Pharmacokinetics of ornidazole in patients with renal insufficiency; influence of haemodialysis and peritoneal dialysis

Ornidazole-Induced Recurrent Encephalopathy in a Chinese Man: A Rare Case Report and Literature Review

Ornidazole-induced encephalopathy (OIE) is seldom seen in the clinic. In this study, we report a new case of a patient who had taken 1,000 mg ornidazole daily for nearly 4 years because of suspected diarrhea and proctitis and presented with subacute symptoms such as unsteady gait, slurred speech, and psychiatric disorder. These symptoms were significantly relieved 3 days after the patient stopped taking ornidazole. When he took this medicine again, however, similar symptoms occurred 4 months later, which were again reduced after 4 days of drug discontinuation. After the second onset, abnormal signals were identified around the aqueduct of the midbrain, around the fourth ventricle, and in the dentate nuclei of the cerebellum bilaterally. After 9 days of drug discontinuation, lesions disappeared in the magnetic resonance imaging (MRI) results. According to the clinical manifestations, imaging features, and the reduced symptoms after drug withdrawal, we clinically diagnosed the patient with OIE. This paper also reviews the literature on OIE. Only five cases (including our case) have been reported, all of whom presented with cerebellar ataxia and dysarthria and three with additional mental symptoms such as agitation and irritability. All five patients had abnormal lesions in the dentate nucleus of the cerebellum bilaterally, among whom four also had lesions in the corpus callosum and three around the periaqueduct of the midbrain. After withdrawal of ornidazole, the symptoms in all patients vanished or were alleviated, and three of them showed reduced or disappeared lesions in a head MRI reexamination. Overall, OIE has rarely been reported. Our case report and literature review show that the lesions in the cerebellum, corpus callosum, and brainstem can be reversed. The main manifestations of the lesions—cerebellar ataxia, dysarthria, and mental symptoms—quickly weaken or disappear after drug withdrawal, with good prognosis. Nevertheless, clear pathogenesis has yet to be further investigated.

Influence of Continuous Ambulatory Peritoneal Dialysis on Elimination of Drugs

Renal failure delays elimination of many drugs thus prolonging their half lives. By knowing the half life and distribution volume, one can estimate total plasma clearance. When measured values have not been reported, endogenous total plasma clearance can be estimated and compared with peritoneal clearance to determine the effect of CAPD on half life. When peritoneal clearance has not been reported, it can be estimated knowing molecular mass and unbound plasma fraction. Such estimates suggest that elimination kinetics of most drugs are not appreciably affected by CAPD. Compared to those of untreated anuric patients, plasma levels of carbenicillin, ticarcillin, some cephalosporins, all aminoglycosides, vancomycin, sfluorocytosine, amantadine, atenolol, sotalol, timolol, chlorpropamide, theophylline and lithium may be reduced somewhat by CAPD. Thus one should monitor plasma levels of these agents to insure therapeutic concentrations rather than simply following the dosage guidelines for anuric patient.

Application of a hemodialysis clearance prediction model using quantitative structure-pharmacokinetic relationship analysis

Hemodialysis (HD) is a method used to remove biogenic substances or blood components that cause disease and some drugs used by patients to treat their diseases. Therefore, dosing schedule must be planned according to HD clearance (CL_HD ) when medical treatment is provided to patients receiving HD. We aimed to clarify the physical properties (eg, octanol-water partition coefficient and molecular electronegativity) or pharmacokinetic parameters (eg, volume of distribution) of compounds affecting CL_HD and to construct a mathematical model to predict CL_HD . The analysis covered individual CL_HD data for nine compounds from the literature. The molecular descriptors which are physical properties or pharmacokinetic parameters were calculated using the structural formula of each compound, and searched for factors related to CL_HD among the calculated 148 molecular descriptors. Nonlinear mixed-effects model analysis with CL_HD as objective variable and molecular descriptors as explanatory variable was conducted to examine the factor affecting CL_HD and develop a model for predicting CL_HD . The logarithm of the brain/blood partition coefficient was detected as a factor affecting CL_HD . The predictive accuracy of CL_HD using the constructed mathematical model with the logarithm of the brain/blood partition coefficient as explanatory variable was adequate.

