Effects of surgery on the pharmacokinetic parameters of drugs

Dose regimen optimization of cephalothin for surgical prophylaxis against Staphylococcus aureus and coagulase negative staphylococci in dogs by pharmacokinetic/pharmacodynamic modeling

First generation cephalosporins such cephalothin of cefazolin are indicated for antimicrobial prophylaxis for clean and clean contaminated surgical procedures because its antimicrobial spectrum, relative low toxicity and cost. Anesthesia and surgery could alter the pharmacokinetic behavior of different drugs administered perioperative by many mechanisms that affect distribution, metabolism or excretion processes. Intravenous administration of the antimicrobial within 30 and 60 min before incision is recommended in order to reach therapeutic serum and tissue concentrations and redosing is recommended if the duration of the procedure exceeds two half-life of the antimicrobial. To the author's knowledge there are no pharmacokinetic studies of cephalothin in dogs under anesthesia/surgery conditions. The aim of this study was (1) to evaluate the pharmacokinetics of cephalothin in anesthetized dogs undergoing ovariohysterectomy by a nonlinear mixed-effects model and to determine the effect of anesthesia/surgery and other individual covariates on its pharmacokinetic behavior; (2) to determine the MIC and conduct a pharmacodynamic modeling of time kill curves assay of cephalothin against isolates of Staphylococcus spp. isolated from the skin of dogs; (3) to conduct a PK/PD analysis by integration of the obtained nonlinear mixed-effects models in order to evaluate the antimicrobial effect of changing concentrations on simulated bacterial count; and (4) to determine the PK/PD endpoints and PK/PDco values in order to predict the optimal dose regimen of cephalothin for antimicrobial prophylaxis in dogs. Anesthesia/surgery significantly reduced cephalothin clearance by 18.78%. Based on the results of this study, a cephalothin dose regimen of 25 mg/kg q6h by intravenous administration showed to be effective against Staphylococcus spp. isolates with MIC values ≤2 μg/mL and could be recommended for antimicrobial prophylaxis for clean surgery in healthy dogs.

Opportunities and challenges in the diagnostic utility of dermal interstitial fluid

The volume of interstitial fluid (ISF) in the human body is three times that of blood. Yet, collecting diagnostically useful ISF is more challenging than collecting blood because the extraction of dermal ISF disrupts the delicate balance of pressure between ISF, blood and lymph, and because the triggered local inflammation further skews the concentrations of many analytes in the extracted fluid. In this Perspective, we overview the most meaningful differences in the make-up of ISF and blood, and discuss why ISF cannot be viewed generally as a diagnostically useful proxy for blood. We also argue that continuous sensing of small-molecule analytes in dermal ISF via rapid assays compatible with nanolitre sample volumes or via miniaturized sensors inserted into the dermis can offer clinically advantageous utility, particularly for the monitoring of therapeutic drugs and of the status of the immune system.

Pharmacokinetic and pharmacodynamic considerations for antifungal therapy optimisation in the treatment of intra-abdominal candidiasis

Intra-abdominal candidiasis (IAC) is one of the most common of invasive candidiasis observed in critically ill patients. It is associated with high mortality, with up to 50% of deaths attributable to delays in source control and/or the introduction of antifungal therapy. Currently, there is no comprehensive guidance on optimising antifungal dosing in the treatment of IAC among the critically ill. However, this form of abdominal sepsis presents specific pharmacokinetic (PK) alterations and pharmacodynamic (PD) challenges that risk suboptimal antifungal exposure at the site of infection in critically ill patients. This review aims to describe the peculiarities of IAC from both PK and PD perspectives, advocating an individualized approach to antifungal dosing. Additionally, all current PK/PD studies relating to IAC are reviewed in terms of strength and limitations, so that core elements for the basis of future research can be provided.

Simultaneous LC-ESI-MS/MS Quantification of Levosimendan and Its Metabolites for Therapeutic Drug Monitoring of Cardiac Surgery Patients

Levosimendan is used in severe chronic cardiac insufficiency, also within the peri-operative setting. Real-life pharmacokinetic data in surgical patients is lacking, making therapeutic drug monitoring (TDM) of levosimendan, its pharmacologically active metabolite OR-1896, and its intermediate OR-1855 important. A simultaneous highly sensitive quantification of levosimendan and its metabolites in small-volume samples has not yet been described. Here, levosimendan (LLOQ 0.450 nM), OR-1896, and OR-1855 (LLOQ both 1.0 nM) were successfully quantified by LC-ESI-MS/MS after liquid-liquid extraction in 300 µL of blood. A short C8 column under reversed-phase conditions enabled simultaneous and fast quantification of levosimendan in the negative and the metabolites in the positive ionization mode in a single run within 2 min. Interestingly and unexpectedly, constitutional isomers of levosimendan metabolites with identical mass transitions and similar retention times were observed in surgical patients’ samples, which we identified as the metamizole metabolites 4-aminoantipyrine and 4-acetamidoantipyrine. A longer C8 column and a modified mobile phase enabled selective quantification of all analytes in a single run within 7 min. We developed, validated, and applied highly sensitive LC-ESI-MS/MS methods for simultaneous quantification of levosimendan and its metabolites, enabling efficient TDM of cardiac surgery patients even with additional metamizole administration.

Plasma and Lung Tissue Pharmacokinetics of Ceftaroline Fosamil in Patients Undergoing Cardiac Surgery with Cardiopulmonary Bypass: an In Vivo Microdialysis Study

