Increase the Gabapentin Dose
The next best step is to increase the gabapentin dose, as the current 100 mg at bedtime is substantially below the therapeutic range for restless legs syndrome. The patient's iron parameters (ferritin 121 ng/mL, iron 81 mcg/dL) are adequate and do not require supplementation at this time.
Rationale for Dose Escalation
The patient is on gabapentin 100 mg nightly, which is far below the effective dose range. According to FDA labeling, gabapentin dosing for therapeutic effect typically ranges from 900-3600 mg daily in divided doses 1. While the 2025 AASM guidelines support gabapentin use in RLS patients 2, the current dose is subtherapeutic.
Target dose: Titrate gabapentin to 300-600 mg three times daily (900-1800 mg total daily dose). Start by increasing to 300 mg at bedtime, then add morning and afternoon doses over 3-7 days as tolerated 1.
Why Not Iron Supplementation?
The patient's ferritin of 121 ng/mL exceeds the threshold for iron supplementation. The 2025 AASM guidelines recommend iron therapy when ferritin is ≤100 ng/mL or transferrin saturation is <20% 2. Recent evidence suggests transferrin saturation ≤35% may predict better response to iron therapy 3, but with ferritin >100 ng/mL, iron is not the priority here.
Iron supplementation would be appropriate if ferritin were ≤100 ng/mL, at which point either oral ferrous sulfate (325-650 mg daily) or IV iron (ferric carboxymaltose 1000 mg) would be recommended 2, 4, 3.
Gabapentinoids as First-Line Therapy
The 2025 AASM guidelines and recent literature consistently support gabapentinoids (gabapentin, pregabalin, gabapentin enacarbil) as first-line pharmacologic therapy for RLS 2, 4, 5. In randomized trials, approximately 70% of patients treated with gabapentinoids showed much or very much improved symptoms versus 40% with placebo 4.
Gabapentinoids are now preferred over dopamine agonists (pramipexole, ropinirole, rotigotine) due to the 7-10% annual risk of augmentation—a paradoxical worsening of RLS symptoms that can be disabling 2, 4, 6.
Special Consideration: Diabetic Neuropathy
This patient has diabetes, raising the possibility of diabetic peripheral neuropathy contributing to nighttime leg pain. The prevalence of RLS in diabetic neuropathy ranges from 17.7-45% 5. Gabapentin is particularly advantageous here because it treats both RLS and neuropathic pain 5, 7.
Key Diagnostic Distinction
- RLS: Urge to move legs, worse with rest, relieved by movement, worse at night
- Diabetic neuropathy: Burning/tingling pain, not necessarily relieved by movement, no circadian pattern
If symptoms don't improve with adequate gabapentin dosing, consider nerve conduction studies to clarify the contribution of neuropathy 7.
Practical Titration Schedule
- Week 1: Increase to 300 mg at bedtime
- Week 2: Add 300 mg in morning (total 600 mg/day)
- Week 3: Add 300 mg afternoon dose (total 900 mg/day)
- Adjust: Titrate up to 1800 mg/day in divided doses if needed for symptom control 1
Monitor for dose-limiting side effects: somnolence (19% vs 9% placebo), dizziness (17% vs 7% placebo), and ataxia (13% vs 6% placebo) 1.
When to Consider Alternative Therapies
If gabapentin at therapeutic doses (1800-3600 mg/day) fails after 4-6 weeks:
- Second-line: Extended-release oxycodone or other opioids (conditional recommendation, moderate certainty) 2
- Alternative: Dipyridamole (conditional recommendation, low certainty) 2
- Avoid: Dopamine agonists as standard therapy due to augmentation risk 2
Critical Pitfalls to Avoid
- Don't use subtherapeutic gabapentin doses: 100 mg is inadequate; therapeutic effect requires ≥900 mg/day
- Don't supplement iron when ferritin >100 ng/mL: No evidence of benefit and potential for iron overload
- Don't start dopamine agonists first-line: The 2025 AASM guidelines explicitly recommend against standard use due to augmentation 2
- Don't forget renal dosing: If creatinine clearance <60 mL/min, adjust gabapentin dose accordingly 1