Tenofovir Gel for the Prevention of Herpes Simplex Virus Type 2 Infection

Mychal Outlaw, Mercer University College of Pharmacy

According to the Centers for Disease Control and Prevention’s (CDC) Sexually Transmitted Disease Guidelines, herpes simplex virus type 2 (HSV-2) causes most cases of recurrent genital herpes. The CDC states that many cases of HSV-2 are undiagnosed due to the fact that many infected persons are asymptomatic and transmit the infection unaware of its existence. The Sexually Transmitted Disease Guidelines specifically mention the following study and the significance of pre-exposure prophylactic treatment with tenofovir for the prevention of HSV-2 and HIV transmission. All other suggested prevention methods by the CDC included non-pharmacological options1.

Tenofovir Gel for the Prevention of Herpes Simplex Virus Type 2 Infection2
Design Double-blind, placebo-controlled, randomized trial
Objective To assess whether tenofovir gel prevents HIV infection in women
Study Groups Four hundred twenty-nine eligible HSV-2 seronegative South African women were enrolled in the study and randomly assigned to receive either tenofovir gel or placebo gel; N= 429
Methods The tenofovir group included 205 women while the placebo group included 224 women. The tenofovir gel and placebo gel had identical appearances and presentations. Subjects were instructed to insert one dose of the gel 12 hours before sex and a second dose as soon as possible after sex (preferably within 12 hours). No more than two doses were permitted in a 24-hour period. At each monthly study visit all used and unused applicators were recorded for assessment of adherence. Vaginal tenofovir concentrations were randomly measured for each participant in order to assess drug exposure.
Duration 2007- 2010
Primary Outcome Measure Positive testing for HSV-2 infection
Baseline Characteristics
Tenofovir Gel Placebo Gel
Variable (n= 205) (n= 224)
Sociodemographic characteristic
Age (yr) 22.2 +/- 3.6 21.6 +/- 3.4
Parity 0.7 +/- 1.0 0.7 +/- 0.8
High school education or more- no. (%) 92 (44.9) 98 (43.8)
Income per month <1000 rands- no/total (%) 167/179 (93.3) 173/185 (93.5)
Using hormonal contraception- no. (%) 202 (98.5) 224 (100)
Stable partner- no. (%) 202 (98.5) 222 (99.1)
Living with regular partner- no. (%) 18 (8.8) 9 (4.0)
Sexual behavior
Age at first sexual experience- yr 17.5 +/- 2.1 17.4 +/- 1.8
Age of oldest partner in past 30 days- yr 25.2 +/- 4.3 24.8 +/- 4.2
No. of lifetime sex partners 2.2 +/- 2.1 3.0 +/- 12.1
No. of sex acts in past 30 days 8.5 +/- 8.2 7.5 +/- 6.8
New sex partner in past 30 days- no. (%) 1 (0.5) 3 (1.3)
Knows sex partner had other sex partners in past 30 days- no. (%) 35 (17.1) 41 (18.3)
Knows sex partner had HIV test in past 30 days- no. (%) 3 (1.5) 7 (3.1)
Reports alcohol consumption by partner and self before sex in general- no. (%) 7 (3.4) 7 (3.1)
Reports alcohol consumption by partner and self before the last time they had sex- no. (%) 51 (24.9) 59 (26.3)
Reports always using condoms during sex- no. (%) 61 (29.8) 63 (28.1)
Location of study site- no. of participants (%)
Urban 57 (27.8) 57 (25.4)
Rural 148 (72.2) 167 (74.6)
Results
Variable Tenofovir (n= 200) Placebo (n= 222) p- value
HSV-2 infection- no. (%) HSV-2 infection- no. (%)
Overall 29 (14.5) 58 (26.1) 0.003

Results demonstrated that the use of tenovofir gel provided a 51% lower risk of HSV-2 acquisition for women when used in preventative treatment.

Adverse Events Common Adverse Events: N/A
Serious Adverse Events: N/A
Percentage that Discontinued due to Adverse Events: N/A
Study Author Conclusions Women may use tenofovir gel in order to reduce the risk of acquiring sexually transmitted viral infections. Further data on the efficacy of tenofovir gel against HSV-2 acquisition are needed.

This study was not originally designed to assess the effectiveness of tenofovir for preventing HSV-2 infections in women. Tenofovir concentrations at the time of HSV-2 acquisition could not be assessed. Therefore, adherence to the treatment cannot be verified, and poor adherence could be explored as a variable for acquiring the infection. Although the tenofovir concentration for each woman was randomly checked, it cannot be assumed that the concentration at that particular time reflected the concentration of drug present during an exposure to HSV-2.

This study shows that tenofovir gel may be an effective option for reducing the risk HSV-2 transmission for women during sexual intercourse. The effectiveness of tenofovir gel was dependent on the adherence of the subjects to the study protocol. If the use of tenofovir was done according to the study protocol, vaginal delivery of the drug would equal to or exceed a concentration of 10,000 ng per milliliter. At this concentration, tenofovir offers a 63% higher rate of protection against HSV-2 compared to women without tenofovir treatment2.

References

  1. Centers for Disease Control and Prevention. Sexually Transmitted Diseases Treatment Guidelines. MMWR 2010;59(No. RR-12):20.
  2. Abdool karim SS, Abdool karim Q, Kharsany AB, et al. Tenofovir Gel for the Prevention of Herpes Simplex Virus Type 2 Infection. N Engl J Med. 2015;373(6):530-9.
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