6 Interactions found for:
Drug Interactions
No drug interactions were found for selected drugs: levothyroxine, Lipitor.
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
- "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
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
Moderate
Lipitor
+ Food
The following applies to the ingredients: Atorvastatin (found in Lipitor)
GENERALLY AVOID: Coadministration with grapefruit juice may increase the plasma concentrations of atorvastatin. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. When a single 40 mg dose of atorvastatin was coadministered with 240 mL of grapefruit juice, atorvastatin peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 16% and 37%, respectively. Greater increases in Cmax (up to 71%) and/or AUC (up to 2.5 fold) have been reported with excessive consumption of grapefruit juice (>=750 mL to 1.2 liters per day). Clinically, high levels of HMG-CoA reductase inhibitory activity in plasma is associated with an increased risk of musculoskeletal toxicity. Myopathy manifested as muscle pain and/or weakness associated with grossly elevated creatine kinase exceeding ten times the upper limit of normal has been reported occasionally. Rhabdomyolysis has also occurred rarely, which may be accompanied by acute renal failure secondary to myoglobinuria and may result in death.
ADJUST DOSING INTERVAL: Fibres such as oat bran and pectin may diminish the pharmacologic effects of HMG-CoA reductase inhibitors by interfering with their absorption from the gastrointestinal tract.
MANAGEMENT: Patients receiving therapy with atorvastatin should limit their consumption of grapefruit juice to no more than 1 liter per day. Patients should be advised to promptly report any unexplained muscle pain, tenderness or weakness, particularly if accompanied by fever, malaise and/or dark colored urine. Therapy should be discontinued if creatine kinase is markedly elevated in the absence of strenuous exercise or if myopathy is otherwise suspected or diagnosed. In addition, patients should either refrain from the use of oat bran and pectin or, if concurrent use cannot be avoided, to separate the administration times by at least 2 to 4 hours.
References
- Richter WO, Jacob BG, Schwandt P "Interaction between fibre and lovastatin." Lancet 338 (1991): 706
- McMillan K "Considerations in the formulary selection of hydroxymethylglutaryl coenzyme a reductase inhibitors." Am J Health Syst Pharm 53 (1996): 2206-14
- "Product Information. Lipitor (atorvastatin)." Parke-Davis PROD (2001):
- Boberg M, Angerbauer R, Fey P, Kanhai WK, Karl W, Kern A, Ploschke J, Radtke M "Metabolism of cerivastatin by human liver microsomes in vitro. Characterization of primary metabolic pathways and of cytochrome P45 isozymes involved." Drug Metab Dispos 25 (1997): 321-31
- Bailey DG, Malcolm J, Arnold O, Spence JD "Grapefruit juice-drug interactions." Br J Clin Pharmacol 46 (1998): 101-10
- Lilja JJ, Kivisto KT, Neuvonen PJ "Grapefruit juice increases serum concentrations of atorvastatin and has no effect on pravastatin." Clin Pharmacol Ther 66 (1999): 118-27
- Neuvonen PJ, Backman JT, Niemi M "Pharmacokinetic comparison of the potential over-the-counter statins simvastatin, lovastatin, fluvastatin and pravastatin." Clin Pharmacokinet 47 (2008): 463-74
Drug and Pregnancy Interactions
Major
Lipitor
+ Pregnancy
The following applies to the ingredients: Atorvastatin (found in Lipitor)
According to some authorities: Use is contraindicated during pregnancy or in patients of childbearing potential not using contraception.
AU TGA pregnancy category: D
US FDA pregnancy category: Not assigned
Risk summary: Based on its mechanism of action, this drug may cause fetal harm when administered during pregnancy.
-Available data on the use of statins in pregnant women have not identified a drug-related risk of major congenital malformations and are insufficient to inform a drug-related risk of miscarriage.
Comments:
-If the patient becomes pregnant while taking this drug, therapy should be discontinued and the patient should be apprised of the potential harm to the fetus.
---According to some authorities: Alternatively, the ongoing needs of the individual patient should be considered.
-According to some authorities: Patients of childbearing potential should use effective contraception during therapy; this drug should be used in patients of childbearing potential only when they are highly unlikely to conceive and have been informed of the potential.
