From Wood Preservatives to the Stratum Corneum
PAs Buchi Neita and Shanna Miranti open the episode by rattling off a list of products their audience has prescribed hundreds of times — Aczone, Clobex spray, ketoconazole shampoo, Rogaine, and Zoryve — before revealing that their guest, David Osborne, PhD, had a hand in formulating, creating, or bringing all of them to market. Osborne, who holds a PhD in physical chemistry and has issued over 54 US patents, over 65 publications, and developed more than 40 topical products, insists the hosts simply call him David.
David traces his path back to his undergraduate days at Missouri State, where he worked part-time as a Quality Control (QC) chemist at a wood preservative company and became fascinated watching a microemulsion deliver a preservative chemical into wood. That fascination followed him to graduate school under a professor he'd already met — Stig Friberg — whose earlier work explained how a small addition of emulsifier could make cosmetic emulsions far more physically stable. A West Baker fellowship connected him to Peter Elias at UCSF, and, as David puts it, 'the rest of my life was kind of charted from that encounter' as he began studying epidermal lipids and how skin softeners interact with them.
Why Solubility, Not Vehicle Type, Drives Delivery
David wants providers to unlearn a rule many were trained on: that ointments are inherently the best delivery vehicle and creams are inferior. That teaching, he explains, came from topical corticosteroids in the '70s and '80s, when drugs stayed soluble longer in ointments—meaning patients were effectively getting a higher dissolved dose, not a better vehicle. Everything changed when propylene glycol was added to creams, keeping the drug fully dissolved and delivering more consistently. His core message: a precipitated drug never permeates and never treats the condition.
Roflumilast (Zoryve) tested that principle. David describes it as a drug that 'hates water' — less soluble than kerosene — and one that loves to supersaturate, dissolving fully in a solvent system only to precipitate out a month later. That tendency is dangerous for clinical testing, because a formulation that works while dissolved can fail entirely once the drug falls out of solution. Using transcutol and a novel emulsifier, Crodofos CES, that cannot extract lipids from skin, his team kept the drug in solution and built a mild, non-barrier-disrupting vehicle designed for a three-month-old with severe facial atopic dermatitis.
David also stresses that penetration enhancers modify the skin barrier over different time courses depending on their structure. Propylene glycol may impact the barrier for 20 minutes or less before passing through or evaporating, while oleyl alcohol can remain in the stratum corneum for two or three days because it isn't water-soluble. Understanding whether an enhancer is short- or long-acting matters when clinicians think about layering products.
The Football Field: Product Stacking and Interactions
Asked about the popular 'sandwich method' and nine-step skincare routines, David offers an analogy Miranti loved, even though neither of them watches football. Picture the drug as the football and the stratum corneum as the defensive line; as the formulator, he's the coach who has handpicked a formulation he knows will reach the end zone every play. But apply multiple products together, and it's like running 14 games on the same field at once — sometimes it works better, sometimes far worse, but the chaos means you're no longer guaranteed either good tolerability or good efficacy.
His practical fix: put time between applications. Ten or twenty minutes helps, and a morning treatment paired with a different nighttime treatment is ideal because the products aren't 'active on the field' simultaneously. When pressed on whether his product should go on before or after moisturizer, David refuses to guess — if his product goes on first, he's confident, but the moment a moisturizer goes on immediately before or after, he can't predict the outcome.
The benzoyl peroxide plus dapsone question gave David a memorable lab story. When he blended BPO into a dapsone gel, the white suspension turned mocha, then hot-chocolate brown within twenty minutes. BPO barely degrades dapsone — assays show maybe a 2% drop over days — but the degradation product is so intensely colored it looks like staining. His bottom line: these two can't be stacked, and it's a perfect tutorial to mix up and show patients.
Expiration Dates, Preservatives, and Compounding
On expiration dates, David reassures that degradation is gradual, not a cliff. Actives typically carry a 90-to-110-percent-of-label spec, and formulators build in a safety margin so a product isn’t marketed if it might dip below 0.95% of a 1% active by the end of shelf life. Using a product a month or two past expiration isn't necessarily harmful, but that promise depends on proper storage. Heat excursions, like a product sitting in a hot Florida car or an Amazon warehouse, can shorten that window, a lesson the field absorbed during the 2024 benzene concerns.
David is candid about preservatives: everyone over-preserves during development because under-preserving after generating clinical data is career-ending, and almost no one goes back post-market to trim preservative levels to the minimum truly needed. He'd like to see companies reassess how much preservative is actually necessary and reduce patient exposure — something he expects Arcutis to take a hard look at.
On cost and access, David is comfortable with FDA-approved generics, which are bioequivalent, though he notes generics can differ in preservatives or contain propylene glycol where the brand doesn't — relevant for allergic patients but always listed on the ingredient list. Compounding pharmacies are another matter. He warns strongly against compounding brand-new drugs like roflumilast: dissolving it in ethanol and blending it into cream drops it out of solution as chunky particles that never penetrate, so patients essentially spend $60 for nothing. He remains a believer in compounding for established, provider-tested blends — like clobetasol combined with something you've used successfully for years — but urges caution with tricky new molecules and BPO formulations.