Last updated on November 18th, 2025 at 06:25 pm

Possible reasons to switch

• S1P modulators are highly effective DMTs and they have been shown to:
  • decrease relapse rates
  • reduce the development of new lesions visible on magnetic resonance imaging
  • reduce disability worsening
  • slow down brain volume loss.
• For people with MS currently on natalizumab and concerned about progressive multifocal leukoencephalopathy (PML), switching to an S1P modulator may reduce the risk of carry-over PML.

Reasons for caution

• S1P modulators cause a transient slowing of the heart rate; they are not recommended if you are already taking medicine(s) that slow your heart rate.
• They cause systemic immunosuppression, which increases the risk of opportunistic infections, for example PML and cryptococcal fungal infections, and secondary malignancies.
• Rebound MS disease activity often occurs when S1P modulators are stopped.
• Visual disturbances can develop owing to swelling of the macula (the central part of the retina). The risk of macular oedema is increased if you have a history of inflammation in the eye or diabetes mellitus.
• Most neurologists will avoid using S1P modulators in patients with pre-existing liver or lung disease.
• Testing for human papillomavirus infection is recommended prior to starting treatment.
• People with MS at high risk of skin lesions (e.g. from previous severe sun damage and/or skin cancer) should be referred for regular skin cancer screening.
• Women of child-bearing potential should avoid pregnancy and breast feeding.

Interferon and glatiramer acetate

In general, S1P modulators can be started immediately after discontinuation of interferon or glatiramer acetate. It is important that all the recommended baseline screening tests and vaccination reviews are done before starting S1P modulators.

S1P modulator to S1P modulator switch

In general, switching from one S1P modulator to another is possible. I would recommend rechecking baseline investigations before making the switch and ensuring a 4-week washout with fingolimod, siponimod and ozanimod prior to starting the new agent. With ponesimod, I limit the washout to 7 days. Overlapping the washout of one S1P modulator with the titration phase of the newer agent should prevent rebound activity and limit off-target effects, particularly cardiac events.

Natalizumab

Most often the reason for switching from natalizumab to an S1P modulator is to reduce the risk of carry-over PML from natalizumab. In our centre, we do an MRI and lumbar puncture for cerebrospinal fluid analysis to exclude JC virus DNA on PCR (polymerase chain reaction test). Provided these two tests are clear, we typically initiate S1P modulators within 4 weeks of the last natalizumab infusion. A prolonged wash-out period (8 weeks or longer) is associated with rebound disease activity on stopping natalizumab and is therefore not recommended. It is important that all the recommended baseline screening tests and vaccination reviews are done before starting an S1P modulator.

Teriflunomide

Because teriflunomide has such a long half-life, some neurologists would recommend an accelerated washout using cholestyramine or activated charcoal. Rheumatologists rarely do this when switching patients with rheumatoid arthritis from leflunomide (teriflunomide prodrug) to other DMTs, so I am not sure this accelerated washout is necessary. It is important that all the recommended baseline screening tests and vaccination reviews are done before starting an S1P modulator.

If the main reason for switching from teriflunomide is leukopaenia or lymphopaenia I would recommend waiting for the neutrophil and lymphocyte counts to go above 1,000/mm³ and 800/mm³ respectively. Similarly, if the switch is for abnormal LFTs on teriflunomide you would ideally want the liver enzymes to normalise or at least drop to below 3x the upper limit of normal.

Fumarates

It is important that all the recommended baseline screening tests and vaccination reviews are done before starting an S1P modulator. If the main reason for switching from a fumarate is lymphopaenia, I would recommend first waiting for the peripheral blood neutrophil and lymphocyte counts to go above 1,000/mm³ and 800/mm³, respectively.

Alemtuzumab

It is important that all the recommended baseline screening tests and vaccination reviews are done before starting an S1P modulator. I would recommend first waiting for the total peripheral blood neutrophil and lymphocyte counts to go above 1,000/mm³ and 800/mm³, respectively.

Anti-CD20 therapies (selective cell depleting DMTs)

It is important that all the recommended baseline screening tests and vaccination reviews are done before starting an S1P modulator.

Cladribine (selective cell depleting DMT)

It is important that all the recommended baseline screening tests and vaccination reviews are done before starting an S1P modulator. I would recommend first waiting for the total peripheral blood neutrophil and lymphocyte counts to go above 1,000/mm³ and 800/mm³, respectively.

Mitoxantrone

It is important that all the recommended baseline screening tests and vaccination reviews are done before starting an S1P modulator. I would recommend first waiting for the total peripheral blood neutrophil and lymphocyte counts to go above 1,000/mm³ and 800/mm³ respectively.

HSCT

It is important that all the recommended baseline screening tests and vaccination reviews are done before starting an S1P modulator. I would recommend first waiting for the peripheral blood neutrophil and lymphocyte counts to go above 1,000/mm³ and 800/mm³ respectively.