The observation was one of several reported in a Form 483 detailing inspections of the facility in Missoula, Montana in August and September this year.
In addition, the Food and Drug Administration (FDA) team observed the use of non-pharmaceutical grade components used in the production of drugs and dust covered equipment.
They also said the firm failed to use adequate containment or cleaning procedures.
The Missoula facility is not registered as an outsourcing facility under the 2013 Drug Quality and Security Act (DQSA).
The DQSA, which came into law in November 2013 to update the Federal Food, Drug, and Cosmetic Act (FDCA), gave compounders the option of registering as an outsourcing facility.
It was introduced to try and improve oversight of the industry after a 2012 meningitis outbreak linked to contaminated methylprednisolone made by the New England Compounding Centre (NECC) in Massachusetts resulted in the death of over 60 people.
Compounders are not obliged to register. Those that do not - so called 503A manufacturers - are monitored by State authorities rather than Federal regulators.