Hydroxychloroquine

How it works

It accumulates in lysosomes and raises intracellular pH, interfering with antigen processing, Toll-like receptor signalling and cytokine production to produce its immunomodulatory effect.

Prescribing in practice

• Irreversible retinal toxicity (maculopathy) is the principal long-term risk, so dose by ideal body weight, arrange baseline and annual screening after the early years of therapy (per Royal College of Ophthalmologists guidance), and avoid exceeding recommended weight-based limits.
• It can prolong the QT interval and cause cardiomyopathy with long-term use; use caution with other QT-prolonging drugs and pre-existing cardiac disease.
• Caution is needed in G6PD deficiency, hepatic or renal impairment, and with concurrent drugs that lower the seizure threshold.

Monitoring

Arrange retinal screening as recommended and monitor for visual symptoms, with assessment of cardiac, hepatic and renal status as clinically indicated.

Counselling the patient

• Attend your eye-screening appointments and report any change in vision or colour perception.
• It may take several weeks to months to work, so continue taking it regularly.
• Keep well out of reach of children, as overdose is dangerous.

Evidence & guidelines

Hydroxychloroquine is a well-established DMARD with efficacy in lupus and rheumatoid arthritis supported by long clinical use and reflected in NICE and specialist society guidance, including retinopathy screening recommendations.