Guaifenesin Dose Conversion Between Tablet and Liquid Forms
There is no dose conversion required between tablet and liquid forms of guaifenesin—the dosing is identical by milligram amount regardless of formulation. 1, 2
Key Principle: Bioequivalence Across Formulations
- Guaifenesin tablets and liquids are bioequivalent on a milligram-per-milligram basis, meaning 400 mg in tablet form delivers the same systemic exposure as 400 mg in liquid form 1, 3
- Pharmacokinetic studies demonstrate that theophylline-guaifenesin tablets and liquids produce plasma concentration curves that are within 10% of each other, with no clinically significant differences in absorption 3
- The extent of absorption (AUC) and peak concentrations (Cmax) are equivalent between formulations when the same milligram dose is administered 1
Standard Dosing Regimens
Immediate-Release Formulations (Both Tablet and Liquid)
- Adults and children ≥12 years: 200-400 mg every 4 hours, up to 6 times daily (maximum 2,400 mg/24 hours) 2
- Flexible dose titration within this range allows optimization of plasma concentrations based on symptom severity 2
- Multiple daily doses are necessary to maintain 24-hour therapeutic effect with immediate-release products 2
Extended-Release Formulations
- Adults and children ≥12 years: 600-1,200 mg every 12 hours 1, 2
- Extended-release tablets provide convenience with twice-daily dosing compared to liquids that require 4-hourly administration 2
- Steady-state exposures are equivalent between 1,200 mg ER every 12 hours and 400 mg IR every 4 hours 1
Practical Considerations
Food Effects (Extended-Release Only)
- Food delays Tmax (time to peak concentration) for extended-release formulations but does not affect total bioavailability (AUC) or peak levels (Cmax) 1
- Extended-release guaifenesin can be taken with or without food without dose adjustment 1
Formulation Selection
- Liquid formulations may be preferred for patients with swallowing difficulties or those requiring precise dose titration 2
- Tablet formulations offer portability and convenience, particularly extended-release versions that eliminate the need for frequent dosing 2
- High-dose tablets (≥600 mg) may present manufacturing challenges due to guaifenesin's poor flowability and compressibility, but approved products have overcome these issues 4
Common Pitfall to Avoid
- Do not assume liquid formulations require higher doses due to presumed lower bioavailability—this is incorrect. The absorption characteristics are comparable across all oral formulations when equivalent milligram doses are used 3
- When switching between immediate-release and extended-release products, ensure the total daily dose remains consistent (e.g., 400 mg IR every 4 hours × 6 doses = 2,400 mg/day is equivalent to 1,200 mg ER every 12 hours × 2 doses = 2,400 mg/day) 1