Prospectively validated dosing nomograms for maximizing the pharmacodynamics of vancomycin administered by continuous infusion in critically ill patients.

The efficacy of vancomycin against methicillin-resistant Staphylococcus aureus (MRSA)-related infections has been called into question by recent findings of higher rates of failure of vancomycin treatment of infections caused by strains with high MICs. Continuous infusion may be the best way to maximize the time-dependent activity of vancomycin. The aim of this study was to create dosing nomograms in relation to different creatinine clearance (CL(Cr)) estimates for use in daily clinical practice to target the steady-state concentrations (C(ss)s) of vancomycin during continuous infusion at 15 to 20 mg/liter (after the administration of an initial loading dose of 15 mg/kg of body weight over 2 h). The correlation between vancomycin clearance (CL(v)) and CL(Cr) was retrospectively assessed in a cohort of critically ill patients (group 1, n = 70) to create a formula for dosage calculation to target C(ss) at 15 mg/liter. The performance of this formula was prospectively validated in a similar cohort (group 2, n = 63) by comparison of the observed and the predicted C(ss)s. A significant relationship between CL(v) and CL(Cr) was observed in group 1 (P < 0.001). The application of the calculated formula to vancomycin dosing in group 2 {infusion rate (g/24 h) = [0.029 x CL(Cr) (ml/min) + 0.94] x target C(ss) x (24/1,000)} led to a significant correlation between the observed and the predicted C(ss)s (r = 0.80, P < 0.001). Two dosing nomograms based on CL(Cr) were created to target the vancomycin C(ss) at 15 and 20 mg/liter in critically ill patients. These nomograms could be helpful in improving the vancomycin treatment of MRSA infections, especially in the presence of borderline-susceptible pathogens and/or of pathophysiological conditions which may enhance the clearance of vancomycin, while potentially avoiding the increased risk of nephrotoxicity observed with the use of high intermittent doses of vancomycin.

Biliary penetration and pharmacodynamic exposure of linezolid in liver transplant patients.

OBJECTIVES: The aim of the study was to assess the biliary penetration of linezolid and the probabilities of attaining optimal pharmacodynamic exposure against vancomycin-resistant enterococci (VRE) in the bile of liver transplant (LTx) patients who received linezolid for the treatment of multidrug-resistant Gram-positive hospital infections. METHODS: After at least 2 days of standard 600 mg twice-daily therapy, simultaneous bile and blood samples for linezolid assay were collected from six LTx patients just prior to drug administration to determine trough concentrations (Cmin) at steady-state in both sites. Linezolid concentrations in plasma and in bile were analysed by means of HPLC. Biliary penetration of linezolid was calculated as the ratio between Cmin in bile and in plasma. Optimal theoretical pharmacodynamic exposure of linezolid against VRE in bile was defined as biliary Cmin>MIC90. RESULTS: C(min) of linezolid in bile achieved very high values at steady-state, which were significantly higher than in plasma (median of 21.77 versus 8.08 mg/L, P=0.021). The very high biliary penetration of linezolid (median value of 1.93; range 1.31-4.83) enabled achievement of optimal theoretical pharmacodynamic exposure against VRE in bile (Cmin>2 mg/L) on all of the occasions. CONCLUSIONS: These preliminary data suggest a potential role for linezolid in the treatment of cholangitis due to VRE in LTx patients. Obviously, further confirmatory data assessing also the AUC/MIC ratio of linezolid in bile are needed.

Drop in trough blood concentrations of tacrolimus after switching from nelfinavir to fosamprenavir in four HIV-infected liver transplant patients.

