Disease-induced variations in plasma protein levels. Implications for drug dosage regimens (Part II)

Tacrolimus Exposure in Obese Patients: and A Case-Control Study in Kidney Transplantation

BACKGROUND

Tacrolimus pharmacokinetics in obese (Ob) patients has been poorly studied. In this article, the authors explored the impact of obesity on tacrolimus exposure in kidney transplant recipients (KTRs) and estimated a more suitable initial dosage in this population.

METHODS

A retrospective, observational, monocentric case-control study was performed in obese KTRs (BMI > 30 kg/m2) who received tacrolimus between 2013 and 2017 (initial dose: 0.15 mg/kg/d) (actual weight). Nonobese (Nob) controls (BMI <30 kg/m2) were matched for age and sex. Weekly centralized monitoring of tacrolimus trough levels was performed by liquid chromatography/mass spectrometry until the third month (M3). Target trough levels were set between 8 and 10 ng/mL. All patients received antilymphocyte globulin, corticosteroids, and mycophenolate mofetil.

RESULTS

Of the 541 KTRs, 28 tacrolimus-treated Ob patients were included and compared with 28 NOb-matched controls. With a mean of 22 assays/patient, tacrolimus trough levels were higher in Ob patients (mean 9.9 versus 8.7 ng/mL; P = 0.008); the weight-related dose of Tac was lower at M3 (mean 0.10 versus 0.13 mg/kg/d, P < 0.0001). The tacrolimus concentration to dose (C0/D) was higher in the Ob cohort [mean 116 versus 76 (ng/mL)/(mg/kg/d); P = 0.001]. In Ob patients, a mean decrease of -4.6 mg/d in the 3 months after tacrolimus initiation was required (versus -1.12 in NOb; P = 0.001) to remain within the therapeutic range. Obesity, high mycophenolate mofetil daily dose at M3, and CYP3A5 expression were independently associated with higher tacrolimus exposure. Four dose-adaptation strategies were simulated and compared with the study results.

CONCLUSIONS

An initial dose calculation based on either ideal or lean body weight may allow for faster achievement of tacrolimus trough level targets in Ob KTRs, who are at risk of overexposure when tacrolimus is initiated at 0.15 mg/kg/d. A prospective study is required to validate alternative dose calculation strategies in these patients.

Changes in the pharmacokinetic of sildenafil citrate in rats with Streptozotocin-induced diabetic nephropathy

Aim

The present investigates deals with the change in the pharmacokinetic of Sildenafil citrate (SIL) in disease condition like diabetic nephropathy (DN).

Method

Diabetes was induced in rats by administering Streptozotocin i.e. STZ (60 mg/kg, IP) saline solution. Assessment of diabetes was done by GOD-POD method and conformation of DN was done by assessing the level of Creatinine, Blood Urea Nitrogen (BUN) and Albuminurea. After the conformation of DN single dose of drug SIL (2.5 mg/kg, p.o.) were given orally and Pharmacokinetic Parameters like [AUC o-t (ug.h/ml), AUC 0-∞, C_max, T_max, Kel, Clast] were estimated in the plasma by the help of HPLC-UV.

Result

There was significant increase (p < 0.01) in the Pharmacokinetic parameters of SIL in DN rat (AUC_0-t, AUC_0-∞, C_max, T_max and T_1/2) compare to normal control rat and significant increase Kel in the DN rat compare to control rat.

Conclusion

The study concluded that there was significant (p < 0.01) increase in the bioavailability of SIL in DN.

Effect of diabetes mellitus on pharmacokinetic and pharmacodynamic properties of drugs

