Estimating glomerular filtration rate with a modification of diet in renal disease equation: Implications for pharmacy

Application of a Physiologically Based Pharmacokinetic Model to Predict Cefazolin and Cefuroxime Disposition in Obese Pregnant Women Undergoing Caesarean Section

Intravenous (IV) cefuroxime and cefazolin are used prophylactically in caesarean sections (CS). Currently, there are concerns regarding sub-optimal dosing in obese pregnant women compared to lean pregnant women prior to CS. The current study used a physiologically based pharmacokinetic (PBPK) approach to predict cefazolin and cefuroxime pharmacokinetics in obese pregnant women at the time of CS as well as the duration that these drug concentrations remain above a target concentration (2, 4 or 8 µg/mL or µg/g) in plasma or adipose tissue. Cefazolin and cefuroxime PBPK models were first built using clinical data in lean and in obese non–pregnant populations. Models were then used to predict cefazolin and cefuroxime pharmacokinetics data in lean and obese pregnant populations. Both cefazolin and cefuroxime models sufficiently described their total and free levels in the plasma and in the adipose interstitial fluid (ISF) in non–pregnant and pregnant populations. The obese pregnant cefazolin model predicted adipose exposure adequately at different reference time points and indicated that an IV dose of 2000 mg can maintain unbound plasma and adipose ISF concentration above 8 µg/mL for 3.5 h post dose. Predictions indicated that an IV 1500 mg cefuroxime dose can achieve unbound plasma and unbound ISF cefuroxime concentration of ≥8 µg/mL up to 2 h post dose in obese pregnant women. Re-dosing should be considered if CS was not completed within 2 h post cefuroxime administration for both lean or obese pregnant if cefuroxime concentrations of ≥8 µg/mL is required. A clinical study to measure cefuroxime adipose concentration in pregnant and obese pregnant women is warranted.

Estimating urine volume from the urine creatinine concentration

Spot determinations of the urine creatinine concentration are widely used as a substitute for 24-hour urine collections. Expressed as the amount excreted per gram of creatinine, urine concentrations in a single-voided sample are often used to estimate 24-hour excretion rates of protein, sodium, potassium, calcium, magnesium, urea, and uric acid. These estimates are predicated on the assumption that daily creatinine excretion equals 1 gm (and that a urine creatinine concentration of 100 mg/dl reflects a 1 Liter 24-hour urine volume). Such estimates are invalid if the serum creatinine concentration is rising or falling. In addition, because creatinine excretion is determined by muscle mass, the assumption that 24-hour urine creatinine excretion equals 1 gm yields a misleading estimate at the extremes of age and body size. In this review we evaluate seven equations for the accuracy of their estimates of urine volume based on urine creatinine concentrations in actual and idealized patients. None of the equations work well in patients who are morbidly obese or in patients with markedly decreased muscle mass. In other patients, estimates based on a reformulation of the Cockroft-Gault equation are reasonably accurate. A recent study based on this relationship found a high strength of correlation between estimated and measured urine output with chronic kidney disease (CKD) studied in the African American Study of Kidney Disease (AASK) trial and for the patients studied in the CKD Optimal Management with Binders and NictomidE (COMBINE) trial. However, the equation systematically underestimated urine output in the AASK trial. Hence, an intercept was added to account for the bias in estimated output. A more rigorous equation, derived from an ambulatory Swiss population, that includes body mass index and models the non-linear accelerated decline in creatinine excretion with age, could potentially be more accurate in overweight and elderly patients. In addition to extremes of body weight and muscle mass, decreased dietary intake or reduced hepatic synthesis of creatine, a precursor of creatinine, or ingestion of creatine supplements will also result in inaccurate estimates. These limitations must be appreciated to rationally use predictive equations to estimate urine volume. If the baseline urine creatinine concentration is determined in a sample of known volume, subsequent urine creatinine concentrations will reveal actual urine output as well as the change in urine output. Given the constraints of the various estimating equations, a single baseline timed collection may be more useful strategy for monitoring urine volume than entering anthropomorphic data into a calculator.

Establishment of a population pharmacokinetics model of vancomycin in 94 infants with septicemia and its application in individualized therapy

Background

We aim to develop a population pharmacokinetics (PopPK) model of vancomycin for the treatment of septicemia in infants younger than one year. Factors influence of the PK was investigated to optimize vancomycin dosing regimen.

