What Are Anhydrous Compounding Bases? A Prescriber's Guide to PCCA's Anhydrous Family
An anhydrous base is a vehicle with water activity below 0.6. That single number decides how long a compounded preparation can be dated, which actives it can hold, and how often your patient returns for a refill. This guide explains the science, the USP rules that follow from it, and what each PCCA anhydrous base is built to do.
What anhydrous means in compounding
In compounding, anhydrous means a water activity below 0.6, not simply a formula with no water listed. The revised USP General Chapter 795, official since November 2023, uses water activity as the measure that separates aqueous from nonaqueous preparations.
Water activity, written aw, is the amount of water that is free to take part in chemical reactions or support microbial growth. It is different from water content, which counts all the water present, including water bound up in the structure of other ingredients.
That distinction is the reason USP moved away from the older labels "nonaqueous" and "water containing." A vehicle can contain a small amount of bound water and still behave as anhydrous, because that water is not available to do anything.
Why water activity matters
Free water does two things a prescriber cares about: it supports microbial growth, and it drives chemical degradation of the active ingredient. Take the free water away and both risks fall together.
On the microbial side, nonaqueous dosage forms with water activity below 0.6 do not support spore germination or microbial growth. That is why an anhydrous preparation can be dated longer without relying on a preservative system.
On the chemical side, many actives degrade through hydrolysis or oxidation in water. Hydroquinone and ascorbic acid are familiar examples in dermatology. As PCCA's Chief Scientific Officer described it when launching an anhydrous oral base, with no water there is nothing to support microbial growth or cause hydrolytic degradation of the active, which opens the door to longer beyond use dates.
The USP 795 beyond use date rules
USP 795 assigns default beyond use dates by water activity, and nonaqueous preparations receive the longest defaults. These limits apply when no USP NF compounded preparation monograph or preparation specific stability data exists.
| Preparation type | Water activity | Default BUD |
|---|---|---|
| Nonpreserved aqueous | 0.6 or above | 14 days, refrigerated |
| Preserved aqueous | 0.6 or above | 35 days, room temperature or refrigerated |
| Nonaqueous oral liquid | Below 0.6 | 90 days |
| Other nonaqueous forms, including topicals, suppositories, troches and capsules | Below 0.6 | 180 days |
Defaults assume storage in tight, light resistant containers. A beyond use date can never exceed the shortest remaining expiration date of any component in the preparation, and the pharmacy's designated person may assign a shorter date when stability information calls for it.
A topical cream in an aqueous base without preservative defaults to 14 days in the refrigerator. The same active in an anhydrous topical base can default to 180 days. For a patient on long term therapy, that is the difference between a refill every two weeks and a refill every six months.
Why an ordinary oil is not enough
Petrolatum, simple ointments and plain oils are anhydrous too, but they were not designed to deliver drugs well or to feel good to use. That is the gap PCCA's engineered anhydrous bases were built to close.
PCCA has noted that most anhydrous bases on the market are oil based, and that many patients, especially children, dislike both the taste of oil based oral vehicles and the oily residue they leave. Topical ointments raise a similar problem: a greasy vehicle is easy to abandon, and a skipped application delivers nothing.
The PCCA anhydrous family starts from the same water activity advantage and then adds a second property matched to the route, such as permeation enhancement, mucoadhesion, self emulsification or an elegant cosmetic finish.
The PCCA anhydrous family at a glance
Each PCCA anhydrous base pairs water activity below 0.6 with a property engineered for a specific route. The table summarizes what each one adds.
| Base | Route | What it adds | USP default category |
|---|---|---|---|
| PermE8 Anhydrous Gel | Topical and transdermal | Permeation enhancement, holds multiple actives including salt forms, silky finish | Nonaqueous topical, 180 days |
| WO6 Anhydrous Topical Gel | Topical | Emollient, elegant finish, holds oxidation prone actives such as hydroquinone and ascorbic acid | Nonaqueous topical, 180 days |
| Ellage Anhydrous Vaginal | Vaginal | Mucoadhesion, self emulsifying, compatible with physiological vaginal pH | Nonaqueous, 180 days |
| Anhydrous SuspendIt | Oral | Self emulsifying, thixotropic, naturally sweetened | Nonaqueous oral liquid, 90 days |
Default categories apply when the finished preparation remains below water activity 0.6 and no monograph or preparation specific stability data exists.