The effects of diabetes mellitus on the pharmacokinetics and pharmacodynamics of drugs have been well described in experimental animal models; however, only minimal data exist for humans and the current knowledge regarding the effects of diabetes on these properties remains unclear. Nevertheless, it has been observed that the pharmacokinetics and pharmacodynamics of drugs are changed in subjects with diabetes. It has been reported that diabetes may affect the pharmacokinetics of various drugs by affecting (i) absorption, due to changes in subcutaneous adipose blood flow, muscle blood flow and gastric emptying; (ii) distribution, due to non-enzymatic glycation of albumin; (iii) biotransformation, due to regulation of enzymes/transporters involved in drug biotransformation; and (iv) excretion, due to nephropathy. Previously published data also suggest that diabetes-mediated changes in the pharmacokinetics of a particular drug cannot be translated to others. Although clinical studies exploring the effect of diabetes on pharmacodynamics are still very limited, there is evidence that disease-mediated effects are not limited only to pharmacokinetics but also alter pharmacodynamics. However, for many drugs it remains unclear whether these influences reflect diabetes-mediated changes in pharmacokinetics rather than pharmacodynamics. In addition, even though diabetes-mediated pharmacokinetics and pharmacodynamics might be anticipated, it is important to study the effect on each drug and not generalize from observed data. The available data indicate that there is a significant variability in drug response in diabetic subjects. The discrepancies between individual clinical studies as well as between ex vivo and clinical studies are probably due to (i) the restricted and focused population of subjects in clinical studies; (ii) failure to consider type, severity and duration of the disease; (iii) histopathological characteristics generally being missing; and (iv) other factors such as varying medication use, dietary protein intake, age, sex and obesity. The obesity epidemic in the developed world has also inadvertently influenced the directions of pharmacological research. This review attempts to map new information gained since Gwilt published his paper in Clinical Pharmacokinetics in 1991. Although a large body of research has been conducted and significant progress has been made, we still have to conclude that the available information regarding the effect of diabetes on pharmacokinetics and pharmacodynamics remains unclear and further clinical studies are required before we can understand the clinical significance of the effect. An understanding of diabetes-mediated changes as well as of the source of the variability should lead to the improvement of the medical management and clinical outcomes in patients with this widespread disease.

The concentration of cyclosporine metabolites is significantly lower in kidney transplant recipients with diabetes mellitus

BACKGROUND

Diabetes mellitus is prevalent among kidney transplant recipients. The activity of drug metabolizing enzymes or transporters may be altered by diabetes leading to changes in the concentration of parent drug or metabolites. This study was aimed to characterize the effect of diabetes on the concentration of cyclosporine (CsA) and metabolites.

METHODS

Concentration-time profiles of CsA and metabolites (AM1, AM9, AM4N, AM1c, AM19, and AM1c9) were characterized over a 12-hour dosing interval in 10 nondiabetic and 7 diabetic stable kidney transplant recipients. All patients were male, had nonfunctional CYP3A5*3 genotype, and were on combination therapy with ketoconazole.

RESULTS

The average daily dose (±SD) of CsA was 65 ± 21 and 68 ± 35 mg in nondiabetic and diabetic subjects, respectively (P = 0.550). Cyclosporine metabolites that involved amino acid 1 (AM1, AM19, AM1c) exhibited significantly lower dose-normalized values of area under the concentration-time curve in patients with diabetes. Moreover, during the postabsorption phase (≥3 hours after dose), metabolite-parent concentration ratios for all metabolites, except AM4N, was significantly lower in diabetic patients. The pharmacokinetic parameters of ketoconazole were similar between the 2 groups thus excluding inconsistent ketoconazole exposure as a source of altered CsA metabolism.

CONCLUSIONS

This study indicates that diabetes mellitus significantly affects the concentration of CsA metabolites. Because CsA is eliminated as metabolites via the biliary route, the decrease in the blood concentration of CsA metabolites during postabsorption phase would probably reflect lower hepatic cytochrome P450 3A4 enzyme activity. However, other mechanisms including altered expression of transporters may also play a role. Results of cyclosporine therapeutic drug monitoring in diabetic patients must be interpreted with caution when nonspecific assays are used.

Effect of Uraemia and Anephric State on the Pharmacokinetics of Tenoxicam in the Rat

Renal alterations, uraemia and nephrotic syndrome induced in experimental animals caused a reduction in the plasma albumin concentration of 25 and 30%, respectively. As a result of this decrease, the unbound fraction of tenoxicam in uraemic rats (0·06 ± 0·02) and in anephric rats (0·11 ± 0·08) increased with respect to the control group (0·03±0·004). The induced hypoalbuminaemia did not modify the blood to plasma concentration ratio. Both plasma clearance (CL) and apparent volume of distribution at steady-state (Vdss) rose significantly with the increase in the unbound fraction: (Vdss 55 ±6 mL (control rats); 69 ± 12 mL (uraemic rats); 96 ± 30 mL (anephric rats); CL = 7± 1 mL h−1 (control rats); 12 ± 4 mL h−1 (uraemic rats); 15 ± 7 mL h−1 (anephric rats)). Tenoxicam elimination was found to be restrictive, with an extraction ratio less than 0·1 in the three groups. The induction of nephrotic syndrome was observed to have a significant effect on intrinsic metabolic activity, intrinsic clearance of tenoxicam being reduced by 30% in the anephric rats (161 ± 38 mL h−1) with respect to the values obtained in the control group (228 ± 22 mL h−1).