Methods

The nonlinear mixed effects modelling software (NONMEM) was used to develop the PopPK model of vancomycin. The stability and predictive ability of the final model were assessed by using normalized prediction distribution errors (NPDE) and bootstrap methods. The final model was subjected to Monte Carlo simulation in order to determine the optimal dose.

Results

A total of 205 trough and peak concentrations in 94 infants (0–1 year of age) with septicemia were analyzed. The interindividual variability of the PK parameter was described by the exponential model. Residual error was better described by the proportional model than the mixed proportional and addition models. Serum creatinine concentration and body weight are the major factors that affect the PK parameters of vancomycin. The clearance was shown to be higher when ceftriaxone was co-treated. More than two model evaluation methods showed better stability than the base model, with superior predictive performance, which can develop individualized dosing regimens for clinical reference. Through prediction of final model, the trough concentration was more likely < 5 mg/L when a routine dose of 10 mg/kg is administered every 6 h to 3–9-month-old infants. Therefore, the dose should be increased in the treatment of infant septicemia.

Conclusions

The stable and effective PopPK model of vancomycin in Chinese infants with septicemia was established. This model has satisfactory predictive ability for clinically individualized dosing regimens in this vulnerable population.

Renal changes and estimation of glomerular filtration rate using different equations in morbidly obese Egyptian patients

BACKGROUND AND AIMS

Obesity is a worldwide pandemic with multiple consequences including kidney affection. This study aimed to assess the effects of obesity on renal functions and to detect the most reliable formula of estimated glomerular filtration rate (eGFR) in morbidly obese patients.

METHODS

A cross-sectional, observational study was conducted on 82 morbidly obese patients. Anthropometric measurements were done for all patients and body adiposity (BAI) and visceral adiposity (VAI) indices were calculated after assessment of abdominal fat tissue analysis by computerized tomography (CT). Serum creatinine was incorporated into six different formulae of eGFR, then eGFR was compared with the 24-h measured creatinine clearance (CL_cr) values.

RESULTS

The mean body mass index was 55.8 ± 9.5 kg/m². Proteinuria and glomerular hyperfiltration (CL_cr > 130 ml/min/1.73 m²) were detected in 68.3% and 91.5% of the patients, respectively. Cockcroft-Gault formula using total (CCG-TBW-eGFR) and adjusted body water (CCG-AjBW-eGFR) had the nearest values to measured CL_Cr. These two formulae had a moderate reliability and the lowest percentage of error (30% and 23%, respectively). Visceral and total abdominal fat tissue surface area and volume assessed by CT were directly correlated to the 24-h urinary protein excretion (r = 0.32, 0.24, 0.37 and 0.34, respectively; p = 0.02, 0.03, 0.004 and 0.002, respectively).

CONCLUSIONS

Glomerular hyperfiltration and proteinuria are highly prevalent in morbidly obese patients. There is no ideal formula for GFR estimation in morbidly obese patients, however, TBW and AjBW incorporated into the Cockcroft-Gault can be helpful in those patients.

Chronic kidney disease stage is a modulator on the association between high-sensitivity C-reactive protein and coronary vasospastic angina

The prevalence of coronary vasospasm and also the factors associated with coronary vasospasm in CKD is still unclear. In this cross-sectional study of 859 consecutive CKD patients with angina pectoris received coronary catheterization, we evaluated the factors associated with coronary vasospasm. Patients with vasospasm were older and had higher peripheral blood white cell counts, higher peripheral blood monocyte cell counts, higher haemoglobin levels, higher hs-CRP levels, and lower levels of serum creatinine than patients without vasospasm. The results of multivariate logistic regression analysis revealed that peripheral blood monocyte count and hs-CRP level were independently associated with coronary vasospasm in patients with stage 1 CKD. Only peripheral blood monocyte count but not hs-CRP was independently associated with coronary vasospasm in patients with stages 2 and 3 of CKD. In conclusion, peripheral blood monocyte count is independently associated with coronary vasospasm in patients with stage 1–3 CKD, whereas hs-CRP is only independently associated with coronary vasospasm in patients with stage 1 CKD.

