Plasma levels of piperacillin and vancomycin used as prophylaxis in liver transplant patients

Piperacillin pharmacokinetics and pharmacodynamics in paediatric patients who received high frequency intra-operative piperacillin/tazobactam dosing

Piperacillin/tazobactam (PTZ) is a broad-spectrum antibiotic, typically dosed every six hours (q6h). Guidelines recommend dosing PTZ every 2 hours (q2h) intra-operatively for complex abdominal surgery, including liver transplant. The data supporting the guidelines for intra-operative dosing are sparse and the pharmacokinetics/pharmacodynamics (PK/PD) of q2h dosing has not been studied by simulation or in humans. In this study, PK/PD parameters of high-frequency intra-operative dosing and q6h post-operative dosing were compared in critically ill children. Paediatric patients who received PTZ during complex abdominal surgery or transplant and who had intra-operative and post-operative opportunistic samples were included. Using a published PK model and observed concentrations, individual piperacillin PK/PD parameters were estimated using Bayesian estimation. Alternative post-operative dosing strategies were simulated using the patients with the highest and lowest estimated piperacillin clearance. Thirteen patients were included (median age: 3.1 years, 85% liver transplant recipients). PK parameters in the intra-operative and post-operative phases were not significantly different (clearance: 15.8 ± 7.2 vs. 12.6 ± 6.3 L/h/70 kg, P=0.070; central volume: 13.4 [13.1, 13.8] vs. 15.2 [12.2, 16.0] L/70 kg, P=0.22). At an individual level, intra-operative clearance values were -35% to 139% of the post-operative values, whereas central volume intra-operative values were -40% to 77% of the post-operative values. Intra-operative piperacillin exposure was higher during high-frequency dosing compared with the post-operative period (AUC/h: 109 [93.4, 127] vs. 62.8 [41.6, 78.3] mg/L, P=0.002). Simulations showed great variation in optimal dosing strategies that would minimise toxicity and maximise efficacy, indicating a role for individualised dosing in paediatric surgical populations.

Pharmacokinetic and pharmacodynamic considerations of antibiotics and antifungals in liver transplantation recipients

The liver plays a major role in drug metabolism. Liver transplantation impacts the intrinsic metabolic capability and extrahepatic mechanisms of drug disposition and elimination. Different levels of inflammation and oxidative stress during transplantation, the process of liver regeneration, and the characteristics of the graft alter the amount of functional hepatocytes and activity of liver enzymes. Binding of drugs to plasma proteins is affected by the hyperbilirubinemia status and abnormal synthesis of albumin and alpha-1-acid glycoproteins. Postoperative intensive care complications such as biliary, circulatory, and cardiac also impact drug distribution. Renally eliminated antimicrobials commonly present reduced clearance due to hepatorenal syndrome and the use of nephrotoxic immunosuppressants. In addition, liver transplantation recipients are particularly susceptible to multidrug-resistant infections due to frequent manipulation, multiple hospitalizations, invasive devices, and frequent use of empiric broad-spectrum therapy. The selection of appropriate anti-infective therapy must consider the pathophysiological changes after transplantation that impact the pharmacokinetics and pharmacodynamics of antibiotics and antifungal drugs.

Choleresis and inhibition of biliary lipid secretion induced by piperacillin in the rat

1. The effects of the administration piperacillin on bile flow and biliary lipid secretion were studied in male Wistar rats. 2. Intravenous injection of piperacillin at doses ranging from 0.3 to 3.0 mmol/kg bodyweight led to an increase in its biliary concentration and excretion rate. Maximal biliary excretion was reached at a dose of 2.0 mmol/kg piperacillin. 3. Excretion of the antibiotic into bile was associated with a marked choleresis. A linear relationship was observed between bile flow and piperacillin excretion, 5.7 micro L bile being produced per micro mol piperacillin excreted into the bile. 4. Continuous i.v. infusion of piperacillin at 2.0 mmol/100 g per min did not result in significant changes in bile acid or cholesterol secretion, but biliary phospholipid secretion was markedly reduced. The inhibitory effect on phospholipid secretion was also present when biliary lipid output had been previously increased by an infusion of taurocholate (200 nmol/100 g per min). Addition of taurocholate did not reverse the impairment of phospholipid secretion induced by piperacillin. 5. These results indicate that acute administration of piperacillin in the rat induces a marked choleresis by stimulating bile acid-independent bile flow. The significant impairment in phospholipid secretion suggests a specific effect on intracellular supply and/or translocation across the canalicular membrane.

Review article: antibiotic prophylaxis for endoscopic retrograde cholangiopancreatography (ERCP)

This review examines the evidence for antibiotic prophylaxis in endoscopic retrograde cholangiopan-creatography (ERCP), and provides detailed advice about suitable antibiotic regimens in appropriate high-risk patients. Ascending cholangitis and infective endocarditis are potential complications of endoscopic ERCP. The pathophysiology of these two complications is quite separate and different sub-groups of patients require prophylaxis with appropriate antibiotic regimens. Ascending cholangitis results from bacterial infection of an obstructed biliary system, usually from enteric Gram-negative microorganisms, resulting in bacteraemia. There is incomplete drainage of the biliary system after ERCP in up to 10% of patients who require stenting. Antibiotics started in these patients will probably reduce the frequency of cholangitis by 80%. If antibiotics are restricted to this group, approximately 90% of all patients having an ERCP will avoid antibiotics, but 80% of cholangitic episodes will be prevented. Infective endocarditis may result from the bacteraemia caused at the time of the ERCP in patients with an abnormal heart valve. Antibiotic prophylaxis, in particular covering alpha-haemolytic streptococci, should be started before the procedure in this defined high-risk group.