Influence of renal impairment on the pharmacokinetics and pharmacodynamics of oral dabigatran etexilate: an open-label, parallel-group, single-centre study

Dabigatran etexilate is an oral direct thrombin inhibitor in clinical development for the prevention and treatment of thromboembolic disorders. Following oral administration, dabigatran etexilate is rapidly absorbed and converted into its active form, dabigatran. The aim of this study was to investigate the effect of renal impairment on the pharmacokinetics and pharmacodynamics of dabigatran following administration of a single oral dose of dabigatran etexilate in subjects with renal impairment (150 mg) or end-stage renal disease (ESRD) on maintenance haemodialysis (50 mg). This open-label, parallel-group, single-centre study enrolled 23 subjects with mild, moderate or severe renal impairment (creatinine clearance >50 to < or =80, >30 to < or =50 and < or =30 mL/min, respectively), 6 patients with ESRD and 6 healthy subjects. Blood and urine samples were collected up to 96 hours after dosing for determination of dabigatran pharmacokinetic and pharmacodynamic parameters. Compared with the values in healthy subjects, the area under the plasma concentration-time curve from time zero to infinity (AUC(infinity)) values were 1.5-, 3.2- and 6.3-fold higher in subjects with mild, moderate and severe renal impairment. Changes in the maximum plasma concentration (C(max)) were modest, and the time to reach the C(max) was unchanged. In subjects with severe renal impairment, the mean terminal elimination half-life was doubled (28 hours vs 14 hours for control). The AUC for prolongation of pharmacodynamic parameters (the activated partial thromboplastin time and ecarin clotting time) increased in line with the pharmacokinetic changes. In patients with ESRD, the dose-normalized AUC(infinity) was approximately twice the value in the control group. Haemodialysis removed 62-68% of the dose. Dabigatran etexilate was well tolerated in all groups. Exposure to dabigatran is increased by renal impairment and correlates with the severity of renal dysfunction. A decrease in the dose and/or an increase in the administration interval in these patients may be appropriate. In patients with ESRD, dabigatran can be partly removed from the plasma by haemodialysis.

Effect of severe renal failure and haemodialysis on the pharmacokinetics of levosimendan and its metabolites

BACKGROUND AND OBJECTIVES

Levosimendan is a calcium sensitiser developed for the treatment of congestive heart failure. It increases myocardial contractility, reduces the filling pressure and dilates both the peripheral and coronary vessels. The circulating metabolites of levosimendan, OR-1855 and OR-1896, are formed and eliminated slowly after intravenous administration of levosimendan. The aim of this study was to investigate the effect of impaired renal function and haemodialysis on the pharmacokinetics of levosimendan, OR-1855 and OR-1896.

STUDY DESIGN

This study was an open-label, nonrandomised, phase I pharmacokinetic study. Levosimendan was administered as a single-dose infusion of 0.1 microg/kg/minute for 24 hours. The follow-up period lasted 3 weeks.

STUDY SETTING

Twenty-fivepatients were included:12 patients with severe chronic renal failure (CRF) with creatinine clearance of < 30 mL/minute/1.73 m(2) and 13 patients with end-stage renal disease (ESRD) undergoing haemodialysis. A group of 12 healthy subjects served as controls.

RESULTS

Levosimendan, the parent drug, was eliminated rapidly from the plasma after discontinuation of its infusion, with an elimination half-life (t(1/2)) [mean +/- standard error of mean] of 1.5 +/- 0.09 hours in ESRD patients undergoing haemodialysis, 1.0 +/- 0.2 hours in patients with severe CRF and 0.91 +/- 0.03 hours in healthy subjects. The t(1/2) of levosimendan was significantly longer (p < 0.001) in ESRD patients undergoing haemodialysis than in healthy subjects. The t(1/2) of OR-1855 and OR-1896 were 94.0 +/- 20.4 hours and 96.5 +/- 19.5 hours, respectively, in ESRD patients undergoing haemodialysis compared with 60.8 +/- 5.2 and 61.6 +/- 5.2 hours, respectively, in healthy subjects (p = not significant). The t(1/2) of OR-1855 was significantly longer (85.0 +/- 13.6 hours) in patients with severe CRF than in healthy subjects (60.8 +/- 5.2 hours, p < 0.05). The area under the plasma concentration-time curve (AUC) and the peak plasma concentration (C(max)) of the metabolites were approximately 2-fold in patients with ESRD undergoing haemodialysis and patients with severe CRF compared with healthy subjects. The mean unbound fraction (f(u)) of levosimendan in plasma was approximately 2% in each study group, whereas the f(u) of the metabolites was considerably higher (63-70%). In contrast to levosimendan, the metabolites were dialysable, with dialysis clearance of approximately 100 mL/minute. The haemodynamic responses and adverse event profiles were similar in the study groups, with headache, palpitations and dizziness being the most frequently recorded adverse events.

