Pharmacokinetics of antimicrobial agents in anuric patients during continuous venovenous haemofiltration

BACKGROUND

The optimal drug dosing in anuric patients undergoing continuous haemofiltration is a difficult task. More pharmacokinetic data is needed to derive practical guidelines for dosage adjustments.

METHODS

Drug elimination of various antimicrobial agents (amikacin, amoxycillin, ceftazidime, ciprofloxacin, flucloxacillin, imipenem, netilmicin, penicillin G, piperacillin, sulphamethoxazole, tobramycin, vancomycin) was studied in 24 patients with acute renal failure treated by pump-assisted continuous venovenous haemofiltration (CVVH). Concentrations of serial blood and ultrafiltrate samples were determined by HPLC or by fluorescence polarization immunoassay. Total body clearance (CL) and haemofilter clearance (CLf) rates were determined by standard model-independent equations. Data from published literature on fractions not bound to proteins (fu), non-renal drug clearance fractions (Qo), and normal clearance values (CLn) were used to derive a pharmacokinetic model, taking into account drug removal by ultrafiltration and by non-renal clearance.

RESULTS

A total of 37 treatment periods was studied. Blood flow through the haemofilters was 100 ml/min resulting in an average ultrafiltrate flow rate (UFR) of 13.2 +/- 4.6 (range 3.2-22.1) ml/min. Acceptable correlations of calculated and measured haemofilter clearances and total body clearances were obtained.

CONCLUSIONS

Total body clearance in anuric patients during CVVH is predictable from drug properties, which are generally known. The individual dosage requirements may be calculated by multiplying Qo + fu.UFR/CLn with the dose considered appropriate in the absence of renal impairment.

[Therapy of urologic complications in 210 consecutive kidney transplantations]

The results of 210 consecutive renal transplant operations between 1969 and 1989 were assessed with respect to urological complications. 17 patients had urological problems. 4.7% of the patients had ureteric complications (obstruction or leakage). 2.8% of this series showed other general urological complications like bladder bleeding, extravasation at the ureterovesical anastomosis and bladder leakage. One patient had interstitial cystitis and an anastomosis of the transplant ureter with an ileal conduit was performed. Ureteric complications were managed in all cases by revisional surgery, excision of the affected segment followed by ureteroneocystostomy or uretero-/pyeloureterostomy. Bladder bleeding and extravasation at the ureterovesical anastomosis were treated by transurethral and percutaneous drainage procedures. Open surgery was necessary for great bladder leakage. In all cases the function of the transplant kidney could be maintained.

[Dialysis quantity and dietary protein during continuous ambulatory peritoneal dialysis]

Calculation of a dialysis index (Teehan; Perit Dial Bull 1985, 3:152-156) and estimations of the protein catabolic rate (PCR) (reflecting protein intake under steady state conditions) were performed in 20 CAPD patients instructed to eat 1.2-1.5 g/kg BW protein per day and treated with 8-101 dialysate exchange per day. Dialysis indices were 1.20 +/- 0.44, greater than 1.0 reflecting adequate treatment. PCR was based on nitrogen loss by dialysis and urine as well as by losses assumed to be constant in stools and through skin; dialysis loss was obtained either by collection of the 24 h dialysate volume or by estimating the equilibration ratio between blood and dialysate for calculation of nitrogen removal from serum urea nitrogen and 24 h dialysate volume. Values obtained were 0.90 +/- 0.23 and 0.89 +/- 0.23 g/kg BW, respectively (r = 0.97, P = 0.0001). These low PCR values were found to correlate with data from dietary surveys (r = 0.77). Total serum protein, albumin content and transferrin concentration were all within the normal range and there was no correlation between these parameters and protein intake. It is concluded that protein intake and dialysis adequacy must be monitored individually. Whereas generally recommended CAPD schedules provide effective treatment, a mean protein intake greater than 0.9 g/kg BW seems to be adequate.

Doppler echocardiographic findings in dialysis patients

We used Doppler echocardiographic techniques firstly to examine left ventricular (LV) filling patterns in dialysis patients, secondly to analyse whether Doppler echocardiographic left ventricular filling pattern is different in patients with recurrent intradialytic hypotension, and thirdly to study the relation between blood pressure decrease during volume subtraction and left ventricular filling pattern. Indices of left ventricular filling patterns of 47 dialysis patients were consistently different when compared to normotensive healthy controls. To further assess the relation of left ventricular filling pattern to blood pressure stability on dialysis, we first compared 24 patients with stable intradialytic blood pressure (BP) and 23 patients with one or more episodes or intradialytic hypotension per month. Patients with recurrent intradialytic hypotension had lower predialysis blood pressure (MAP 89 +/- 13 vs 96 +/- 14 mmHg), more severe concentric hypertrophy (left ventricular mass/volume ratio 2.7 +/- 1.4 vs 2.0 +/- 0.7), and impaired left ventricular filling (Doppler) as indicated by the ratio of early diastolic vs late (atrial) filling (0.66 +/- 0.2 vs 0.95 +/- 0.22). Subsequently we assessed by Doppler technique the effect of a predetermined rate of volume subtraction (during one dialysis session) in patients with or without recurrent intradialytic hypotension. Diastolic filling indices deteriorated consistently prior to the reduction in blood pressure (early diastolic filling 26.8 +/- 15.2 vs 45.4 +/- 10.9% of diastolic filling). It is suggested that impaired left ventricular filling, presumably reflecting disturbed left ventricular compliance, is common in dialysis patients. Findings by noninvasive Doppler techniques suggest a role of abnormal left ventricular distensibility in recurrent dialysis hypotension.