Ceftaroline fosamil, a fifth-generation cephalosporin antibiotic with activity against methicillin-resistant Staphylococcus aureus (MRSA), is currently approved for the treatment of pneumonia and complicated skin and soft tissue infections. However, pharmacokinetics data on free lung tissue concentrations in critical patient populations are lacking. The aim of this study was to evaluate the pharmacokinetics of the high-dose regimen of ceftaroline in plasma and lung tissue in cardiac surgery patients during intermittent and continuous administration. Nine patients undergoing elective cardiac surgery on cardiopulmonary bypass were included in this study and randomly assigned to intermittent or continuous administration. Eighteen hundred milligrams of ceftaroline fosamil was administered intravenously as either 600 mg over 2 h every 8 h (q8h) (intermittent group) or 600 mg over 2 h (loading dose) plus 1,200 mg over 22 h (continuous group). Interstitial lung tissue concentrations were measured by in vivo microdialysis. Relevant pharmacokinetics parameters were calculated for each group. Plasma exposure levels during intermittent and continuous administration were comparable to those of previously published studies and did not differ significantly between the two groups. In vivo microdialysis demonstrated reliable and adequate penetration of ceftaroline into lung tissue during intermittent and continuous administration. The steady-state area under the concentration-time curve from 0 to 8 h (AUCss 0-8) and the ratio of AUCSS 0-8 in lung tissue and AUC in plasma (AUClung/plasma) were descriptively higher in the continuous group. Continuous administration of ceftaroline fosamil achieved a significantly higher proportion of time for which the free drug concentration remained above 4 times the minimal inhibitory concentration (MIC) during the dosing interval (% fT>4xMIC) than intermittent administration for pathogens with a MIC of 1 mg/liter. Ceftaroline showed adequate penetration into interstitial lung tissue of critically ill patients undergoing major cardiothoracic surgery, supporting its use for pneumonia caused by susceptible pathogens.

Pharmacokinetic modeling of R and S-Methadone and their metabolites to study the effects of various covariates in post-operative children

Methadone is a synthetic opioid used as an analgesic and for the treatment of opioid abuse disorder. The analgesic dose in the pediatric population is not well-defined. The pharmacokinetics (PKs) of methadone is highly variable due to the variability in alpha-1 acid glycoprotein (AAG) and genotypic differences in drug-metabolizing enzymes. Additionally, the R and S enantiomers of methadone have unique PK and pharmacodynamic properties. This study aims to describe the PKs of R and S methadone and its metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in pediatric surgical patients and to identify sources of inter- and intra-individual variability. Children aged 8-17.9 years undergoing orthopedic surgeries received intravenous methadone 0.1 mg/kg intra-operatively followed by oral methadone 0.1 mg/kg postoperatively every 12 h. Pharmacokinetics of R and S methadone and EDDP were determined using liquid chromatography tandem mass spectrometry assays and the data were modeled using nonlinear mixed-effects modeling in NONMEM. R and S methadone PKs were well-described by two-compartment disposition models with first-order absorption and elimination. EDDP metabolites were described by one compartment disposition models with first order elimination. Clearance of both R and S methadone were allometrically scaled by bodyweight. CYP2B6 phenotype was a determinant of the clearance of both the enantiomers in an additive gene model. The intronic CYP3A4 single-nucleotide polymorphism (SNP) rs2246709 was associated with decreased clearance of R and S methadone. Concentrations of AAG and the SNP of AAG rs17650 independently increased the volume of distribution of both the enantiomers. The knowledge of these important covariates will aid in the optimal dosing of methadone in children.

Perioperative administration of cefazolin and metronidazole in obese and non-obese patients: a pharmacokinetic study in plasma and interstitial fluid

OBJECTIVES

To assess plasma and tissue pharmacokinetics of cefazolin and metronidazole in obese patients undergoing bariatric surgery and non-obese patients undergoing intra-abdominal surgery.

PATIENTS AND METHODS

Fifteen obese and 15 non-obese patients received an IV short infusion of 2 g cefazolin and 0.5 g metronidazole for perioperative prophylaxis. Plasma and microdialysate from subcutaneous tissue were sampled until 8 h after dosing. Drug concentrations were determined by HPLC-UV. Pharmacokinetic parameters were calculated non-compartmentally.

RESULTS

In obese patients (BMI 39.5-69.3 kg/m2) compared with non-obese patients (BMI 18.7-29.8 kg/m2), mean Cmax of total cefazolin in plasma was lower (115 versus 174 mg/L) and Vss was higher (19.4 versus 14.2 L). The mean differences in t½ (2.7 versus 2.4 h), CL (5.14 versus 4.63 L/h) and AUC∞ (402 versus 450 mg·h/L) were not significant. The influence of obesity on the pharmacokinetics of metronidazole was similar (Cmax 8.99 versus 14.7 mg/L, Vss 73.9 versus 51.8 L, t½ 11.9 versus 9.1 h, CL 4.62 versus 4.13 L/h, AUC∞ 116 versus 127 mg·h/L). Regarding interstitial fluid (ISF), mean concentrations of cefazolin remained >4 mg/L until 6 h in both groups, and those of metronidazole up to 8 h in the non-obese group. In obese patients, the mean ISF concentrations of metronidazole were between 3 and 3.5 mg/L throughout the measuring interval.

CONCLUSIONS

During the time of surgery, cefazolin concentrations in plasma and ISF of subcutaneous tissue were lower in obese patients, but not clinically relevant. Regarding metronidazole, the respective differences were higher, and may influence dosing of metronidazole for perioperative prophylaxis in obese patients.

Pharmacokinetics and safety of aztreonam/avibactam for the treatment of complicated intra-abdominal infections in hospitalized adults: results from the REJUVENATE study

Objectives

To investigate pharmacokinetics (PK) and safety (primary objectives) and efficacy (secondary objective) of the investigational monobactam/β-lactamase inhibitor combination aztreonam/avibactam in patients with complicated intra-abdominal infection (cIAI).

Methods

This Phase 2a open-label, multicentre study (NCT02655419; EudraCT 2015-002726-39) enrolled adults with cIAI into sequential cohorts for 5–14 days treatment. Cohort 1 patients received an aztreonam/avibactam loading dose of 500/137 mg (30 min infusion), followed by maintenance doses of 1500/410 mg (3 h infusions) q6h; Cohort 2 received 500/167 mg (30 min infusion), followed by 1500/500 mg (3 h infusions) q6h. Cohort 3 was an extension of exposure at the higher dose regimen. Doses were adjusted for creatinine clearance of 31–50 mL/min (Cohorts 2 + 3). All patients received IV metronidazole 500 mg q8h. PK, safety and efficacy were assessed.

Results

Thirty-four patients (Cohort 1, n = 16; Cohorts 2 + 3, n = 18) comprised the modified ITT (MITT) population. Mean exposures of aztreonam and avibactam in Cohorts 2 + 3 were consistent with those predicted to achieve joint PK/pharmacodynamic target attainment in >90% patients. Adverse events (AEs) were similar between cohorts. The most common AEs were hepatic enzyme increases [n = 9 (26.5%)] and diarrhoea [n = 5 (14.7%)]. Clinical cure rates at the test-of-cure visit overall were 20/34 (58.8%) (MITT) and 14/23 (60.9%) (microbiological-MITT population).

