SIMVASTATIN

• Take simvastatin tablets USP orally once daily in the evening.
• The maximum recommended dosage is simvastatin tablets USP 40 mg once daily [see DOSAGE AND ADMINISTRATION(2.2, 2.3)]. An 80 mg daily dosage of simvastatin tablets USP is restricted to patients who have been taking simvastatin tablets USP 80 mg daily chronically (e.g., for 12 months or more) without evidence of muscle toxicity [see WARNINGS AND PRECAUTIONS(5.1)].
• If as dose is missed, take the missed dose as soon as possible. Do not double the next dose.
• For patients that require a high-intensity statin or are unable to achieve their LDL-C goal receiving simvastatin tablets USP 40 mg daily, prescribe alternative LDL-C-lowering treatment.
• Assess LDL-C when clinically appropriate, as early as 4 weeks after initiating simvastatin tablets USP, and adjust the dosage if necessary.

The recommended dosage range of simvastatin tablets USP is 20 mg to 40 mg once daily

The recommended dosage range of simvastatin tablets USP is 10 mg to 40 mg daily.

For patients with severe renal impairment [creatinine clearance (CLcr) 15 – 29 mL/min], the recommended starting dosage of simvastatin is 5 mg once daily [see WARNINGS AND PRECAUTIONS (5.1) AND USE IN SPECIFIC POPULATIONS (8.6)].

Use another simvastatin product to initiate dosing in such patients [see DOSAGE AND ADMINISTRATION (2.1 )].

There are no dosage adjustment recommendations for patients with mild or moderate renal impairment.

Concomitant use of simvastatin tablets USP with the following drugs requires dosage modification of simvastatin tablets USP [see WARNINGS AND PRECAUTIONS (5.1) AND DRUG INTERACTIONS (7.1)].

Patients taking Lomitapide

Reduce the dosage of simvastatin tablets USP by 50%. Do not exceed simvastatin tablets USP 20 mg once daily (or 40 mg once daily for patients who have previously taken an 80 mg daily dosage of simvastatin tablets USP chronically while taking lomitapide) [see DOSAGE AND ADMINISTRATION (2.1)]. 

Patients taking Verapamil, Diltiazem, or Dronedarone

Do not exceed simvastatin tablets USP 10 mg once daily.

Patients taking Amiodarone, Amlodipine, or Ranolazine

Do not exceed simvastatin tablets USP 20 mg once daily.

Simvastatin may cause myopathy and rhabdomyolysis. Acute kidney injury secondary to myoglobinuria and rare fatalities have occurred as a result of rhabdomyolysis in patients treated with statins, including simvastatin.

In clinical studies of 24,747 simvastatin -treated patients with a median follow-up of 4 years, the incidence of myopathy, defined as unexplained muscle weakness, pain, or tenderness accompanied by creatinine kinase (CK) increases greater than ten times the upper limit of normal (10xULN), were approximately 0.03%, 0.08%, and 0.61% in patients treated with simvastatin 20 mg, 40 mg, and 80 mg daily, respectively. In another clinical study of 12,064 simvastatin -treated patients (with a history of myocardial infarction) with a mean follow-up of 6.7 years, the incidences of myopathy in patients taking simvastatin 20 mg and 80 mg daily were approximately 0.02% and 0.9%, respectively. The incidences of rhabdomyolysis (defined as myopathy with a CK >40xULN) in patients taking simvastatin 20 mg and 80 mg daily were approximately 0% and 0.4%, respectively [see ADVERSE REACTIONS (6.1)].

Risk Factors for Myopathy

Risk factors for myopathy include age 65 years or greater, uncontrolled hypothyroidism, renal impairment, concomitant use with certain other drugs (including other lipid-lowering therapies), and higher simvastatin dosage; Chinese patients on simvastatin may be at higher risk for myopathy [see CONTRAINDICATIONS (4), DRUG INTERACTIONS (7.1), AND USE IN SPECIFIC POPULATIONS (8.8)]. The risk of myopathy is increased by elevated plasma levels of simvastatin and simvastatin acid. The risk is also greater in patients taking simvastatin 80 mg daily compared with patients taking lower simvastatin dosages and compared with patients using other statins with similar or greater LDL-C-lowering efficacy [see ADVERSE REACTIONS (6.1)].

