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6 Interactions found for:

Prilosec and Synthroid
Interactions Summary
  • 2 Major
  • 2 Moderate
  • 2 Minor
  • Prilosec
  • Synthroid

Drug Interactions

Moderate
Synthroid + Prilosec

The following applies to the ingredients: Levothyroxine (found in Synthroid) and Omeprazole (found in Prilosec)

MONITOR: Concurrent administration of proton pump inhibitors (PPI) may decrease the oral bioavailability of levothyroxine. Pharmacologic effects of levothyroxine may be reduced. The mechanism of interaction is suspected to be PPI induced hypochlorhydria leading to reduced levothyroxine absorption since gastric acidity is an essential requirement for levothyroxine absorption. However, the PPIs pantoprazole, omeprazole and lansoprazole did not affect the absorption of oral levothyroxine in some studies. It is not known whether this interaction occurs with other thyroid hormone preparations. This interaction may extend to potassium-competitive acid blockers (PCAB), as they also cause potent acid suppression.

MANAGEMENT: Caution is advised if levothyroxine is used concomitantly with PPI or PCAB. Consider the alteration in gastric pH caused by the PPI and PCAB. Some authorities recommend separating administration of PPI and levothyroxine by several hours, however there are no studies showing improved absorption when PPIs are administered separately from levothyroxine. If concomitant administration is necessary, consider monitoring TSH level and watching for clinical evidence of reduced levothyroxine effects. Patients should be advised to contact their physician if they experience symptoms of hypothyroidism, such as fatigue, cold intolerance, constipation, unexplained weight gain, depression, joint or muscle pain, thinning hair or hair loss, dry skin, hoarseness, and abnormal menstrual periods.

References

  1. "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical PROD (2002):
  2. "Product Information. Levothyroxine Sodium (levothyroxine)." Lannett Company Inc (2024):
  3. "Product Information. Levothyroxine Sodium (levothyroxine)." Zentiva Pharma UK Ltd (2023):
  4. "Product Information. Levothyroxine (Sandoz) (levothyroxine sodium)." Sandoz Pty Ltd (2023):
  5. JW Dietrich, K Gieselbrecht, RW Holl, BO Boehm "Absorption Kinetics of Levothyroxine Is Not Altered by Proton-pump Inhibitor Therapy" Horm Metab Res 38 (2006): 57-59
  6. Ananthakrishnan S, Braverman LE, levin rm, Magnani B, Pearce EN "The effect of famotidine, esomeprazole, and ezetimibe on levothyroxine absorption" National Library of Medicine 18 (2008): 493-498
  7. "Product Information. Eltroxin (levothyroxine)." Shire US Inc (2024):
  8. Raquel de Carvalho Abi-Abib, Mário Vaisman "Is it necessary to increase the dose of levothyroxine in patients with hypothyroidism who use omeprazole?" Arq Bras Endocrinol Metabol 58(7) (2014): 731-6
  9. Issac Sachmechi, David M. Reich, Michael Aninyei, Francisca Wibowo, Garima Gupta, Paul J. Kim "Effect of Proton Pump Inhibitors on Serum Thyroid-Stimulating Hormone Level in Euthyroid Patients Treated with Levothyroxine for Hypothyroidism" Endocr Pract 13 (2007): 345-349

Drug and Food Interactions

Moderate
Synthroid + Food

The following applies to the ingredients: Levothyroxine (found in Synthroid)

ADJUST DOSING INTERVAL: Consumption of certain foods as well as the timing of meals relative to dosing may affect the oral absorption of T4 thyroid hormone (i.e., levothyroxine). T4 oral absorption is increased by fasting and decreased by foods such as soybean flour (e.g., infant formula), cotton seed meal, walnuts, dietary fiber, calcium, and calcium fortified juices. Grapefruit or grapefruit products may delay the absorption of T4 thyroid hormone and reduce its bioavailability. The mechanism of this interaction is not fully understood.

MANAGEMENT: Some manufacturers recommend administering oral T4 as a single daily dose, on an empty stomach, one-half to one hour before breakfast. In general, oral preparations containing T4 thyroid hormone should be administered on a consistent schedule with regard to time of day and relation to meals to avoid large fluctuations in serum levels. Foods that may affect T4 absorption should be avoided within several hours of dosing if possible. Consult local guidelines for the administration of T4 in patients receiving enteral feeding.

