients with and without meningitis has been quite variable. Although early studies suggested that adequate CSF concentrations may not be achieved in subjects with uninflamed meninges, more recent investigations have reported contradictory results. Therapeutic concentrations of vancomycin, i.e. greater than 2.5 mg/L, have, however, been reported in ascitic, pericardial, pleural and synovial fluids. Tissue concentrations of vancomycin have exceeded simultaneous serum concentrations in heart, kidney, liver and lung sp

In vitro evaluation of a vancomycin radioimmunoassay and observations on vancomycin pharmacokinetics in dialysis patients

A recently marketed radioimmunoassay (RIA) for vancomycin (Monitor Science Corp.) was evaluated in vitro and in vivo. The RIA and bioassay results on 15 spiked serum samples found no significant difference between the two assays, although RIA results were significantly less variable. The coefficient of variation (RIA) was 5.5%. Vancomycin showed no significant degradation in plasma at 4 degrees C and -20 degrees C for up to 36 days. Five dialysis patients had a total of 62 serum levels determined. When vancomycin 1 g was given weekly to two anuric adults, marked accumulation occurred. This finding was consistent with vancomycin's long terminal half-life (19.8 and 17.8 days) obtained from a new computer subroutine which obtains least square estimators of model parameters from multiple dose data. Despite serum levels well above the MIC, two patients remained bacteremic. Peritoneal levels of vancomycin in two patients with suspected peritonitis equalled corresponding serum levels.

Vancomycin therapy of bacterial endocarditis

Fifteen patients with bacterial endocarditis were treated with vancomycin between 1967 and 1976. The indications for vancomycin therapy were penicillin-cephalosporin allergy in six patients, antibiotic resistant bacteria in six, initial therapy in one and culture-negative endocarditis in two. The causative microorganisms were Staph. epidermidis (four patients), Staph. aureus (two patients), diphtheroids (four patients), viridans streptococci (two patients) and enterococci (one patient). Minimum inhibitory concentrations of vancomycin for these organisms ranged from 0.8 to 3.1 micrograms/ml. The patients received vancomycin for two to 10 weeks (mean five weeks). Cure was achieved in 13 patients, including six with prosthetic valve endocarditis (PVE). Two patients had a relapse of PVE and cultures of blood or heart valve were positive within two months of vancomycin therapy. Vancomycin serum levels did not exceed 50 micrograms/ml, and no serious drug toxicity was encountered in any patient. Three patients had minimal audiogram changes beyond the social hearing range. One patient had mild phlebitis and a rash, and one patient had a transient leukopenia. Vancomycin is an effective nontoxic antibiotic in patients with endocarditis when penicillin or cephalosporin therapy is not appropriate.

Vancomycin for staphylococcal shunt site infections in patients on regular haemodialysis

Six anuric patients with Scribner shunt site infections were treated by intermittent infusion of vancomycin into the shunt, and a satisfactory clinical response was obtained in five. Serum levels of the antibiotic were estimated frequently. From estimating serum levels and the minimum inhibitory concentrations of vancomycin for a range of hospital staphylococci a dose of 1g. vancomycin every seven days is recommended as a suitable schedule for treating staphylococcal infection in this situation.