Conclusions

Observed AEs were consistent with the known safety profile of aztreonam monotherapy, with no new safety concerns identified. These data support selection of the aztreonam/avibactam 500/167 mg (30 min infusion) loading dose and 1500/500 mg (3 h infusions) maintenance dose q6h regimen, in patients with creatinine clearance >50 mL/min, for the Phase 3 development programme.

Influence of general anaesthesia on the intravenous acetaminophen pharmacokinetics in Beagle dogs

OBJECTIVE

To determine if general anaesthesia influences the intravenous (IV) pharmacokinetics (PK) of acetaminophen in dogs.

STUDY DESIGN

Prospective, crossover, randomized experimental study.

ANIMALS

A group of nine healthy Beagle dogs.

METHODS

Acetaminophen PK were determined in conscious and anaesthetized dogs on two separate occasions. Blood samples were collected before, and at 5, 10, 15, 30, 45, 60 and 90 minutes and 2, 3, 4, 6, 8, 12 and 24 hours after 20 mg kg^-1 IV acetaminophen administration. Haematocrit, total proteins, albumin, alanine aminotransferase, aspartate aminotransferase, urea and creatinine were determined at baseline and 24 hours after acetaminophen. The anaesthetized group underwent general anaesthesia (90 minutes) for dental cleaning. After the administration of dexmedetomidine (3 μg kg^-1) intramuscularly, anaesthesia was induced with propofol (2-3 mg kg^-1) IV, followed by acetaminophen administration. Anaesthesia was maintained with isoflurane in 50% oxygen (Fe'Iso 1.3-1.5%). Dogs were mechanically ventilated. Plasma concentrations were analysed with high-performance liquid chromatography. PK analysis was undertaken using compartmental modelling. A Wilcoxon test was used to compare PK data between groups, and clinical laboratory values between groups, and before versus 24 hours after acetaminophen administration. Data are presented as median and range (p < 0.05).

RESULTS

A two-compartmental model best described time-concentration profiles of acetaminophen. No significant differences were found for volume of distribution values 1.41 (0.94-3.65) and 1.72 (0.89-2.60) L kg^-1, clearance values 1.52 (0.71-2.30) and 1.60 (0.91-1.78) L kg^-1 hour^-1 or terminal elimination half-life values 2.45 (1.45-8.71) and 3.57 (1.96-6.35) hours between conscious and anaesthetized dogs, respectively. Clinical laboratory variables were within normal range. No adverse effects were recorded.

CONCLUSIONS AND CLINICAL RELEVANCE

IV acetaminophen PK in healthy Beagle dogs were unaffected by general anaesthesia under the study conditions. Further studies are necessary to evaluate the PK in different clinical contexts.

Meropenem Plasma and Interstitial Soft Tissue Concentrations in Obese and Nonobese Patients-A Controlled Clinical Trial

BACKGROUND

This controlled clinical study aimed to investigate the impact of obesity on plasma and tissue pharmacokinetics of meropenem.

METHODS

Obese (body mass index (BMI) ≥ 35 kg/m²) and age-/sex-matched nonobese (18.5 kg/m² ≥ BMI ≤ 30 kg/m²) surgical patients received a short-term infusion of 1000-mg meropenem. Concentrations were determined via high performance liquid chromatography-ultraviolet (HPLC-UV) in the plasma and microdialysate from the interstitial fluid (ISF) of subcutaneous tissue up to eight h after dosing. An analysis was performed in the plasma and ISF by noncompartmental methods.

RESULTS

The maximum plasma concentrations in 15 obese (BMI 49 ± 11 kg/m²) and 15 nonobese (BMI 24 ± 2 kg/m²) patients were 54.0 vs. 63.9 mg/L (95% CI for difference: -18.3 to -3.5). The volume of distribution was 22.4 vs. 17.6 L, (2.6-9.1), but the clearance was comparable (12.5 vs. 11.1 L/h, -1.4 to 3.1), leading to a longer half-life (1.52 vs. 1.31 h, 0.05-0.37) and fairly similar area under the curve (AUC)_8h (78.7 vs. 89.2 mg*h/L, -21.4 to 8.6). In the ISF, the maximum concentrations differed significantly (12.6 vs. 18.6 L, -16.8 to -0.8) but not the AUC_8h (28.5 vs. 42.0 mg*h/L, -33.9 to 5.4). Time above the MIC (T > MIC) in the plasma and ISF did not differ significantly for MICs of 0.25-8 mg/L.

CONCLUSIONS

In morbidly obese patients, meropenem has lower maximum concentrations and higher volumes of distribution. However, due to the slightly longer half-life, obesity has no influence on the T > MIC, so dose adjustments for obesity seem unnecessary.

All disease begins in the gut: Influence of gastrointestinal disorders and surgery on oral drug performance

The term "disease" conjures a plethora of graphic imagery for many, and the use of drugs to combat symptoms and treat underlying pathology is at the core of modern medicine. However, the effects of the various gastrointestinal diseases, infections, co-morbidities and the impact of gastrointestinal surgery on the pharmacokinetic and pharmacodynamic behaviour of drugs have been largely overlooked. The better elucidation of disease pathology and the role of underlying cellular and molecular mechanisms have increased our knowledge as far as diagnoses and prognoses are concerned. In addition, the recent advances in our understanding of the intestinal microbiome have linked the composition and function of gut microbiota to disease predisposition and development. This knowledge, however, applies less so in the context of drug absorption and distribution for orally administered dosage forms. Here, we revisit and re-evaluate the influence of a portfolio of gastrointestinal diseases and surgical effects on the functionality of the gastrointestinal tract, their implications for drug delivery and attempt to uncover significant links for clinical practice.

Controlling postoperative use of i.v. acetaminophen at an academic medical center

PURPOSE

Results of an interprofessional formulary initiative to decrease postoperative prescribing of i.v. acetaminophen are reported.

