Can I switch from shots to drops — do I start over?

Yes. The switch is medically safe and clinically straightforward, though it is considered a new treatment course rather than a seamless continuation. Here is what the published evidence says about how, when, and whether to make the transition.

The Brazilian Association of Allergy and Immunology (ASBAI) published the only formal position paper on route switching in 2024 (Aarestrup et al., PMID: 38975257). Key recommendations: preferably use allergen extracts from the same supplier for both SCIT and SLIT; if the SCIT patient has completed induction, start SLIT at maintenance doses from the beginning (no re-escalation needed); no formal washout period is required between stopping SCIT and starting SLIT; the immunomodulation from both routes may be complementary; and initial clinical evaluation should occur monthly after the switch.

No published guidelines from AAAAI, ACAAI, EAACI, or WAO specifically address mid-course SCIT-to-SLIT switching. The Joint Task Force Practice Parameters and EAACI Guidelines on AIT address each route separately without transition protocols.

The largest published dataset on route switching comes from Pajno et al. (2013, PMID: 24169060), who surveyed 4,933 children receiving immunotherapy over 18 years. Of 648 SCIT patients, 54 (8.3%) switched to SLIT. In 85% of cases, the reason was local or systemic side effects from shots — not poor efficacy. Safety was confirmed: no increase in adverse events from the switch.

During COVID-19, the EAACI international survey (Pfaar et al. 2021, PMID: 33655519) of 417 respondents found 16% of physicians switched SCIT patients to SLIT during induction and 6% during maintenance. No tolerability concerns arose. The ARIA-EAACI statement (Klimek et al. 2020, PMID: 32329930) recommended SLIT at home supported by telemedicine during the pandemic — validating home-based SLIT as a viable alternative when clinic access is limited.

If you are in year 4 of a 5-year shot course, finish the shots. The immune tolerance you have built is substantial, and switching to SLIT at this point means starting a new 3-year treatment course — potentially adding years to your total treatment time. The cost of one more year of shots (even with copays) is likely less than 3 new years of SLIT.

The math changes if side effects are the driver. SCIT systemic reactions are more common and more severe than SLIT reactions. If you are experiencing repeated systemic reactions despite dose adjustments, switching to SLIT is medically justified regardless of where you are in the shot timeline.

Save your money if you are close to completing your shot course (year 4-5 of 5) and tolerating shots well — finishing is faster and cheaper than restarting with drops. Save your money if your reason for switching is cost alone and your insurance covers shots with low copays — shots with insurance may be cheaper than self-pay SLIT at $99-110/month. Save your money if your allergies are mild enough that you could simply stop immunotherapy altogether — if Zyrtec at $15/month handles your symptoms, you may not need either route.