CONCLUSION

The t(1/2) of the levosimendan metabolites was prolonged 1.5-fold and their AUC and C(max) were 2-fold in patients with severe CRF and ESRD patients undergoing haemodialysis as compared with healthy subjects. These results suggest that the dose should be reduced when levosimendan is used for the treatment of congestive heart failure in patients with severe renal insufficiency.

Pharmacokinetics of mycophenolic acid and metabolites in diabetic kidney transplant recipients

Mycophenolate mofetil (MMF), the prodrug of mycophenolic acid (MPA), is an immunosuppressive agent commonly used after organ transplantation. Because diabetes mellitus may affect disposition of pharmacologic agents, we investigated the influence of diabetes on the pharmacokinetics of MPA, unbound MPA (fMPA) and its phenyl and acyl glucuronide metabolites (MPAG and AcMPAG respectively). The study included 13 diabetic and 11 nondiabetic, stable, kidney-transplant recipients who were receiving a triple maintenance immunosuppressive regimen. Serial plasma samples were obtained predose and at regular intervals for 12 hours. Gastric emptying was assessed using an acetaminophen absorption test and glomerular filtration rate was estimated using iohexol clearance. Treatment groups were well matched. The time to maximum concentration (Tmax) of MPA was 86.4 +/- 41.4 minutes versus 52.8 +/- 31.8 minutes in D and ND patients respectively (P = 0.04) indicating a delay in MMF absorption. Neither the maximum MPA concentration nor the 0- to 12-hour area under the concentration-time curve were different. All parameters derived for fMPA and the MPA metabolites were comparable between the 2 groups, except for the metabolite ratio of MPAG and AcMPAG, which was higher for diabetic patients (P = 0.03). Delayed gastric emptying seemed to have reduced the initial rate but not the extent of MPA absorption in diabetic patients. The profiles of fMPA were similar in both patient groups. With the exception of metabolite concentration ratio, none of the other parameters associated with MPA metabolism were different between the 2 groups.

Effect of Impaired Renal Function and Haemodialysis on the Pharmacokinetics of Aprepitant

BACKGROUND

The neurokinin NK(1)-receptor antagonist aprepitant has demonstrated efficacy in preventing highly emetogenic chemotherapy-induced nausea and vomiting.

OBJECTIVE

The objective of the present study was to investigate the effects of impaired renal function on the pharmacokinetics and safety of aprepitant.

SUBJECTS AND METHODS

A total of 32 patients and healthy subjects were evaluated in this open-label, two-part study. Pharmacokinetic parameters after a single oral dose of aprepitant 240 mg were measured in eight patients with end-stage renal disease (ESRD) requiring haemodialysis, eight patients with severe renal insufficiency (SRI [24-hour creatinine clearance <30 mL/min/1.73 m(2)]) and 16 healthy and age-, sex- and weight-matched subjects (controls).

RESULTS

In ESRD patients, the area under the plasma concentration-time curve (AUC) from 0 to 48 hours (AUC(48)) for aprepitant was on average approximately 36% lower than that observed in control subjects (ratio [ESRD patients/healthy controls] of geometric means = 0.64), but the 90% confidence interval 0.52, 0.78 for the ratio of true mean AUC(48) fell within the predefined target interval of 0.5, 2.0. Also in ESRD patients, there was no statistically or clinically significant difference in unbound aprepitant AUC (which may be more clinically relevant than total aprepitant AUC) when compared with healthy control subjects. Aprepitant pharmacokinetic parameters in ESRD patients were clinically similar when haemodialysis was initiated at 4 hours or 48 hours after aprepitant administration. In SRI patients, the ratio (SRI patients/healthy controls) of aprepitant AUC from zero to infinity (AUC(infinity)) geometric mean value was 0.79 with a 90% confidence interval of 0.56, 1.10. On average, in SRI patients the principal aprepitant pharmacokinetic parameters (AUC(infinity), initial maximum plasma concentration [C(max)], time to initial C(max), and apparent elimination half-life) were not statistically different from those obtained in healthy control subjects. Aprepitant was generally well tolerated in both ESRD and SRI patients.

CONCLUSION

The results of this study demonstrate that ESRD, haemodialysis and SRI have no clinically meaningful effect on aprepitant pharmacokinetics. Therefore, no dosage adjustment of aprepitant is warranted in SRI or ESRD patients.