Pharmacokinetics and pharmacodynamics of the nitroimidazole antimicrobials

Metronidazole, the prototype nitroimidazole antimicrobial, was originally introduced to treat Trichomonas vaginalis, but is now used for the treatment of anaerobic and protozoal infections. The nitroimidazoles are bactericidal through toxic metabolites which cause DNA strand breakage. Resistance, both clinical and microbiological, has been described only rarely. Metronidazole given orally is absorbed almost completely, with bioavailability > 90% for tablets; absorption is unaffected by infection. Rectal and intravaginal absorption are 67 to 82%, and 20 to 56%, of the dose, respectively. Metronidazole is distributed widely and has low protein binding (< 20%). The volume of distribution at steady state in adults is 0.51 to 1.1 L/kg. Metronidazole reaches 60 to 100% of plasma concentrations in most tissues studied, including the central nervous system, but does not reach high concentrations in placental tissue. Metronidazole is extensively metabolised by the liver to 5 metabolites. The hydroxy metabolite has biological activity of 30 to 65% and a longer elimination half-life than the parent compound. The majority of metronidazole and its metabolites are excreted in urine and faeces, with less than 12% excreted unchanged in urine. The pharmacokinetics of metronidazole are unaffected by acute or chronic renal failure, haemodialysis, continuous ambulatory peritoneal dialysis, age, pregnancy or enteric disease. Renal dysfunction reduces the elimination of metronidazole metabolites; however, no toxicity has been documented and dosage alterations are unnecessary. Liver disease leads to a decreased clearance of metronidazole and dosage reduction is recommended. Recent pharmacodynamic studies of metronidazole have demonstrated activity for 12 to 24 hours after administration of metronidazole 1 g. The post-antibiotic effect of metronidazole extends beyond 3 hours after the concentration falls below the minimum inhibitory concentration (MIC). The concentration-dependent bactericidal activity, prolonged half-life and sustained activity in plasma support the clinical evaluation of higher doses of metronidazole given less frequently. Metronidazole-containing regimens for Helicobacter pylori in combination with proton pump inhibitors demonstrate higher success rates than antimicrobial regimens alone. The pharmacokinetics of metronidazole in gastric fluid appear contradictory to these results, since omeprazole reduces peak drug concentration and area under the concentration-time curve for metronidazole and its hydroxy metabolite; however, concentrations remain above the MIC. Other members of this class include tinidazole, ornidazole and secnidazole. They are also well absorbed and distributed after oral administration. Their only distinguishing features are prolonged half-lives compared with metronidazole. The choice of nitroimidazole may be influenced by the longer administration intervals possible with other members of this class; however, metronidazole remains the predominant antimicrobial for anaerobic and protozoal infections.

Drug dosage in patients during continuous renal replacement therapy. Pharmacokinetic and therapeutic considerations