Solid organ transplantation in HIV-infected individuals requires concomitant use of immunosuppressants and antiretrovirals that may cause significant drug interactions. Here we report on a peculiar pharmacokinetic interaction between tacrolimus and protease inhibitors (PIs) which occurred in four HIV-infected liver transplant patients who had to shift PI therapy from nelfinavir to fosamprenavir as a consequence of regulatory restrictions. After the switch, tacrolimus trough blood concentrations significantly dropped in all patients (mean +/- SD 6.9 +/- 2.6 versus 3.2 +/- 2.0 ng/ml before and after the switch, respectively; P=0.01), so that a marked dosage increase was needed (0.29 +/- 0.14 versus 0.88 +/- 0.48 mg/day, 1-3 days before and 3 weeks after the switch, respectively; P=0.046) to attain the desired target (8.7 +/- 2.3 ng/ml). Consistently, marked changes of the concentration/dose ratio of tacrolimus were observed in all cases (27.2 +/- 9.7 ng/ml per mg/kg/day versus 9.7 +/- 4.0 ng/ml per mg/kg/day before and after the switch, respectively; P<0.001). Our findings suggest that fosamprenavir may be less potent than nelfinavir in inhibiting tacrolimus clearance and support the need for higher tacrolimus dosage to avoid insufficient immunosuppression in HIV-infected liver transplant patients when switching from nelfinavir to fosamprenavir or even when directly starting antiretroviral therapy with fosamprenavir.

Clinical relevance of pharmacokinetics and pharmacodynamics in cardiac critical care patients.

Pharmacokinetics is a discipline aimed at predicting the best dosage and dosing regimen for each single drug in order to ensure and maintain therapeutically effective concentrations at the action sites. In cardiac critical care patients, various pathophysiological conditions may significantly alter the pharmacokinetic behaviour of drugs. Gastrointestinal drug absorption may be erratic and unpredictable in the early postoperative period, and so patients may be unresponsive to oral therapy; thus the intravenous route should be preferred for life-saving drugs whenever feasible. Variations in the extracellular fluid content as a response to the trauma of surgery and the fluid load or significant drug loss through thoracic drainages may significantly lower plasma concentrations of extracellularly distributed hydrophilic antimicrobials (beta-lactams, aminoglycosides and glycopeptides). Drug metabolism may be altered by the systemic inflammatory response and/or multiple organ failure and/or drug-drug pharmacokinetic interactions that can potentially occur during polytherapy, especially in immunosuppressed cardiac transplant patients. Instability of renal function may promote significant changes in body fluid concentrations of renally eliminated drugs, even in a brief period of hours. Finally, the application of extracorporeal circulation by means of cardiopulmonary bypass may significantly alter the disposition of several drugs during the operation because of acute haemodilution, hypoalbuminaemia, hypothermia and/or adsorption to the bypass equipment. Accordingly, to avoid either overexposure and the consequent increased risk of toxicity or underexposure and the consequent risk of therapeutic failure in critically ill cardiac patients, the dosing regimens of several drugs are expected to be significantly different from those suggested for clinically stable patients. Additionally, therapeutic drug monitoring may be helpful in the management of drug therapy and should be routinely used to guide individualized dose adjustments for (i) immunosuppressants whenever cytochrome P450 3A4 isoenzyme inhibitors (e.g. macrolide antibacterials, azole antifungals) or inducers (e.g. rifampicin [rifampin]) are added to or withdrawn from the regimen; and (ii) glycopeptide and aminoglycoside antibacterials whenever haemodynamically active agents (such as dopamine, dobutamine and furosemide [frusemide]) are added to or withdrawn from the regimen, and also whenever significant changes of haemodynamics and/or of renal function occur.

Pharmacokinetic considerations for antimicrobial therapy in patients receiving renal replacement therapy.