Base by base profiles
Here is what PCCA reports about each base, drawn from its product literature and published studies.
PermE8 Anhydrous Gel
Topical • TransdermalPCCA describes PermE8 as a next generation permeation enhancing base in a silky, smooth anhydrous system. With water activity below 0.6, it allows extended default beyond use dates for preparations that do not have their own stability studies, which PCCA notes can otherwise cost compounders thousands of dollars to generate.
PermE8 can hold several actives at once, including actives in salt form. In PCCA's in vitro testing it delivered ketoprofen comparably to Lipoderm and at roughly four times the level of Anhydrous Lipoderm. It is commonly used for pain, hormone and multi active dermatology preparations.
WO6 Anhydrous Topical Gel
TopicalWO6 is an elegant, emollient anhydrous base for dermatological and cosmetic applications. Because its water activity is below 0.6, it accommodates actives that are unstable in water, and PCCA states that WO6 preparations containing hydroquinone or ascorbic acid can be stored at room temperature when no aqueous ingredients are added.
It leaves a light, smooth finish without greasy or tacky residue, and it moisturizes as it delivers. PCCA specifies WO6 for topical use and recommends EMP jars as the preferred dispensing device, since some formulations can separate in pump or click devices.
Ellage Anhydrous Vaginal
VaginalEllage is the first anhydrous base in pharmacy compounding developed specifically for vaginal use. It is designed to be gentle on vaginal tissue, release drugs, and keep contact with the mucosa while giving patients a pleasant experience.
A PCCA study published in Pharmaceuticals evaluated the base in vitro and ex vivo. It reported cell viability above 78 percent, a non irritant score of 2.5, a maintained physiological vaginal pH of 4.56, mucoadhesion comparable to commercial products, minimal leakage, and prolonged retention on vaginal tissue. On contact with vaginal fluid simulant it formed stable emulsions that distributed both lipophilic and hydrophilic compounds.
Anhydrous SuspendIt
OralAnhydrous SuspendIt is an oral suspending vehicle for actives that are unstable in water or incompatible with aqueous vehicles. PCCA built it to avoid the taste and residue problems of oil based anhydrous vehicles.
It is self emulsifying, which PCCA reports improves miscibility and dispersibility in aqueous environments and may improve active solubility. It is thixotropic, thinning when shaken for rapid redispersion and thickening at rest to limit sedimentation. It contains a natural sweetener and can be mixed with juice or water at the moment of administration.
PCCA's anhydrous family also includes PracaSil Plus, a silicone and pracaxi oil base used for the appearance of scars. Mixwell can tell you which bases suit a particular formulation.
Want to talk through which anhydrous base suits an active and a route?
Call (909) 378-7301Matching the base to the prescription
The right anhydrous base depends on where the preparation goes and what the active needs. These are the common matches.
| If the prescription needs | Consider |
|---|---|
| Transdermal delivery of one or several actives, including salts | PermE8 |
| An elegant cosmetic finish with an oxidation prone active | WO6 |
| Vaginal delivery with mucosal retention | Ellage Anhydrous Vaginal |
| Topical bioidentical hormones | PermE8 |
| An oral liquid for a water unstable active | Anhydrous SuspendIt |
You can name the base on the prescription or write pharmacist's choice. Related reading covers why the base is a prescribing variable and why we compound with PCCA formulas.
What keeps a preparation anhydrous
The anhydrous classification belongs to the finished preparation, not just the base. Three practical points keep the longer dating valid.
Adding an aqueous ingredient can raise water activity above 0.6 and move the preparation into an aqueous category with a much shorter default date. The beyond use date also cannot exceed the shortest remaining expiration of any component. And each base has an intended route, so WO6, for example, is specified by PCCA for topical use rather than vaginal or rectal use. Our pharmacists check each formulation against these rules before assigning a date.
Writing the prescription
Name the active, strength, dosage form, route and base, or write pharmacist's choice. Then fax or e prescribe to our Chino pharmacy.
- State each active with its strength and the dosage form.
- Name the anhydrous base, or write pharmacist's choice so we match the base to the route.
