Pharmacokinetics of parenteral imipenem/cilastatin in patients on continuous ambulatory peritoneal dialysis

Pharmacokinetics of meropenem in patients with renal failure and patients receiving renal replacement therapy

Meropenem is a well established carbapenem antibacterial with a wide spectrum of activity against Gram-positive and Gram-negative bacteria, including beta-lactamase producers and Pseudomonas aeruginosa. Because of its clinical and bacteriological efficacy, meropenem is an important antimicrobial drug in the treatment of serious infections in adults and in children. Meropenem is predominately excreted unchanged in the urine, and thus dosage adjustments are necessary in patients with renal insufficiency and those undergoing intermittent haemodialysis (IHD) or various forms of continuous renal replacement therapy (CRRT), such as continuous venovenous haemodialysis, continuous venovenous haemodiafiltration (CVVHDF), continuous venovenous haemofiltration (CVVHF) or continuous ambulatory peritoneal dialysis (CAPD). The half-life of meropenem (approximately 1 hour in healthy volunteers) is prolonged up to 13.7 hours in anuric patients with end-stage renal disease. In patients receiving renal replacement therapy, half-life is influenced by drug-specific factors as well by membrane and treatment modalities (IHD, CRRT or CAPD). Plasma meropenem concentrations reach a peak of between 53 and 62 mg/L after the administration of meropenem 1g intravenously to healthy volunteers, up to 53 mg/L after meropenem 0.5g in haemodialysis patients, and between 18 and 45 mg/L after meropenem 1g during CRRT in critically ill patients. Approximately 50% of meropenem is eliminated by IHD, 25 to 50% by CVVHF and 13 to 53% by CVVHDF. Such differences are not negligible and demonstrate the great influence of the treatment modality on the elimination of the drug during renal replacement therapy. Thus, physicians run the risk of underdosing with this antimicrobial drug because of the quite different recommendations in the literature. Because of the excellent tolerability profile of meropenem, such underadministration should be avoided.

Use of low-dose low molecular weight heparin in hemodialysis

We investigated the lowest effective dosage of low molecular weight (LMW) heparin for hemodialysis in comparison to unfractionated (UF) heparin. Initial hemodialysis sessions were undertaken in 10 uremic patients with UF heparin of the dose habitually required for each patient. Four-hour hemodialysis sessions were then undertaken with LMW heparin (nadroparin) in a single bolus (200 anti-Xa unit Institut Choay/kg [aXaU IC/kg], 175 aXaU IC/kg, 150 aXaU IC/kg, or 125 aXaU IC/kg; two sessions for each dosage). Anti-Xa levels and activated partial thromboplastin time (APTT) were monitored hourly during dialysis. Fiber bundle volume of dialyzer was measured before and after dialysis. Urea clearance was determined at the onset and completion of dialysis. There were no episodes of excessive bleeding, clotting of dialyzers, or clots in air traps with UF heparin or LMW heparin. A 35% increase in APTT above baseline was observed in all dialysis sessions 1 hour after LMW heparin bolus, but the APTT decreased rapidly thereafter. The anti-Xa levels exceeded 0.5 U/mL for all sessions using LMW heparin irrespective of the dosage. No significant reduction of urea clearance was found in dialysis with either UF or LMW heparin. No reduction of fiber bundle volume of dialyzer was observed in dialysis with either UF or LMW heparin, although a small reduction (3%) was observed in dialysis with LMW heparin at 125 aXaU IC/kg. We concluded that the use of LMW heparin for hemodialysis is safe and effective as compared with UF heparin. The lowest effective dosage can be reduced to 125 aXaU IC/kg in high-risk patients to reduce hemorrhagic complications.

Mucosal pharmacokinetics and pilot study of short course of parenteral imipenem in the eradication of Helicobacter pylori

Eradication of Helicobacter pylori infection is known to reduce the incidence of duodenal ulcer recurrence. The most commonly used regimen for H. pylori infection is triple antimicrobial therapy for 1-2 weeks. This treatment is associated with frequent side effects and hence unsatisfactory compliance. As in vitro data showed that H. pylori is sensitive to imipenem, the pharmacokinetics of this drug in the gastric milieu, and the clinical efficacy of imipenem with omeprazole in eradicating H. pylori infection were studied. Imipenem/cilastatin levels in serum, gastric secretion and gastric mucosa were assayed in four patients after intravenous injection of a bolus dose of 500 mg. The serum and gastric secretion levels of imipenem achieved were more than 10 times the minimum inhibitory concentration of the drug for H. pylori. Gastric mucosal levels of imipenem vary considerably with time, which probably indicates rapid elimination of the drug into the gastric lumen. In the second part of this study, imipenem/cilastatin was given intravenously for the first 2 days after diagnosis of H. pylori infection in patients with endoscopically confirmed duodenal ulcers. The patients were also treated with 4 weeks of omeprazole. Clearance of H. pylori was initially achieved at the end of 2 days in 20 out of 22 (91%) patients. However, when the biopsies were repeated at 8 weeks, recurrence of H. pylori infection was evident in 19 cases (86.3%) indicating a failure of eradication. It was concluded that imipenem/cilastatin in combination with omeprazole failed to eradicate H. pylori infection.

Effect of biliary obstruction on the hepatic excretion of imipenem-cilastatin

The biliary excretion of imipenem-cilastatin studied by endoscopic cannulation of the common bile duct in patients with complete obstruction and in a group without obstruction showed that despite a 24-h prophylaxis, the bile obtained from patients with obstruction immediately after cannulation contained neither imipenem nor cilastatin, while there were 2 and 5% of peak concentrations in serum for imipenem and cilastatin, respectively, in the bile from patients without obstruction. Biliary excretion of both compounds increased rapidly after decompression, reaching a maximum of 15% of peak levels in serum within 2 h. Twenty-four hours after drainage, the biliary excretion of the drugs further improved. We conclude that since biliary obstruction impairs excretion of antibiotics, drainage is necessary for the control of sepsis in obstructed cholangitis.