Heparin dosing in the morbidly obese patient

Pediatric Obesity: Pharmacokinetic Alterations and Effects on Antimicrobial Dosing

Limited data exist for appropriate drug dosing in obese children. This comprehensive review summarizes pharmacokinetic (PK) alterations that occur with age and obesity, and these effects on antimicrobial dosing. A thorough comparison of different measures of body weight and specific antimicrobial agents including cefazolin, cefepime, ceftazidime, daptomycin, doripenem, gentamicin, linezolid, meropenem, piperacillin-tazobactam, tobramycin, vancomycin, and voriconazole is presented. PubMed (1966-July 2015) and Cochrane Library searches were performed using these key terms: children, pharmacokinetic, obesity, overweight, body mass index, ideal body weight, lean body weight, body composition, and specific antimicrobial drugs. PK studies in obese children and, if necessary, data from adult studies were summarized. Knowledge of PK alterations stemming from physiologic changes that occur with age from the neonate to adolescent, as well as those that result from increased body fat, become an essential first step toward optimizing drug dosing in obese children. Excessive amounts of adipose tissue contribute significantly to body size, total body water content, and organ size and function that may modify drug distribution and clearance. PK studies that evaluated antimicrobial dosing primarily used total (or actual) body weight (TBW) for loading doses and TBW or adjusted body weight for maintenance doses, depending on the drugs' properties and dosing units. PK studies in obese children are imperative to elucidate drug distribution, clearance, and, consequently, the dose required for effective therapy in these children. Future studies should evaluate the effects of both age and obesity on drug dosing because the incidence of obesity is increasing in pediatric patients.

Delayed efficient anticoagulation with heparin in patients with a weight of 110 kg and more treated for acute coronary syndrome

OBJECTIVE

The use of a weight-based nomogram is considered as standard care for prescribing appropriate doses of unfractionated heparin (UFH). Because of the need for multiple other medications that may affect bleeding and that clinical data have relied on similar dosing algorithms, maximum initial bolus and infusion rates have been suggested (capped initial dose). Whether these weight-based heparin nomograms properly address therapeutic dosing in obese patients remains questionable.

DESIGN AND METHODS

Thirty patients treated for acute coronary syndrome and weighing ≥110 kg were retrospectively compared with 90 controls (three groups of 30 patients, weighting 50-69.9, 70-89.9, or 90-109.9 kg), all treated with UFH, July 2008 to April 2009. The primary end point was the time required to obtain a threshold activated partial thromboplastin time (aPTT).

RESULTS

Mean time to achieve threshold aPTT was longer for obese patients weighing ≥110 kg than for controls (31.47 vs. 12.89 hours; P < 0.0001). At 24 hours, 63% of obese patients weighing ≥110 kg had not reached threshold aPTT vs. 7% of controls (P < 0.0001). However, threshold infusion rate did not differ between weight categories (13.0 vs. 13.1 U/kg/h; P = NS) and approximated the initial infusion rate recommended by nomograms without applying the dose cap (12 U/kg/h).

CONCLUSIONS

Adequate anticoagulation time doubled in patients weighing ≥110 kg, suggesting that these patients were not receiving appropriate heparin doses initially to achieve threshold aPTT rapidly. Using initial infusion rate recommended by a nomogram without capping for total body weight is suggested as acceptable in this study. This approach should be further evaluated in a prospective study.

Identifying Optimal Initial Infusion Rates for Unfractionated Heparin in Morbidly Obese Patients

Background:

Most literature available for unfractionated heparin (UFH) supports the use of actual body weight for dosing all patients, yet a small proportion of the patients in these studies were morbidly obese. The most appropriate dosing strategy for therapeutic UFH in this patient population is not clearly defined.

Objective:

To better define appropriate UFH dosing strategies in morbidly obese patients and to evaluate the safety of a weight-based heparin nomogram in this patient population.

Methods:

Patients with class III (morbid) obesity receiving therapeutic doses of a UFH infusion for greater than 24 hours were evaluated. Two comparator groups of overweight/class I–II obesity and normal/underweight patients were created by matching patients to the class III obesity group. Doses and times to therapeutic activated partial thromboplastin time (aPTT), bleeding rates, and mortality were assessed.