References

  1. "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical PROD (2002):
  2. "Product Information. Armour Thyroid (thyroid desiccated)." Forest Pharmaceuticals (2022):
  3. Wohlt PD, Zheng L, Gunderson S, Balzar SA, Johnson BD, Fish JT "Recommendations for the use of medications with continuous enteral nutrition." Am J Health Syst Pharm 66 (2009): 1438-67

The following applies to the ingredients: Levothyroxine (found in Synthroid)

ADJUST DOSING INTERVAL: Concurrent administration of calcium-containing products may decrease the oral bioavailability of levothyroxine by one-third in some patients. Pharmacologic effects of levothyroxine may be reduced. The exact mechanism of interaction is unknown but may involve nonspecific adsorption of levothyroxine to calcium at acidic pH levels, resulting in an insoluble complex that is poorly absorbed from the gastrointestinal tract. In one study, 20 patients with hypothyroidism who were taking a stable long-term regimen of levothyroxine demonstrated modest but significant decreases in mean free and total thyroxine (T4) levels as well as a corresponding increase in mean thyrotropin (thyroid-stimulating hormone, or TSH) level following the addition of calcium carbonate (1200 mg/day of elemental calcium) for 3 months. Four patients had serum TSH levels that were higher than the normal range. Both T4 and TSH levels returned to near-baseline 2 months after discontinuation of calcium, which further supported the likelihood of an interaction. In addition, there have been case reports suggesting decreased efficacy of levothyroxine during calcium coadministration. It is not known whether this interaction occurs with other thyroid hormone preparations.

MANAGEMENT: Some experts recommend separating the times of administration of levothyroxine and calcium-containing preparations by at least 4 hours. Monitoring of serum TSH levels is recommended. Patients with gastrointestinal or malabsorption disorders may be at a greater risk of developing clinical or subclinical hypothyroidism due to this interaction.

References

  1. Schneyer CR "Calcium carbonate and reduction of levothyroxine efficacy." JAMA 279 (1998): 750
  2. Singh N, Singh PN, Hershman JM "Effect of calcium carbonate on the absorption of levothyroxine." JAMA 283 (2000): 2822-5
  3. Csako G, McGriff NJ, Rotman-Pikielny P, Sarlis NJ, Pucino F "Exaggerated levothyroxine malabsorption due to calcium carbonate supplementation in gastrointestinal disorders." Ann Pharmacother 35 (2001): 1578-83
  4. Neafsey PJ "Levothyroxine and calcium interaction: timing is everything." Home Healthc Nurse 22 (2004): 338-9

Drug and Pregnancy Interactions

The following applies to the ingredients: Omeprazole (found in Prilosec)

This drug should be used during pregnancy only if the benefit outweighs the risk to the fetus.

AU TGA pregnancy category: B3
US FDA pregnancy category: Not assigned.

Risk Summary: Epidemiologic studies have demonstrated that major malformative risks with use in pregnant patients are unlikely.

Comment: Some experts recommend that use is considered acceptable.

Animal models have revealed evidence of dose-related increases in embryolethality, fetal resorptions, and pregnancy disruptions when animal models were given this drug during organogenesis. Major fetal malformations were not frequently observed in animal models. Embryofetal and postnatal developmental toxicities were observed in offspring of parents given at least 3.4 times an oral human dose of 40 mg.

Embryofetal toxicity is associated with maternally toxic doses given throughout gestation as well as in high doses given to males prior to mating.

AU TGA pregnancy category B3: Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals have shown evidence of an increased occurrence of fetal damage, the significance of which is considered uncertain in humans.

US FDA pregnancy category Not Assigned: The US FDA has amended the pregnancy labeling rule for prescription drug products to require labeling that includes a summary of risk, a discussion of the data supporting that summary, and relevant information to help health care providers make prescribing decisions and counsel women about the use of drugs during pregnancy. Pregnancy categories A, B, C, D, and X are being phased out.

References

  1. "Product Information. PriLOSEC (omeprazole)." Merck & Co., Inc (2022):
  2. "Product Information. Omeprazole (omeprazole)." Mylan Pharmaceuticals Inc (2003):
  3. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  4. Cerner Multum, Inc. "Australian Product Information." O 0

The following applies to the ingredients: Levothyroxine (found in Synthroid)

Use is considered acceptable

AU TGA pregnancy category: A
US FDA pregnancy category: Not Assigned

Risk Summary: No increased rates of major birth defects or miscarriages have been reported with use during pregnancy; untreated hypothyroidism during pregnancy is associated with risks to the mother and fetus

Comments:
-Thyroid replacement therapy should not be discontinued during pregnancy; hypothyroidism diagnosed during pregnancy should be promptly treated.
-Monitor TSH levels and adjust doses as needed.

