Factors influencing nonoxynol-9 permeation and bioactivity in cervical mucus

The effects of delivery gel pH and osmolarity on both the mass transport and 'biodiffusion' of the spermicide nonoxynol-9 (N9) in bovine cervical mucus were evaluated. Delivery gels were calcium chloride crosslinked alginate containing 3% N9, and were manufactured over a pH range of 3.4 to 5.9 and an osmolarity range of 300 to 900 mosmol. Mass transfer parameters (diffusion coefficients and total drug loading) were determined using a new UV spectrophotometric technique while biodiffusion (the diffusion distance into mucus at which sperm are killed) was assessed using the Double Ended Test. It was found that delivery gel pH had a significant effect on spermicidal efficacy of the alginate-N9 system; biodiffusion increased with decreasing pH. Actual N9 diffusion into mucus was found to be influenced by both the delivery gel pH and osmolarity. At high N9 concentration (near the gel/mucus interface), mass transport tended to decrease with decreasing pH at the highest osmolarity. At low concentration, mass transport tended to decrease with increasing osmolarity and decrease with increasing pH at the highest osmolarity. The difference between low and high concentration behavior can be attributed to N9 micelle formation. These findings are interpreted in the context of the design of intravaginal drug delivery vehicles for spermicides.