SUMMARY

After a medical center added i.v. acetaminophen to its formulary, increased prescribing of the i.v. formulation and a 3-fold price increase resulted in monthly spending of more than $40,000, prompting an organizationwide effort to curtail that cost while maintaining effective pain management. The surgery, anesthesia, and pharmacy departments applied the Institute for Healthcare Improvement's Model for Improvement to implement (1) pharmacist-led enforcement of prescribing restrictions, (2) retrospective evaluation of i.v. acetaminophen's impact on rates of opioid-related adverse effects, (3) restriction of prescribing of the drug to 1 postoperative dose on select patient care services, and (4) guideline-driven pain management according to an enhanced recovery after surgery (ERAS) protocol. Monitored metrics included the monthly i.v. acetaminophen prescribing rate, the proportion of i.v. acetaminophen orders requiring pharmacist intervention to enforce prescribing restrictions, and prescribing rates for select adjunctive analgesics. Within a year of project implementation, the mean monthly i.v. acetaminophen prescribing rate decreased by 83% from baseline to about 6 doses per 100 patient-days, with a decline in the monthly drug cost to about $4,000. Documented pharmacist interventions increased 2.7-fold, and use of oral acetaminophen, ketorolac, and gabapentin in ERAS areas increased by 18% overall.

CONCLUSION

An interprofessional initiative at a large medical center reduced postoperative use of i.v. acetaminophen by more than 80% and yielded over $400,000 in annual cost savings.

Surgical stress response and promotion of metastasis in colorectal cancer: a complex and heterogeneous process

Surgery remains the curative treatment modality for colorectal cancer in all stages, including stage IV with resectable liver metastasis. There is emerging evidence that the stress response caused by surgery as well as other perioperative therapies such as anesthesia and analgesia may promote growth of pre-existing micro-metastasis or potentially initiate tumor dissemination. Therapeutically targeting the perioperative period may therefore reduce the effect that surgical treatments have in promoting metastases, for example by combining β-adrenergic receptor antagonists and cyclooxygenase-2 (COX-2) inhibitors in the perioperative setting. In this paper, we highlight some of the mechanisms that may underlie surgery-related metastatic development in colorectal cancer. These include direct tumor spillage at the time of surgery, suppression of the anti-tumor immune response, direct stimulatory effects on tumor cells, and activation of the coagulation system. We summarize in more detail results that support a role for catecholamines as major drivers of the pro-metastatic effect induced by the surgical stress response, predominantly through activation of β-adrenergic signaling. Additionally, we argue that an improved understanding of surgical stress-induced dissemination, and more specifically whether it impacts on the level and nature of heterogeneity within residual tumor cells, would contribute to the successful clinical targeting of this process. Finally, we provide a proof-of-concept demonstration that ex-vivo analyses of colorectal cancer patient-derived samples using RGB-labeling technology can provide important insights into the heterogeneous sensitivity of tumor cells to stress signals. This suggests that intra-tumor heterogeneity is likely to influence the efficacy of perioperative β-adrenergic receptor and COX-2 inhibition, and that ex-vivo characterization of heterogeneous stress response in tumor samples can synergize with other models to optimize perioperative treatments and further improve outcome in colorectal and other solid cancers.

Cefazolin tissue concentrations with a prophylactic dose administered before sleeve gastrectomy in obese patients: a single centre study in 116 patients

BACKGROUND

In obese patients undergoing sleeve gastrectomy, the blood and fatty-tissue concentrations of cefazolin required for adequate antibiotic prophylaxis are uncertain.

METHODS

This was a single centre prospective study in obese (Group A: 40≤ BMI ≤50 kg m^-2) and severely obese (Group B: 50< BMI ≤65 kg m^-2) patients undergoing bariatric surgery. Blood and fatty-tissue samples were collected after a cefazolin 4 g i.v. injection. The primary aim was to compare cefazolin concentrations in subcutaneous fatty tissue with a targeted tissue concentration of 4 μg g^-1 according to Staphylococcus aureus resistance breakpoint.

RESULTS

One hundred and sixteen patients were included: 79 in Group A and 37 in Group B. At the beginning of the surgery, cefazolin concentration in subcutaneous fatty tissue was 12.2 (5.4) μg g^-1 in Group A and 12 (6.1) μg g^-1 in Group B (P=0.7). At the end, cefazolin concentrations in subcutaneous fatty tissue were 9.0 (4.9) and 7.8 (4.2) μg g^-1 in Groups A and B, respectively (P=0.2). The plasma concentration of free cefazolin during surgery was higher in Group A than in Group B (P<0.0001). Fatty-tissue concentrations of 95% and 83% patients in Groups A and B, respectively, were above S. aureus resistance breakpoint.

CONCLUSIONS

After a 4 g dose, the concentrations of cefazolin in fatty tissue were above the 4 μg g^-1 tissue concentration target, providing adequate antibiotic tissue concentrations during bariatric surgery. As cefazolin concentration in fatty tissue is a surrogate endpoint, the results should be considered in conjunction with the results on free cefazolin concentrations in subcutaneous tissue.

CLINICAL TRIAL REGISTRATION

NCT01537380.

Pharmacokinetic Alterations of Antimicrobials in the Critically Ill

Critical illness is accompanied by multiple physiologic alterations that affect the pharmacokinetics of antimicrobials. Although the pharmacokinetics of a number of antimicrobials have been studied in critically ill individuals, an understanding of the physiological alterations in critical illness and general pharmacokinetic principles of antimicrobials is imperative for appropriate selection, dosing, and prediction of toxicity.

The effect of surgery (Ovariohysterectomy) on the plasma disposition of meloxicam following intravenous administration in dogs

Background

Meloxicam (MLX) is a nonsteroidal anti-inflammatory drug used in the relief of postoperative pain for human and veterinary medicine. This study was designed to investigate the effect of surgery on the plasma disposition of MLX in dogs undergoing ovariohysterectomy following a single intravenous injection at a dose of 0.2 mg/kg bodyweight. Eight crossbred bitches were used in the study. A two-phase experimental design with a 10-day washout period was used. Pre-operative MLX was administered intravenously to 8 bitches about 10 days before surgery (Phase I, control) at a dose of 0.2 mg/kg bodyweight and peri-operative MLX was administered intravenously after anaesthesia and 15 min before the start of surgery (Phase II). Blood samples were collected from all animals at various times between 1 and 96 h after the drug administrations in both phases. The drug concentrations were analysed using high performance liquid chromatography.

Results

The volume of plasma MLX distribution at steady-state (Vd_ss) of the control group (Vd_ss: 263.0 ml/kg) was significantly greater (P < 0.05) compared to that of the surgery group (Vd_ss: 149.3 ml/kg). The AUC values were higher (29.5 vs. 23.0 μg.h²/ml) and the CL values were lower (7.7 vs. 10.5 ml.h/kg) in the surgery group compared to the control group, respectively, but differences were not significant.