Results:

The mean infusion rate required to obtain a first therapeutic aPTT was 11.5 units/kg/h in the class III obesity group (n = 94) versus 12.5 units/kgm and 13.5 units/kg/h for the overweight/class I–II obesity (n = 92) and normal/underweight (n = 87) groups, respectively (p = 0.001). The mean times to a first therapeutic aPTT were 21.3, 22.1, and 29.9 hours, respectively (p = 0.421). There was a statistically significant difference in the infusion rate required to obtain 2 consecutive therapeutic aPTTs between groups (p = 0.016), with higher weight groups requiring smaller (per kilogram actual body weight) infusion rates, but there was no significant difference in the time to reach 2 consecutive therapeutic aPTTs (p = 0.776). There was no significant difference in bleeding (p = 0.517) or mortality (p = 0.475) among groups.

Conclusions:

Morbidly obese patients require smaller UFH infusion rates per kilogram actual body weight compared to patients with lower body mass indices. UFH dosing recommendations should be modified to reflect body mass index classification.

Effect of body mass index on bleeding frequency and activated partial thromboplastin time in weight-based dosing of unfractionated heparin: a retrospective cohort study

OBJECTIVE

To assess bleeding and activated partial thromboplastin time (APTT) in relation to body mass index (BMI) in patients prescribed weight-based dosing of intravenous unfractionated heparin (UFH) for cardiac indications without a maximum (dose-capped) initial bolus or capped initial infusion rate.

PATIENTS AND METHODS

Consecutive patients admitted to an academic medical center from February 1, 2002, through November 31, 2003, who were treated with a UFH nomogram consisting of a 60-U/kg intravenous bolus plus an initial continuous intravenous infusion of 12 U/kg hourly and titrated to a goal APTT range corresponding to thromboplastin-adjusted target heparin levels of 0.3 to 0.7 U/mL by anti-Xa assay were evaluated for this retrospective cohort study. Patients were excluded if they concomitantly received a fibrinolytic, glycoprotein IIb/IIIa inhibitor, or any other antithrombotic agent (except warfarin). Study patients were divided into quartiles by BMI.

RESULTS

Of the 1054 patients included in the study, 807 (76.6%) had an initial bolus dose higher than 4000 U, and 477 (45.3%) had an initial infusion rate higher than 1000 U/h. Despite a significant difference among BMI quartiles in proportion of supratherapeutic first APTT values (P<.001), no statistically significant difference was found in bleeding frequency (P=.26) or frequency of first APTT within the goal range (P=.27). Logistic regression analyses revealed that BMI was not a significant predictor of bleeding or first APTT within the goal range.

CONCLUSION

We did not find any difference in the proportion of first APTT values in the goal range or an increased risk of bleeding in obese patients treated with UFH without a capped initial dose. Our data demonstrate the safe use of weight-based UFH without a capped initial bolus dose or capped initial infusion rate in patients with medical cardiac conditions.

Safety and Efficacy of a High-Intensity, Weight-Based, Intravenous Heparin Protocol Revision in Patients who are Obese

Purpose

Data collected previously within this institution concluded that the initial heparin infusion rate in the high-intensity, weight-based, intravenous (IV) heparin protocol should be adjusted from 18 to 15 units/kg/h (based on actual body weight) in patients who are more than 50% above ideal body weight (IBW). The purpose of this study was evaluation of the safety and efficacy of the revised protocol.

Methods

A retrospective chart review was conducted from the initiation of the revised protocol on October 28, 2006, through March 15, 2007. All patients receiving high-intensity, weight-based heparin dosing were eligible for inclusion. Outcome measures included percentage of patients achieving therapeutic activated partial thromboplastin time (aPTT), time to first therapeutic aPTT, follow-up aPTT levels, adverse event occurrence, venous thromboembolism recurrence, and influence of concomitant disease states.

Results

A total of 55 regimens met inclusion criteria. There were no statistically significant differences between patients who were obese (greater than 50% above IBW) and those who were not obese (less than 50% above IBW) with respect to percentage achieving a therapeutic aPTT, time to therapeutic aPTT, or follow-up aPTT values. Patients who were more than 50% above IBW had improved therapeutic anticoagulation parameters postrevision, whereas patients who were 30% to 50% above IBW had worsened therapeutic anticoagulation parameters postrevision. Although the 30% to 50% IBW class had the highest incidence of end-stage renal disease, it appears that the group of patients in this class was overanticoagulated as a whole.

Conclusion

The institution's revised, high-intensity, weight-based, IV heparin protocol was found safe and effective, validating a potential heparin dosing adjustment for patients who are obese.