Table 1 Participant eligibility criteria for participation in the SMILES trial

Aged between 3.00 and 7.99 years

Developmental or psychiatric disorders including craniofacial abnormalities, neuromuscular disorder, and other chronic conditions

HbSS or HbSβ₀ thalassaemia diagnosed by standard techniques (HPLC, IEF, MS or alkaline electrophoresis, DNA analysis, family studies)

Patient already taking/prescribed montelukast

History of sleep-disordered breathing (SDB), (i.e. caregiver-reported symptoms of SDB or any abnormality on overnight oximetry compared with published data in children of the same age (e.g. nadir SaO₂ < 93%; mean SaO₂ < 96%))

The patient has experienced side effects or an adverse reaction to montelukast at any time the past

Patient in a steady-state (i.e. haemoglobin not decreased by > 10% during the previous year, no painful episodes requiring opioids for at least 1 month and at least 1 month after any hospital admission)

Patient on CYP 3A4, 2C8, and 2C9 inducers, such as phenytoin, phenobarbital, and rifampicin

Likely to comply with treatment for 3 months as determined by the local paediatrician or haematologist

Presence or history of another haemoglobinopathy or blood dyscrasia

Able to speak and understand English

Concomitant treatment with any other leukotriene antagonist within the enrolment period

Enrolled concurrently in any other SCA/montelukast trials