Clinical trial data can be difficult to interpret and understand. In this piece, we will try to simplify and summarise what the clinical trial data for ritlecitinib shows.

718 people aged 12 years or older with severe alopecia areata were included in the trial, for an initial period of 24 weeks. The 24-week data can be summarised as follows:

• Patients given the highest dose of 200mg + 50mg (daily) for weeks 1-4 (known as a loading dose), then 50mg for weeks 4-24, 31% achieved a SALT score of 20 or less after 24 weeks. 
• Patients given 50mg (daily), 23% achieved a SALT score of 20 or less after 24 weeks.
• Patients given 200mg + 30mg (daily) for weeks 1-4 (loading dose), then 30mgs for weeks 4-24, 22% achieved a SALT score of 20 or less after 24 weeks.
• Patients given 30mg (daily), 14% achieved a SALT score of 20 or less after 24 weeks.
• Patients given the placebo (0mg), 2% achieved a SALT score of 20 or less after 24 weeks.

After the initial 24 weeks, a second 24 week ‘extension period’ followed in which those on ritlecitinib continued the same dose and those on the placebo switched to 50mg daily, or 200mg loading dose + 50mg. To avoid bias in the results, neither the investigators nor the patients knew which dose patients were receiving. This is called double-blinding. A double-blind randomised controlled trial is considered the gold standard level of proof where testing new treatments are concerned. The 48-week data can be summarised as follows:

• Patients given the loading dose and then 50mg, 40% achieved a SALT score of 20 or less after 48 weeks.
• Patients given 50mg (daily), 43% achieved a SALT score of 20 or less after 48 weeks.
• Patients given the loading dose and then 30mg, 34% achieved a SALT score of 20 or less after 48 weeks.
• Patients given 30mg (daily), 31% achieved a SALT score of 20 or less after 48 weeks.
• For those who switched from placebo to 200mg + 50mg (daily) for weeks 24-28, then 50mg for weeks 28-48, 34% achieved a SALT score of 20 or less after 48 weeks.  
• For those who switched from placebo to 50mg (daily), 19% achieved a SALT score of 20 or less after 48 weeks.

Common side effects reported in the trial were headaches, colds and infections. The proportion of serious adverse events during the trial was very low, and the drug was generally safe and well-tolerated.

In summary, the clinical trial data showed that ritlecitinib is effective in regrowing hair in up to 43% of patients after 48 weeks. A trial to monitor long-term safety and effectiveness is ongoing.

For anyone interested, a graphical abstract of the trial can be found here.