Conclusions

The results of the present study indicated that surgery could alter the plasma disposition of MLX and thus the drug efficacy and side effects such as gastrointestinal ulceration, unusual bleeding and loss of kidney function/failure when repeated doses are used.

Model-based exposure-response analysis of apixaban to quantify bleeding risk in special populations of subjects undergoing orthopedic surgery

Population pharmacokinetic (PK) and exposure-response analyses of apixaban were performed using data from phase I-III studies to predict bleeding risks for patients receiving apixaban 2.5 mg b.i.d. after total knee or hip replacement (TKR, THR) surgery (N = 5,510). Renal function, age, gender, and body weight impacted apixaban exposure. Bleeding risk increased as a function of exposure. Predicted bleeding frequencies for TKR and THR populations at risk for high apixaban exposure (female, age > 75 years, calculated creatinine clearance (cCrCL) < 30 ml/min, body weight < 50 kg) (6.85 and 10.3%, respectively) were comparable to the reference population (male/female, age 65-75 years, cCrCL ≥ 80 ml/min, body weight 65-85 kg) (6.18 and 9.32%, respectively). A 100% increase in apixaban exposure is expected to raise bleeding frequencies to 7.25% (TKR) and 10.9% (THR), whereas a 200% increase would raise them to 8.49 and 12.7%. Coexistence of combined patient risk factors or doubling of exposure is not likely to result in a substantial, clinically relevant increase in bleeding risk with 2.5 mg b.i.d. apixaban.

Population pharmacokinetics of cyclosporine in transplant recipients

A number of classical pharmacokinetic studies have been conducted in transplant patients. However, they suffer from some limitations, for example, (1) the study design was limited to intense blood sampling in small groups of patients during a certain posttransplant period, (2) patient factors were evaluated one at a time to identify their association with the pharmacokinetic parameters, and (3) mean pharmacokinetic parameters often cannot be precisely estimated due to large intraindividual variability. Population pharmacokinetics provides a potential means of addressing these limitations and is a powerful tool to evaluate the magnitude and consistency of drug exposure. Population pharmacokinetic studies of cyclosporine focused solely on developing limited sampling strategies and Bayesian estimators to estimate drug exposure, have been summarized before, and are, therefore, not a subject of this review. The major focus of this review is to describe factors (demographic factors, hepatic and gastrointestinal functions, drug-drug interactions, genetic polymorphisms of drug metabolizing enzymes and transporters) that have been identified to contribute to the large portion of observed variability in the pharmacokinetics of cyclosporine in transplant patients. This review summarizes and interprets the conclusions as well as the nonlinear mixed-effects modeling methodologies used in such studies. A highly diversified collection of structural models, variability models, and covariate submodels have been evaluated and validated using internal or external validation methods. This review also highlights areas where additional research is warranted to improve the models since a portion of model variability still remains unexplained.

The pharmacokinetic profile of intravenous paracetamol in adult patients undergoing major abdominal surgery

BACKGROUND

Intravenous (IV) paracetamol is commonly used in the postoperative period for the treatment of mild to moderate pain. The main pathways for paracetamol metabolism are glucuronidation, sulfation, and oxidation, accounting for approximately 55%, 30%, and 10% of urinary metabolites, respectively. The aim of this study was to describe the pharmacokinetics of IV paracetamol and its metabolites in adult patients after major abdominal surgery.

METHODS

Twenty patients were given 1 g of paracetamol by IV infusion at induction of anesthesia (Interval 1) and every 6 hours thereafter, with the final dose given at 48-72 hours (Interval 2). Plasma and urine samples were collected for up to 8 hours after infusion for both intervals. The samples were analyzed by high-performance liquid chromatography to determine the amount of paracetamol and its metabolites. The data were modeled in Phoenix WinNonlin using a user-defined ASCII parent-metabolite model with linear disposition, to obtain the estimates for volume of distribution, metabolic and urinary clearance.

RESULTS

Mean (95% confidence interval) metabolic clearance to paracetamol glucuronide increased from 0.06 (0.05-0.08) to 0.14 (0.11-0.18) L · h⁻¹ · kg⁻¹, P value <0.001 and urinary clearance increased from 0.08 (0.07-0.09) to 0.14 (0.10-0.17) L · h⁻¹ · kg⁻¹, P value 0.002. The mean (95% confidence interval) volume of distribution of paracetamol increased from 0.17 (0.12-0.21) to 0.43 (0.27-0.59) L · kg⁻¹, P value 0.032.

CONCLUSIONS

After major abdominal surgery, there were apparent increases in the metabolic conversion to paracetamol glucuronide and its urinary clearance suggesting potential induction of paracetamol glucuronidation.

The influence of bypass procedures and other anatomical changes in the gastrointestinal tract on the oral bioavailability of drugs

The gastrointestinal (GI) tract plays an important role in the absorption of orally administered drugs. However, in some cases the anatomy of the GI tract is changed due to GI surgery, which has the potential of influencing drug bioavailability. In this review, we aim to compile, review, and comment the existing but sometimes fragmented scientific data regarding the impact of GI surgery on the oral bioavailability of drugs. Relevant reports were gathered through the PubMed database from database inception through January 2012. Drugs for which at least one trial or case report suggested a change in oral bioavailability or absorption caused by GI surgery are discussed in detail. Major methodological differences, such as study design, number of subjects and choice of reference group, were observed in the reported studies. Predicting the impact of GI surgery on the oral bioavailability was therefore difficult to perform, even the most sophisticated classification systems could not be used for predicting purposes.

The effect of isoflurane anaesthesia and vasectomy on circulating corticosterone and ACTH in BALB/c mice

The use of blood corticosterone and faecal corticosterone metabolites as biomarkers of post-surgical stress and pain in laboratory animals has increased during the last decade. However, many aspects of their reliability in laboratory mice remain uninvestigated. This study investigated serum corticosterone and adrenocorticotropic hormone (ACTH) in mice subjected to isoflurane anaesthesia and vasectomy, and mice subjected to isoflurane anaesthesia without surgery. Serum levels of corticosterone and ACTH after pre-treatment with dexamethasone were analysed to provide further information about the stress hormone profiles. Vasectomy resulted in an increase in corticosterone for at least four hours after surgery with a peak 30min after the mice regained righting reflex. Mice subjected to isoflurane anaesthesia without surgery had the highest level of serum corticosterone 5min after regained righting reflex and the level returned to baseline levels four hours after the procedure. In vasectomised mice, treated with dexamethasone, high levels of corticosterone remained 30min after the procedure, whereas the anaesthetised mice, treated with dexamethasone, had significantly lower levels of corticosterone compared to anaesthetised mice not treated with dexamethasone. Thus, dexamethasone effectively inhibited the corticosterone response in the anaesthetised-only mice, but not in the mice subjected to surgery. In conclusion, both isoflurane anaesthesia and vasectomy during isoflurane anaesthesia resulted in an increase in serum glucocorticoids, but the negative feedback mechanism of newly operated mice, was altered. This may have consequences for the interpretation of glucocorticoids measurements as a biomarker of post-surgical stress in mice.