Continuous renal replacement therapy (CRRT), particularly continuous venovenous haemofiltration (CVVH) and continuous venovenous haemodiafiltration (CVVHDF), are gaining increasing relevance in routine clinical management of intensive care unit patients. The application of CRRT, by leading to extracorporeal clearance (CL(CRRT)), may significantly alter the pharmacokinetic behaviour of some drugs. This may be of particular interest in critically ill patients presenting with life-threatening infections, since the risk of underdosing with antimicrobial agents during this procedure may lead to both therapeutic failure and the spread of breakthrough resistance. The intent of this review is to discuss the pharmacokinetic principles of CL(CRRT) of antimicrobial agents during the application of CVVH and CVVHDF and to summarise the most recent findings on this topic (from 1996 to December 2006) in order to understand the basis for optimal dosage adjustments of different antimicrobial agents. Removal of solutes from the blood through semi-permeable membranes during RRT may occur by means of two different physicochemical processes, namely, diffusion or convection. Whereas intermittent haemodialysis (IHD) is essentially a diffusive technique and CVVH is a convective technique, CVVHDF is a combination of both. As a general rule, the efficiency of drug removal by the different techniques is expected to be CVVHDF > CVVH > IHD, but indeed CL(CRRT) may vary greatly depending mainly on the peculiar physicochemical properties of each single compound and the CRRT device's characteristics and operating conditions. Considering that RRT substitutes for renal function in clearing plasma, CL(CRRT) is expected to be clinically relevant for drugs with dominant renal clearance, especially when presenting a limited volume of distribution and poor plasma protein binding. Consistently, CL(CRRT) should be clinically relevant particularly for most hydrophilic antimicrobial agents (e.g. beta-lactams, aminoglycosides, glycopeptides), whereas it should assume much lower relevance for lipophilic compounds (e.g. fluoroquinolones, oxazolidinones), which generally are nonrenally cleared. However, there are some notable exceptions: ceftriaxone and oxacillin, although hydrophilics, are characterised by primary biliary elimination; levofloxacin and ciprofloxacin, although lipophilics, are renally cleared. As far as CRRT characteristics are concerned, the extent of drug removal is expected to be directly proportional to the device's surface area and to be dependent on the mode of replacement fluid administration (predilution or postdilution) and on the ultrafiltration and/or dialysate flow rates applied.Conversely, drug removal by means of CVVH or CVVHDF is unaffected by the drug size, considering that almost all antimicrobial agents have molecular weights significantly lower (<2000Da) than the haemofilter cut-off (30,000-50,000Da). Drugs that normally have high renal clearance and that exhibit high CL(CRRT) during CVVH or CVVHDF may need a significant dosage increase in comparison with renal failure or even IHD. Conversely, drugs that are normally nonrenally cleared and that exhibit very low CL(CRRT) during CVVH or CVVHDF may need no dosage modification in comparison with normal renal function. Bearing these principles in mind will almost certainly aid the management of antimicrobial therapy in critically ill patients undergoing CRRT, thus containing the risk of inappropriate exposure. However, some peculiar pathophysiological conditions occurring in critical illness may significantly contribute to further alteration of the pharmacokinetics of antimicrobial agents during CRRT (i.e. hypoalbuminaemia, expansion of extracellular fluids or presence of residual renal function). Accordingly, therapeutic drug monitoring should be considered a very helpful tool for optimising drug exposure during CRRT.

Major role of levofloxacin in the treatment of a case of Listeria monocytogenes meningitis.

We report a case of acute bacterial meningitis due to Listeria monocytogenes whose successful treatment was mainly attributable to high-dose levofloxacin therapy (500 mg iv bid). This supports the hypothesis that levofloxacin may be an effective option for the treatment of listerial meningitis.

Pharmacokinetic and pharmacodynamic aspects of oral moxifloxacin 400 mg/day in elderly patients with acute exacerbation of chronic bronchitis.

