Inclusion Criteria:  Patients aged ≥ 18 years Patients who, after the nature of the study has been explained to them, and before any protocol-specific procedures are performed, give informed consent in writing, in accordance with local regulatory requirements Patients with or without HIV infection and with syphilis infection in the early stages according to CDC criteria (primary syphilis, secondary syphilis and early latent syphilis of less than one year's duration) Patients with a positive non-treponemal assay result Patients available for participation and follow-up during the 6 months of the study Patients covered by the French health insurance system  Exclusion Criteria:  Individuals with a history of known hypersensitivity to doxycycline or any other antibiotic of the tetracycline family, BPG (hypersensitivity to the active substance benzathine benzylpenicillin, to other penicillins, to soy phospholipids, peanuts or any of the excipients in the product ; history of severe immediate hypersensitivity reactions (eg anaphylaxis) to other beta-lactams (examples: cephalosporins, carbapenemes or monobactams), lidocaïne (hypersensitivity to lidocaine hydrochloride, amide-linked local anesthetics, or any of the excipients listed in SPC) and / or any of the excipients of the specialties used in the study Patients with a negative non-treponemal assay result Patients receiving an anticoagulant therapy Individuals with contraindications for either of the study drugs Individuals treated with retinoids by general route Individuals with early and late neurosyphilis Individuals requiring doxycycline treatment Individuals with late syphilis, whether or not latent (e.g. cutaneous) Individuals with thrombocytopenia or coagulation disorders contraindicating intramuscular injections Women who are pregnant or breast-feeding, or of childbearing age not using or planning to use acceptable birth control measures; Individuals under a measure of legal protection or unable to consent Individuals participating in any clinical trial with another investigational product in the 28 days preceding the first study visit or intending to participate in another clinical study at any time during the course of this study. Recent exposure