Steps to Prevent or Reduce the Risk of Myopathy and Rhabdomyolysis

The concomitant use of strong CYP3A4 inhibitors with simvastatin is contraindicated. If short-term treatment with strong CYP3A4 inhibitors is required, temporarily suspend simvastatin during the duration of strong CYP3A4 inhibitor treatment. The concomitant use of simvastatin with gemfibrozil, cyclosporine, or danazol is also contraindicated [see CONTRAINDICATIONS (4) AND DRUG INTERACTIONS (7.1)]. 

Simvastatin dosage modifications are recommended for patients taking lomitapide, verapamil, diltiazem, dronedarone, amiodarone, amlodipine or ranolazine [see DOSAGE AND ADMINISTRATION (2.5)]. Simvastatin use should be temporarily suspended in patients taking daptomycin. Lipid modifying doses (≥1 gram/day) of niacin, fibrates, colchicine, and grapefruit juice may also increase the risk of myopathy and rhabdomyolysis [see DRUG INTERACTIONS (7.1)]. 

Use the 80 mg daily dosage of simvastatin only in patients who have been taking simvastatin 80 mg daily chronically without evidence of muscle toxicity [see DOSAGE AND ADMINISTRATION (2.1)]. If patients treated with an 80 mg daily dosage of simvastatin tablet USP are prescribed an interacting drug that increases the risk for myopathy and rhabdomyolysis, switch to an alternate statin [SEE DRUG INTERACTIONS (7.1)].  

Discontinue simvastatin if markedly elevated CK levels occur or if myopathy is either diagnosed or suspected. Muscle symptoms and CK increases may resolve if simvastatin is discontinued. Temporarily discontinue simvastatin in patients experiencing an acute or serious condition at high risk of developing renal failure secondary to rhabdomyolysis, e.g., sepsis; shock; severe hypovolemia; major surgery; trauma; severe metabolic, endocrine, or electrolyte disorders; or uncontrolled epilepsy.

Inform patients of the risk of myopathy and rhabdomyolysis when starting or increasing the simvastatin dosage and advise patients receiving an 80 mg daily dosage of simvastatin tablet USP of the increased risk of myopathy and rhabdomyolysis. Instruct patients to promptly report any unexplained muscle pain, tenderness or weakness, particularly if accompanied by malaise or fever.

There have been rare reports of immune-mediated necrotizing myopathy (IMNM), an autoimmune myopathy, associated with statin use, including reports of recurrence when the same or a different statin was administered. IMNM is characterized by: proximal muscle weakness and elevated serum creatine kinase that persist despite discontinuation of statin treatment; positive anti-HMG CoA reductase antibody; muscle biopsy showing necrotizing myopathy without significant inflammation; and improvement with immunosuppressive agents. Additional neuromuscular and serologic testing may be necessary. Treatment with immunosuppressive agents may be required. Discontinue simvastatin if IMNM is suspected

Increases in serum transaminases have been reported with use of simvastatin [see ADVERSE REACTIONS (6.1)]. In most cases, these changes appeared soon after initiation, were transient, were not accompanied by symptoms, and resolved or improved on continued therapy or after a brief interruption in therapy. Persistent increases to more than 3xULN in serum transaminases have occurred in approximately 1% of patients receiving simvastatin in clinical studies. Marked persistent increases of hepatic transaminases have also occurred with simvastatin. There have been rare postmarketing reports of fatal and non-fatal hepatic failure in patients taking statins, including simvastatin.

Patients who consume substantial quantities of alcohol and/or have a history of liver disease may be at increased risk for hepatic injury.

