Treatment Responses of Early Syphilis to Single-dose Ceftriaxone Plus Doxycycline Versus Single-dose Benzathine Penicillin G Plus Doxycycline in People Living With HIV (PLWH)
Phase: PHASE4
Conditions: Early Syphilis
Sponsor: National Taiwan University Hospital

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Comparisons of treatment responses of early syphilis to 1.0 g single-dose ceftriaxone plus 
doxycycline versus 2.4 MU single-dose benzathine penicillin G plus doxycycline in people 
living with HIV 

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Background 
While improvement of access to antiretrovirals for HIV treatment and prevention 
continue and the case numbers of newly diagnosed HIV infection have stabilized or 
decreased, sexually transmitted infections (STIs) have been increasing worldwide since late 
1990s.1 Concurrent with the increases in established STIs are emerging epidemics of non-
classical sexually transmissible pathogens and co-infections with more than one STI. 
Furthermore, increases in antimicrobial resistance have limited therapeutic options for STIs, 
particularly Neisseria gonorrhoeae and Mycoplasma genitalium infections.2  
 
In Taiwan, we had experienced epidemics and outbreaks of non-classical STIs 
predominantly affecting men who have sex with men (MSM) living with HIV, such as 
shigellosis since 2015, acute hepatitis A during 2015-2017, and acute hepatitis C since 2017.3-
5 In addition, syphilis and gonorrhea have been increasingly reported as notifiable diseases 
over the past decade, while the incidence of HIV infection has significantly decreased since 
2018. To facilitate early detection and treatment of individuals with STIs, we have 
established regular screening for chlamydia, gonorrhea, and syphilis in people living with 
HIV (PLWH) and MSM receiving pre-exposure prophylaxis (PrEP) in our hospital. In our 
prospective study investigating the prevalence of STIs among at-risk PLWH, the prevalence 
of Chlamydia trachomatis and N. gonorrhoeae was 24.7% and 12.1%, respectively. 
Surprisingly, we found high rates of C. trachomatis and/or N. gonorrhoeae co-infections in 
PLWH with recent hepatitis C virus (HCV) infection (50%), HBsAg positivity (44%), and 
early syphilis (36%).6 Although C. trachomatis co-infections have been reported in 20-42% 
of individuals with N. gonorrhoeae infections, few studies document the prevalence of C. 
trachomatis and N. gonorrhoeae co-infections among patients with syphilis and viral 
hepatitis. However, a recent sub-study nested in a randomized controlled trial comparing the 
efficacy of single dose versus 3 weekly doses of benzathine penicillin G (BPG) for early 
syphilis also showed a high rate of sexually transmitted co-infections (27%) in patients with 
early syphilis, including C. trachomatis, N. gonorrhoeae, and non-gonococcal urethritis.7 The 
findings highlight the importance of integrating bacterial STI screening and treatment into 
management of early syphilis.  
Benzathine penicillin G (BPG) (2.4 million units [MU] intramuscularly once) has 
been the recommended treatment for early syphilis, but is not effective for treating C. 
trachomatis and N. gonorrhoeae co-infections.8 The recurrence of BPG shortages has also 
created an urgent need to identify other alternative treatment that is as effective as BPG for 
treating early syphilis. Ceftriaxone and doxycycline have been the alternative treatments for 

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early syphilis; in addition, ceftriaxone (500 mg intramuscularly once) is effective for treating 
N. gonorrhoeae infection, and doxycycline (100 mg orally twice daily for 7 days) effective 
for treating C. trachomatis infection.8 However, the current suggested dose of ceftriaxone for 
early syphilis (1 g intramuscularly or intravenously once daily for 10-14 days) is 
inconvenient as an outpatient treatment option. Ceftriaxone is long-acting, with 
treponemacidal levels remaining at 24 hours following injection. According to a small 
clinical trial, single-dose ceftriaxone achieved a serological response similar to that of BPG.9 
Considering the high rate of sexually transmitted co-infections, combination therapy of 
single-dose ceftriaxone plus 7-day doxycycline for early syphilis may provide convenience 
and benefit to treatment of N. gonorrhoeae and C. trachomatis co-infections at a single clinic 
encounter. In the present study, we aim to compare the efficacy of ceftriaxone plus 
doxycycline versus BPG plus doxycycline as the treatment for early syphilis among PLWH.  
 