Evaluation of dose requirements for prolonged bivalirudin administration in patients with renal insufficiency and suspected heparin-induced thrombocytopenia

Bivalirudin, a direct thrombin inhibitor, is indicated for patients with suspected heparin-induced thrombocytopenia (HIT) with anticipated percutaneous coronary intervention (PCI). Data is limited on dose selection among patients with renal insufficiency, particularly with prolonged infusion durations. The study cohort comprised 73 patients with renal dysfunction who received bivalirudin for suspected HIT with or without acute coronary syndrome. We reviewed individual pharmacy and medical records for laboratory and bivalirudin dosing information, medical comorbidities, and adverse clinical outcomes during administration. When estimated glomerular filtration rate (eGFR) was calculated by the Cockcroft-Gault (CG; ml/min) formula, the average bivalirudin dose (mg/kg/h) achieving a therapeutic activated partial thromboplastin time (aPTT) was 0.07 ± 0.04, 0.15 ± 0.08, and 0.16 ± 0.07 for patients with eGFR between 15-30, 31-60, and >60, respectively. When eGFR was calculated by the modification of diet in renal disease (MDRD; ml/min/1.73 m(2)) formula, the average bivalirudin dose achieving a therapeutic aPTT was 0.07 ± 0.04, 0.12 ± 0.07, and 0.20 ± 0.07 for patients with eGFR between 15-30, 31-60, >60, respectively. The difference between the dose achieving a therapeutic aPTT for patients with eGFR >60 when calculated by MDRD versus CG was completely abolished when obese patients were excluded from the CG cohort. The results of our series of patients with renal dysfunction receiving prolonged duration of bivalirudin in the setting of acute coronary syndrome (ACS) suggests that dose adjustment is safe and should be considered for patients with moderate to severe renal impairment (eGFR < 60 ml/min/1.73 m(2)).

Population pharmacokinetics of vancomycin in Thai patients

Population pharmacokinetics of vancomycin in Thai adult patients was determined by non-linear mixed-effects approach using 319 vancomycin serum concentrations from 212 patients. The data were best fitted by a two-compartment model and it was used to examine the effect of patient characteristics on the vancomycin pharmacokinetics. In the final model, there was a linear relationship between vancomycin clearance, CL (L/h), and creatinine clearance calculated by Cockcroft-Gault equation, CL_Cr (mL/min): CL  =0.044  ×  CL_Cr. Meanwhile, volume of central compartment, V₁ (L), was linearly related with the age (years old): V₁ = 0.542  × Age. Intercompartment clearance (Q) and volume of peripheral compartment (V₂) was 6.95 L/h and 44.2 L, respectively. The interindividual variability for CL, V₁, Q, and V₂ was 35.78, 20.93, 39.50, and 57.27%, respectively. Whereas, the intraindividual variability was 4.51 mg/L. Final model then was applied to predict serum vancomycin concentrations on validation group. Predictive performance revealed a bias of −1.43 mg/L (95% CI: −5.82–2.99) and a precision of 12.2 mg/L (95% CI: −1.60–26.16). In conclusion, population pharmacokinetic of vancomycin in Thai adult patients was developed. The model could be used to create vancomycin dosage regimen in the type of patient similar with the present study.

Application of a systems approach to the bottom-up assessment of pharmacokinetics in obese patients: expected variations in clearance

BACKGROUND AND OBJECTIVES

The maintenance dose of a drug is dependent on drug clearance, and thus any biochemical and physiological changes in obesity that affect parameters such as cardiac output, renal function, expression of drug-metabolizing enzymes and protein binding may result in altered clearance compared with that observed in normal-weight subjects (corrected or uncorrected for body weight). Because of the increasing worldwide incidence of obesity, there is a need for more information regarding the optimal dosing of drug therapy to be made available to prescribers. This is usually provided via clinical studies in obese people; however, such studies are not available for all drugs that might be used in obese subjects. Incorporation of the relevant physiological and biochemical changes into predictive bottom-up pharmacokinetic models in order to optimize dosage regimens may offer a logical way forward for the cases where no clinical data exist. The aims of the current report are to apply such a 'systems approach' to identify the likelihood of observing variations in the clearance of drugs in obesity and morbid obesity for a set of compounds for which clinical data, as well as the necessary in vitro information, are available, and to provide a framework for assessing other drugs in the future.