OBJECTIVE: To assess the pharmacokinetic and pharmacodynamic behaviour of moxifloxacin in 15 consecutive elderly patients with acute exacerbation of chronic bronchitis (AECB) treated with the fixed oral moxifloxacin 400 mg/day regimen with the intent of verifying which degree of exposure may be ensured by this standard regimen against AECB pathogens. METHODS: This was an open-label, observational, pharmacokinetic-pharmacodynamic study. Blood samples were collected at steady state at appropriate intervals. Moxifloxacin plasma concentrations were analysed by means of high-performance liquid chromatography. Standard pharmacokinetic parameters and pharmacodynamic determinants (peak concentration [C(max)]/minimum inhibitory concentration [MIC], area under the plasma concentration-time curve during the 24-hour observational period [AUC(24)]/MIC, pharmacodynamic breakpoints [PDBPs]) were assessed. RESULTS: The mean estimated pharmacokinetic parameters (C(max) 4.40 mg/L at 1.4 hours, AUC(24) 42.67 mg . h/L, elimination half-life 12.55 hours, total body clearance 0.16 L/h/kg) were generally similar to those observed in both young and elderly historic controls (except for higher-dose normalised C(max) and lower volume of distribution of the central compartment). Median C(max)/MIC and AUC(24)/MIC ratios for moxifloxacin in the fully assessable cases were, respectively, 67.5 and 823.9 against Streptococcus pneumoniae, 25 and 310.2 against Moraxella catharralis and 416.5 and 3647.5 against Haemophilus influenzae. Mean estimates of PDBP for achieving C(max)/MIC values of 12.2 and AUC(24)/MIC values of 125 were 0.36 and 0.35 mg/L, respectively. CONCLUSION: In patients with AECB the pharmacokinetic behaviour of moxifloxacin is not significantly altered by aging processes. This is consistent with moxifloxacin being metabolised mainly by means of phase II hepatic reactions, the activity of which was shown not to decline with age. Both the pharmacokinetic and pharmacodynamic analyses suggest that moxifloxacin 400 mg/day may be a valid therapeutic approach in the treatment of AECB in the elderly. Of note, the unmodified pharmacokinetic behaviour with no need for age-related dosage adjustments combined with the once-daily administration favouring compliance and the low potential for drug-drug pharmacokinetic interactions in case of polytherapy, make moxifloxacin particularly attractive in the treatment of elderly subpopulations at a very high risk of AECB.

The effect of multifactorial, multidisciplinary educational interventions on appropriate use of teicoplanin.

The aim of this study was to determine the effect of multifactorial, multidisciplinary educational interventions over a 3-year period on the appropriate use of teicoplanin. Teicoplanin was considered a valid surrogate marker of good antibiotic use in clinical practice owing to its peculiar pharmacokinetics (i.e. necessity for an initial loading dose regardless of the patient's renal function for early achievement of optimal exposure, namely C(min) > or = 10 mg/L) and to the opportunity of comparing current routine therapeutic drug monitoring (TDM) results with those of a historical retrospective study. A significantly higher proportion of patients received appropriate loading doses of teicoplanin in the present prospective study than in the retrospective study, both when considered as a whole (66.6% versus 38.6%, respectively; P<0.001) or when stratified according to the degree of estimated renal function (78.4% versus 60.4% for creatinine clearance (CL(Cr)) > 50 mL/min; 59.8% versus 26.8% for CL(Cr) 20-50 mL/min; and 27.7% versus 5.5% for CL(Cr) <20 mL/min). The highest adherence was observed in haematological wards (97.7%). The percentages of patients with teicoplanin C(min) > or = 10 mg/L during the treatment period in the present and retrospective study, respectively, were: 61.4% versus 3.2% on Day 2; 88% versus 35% on Day 4; 94% versus 70% on Day 7; and 99% versus 90% on Day 11. Our findings suggest that continuous application of a multifactorial educational programme including active TDM may be efficacious in improving and maintaining over time the appropriate use in a hospital setting of a theoretically difficult-to-use drug such as teicoplanin.

Pharmacokinetic-pharmacodynamic aspects of antimicrobial prophylaxis with teicoplanin in patients undergoing major vascular surgery.

