Pharmacokinetics of piperacillin and tazobactam in critically ill patients with renal failure, treated with continuous veno-venous hemofiltration (CVVH)

Objective: Kinetics of piperacillin (pip), in combination with the beta-lactamase inhibitor tazobactam (taz) have been studied in volunteers and patients in relatively stable conditions. The fixed drug preparation appeared to have ideal pharmacokinetic properties if renal function was normal or slightly impaired, but no data are available for critically ill patients in anuric renal failure. This study should provide such data. Patients, design: We studied the pharmacokinetics in nine patients with multiple organ failure, including anuric renal failure, treated with continuous veno-venous hemofiltration (CVVH). Patients received a standard schedule of 4 g pip and 0.5 g taz administered over 0.5 h intravenously, 8 hourly. During 2 consecutive days, the serum levels of both compounds were determined, and total clearance (CI_T) was calculated from serum concentrations. Results: All nine patients completed day 1, and 8 completed day 2 of the protocol. On day 1, single-dose kinetics showed considerable spread, but pip/taz serum levels followed the pattern as expected, with a pip / taz concentration ratio of 20 : 1. On day 2, however, taz serum concentrations showed a relative increase as compared to pip, resulting in a change in the serum pip/taz concentration ratio to 10 : 1 on day 2. The CI_T of pip was 2.52 ± 1.38 l/h (t ¹/₂ : 5.9 ± 2.9 h), and CI_T of taz 4.44 ± 2.28 l/h (t ¹/₂ : 8.1 ± 3.7 h). The CI_T and t ¹/₂ of pip and taz correlated highly significantly with clearance by CVVH. Despite a higher CI_T, taz has a longer half-life, because of a higher volume of distribution. Conclusion: In CVVH dependent patients, pip/taz fixed drug preparations can be used initially, but the pip dosage should be increased relative to that of taz (or interval-adjusted) to prevent cumulation of taz, as compared to the active antimicrobial agent pip. Received: 19 February 1997 Accepted: 20 May 1997     

Acquired medical condition and driving ability

Under Dutch law a driver's licence requires a written statement of physical and mental health from the applicant. However, after the licence has been issued, no further statements are required, not even when the person involved develops a medical condition that poses a threat to safe driving. If an accident occurs and it is established that the driver suffered from an intercurrently acquired condition, the insurance companies will not pay. Physicians have a moral obligation to advise patients in their care whom this may affect to report to the physician of the licence administration.     

A simple and sensitive fully validated HPLC-UV method for the determination of 5-fluorouracil and its metabolite 5,6-dihydrofluorouracil in plasma

The authors developed a simple and sensitive, fully validated HPLC-UV method for the determination of both 5-FU and its metabolite DHFU in small-volume plasma samples. The analytes were separated on a 4.6 x 250 mm ID Atlantis dC18 5-microm column with isocratic elution at room temperature. Chlorouracil was used as internal standard. The analytes were detected with an UV diode array detector. DHFU was detected at 205 nm, 5-FU at 266 nm, and chlorouracil at both wavelengths. The limits of quantification in plasma were 0.040 mug /mL for 5-FU and 0.075 microg/mL for DHFU. Linearity, accuracy, precision, recovery, dilution, freeze-thaw stability, and stability in the sample compartment were evaluated. The method appeared linear over a range from 0.04 to 15.90 microg/mL for 5-FU and from 0.075 to 3.84 microg/mL for DHFU. The method appeared very suitable for therapeutic drug monitoring and pharmacokinetic studies of 5-FU because of its simple extraction and small sample volume. Problems in earlier published methods with interfering peaks and variable retention times were overcome. The method appeared also to be suitable for detection of uracil and its metabolite dihydrouracil in plasma.     