METHODS

The population-specific changes in demographic, physiological and biochemical parameters that are known to be relevant to obese and morbidly obese subjects were collated and incorporated into two separate population libraries. These libraries, together with mechanistic in vitro-in vivo extrapolations (IVIVE) within the Simcyp Population-based Simulator™, were used to predict the clearance of oral alprazolam, oral caffeine, oral chlorzoxazone, oral ciclosporin, intravenous and oral midazolam, intravenous phenytoin, oral theophylline and oral triazolam. The design of the simulated studies was matched as closely as possible with that of the clinical studies. Outcome was measured by the predicted ratio of the clearance of the drug in obese and lean subjects ± its 90% confidence interval, compared with observed values. The overall statistical measures of the performance of the model to detect differences in compound clearance between obese and lean populations were investigated by measuring sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). A power calculation was carried out to investigate the impact of the sample size on the overall outcome of clinical studies.

RESULTS

The model was successful in predicting clearance in obese subjects, with the degree to which simulations could mimic the outcome of in vivo studies being greater than 60% for six of the eight drugs. A clear difference in the clearance of chlorzoxazone was correctly picked up via simulation. The overall statistical measures of the performance of the Simcyp Simulator were 100% sensitivity, 66% specificity, 60% PPV and 100% NPV. Studies designed on the basis of the ratio of the absolute values required substantial numbers of participants in order to detect a significant difference, except for phenytoin and chlorzoxazone, where the ratios of the weight-normalized clearances generally showed statistically significant differences with a smaller number of subjects.

CONCLUSION

Extension of a mechanistic predictive pharmacokinetic model to accommodate physiological and biochemical changes associated with obesity and morbid obesity allowed prediction of changes in drug clearance on the basis of in vitro data, with reasonable accuracy across a range of compounds that are metabolized by different enzymes. Prediction of the effects of obesity on drug clearance, normalized by various body size scalars, is of potential value in the design of clinical studies during drug development and in the introduction of dosage adjustments that are likely to be needed in clinical practice.

Estimating creatinine clearance: a meta-analysis

STUDY OBJECTIVES

To determine which body weight descriptor most accurately predicts measured creatinine clearance (Cl(cr)) and whether rounding serum creatinine concentration (S(cr)) to 1 mg/dl when it is less than 1 mg/dl accurately predicts measured Cl(cr).

DESIGN

Meta-analysis of 13 English-language trials comparing 24-hour measured Cl(cr) with Cockcroft-Gault estimated Cl(cr) by using various body weights or rounded S(cr) values.

PATIENTS

A total of 1197 patients (mean age 53.3 yrs, 48.7% male) were included in the meta-analysis.

MEASUREMENTS AND MAIN RESULTS

A thorough literature search of the PubMed, MEDLINE, and the Cochrane Library databases was performed (1976-June 2010) to identify relevant clinical trials. Patient population, number of subjects, age, and 24-hour measured and estimated Cl(cr) were extracted independently by two investigators by using standardized data collection forms. Mean difference (MD) between estimated and measured Cl(cr) was assessed. Thirteen studies met all selection criteria. A random-effects model was applied secondary to a high level of heterogeneity among the studies (I(2)>50%). Total body weight in the Cockcroft-Gault equation overestimated measured Cl(cr) (MD 15.91 ml/min, 95% confidence interval [CI] 7.17-24.65 ml/min). Ideal body weight underestimated Cl(cr) (MD-5.15 ml/min, 95% CI -9.92 to -0.38 ml/min). No body weight (i.e., assumes body weight is 72 kg, thus removing the factor of 72 from the denominator of the equation) closely estimated Cl(cr) (MD 0.43 ml/min, 95% CI -5.42-6.27 ml/min). Adjusted body weight with correction factors of 0.3 or 0.4 also closely estimated Cl(cr) (MD 4.55 ml/min, 95% CI -11.41-20.50 ml/min, and MD 19.94 ml/min, 95% CI -9.6-49.49 ml/min, respectively). Total body weight with a rounded S(cr) value closely estimated measured Cl(cr) (MD 3.51 ml/min, 95% CI -17.18-24.20 ml/min). Ideal body weight with a rounded S(cr) value underestimated Cl(cr) (MD -29.45 ml/min, 95% CI -48.46 to -10.43).

CONCLUSION

Using the Cockcroft-Gault equation with no body weight and actual S(cr) value most closely estimated measured Cl(cr). In obese patients, it may be reasonable to use actual body weight with a correction factor of 0.3 or 0.4 and actual S(cr) value in the Cockcroft-Gault equation. Based on this analysis, the use of total body weight, ideal body weight, and a rounded S(cr) value cannot be recommended.

