Ortho-phthalaldehyde: A Tale of Three Labels

This 3-part article, written by Lawrence F Muscarella, PhD, discusses the evolution of the labeling of a medical device – namely, of the “Instructions for Use” of the disinfectant “Cidex OPA” (which is used to high-level disinfection semi-critical devices, including gastrointestinal endoscopes).

This article’s Part 1 and Part 2 are featured below. Guidance for the save and proper use of this product is also provided, but in this article’s Part 3, which is provided in another of Dr. Muscarella’s article entitled “Recommendations for the Safe and Effective Use of ortho-phthalaldehyde” and which is available by clicking here.

Although this article focuses on Cidex OPA, some of its content, including the provided recommendations, may also be applicable to other similar, products whose active ingredient is also “OPA,” known generically as ortho-phthalaldehyde. (This article was originally written in 2006.)

A copy of Cidex OPA’s current labeling may be downloaded by clicking here; of Metricide OPA Plus’s labeling, by clicking here (oops! It’s not available on-line); and of Rapicide OPA 28’s labeling, by clicking here.


I recently learned that under some circumstances Cidex OPA is contraindicated for processing urological instrumentation. But I am confused, because the label insert my endoscopy unit has on file for Cidex OPA does not include this contraindication. Dr. Muscarella, please explain the details of this contraindication and why my unit’s label insert does not include it.”


Cidex OPA is a liquid chemical sterilant/disinfectant (LCS) that is used to high level disinfect gastrointestinal (GI) endoscopes and other types of reusable semi-critical instruments.

This product, which is often referred to simply as “OPA” because of its active ingredient—0.55% ortho-phthalaldehyde—is a clear, light blue reusable solution that provides healthcare facilities with an alternative to 2% glutaraldehyde.

Although its chemical structure classifies it as an aldehyde, Cidex OPA is different from, and is not to be confused with, “Cidex” or another glutaraldehyde solution (such as Metricide). Cidex OPA has a slightly alkaline pH of 7.5; does not require chemical activation; is rapidly tuberculocidal; can be reused for as many as 14 days; has a shelf-life of up to 75 days; and, like most LCSs, requires that its concentration be monitored for effectiveness. Like Cidex, Cidex OPA is marketed and distributed by Advanced Sterilization Products (ASP).

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Primarily because of its short immersion time, Cidex OPA may be favored by busy endoscopy units. Whereas 2% glutaraldehyde solutions usually require 20 or 45 minutes to achieve high-level disinfection, Cidex OPA is labeled to achieve high-level disinfection in 12 minutes (at a minimum temperature of 20o C, or 68o F, which is room temperature), making it one of the first LCSs marketed in the U.S. to achieve high-level disinfection in less than 20 minutes.

Today, other disinfectants, such as Resert XL and Rapicide OPA-28, may achieve high-level disinfection in less than 10 minutes at room temperature. (Refer to the individual product’s labeling.)

Medical department that might use Cidex OPA to reprocess flexible endoscopes and other types of reusable semi-critical instruments include gastrointestinal endoscopy, bronchoscopy, urology, cardiology, gynecology, and the operating room.

Demonstrating a shift in a long-standing regulatory paradigm, the FDA cleared Cidex OPA in 1999 without a specific “sterilization” claim. All previously cleared LCSs labeled for reprocessing flexible endoscopes include a label claim not only for high-level disinfection (typically during a short immersion time of, for example, 45 minutes), but also for “sterilization” (typically during a long immersion time of, for example, 10 hours).

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Though the label of Cidex OPA does not include a “sterilization” claim, a company brochure confirms that during sporicidal testing Cidex OPA satisfied the current regulatory requirements to claim “sterilization” during an exposure time and temperature of 32 hours and 20o C, respectively.


As a result of this practitioner’s question and understandable confusion about contraindications associated with Cidex OPA, this product’s labeling was reviewed to determine whether Cidex OPA is contraindicated, under some circumstances, for processing urological instrumentation and, if so, why this contraindication is not included in the label that this inquiring practitioner’s endoscopy unit has on file.

Further, this article’s review is divided into three parts. The first provides this review’s results. The second discusses the significance and implications of these results. And the third part provides a number of recommendations for the safe and proper use of Cidex OPA (and other, similar high-level disinfectants whose active ingredient is ortho-phthalaldehyde, including Metricide OPA Plus and Rapicide OPA 28).


This review revealed that the labeling of Cidex OPA has been changed twice since 1999, resulting in the publication of (at least) three different versions of labeling, each version containing additional information regarding the safe use of Cidex OPA.

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Salient information and instructions that are provided in the first and original label of Cidex OPA are highlighted in Table 1 (embedded below). The two subsequent versions of Cidex OPA’s labeling, which are different from one another, are discussed in Tables 2 and 3 (also embedded, further below) and contain significant changes and additions to Cidex OPA’s original labeling. (Due to space constraints, not all of the contents of each respective version of Cidex OPA’s label are listed in Tables 1-3.)

A side-by-side comparison of these three tables displays both the differences between each of these three versions of Cidex OPA’s label and the significant additions to each subsequent version. — Lawrence F Muscarella PhD


Table 1.

Table 1. Original Cidex OPA label (1999). Important information about the safe use of Cidex OPA that is included in its first and original label. Some of these instructions, such as the requirement to use Cidex OPA in a well-ventilated area to minimize exposure to its vapors, apply to virtually all types of liquid chemical disinfectant/sterilants (LCSs) used to reprocess endoscopes.

(Article continued on next page …)

This entry was posted in Automated Endoscope Reprocessor, Best Practices, Bronchoscopes, Colonoscopes, Cystoscopes, Disease Transmission, Endoscopic Retrograde Cholangiopancreatography (ERCP), Esophagogastroduodenoscopy (EGD), Food and Drug Administration, Gastrointestinal Endoscopy, GI Endoscopes, Glutaraldehyde, High-Level Disinfection, Infection Control, ortho-phthalaldehyde, Peracetic Acid, Product Labeling, Semicritical, TEE (Transesophageal Echocardiography) Probes. Bookmark the permalink.

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