Massive venlafaxine overdose resulted in a false positive Abbott AxSYM urine immunoassay for phencyclidine

CASE REPORT: A 13-yr-old girl overdosed on 48 x 150 mg venlafaxine (Effexor XR). She was taking venlafaxine regularly for depression. Her only other medications included topical Benzamycin and pyridoxine 50 mg daily for acne. The Abbott AxSYM assay was positive only for phencyclidine, but GC/MS did not confirm the presence of phencyclidine. Toxilab identified only one substance, confirmed by GC/MS as venlafaxine. A serum sample obtained 3 h after her ingestion revealed a venlafaxine concentration of 24460 ng/mL and an O-desmethylvenlafaxine concentration of 3930 ng/mL, confirming the massive acute overdose (therapeutic range of venlafaxine and O-desmethylvenlafaxine together is 250-750 ng/mL). Urine spiked with 4.2 mg/mL ofvenlafaxine and 0.7 mg/mL of O-desmethylvenlafaxine was interpreted as positive with the Abbott AxSYM fluorescent polarized immunoassay for phencyclidine (readout of 28 ng/mL). CONCLUSION: Venlafaxine may cause a false positive Abbott AxSYM phencyclidine assay when present in very high concentrations. Physicians should be aware of this potential reaction when interpreting urine drug immunoassays.     

Continuous infusion carboplatin on a 21-day schedule: a phase I and pharmacokinetic study

A phase I study with continuous infusion carboplatin for 21 days every 6 weeks using a venous access port and portable pump was performed over a dose range of 12 to 32 mg/m2/d, with increments of 2 mg/m2/d. Forty-four patients received 107 courses (median, two; range, one to nine). World Health Organization (WHO) grade III/IV leukopenia and thrombocytopenia occurred in one of seven patients at 30 mg/m2/d, and in two of six and four of six patients at 32 mg/m2/d. Cumulative platelet depression was found at dose levels of 28 mg/m2/d or more. Median glomerular filtration rate (GFR) and effective renal plasma flow, monitored by radioisotope clearances at doses greater than or equal to 20 mg/m2/d, decreased 8.2% (P less than .05) and 10.9% (P less than .01) after two courses. There was a relationship (r = .50, P less than .0002) between the percentage of platelet depression and GFR. No other toxicity was observed. Of the 17 patients who were evaluable, one complete response and four partial responses were observed. In addition, six patients had stable disease. Pharmacokinetic analysis of total and ultrafiltrable platinum (UFPt) was performed by atomic absorption spectrophotometry. Steady-state plasma levels for UFPt were reached after 8 hours. These levels could be detected from the 20 mg/m2/d dose. During steady state, carboplatin dose and UFPt plasma levels were not correlated, but steady-state UFPt and GFR (r = -.27, P less than .05) were. Twenty-four percent of total platinum (Pt) was present as UFPt during steady state (x = 160 +/- 10 micrograms/L). Total body clearance of UFPt exceeded GFR 2.2 times. Mean area under the curve (AUC) for UFPt during continuous infusion was 4,921.8 +/- 301.72 mg.min/L. For total Pt, steady-state plasma levels were not reached; total Pt plasma levels increased between day 7 and day 21 (P less than .0001). There was a significant relation between total Pt serum levels day 7, 14, and 21 and the drug dose administered. Immunohistochemical analysis of DNA-bound Pt in leukocytes showed a linear increase from day 7 to day 14 to day 21 (r = .97) between DNA-bound Pt and duration of infusion in individual patients. The maximum-tolerable dose of carboplatin is 30 mg/m2/d for 21 days (total dose 630 mg/m2) and is recommended for phase II studies.     

Impairment of organ function after oral ingestion of refined petrol

After oral ingestion of 600 ml of refined petrol a 23-year-old male developed multiple organ failure. Acute renal insufficiency due to nephrotoxic tubular necrosis requiring hemodialysis was a major manifestation. Moreover, respiratory failure, seizures, hemolysis, disseminated intravascular coagulation, liver damage and erosions of mucous membranes occurred. The patient subsequently recovered completely. In spite of the poor absorption from the gastrointestinal tract and the high first-pass effect in the liver, massive petrol intoxication may lead to reversible multisystemic lesions.