Interpreting different measures of glomerular filtration rate in obesity and weight loss: pitfalls for the clinician

To combat the increasing incidence of obesity, much research has been devoted to devising successful strategies for weight loss, including manipulation of diet and gastric surgery. Obesity itself can be associated with renal dysfunction, and the degree of reversibility of this with weight loss has being studied. However, there are significant limitations and flaws in the methods we have available to measure glomerular filtration rate (GFR) in overweight and obese subjects. Obesity is associated with changes in body composition including lean and fat mass. This has implications for assumptions that underpin creatinine-based measures such as creatinine clearance, estimated GFR and other equations devised for obesity including the Salazar-Corcoran equation. These changes in body composition also affect measures of glomerular filtration such as cystatin C and nuclear medicine isotope scans. This article will review the accuracy of these current measures of renal function in the obese and consider the evidence for adjusting for body surface area or adjusting for lean body mass. Finally, the effect of weight loss itself on serial measurements of renal function in a given individual, independent of a true change in renal function, will be reviewed. Ultimately using the Cockcroft-Gault equation with an adjustment for lean body mass seems to be the best measure for renal function in obesity. No method for measuring renal function in situations of weight loss has been shown to be unequivocally superior.

Use of estimated glomerular filtration rate for drug dosing in the chronic kidney disease patient

PURPOSE OF REVIEW

Assessment of kidney function is necessary to stage chronic kidney disease (CKD) and appropriately dose medications. The Cockcroft-Gault equation provides an estimate of creatinine clearance (eClCr) and is the method commonly referenced in pharmacokinetic studies. The Modification of Diet in Renal Disease (MDRD) and CKD-Epidemiology Collaboration (EPI) equations provide an estimate of glomerular filtration rate (eGFR), with the MDRD eGFR now automatically reported by most clinical laboratories. This review describes the differences in the Cockcroft-Gault, MDRD, and CKD-EPI equations and considerations when applying estimates from these equations for drug dosing.

RECENT FINDINGS

Studies evaluating drug-dosing regimens using eClCr and eGFR differ in their results depending on the population in which the equation is applied, the adjustment factors used to account for body size, and the number of dosing levels for a particular medication. The largest study to evaluate drug regimen design by method concluded that either the eGFR or Cockcroft-Gault estimates could be used for drug dosing. Differences in methodology among studies are a key factor in evaluating these results and will be highlighted in this review.

SUMMARY

The Cockcroft-Gault, MDRD, and CKD-EPI equations provide reasonable estimates of kidney function; however, clinicians must understand the limitations when using these estimates for drug regimen design.

Drug dosing consideration in patients with acute and chronic kidney disease-a clinical update from Kidney Disease: Improving Global Outcomes (KDIGO)

Drug dosage adjustment for patients with acute or chronic kidney disease is an accepted standard of practice. The challenge is how to accurately estimate a patient's kidney function in both acute and chronic kidney disease and determine the influence of renal replacement therapies on drug disposition. Kidney Disease: Improving Global Outcomes (KDIGO) held a conference to investigate these issues and propose recommendations for practitioners, researchers, and those involved in the drug development and regulatory arenas. The conference attendees discussed the major challenges facing drug dosage adjustment for patients with kidney disease. In particular, although glomerular filtration rate is the metric used to guide dose adjustment, kidney disease does affect nonrenal clearances, and this is not adequately considered in most pharmacokinetic studies. There are also inadequate studies in patients receiving all forms of renal replacement therapy and in the pediatric population. The conference generated 37 recommendations for clinical practice, 32 recommendations for future research directions, and 24 recommendations for regulatory agencies (US Food and Drug Administration and European Medicines Agency) to enhance the quality of pharmacokinetic and pharmacodynamic information available to clinicians. The KDIGO Conference highlighted the gaps and focused on crafting paths to the future that will stimulate research and improve the global outcomes of patients with acute and chronic kidney disease.

