Fluoxetine 20% Topical Gel (PermE8® Anhydrous)

Anhydrous Base

A compounded fluoxetine gel in PermE8® anhydrous base, prepared to each prescriber's order for measured application to the inner ear flap.

Reviewed by Linda Pungpravat, Compounding Pharmacist, RPh Mixwell Compounding Pharmacy, Chino, CA

USP <795> compliant
USP <800> hazardous drug lab
PCCA member

At a Glance

Preparation details for Fluoxetine 20% Topical Gel (PermE8® Anhydrous)
Dosage form	Gel
Route	Transdermal
Active ingredients	Fluoxetine
Technology	Anhydrous Base
Strengths in literature	Fluoxetine 15% pluronic lecithin organogel in the published feline pharmacokinetic study
Commercial product	Commercial product in a different dosage form
Strength and directions	Per prescriber
Dispensing	Valid prescription

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Phone (909) 378-7301. Fax (909) 378-7071

Clinical Advantages

Custom strength available
Measured dose applicator
Bypasses oral administration
Alternative to swallowing pills
Formulated for feline dosing

How It Works

What is Fluoxetine 20% Topical Gel?

Fluoxetine 20% Topical Gel is a compounded transdermal preparation of fluoxetine, a selective serotonin reuptake inhibitor, in PermE8® Anhydrous Gel. It is applied to the inner ear flap, most often in cats that will not accept a tablet or an oral liquid.

How it works

Fluoxetine blocks the reuptake of serotonin, and its active metabolite norfluoxetine has the same action [1].
Applying the gel to the thin, sparsely haired skin of the inner pinna places the drug where the skin barrier is thinnest [2].
PermE8® is an anhydrous permeation enhancing base, with water activity below 0.6, which places it in the nonaqueous category under USP 795 [6].
A 20% gel delivers 20 mg of fluoxetine in each 0.1 mL, so a full dose fits in a small ribbon of gel.

When prescribers choose it

Veterinary behaviorists and general practitioners treating cats that refuse tablets and flavored liquids
Veterinarians whose feline patients vomit or salivate after oral dosing
Owners who cannot safely pill a cat daily over months of therapy
Prescribers who want a measured dose applied by syringe rather than hidden in food

Clinical Details

What does the evidence show?

Ciribassi and colleagues (2003, American Journal of Veterinary Research) applied fluoxetine in a 15% pluronic lecithin organogel to the pinnae of 12 healthy cats at 5 or 10 mg/kg and compared it with 1 mg/kg given orally. Relative bioavailability by the transdermal route was about 10% of the oral route, with a lower peak concentration and a longer time to peak [2].
Eichstadt and colleagues (2017, International Journal of Pharmaceutical Compounding) gave 16 client owned cats either oral fluoxetine at 1 mg/kg or transdermal fluoxetine at 5 mg/kg in a Lipoderm base for 60 days. Oral concentrations were consistently higher, and the authors noted that without established effective blood levels it is unclear whether the transdermal concentrations would produce a clinical response [3].
Pryor and colleagues (2001, Journal of the American Veterinary Medical Association) studied oral fluoxetine for urine spraying in cats and reported a considerable reduction in marking [4].
A meta analysis of treatments for feline urine spraying (Mills and colleagues, 2011, PLoS ONE) found that fluoxetine, clomipramine, and pheromone therapy each may help beyond placebo, while no intervention resolved the behavior in every cat [5].

Findings come from the cited studies and do not promise any individual outcome.

Why is it compounded, and how is it typically used?

Why it is compounded

No fluoxetine product is approved for cats, and the approved human products are tablets, capsules, and an oral solution [1]. Fluoxetine tastes bitter, and a cat that fights daily dosing may go untreated. A transdermal gel gives the prescriber a route that does not involve the mouth.

Dosage forms and strengths

Concentration set by the prescriber, commonly measured in mg per 0.1 mL
Supplied in a graduated syringe for measured application to the inner ear flap
PermE8® Anhydrous Gel, or another base the prescriber specifies
Dye free and fragrance free by request

Published feline studies used 5 mg/kg transdermally against 1 mg/kg orally and still measured lower drug concentrations from the skin [2][3]. Prescribers choosing this route weigh that difference, and some reserve it for cats that cannot be dosed by mouth at all. Dosing, monitoring, and duration are the prescriber's decision.

How Mixwell prepares it

Mixwell compounds this gel in Chino, California under USP 795 standards for non sterile preparations [6]. Because PermE8® has water activity below 0.6, it falls in the nonaqueous category, which carries longer default beyond use dates than water based preparations [6]. Batch records document each preparation, and finished gels ship across California.

Safety information

Fluoxetine labeling carries a boxed warning about suicidal thoughts and behavior in children, adolescents, and young adults taking antidepressants [1]. The label also describes serotonin syndrome, and it contraindicates use with monoamine oxidase inhibitors, pimozide, and thioridazine [1].

The monoamine oxidase inhibitor warning matters in veterinary practice, because selegiline is a monoamine oxidase inhibitor used in animals. Prescribers review the full medication list, including trazodone, tramadol, and other serotonergic drugs, before adding fluoxetine [1].

Application site irritation has been reported with transdermal fluoxetine at higher concentrations [2]. Anyone applying the gel should avoid skin contact, since the dose is absorbed through skin. Keep the preparation away from children and other pets. Patient selection, dosing, monitoring, and duration are the prescriber's responsibility.

References

PROZAC (fluoxetine) capsules. Prescribing information. U.S. Food and Drug Administration, 2023. FDA label
Ciribassi J, Luescher A, Pasloske KS, et al. Comparative bioavailability of fluoxetine after transdermal and oral administration to healthy cats. Am J Vet Res. 2003;64(8):994 to 998. doi:10.2460/ajvr.2003.64.994
Eichstadt LR, Corriveau LA, Moore GE, et al. Absorption of transdermal fluoxetine compounded in a Lipoderm base compared to oral fluoxetine in client owned cats. Int J Pharm Compd. 2017;21(3):242 to 246. PubMed 28557786
Pryor PA, Hart BL, Bain MJ, Cliff KD. Effects of a selective serotonin reuptake inhibitor on urine spraying behavior in cats. J Am Vet Med Assoc. 2001;219(11):1557 to 1561.
Mills DS, Redgate SE, Landsberg GM. A meta analysis of studies of treatments for feline urine spraying. PLoS One. 2011;6(4):e18448. PubMed Central
United States Pharmacopeia. General Chapter 795, Pharmaceutical Compounding: Nonsterile Preparations. USP NF. Official November 1, 2023.

What to include on the prescription

APIs and strengths
Base or vehicle
Quantity
Directions for use
Refills
Allergies or dye free needs

Call (909) 378-7301 Fax (909) 378-7071

Compounded in Chino, CA. Delivered across California.

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Mixwell Compounding Pharmacy 13788 Roswell Ave, Ste 158, Chino, CA 91710
(909) 378-7301

Compounded medications are not reviewed or approved by the FDA. Dispensed only with a valid prescription. Mixwell is a non sterile pharmacy and does not prepare sterile products or injectables. Compounded preparations are not presented as superior to commercially available products, and nothing here promises a specific result. Mixwell does not accept insurance. Call for pricing.

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