Characterisation of exposure versus response of edoxaban in patients undergoing total hip replacement surgery

Edoxaban is an oral direct factor Xa inhibitor approved for the prevention of venous thromboembolism (VTE) in Japan. The objectives of this analysis were to characterise the population pharmacokinetics (PK) of edoxaban and the relationships between edoxaban exposure and clinical outcomes in a phase IIb study of surgical patients following total hip replacement (THR). A total of 1,795 subjects from a phase IIb study, 10 phase I studies, and three phase IIa studies were included in the PK analysis. The exposure-response analysis included data from surgical patients assigned to edoxaban in the phase IIb study. Edoxaban disposition in healthy and post-surgical patients was well-described with a linear, two-compartment model. Creatinine clearance was significantly correlated with edoxaban clearance and the rate of oral absorption was affected by surgery. The probability of a post-operative VTE was significantly correlated with steady-state metrics of edoxaban exposure estimated for each subject by Bayesian post-hoc methods with age and gender being the significant and expected covariates. The incidence of bleeding was low in these studies and hence no exposure-response relationship could be identified. These analyses suggest that edoxaban has a predictable anticoagulant effect in this patient population leading to dose-proportional reduction in incidence of VTE with low incidence of bleeding.

Antimicrobial chemotherapy and lung microdialysis: a review

Pneumonia is a form of lung infection that may be caused by various micro-organisms. The predominant site of infection in pneumonia is debatable. Advances in the fields of diagnostic and therapeutic medicine have had a less than optimal effect on the outcome of pneumonia and one of the many causes is likely to be inadequate antimicrobial concentrations at the site of infection in lung tissue. Traditional antimicrobial therapy guidelines are based on indirect modelling from blood antimicrobial levels. However, studies both in humans and animals have shown the fallacy of this concept in various tissues. Many different methods have been employed to study lung tissue antimicrobial levels with limited success, and each has limitations that diminish their utility. An emerging technique being used to study the pharmacokinetics of antimicrobial agents in lung tissue is microdialysis. Development of microdialysis catheters, along with improvement in analytical techniques, has improved the accuracy of the data. Unfortunately, very few studies have reported the use of microdialysis in lung tissue, and even fewer antimicrobial classes have been studied. These studies generally suggest that this technique is a safe and effective way of assessing the pharmacokinetics of antimicrobial agents in lung tissue. Further descriptive studies need to be conducted to study the pharmacokinetics and pharmacodynamics of different antimicrobial classes in lung tissue. Data emanating from these studies could inform decisions for appropriate dosing schedules of antimicrobial agents in pneumonia.

Bioavailability and population pharmacokinetics of voriconazole in lung transplant recipients

This study was undertaken to characterize the pharmacokinetics and bioavailability of voriconazole in adult lung transplant patients during the early postoperative period, identify factors significantly associated with various pharmacokinetic parameters, and make recommendations for adequate dosing regimens. Thirteen lung transplant patients received two intravenous infusions (6 mg/kg, twice daily [b.i.d.]) immediately posttransplant followed by oral doses (200 mg, b.i.d.) for prophylaxis. Blood samples (9/interval) were collected during one intravenous and one oral dosing interval from each patient. Voriconazole plasma concentrations were measured by high-pressure liquid chromatography (HPLC). NONMEM was used to develop pharmacokinetic models, evaluate covariate relationships, and perform Monte Carlo simulations. There was a good correlation (R(2) = 0.98) between the area under the concentration-time curve specific for the dose evaluated (AUC(0-∞)) and trough concentrations. A two-compartment model adequately described the data. Population estimates of bioavailability, clearance, V(c), and V(p) were 45.9%, 3.45 liters/h, 54.7 liters, and 143 liters. Patients with cystic fibrosis (CF) exhibited a significantly lower bioavailability (23.7%, n = 3) than non-CF patients (63.3%, n = 10). Bioavailability increased with postoperative time and reached steady levels in about 1 week. V(p) increased with body weight. Bioavailability of voriconazole is substantially lower in lung transplant patients than non-transplant subjects but significantly increases with postoperative time. CF patients exhibit significantly lower bioavailability and exposure of voriconazole and therefore need higher doses. Intravenous administration of voriconazole during the first postoperative day followed by oral doses of 200 mg or 400 mg appeared to be the optimal dosing regimen. However, voriconazole levels should be monitored, and the dose should be individualized based on trough concentrations as a good measure of drug exposure.

The impact of intestinal failure on oral drug absorption: a review

INTRODUCTION

Intestinal failure is a complex gastroenterological condition that occurs as a result of reduced intestinal absorption of nutrients and/or water and electrolytes. Without treatment, nutritional depletion and/or dehydration will result. It can be acute or chronic and occurs secondary to a variety of causes, including massive bowel resection, inflammatory bowel diseases of the bowel, and small bowel dysfunction.

RESULTS AND DISCUSSION

Resection of the small bowel results in a range of physiological changes that affect the absorption of nutrients, water, and electrolytes. In addition, these changes may also affect the absorption of orally administered medication. However, there is only minimal published literature regarding this, with the publications limited to case reports of failure or efficacy of certain medicines such as digoxin and warfarin in individual patients. Due to the highly heterogeneous nature of intestinal failure patients, there is little generalizability of the information within these articles to other patients. Only one article seeks to provide limited practical advice regarding prescribing in this complex patient group.

CONCLUSION

The input of specialist pharmacists is necessary in the management of these patients to ensure that appropriate drugs and formulations are prescribed in a timely manner to optimize absorption and resultant efficacy.

