Pharmacokinetics of ticarcillin/clavulanate in severely burned patients

Gap analysis of pharmacokinetics and pharmacodynamics in burn patients: a review

Severe burn injury results in a multifaceted physiological response that significantly alters drug pharmacokinetics and pharmacodynamics (PK/PD). This response includes hypovolemia, increased vascular permeability, increased interstitial hydrostatic pressure, vasodilation, and hypermetabolism. These physiologic alterations impact drug distribution and excretion-thus varying the drug therapeutic effect on the body or microorganism. To this end, in order to optimize critical care for the burn population it is essential to understand how burn injury alters PK/PD parameters. The purpose of this article is to describe the relationship between burn injury and drug PK/PD. We conducted a literature review via PubMed and Google to identify burn-related PK/PD studies. Search parameters included "pharmacokinetics," "pharmacodynamics," and "burns." Based on our search parameters, we located 38 articles that studied PK/PD parameters specifically in burns. Twenty-seven articles investigated PK/PD of antibiotics, 10 assessed analgesics and sedatives, and one article researched an antacid. Out of the 37 articles, there were 19 different software programs used and eight different control groups. The mechanisms behind alterations in PK/PD in burns remain poorly understood. Dosing techniques must be adapted based on burn injury-related changes in PK/PD parameters in order to ensure drug efficacy. Although several PK/PD studies have been undertaken in the burn population, there is wide variation in the analytical techniques, software, and study sample sizes used. In order to refine dosing techniques in burns and consequently improve patient outcomes, there must be harmonization among PK/PD analyses.

Pharmacokinetics/pharmacodynamics of antibacterials in the Intensive Care Unit: setting appropriate dosing regimens

Patients admitted to Intensive Care Units (ICUs) are at very high risk of developing severe nosocomial infections. Consequently, antimicrobials are among the most important and commonly prescribed drugs in the management of these patients. Critically ill patients in ICUs include representatives of all age groups with a range of organ dysfunction related to severe acute illness that may complicate long-term illness. The range of organ dysfunction, together with drug interactions and other therapeutic interventions (e.g. haemodynamically active drugs and continuous renal replacement therapies), may strongly impact on antimicrobial pharmacokinetics in critically ill patients. In the last decade, it has become apparent that the intrinsic pharmacokinetic (PK) and pharmacodynamic (PD) properties are the major determinants of in vivo efficacy of antimicrobial agents. PK/PD parameters are essential in facilitating the translation of microbiological activity into clinical situations, ensuring a successful outcome. In this review, we analyse the typical patterns of antimicrobial activity and the corresponding PK/PD parameters, with a special focus on a PK/PD dosing approach of the antimicrobial agent classes commonly utilised in the ICU setting.

Antimicrobial therapy in critically ill patients: a review of pathophysiological conditions responsible for altered disposition and pharmacokinetic variability

Antimicrobials are among the most important and commonly prescribed drugs in the management of critically ill patients. Selecting the appropriate antimicrobial at the commencement of therapy, both in terms of spectrum of activity and dose and frequency of administration according to concentration or time dependency, is mandatory in this setting. Despite appropriate standard dosage regimens, failure of the antimicrobial treatment may occur because of the inability of the antimicrobial to achieve adequate concentrations at the infection site through alterations in its pharmacokinetics due to underlying pathophysiological conditions. According to the intrinsic chemicophysical properties of antimicrobials, hydrophilic antimicrobials (beta-lactams, aminoglycosides, glycopeptides) have to be considered at much higher risk of inter- and intraindividual pharmacokinetic variations than lipophilic antimicrobials (macrolides, fluoroquinolones, tetracyclines, chloramphenicol, rifampicin [rifampin]) in critically ill patients, with significant frequent fluctuations of plasma concentrations that may require significant dosage adjustments. For example, underexposure may occur because of increased volume of distribution (as a result of oedema in sepsis and trauma, pleural effusion, ascites, mediastinitis, fluid therapy or indwelling post-surgical drainage) and/or enhanced renal clearance (as a result of burns, drug abuse, hyperdynamic conditions during sepsis, acute leukaemia or use of haemodynamically active drugs). On the other hand, overexposure may occur because of a drop in renal clearance caused by renal impairment. Care with all these factors whenever choosing an antimicrobial may substantially improve the outcome of antimicrobial therapy in critically ill patients. However, since these situations may often coexist in the same patient and pharmacokinetic variability may be unpredictable, the antimicrobial policy may further benefit from real-time application of therapeutic drug monitoring, since this practice, by tailoring exposure to the individual patient, may consequently be helpful both in improving the outcome of antimicrobial therapy and in containing the spread of resistance in the hospital setting.