A prospective, two-arm, open study assessing plasma exposure to teicoplanin with two different prophylactic regimens (Group A (n = 23), 800 mg pre-operatively versus Group B (n = 24), 400 mg pre-operatively plus two doses of 200 mg 24 h apart) was carried out in patients undergoing major vascular surgery. The intent was to define the feasibility and the possible advantages of the single pre-operative high dose in ensuring therapeutically effective plasma concentrations (>10 mg/L) of teicoplanin even during long-lasting operations. At the end of the intervention, mean teicoplanin concentrations (+/-S.D.) were 14.05 +/- 5.13 mg/L and 5.39 +/- 2.13 mg/L in Groups A and B, respectively. At 24 h, average teicoplanin levels were 5.10 +/- 1.25 mg/L and 2.08 +/- 0.73 mg/L in Groups A and B, respectively; at 48 h they declined to 2.86 +/- 0.70 mg/L in Group A, whereas they rose to 2.67 +/- 0.82 mg/L after administration of 2.63 +/- 0.51 mg/kg at 24 h in Group B. Single pre-operative high-dose teicoplanin may ensure effective plasma levels even in cases of very long-lasting operations (>8 h) with no need for intraoperative re-dosing and may enable more appropriate prophylactic exposure than that achievable with the same total dose given in three administrations 24 h apart.

Teicoplanin in patients with acute leukaemia and febrile neutropenia: a special population benefiting from higher dosages.

OBJECTIVE: To define the optimal dosage regimen of teicoplanin that ensures early therapeutically relevant trough concentrations (C(min)) [>10 mg/L at 24 hours and possibly close to 20 mg/L at 48 hours] in patients with acute leukaemia who develop febrile neutropenia after chemotherapy. DESIGN: Prospective observational pharmacokinetic study. PARTICIPANTS: Adult patients (n = 33) with normal renal function previously treated with antineoplastic chemotherapy because of acute lymphocytic or acute nonlymphocytic leukaemia, and subsequently developing febrile neutropenia treated with empirical antimicrobial therapy. DESIGN: First, the standard dosage group (n = 11) was administered standard loading and maintenance doses of teicoplanin (400 mg every 12 hours for three doses followed by 400 mg once daily). Blood samples were collected at defined times as part of routine monitoring and assessed for teicoplanin plasma concentration by fluorescence polarisation immunoassay. Secondly, the high dosage group (n = 22) received a high loading regimen (800 + 400 mg 12 hours apart on day 1, 600 + 400mg 12 hours apart on day 2) followed by a high maintenance regimen (400 mg every 12 hours) from day 3 on. RESULTS: In the standard dosage group, no patient had the recommended teicoplanin C(min) of >or=10 mg/L within the first 72 hours, and only five of the 11 patients (45%) had a C(min) of >or=10 mg/L after 120 hours. No patient had a C(min) of >or=20 mg/L. In the high dosage group, teicoplanin C(min) averaged >or=10 mg/L within 24 hours, and this value was achieved within 48 hours in all but one patient. Of note, C(min) at 72 hours exceeded 20 mg/L in ten of the 22 patients (45%). No patient experienced significant impairment of renal function. CONCLUSIONS: In this patient group, therapeutically relevant C(min) may be achieved very early in the treatment period with loading doses of 12 mg/kg and 6 mg/kg 12 hours apart on day 1, and 9 mg/kg and 6 mg/kg 12 hours apart on day 2, regardless of renal function. Subsequently, in patients with normal renal function a maintenance dosage of 6 mg/kg every 12 hours may be helpful in ensuring C(min) close to 20 mg/L. Assessment of C(min) after 48-72 hours may be useful to individualise teicoplanin therapy. Factors increasing volume of distribution and/or renal clearance of teicoplanin (fluid load, hypoalbuminaemia, leukaemic status) may explain the need for higher dosages.

Linezolid disposition after standard dosages in critically ill patients undergoing continuous venovenous hemofiltration: a report of 2 cases.

