Both Boniva (ibandronate) and levothyroxine (brand name Synthroid) have special administration requirements due to their unique absorption characteristics. Any factor that affects absorption of either medication can significantly decrease their respective effectiveness.

Levothyroxine (Synthroid) Dosing

Levothyroxine, a synthetic thyroid replacement hormone, is generally recommend to be dosed as follows:

  • Take on an empty stomach with a full glass of water at least 30 to 60 minutes before food (easiest for before breakfast dosing). Be sure to take apart from medications and food as these will decrease both the rate and extent of absorption of the drug.

Levothyroxine has these requirements due to the drug having a small therapeutic window. This essentially means that a small deviations in drug dose can result in significant differences in medication effect. Levothyroxine is dosed in micrograms, which is 1/1000th of a mg. We are talking small doses here. As such, any factor that affects how much drug is absorbed (such as food/medication in the stomach) can alter the effect of the medication.

Boniva (Ibandronate) Dosing

Boniva is classified as a bisphosphonate and is indicted for the treatment of osteoporosis. It is dosed only once per month and like levothyroxine, is has specific dosing requirements:

  • Take in the morning with a full glass water at least 1 hour before the first food, beverage (aside from water), or medication. Do not lie down for at least 1 hour after dosing to reduce the chance of esophageal irritation.

Boniva has these dosing requirements due to low bioavailability (i.e. rate and extent of absorption) of the drug, as discussed below.

Dosing Levothyroxine And Boniva Together

Problems can arise when both of these medications are prescribed for someone due to their conflicting administration requirements. As Boniva is only dosed once per month, it is generally recommended that appropriate dosing of Boniva is the first priority over your other medications.

Taking Boniva on an empty stomach (one hour before food and other medications) is critical for the drug to have the desired effect. After taking by mouth, absorption of Boniva is extremely poor. In fact, only 0.6% of an oral dose is absorbed when compared to dosing the drug intravenously! If taken with food or other medication, oral absorption is essentially negligible. 

So first and foremost, proper dosing of Boniva is your primary concern the one time a month you are due to take the medication. With levothyroxine, you have a little more flexibility as you take the drug every day.

While food and medication do affect absorption of levothyroxine, taking the medication daily allows the drug to essentially reach consistent drug levels in the body. If you are consistent in how you take the medication, a small change in dosing one time per month is relatively uneventful and should not cause significant dips in drug levels in your body.

In regard to how you should take your levothyroxine on the day you take Boniva, I would recommend you speak to your doctor as to the most appropriate time. You may be instructed to simply take the medication one hour after Boniva dosing. If that is the case, it would be recommended to skip the yogurt that day as calcium is particularly known to decrease levothyoxine absorption. You may also be instructed to take the levothyroxine 1 to 2 hours after your breakfast. You have a few options available but remember, your once a month Boniva dose should take precedence when taking both on the same day.