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5 Interactions found for:

Fish Oil and levothyroxine
Interactions Summary
  • 1 Major
  • 1 Moderate
  • 3 Minor
  • Fish Oil
  • levothyroxine

Drug Interactions

No drug interactions were found for selected drugs: Fish Oil, levothyroxine.

This does not necessarily mean no interactions exist. Always consult your healthcare provider.

Drug and Food Interactions

Moderate
Levothyroxine + Food

The following applies to the ingredients: Levothyroxine

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

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: Omega-3 Polyunsaturated Fatty Acids (found in Fish Oil)

Use is recommended only if clearly needed.

AU TGA pregnancy category: B1
US FDA pregnancy category: Not assigned

Comments:
-There is insufficient data on use in pregnancy to identify drug-associate risks for major birth defects, miscarriage, or adverse fetal or maternal outcomes.
-Animal studies of dams given oral omega-3-acid ethyl esters from mating through lactation did not show adverse reproductive or developmental effects at 5 times the maximum recommended human dose (MRHD).
-Animal studies of oral dosing at clinically relevant doses during organogenesis did not show teratogenicity.
-There is no official RDA for omega-3 fatty acids during pregnancy, but the US Institute of Medicine and the Food and Nutrition Board suggest that 1400 mg per day should be adequate during lactation.
-Pregnant women may not consume adequate amounts of omega-3 fatty acids from their diet due to recommendations to limit fish consumption to no more than twice weekly (due to mercury content of fish).

Animal studies of oral administration from 2 weeks prior to mating through lactation showed no adverse effects at 5 times the recommended human dose (MRHD). A dose ranging study of oral administration from 2 weeks prior to mating to postpartum day 7 showed a 20% reduction in live births and a 40% reduction in pup survival to postnatal day 4 at or above 3000 mg/kg/day (7 times the MRHD). Oral doses up to 14 times the MRHD (a maternotoxic dose) administered during organogenesis showed no fetal adverse effects. Animals given oral doses up to 5 times the MRHD from gestation day 14 through lactation day 21 showed no adverse effects. Skeletal malformations and reduced fetal growth were seen at maternally toxic doses (4 times the MRHD) and embryolethality occurred at 7 times the MRHD in rabbits. There are no controlled data in human pregnancy. Adequate omega-3 fatty acid intake during pregnancy may reduce preterm birth, increase birth length, weight, and head circumference, improve cognitive and visual development, and reduce risk of allergies. The background birth defect and miscarriage risk for the indicated population is not known. In the US general population, the estimated major birth defect risk is 2 to 4% and the miscarriage risk is 15 to 20%.


AU TGA pregnancy category B1: 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 not shown evidence of an increased occurrence of fetal damage.

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. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  2. Cerner Multum, Inc. "Australian Product Information." O 0
  3. "Product Information. Lovaza (omega-3 polyunsaturated fatty acids)." GlaxoSmithKline (2012):
  4. Briggs GG, Freeman RK. "Drugs in Pregnancy and Lactation." Philadelphia, PA: Wolters Kluwer Health (2015):
  5. "Product Information. Omega-3-Acid Ethyl Esters (omega-3 polyunsaturated fatty acids)." Apotex Corporation (2017):
  6. "Product Information. Omega-3 D-3 Wellness Pack (obsolete) (omega-3 polyunsaturated fatty acids)." TMIG Inc (2017):

The following applies to the ingredients: Levothyroxine

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: Levothyroxine

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):

The following applies to the ingredients: Omega-3 Polyunsaturated Fatty Acids (found in Fish Oil)

Safety has not been established; use is not recommended.

Excreted into human milk: Yes

Comments:
-There is no information regarding this drug on the effects on a breastfed infant, or effects on milk production.
-Consider the developmental and health benefits of breastfeeding along with the mother's clinical need for this medication as well as any potential adverse effects from this drug or the underlying maternal condition.
-Higher omega-3 fatty acid levels have been seen in lactating patients receiving oral omega-3 fatty acid supplementation.
-Infant needs for docosahexaenoic acid (DHA) is approximately 70 to 80 mg per day.
-There is no official RDA for omega-3 fatty acids during lactation, but the US Institute of Medicine and the Food and Nutrition Board suggest that 1300 mg per day should be adequate during lactation.

References

  1. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  2. Briggs GG, Freeman RK. "Drugs in Pregnancy and Lactation." Philadelphia, PA: Wolters Kluwer Health (2015):
  3. "Product Information. Omega-3-Acid Ethyl Esters (omega-3 polyunsaturated fatty acids)." Apotex Corporation (2017):
  4. "Product Information. Omega-3 D-3 Wellness Pack (obsolete) (omega-3 polyunsaturated fatty acids)." TMIG Inc (2017):

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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