Non-Hodgkin's lymphoma in the elderly

The expansion of older population segments and the continuous increase in the incidence of non-Hodgkin's lymphoma (NHL) makes this group of neoplasms an important and growing problem. Older NHL patients have increased risk of therapy-related toxicity as a result of age-related physiological changes and frequent co-morbidities. A functional assessment of the elderly patient is necessary to determine the likelihood of tolerating and responding to therapy. The comprehensive geriatric assessment (CGA) is one multidisciplinary tool that has been applied successfully to older cancer patients and aids in identification of subjects who will or will not benefit from anti-neoplastic treatment. Although indolent lymphomas present more frequently at advanced stage, randomized trials do not show better outcomes with early therapy, supporting close observation until specific therapeutic indications arise. Use of the monoclonal antibody rituximab as a single agent or in combination with chemotherapy improves survival and has become the standard of care in first-line treatment. Radioimmunoconjugates, bendamustine, and other monoclonal antibodies as well as novel targeted agents also are active against indolent lymphomas. Diffuse large B-cell lymphoma is an aggressive but potentially curable disease. Several trials performed exclusively in elderly patients have demonstrated improved response rates and survival with the addition of rituximab to CHOP (cyclophosphamide, doxorubicin [adriamycin], vincristine, prednisone) chemotherapy in the front-line setting. Salvage chemotherapy followed by autologous haematopoietic cell transplant (autoHCT) has been shown to have better failure-free and overall survival in randomized trials involving younger patients. Highly selected individuals up to age 70 years may attain long-term survival benefit from autoHCT, although transplant-related mortality is higher than in younger patients.

Drug Use and Dosing in Chronic Kidney Disease

One of the most important drug-related problems in patients with chronic kidney disease (CKD) is medication dosing errors. Many medications and their metabolites are eliminated through the kidney. Thus, adequate renal function is important to avoid toxicity. Patients with renal impairment often have alterations in their pharmacokinetic and pharmacodynamic pa-rameters. The clearance of drugs eliminated primarily by renal filtration is decreased by renal disease. Therefore, special consideration should be taken when these drugs are prescribed to patients with impaired renal function. Despite the importance of dosage adjustment in patients with CKD, such adjustments are sometimes ignored. Physicians and pharmacists can work together to accomplish safe drug prescribing. This task can be complex and require a stepwise approach to ensure effectiveness, minimise further damage and prevent drug nephrotoxicity. Key words: Dosage adjustment, Renal impairment, Stepwise approach

Impact of a Renal Drug Dosing Service on Dose Adjustment in Hospitalized Patients with Chronic Kidney Disease

Background:

Appropriate drug selection and dosing for patients with chronic kidney disease (CKD) is important to avoid unwanted drug effects and ensure optimal patient outcomes.

Objective:

To assess the rate of inappropriate dosing in patients with CKD in a nephrology unit and to evaluate the impact on dose adjustment, adverse drug events (ADEs), and drug cost of having a pharmacist accompany a team of physicians on their rounds.

Methods:

This was a comparative study with a preintervention and postintervention design. The preintervention phase served as the control; it was prospective and observational only and was conducted from the beginning of February to the end of May 2007. The second phase (intervention phase) was conducted from the beginning of March to the end of June 2008. Two random samples of 300 patients with an estimated creatinine clearance less than or equal to 50 mL/min were included. During the intervention phase, a clinical pharmacist made rounds with the nephrology unit team and gave dosing adjustment recommendations when needed. A collection of reliable and up-to-date drug information references that are commonly used globally were used during the intervention.

Results:

In the preintervention group, drug dosage adjustment or avoidance, based on renal function, was necessary in 607 of 2814 (21.6%) prescriptions. Of these, 322 (53.0%) did not comply with guidelines. In the intervention group, adjustment was necessary for 640 of 2981 (21.5%) prescriptions. The pharmacist made 388 recommendations related to dosing adjustment, 212 (54.6%) of which were accepted by physicians. Clinicians' noncompliance with dosing guidelines decreased to 176 (27.5%) (p < 0.001). In the preintervention group, 64 (21.3%) patients had a suspected ADE, with a total of 73 events. In the intervention group, this number was significantly lower with 49 events in 48 (16.0%) patients (p < 0.05). The intervention resulted in drug cost savings of $2250 US.

Conclusions:

A renal drug dosing service for patients hospitalized with CKD can increase the proportion of drug dosing that is adjusted to take into account renal function. This can save drug costs and may prevent ADEs.

Evaluation of creatinine-based formulas in dosing adjustment of cancer drugs other than carboplatin

Background. Glomerular filtration rate (GFR) is often used to determine initial dosing of renally excreted cancer drugs. GFR can be calculated using the Cockcroft-Gault (CG) or the modified diet in renal diseases (MDRD) study formulas, both of which are based on serum creatinine levels. The MDRD formula is more accurate in noncancer patients, does not require patient weight, and is reported automatically by all laboratories in British Columbia, Canada. We previously showed that the CG and MDRD formulas have similar accuracy for carboplatin dosing in patients with gynecological malignancies. We now examine dosing of all renally excreted cancer drugs in the general cancer population. Since this setting does not include routine measurement of GFR, we report the concordance of estimates of GFR derived from the CG and MDRD formulas.

