BACKGROUND: Semifluorinated alkanes (SFAs) are amphiphilic molecules with a fluorinated carbon segment (F) and a hydrocarbon segment (H) of differing chain lengths. This in vitro study evaluated the impact of chain length on SFA evaporation rate (Revap) and inhibition of Revap of saline. SFA dry eye drops include one consisting of 100% SFA (perfluorohexyloctane; F6H8; MIEBO) and one with the SFA perfluorobutylpentane (F4H5) as a vehicle (cyclosporine ophthalmic solution 0.1%; CsA 0.1%; VEVYE).

METHODS: Evaporation rates were measured gravimetrically at 35øC in a masked study. The following SFA-containing dry eye drops and comparator SFAs were evaluated: F4H2, F4H5/CsA 0.1%, F6H7, F6H8, and F6H10. Revap of 1 mL of each SFA and saline alone or saline with an 11- or 100-æL aliquot of SFA layered over the top was evaluated in a container with an exposed surface area similar to that of the human ocular surface. Total sample weight was recorded to five decimal places every 10 minutes over 100 minutes. Revap for each sample was obtained from the slope of the best-fit line using least squares linear regression analysis.

RESULTS: Mean (SEM) Revap in mg/min were 102 (25), 6.0 (0.6), 0.58 (0.20), 0.15 (0.017), and 0.12 (0.09) for F4H2, F4H5, F6H7, F6H8, and F6H10 alone, respectively (n=3-9). Revap of saline alone was 10.53 (0.06) æm/min. Layering 100 æL F4H5/CsA 0.1% over saline had no effect on Revap (P=0.52) while F4H2, F6H7, F6H8, and F6H10 inhibited the Revap of saline by 8.4%, 16.7%, 73.9%, and 60.7%, respectively (P<0.001 for all vs saline. none of the sfas had a significant inhibitory effect on revap of saline when applying a single 11 l drop except for f6h8 p><0.0001 vs saline n="10-25).">

CONCLUSIONS: Chain length and volatility of SFAs appeared to impact their ability to inhibit Revap of saline in this in vitro model. Shorter chain length SFAs F4H2 and F4H5/CsA 0.1% had minimal or no effect on Revap while longer chain length SFAs F6H8 and F6H10 had the maximal effect. The data reinforce the suitability of F6H8 as an anti-evaporative agent for the treatment of signs and symptoms of dry eye disease.