Critical Clarification: This Question Appears to Confuse HIV Treatment with Rabies Vaccination
The question conflates "ARV" (antiretroviral therapy for HIV) with vaccine administration routes, which is a fundamental category error—antiretrovirals are oral/IV medications for HIV treatment, not vaccines administered IM or ID. If this question actually refers to rabies post-exposure prophylaxis (PEP), where "ARV" means anti-rabies vaccine, the answer is entirely different than if discussing HIV antiretroviral therapy.
If This Question Is About Rabies Vaccination (Most Likely Interpretation):
Do Not Switch Routes Mid-Series
Switching from intramuscular (IM) to intradermal (ID) rabies vaccination mid-regimen is not recommended and should be avoided. The rabies vaccine series must maintain consistency in route, dose, and schedule to ensure adequate immunogenicity and protection against this universally fatal disease.
Key Principles:
Complete the series as started: If rabies PEP was initiated via IM route (1.0 mL doses), continue all subsequent doses IM at the same dosing schedule 1, 2
ID and IM are not interchangeable protocols: The ID route uses reduced antigen doses (0.1 mL) compared to IM (1.0 mL), with different immunologic kinetics and schedules 1, 2
Mortality risk is absolute: Rabies has >99% case fatality rate once clinical symptoms develop, making any compromise in vaccine efficacy unacceptable from a mortality standpoint
Clinical Pitfalls:
Switching routes mid-series creates uncertainty about adequate immune response, as the two routes have different dose-response relationships 1, 3, 4
No clinical trial data support the safety or efficacy of mixed-route rabies vaccination regimens 1
If a switch is unavoidable due to supply issues, expert consultation is mandatory and serologic testing (rabies virus neutralizing antibody titers) should be performed to confirm adequate response 2
If This Question Is About HIV Antiretroviral Therapy (Less Likely but Addressed):
This interpretation makes no clinical sense, as antiretroviral medications for HIV (NRTIs, NNRTIs, PIs, INSTIs) are administered orally or intravenously, not via IM or ID injection routes. The guidelines provided 5, 6, 7 discuss changing antiretroviral drug regimens due to treatment failure, toxicity, or resistance—not changing routes of administration, because such routes do not exist for standard HIV treatment.
If Referring to HIV Vaccine Research:
Research on HIV vaccine candidates (DNA vaccines, adenoviral vectors) has compared IM versus ID routes, but these are investigational vaccines, not approved HIV treatment 1, 8
Studies show no significant immunogenicity advantage of ID over IM routes for HIV vaccine candidates, with ID causing more local reactions 1
These experimental vaccines are not part of clinical HIV management and are irrelevant to treating HIV-infected patients 1, 8
Clinical Action Required: Clarify whether this question concerns rabies post-exposure prophylaxis or another vaccine, as the current phrasing creates dangerous ambiguity in a life-threatening context.