Linezolid is a new oxazolidinone antibiotic active against most Gram-positive microorganisms the renal elimination of which accounts for about 30% to 35% of all the clearance. Its pharmacokinetic ability was assessed during continuous venovenous hemofiltration (CVVH) in 2 anuric patients with severe postsurgical intraabdominal infections who were receiving standard dosages (600 mg intravenously twice a day). Blood samples for quantification of linezolid in plasma and in filtrate were collected after more than 4 days of therapy before dosing and at 0, 0.5, 1, 2, 3, 5, 7, 9, and 11 hours after the morning 1-hour intravenous infusion, and concentrations were determined by means of high-performance liquid chromatography. Linezolid was partially cleared by CVVH in both the patients (hemofiltration clearance [CL CVVH ] = 0.38 and 0.35 mL/min/kg), with high sieving coefficient values (0.76 to 0.92). Efficacious plasma exposure for time-dependent antibacterial activity of linezolid, either in terms of trough levels above minimum inhibitory concentration (MIC) at which 90% of the isolates are inhibited (Cmin >MIC90 ) or of area under the plasma concentration time curve to MIC90 ratio (AUC/MIC90 ) >100 hours, was ensured during CVVH in both patients. However, despite similar CL CVVH , significant interindividual pharmacokinetic variability was found in the 2 patients (AUC during the observational period [AUC 0-tau ] 334.71 versus 109.34 mg/L x h), mainly owing to substantial differences in non-CVVH-related clearance of linezolid (total CL, 0.55 versus 1.21 mL/min/kg). Our findings indicate that linezolid, although partially removed, does not warrant dosage modification during the first 48 hours when CVVH (with polysulfide hemofilter) at standard 2,000 mL/h substitution flow rate in predilution is applied to anuric patients. Thereafter, this choice is a reasonable one with the exception of those patients who have other features of linezolid toxicity and in which non-CVVH-related clearance might be impaired, although further evaluations are warranted.

Treatment of pyogenic (non-tuberculous) spondylodiscitis with tailored high-dose levofloxacin plus rifampicin.

The purpose of this study was to assess the clinical efficacy of high-dose levofloxacin plus rifampicin in the empirical treatment of non-tuberculous spondylodiscitis in an epidemiological context of low incidence of staphylococcal fluoroquinolone resistance. All consecutive adult patients with spondylodiscitis (January 2003 to December 2006) were empirically treated with high-dose levofloxacin (500 mg every 12 h normalised to renal function and optimised by means of therapeutic drug monitoring whenever feasible) plus rifampicin 600 mg every 24 h. Trough and peak plasma concentrations were targeted at 1-3 mg/L and 6-9 mg/L, respectively, to maximise the concentration-dependent activity of levofloxacin in bone. Follow-up was performed until 9 months after the end of therapy. Forty-eight patients were included. Eleven patients underwent a surgical approach for spine stabilisation. Among the 29 bacterial isolates, Staphylococcus aureus was the most frequent (65.5%) (all meticillin-susceptible strains). Tailored levofloxacin plasma exposure over time was ensured in most cases. Median treatment duration was 15.1 weeks. Overall response rates were: 77.1% at the intent-to-treat analysis; 84.1% among patients who completed therapy (N=44); and 96.3% among those receiving targeted therapy against documented levofloxacin-susceptible isolates (N=27). No patient had evidence of disease relapse at follow-up. Our findings suggest that high-dose levofloxacin regimens may be highly effective in the treatment of non-tuberculous spondylodiscitis and support its putative role in combination with rifampicin against S. aureus.

Penetration of levofloxacin into paranasal sinuses mucosa of patients with chronic rhinosinusitis after a single 500 mg oral dose.