Infusions of albumin increase free fraction of naproxen in healthy volunteers: a randomized crossover study

BACKGROUND

In vitro and in vivo studies have indicated that stabilizers present in pharmaceutical-grade albumin influence the albumin-binding capacity for highly protein-bound drugs. However, the half-life of the stabilizers and the quantitative effect have been difficult to determine.

METHOD

A randomized crossover study including six healthy volunteers was performed. The study subjects received 750 mg of oral naproxen 2 h before the study. They were randomized to receive either 100 ml of 20% albumin or 100 ml of Ringer's acetate solution intravenously. Frequent blood samples were obtained. The experiment was repeated 4 weeks later with the alternate solution. The serum samples were analysed to determine the concentrations of albumin, N-acetyl-DL-tryptophan, caprylate, and naproxen.

RESULTS

The free fraction of naproxen increased significantly after the infusion of albumin (P<0.05). The increase was concurrent with the appearance of N-acetyl-DL-tryptophan and caprylate in serum. The free fraction of naproxen declined rapidly after the albumin infusion was completed. N-acetyl-DL-tryptophan had a half-life of approximately 30 min. The half-life of caprylate was <15 min.

CONCLUSION

A transfusion of albumin results in an increase in the free fraction of naproxen. The transient increase in free-fraction naproxen decreased together with the detectable levels of the stabilizers N-acetyl-DL-tryptophan and caprylate. N-acetyl-DL-tryptophan and caprylate have a short half-life in serum.

Effect of abdominal surgery on the intestinal absorption of lipophilic drugs: possible role of the lymphatic transport

Although abdominal surgery is a routine procedure in clinical practice and in preclinical investigation, little is known regarding its effect on the intestinal absorption of drugs. The aim of this study was to investigate the effect of abdominal surgery on the intestinal absorption of highly lipophilic compounds with different absorption mechanisms following oral administration. The 2 compounds that were tested were biopharmaceutical classification system (BCS) class 2 model lipophilic cannabinoid derivatives, dexanabinol and PRS-211,220. Although dexanabinol is mostly absorbed via passive diffusion to the portal blood, PRS-211,220 is absorbed mostly via lymphatic transport. In this work, we compared the absorption of these compounds after abdominal surgery in rat with the absorption data obtained from naïve animals. The outcomes of this investigation showed that the abdominal surgery mostly affected the absorption process on the preenterocyte level, as indicated by the 2-fold increase in the extent of intestinal absorption of dexanabinol, which is a compound with a low degree of intestinal lymphatic transport. However, the lymphatic transport was not affected by the surgical procedure as evident by the absence of change in the extent of absorption of PRS-211,220, which is transported to the systemic circulation mainly by intestinal lymphatics. In conclusion, abdominal surgery can significantly affect the intestinal absorption of lipophilic drugs; however, intestinal lymphatic transport seems to be less affected by the abdominal surgery.

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.

American Society of Anesthesiologists classification of physical status as a predictor of wound infection

BACKGROUND

Wound infection occurs when bacterial contamination overcomes the hosts' defences against bacterial growth. Wound categories are a measurement of wound contamination. The American Society of Anesthesiologists (ASA) classification of physical status may be an effective indirect measurement of the hosts' defence against infection. This study examines the association between the ASA score of physical status and wound infection.

METHODS

A retrospective review of a prospective study of antibiotic prophylaxis was carried out. Patients with a documented ASA score who received optimal prophylactic antibiotics were included. The anaesthetist scored the ASA classification of physical status in theatre. Other risk factors for wound infection were also documented. Patients were assessed up to 30 days postoperatively.

RESULTS

Of 1013 patients there were 483 with a documented ASA score. One hundred and one may not have received optimal prophylaxis, leaving a database of 382 patients. There were 36 wound infections (9.4%). Both the ASA classification of physical status (P = 0.002) and the wound categories (P = 0.034) significantly predicted wound infection. The duration of surgery, patient's age, acuteness of surgery and the organ system being operated on did not predict wound infection. On logistic regression analysis the ASA score was the strongest predictor of wound infection.

CONCLUSION

When effective prophylactic antibiotics were used the ASA classification of physical status was the most significant predictor of wound infection.

Impaired target site penetration of vancomycin in diabetic patients following cardiac surgery

Soft tissue infections constitute a serious complication following surgery in diabetic patients and frequently require the administration of vancomycin. However, despite antibiotic treatment, mortality of patients with postoperative infections remains high and might be related to an impaired penetration of anti-infective agents to target tissues. Therefore, the present study was designed to measure vancomycin tissue concentrations in six diabetic and six nondiabetic patients after cardiac surgery. Vancomycin was administered as a continuous intravenous infusion at an infusion rate of 80 to 120 mg/h. Vancomycin concentrations in soft tissues and plasma were measured in all patients during steady state as "therapeutic window" concentrations in plasma by microdialysis on day 8+/-4 after initiation of vancomycin treatment. Vancomycin tissue concentrations in diabetic patients were significantly lower than in nondiabetics (3.7 mg/liter versus 11.9 mg/liter; P=0.002). The median vancomycintissue/vancomycinplasma concentration ratio was 0.1 in diabetic patients and 0.3 in nondiabetics (P=0.002). Our study demonstrated that vancomycin penetration into target tissues is substantially impaired in diabetic patients versus nondiabetics. Insufficient tissue concentrations could therefore possibly contribute to failure of antibiotic treatment and the development of antimicrobial resistance in diabetic patients.

Lack of effect of experimental hypovolemia on imipenem muscle distribution in rats assessed by microdialysis

The aim of this study was to investigate the influence of hypovolemia on the distribution of imipenem in muscle extracellular fluid determined by microdialysis in awake rats. Microdialysis probes were inserted into the jugular vein and hind leg muscle. Imipenem recoveries in muscle and blood were determined in each rat by retrodialysis by drug before drug administration. Hypovolemia was induced by removing 40% of the initial blood volume over 30 min. Imipenem was infused intravenously at a dose of 70 mg . kg(-1) over 30 min, and microdialysis samples were collected for 120 min from hypovolemic (n = 8) and control (n = 8) rats. The decay of the free concentrations in blood and muscle with time were monoexponential, and the concentration profiles in muscle and blood were virtually superimposed in both groups. Accordingly, the ratios of the area under the concentration-time curve (AUC) for tissue (muscle) to the AUC for blood were always virtually equal to 1. Hypovolemia induced a 23% decrease in the clearance (P < 0.05) of imipenem, with no statistically significant alteration of its volume of distribution. This study showed that imipenem elimination was altered in hypovolemic rats, probably due to decreased renal blood flow, but its distribution characteristics were not. In particular, free imipenem concentrations in blood and muscle were always virtually identical.