The advantages of continuous haemofiltration and haemodialysis over intermittent haemodialysis for the treatment of acute renal failure are well recognised. In intensive care patients, 4 different continuous procedures, arteriovenous and venovenous haemofiltration (CAVH and CVVH) or haemodialysis (CAVHD and CVVHD), are employed. These effective detoxification treatments require knowledge of their influence on drug disposition. Data on kinetics of drugs during continuous treatment are scarce and limited almost exclusively to the oldest and least effective procedure (CAVH). Selected dialysis membranes may adsorb drugs, as in the case of aminoglycosides. In addition, elimination of substances with large molecular weights may vary depending on the pore size of the membrane, as in the case of vancomycin. Thus, even if drug dosages can be based on pharmacokinetic studies, selection of a dialysis membrane not studied may cause unpredictable drug concentrations. With these limitations in mind and considering the available literature on pharmacokinetics in patients with renal failure, general guidelines for drug dosage during continuous renal replacement therapy can be given. In haemofiltration, drug protein binding is the major factor determining sieving, i.e. the appearance of the drug in the ultrafiltrate. In haemodialysis, diffusion is added to ultrafiltration, and therefore the saturation of the combined dialysate and ultrafiltrate will decrease further with increasing dialysate flow rate. In continuous haemofiltration or haemodialysis the extracorporeal clearance can be calculated by multiplying the saturation value (estimated or, better, measured) with the ultrafiltrate and dialysate flow rate. Dividing the extracorporeal clearance by the total clearance (including the nonrenal clearance) gives the fraction of the dose removed due to extracorporeal elimination. Whether dosage recommendations available for anuric patients have to be modified or not can be decided on the basis of this value. In case of high nonrenal clearance, the degree of saturation is without clinical significance. Based on these considerations guidelines have been constructed for the effect of extracorporeal elimination on more than 120 different drugs commonly used in intensive care patients.

Clinical pharmacokinetics of metronidazole and other nitroimidazole anti-infectives

Metronidazole was first introduced for the treatment of trichomoniasis. Its therapeutic use has subsequently been expanded to include amoebiasis, giardiasis and, more recently, anaerobic infections. Most of the early pharmacokinetic studies employed nonspecific assays such as microbiological and chemical assays. These assays were not able to differentiate the parent drug from the metabolites or other interfering substances. Pharmacokinetic data obtained through the use of specific chromatographic techniques provide the basis for this review of recent pharmacokinetic findings concerning metronidazole and other nitroimidazole antibiotics. When given intravenously or orally at usual recommended doses, metronidazole attains concentrations well above the minimum inhibitory concentrations for most susceptible micro-organisms. The drug has an oral bioavailability approaching 100%. Rectal and vaginal administration results in a smaller amount of drug absorption and lower serum concentrations. Metronidazole has limited plasma protein binding but can attain very favourable tissue distribution, including into the central nervous system. The drug is extensively metabolised by the liver to form 2 primary oxidative metabolites: the hydroxy and acetic acid metabolites. The kidney is responsible for the elimination of only a small amount of the parent drug; however, normal excretion of the 2 metabolites is dependent on the integrity of kidney function. The metabolism of metronidazole was found to vary among patient groups. Preterm and term infants have lower total body clearance (CL) and prolonged elimination half-lives. However, children older than 4 years old were observed to have pharmacokinetic parameters similar to those in adults. Reduced CL was also observed in children who are malnourished. Elderly patients have reduced renal excretion of both the parent drug and hydroxy metabolite. Pharmacokinetic parameters in pregnant patients were not significantly different from those in nonpregnant women; however, the drug is distributed into breastmilk and the infant will be exposed to the drug through the nursing mother. Patients undergoing gastrointestinal surgery or having enteric diseases and those who are hospitalised or critically ill also have altered pharmacokinetics. Metabolism of the drug is reduced in patients with liver dysfunction, giving delayed production of metabolites. In contrast, renal failure has little effect on the elimination of the parent drug, but affects the excretion of the metabolites more significantly. Haemodialysis was found to remove a substantial amount of the metronidazole while the effect of peritoneal dialysis was more limited. Energy and protein deficient diets as well as occupational exposure to gasoline did not alter metronidazole pharmacokinetics. However, the effect of alcohol consumption on metronidazole CL requires further study.(ABSTRACT TRUNCATED AT 400 WORDS)

High haemodialysis clearance of ornidazole in the presence of a negligible renal clearance

