In a patient with restless legs syndrome previously controlled with gabapentin 600 mg at bedtime who has been uncontrolled for three weeks, what workup is indicated?

Workup for Uncontrolled RLS on Gabapentin 600 mg

Check serum ferritin and transferrin saturation immediately—this is the single most critical workup step for any patient with uncontrolled RLS, as iron deficiency is a reversible cause that fundamentally influences treatment decisions. 1

Essential Laboratory Testing

The 2025 AASM guidelines establish iron studies as a good practice statement for all patients with clinically significant RLS 1. Specifically:

• Serum ferritin and transferrin saturation (calculated from iron and total iron binding capacity)
• Draw in the morning, avoiding all iron-containing supplements and foods for at least 24 hours prior
• These results directly determine whether to add or switch to iron therapy

Iron Supplementation Thresholds

Based on the iron studies results 1:

• Ferritin ≤75 ng/mL OR transferrin saturation <20%: Institute oral or IV iron
• Ferritin 75-100 ng/mL: Use IV iron only (not oral)
• Ferritin >100 ng/mL: Iron supplementation not indicated

Review Exacerbating Factors

Before escalating pharmacotherapy, systematically assess 1:

• Medications: Antihistamines, serotonergic agents (SSRIs, SNRIs), antidopaminergic medications (antipsychotics, metoclopramide)
• Substances: Alcohol, caffeine intake
• Comorbidities: Untreated obstructive sleep apnea
• Pregnancy status (if applicable)

Medication Adjustment Algorithm

If iron studies are adequate and exacerbating factors are addressed, the gabapentin dose is likely insufficient:

Option 1: Optimize Current Gabapentin Therapy

• Current dose (600 mg) is below the therapeutic range demonstrated in clinical trials 2
• Increase to 1200-1800 mg/day divided three times daily
• Studies showed responder rates of 16% at 1200 mg/day and 26% at 1800 mg/day versus 8% for placebo 2

Option 2: Switch to Gabapentin Enacarbil

• Strong recommendation from AASM guidelines 1
• Dose: 600 mg once daily (FDA-approved dose)
• Superior pharmacokinetics with sustained absorption compared to immediate-release gabapentin 3, 4
• Demonstrated 64% responder rate at 600 mg and 74% at 1200 mg in severe RLS 3

Option 3: Switch to Pregabalin

• Strong recommendation from AASM guidelines 1
• Alternative alpha-2-delta ligand with more predictable absorption
• Typical dosing: 150-450 mg/day

Option 4: Add IV Iron (if ferritin 75-100 ng/mL)

• Ferric carboxymaltose has strong recommendation 1
• Can be combined with continued gabapentin therapy

Common Pitfalls to Avoid

1. Do not add a dopamine agonist at this stage—the 2025 AASM guidelines now suggest against standard use of pramipexole, ropinirole, and rotigotine due to augmentation risk with long-term use 1

2. Do not assume the current gabapentin dose is adequate—600 mg is at the lower end of the therapeutic range 2

3. Do not skip iron studies—this is explicitly a good practice statement that should be followed in all cases 1

4. Do not overlook medication interactions—gabapentin absorption is reduced by 20% with antacids containing aluminum/magnesium hydroxide 2

Additional Considerations

If the patient has renal impairment, gabapentin dosing requires adjustment as it is renally cleared 2. Check creatinine clearance if not recently done.

If symptoms include significant pain, gabapentin remains an appropriate choice, but ensure adequate dosing before switching agents 5.

The workup should be completed efficiently—iron studies can be drawn immediately, exacerbating factors reviewed at the same visit, and medication adjustment initiated within 1-2 weeks based on results.