5 Interactions found for:
Drug Interactions
No drug interactions were found for selected drugs: Crestor, Synthroid.
This does not necessarily mean no interactions exist. Always consult your healthcare provider.
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
- "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical PROD (2002):
- "Product Information. Armour Thyroid (thyroid desiccated)." Forest Pharmaceuticals (2022):
- 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
- Schneyer CR "Calcium carbonate and reduction of levothyroxine efficacy." JAMA 279 (1998): 750
- Singh N, Singh PN, Hershman JM "Effect of calcium carbonate on the absorption of levothyroxine." JAMA 283 (2000): 2822-5
- 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
- Neafsey PJ "Levothyroxine and calcium interaction: timing is everything." Home Healthc Nurse 22 (2004): 338-9
Drug and Pregnancy Interactions
Major
Crestor
+ Pregnancy
The following applies to the ingredients: Rosuvastatin (found in Crestor)
Contraindicated
AU TGA pregnancy category: D
US FDA pregnancy category: Not assigned
Risk Summary: Safety in pregnant women has not been established and there is no apparent benefit to use during pregnancy. Because HMG-CoA reductase inhibitors (statins) decrease cholesterol synthesis and possibly the synthesis of other biologically active substances derived from cholesterol, this drug may cause fetal harm during pregnancy.
Comments:
-This drug should be discontinued as soon as pregnancy is recognized, and the patient should be apprised of the potential harm to the fetus.
-Women of childbearing potential should use adequate methods of contraception during therapy.
Animal studies have failed to reveal evidence of teratogenicity in doses approximating the maximum human dose of 40 mg/day. Limited published data has not shown an increased risk of major congenital malformations or miscarriage, although there have been rare reports of congenital anomalies following intrauterine exposure to other statins. Several cases of serious fetal abnormalities were reported in 2 series of 178 and 143 cases among pregnant women taking a HMG-CoA reductase inhibitor (statin) during the first trimester of pregnancy. These included limb and neurological defects, spontaneous abortions and fetal deaths. In a review of approximately 100 prospectively followed pregnancies in women exposed to simvastatin or lovastatin, the incidences of congenital anomalies, spontaneous abortions, and fetal deaths/stillbirths did not exceed what would be expected in the general population. There are no controlled data in human pregnancy.
Serum cholesterol and triglycerides increase during normal pregnancy, and cholesterol products are essential for fetal development. Since atherosclerosis is a chronic process, discontinuation of lipid-lowering drugs during pregnancy should have little impact on long term outcomes of primary hyperlipidemia therapy.
AU TGA pregnancy category D: Drugs which have caused, are suspected to have caused or may be expected to cause, an increased incidence of human fetal malformations or irreversible damage. These drugs may also have adverse pharmacological effects. Accompanying texts should be consulted for further details.
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
- "Product Information. Crestor (rosuvastatin)." AstraZeneca Pharma Inc (2003):
- Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
- TGA. Therapeutic Goods Administration. Australian Drug Evaluation Committee "Prescribing medicines in pregnancy: an Australian categorisation of risk of drug use in pregancy. http://www.tga.gov.au/docs/pdf/medpreg.pdf" (2007):
- Cerner Multum, Inc. "Australian Product Information." O 0
Minor
Synthroid
+ Pregnancy
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
- "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical PROD (2002):
- Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
- Pharmaceutical Society of Australia "APPGuide online. Australian prescription products guide online. http://www.appco.com.au/appguide/default.asp" (2006):
- Cerner Multum, Inc. "Australian Product Information." O 0
Drug and Breastfeeding Interactions
Major
Crestor
+ Breastfeeding
The following applies to the ingredients: Rosuvastatin (found in Crestor)
Contraindicated
Excreted into human milk: Yes (in low amounts)
Comments:
-Due to the potential for serious adverse events in nursing infants and the concern over disruption of infant lipid metabolism, women who require treatment with this drug should not breastfeed.
References
- "Product Information. Crestor (rosuvastatin)." AstraZeneca Pharma Inc (2003):
- Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
- Cerner Multum, Inc. "Australian Product Information." O 0
- United States National Library of Medicine "Toxnet. Toxicology Data Network. http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?LACT" (2013):
Minor
Synthroid
+ Breastfeeding
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
- "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical PROD (2002):
- Jansson L, Ivarsson S, Larsson I, Ekman R "Tri-iodothyronine and thyroxine in human milk." Acta Paediatr Scand 72 (1983): 703-5
- 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
- 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
- Hahn HB, Spiekerman AM, Otto R, Hossalla DE "Thyroid function tests in neonates fed human milk." Am J Dis Child 137 (1983): 220-2
- Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
- Pharmaceutical Society of Australia "APPGuide online. Australian prescription products guide online. http://www.appco.com.au/appguide/default.asp" (2006):
- Cerner Multum, Inc. "Australian Product Information." O 0
- 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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