- State the quantity and directions, including the application site for topicals.
- Call (909) 378-7301 to confirm the formulation and the beyond use date we can assign.
For a full walkthrough, see our prescriber's guide to writing compounded prescriptions.
Serving prescribers in California
Mixwell Compounding Pharmacy is a PCCA member pharmacy in Chino, CA, operating a USP 795 and USP 800 compliant non sterile lab. We work with prescribers across the Inland Empire, Los Angeles County and Orange County, and deliver across California.
- Chino
- Chino Hills
- Ontario
- Rancho Cucamonga
- Upland
- Pomona
- Diamond Bar
- Corona
- Riverside
- Eastvale
- Brea
- Fullerton
Common questions
What is an anhydrous compounding base?
An anhydrous compounding base is a vehicle with water activity below 0.6. Under USP General Chapter 795, preparations below that threshold are classified as nonaqueous, do not support microbial growth, and receive longer default beyond use dates than aqueous preparations.
Is anhydrous the same as containing no water?
Not exactly. Anhydrous refers to water activity, the free water available for chemical reactions or microbial growth, rather than total water content. A vehicle can contain a small amount of bound water and still have water activity below 0.6.
How long is the default beyond use date for an anhydrous compounded topical?
Under USP 795, nonaqueous preparations other than oral liquids, including topicals, suppositories, troches and capsules, default to 180 days when no monograph or preparation specific stability data exists. Nonaqueous oral liquids default to 90 days. The date cannot exceed the shortest remaining expiration of any component.
What happens if an aqueous ingredient is added to an anhydrous base?
Adding an aqueous ingredient can raise water activity to 0.6 or above, which moves the preparation into an aqueous category with a shorter default date of 14 days unpreserved or 35 days preserved. The classification applies to the finished preparation, not only the base.
Why use a PCCA anhydrous base instead of petrolatum or an oil?
Simple oils and ointments are anhydrous but were not designed for drug delivery or patient experience. PCCA's anhydrous bases add a route specific property on top of the water activity advantage, such as permeation enhancement in PermE8, mucoadhesion in Ellage, or palatability and self emulsification in Anhydrous SuspendIt.
Can WO6 be used for vaginal or rectal preparations?
No. PCCA specifies WO6 for topical use, since its safety for intravaginal or intrarectal use has not been studied. For vaginal preparations, Ellage Anhydrous Vaginal was developed specifically for that route.
Does Mixwell accept insurance?
Mixwell does not accept insurance. Call (909) 378-7301 to discuss current pricing.
Key Takeaways
- In compounding, anhydrous means water activity below 0.6, which is a measure of free water rather than total water content.
- Below 0.6, a preparation does not support microbial growth, and water driven degradation of the active is reduced.
- USP 795 defaults nonaqueous topicals, suppositories, troches and capsules to 180 days and nonaqueous oral liquids to 90 days, against 14 or 35 days for aqueous preparations.
- PCCA's anhydrous bases pair that advantage with route specific engineering, including permeation enhancement, mucoadhesion, elegance and palatability.
- The classification applies to the finished preparation, so adding aqueous ingredients or exceeding a component's expiration changes the date.
Sources
- PCCA. Anhydrous Family of compounding bases, product overview. pccarx.com
- United States Pharmacopeia. General Chapter 795, Pharmaceutical Compounding, Nonsterile Preparations, Table 4, BUD limits by type of preparation. Official November 1, 2023.
- Understanding water activity: a key component in determining beyond use date in pharmaceutical compounding. Journal of Pharmaceutical Compounding and Therapeutics. 2024. jpcts.com
- Comprehensive evaluation of a mucoadhesive self emulsifying anhydrous base for vaginal drug delivery. Pharmaceuticals. mdpi.com
- PCCA. PCCA introduces innovative new compounding base, SuspendIt Anhydrous. News release, January 11, 2023. pccarx.com
- PCCA. PermE8 Anhydrous Gel product information.
- PCCA. WO6 Anhydrous Topical Gel product information and frequently asked questions.
- PCCA. Anhydrous VersaBase HRT, including the progesterone skin penetration study reported in the Archives of Dermatological Research.
- PCCA Science. Publications index by product. pccarx.com/science