The pharmacokinetics of ornidazole was studied in 6 patients treated by haemodialysis and in 8 subjects with a creatinine clearance between 4 and 99 ml/min x 1.73 m2. Blood and urine collections were performed for 72 h after i.v. and oral administration of 1.0 g ornidazole. Total body clearance, half-life, volume of distribution and systemic availability were independent of renal function and did not differ from previously reported values in normal volunteers. The haemodialysis clearance of ornidazole was greater than 100% higher than the total body clearance. The renal clearance of ornidazole accounted for less than 7% of the total body clearance. The percentage of the dose of ornidazole recovered in urine as parent compound or as the biologically active metabolites [alpha-(chloromethyl)-2 hydroxymethyl-5 nitroimidazole-1 ethanol and 3-(2 methyl-5 nitroimidazole-1-yl)1,2 propanediol] decreased linearly with decreasing renal function. Although the sum of those three compounds recovered in urine accounted for less than 10% of the total dose of ornidazole administered, they yielded therapeutic concentrations (greater than 4 micrograms/ml) in urine over 24 h after dosing. Due to the peculiar pharmacokinetic behaviour of ornidazole, i.e. high haemodialysis clearance in the absence of significant renal clearance, no dosage adjustment is necessary while renal function declines, but an increased dose is mandatory while patients are on dialysis.

Pharmacokinetics of intraperitoneal teicoplanin in patients with chronic renal failure on continuous ambulatory peritoneal dialysis

The pharmacokinetic profile of teicoplanin, a new glycopeptide antibiotic active against Gram-positive aerobic and anaerobic bacteria, is described in five patients with end-stage renal disease on continuous ambulatory peritoneal dialysis (CAPD). A single 3 mg kg-1 dose was given intraperitoneally in the dialysate during a 6 h dwell time. The drug appeared in the plasma within 15 min at 1.00-0.28 mg l-1 (mean +/- s.d. = 0.70 +/- 0.45) in all five subjects, and peak serum concentrations ranged from 5.53 to 2.80 mg l-1 (4.84 +/- 1.43) at 6 h. Approximately 70% (71 +/- 12) of teicoplanin was absorbed from the peritoneal dialysis fluid during a single 6 h dwell time. The rate constant for peritoneal transfer (lambda d) averaged 0.318 h-1 and the half-life (t1/2 lambda d) was 2.18 h. Further values were serum elimination half-life 114-173 h; total body clearance 263-532 ml h-1; steady-state volume of distribution 68-93 l. This drug profile closely agrees with data reported after intravenous injection in patients on CAPD and suggests that teicoplanin has bidirectional exchange characteristics through the peritoneal membrane, although transfer from the systemic circulation to peritoneal fluid is consistently low. Instillation of teicoplanin in CAPD fluid may be a useful route of administration for treatment of peritonitis and exit site infections in CAPD patients.

Teicoplanin pharmacokinetics in patients with chronic renal failure

The pharmacokinetic profile of teicoplanin, a new glycopeptide antibiotic active against Gram-positive aerobic and anaerobic bacteria, was studied in 5 healthy male volunteers and 29 adult patients with various degrees of renal impairment, given a single 3 mg/kg intravenous dose. Teicoplanin was assayed in plasma and urine specimens by a microbiological method. Pharmacokinetic parameters for teicoplanin were estimated both by a 3-compartment open pharmacokinetic model and by non-compartmental analysis. Elimination half-life increased with the decrease in creatinine clearance and mean values ranged from 41 hours in volunteers to 163 hours in anuric patients. Renal failure did not affect either the volume of distribution of the central compartment (mean approximately 0.09 L/kg) or the steady-state volume of distribution (mean approximately 0.9 L/kg). Both total and renal clearance decreased with severity of disease, particularly the latter, while non-renal clearance was unaffected by renal failure. Average values were from 19 to 6 ml/min for total clearance and from 12 to 0.4 ml/min for renal clearance. There was a linear correlation between the total clearance of teicoplanin and creatinine clearance, as well as between renal clearance and creatinine clearance. The total urinary excretion of active teicoplanin averaged 65% of the administered dose in normal subjects, but was significantly reduced in the presence of renal insufficiency. Guidelines for administration of teicoplanin in patients with renal failure are given.

