OBJECT DRUGS

Thyroid:

• Levothyroxine (Synthroid, etc.)
• Liothyronine (Cytomel, etc.)
• Liotrix (Thyrolar, etc.)
• Thyroid USP

PRECIPITANT DRUGS

Binding Agents:

• Antacids
• Cholestyramine (Questran, etc.)
• Colesevelam (WelChol)
• Colestipol (Colestid)
• Iron Products
• Lanthanum Carbonate (Fosrenol)
• Sevelamer (Renagel, etc.)
• Sucralfate (Carafate)

Comment:

These binding agents may inhibit thyroid hormone absorption if given concurrently. The reduction in thyroid bioavailability can be marked; in one study colesevelam reduced thyroxine absorption by 96%. There is a large variability in the magnitude of this interaction on circulating thyroid hormones from one person to another, however, probably because some people on thyroid have some residual thyroid function. Limited evidence suggests that thyroxine absorption may also be inhibited by ciprofloxacin (Cipro), caffeine, and sertraline (Zoloft), but more evidence is needed to assess the clinical importance of these interactions.

Class 3: Assess Risk & Take Action if Necessary

• Circumvent/Minimize: Minimize interactions by giving thyroid 2 hours before or 6 hours after the binding agent; keep a constant interval between doses of thyroid and binding agents. Some reduction in thyroid levels may still occur due to enterohepatic circulation of thyroxine.
• Monitor: Monitor If thyroid hormones are administered with binding agents, monitor for reduced thyroid effect.