Methods. Patient data were collected retrospectively at the BC Cancer Agency. The primary outcome was the proportion of patients who would have received a different initial dose due to difference in the GFR. Each patient’s dose was determined from dose adjustment tables stated in specific treatment protocols. The secondary outcome was concordance of the GFR derived from CG and MDRD, using the method of Bland and Altman. A difference of >30% was assumed to be clinically significant because this difference would usually lead to dose adjustment based on reclassification of renal function.

Results. A total of 313 patients were evaluated, with 40% male. The median age was 56 years, weight 67.5 kg, height 166 cm, and serum creatinine 74 µmol/L (0.84 mg/dL). The median GFR derived from the CG and MDRD formulas were 86.8 mL/min (mean 91 mL/min, SD ± 30 mL/min) and 87.6 mL/min (mean 88 mL/min, SD ± 26 mL/min), respectively. A total of 8.6% (27/313) of patients would have received a different dose due to difference in the GFR; of these, 67% (18/27) would have received a higher dose. A difference of >30% in GFR was found in 17.9% (56/313) of patients.

Conclusions. There is good concordance of the GFR derived from the CG and MDRD formulas for most cancer patients, with less than 10% of patients expected to receive a different initial dose of chemotherapy. The MDRD formula may be a reasonable alternative to the CG formula for dosing of cancer drugs which are renally excreted or nephrotoxic. J Oncol Pharm Practice (2010) 16: 113—119.

Drug Dosage Adjustment Using Renal Estimation Equations: A Review of the Literature

Purpose

To examine the factors affecting drug clearance and the available evidence for drug dosing based on the Cockcroft-Gault (CG) equation and the abbreviated Modification of Diet in Renal Disease (abbrMDRD) equation. Factors that would distort the accuracy of these formulas and the affect of this distortion on the use of either formula in drug dosage adjustment were reviewed.

Methods

An updated review of the literature was performed that pertained to the accuracy of the CG and abbrMDRD equations and their use in drug dosage adjustment. MEDLINE was searched using the OVIDSP database, from the inception of the database (1950) through June 2008.

Discussion

To cover the major issues concerning the use of renal estimation equations in drug dosing adjustment, various areas were examined. Topics included the accuracy of the CG and abbrMDRD formulas, variability in these equations because of patient and laboratory factors, the isotope dilution-mass spectrometry standardization initiative, and the applicability of each formula to modifying medication doses.

Conclusion

Although the abbrMDRD equation has many advantages as compared with the CG equation, too little research has been completed at this time to recommend the clinical use of the abbrMDRD equation in pharmacy practice.

Estimation of creatinine clearance in morbidly obese patients

PURPOSE

Estimates of creatinine clearance (CL(cr)) based on equations and various body-size descriptors were compared with 24-hour measured CL(cr) values in morbidly obese patients.

METHODS

Patients age 18-75 years with a body mass index (BMI) of >/=40 kg/m(2) with stable serum creatinine values were enrolled. Covariates known to contribute to alteration in CL(cr) were used to exclude patients. Twenty-four-hour urine collection was performed to measure CL(cr). Bioelectric impedance analysis was used to estimate fat-free weight (FFW). Glomerular filtration rate was estimated using the four-variable Modification of Diet in Renal Disease (MDRD4) equation. CL(cr) was estimated using the Cockcroft-Gault and Salazar-Corcoran methods using total body weight (TBW). Body-size descriptors, such as ideal body weight (IBW), adjusted body weight (ABW), and lean body weight (LBW), and FFW were substituted in the Cockcroft-Gault equation to generate additional estimates of CL(cr).

RESULTS

Fifty-four patients (mean +/- S.D. age, 48.4 +/- 12.9 years; TBW, 142.3 +/- 41.7 kg; BMI, 50.5 +/- 12.6 kg/m(2)) completed the study. All three equations were biased in their estimation of CL(cr). Use of MDRD4 and IBW in the Cockcroft-Gault equation underestimated CL(cr), while the Salazar-Corcoran equation and use of TBW or ABW in the Cockcroft-Gault equation overestimated this value. Substitution of fat-free weight or LBW in the Cockcroft-Gault equation provided unbiased estimates of CL(cr).

