Background: Doxycycline post-exposure prophylaxis (DoxyPEP) has demonstrated efficacy for prevention of bacterial sexually transmitted infections. To inform policy decisions on the use of DoxyPEP for gonorrhea prevention, we used a mathematical model to investigate its impact on resistance dynamics and the burden of infection in men who have sex with men (MSM).
Methods and findings: Using a deterministic compartmental model of gonorrhea transmission in an MSM population, we introduced DoxyPEP at various uptake levels (10-75%) and compared 20-year prevalence and resistance dynamics relative to those at baseline (i.e., no DoxyPEP introduction). Uptake of DoxyPEP resulted in initial drops in the prevalence and incidence of gonorrhea infection, but also accelerated the spread of doxycycline resistance, with increasing DoxyPEP use driving steeper initial declines followed by faster spread of resistance. This resulted in the total loss of DoxyPEP's clinical efficacy within 1-2 decades in almost all scenarios explored. The magnitude by which DoxyPEP initially reduced the prevalence of infection was constrained by the extent of pre-existing doxycycline resistant strains in the population. De novo emergence of doxycycline resistance did not influence these dynamics. Additionally, the implementation of DoxyPEP had minimal impact on extending the clinically useful lifespan of ceftriaxone monotherapy.
Conclusions: Model findings suggest DoxyPEP can be an effective but short-term solution for reducing the burden of gonorrhea infection, as its selection for doxycycline-resistant strains results in loss of its prophylaxis benefit. Increasing levels of DoxyPEP uptake and higher starting prevalence of doxycycline resistance resulted in faster loss of its efficacy and had little change on extending the clinical lifespan of ceftriaxone for treatment of N. gonorrhoeae infections.