Respiratory fluoroquinolones are currently considered by several guidelines among the most effective antimicrobial agents for the treatment of acute bacterial rhinosinusitis. The aim of this study was to assess levofloxacin penetration into paranasal sinuses mucosa of 15 patients with chronic rhinosinusitis 1h (n = 4), 2 h (n = 5) and 3 h (n = 6) after a single 500 mg oral dose. Levofloxacin concentrations in plasma and tissue samples were assessed by means of HPLC. Median of mucosal concentrations were 0.96 mg l(-1) at 1 h, 2.50 mg l(-1) at 2 h, 5.84 mg l(-1) at 3 h. Average paranasal sinuses mucosa-to-plasma ratios raised from 1.46 at 1 h, to 1.81 at 2 h and to 2.56 at 3 h. These data are consistent with 500 mg oral levofloxacin ensuring appropriate therapeutic exposure in sinonasal tissue of patients with chronic rhinosinusitis, the concentrations between 1 and 3 h post-dosing being almost always higher than the MIC90 against the major bacterial pathogens responsible for upper respiratory tract infections.

Which reliable pharmacodynamic breakpoint should be advised for ciprofloxacin monotherapy in the hospital setting? A TDM-based retrospective perspective.

OBJECTIVES: To define in critically ill patients receiving intravenous (iv) ciprofloxacin (200 mg or 400 mg twice daily) and undergoing routine therapeutic drug monitoring (TDM) the interindividual pharmacokinetic variability and the reliable pharmacodynamic breakpoint enabled by these fixed dosing regimens according to the PK/PD principles and to the pattern of susceptibility to this antibiotic. METHODS: Ciprofloxacin plasma concentrations [trough (Cmin) and 30 min post-dose peak (Cmax) levels] were analysed by means of an HPLC method. Optimal pharmacodynamic exposure was assessed by estimating the theoretical pharmacodynamic breakpoints (PD BP) for either Cmax or AUC. RESULTS: The final database included 177 sets of Cmin and Cmax performed in 89 patients (200 mg twice daily group, n=68; 400 mg twice daily group, n=21). A very wide interindividual scatter of results was observed for both the 200 mg group and the 400 mg group. Interestingly, for both groups only moderate log-linear relationships between estimated renal function (CLCR) on one hand and either Cmin (r2=0.08, 0.28) or estimated AUC24 (r2=0.10, 0.34) on the other hand were found. Median PD BP, respectively, in the 200 mg twice daily group and the 400 mg twice daily group, were 0.16 and 0.28 mg/L for Cmax, and 0.19 and 0.29 mg/L for AUC24. CONCLUSIONS: Lowering ciprofloxacin dosage in the presence of renal failure seems in most cases unnecessary, since drug accumulation occurred only in a few cases. Optimal pharmacodynamic exposure with fixed 200 or 400 mg twice daily regimens of ciprofloxacin may be ensured only against fully susceptible microorganisms with an MIC<0.3 mg/L. This supports the use of higher dosages in critically ill hospitalized patients, whereas the wide unpredictable interindividual pharmacokinetic variability suggests the usefulness of TDM with the intent of optimizing efficacy with ciprofloxacin therapy.

Ceftazidime in acute myeloid leukemia patients with febrile neutropenia: helpfulness of continuous intravenous infusion in maximizing pharmacodynamic exposure.

The pharmacokinetic-pharmacodynamic profile of a fixed 6-g daily continuous intravenous infusion of ceftazidime was assessed in 20 febrile neutropenic patients with acute myeloid leukemia. Mean steady-state ceftazidime concentrations averaging 40 mg/liter from day 2 on ensured maximized pharmacodynamic exposure (values close to four to five times the MIC breakpoint against Pseudomonas aeruginosa). However, large intra- and interindividual pharmacokinetic variability was documented throughout the study period.

Levofloxacin disposition over time in aqueous humor of patients undergoing cataract surgery.

