Hydroxychloroquine (Ophthalmic Toxicity Monitoring)

SCOPE — READ FIRST: hydroxychloroquine is not an ophthalmic drug; this page exists for the ophthalmic toxicity monitoring of the SYSTEMIC oral dose, and that oral regimen is what is published here. The RCOphth 2018 monitoring schedule and its '5 mg/kg/day ideal body weight' threshold are NOT in this bundle and are not reproduced. VERBATIM (eMC §4.2, 'Adults (including the elderly)'): 'The minimum effective dose should be employed. This dose should not exceed 6.5/kg/day (calculated from ideal body weight) and will be either 200mg, 300mg or 400mg per day. In patients able to receive 300mg daily: Initially 300mg daily in a single dose. The dose can be reduced to 200mg when no further improvement is evident. The maintenance dose should be increased to 300mg daily if the response lessens.' (The SPC prints '6.5/kg/day' without a unit; the paediatric paragraph of the same section states the unit as '6.5mg/kg/day based on ideal body weight'.) THE SAFETY CEILING IS PER-KG AND SO CANNOT SIT IN maxDose — it is recorded here instead, and the two labels DISAGREE: UK SPC, must not exceed 6.5 mg/kg/day calculated from IDEAL body weight; US label §2.3 (cross-check), 'Daily doses exceeding 5 mg/kg (actual weight) of hydroxychloroquine sulfate increase the incidence of retinopathy'. Different number AND different weight basis — check which your local guideline follows. Neither label states an absolute mg/day maximum, so maxDose is empty. ONSET AND REVIEW: 'Hydroxychloroquine is cumulative in action and will require several weeks to exert its beneficial effects, whereas minor side effects may occur relatively early. For rheumatic disease treatment should be discontinued if there is no improvement by 6 months. In light-sensitive diseases, treatment should only be given during periods of maximum exposure to light.' RETINOPATHY (§4.4, verbatim): 'The occurrence of retinopathy is uncommon if the recommended daily dose is not exceeded. The administration of doses in excess of the recommended maximum is likely to increase the risk of retinopathy, and accelerate its onset. Other risk factors are concomitant tamoxifen use and impaired renal function (estimated glomerular filtration rate of less than 60ml/min/1.73m2)... It should be emphasized that the lowest effective dose should be used to minimize the risk of ocular toxicity. Hydroxychloroquine sulfate should be discontinued immediately in any patient who develops a pigmentary abnormality, visual field defect, or any other abnormality not explainable by difficulty in accommodation or presence of corneal opacities. Patients should continue to be observed for possible progression of the changes. Patients should be advised to stop taking the drug immediately and seek the advice of their prescribing doctor if any disturbances of vision are noted, including abnormal colour vision.' US dosing for the same systemic indications, for cross-reference only: rheumatoid arthritis initial 400 mg to 600 mg daily, chronic 200 mg to 400 mg daily; systemic lupus erythematosus and chronic discoid lupus erythematosus 200 mg once daily, or 400 mg once daily or in two divided doses. Do not crush or divide the tablets (US label). Some sections of the product information we used were incomplete — check the full SPC.

dosePerKg is DELIBERATELY null: the only per-kg number in the SPC is a CEILING, not a recommended dose, and feeding a ceiling to a weight calculator would output the maximum permissible dose as though it were the dose to give. VERBATIM (eMC §4.2, Paediatric Population): 'The minimum effective dose should be employed and should not exceed 6.5mg/kg/day based on ideal body weight. The 300mg tablet is therefore not suitable for use in children with an ideal body weight of less than 46kg.' Two further reasons a calculator cannot be used safely here: the ceiling is based on IDEAL body weight, which a plain weight entry does not capture, and the tablet strengths cannot be divided — the US label states 'Hydroxychloroquine sulfate tablets are not recommended in pediatric patients less than 31 kg because the lowest available strength (200 mg) exceeds the recommended dose for these patients and it cannot be divided' and that the film-coated tablets cannot be crushed or divided. The US label also states that safety and effectiveness in paediatric patients have NOT been established for rheumatoid arthritis, chronic discoid lupus erythematosus or systemic lupus erythematosus. Verify any under-18 dose against a children's formulary and paediatric rheumatology advice, and arrange the same ophthalmic monitoring.