Animal studies have not been conducted. There is a long history of using this drug in pregnant women and this experience has not shown increased rates of fetal malformations, miscarriages or other adverse maternal or fetal outcomes. Hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, pre-eclampsia, stillbirth and premature delivery. Maternal hypothyroidism may have an adverse effect on fetal neurocognitive development. Pregnant women taking this drug should have their TSH measured during each trimester and dose adjusted as appropriate. Patients will generally return to their pre-pregnancy dose after delivery. There are no controlled data in human pregnancy.

AU TGA pregnancy category A: Drugs which have been taken by a large number of pregnant women and women of childbearing age without any proven increase in the frequency of malformations or other direct or indirect harmful effects on the fetus having been observed.

US FDA pregnancy category Not Assigned: The US FDA has amended the pregnancy labeling rule for prescription drug products to require labeling that includes a summary of risk, a discussion of the data supporting that summary, and relevant information to help health care providers make prescribing decisions and counsel women about the use of drugs during pregnancy. Pregnancy categories A, B, C, D, and X are being phased out.

References

  1. "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical PROD (2002):
  2. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  3. Pharmaceutical Society of Australia "APPGuide online. Australian prescription products guide online. http://www.appco.com.au/appguide/default.asp" (2006):
  4. Cerner Multum, Inc. "Australian Product Information." O 0

Drug and Breastfeeding Interactions

The following applies to the ingredients: Omeprazole (found in Prilosec)

Use is not recommended.

Excreted into human milk: Yes

Comments:
-This drug is associated with tumorigenicity in animal models, and may suppress gastric acid secretion in the nursing infant.
-The American Academy of Pediatrics state that this drug should be avoided until additional studies can confirm the safe use of this drug during breastfeeding.

In animal models, decreased postpartum offspring growth rates were observed when this drug was administered during late gestation and throughout lactation at oral doses of at least 138 mg/kg/day and IV doses of 3.2 mg/kg/day.

References

  1. "Product Information. PriLOSEC (omeprazole)." Merck & Co., Inc (2022):
  2. "Product Information. Omeprazole (omeprazole)." Mylan Pharmaceuticals Inc (2003):
  3. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  4. Cerner Multum, Inc. "Australian Product Information." O 0
  5. United States National Library of Medicine "Toxnet. Toxicology Data Network. http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?LACT" (2013):
  6. Briggs GG, Freeman RK. "Drugs in Pregnancy and Lactation." Philadelphia, PA: Wolters Kluwer Health (2015):

The following applies to the ingredients: Levothyroxine (found in Synthroid)

Use is considered acceptable

Excreted into human milk: Yes

Comments:
-Levothyroxine (T4) is a normal component of human milk; limited data on exogenous replacement doses during breastfeeding have not shown an adverse effect in nursing infants.
-Levothyroxine dose requirements may be increased in the postpartum period compared to prepregnancy requirements in patients with Hashimoto's thyroiditis.
-The presence of thyroid hormone in breast milk does not appear to interfere with neonatal thyroid screening.

References

  1. "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical PROD (2002):
  2. Jansson L, Ivarsson S, Larsson I, Ekman R "Tri-iodothyronine and thyroxine in human milk." Acta Paediatr Scand 72 (1983): 703-5
  3. Moller B, Bjorkhem I, Falk O, Lantto O, Lafsson A "Identification of thyroxine in human breast milk by gas chromatography-mass spectrometry." J Clin Endocrinol Metab 56 (1983): 30-4
  4. Mizuta H, Amino N, Ichihara K, et al. "Thyroid hormones in human milk and their influence on thyroid function of breast-fed babies." Pediatr Res 17 (1983): 468-71
  5. Hahn HB, Spiekerman AM, Otto R, Hossalla DE "Thyroid function tests in neonates fed human milk." Am J Dis Child 137 (1983): 220-2
  6. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  7. Pharmaceutical Society of Australia "APPGuide online. Australian prescription products guide online. http://www.appco.com.au/appguide/default.asp" (2006):
  8. Cerner Multum, Inc. "Australian Product Information." O 0
  9. United States National Library of Medicine "Toxnet. Toxicology Data Network. http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?LACT" (2013):

Therapeutic Duplication Warnings

No warnings were found for your selected drugs.

Therapeutic duplication warnings are only returned when drugs within the same group exceed the recommended therapeutic duplication maximum.

Switch to: Consumer Interactions

Drug Interaction Classification

These classifications are only a guideline. The relevance of a particular drug interaction to a specific individual is difficult to determine. Always consult your healthcare provider before starting or stopping any medication.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.
Unknown No interaction information available.

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