Animal studies have failed to reveal evidence of embryofetal toxicity or teratogenicity; however, at maternally toxic doses, increased postimplantation loss and decreased fetal body weights have been observed. No adverse developmental effects were observed in pregnant rats or rabbits administered oral doses that resulted in up to 30 and 20 times, respectively, the human exposure at the maximum recommended human dose (MRHD) of 80 mg (based on body surface area [mg/m2]); in rats administered this drug during gestation and lactation, decreased postnatal growth and development delay were observed at doses at least 6 times the MRHD. This drug crosses the rat placenta and reaches levels in the fetal liver equivalent to that of maternal plasma. A study of statin-exposed pregnant women compared to controls did not find a significant teratogenic effect from maternal use of statins in the first trimester, after adjusting for potential confounders. Rare cases of congenital anomalies after intrauterine exposure to HMG-CoA reductase inhibitors have been reported. There are no controlled data in human pregnancy.
Cholesterol and other products of cholesterol biosynthesis are essential components for fetal development (including synthesis of steroids and cell membranes). Because this drug decreases synthesis of cholesterol and possibly other biologically active substances derived from cholesterol, it may cause fetal harm when used during pregnancy.
Treatment of hyperlipidemia is not generally necessary during pregnancy. Since atherosclerosis is a chronic process, discontinuation of lipid-lowering drugs during pregnancy should have little impact on the outcome of long-term primary hypercholesterolemia therapy for most patients.
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. Lipitor (atorvastatin)." Viatris Specialty LLC SUPPL-81 (2024):
- "Product Information. Atorvaliq (atorvastatin)." Carolina Medical Products Company SUPPL-2 (2024):
- "Product Information. Lipitor (atorvastatin)." Aspen Pharmacare Australia Pty Ltd (2023):
- "Product Information. Lorstat (atorvastatin)." Alphapharm Pty Ltd (2024):
- "Product Information. Lipitor (atorvastatin)." Viatris UK Healthcare Ltd (2024):
- "Product Information. Atorvastatin (atorvastatin)." Rosemont Pharmaceuticals Ltd (2024):
Minor
Levothyroxine
+ Pregnancy
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
- "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
Lipitor
+ Breastfeeding
The following applies to the ingredients: Atorvastatin (found in Lipitor)
Until more data are available, an alternate agent may be preferred, particularly while breastfeeding newborn or preterm infants.
-According to some authorities: Breastfeeding is not recommended during use of this drug.
-According to some authorities: Use is contraindicated.
Excreted into human milk: Unknown
Excreted into animal milk: Yes
Comments:
-Another drug in this class is excreted into human milk.
-Statins (including this drug) decrease synthesis of cholesterol and possibly other biologically active substances derived from cholesterol; they may cause harm to the breastfed infant.
-The effects in the nursing infant are unknown; based on the mechanism of action, there is the potential for serious adverse reactions in nursing infants.
Due to a concern over disruption of infant lipid metabolism, it is generally agreed that women taking a statin should not breastfeed; however, others have argued that children homozygous for familial hypercholesterolemia are treated with statins starting at 1 year of age, statins have low oral bioavailability, and risks to the breastfed infant are low. Some evidence indicates that this drug can be taken by nursing mothers with no obvious developmental problems in their infants.
In cases of patients with homozygous familial hypercholesterolemia, 6 patients breastfed 11 infants after restarting statin therapy postpartum; the specific statin was not reported, but most of the women on statin therapy were using this drug (40 or 80 mg/day). Normal early child development was reported for all offspring; children started school at the appropriate age with no learning difficulties reported.
References
- Bethesda (MD): National Institute of Child Health and Human Development (US) "Atorvastatin - Drugs and Lactation Database (LactMed) https://www.ncbi.nlm.nih.gov/books/NBK501361/" (2024):
- "Product Information. Lipitor (atorvastatin)." Viatris Specialty LLC SUPPL-81 (2024):
- "Product Information. Atorvaliq (atorvastatin)." Carolina Medical Products Company SUPPL-2 (2024):
- "Product Information. Lipitor (atorvastatin)." Aspen Pharmacare Australia Pty Ltd (2023):
- "Product Information. Lorstat (atorvastatin)." Alphapharm Pty Ltd (2024):
- "Product Information. Lipitor (atorvastatin)." Viatris UK Healthcare Ltd (2024):
- "Product Information. Atorvastatin (atorvastatin)." Rosemont Pharmaceuticals Ltd (2024):
Minor
Levothyroxine
+ Breastfeeding
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
- "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 | |
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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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