Methods 
1. Study design: randomized controlled, open-label, non-inferiority study 
2. Study site: infectious diseases clinics at the National Taiwan University Hospital (NTUH) 
3. Study duration: 2022-2025 
4. Enrolled criteria:  
(1) PLWH aged 20 years or more  
(2) PLWH with early syphilis (i.e. primary, secondary, or early latent syphilis), confirmed by  
a positive rapid plasma reagin (RPR) titer with a reactive Treponema pallidum particle 
agglutination (TPPA) assay. 
(3) PLWH has provided informed consent  
*A participant with repeated syphilis can be repeated enrolled after signing an informed 
consent if the previous episode of early syphilis was successfully treated with achieving at 
least a 4-fold decrease in RPR titers and 48-week follow-up is completed. 
5. Exclusion criteria: 
(1) PLWH with RPR titers of less than 4  
(2) Exposure to antibiotics with activity against T. pallidum, such as penicillins, third-
generation cephems, doxycycline, or macrolides, within the preceding 4 weeks 
(3) A known or suspected infection other than syphilis requiring additional treatment with an 
antimicrobial active against T. pallidum  
(4) A history of intolerance to penicillin, ceftriaxone, or doxycycline 
(5) Pregnancy 

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6. Study procedures: participants will be randomized in a 1:1 ratio to receive ceftriaxone 
plus doxycycline or BPG plus doxycycline. Randomization will be stratified by the stage of 
syphilis and RPR titer at baseline. 
Arm 1: single-dose ceftriaxone (1g intramuscularly once) plus doxycycline (100 mg orally 
twice daily for 7 days) 
Arm 2: single-dose BPG (2.4 MU intramuscularly once) plus doxycycline (100 mg orally 
twice daily for 7 days) 
7. Baseline and follow-up testing:  
Proof of concept phase: (enrolled 50 participants in each group) 
(1) Questionnaire for socio-epidemiologic characteristics and sexual history at baseline and 
weeks 24, 48 
(2) Serum RPR at baseline and weeks 4, 12, 24, 36, and 48 
(3) T. pallidum PCR (TP-PCR) for self-collected specimens from oral rinse, urethral, and 
rectal sites at baseline, weeks 1, 2, 3, 4, 12, 24, 36, and 48 (specimens collected in weeks 1, 2, 
and 3 were optional) 
(4) Bacterial STIs (C. trachomatis, N. gonorrhoeae, Mycoplasma genitalium, M. hominis, 
Ureaplasma urealyticum, U. parvum) for self-collected specimens from oral rinse, urethral, 
and rectal sites at baseline and week 4  
(5) Resistance-associated mutations (RAM) of T. pallidum and other sexually transmitted 
bacteria at baseline  
 
Baseline 
Wk1 
(±2 
days) 
Wk2 
(±2 
days) 
Wk3 
(±2 
days) 
Wk4 
(±2 
days) 
Wk12 
(±2 weeks) 
Wk24 
(±2 weeks) 
Wk36 
(±2 weeks) 
Wk48 
(±2 weeks) 
Questionnaire 
v 
 
 
 
 
 
v 
 
v 
Doxycycline 
compliance 
record 
 
v 
 
 
 
 
 
 
 
RPR 
v 
 
 
 
v 
v 
v 
v 
v 
TP-PCR 
v 
v 
v 
v 
v 
v 
v 
v 
v 
(optional) 
Bacterial STIs 
v 
 
 
 
v 
 
 
 
 
RAM 
v 
 
 
 
 
 
 
 
 
 
Continuation phase: (enrolled 100 participants in each group) 
(1) Questionnaire for socio-epidemiologic characteristics and sexual history at baseline and 

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weeks 24, 48 
(2) Serum RPR at baseline and weeks 4, 12, 24, 36, and 48 
(3) T. pallidum PCR (TP-PCR) for self-collected specimens from oral rinse, urethral, and 
rectal sites at baseline, weeks 4, 12, 24, 36, and 48 
(4) Bacterial STIs (C. trachomatis, N. gonorrhoeae, M. genitalium, M. hominis, U. 
urealyticum, U. parvum) for self-collected specimens from oral rinse, urethral, and rectal sites 
at baseline and week 4  
(5) Resistance-associated mutations (RAM) of T. pallidum and other sexually transmitted 
bacteria at baseline  
 
Baseline 
Wk1 
(±2 
days) 
Wk2 
(±2 
days) 
Wk3 
(±2 
days) 
Wk4 
(±2 
days) 
Wk12 
(±2 weeks) 
Wk24 
(±2 weeks) 
Wk36 
(±2 weeks) 
Wk48 
(±2 weeks) 
Questionnaire 
v 
 