Methadone Reincarnated: Novel Clinical Applications with Related Concerns

Methadone has numerous advantages as an analgesic, which have supported its recent increase in use. However, methadone also has a pharmacological profile as an opioid that differentiates it from other, better known or more widely used opioids. It also has unusual pharmacodynamics, pharmacokinetics, and metabolism that must be considered for safe use of methadone as an analgesic. This review looks at the history of methadone use as an analgesic and its properties that distinguish it as an unusual, and potentially, unstable opioid.

Pharmacokinetics and pharmacodynamics of vecuronium in children receiving phenytoin or carbamazepine for chronic anticonvulsant therapy

The pharmacokinetics and time course of action of vecuronium in normal children and children receiving anticonvulsant drugs for prolonged periods were characterized. A bolus dose of vecuronium 0.15 mg kg(-1) was administered i.v. to 10 non-epileptic children and to 10 children on phenytoin and 10 children on carbamazepine, who were matched for age and weight. Plasma concentrations of vecuronium, 3-OH desacetylvecuronium (the primary metabolite of vecuronium) and alpha1-acid glycoprotein (AAG) were determined. Pharmacokinetic variables were derived from plasma samples collected before and after administration of vecuronium. Neuromuscular transmission was monitored by evoked compound electromyography. Recovery of the first twitch of the train-of-four (T1/T0) and the recovery index (RI), the time for 25-75% recovery of T1/T0, were determined. The elimination half-life of vecuronium was significantly reduced in both anticonvulsant groups compared with control [control 48.2 (SD 40.3), phenytoin 23.5 (13.1), carbamazepine 18.4 (16.6) min, P<0.05]. Vecuronium clearance was increased in both anticonvulsant groups [control 9.0 (3.6), phenytoin 15.1 (8.9), carbamazepine 18.8 (13.1) ml kg(-1) min(-1), 0.05<P<0.1]. Children on chronic anticonvulsant therapy had a significantly shorter RI than control [control 21.8 (11), phenytoin 12.5 (8.3), carbamazepine 10.6 (5.9) min, P<0.05]. Concentrations of vecuronium at different degrees of recovery of T1, volumes of distribution and AAG concentrations were not different between groups. Our data confirm anticonvulsant-induced resistance to vecuronium in children and support a pharmacokinetic component contributing to the resistance.

Pharmacokinetics and safety of single intravenous infusions of the adenosine agonist, AMP 579, in patients with end-stage renal insufficiency

The pharmacokinetics of an adenosine agonist (AMP 579) were characterized in patients with end-stage renal disease compared to sex- and age-matched healthy volunteers. All study participants were administered single AMP 579 doses of 50 micrograms/kg as a 6-hour, constant-rate intravenous infusion. Serial blood samples were obtained for measurement of plasma AMP 579 concentration, and predose samples were collected for determination of AMP 579 plasma protein binding. The safety of AMP 579 administration in renally impaired patients also was evaluated. AMP 579 was rapidly cleared from the systemic circulation in all subjects as plasma concentrations were below the limit of detection by 2 to 4 hours after terminating the infusion. Noncompartmental analysis yielded mean values for the plasma AMP 579 concentration at the end of the 6-hour infusion (C6 h) of 9.6 and 10.5 ng/mL and for systemic clearances (Cl) of 0.91 and 0.72 L/h/kg in renally impaired patients and healthy volunteers, respectively. Mean volumes of distribution (Vss) in the renally impaired and healthy volunteers were 0.92 and 0.84 L/kg, and terminal elimination half-life values (t1/2) were 1.61 and 1.33 hours, respectively. The extent to which AMP 579 is bound to plasma protein was not altered in renally impaired patients since the free fractions were 4.0% and 3.4% for renally impaired and healthy volunteers, respectively. It was concluded that the pharmacokinetic parameters of AMP 579 were similar in both groups. The 6-hour AMP 579 infusion was generally well tolerated by both renal patients and healthy volunteers. There were no serious adverse events, and there were only two mild adverse events in 1 renally impaired patient judged possibly related to the study drug that quickly resolved. There were no clinically significant changes in laboratory values or clinical evaluations during the study. There was a slight increase in heart rate during the infusion of similar magnitude for both the renal patients and healthy volunteers. These data suggest that AMP 579 may be administered to renally impaired patients with minimal cardiovascular effects and adverse events. These results in end-stage renal patients (worst-case scenario) indicate that dose adjustment in patients with renal insufficiency of any degree is not indicated in future studies of AMP 579.

