USP <61> and <62> Microbial Limits: What Nonsterile Compounding Teams Should Know

Nonsterile does not mean “microbiology optional”

USP <795> nonsterile compounding still depends on microbiological control of ingredients, process hygiene, and—when your quality system requires it—finished preparation testing. The workhorse chapters for enumeration and objectionable organisms are USP <61> Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests and USP <62> Tests for Specified Microorganisms.

Pharmacies outsource these methods when in-house incubators, media control, or analyst capacity cannot support a defensible program. This guide explains what the chapters are for, how to brief a contract testing lab (CTL), and how to use results inside a real quality system.

What USP <61> covers

USP <61> is about how many microorganisms are present, typically expressed as:

• TAMC — Total Aerobic Microbial Count
• TYMC — Total Combined Yeasts and Molds Count

It is an enumeration framework with method suitability considerations so the product matrix does not hide growth or kill challenge organisms inappropriately. It is not a sterility test and it is not a full identification panel.

What USP <62> covers

USP <62> focuses on whether specified objectionable organisms are absent (or within defined expectations) for the product category—classic examples include organisms such as Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Salmonella species depending on the monograph / product type context.

Together, <61> and <62> answer different questions:

Chapter	Core question
<61>	How heavy is the bioburden?
<62>	Are particular undesirable organisms present?

A low TAMC does not automatically mean <62> is unnecessary when your SOP or monograph structure requires specified-organism testing.

When compounding teams typically order these tests

Common triggers:

1. New formula onboarding — establish a microbiological baseline
2. Ingredient qualification — especially botanicals, powders, and water-containing components with higher bioburden risk
3. Complaint / odor / visible growth investigations
4. Process changes — new mixer, new container-closure, new supplier
5. Periodic verification defined by your quality risk assessment
6. Board / customer / 503B customer expectations that require documented microbial limits data

Your SOP—not a vendor’s menu—should decide frequency. CTLs execute; pharmacies own the rationale.

Build a microbial limits brief before you request quotes

Include:

• Dosage form (oral solid, topical, aqueous oral liquid, etc.)
• Preservative system (if any)
• Whether you need <61>, <62>, or both
• Acceptance criteria you will apply (and their source)
• Sample size you can provide
• Need for organism ID if counts are elevated
• TAT needs and shipping constraints

Ambiguous RFQs produce quotes that exclude suitability or ID—then surprise invoices appear later.

Method suitability still matters for nonsterile products

Even “simple” topicals can inhibit recovery. Ask the lab:

• Will you perform suitability for this matrix?
• What dilution / neutralization approach do you expect?
• How are invalid tests communicated?

If a lab treats every cream as identical to purified water, keep interviewing.

How to choose a CTL for <61>/<62>

Prioritize:

1. Pharmaceutical (not only food) microbiology experience
2. ISO/IEC 17025 scope that credibly covers microbial enumeration / specified organisms
3. Clear ID pathway when action is needed
4. Practical shipping guidance for refrigerated vs ambient samples
5. Report formats your QMS can trend

Search LabCompare Rx for labs with USP <61>/<62> capabilities and send the same brief to two or three options.

Interpreting results without panic—or denial

Elevated counts

Ask whether the elevation is:

• Ingredient-driven
• Process hygiene-driven
• Container / water-driven
• Lab / transport artifact

Do not immediately “retest until pass” without investigation logic.

Specified organism recovery

Treat as a quality event. Preserve retains, review cleaning and personnel practices, and involve the lab early for colony morphology / ID clarity.

Passing results

File them, trend them, and resist the urge to skip the next scheduled check because “we always pass.”

Trending is the real product

One CoA is a snapshot. A year of <61>/<62> data tied to formulas and lots is a control strategy. Assign an owner to:

• Chart counts by formula family
• Flag supplier changes that correlate with spikes
• Bring summaries to quality meetings

Contract labs can supply clean data. They rarely own your trending culture.

Quote comparison checklist

• <61> and/or <62> explicitly listed
• Suitability approach stated
• ID fees (if any) stated
• Sample quantity confirmed
• TAT includes accessioning reality
• Performing site address confirmed

Bottom line

USP <61> and <62> help nonsterile compounding prove microbiological control with quantitative and specified-organism evidence. Outsource to labs that understand pharmaceutical matrices—not commodity plate counting—and keep interpretation inside your quality system.

When you are ready, shortlist microbiology CTLs on LabCompare Rx and request quotes with a complete microbial limits brief.