How much time should be spaced between levothyroxine and Fosamax (alendronate)?

Timing Between Levothyroxine and Fosamax (Alendronate)

Administer levothyroxine and Fosamax (alendronate) at least 4 hours apart, with levothyroxine taken first thing in the morning on an empty stomach and Fosamax taken either 4+ hours later or the following morning.

Optimal Administration Schedule

Levothyroxine Timing

• Take levothyroxine as a single daily dose on an empty stomach, one-half to one hour before breakfast with a full glass of water 1
• Administer levothyroxine at least 4 hours before or after drugs known to interfere with its absorption 1

Fosamax (Alendronate) Timing

• Take alendronate on an empty stomach with a full glass of water, at least 30 minutes before consuming any food or beverages 2
• Remain upright for at least 30 minutes after taking alendronate to minimize esophageal irritation 2, 3

Practical Dosing Strategy

• Morning option: Take levothyroxine immediately upon waking (e.g., 6 AM), then take alendronate at least 4 hours later (e.g., 10 AM or later), ensuring you've had nothing to eat or drink except water 1, 2
• Split-day option: Take levothyroxine first thing in the morning, then take alendronate the following morning before breakfast 1, 2
• The once-weekly alendronate formulation (70 mg) makes the split-day approach particularly convenient, as you only need to coordinate timing one day per week 4, 5

Why This Spacing Matters

Calcium and Mineral Interference

• Calcium supplements must be taken at a different time than alendronate because calcium binds and inactivates bisphosphonates 6
• Calcium supplements should also be spaced at least 4 hours apart from levothyroxine to prevent absorption interference 7
• All patients taking alendronate require calcium supplementation (1,000-1,200 mg daily) and vitamin D (800-1,000 IU daily), but these must be timed separately 6, 3

Absorption Considerations

• Both levothyroxine and alendronate have strict empty-stomach requirements for optimal absorption 1, 2
• Alendronate is poorly absorbed and must be taken in the fasting state with water at least 30 minutes before consuming food or beverages 4
• A recent pharmacokinetic study of a new effervescent alendronate formulation demonstrated no clinically important interference when coadministered with levothyroxine, though this formulation may not be widely available 8

Critical Administration Instructions

For Alendronate Safety

• Take with a full glass of water (6-8 ounces) 2
• Remain upright (sitting or standing) for at least 30 minutes after administration 2, 3
• Do not lie down until after eating your first food of the day 2
• Patients who cannot sit or stand upright for at least 30 minutes should not take alendronate 3

For Levothyroxine Efficacy

• Take on an empty stomach with a full glass of water 1
• Wait one-half to one hour before eating breakfast 1
• Maintain consistent timing daily for stable thyroid hormone levels 1

Common Pitfalls to Avoid

• Do not take both medications simultaneously, even though one pharmacokinetic study suggested minimal interaction with a specific effervescent formulation—standard alendronate tablets require separate timing 8, 1
• Do not take calcium supplements at the same time as either medication, as calcium interferes with both levothyroxine and alendronate absorption 7, 6
• Do not assume you can take alendronate immediately after levothyroxine—the 4-hour separation is necessary to ensure levothyroxine has been absorbed before introducing other medications 1
• Monitor thyroid function if changing medication timing, as alterations in levothyroxine absorption may require dosage adjustments 9, 1