Disease-induced alterations in plasma drug-binding proteins and their influence on drug binding percentages in dogs

Disease-induced variations of plasma albumin (ALB) and alpha 1-acid glycoprotein (AAG) levels were investigated in dogs. Lower ALB (sometimes > 50% reduction) and higher AAG (sometimes > 10-fold increase) levels were observed in dogs with various diseases. Drug binding was determined at therapeutic concentrations using normal, low-ALB and high-AAG dog plasma. The binding percentages of the ALB-binding drugs decreased in low-ALB plasma, resulting in a large increase in unbound drug, particularly for naproxen (a 13-fold increase). The binding percentages of all AAG-binding drugs investigated in this study increased in high-AAG plasma, resulting in a large decrease in unbound drug, particularly for quinidine (99% decrease). The fluctuation in the unbound fraction of drugs could affect their efficacy or could cause side-effects. Veterinary clinicians should monitor the ALB and AAG levels in the plasma of patients and correct dosage regimens according to these levels, where field conditions permit this, in order to ensure the proper usage of drugs with high affinity for ALB or AAG.

The interdisciplinary team's approach to lupus nephritis

The interdisciplinary team approach in assessment and treatment of patients with chronic disease in general and lupus nephritis in particular provides a global format for identifying the multiple problem areas that retard or prevent optimal patient functioning. These areas include the physical, emotional, economic, psychosocial, and functional. Benefits to the individual patient include a thorough multifaceted assessment by professionals who have the benefit of peer collaboration and validation. This increases the likelihood that the whole patient is considered, not just the problem of nephritis. For example, how does the patient and her or his family cope with the impact of such a disease and how, in turn, do the coping abilities of the patient and family affect the disease. The interdisciplinary team also assesses how the treatment strategies for each problem area influence each other. Finally, the interdisciplinary team serves as a positive role model for effective collaboration among health professionals and for students in their respective disciplines.

Drug administration in patients with renal insufficiency. Minimising renal and extrarenal toxicity

Renal insufficiency has been associated with an increased risk of adverse effects with many classes of medications. The risk of some, but not all, adverse effects has been linked to the patient's degree of residual renal function. This may be the result of inappropriate individualisation of those agents that are primarily eliminated by the kidney, or an alteration in the pharmacodynamic response as a result of renal insufficiency. The pathophysiological mechanism responsible for alterations in drug disposition, especially metabolism and renal excretion, is the accumulation of uraemic toxins that may modulate cytochrome P450 enzyme activity and decrease glomerular filtration as well as tubular secretion. The general principles to enhance the safety of drug therapy in patients with renal insufficiency include knowledge of the potential toxicities and interactions of the therapeutic agent, consideration of possible alternatives therapies and individualisation of drug therapy based on patient level of renal function. Although optimisation of the desired therapeutic outcomes are of paramount importance, additional pharmacotherapeutic issues for patients with reduced renal function are the prevention or minimisation of future acute or chronic nephrotoxic insults, as well as the severity and occurrence of adverse effects on other organ systems. Risk factors for the development of nephrotoxicity for selected high-risk therapies (e.g. aminoglycosides, nonsteroidal anti-inflammatory drugs, ACE inhibitors and radiographic contrast media) are quite similar and include pre-existing renal insufficiency, concomitant administration of other nephrotoxins, volume depletion and concomitant hepatic disease or congestive heart failure. Investigations of prophylactic approaches to enhance the safety of these agents in patients with renal insufficiency have yielded inconsistent outcomes. Hydration with saline prior to drug exposure has given the most consistent benefit, while sodium loading and use of pharmacological interventions [e.g. furosemide (frusemide) dopomine/dobutamine, calcium antagonists and mannitol] have resulted in limited success. The mechanisms responsible for altered dynamic responses of some agents (benzodiazepines, theophylline, digoxin and loop diuretics) in renally compromised patients include enhanced receptor sensitivity secondary to the accumulation of endogenous uraemic toxins and competition for secretion to the renal tubular site of action. Application of the pharmacotherapeutic principles discussed into clinical practice will hopefully enhance the safety of these agents and optimise patient outcomes.

Pharmacokinetics of abecarnil in patients with renal insufficiency

OBJECTIVE

To characterize the pharmacokinetics of a single 5 mg oral dose of abecarnil in subjects with varying degrees of renal impairment.