CONCLUSION

An LBW estimate, based on TBW and BMI, incorporated into the Cockcroft-Gault equation provided an unbiased, relatively precise, accurate, and clinically practical estimate of 24-hour measured CL(cr) in morbidly obese patients.

Pitfalls of the Application of the Modification of Diet in Renal Disease Equation to Drug-Dosing Practices: A Tertiary Care Teaching Hospital Experience

Medications that are predominantly renally eliminated can result in accumulation and/or toxic adverse effects if prescribed in normal doses to a patient with renal dysfunction. Methods including mathematical formulas such as the Cockcroft-Gault equation have been used to estimate renal function. The Modification of Diet in Renal Disease (MDRD) equation has proven useful in staging the degree of renal dysfunction that a patient may have. However, the application of the MDRD equation for the purpose of determining drug dosage adjustments in patients with renal dysfunction has not yet been validated. Several examples are reported that depict how the use of the MDRD equation for the basis of drug dosing could lead to negative patient outcomes. The process undertaken at our institution to implement a policy prohibiting the use of the MDRD equation for the purpose of drug-dosing adjustments is described.

Individualizing Therapy in Patients With Chronic Kidney Disease

Patients with chronic kidney diseases have multiple clinical abnormalities that may affect disposition of drugs, including alterations in glomerular filtration rate, excretion of plasma proteins, reductions in serum albumin, and reductions in drug metabolizing enzyme activity. Inflammation may also influence the previous factors. Concomitant drug therapies can lead to drug— drug interactions that may affect the pharmacokinetics of administered drugs. Pharmacogenomics has begun to be evaluated for effects of genotype and haplotype of drug metabolizing enzymes and transporters on drug disposition. Because of the multiple potential etiologies for alterations in drug disposition in patients with chronic kidney diseases, they require appropriate evaluation for implementation of individualized strategies in therapies to enhance efficacy and reduce toxicities. This review will highlight the disease- and patient-specific variables that are targets for patient-centered approaches to therapeutic interventions. The field of pharmacogenomics will be reviewed with reference to common therapies for transplantation and glomerular diseases.

Risk for cardiovascular outcomes among subjects with atherosclerotic cardiovascular disease and greater-than-normal estimated glomerular filtration rate

BACKGROUND AND OBJECTIVES

Estimating equations for calculating glomerular filtration rate (eGFR) occasionally identify patients with elevated eGFR, yet the prognostic significance remains to be determined. This study sought to define the association of an elevated eGFR on the risk for death and cardiovascular outcomes among subjects with atherosclerotic cardiovascular disease.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Data from 8941 subjects who had a history of atherosclerotic vascular disease and were enrolled in the Blockade of the Glycoprotein IIb/IIIa Receptor to Avoid Vascular Occlusion trial were analyzed. Time to the composite end point of death, congestive heart failure, myocardial infarction, or stroke was modeled using Cox proportion hazards regression. Glomerular filtration rate was estimated using the Modification of Diet in Renal Disease and Cockcroft-Gault formulas.

RESULTS

Compared with subjects with eGFR of 100 to 125 ml/min per 1.73 m2, subjects with eGFR > or = 125 (n = 462) were younger, female, and nonwhite. In addition, subjects with an elevated eGFR were more likely to have diabetes and congestive heart failure. In adjusted analyses, every 10-ml/min per 1.73 m2 decrease in eGFR < 100 was associated with a 13% increased hazard for the composite end point. In addition, every 10-ml/min per 1.73 m2 increase in eGFR > or = 100 was associated with a 9% increased hazard for the composite end point.

CONCLUSIONS

In individuals with a history of vascular disease, the relationship between eGFR and cardiovascular outcomes may be parabolic, with increased risk among patients with both reduced and elevated eGFR.

Hospital Pharmacy Pulse - Recent Publications on Medications and Pharmacy

Hospital Pharmacy presents this feature to keep pharmacists abreast of new publications in the medical/pharmacy literature. Articles of interest will be abstracted monthly regarding a broad scope of topics. Suggestions or comments may be addressed to: Jacyntha Sterling, Drug Information Specialist at Saint Francis Hospital, 6161 S Yale Ave., Tulsa, OK 74136 or e-mail: jasterling@saintfrancis.com .