 
 
 
 
v 
 
v 
Doxycycline 
compliance 
record 
 
v 
 
 
 
 
 
 
 
RPR 
v 
 
 
 
v 
v 
v 
v 
v 
TP-PCR 
v 
 
 
 
v 
v 
v 
v 
v 
Bacterial STIs 
v 
 
 
 
v 
 
 
 
 
RAM 
v 
 
 
 
 
 
 
 
 
 
8. Duration of study: Participants will be followed for at least 48 weeks. 
9. Primary outcome:  
Serologic response at month 6 (defined as either a 4-fold or greater decline in RPR titer 
compared to baseline or being RPR-nonreactive)  
10. Secondary outcomes:  
(1) Microbiologic response of syphilis (defined as T. pallidum PCR Ct value >38) at week 4  
(2) Microbiologic response of bacterial STIs (defined as negative PCR results) at week 4  
(3) Serologic response at months 3 and 12  
(4) Safety of study treatment recorded by using a diary (all adverse events will be coded and 
graded according to Common Terminology Criteria for Adverse Events [CTCAE] v4.0.) 
(5) Adherence evaluation (the noting of tablet intake in the diary for the 7 days of the 
treatment period) 
11. Futility stopping rules: 
(1) In the proof-of-concept phase, microbiologic and/or serologic response of syphilis 

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(microbiologic response was defined as T. pallidum PCR Ct value >38, and serologic 
response was defined as at least a 4-fold decrease in RPR titers) at week 4 will be compared 
between study groups. The non-inferiority margin of 10% will be used as the futility stopping 
rule in the proof-of-concept phase. 
(2) Participants with treatment failure at week 24 will receive standard-of-care treatment 
(BPG 2.4 MU intramuscularly once). Treatment failure is defined as at least a 4-fold increase 
in RPR titers compared with the baseline RPR or at least a 4-fold increase in RPR titers after 
achieving serologic response during follow-up. Participants who received additional 
treatment with an antimicrobial active against T. pallidum (i.e. penicillins, third-generation 
cephems, doxycycline, or macrolides) will also be excluded from the study. 
(3) The continuation phase will be conducted only if microbiologic response of syphilis is 
non-inferior in the ceftriaxone plus doxycycline group compared with the BPG plus 
doxycycline group. 
 
Laboratory investigations 
1. T. pallidum PCR: 
T. pallidum PCR will be performed on specimens from oral rinse, urine, rectal sites, blood, 
and lesions of syphilis. Treponemal DNA will be extracted with the QIAamp DNA mini Kit. 
The diagnostic PCR assay will be used to amplify the 47 kDa protein membrane gene 
(tpp47). 
2. Bacterial STIs screening: 
The screening for bacterial STIs, including C. trachomatis, N. gonorrhoeae, Trichomonas 
vaginalis, Mycoplasma spp., and Ureaplasma spp.) will be performed on self-collected 
specimens from oral rinse, urethral, and rectal sites with the use of multiplex real-time PCR 
assay on an automated system. 
3. Resistance-associated mutation of T. pallidum 
Single-nucleotide polymorphisms (SNPs) will be determined at positions A2058G or 
A2059G of the 23S rRNA gene, as well as positions 965–967, 926–928, 939 and 1058 of the 
16S rRNA gene. 
 
Statistical analysis 
According to the previous randomized controlled, open-label study conducted by Cao Y et al, 
the serological response of early syphilis at 6 months of follow up was observed in 90.2% in 
ceftriaxone group and 78.0% in BPG group.10 Therefore, at least 150 participants would be 

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required for each treatment group to detect a between-group difference, with a two-sided 
significance level of 5% and a power of 80%. The intention-to-treat population is defined as 
all patients who undergo randomization except for those who do not provide consent for the 
use of their data. The analyses will be performed through the FDA snapshot algorithm in the 
ITT population, which categorizes outcomes into success, failure, and no data in window. The 
Categorical variables will be compared by Fisher’s exact test or Chi-square test. Non-
categorical variables will be compared by Mann-Whitney U test. Factors with P value ≦0.2, 
or with biological significance will be included for multivariate analysis. Logistic regression 
analysis will be used to determine the factors associated with serologic responses after 
treatment. All comparisons will be two-tailed and a P value <0.05 is considered significant. 
All statistical analyses were performed with the use of STATA software version 17.0 (Stata 
Corporation, College Station, TX). 
 
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