METHODS

Twenty-six subjects were enrolled in this open-label parallel-group study. Ten subjects had normal renal function (NRF; creatinine clearance [CLCR] > or = 85 ml/min/1.73 m2), six subjects had mild to moderate renal insufficiency (MMRI; CLCR between 25 and 73 ml/min/1.73 m2), and 10 subjects had severe renal insufficiency (SRI; CLCR < or = 10 ml/min/1.73 m2). Abecarnil plasma concentrations were determined by means of HPLC, and plasma protein binding was determined by use of ultracentrifugation. Pharmacokinetic parameters were obtained with use of model-independent and model-dependent methods.

RESULTS

In subjects with SRI, area under the concentration-time curve and maximum plasma concentration were reduced by 36% and 31%, respectively, compared with demographically matched subjects with NRF. The apparent total body clearance in the NRF, MMRI, and SRI groups was 13.0 +/- 6.89, 12.9 +/- 3.64, and 25.0 +/- 13 ml/min/kg, and the apparent volume of distribution was 14.0 +/- 3.78, 12.8 +/- 2.4, and 19.4 +/- 5.76 L/kg, respectively (mean +/- SD). The patients with SRI had a significantly lower protein bound fraction than subjects with NRF (0.850 +/- 0.077 versus 0.948 +/- 0.023). Despite an increase in the free fraction of abecarnil (f(u)), there was no significant change in the apparent unbound total body clearance and unbound volume of distribution between the SRI and NRF groups. The anticipated full effect of the increase in f(u) among the patients with SRI was not realized and suggests that the f(u) in tissue may be increased in patients with SRI.

CONCLUSION

Dose adjustment will need to be made on the basis of titration to the desired clinical response and tolerability in patients with SRI just as in subjects with NRF.

Drug-protein binding sites. New trends in analytical and experimental methodology

In the last few years, continuous progress in instrumental analytical methodology has been achieved with a substantial increase in the number of new, more specific and more flexible methods for ligand-protein assays. In general, the methods used for drug-protein binding studies can be divided into two main groups: separation methods (enabling the calculation of binding parameters, i.e. the number of binding sites and their respective affinity constants) and non-separation methods (describing predominantly qualitative parameters of the ligand-protein complex). This review will be focussed particularly on recent trends in the development of drug-protein binding methods including stereoselective and non-stereoselective aspects using chromatography, capillary electrophoresis and microdialysis as compared to the "conventional approach" using equilibrium dialysis, ultrafiltration or size exclusion chromatography. The advantages and limitations of various methods will be discussed including a focus on "optimal" experimental strategies taking into account in vitro, ex vivo and/or in vivo studies. Furthermore, the importance of some particular aspects concerning the drug binding to proteins (covalent binding of drugs and metabolites, stereoselective interactions and evaluation of binding data) will be outlined in more detail.

The effect of renal insufficiency and hemodialysis on the pharmacokinetics of nalmefene

The disposition of nalmefene, an opioid antagonist intended for the reversal of opioid-induced respiratory depression, and its primary metabolite nalmefene glucuronide, were characterized in adult volunteers with normal renal function and in patients with end-stage renal disease (ESRD). The effect of hemodialysis on the elimination of nalmefene and nalmefene glucuronide also was assessed. Participants with normal renal function received a single intravenous dose of 2 mg, and patients with ESRD received two separate doses of 1 mg nalmefene hydrochloride. Terminal elimination half-life (t1/2) of both nalmefene and nalmefene glucuronide was prolonged in patients with ESRD compared with that in participants with normal renal function. The steady-state volume of distribution (Vdss) of nalmefene was significantly higher and total body clearance lower in patients with ESRD than in participants with normal renal function. Hemodialysis clearance of nalmefene was approximately 3.3% of total body clearance. Although the hemodialysis clearance of nalmefene glucuronide was 179.3 +/- 24.1 mL/min and its t1/2 was significantly reduced during dialysis to 5.2 +/- 2.3 hours, a dramatic rebound of nalmefene glucuronide concentrations of 75.7% was observed 7.7 +/- 5.4 hours after the end of hemodialysis. Thus, hemodialysis does not result in clinically significant alterations in the disposition of nalmefene or its primary metabolite, nalmefene glucuronide. These data suggest that there is no pharmacokinetic basis for modification of the initial dosage, but maintenance doses, if needed, should be administered less frequently due to the prolonged elimination of the active moiety, nalmefene.

