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Based on what is known today, is the basis for CDC's "preference" toward 2% CHG-based antiseptics appropriate for catheter site care?

The short answer is “no”. 

CDC’s 2002 Guidelines for the Prevention of Intravascular Catheter-Related Infections state …

VI. Catheter site care
         A. Cutaneous antisepsis

1. Disinfect clean skin with an appropriate antiseptic before catheter insertion and during dressing changes.  Although a 2% chlorhexidine-based preparation is preferred, tincture of iodine, an iodophor, or 70% alcohol can be used (references). Category IA

The preference of 2% chlorhexidine-based preparations in this guidance was largely based on a 1991 study published by Maki et al.¹ which states “We conclude that use of 2% chlorhexidine, rather than 10% povidone-iodine or 70% alcohol, for cutaneous disinfection before insertion of an intravascular device and for post-insertion site care can substantially reduce the incidence of device-related infection.” However, it’s important to understand several key points about this study which render its preference toward CHG-based products erroneous.

First, the study evaluated an experimental (i.e., not commercially available) aqueous 2% CHG formulation; not ChloraPrep^® which contains 2% CHG and 70% IPA. Because its inherent capacity to cause irritation with repeated use, ChloraPrep is not approved by the FDA for repeated uses such as catheter site maintenance; it is only approved for preparation of the skin prior to catheter insertion (i.e., preparation of the skin prior to surgery). See US Food and Drug Administration Center for Drug Evaluation and Research.  Medical review of NDA 20-832 available at http://www.fda.gov/cder/foi/nda/2000/20-832_CHLORAPREP%20ONE-STEP%20ANTISEPTIC_medr.pdf.

Second, the study compared the performance of a CHG-based formulation individually against a 10% povidone-iodine (PVP-I) formulation and 70% isopropyl alcohol (IPA).  It did not include the evaluation of the common practice of using 70% IPA followed by 10% PVP-I as follows: Using an outward circular motion, prep with the first alcohol swabstick for thirty (30) seconds.  Allow to dry.  Repeat with the second and third alcohol swabsticks, allowing to air dry after each.  Repeat with each of the three PVP-I swabsticks, allowing to air dry after each.  The use of IPA followed by PVP-I may well have performed equally to the CHG-based formulation.

Last, according the Materials and Methods section of the study, prior to catheter insertion, each product “was applied with vigorous scrubbing for about 30 seconds; after excess solution had been wiped from the site with sterile gauze, the site was allowed to dry and the catheter was inserted.”  Unfortunately, the amount of solution applied was not provided; nor were the application instructions for subsequent catheter site care.  Since studies do not compare active ingredients or even formulations, but rather products which contain specific volumes of both active and inactive ingredients in specific concentrations applied with specific applicators using specific directions for use², without this information, it’s impossible to conclude that any given application regimen is more effective than another. 

¹Maki DG, Ringer M, Alvarado CJ. Prospective randomized trial of povidone-iodine, alcohol, and chlorhexidine for prevention of infection associated with central venous and arterial catheters. Lancet 1991; 338: 339-343.

²Art, GR. Comparison of the safety and efficacy of two topical antiseptic products: chlorhexidine gluconate + isopropyl alcohol (CHG+IPA) and povidone-Iodine + isopropyl alcohol (PVP-I +IPA). JAVA 2007;12(3):156-163.

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