Almost every oral strip on the market is solvent-cast: a water-based mass of film polymer, plasticizer, active, sweetener, and flavor is spread as a wet layer, dried at roughly 40 to 60 °C into a film about 50 to 150 μm thick, slit and cut into strips, sealed into foil sachets, and released against a written specification. The chemistry is not exotic. The discipline is in the numbers.
| Polymer | Typical grade | What it gives | Watch for |
|---|---|---|---|
| HPMC (hypromellose 2910) | E5, E15, E50 (5/15/50 mPa·s, 2 % at 20 °C) | Clear, tough film; E15 films disintegrated in about 3 to 4 s in one study | Slower dissolve as viscosity rises |
| Pullulan | Food/pharma grade, first ingredient in PocketPaks | Fast dissolve, low oxygen permeability, keeps strength when humid | Highest water uptake of the common polymers; cost |
| Polyvinyl alcohol | 87 to 89 % hydrolysis | Strong, flexible film | Most moisture-sensitive when plasticized with 10 to 20 % glycerin |
| Maltodextrin | Low dextrose equivalent | Cheapest, fastest disintegration (17.6 to 27.8 s reported) | Hygroscopic; usually blended with HPMC or PEO |
Start with the brief, not the beaker
Write down the active and amount per strip, serving plan, flavor direction, strip size, box count, market, and claims, and separate requirements from preferences. "25 mg caffeine, one strip, lemon-mint, 20 per box" gets a straight feasibility answer. "As much as possible, tastes great" gets a longer program.
Choosing the film polymer
The polymer is 50 to 65 % of the dry film. Low-viscosity HPMC 2910 (E5, E15, E50: 5, 15, and 50 mPa·s at 2 %) gives clear, tough films. Pullulan, first ingredient on the Listerine PocketPaks label, dissolves fast and keeps its strength when humid. Partially hydrolyzed PVA (87 to 89 %) and low-DE maltodextrin round out the set; a DailyMed-listed simethicone strip blends maltodextrin, polyethylene oxide, and hypromellose. Plasticizer runs 0 to 20 % of polymer. We usually start from an HPMC and pullulan blend.
Mixing and casting
Solids go into deionized water, the mass is deaerated, and a wet layer is laid down at a thickness set by gap and viscosity. Dry film is roughly a fifth of wet, so a 130 μm dry film from a 20 % solids mass needs about 0.65 mm wet. Published work treats 100 μm as the reference thickness; our targets are 50 to 150 μm and 100 to 300 mg per 22 × 32 mm strip.
Drying is where most films go wrong
Films dry in moving air at 40 to 60 °C, lower and slower for heat-sensitive actives. Residual water matters as much: one study measured about 2 % water at 44 % RH and 7 % at 75 % RH, with tensile strength falling as water rose. Too dry cracks in the slitter; too wet tacks in the sachet. That is why moisture or water activity is on every lot's release panel.
Slitting, cutting, and pouching
The web is slit, cut, and sealed one strip per sachet. For scale, the prescription buprenorphine/naloxone film is 22.0 × 12.8 mm in child-resistant polyester/foil pouches, 30 per carton. Ours is 22 × 32 mm in a PET/aluminum/PE sachet without desiccant, 10 to 60 per carton.
Release testing
Every lot leaves against the same panel: appearance, dimensions and weight, moisture or water activity, seal integrity and coding, potency, content uniformity where dose-critical (USP <905>), and micro by USP <2021> and <2022>. Disintegration follows the method in the spec, because the USP <701> basket gives no clean endpoint for films. Third-party work runs through ILS Lab; results land in a Lot Release Packet.
Worked example: a 25 mg caffeine strip
A hypothetical brand, Northline Focus, wants 25 mg caffeine per strip. Target a 120 mg strip at 22 × 32 mm (7.04 cm²): caffeine is 20.8 % of dry weight, inside the 5 to 30 % loading reported for cast films. The rest is about 65 mg HPMC E15/pullulan, 6 mg glycerin, 1.5 mg sucralose, 3 mg lemon flavor, citric acid, and 4 to 7 % water. A 20 % solids mass at 0.6 mm wet, dried at 50 °C, gives that strip. The 500-box pilot is 10,000 strips, about 7 m² of film before trim.
Common questions
Published films run from about 25 μm up to 170 μm, with 100 μm treated as a standard reference. We develop to 50 to 150 μm dry.
The FDA's ODT guidance treats about 30 s in vitro as the benchmark for orally disintegrating forms, and ODF reviews use not more than 60 s. We target 30 to 60 s in the mouth and write the test method into the spec.
It exists, but solvent casting is the dominant commercial method because it runs at low temperature and handles water-soluble polymers directly.
Primary sources
- Orodispersible Films: Current Innovations and Emerging Trends (Pharmaceutics, 2023, PMC10747242)
- HPMC viscosity grades: selection, uses and QC guide
- HPMC E15 orodispersible films by syringe-extrusion 3D printing (Pharmaceutics, 2020, PMC7696250)
- Pullulan and maltodextrin oral fast-dissolving films, Box-Behnken design (Pharmaceutics, 2022, PMC9146677)
- Characterization and optimization of orodispersible mosapride film formulations (AAPS PharmSciTech, 2011)
- Orally disintegrating films: the effects of water content on disintegration and mechanical properties (J Drug Deliv Sci Technol, 2021)
- US 6,528,569, solid water-soluble or water-dispersible compositions (drying of cast films)
- Listerine PocketPaks Cool Mint breath strips, ingredient listing (CVS)
- DailyMed: Anti-Gas Strip, simethicone 62.5 mg oral strip (Drug Facts label)
- SUBOXONE sublingual film prescribing information (FDA label, 2021)
- USP <905> Uniformity of Dosage Units, FAQ
- USP <2023> Microbiological Attributes of Nonsterile Nutritional and Dietary Supplements
- USP <2021> Microbial Enumeration Tests, Nutritional and Dietary Supplements
- USP <2022> Microbiological Procedures for Absence of Specified Microorganisms, Nutritional and Dietary Supplements
- Disintegration time of orally dissolving films: methodologies and in-vitro/in-vivo correlation (Pharmazie, 2019)
- FDA Guidance for Industry: Orally Disintegrating Tablets (2008)
- Impact of plasticizer and degree of hydrolysis on free volume of PVA films (PMC6403818)
Formula feasibility, packaging, testing, claims, timing, and final quantities depend on the exact product. Use this guide to prepare better questions, then confirm the production plan for your project.