[Role of substitution albumin therapy in drugs, hormones, electrolytes and miscellanous substances transport]

Human serum albumin (HSA) is quantitatively the most important non specific transport protein. HSA binds a wide variety of both endogenous and exogenous ligands. Hypoalbuminaemia may lead to a decreased plasma binding capability of some compounds. Biological/pharmacological consequences depend on the ligand and the target tissue. Many experimental studies suggest that hypoalbuminaemia may influence the metabolism and toxicity of endogenous ligands (bilirubin, metallic ions, oxygen radicals) and the pharmacological effect of some drugs (among others: furosemide, phenytoin, warfarin). The relevance of such information for human surgical situations remains unclear. Clinical studies are scarce and inconclusive. There is a lack of pertinent data supporting the necessity of HSA infusions in order to maintain a minimal plasma concentration and a convenient plasma transport. However, experimental data indicate that major hypoalbuminaemia should be considered with caution.

Tenoxicam pharmacokinetics in rats: a population model

This study was designed to establish the in vivo relationship between tenoxicam disposition and changes in plasma protein binding measured as an unbound fraction in plasma (fu). Tenoxicam was administered as a bolus 5-mg/kg dose, and total plasma concentrations, plasma albumin percentage, and fu were examined in five groups of rats (uremia or anephric states were experimentally induced in four groups to decrease plasma protein levels). Albumin levels were significantly decreased in all experimentally altered groups with respect to control animals (p < 0.01). A two-compartment population pharmacokinetic model that includes the effect of fu on the kinetic parameters was proposed to describe tenoxicam plasma concentration profiles. Plasma clearance (CL) increased but not proportionally with fu. Apparent volume of distribution of the central compartment (V) was linearly related to changes in fu and intercompartmental clearance was not affected by altered plasma protein binding. Expressing pharmacokinetic parameters as a function of fu resulted in a three- and five-fold decrease in the variability associated with CL and V, respectively.

Developmental principles of antiepileptic drug therapy

Antiepileptic drug therapy in children can be challenging because seizure semiology and drug disposition change dramatically over time. Close monitoring of drug clearance is required in early life because of the rapid ontogenesis of drug-eliminating organs. Large variations in serum peak and trough antiepileptic drug concentrations increase the risk for both adverse drug effects and unsatisfactory seizure control. Antiepileptic drug adverse effects also differ, probably relative to different receptor sensitivities in children. Failure to appreciate the developmental differences between children and adults can result in medication noncompliance, breakthrough seizures, and unacceptable adverse effects.

Erythromycin-induced hypoacusis: 11 new cases and literature review

OBJECTIVE

To report 11 cases of possible erythromycin-induced hearing loss and to review all cases reported in the literature.

CASE SUMMARY

In the 11 cases reported, the following are reviewed: age, gender, time to onset of and recovery from hypoacusis in relation to erythromycin administration, presence or absence of renal or hepatic disease, underlying disorders, and concurrent administration of other drugs. Hypoacusis appeared with dosages equal to or higher than 4 g/d in patients with a mean age of 52.5 +/- 19 years, a high percentage of whom (45 percent) presented with renal impairment. The hearing loss was reversible in all cases, and subsided a few days (median = 3) after dosage reduction or drug discontinuation.

DISCUSSION

Our patients' characteristics are similar to those of patients reported in the literature. Most data indicate that erythromycin-induced hypoacusis is a dose-dependent effect; however, its occurrence in patients otherwise free from disposing factors suggests that it is idiosyncratic.

CONCLUSIONS

Erythromycin administered for appropriate indications and dosage adjustments in patients with impaired renal and/or liver function may prevent or reduce the incidence of erythromycin-induced hypoacusis.

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.

Considerations in dosage selection for third generation cephalosporins

Pharmacokinetic parameters of third generation cephalosporins vary widely, requiring different dosage regimens and adjustment methods for each agent. Although their antibacterial spectrum favours their usage in infections caused by aerobic Gram-negative organisms, due to their limited post-antibiotic effect against these organisms, dosage regimens should ensure that free drug concentrations at the site of infection remain above the minimum inhibitory concentration for as much of the dosage interval as possible in patients with normal host defence mechanisms and for the entire dosage interval in immunocompromised patients. Altered protein binding encountered in various disease states can affect both microbiological and pharmacokinetic properties especially for drugs with high protein binding. Since the concentrations at the site of action are often different from those in serum, a higher or lower range of dosages needs to be selected depending on the target site. Decreased renal function affects the elimination of most third generation cephalosporins, whereas the presence of hepatic disease does not generally necessitate dosage adjustment. Because of the complex age-related physiological changes in paediatric and elderly patients, dosage should be adjusted on the basis of the reported pharmacokinetic data in these populations. The usual recommended dose may or may not be optimal in a given condition depending on the complex interactions between pharmacokinetic, microbiological and other host factors.