The ocular disposition of levofloxacin in patients receiving two 500-mg oral doses 10 h apart before cataract surgery was assessed with the intent of defining drug ocular exposure over time. The mean aqueous humor concentrations persisted above 1.5 mg/liter between 1.5 and 6.0 h after the second dose, with average aqueous-to-plasma ratios ranging between 0.33 and 0.57. This favorable ocular disposition provides support for trials of systemic levofloxacin for prophylaxis of postoperative endophthalmitis in selected patients or as adjunctive therapy for the treatment of this potentially devastating infective complication.

Teicoplanin therapeutic drug monitoring in critically ill patients: a retrospective study emphasizing the importance of a loading dose.

Data obtained as part of our routine drug monitoring of teicoplanin therapy (therapeutic drug monitoring, TDM) in adult critically ill patients being treated for suspected or documented Gram-positive multiresistant infections were assessed, retrospectively. Data were available for 202 patients (146 male, 56 female; age 58 +/- 16 years) with a total number of 829 teicoplanin trough plasma levels (C(min)) assessed. The percentage of patients with adequate teicoplanin concentrations (C(min) >/= 10 mg/L) during the treatment period substantially increased from 3.2% on day 2, to 35%, 70%, 90% and approximately 95% on days 4, 7, 11 and 15, respectively. The findings suggest that optimal teicoplanin therapy was achieved only after at least 4, and probably 7, days of therapy in most cases, mainly because of a failure to use an appropriate loading dose. Among the possible causes for the reluctance to use a loading dose, concern over the potential nephrotoxicity of teicoplanin was a major factor. We conclude that loading doses of teicoplanin (6 mg/kg every 12 h for at least three doses) must be considered mandatory in all patients, regardless of their renal function, to enable optimal drug concentrations to be achieved early in the treatment period. Subsequently, TDM is important to ensure that dose regimens are optimized to the individual requirements of the patients.

Levofloxacin disposition in cerebrospinal fluid in patients with external ventriculostomy.

In vitro levofloxacin exhibits both potent or intermediate activity against most of the pathogens frequently responsible for acute bacterial meningitis and synergistic activity with some beta-lactams. Since levofloxacin was shown to penetrate the cerebrospinal fluid (CSF) during meningeal inflammation both in animals and in humans, the disposition of levofloxacin in CSF was studied in 10 inpatients with external ventriculostomy because of communicating hydrocephalus related to subarachnoid occlusion due to cerebral accidents who were treated with 500 mg of levofloxacin intravenously twice a day because of extracerebral infections. Plasma and CSF concentration-time profiles and pharmacokinetics were assessed at steady state. Plasma and CSF levofloxacin concentrations were analyzed by high-pressure liquid chromatography. The peak concentration of levofloxacin at steady state (C(max ss))was 10.45 mg/liter in plasma and 4.06 mg/liter in CSF, respectively, with the ratio of the C(max ss) in CSF to the C(max ss) in plasma being 0.47. The areas under the concentration-time curves during the 12-h dosing interval (AUC(0-tau)s) were 47.69 mg. h/liter for plasma and 33.42 mg. h/liter for CSF, with the ratio of the AUC(0-tau) for CSF to the AUC(0-tau) for plasma being 0.71. The terminal-phase half-life of levofloxacin in CSF was longer than that in plasma (7.02 +/- 1.57 and 5.51 +/- 1.36 h, respectively; P = 0.034). The ratio of the levofloxacin concentration in CSF to the concentration in plasma progressively increased with time, from 0.30 immediately after dosing to 0.99 at the end of the dosing interval. In the ventricular CSF of patients with uninflamed meninges, levofloxacin was shown to provide optimal exposure, which approximately corresponded to the level of exposure of the unbound drug in plasma. The findings provide support for trials of levofloxacin with twice-daily dosing in combination with a reference beta-lactam for the treatment of bacterial meningitis in adults. This cotreatment could be useful both for overcoming Streptococcus pneumoniae resistance and for enabling optimal exposure of the CSF to at least one antibacterial agent for the overall treatment period.