Pharmacokinetics of cefepime in patients with thermal burn injury

The pharmacokinetics of cefepime following administration of a single 2-g dose were evaluated for 12 adult patients with thermal burn injury and suspected or documented infection. Serial blood and urine samples for cefepime concentration determination were obtained for 24 h following drug administration. Serum and urine cefepime concentrations were determined by high-performance liquid chromatography and serum concentrations were fit to a two-compartment pharmacokinetic model. Mean (standard deviation [SD]) age, actual body weight (ABW), percent total body surface area burned, and days postburn at the time of study were 41 (13) years, 84 (22) kg, 36 (17)%, and 9 (3) days, respectively. Mean (SD) measured creatinine clearance (CL(CR)), total clearance (CL(T)), renal clearance (CL(R)), alpha phase half-life, beta phase half-life, and volume of distribution at steady state (V(SS)) were 135 (31) ml/min, 8.8 (2.4) liters/h, 8.1 (2.0) liters/h, 0.33 (0.14) h, 2.8 (0.6) h, and 0.43 (0.10) liters/kg ABW, respectively. Cefepime CL(T) and CL(R) in burn patients were similar to previously reported values for healthy volunteers when normalized by CL(CR). Stepwise multiple regression was used to associate CL(T) with CL(CR) and days postburn (r(2) = 0.861), CL(R) with CL(CR) and days postburn (r(2) = 0.773), nonrenal clearance with percent third-degree (% 3 degrees ) burn and albumin concentration (r(2) = 0.550), and V(SS) only with % 3 degrees burn (r(2) = 0.624). Simulated steady-state serum concentrations obtained by using the patients' pharmacokinetic parameters exceeded the susceptibility interpretive standard (breakpoint) of cefepime for at least 60% of the dosing interval with dosing regimens of 1 g every 8 h (q8h), 2 g q8h, and 2 g q12h. Despite differences in pharmacokinetic parameters between our patients and healthy volunteers, it appears that these dosing regimens may be adequate in similar burn patients.

Pharmacokinetics of antibiotics in burn patients

Drug pharmacokinetics are significantly altered in the burned patient but the interplay of a large number of variables is involved in deciding how an individual will deal with a drug. Consequently the burn patient population shows significant inter- and intrapatient variation. In 1976 altered aminoglycoside pharmacokinetics and the need for increased dosage in burn patients was reported but, despite this early study, a review of the currently available literature shows that for many drugs there is a paucity of information to support current dosage recommendations. In addition, many reports are based upon small numbers of patients, and even in larger studies there is no standardization of the study population with regard to the important variables known to affect drug handling. For the sub-population of burn patients who eliminate drugs extremely rapidly, a concern exists over the adequacy of antibiotic dosing. It is suggested that antibiotic serum concentrations be measured for all drugs in every patient to ascertain whether there is a significant problem with dosing. Additionally, future pharmacokinetic studies need to be standardized in burn patients.

Fluconazole pharmacokinetics in burn patients

The pharmacokinetics of fluconazole in nine adult patients with severe (30 to 95% total body surface area) burns were studied. There was no significant difference in half-life (t1/2), clearance (CL), or volume of distribution (V) over time in five patients on days 3 and 8 of the study (P > 0.05). Combined parameter estimates (means +/- standard deviations) for all nine patients for the two study periods were as follows: t1/2, 24.4 +/- 5.8 h; CL, 0.36 +/- 0.09 ml/min/kg; and V, 0.72 +/- 0.12 liters/kg. These estimates of t1/2 and CL in burn patients were approximately 13% shorter and 30% more rapid, respectively, than the most extreme estimates reported for other populations.

Antibiotic susceptibility profile of Xanthomonas maltophilia. In vitro activity of beta-lactam/beta-lactamase inhibitor combinations

The susceptibility of 42 strains of Xanthomonas (Pseudomonas) maltophilia to 37 antibiotics (mainly beta-lactams, aminoglycosides, and fluorinated quinolones) was tested. Xanthomonas maltophilia was resistant to most beta-lactams, with ceftazidime, moxalactam, and ICI-194008 being the most active ones. Aminoglycosides had a very modest activity, with quinolones showing only moderate activity against this species. Trimethoprim/sufamethoxazole was effective against all strains tested. We also tested the synergy of several beta-lactam/beta-lactamase inhibitors against X. maltophilia. Only aztreonam/clavulanic acid at 3:1, 1:1 and, mainly, 2:1 combinations had synergistic activity, decreasing the rate of resistance from 92.8% for aztreonam alone to 32.4% for aztreonam-clavulanic acid at 1:1 and 0% for aztreonam-clavulanic acid at 2:1.