Susceptibility of Cutibacterium acnes to topical minocycline foam.

FMX101 4% minocycline foam (FMX101 4%) is a novel, topical minocycline formulation for treatment of acne vulgaris. We report that FMX101 4% had an MIC90 of 0.25 µg/ml and was ≥4-fold more active than comparator antimicrobials against a panel of 98 clinical Cutibacterium acnes isolates. The panel was diverse by clonal complex and sequence type, having 20 novel multi-locus sequence types including clonal complexes and sequence types associated with acne (CC1, CC3, and CC4; ST1 and ST3). Some isolates were phenotypically resistant to clindamycin (6.1%), erythromycin (14.3%), and tetracycline (2.0% intermediate resistance). Six isolates (6.4%) carried a mutation in the quinolone resistance-determining region of gyrA. With C. acnes, spontaneous resistance to FMX101 4% occurred at frequencies ranging from ≤5 × 10-9 to <1 × 10-8; mutations were identified in rpsJ, a gene encoding 30S ribosomal protein S10. No mutant exhibited a minocycline MIC above 0.5 µg/ml. No second-step mutation in previously isolated mutants or strains containing rpsJ ± 16S rRNA mutations was detected following minocycline challenge. Minocycline retained antibacterial activity against C. acnes over 15 multiple passages; thus, no selective growth advantage for minocycline-resistant mutants occurred under the experimental conditions. FMX101 4% has the potential to retain the favorable resistance profile of minocycline in diverse C. acnes isolates while providing the benefits of a topical formulation for treatment of acne vulgaris.

Influence of propylene glycol on aqueous silica dispersions and particle-stabilized emulsions.

We have studied the influence of adding propylene glycol to both aqueous dispersions of fumed silica nanoparticles and emulsions of paraffin liquid and water stabilized by the same particles. In the absence of oil, aerating mixtures of aqueous propylene glycol and particles yields either stable dispersions, aqueous foams, climbing particle films, or liquid marbles depending on the glycol content and particle hydrophobicity. The presence of glycol in water promotes particles to behave as if they are more hydrophilic. Calculations of their contact angle at the air-aqueous propylene glycol surface are in agreement with these findings. In the presence of oil, particle-stabilized emulsions invert from water-in-oil to oil-in-water upon increasing either the inherent hydrophilicity of the particles or the glycol content in the aqueous phase. Stable multiple emulsions occur around phase inversion in systems of low glycol content, and completely stable, waterless oil-in-propylene glycol emulsions can also be prepared. Accounting for the surface energies at the respective interfaces allows estimation of the contact angle at the oil-polar phase interface; reasonable agreement between measured and calculated phase inversion conditions is found assuming no glycol adsorption on particle surfaces.

Membrane permeation of testosterone from either solutions, particle dispersions, or particle-stabilized emulsions.

We derive a unified model that accounts for the variation in extent and rate of membrane permeation by a permeating species with the type of donor compartment formulation (aqueous and oil solutions, particle dispersions, and oil-in-water and water-in-oil emulsions stabilized by particles) initially containing the permeant. The model is also applicable to either closed-loop or open-flow configurations of the receiver compartment of the permeation cell. Predictions of the model are compared with measured extents and rates of permeation of testosterone across an 80 µm thick polydimethylsiloxane (PDMS) membrane from donor compartments initially containing testosterone dissolved in either aqueous or isopropylmyristate (IPM) solutions, aqueous or IPM dispersions of silica nanoparticles or IPM-in-water or water-in-IPM emulsions stabilized by silica nanoparticles. Using a single set of input parameters, the model successfully accounts for the wide variations in permeation behavior observed for the different donor formulation types with either closed-loop or open flow configurations of the permeation cell receiver compartment.

How membrane permeation is affected by donor delivery solvent.

We investigate theoretically and experimentally how the rate and extent of membrane permeation is affected by switching the donor delivery solvent from water to squalane for different permeants and membranes. In a model based on rate-limiting membrane diffusion, we derive explicit equations showing how the permeation extent and rate depend mainly on the membrane-donor and membrane-receiver partition coefficients of the permeant. Permeation results for systems containing all combinations of hydrophilic or hydrophobic donor solvents (aqueous solution or squalane), permeants (caffeine or testosterone) and polymer membranes (cellulose or polydimethylsiloxane) have been measured using a cell with stirred donor and re-circulating receiver compartments and continuous monitoring of the permeant concentration in the receiver phase. Relevant partition coefficients are also determined. Quantitative comparison of model and experimental results for the widely-differing permeation systems successfully enables the systematic elucidation of all possible donor solvent effects in membrane permeation. For the experimental conditions used here, most of the permeation systems are in agreement with the model, demonstrating that the model assumptions are valid. In these cases, the dominant donor solvent effects arise from changes in the relative affinities of the permeant for the donor and receiver solvents and the membrane and are quantitatively predicted using the separately measured partition coefficients. We also show how additional donor solvent effects can arise when switching the donor solvent causes one or more of the model assumptions to be invalid. These effects include a change in rate-limiting step, permeant solution non-ideality and others.

Formulation and Profile of FMX101 4% Minocycline Topical Foam for the Treatment of Acne Vulgaris.

FMX101 4% minocycline is a hydrophobic, topical foam formulation of minocycline recently approved by the United States Food and Drug Administration (FDA) for the treatment of non-nodular inflammatory lesions in moderate-to-severe acne vulgaris. It was developed to harness the anti-inflammatory and antibiotic activity of minocycline while minimizing potentially serious systemic adverse events associated with oral delivery. The composition and profile of this novel treatment have yet to be described. This article discusses the components of the foam-based product and the rationale for their selection. It reviews microbiologic data for FMX101 4% and presents previously unpublished data regarding sebum penetration, minocycline permeation, and disposition into skin structures. The effects of FMX101 4% were compared with those of several commercially available acne preparations to determine how the FMX101 4% formulation affects the physical properties of model human sebum in vitro. The hydrophobic formulation of FMX101 4% was found to lower the melting temperature of model human sebum below that of normal skin temperature, decreasing its viscosity. FMX101 4% achieved high concentrations of minocycline in the sebaceous appendage, while minimizing permeation beyond the dermal layer. Finally, this article summarizes efficacy and safety data for FMX101 4% from three Phase III studies (FX2014-04, FX2014-05, and FX2017-22). FMX101 4% appeared to be safe, effective, and well tolerated for the treatment of non-nodular inflammatory lesions in moderate-to-severe acne vulgaris. In conclusion, the topical formulation of minocycline in FMX101 4% represents a unique treatment for acne vulgaris and a viable alternative to oral administration.