Pharmacokinetics of ciprofloxacin tablets in renal failure; influence of haemodialysis

The pharmacokinetics of ciprofloxacin has been studied after a single oral dose of 500 mg given to 5 normal subjects (N) and to 15 patients grouped according to their residual renal creatinine clearance: Group I, 8-30 ml X min-1, Group II, less than 8 ml X min-1, and Group III, haemodialysed patients studied twice--during an interdialysis period (IIIa) and in a 4 h haemodialysis session (IIIb). Ciprofloxacin was assayed by reverse phase HPLC using a spectrofluorimetric detection. The peak plasma concentration (2-5 mg X l-1) was reached within 2 h after drug administration. Apparent volume of distribution, 6.6 (N), 5.0 (I), 2.7 (II) and 4.2 (IIIa) l X kg-1 and total plasma clearance, 770 (N), 440 (I), 378 (II) and 314 (IIIa) ml X min-1 were decreased in relation to the degree of renal impairment. Mean plasma half-lives for patients in the 4 groups were 7.3 (N), 10.4 (I), 7.2 (II) and 9.3 (IIIa) h. In groups N, I and II, 40, 16 and 8% of the administered dose was eliminated through the kidney, with mean renal clearances of 305 +/- 63, 61 +/- 21 and 21 +/- 3 ml X min-1. A linear relationship was found between the renal clearance of ciprofloxacin and the glomerular filtration rate (r = 0.75, n = 15). Ciprofloxacin was partly removed by haemodialysis (IIIb): the dialyser extraction ratio was 23% and the dialysis clearance was 40 ml X min-1.

Renal disease and drug metabolism: an overview

Renal disease will perturb the disposition of drugs that primarily depend upon renal excretory function for elimination. While changes in drug half-life (T1/2) are often cited as evidence of altered drug disposition, it must be remembered that T1/2 is a dependent variable whose magnitude varies directly with volume of distribution (Vd) and indirectly with total body clearance (ClT). ClT is the one term that succinctly describes drug elimination. ClT is defined as the sum of the renal (ClR) and nonrenal (ClNR), or metabolic, clearances of a drug. Renal failure has been shown to alter the hepatic microsomal mixed-function oxidase system of drug metabolizing enzymes. Therefore, in end-stage renal failure, the potential exists for the modification of the disposition of drugs whose elimination is primarily hepatic. The kidneys themselves contain many of the enzymes important in hepatic drug metabolism. Drugs such as morphine, paracetamol, and p-aminobenzoic acid are metabolized in the kidney and experimental renal disease has been shown to reduce drug metabolism in the diseased kidney compared with the contralateral normal kidney. Renal disease, then, has the potential to alter not only the renal clearance of unchanged drug but also may substantially modify the metabolic transformation of drugs in both the liver and the kidneys. It can no longer be assumed that the pharmacokinetics of drugs that are disposed mainly by metabolism will be unaltered in renal failure.

Pharmacokinetics of teicoplanin in patients on continuous ambulatory peritoneal dialysis

We have studied the pharmacokinetics of teicoplanin, a new glycopeptide antibiotic active against Gram-positive aerobic and anaerobic bacteria, in five patients with end-stage renal disease on continuous ambulatory peritoneal dialysis (CAPD). Although teicoplanin was eliminated in the peritoneal fluid, relatively little was recovered (6.8 +/- 1.2% of the given dose). The following values were obtained: elimination half-time 102-347 h; total body clearance 4.16-7.38 ml X h-1 X kg-1, peritoneal clearance 0.31-0.37 ml X h-1 X kg-1. Because the elimination of teicoplanin is about four times less in patients undergoing CAPD compared with subjects with normal renal function, the dose of teicoplanin should be reduced appropriately in such cases.