What are the differences between lithium capsule and lithium tablet formulations?

Differences Between Lithium Capsule and Tablet Formulations

The main differences between lithium capsule and tablet formulations are in their pharmaceutical composition and release characteristics, with capsules containing specific inactive ingredients like colloidal silicon dioxide and gelatin, while tablets may be available in immediate-release or extended-release formulations that affect absorption rates and peak plasma concentrations. 1, 2

Pharmaceutical Composition

• Capsules:

  • Contain lithium carbonate with specific inactive ingredients including colloidal silicon dioxide, gelatin, sodium lauryl sulfate, talc, titanium dioxide, and various colorants 1
  • Available in strengths of 150 mg, 300 mg, and 600 mg 1

• Tablets:

  • Available as immediate-release or extended-release formulations
  • Extended-release tablets include products like Eskalith CR (450 mg) and Lithobid (300 mg) 3

Pharmacokinetic Differences

Absorption and Peak Concentrations

• Immediate-release tablets:

  • Peak plasma concentration reached in 1-2 hours 2
  • Higher maximum plasma concentration (Cmax) compared to extended-release formulations 3

• Extended-release tablets:

  • Peak plasma concentration reached in 4-5 hours 2
  • 25-50% lower maximum plasma concentrations than immediate-release formulations 3, 2
  • Different extended-release products have varying pharmacokinetics (Lithobid produces 23% higher Cmax than Eskalith CR) 3

• Capsules:

  • Similar absorption profile to immediate-release tablets
  • Bioavailability comparable to immediate-release tablets

Clinical Implications

Dosing Considerations

• Therapeutic monitoring:

  • Target serum concentration for all formulations: 0.6-1.2 mEq/L 4
  • With extended-release preparations, serum concentrations should be maintained in the upper range (0.8-1.0 mmol/L) compared to 0.6-0.8 mmol/L for standard formulations 2

• Dosing frequency:

  • Immediate-release tablets/capsules: typically administered 2-3 times daily
  • Extended-release tablets: can be administered twice daily or even once daily in some cases 2

Side Effect Profile

• Extended-release formulations may reduce gastrointestinal side effects due to lower peak concentrations 2
• All formulations have the same potential for toxicity when serum levels exceed 1.5 mM 5
• Regardless of formulation, serum levels >2.0 mM may cause neurological symptoms and permanent brain damage with prolonged exposure 5

Practical Considerations

• Extended-release formulations may improve medication adherence due to less frequent dosing 2
• Capsules may be easier to swallow for some patients compared to tablets
• Both formulations are bioequivalent in terms of overall drug exposure (AUC) when properly dosed 6
• When switching between formulations, maintain the same total daily dose but adjust the dosing schedule accordingly
• Regular monitoring of serum lithium levels is essential regardless of formulation used 4, 7

Cautions and Monitoring

• All lithium formulations require the same monitoring protocols:

  • Regular serum level monitoring (12 hours after last dose)
  • Thyroid function tests
  • Renal function tests
  • Electrolyte levels, particularly sodium 7

• Special populations:

  • Elderly patients require lower doses regardless of formulation 2
  • Patients with renal impairment need dose adjustments and more frequent monitoring 7
  • Pregnant women experience increased lithium clearance by 30-50% in later pregnancy 2