What is the treatment regimen for a patient prescribed hydroxychloroquine (Plaquenil) 200mg, with 100 tablets available, for conditions such as rheumatoid arthritis or lupus?

Hydroxychloroquine (Plaquenil) 200mg Dosing Regimen

For rheumatoid arthritis and systemic lupus erythematosus, hydroxychloroquine should be dosed at ≤5 mg/kg actual body weight per day, typically starting at 200-400 mg daily, with mandatory dose reduction of 25% when eGFR <30 ml/min per 1.73 m². 1

Standard Dosing by Indication

Systemic Lupus Erythematosus (SLE)

• Start with 200 mg once daily or 400 mg once daily (can be divided into twice-daily dosing if gastrointestinal side effects occur) 1, 2
• Maximum safe dose is ≤5 mg/kg actual body weight per day to maintain retinopathy risk below 2% over 10 years 1
• All patients with SLE should receive hydroxychloroquine unless contraindicated, as it reduces disease flares, prevents organ damage, and improves survival 3, 1, 2
• For lupus nephritis (Class III/IV), hydroxychloroquine is strongly recommended as adjunctive therapy alongside immunosuppressives 3

Rheumatoid Arthritis

• Typical dosing is 200-400 mg daily 1, 4
• The 200 mg daily dose is as effective as 400 mg daily but with three times fewer side effects 5
• Long-term continuation rates are lower in RA (46% at 24 months) compared to SLE (76% at 24 months), primarily due to inadequate disease control rather than toxicity 6

Critical Dosing Adjustments

Renal Impairment

• Reduce dose by 25% when eGFR <30 ml/min per 1.73 m² 1, 2
• Reduced renal function is the greatest additional risk factor for retinopathy 1
• Patients with eGFR <60 ml/min require earlier ophthalmologic screening (after 1 year instead of 5 years) 1

Body Weight Considerations

• Always use actual body weight for dose calculation, not ideal body weight 1
• Retinopathy risks are statistically similar across BMI groups (15-35 kg/m²) when actual body weight is used 1
• Lower doses (2-3 mg/kg/day) may not achieve adequate blood levels and are associated with higher flare rates in lupus nephritis 1

Pre-Treatment Requirements

Mandatory Baseline Testing

• G6PD testing in men of African, Asian, or Middle Eastern origin to prevent hemolysis risk 1, 2
• Baseline ECG due to QT prolongation and cardiomyopathy risk 7, 1
• Baseline renal function (eGFR) to determine if dose adjustment needed 1, 2
• Baseline ophthalmologic examination within first few months of therapy 1

Monitoring Requirements

Ophthalmologic Surveillance

• Annual screening beginning after 5 years for low-risk patients 1, 2
• Annual screening beginning after 1 year for high-risk patients (eGFR <60 ml/min, daily dose >5 mg/kg, concomitant tamoxifen use, pre-existing retinal disease) 1
• East Asian patients require screening beyond central macula due to different retinopathy phenotype (pericentral vascular arcade involvement) 1

Disease Activity Monitoring

• For SLE: Monitor disease activity at least once per trimester during pregnancy with clinical history, examination, CBC, urinalysis, protein:creatinine ratio, anti-DNA, C3, and C4 levels 3
• For lupus nephritis: Regular monitoring frequency varies with clinical status and medications 3

Supply Duration with 100 Tablets

At 200 mg Daily Dosing

• 100 tablets provides 100 days (approximately 3.3 months) of therapy 4

At 400 mg Daily Dosing

• 100 tablets provides 50 days (approximately 1.7 months) of therapy 4

Critical Safety Considerations

Primary Risk Factors for Retinopathy

• Daily dose >5 mg/kg actual body weight 1
• Duration of treatment 1
• Chronic kidney disease 1
• Concomitant tamoxifen use 1
• Pre-existing retinal or macular disease 1

Cardiomyopathy Risk

• Risk factors include high cumulative exposure, treatment duration, renal impairment, and concomitant cardiotoxic agents 7
• If cardiomyopathy develops, immediate cessation combined with heart failure management can halt progression and even improve clinical status 7

Common Pitfalls to Avoid

• Do not use ideal body weight for dosing calculations—this increases retinopathy risk 1
• Do not fail to adjust for renal impairment—this is the greatest modifiable risk factor for toxicity 1
• Do not use inadequate doses (2-3 mg/kg/day)—these may not achieve adequate blood levels and increase flare rates 1
• Do not discontinue hydroxychloroquine casually in SLE patients—the goal is safe long-term maintenance 1
• Do not miss pericentral toxicity in East Asian patients—they require expanded screening fields 1

Pregnancy Considerations

• All women with SLE should continue hydroxychloroquine during pregnancy if already taking it 3
• If not already taking it, conditionally recommend starting unless contraindicated 3
• Women should be counseled to delay pregnancy until complete remission of lupus nephritis is achieved 3
• Add low-dose aspirin (81 mg daily) starting in first trimester for preeclampsia prophylaxis 3

Drug Interactions

• Avoid concomitant use with other QT-prolonging medications 4
• Monitor closely if used with insulin or antidiabetic drugs due to hypoglycemia risk 4
• Avoid antacids and kaolin within 4 hours of hydroxychloroquine dose 4