Cytochrome p450 gene expression levels in peripheral blood mononuclear cells in comparison with the liver

Cytochromes p450 (CYPs) compose a superfamily of similar proteins involved in detoxification and elimination, as well as activation of a wide variety of compounds. Most CYP family members are localized in the liver. In order to assess whether peripheral blood leukocytes (PBL) are available as a surrogate for the determination of CYP gene expression levels in the liver, we compared CYP gene expression levels in PBL with those in liver tissues from patients with hepatocellular carcinoma (HCC). We measured CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 2F1, 2J2, 3A4, 3A5, 3A7, 4A11, 4B1 and CYP27 gene expressions in PBL and in the liver by real-time reverse-transcription (RT)-PCR. We could detect expression of CYP1A1, 1A2, P1B1, 2A6, 2B6 and 2E1 genes in PBL and all the genes except for CYP2F1 in the liver. Although gene expression levels within each subfamily were closely correlated within PBL and within the liver, a clear correlation of gene expression levels between PBL and liver tissues was found only for CYP4B1. Although inter-individual variation of the expression level of each CYP gene was wide, the induced level was proportional to the basal expression level. Therefore, monitoring of CYP gene expression levels in PBL, especially those of CYP4B1, could be available as a biomarker for monitoring of exposure to environmental pollutants and assessing the associated risk. Compared with non-tumor tissue, HCC tissues tended to show overexpression of multiple CYP genes, indicating that individualized selection and more effective administration of chemotherapeutic agents could perhaps be based on the pattern of CYP overexpression.

Pharmacodynamics of piperacillin in severely ill patients evaluated by using a PK/PD model

Penetration of antiinfective drugs into soft tissues is essential for antimicrobial killing at the target site, but is substantially lower in severely ill patients compared with healthy subjects. The present study was conducted to assess the antimicrobial effect of piperacillin in severely ill patients. Strains of Staphylococcus aureus and Pseudomonas aeruginosa were exposed in vitro to concentrations of piperacillin, simulating the pharmacokinetic profiles measured in soft tissue of patients and healthy subjects. The simulation for patients resulted in effective killing, whereas bacterial regrowth was detected for healthy subjects. Our in vitro simulation showed that bacterial killing may be effective in severely ill patients despite relatively low concentrations of piperacillin at the target site. This finding is due to impaired renal function and subsequently prolonged tissue and plasma half-lives of piperacillin in intensive care patients.

Enteral Drug Absorption in Patients with Short Small Bowel

Drug therapy may become difficult when a significant amount of the small intestine is resected, as happens in patients with a short small bowel. Drug absorption from the gastrointestinal tract is altered in these patients; however, this effect is variable in patients and differs with each drug. Literature regarding clinical outcomes of normal or alternative administration routes in patients with a short small bowel is limited. We explored what is written about the normal absorption of commonly used drugs and what difference the resection of different but substantial parts of the small intestine makes. Changes in the gastrointestinal tract after resection of >50% of the small intestine causes malabsorption of macronutrients and micronutrients, and may alter the drug absorption process. The metabolic activity of the abundantly present intestinal lactobacilli can also affect the enteral drug absorption in patients with short small bowel as this results in the production of lactic acid, gaseous CO(2), ethanol and an increased bile acid deconjugation. Accelerated intestinal luminal transit time causes a reduction in absorption of certain antimicrobial agents, digoxin, hydrochlorothiazide, ciclosporin, cimetidine, mesalazine (5-aminosalicylic acid), oral contraceptives and levothyroxine. Gastric hypersecretion and lack of sufficient contact time with the intestinal mucosa in patients with short small bowel leads to insufficient absorption of drugs such as omeprazole. Successful treatment with warfarin, tricyclic antidepressants, metronidazole, fluconazole, procainamide, sotalol and pindolol are reported in several studies. Many different factors cause this variability in drug absorption in such patients. Monitoring the serum drug concentration in these patients may ease dealing with the management problems.

Pharmacokinetic and pharmacodynamic considerations when treating patients with sepsis and septic shock

Sepsis and septic shock are accompanied by profound changes in the organism that may alter both the pharmacokinetics and the pharmacodynamics of drugs. This review elaborates on the mechanisms by which sepsis-induced pathophysiological changes may influence pharmacological processes. Drug absorption following intramuscular, subcutaneous, transdermal and oral administration may be reduced due to a decreased perfusion of muscles, skin and splanchnic organs. Compromised tissue perfusion may also affect drug distribution, resulting in a decrease of distribution volume. On the other hand, the increase in capillary permeability and interstitial oedema during sepsis and septic shock may enhance drug distribution. Changes in plasma protein binding, body water, tissue mass and pH may also affect drug distribution. For basic drugs that are bound to the acute phase reactant alpha(1)-acid glycoprotein, the increase in plasma concentration of this protein will result in a decreased distribution volume. The opposite may be observed for drugs that are extensively bound to albumin, as the latter protein decreases during septic conditions. For many drugs, the liver is the main organ for metabolism. The determinants of hepatic clearance of drugs are liver blood flow, drug binding in plasma and the activity of the metabolic enzymes; each of these may be influenced by sepsis and septic shock. For high extraction drugs, clearance is mainly flow-dependent, and sepsis-induced liver hypoperfusion may result in a decreased clearance. For low extraction drugs, clearance is determined by the degree of plasma binding and the activity of the metabolic enzymes. Oxidative metabolism via the cytochrome P450 enzyme system is an important clearance mechanism for many drugs, and has been shown to be markedly affected in septic conditions, resulting in decreased drug clearance. The kidneys are an important excretion pathway for many drugs. Renal failure, which often accompanies sepsis and septic shock, will result in accumulation of both parent drug and its metabolites. Changes in drug effect during septic conditions may theoretically result from changes in pharmacodynamics due to changes in the affinity of the receptor for the drug or alterations in the intrinsic activity at the receptor. The lack of valid pharmacological studies in patients with sepsis and septic shock makes drug administration in these patients a difficult challenge. The patient's underlying pathophysiological condition may guide individual dosage selection, which may be guided by measuring plasma concentration or drug effect.