Clinical and pharmacokinetic profiles of digoxin immune Fab in four patients with renal impairment

Extracorporeal Removal Techniques for the Poisoned Patient: A Review for the Intensivist

The kidney is able to rapidly eliminate many water-soluble xenobiotics (exogenous chemicals). However, in the face of extraordinary serum concentrations of these xenobiotics or renal dysfunction, alternative elimination techniques often become necessary. Extracorporeal removal (ECR) techniques are used to increase the clearance of xenobiotics. These techniques include hemodialysis (HD), charcoal hemoperfusion (HP), and modalities grouped under the heading of continuous renal replacement therapy (CRRT): continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodiafiltration (CVVHDF). Extracorporeal removal is limited to patients with significant or potentially significant clinical poisoning because the resources required to perform ECR are great. Therefore, most patients who are treated with these techniques are being cared for in intensive care units (ICUs). Our goal in this review is to discuss the properties that make xenobiotics amenable to removal by ECR and the advantages and disadvantages of the individual techniques. We discuss xenobiotics that constitute clear indications for ECR, including the toxic alcohols, salicylates, and lithium. We review the use of CRRT, a modality for which clear indications for treatment of poisonings are currently lacking.

Antibody pharmacokinetics and pharmacodynamics

The U.S. Food and Drug administration (FDA) has approved several polyclonal antibody preparations and at least 18 monoclonal antibody preparations (antibodies, antibody fragments, antibody fusion proteins, etc.). These drugs, which may be considered as a diverse group of therapeutic proteins, are associated with several interesting pharmacokinetic characteristics. Saturable binding with target antigen may influence antibody disposition, potentially leading to nonlinear distribution and elimination. Independent of antigen interaction, concentration-dependent elimination may be expected for IgG antibodies, due to the influence of the Brambell receptor, FcRn, which protects IgG from catabolism. Antibody administration may induce the development of an endogenous antibody response, which may alter the pharmacokinetics of the therapeutic antibody. Additionally, the pharmacodynamics of antibodies are also complex; these drugs may be used for a wide array of therapeutic applications, and effects may be achieved by a variety of mechanisms. This article provides an overview of many of the complexities associated with antibody pharmacokinetics and pharmacodynamics.

Recurrence phenomena after immunoglobulin therapy for snake envenomations: Part 1. Pharmacokinetics and pharmacodynamics of immunoglobulin antivenoms and related antibodies

The production of immunoglobulin antivenoms has evolved over the past 50 years, resulting in a choice of source animals and highly purified, target-specific immunoglobulin fragments (IgG, Fab2, and Fab). Differences in pharmacokinetic and pharmacodynamic properties of these fragments may affect clinical efficacy. For example, both local and systemic recurrences (worsening after initial improvement) with intact or fragmented immunoglobulin antivenoms have been observed. Local recurrence may result in greater tissue injury, and coagulopathic recurrence may result in the risk of hemorrhage. The latter is of particular concern because coagulopathic recurrence usually occurs after patient discharge. Similar phenomena of symptom recurrence have been observed with ovine, digoxin-specific Fab, and with Fab2 and IgG antivenoms from a variety of source animals as well. Recurrence of venom effects in Fab-treated patients appears to be the result of a pharmacokinetic and pharmacodynamic mismatch between the antivenom and target venom components. That is, tissue penetration and venom neutralization is incomplete, and clearance of unbound antivenom (antivenom that has not bound its venom target) is significantly faster than the clearance of some venom components, allowing signs and symptoms of envenomation to recur. Understanding the relative kinetics and dynamics of immunoglobulins and their targets may allow the physician to anticipate their clinical implications and may suggest modifications of the drug or dose to produce better clinical results.

Analysis of the use of digoxin immune fab for the treatment of non-life-threatening digoxin toxicity

BACKGROUND

Studies indicate that digoxin toxicity often results in lengthy hospitalizations and considerable costs, both of which may be decreased through the routine use of digoxin immune Fab (FAB).

METHODS

A computer-based decision analysis model was developed to compare the treatment of non-life-threatening digoxin toxicity with either FAB or standard therapy from the hospital perspective. A cost-minimization analysis was then performed to compare overall total costs (primary endpoint) for each treatment branch. A secondary endpoint of length of hospital stay (LOS) was also compared between the 2 groups. Clinical variables (serum digoxin concentration [SDC], creatinine clearance [Clcr], and body weight), event probabilities, and other model-specific variables were varied in univariate and multivariate sensitivity analyses.

RESULTS

FAB was associated with an incremental cost of $54 compared with standard therapy ($2,784 vs. $2,730, respectively) but reduced LOS by 1.5 days (1.5 days vs. 3.0 days, respectively). Sensitivity analyses show that FAB is less costly at SDC > 3.5 ng/mL and Clcr < 22 mL/min. FAB reduced LOS at SDC > 2.3 ng/mL. Monte Carlo simulation revealed that FAB was less costly in 37% of the cases and reduced LOS 72% of the time compared with standard therapy.

CONCLUSIONS

The abbreviated LOS associated with the use of FAB in patients with non-life-threatening digoxin toxicity may translate into lower treatment costs in many clinical scenarios, making it a cost-saving alternative to standard therapy in patients with high SDC and renal dysfunction.