Clinical pharmacology of drugs used in PrEP was discussed by Marta Boffito from the Chelsea and Westminster Hospital London. They measured drug concentrations in cervicovaginal fluid, rectal lavage fluid and in tissue from both sites.
All data was not presented today. In cervicovaginal fluid, CCR5 is high and maraviroc is less protein bound than in plasma. Raltegravir concentrates in cervicovaginal fluid, reaching steady state by 4 days; the half life is 17 hours in cervicovaginal fluid compared with seven hours in blood.
Both maraviroc and raltegravir had high concentrations when measured in rectal tissue in woman. There is data in men but little was presented. Dolutegravir was detected three hours after a single dose and had a half life of 13 hours.
Injectable long acting rilpilvirine was trialed in two doses, 1200 and 600 mg. Sampling of cervcocervical fluid, rectal fluid and tissue showed high levels in cervicovaginal fluid but low levels rectally. There were high levels of drug at one month. A higher BMI was associated with lower concentrations of rilpilvirine. There were no reports of increased toxicity with any of the medications.
When asked to express an opinion on the negative protection described in the FACTS 001 phase III trial of precoital tenofovir gel presented the day before, Marta thought that systemic PrEP was probably easier for users than local PrEP. In that study of young women, mean age 23, many of them were living at home and questions of privacy were thought to be germane.