Consider liver enzyme testing before simvastatin initiation and when clinically indicated thereafter. Simvastatin is contraindicated in patients with acute liver failure or decompensated cirrhosis [see CONTRAINDICATIONS (4)]. If serious hepatic injury with clinical symptoms and/or hyperbilirubinemia or jaundice occurs, promptly discontinue simvastatin.

Increases in HbA1c and fasting serum glucose levels have been reported with statins, including simvastatin. Optimize lifestyle measures, including regular exercise, maintaining a healthy body weight, and making healthy food choices.

Because clinical studies are conducted under widely varying conditions, adverse reaction rates observed in the clinical studies of a drug cannot be directly compared to rates in the clinical studies of another drug and may not reflect the rates observed in practice.

In clinical studies, 2,423 adult patients were exposed to simvastatin with a median duration of follow-up of approximately 18 months. The most commonly reported adverse reactions (incidence ≥5%) in these simvastatin clinical studies were: upper respiratory infections (9%), headache (7%), abdominal pain (7%), constipation (7%), and nausea (5%). Overall, 1.4% of patients discontinued simvastatin due to adverse reactions. The most common adverse reactions that led to discontinuation were: gastrointestinal disorders (0.5%), myalgia (0.1%), and arthralgia (0.1%).

In a Cardiovascular Outcomes Study (the Scandinavian Simvastatin Survival Study [Study 4S]), adult patients (age range 35-71 years, 19% women, 100% Caucasians) were treated with 20-40 mg per day of simvastatin or placebo over a median of 5.4 years [see CLINICAL STUDIES (14)]; adverse reactions reported in ≥2% of patients and at a rate greater than placebo are shown in Table 1.

Myopathy/Rhabdomyolysis

In clinical studies with a median follow-up of at least 4 years, in which 24,747 patients received simvastatin, the incidence of myopathy (defined as unexplained muscle weakness, pain, or tenderness accompanied by CK increases greater than 10xULN) was approximately 0.03%, 0.08%, and 0.61% for the simvastatin 20 mg, 40 mg, and 80 mg daily groups, respectively.

In a clinical outcomes study in which 12,064 adult patients with a history of myocardial infarction were treated with simvastatin (mean follow-up 6.7 years), the incidence of myopathy (defined as unexplained muscle weakness or pain with a serum CK >10x [1200 U/L] ULN) in patients taking simvastatin 20 mg and 80 mg daily was approximately 0.02% and 0.9%, respectively. The incidence of rhabdomyolysis (defined as myopathy with a CK >40xULN) in patients on simvastatin 20 mg and 80 mg daily was approximately 0% and 0.4%, respectively. The incidence of myopathy and rhabdomyolysis were highest during the first year and then decreased during the subsequent years of treatment.

In another clinical outcomes study in which 10,269 adult patients were treated with simvastatin 40 mg per day (mean follow-up of 5 years), the incidence of myopathy/rhabdomyolysis was <0.1% in patients treated with simvastatin.

Elevations in Liver Enzyme Tests

Moderate (less than 3xULN) elevations of serum transaminases have been reported with use of simvastatin.

Persistent increases to more than 3xULN in serum transaminases have occurred in approximately 1% of patients receiving simvastatin in clinical studies. Marked persistent increases of hepatic transaminases have occurred with simvastatin. Elevated alkaline phosphatase and γ-glutamyl transpeptidase have also been reported.

In Study 4S, with a median follow-up of 5.4 years, 1,986 adult patients were treated with simvastatin 20 mg once daily, of whom 37% titrated to 40 mg once daily. The percentage of patients with one or more occurrences of transaminase elevations to >3xULN was 0.7% in patients taking simvastatin compared with 0.6% in patients taking placebo. Elevated transaminases leading to discontinuation of study treatment occurred in 0.4% of patients taking simvastatin and 0.2% of patients taking placebo. The majority of elevated transaminases leading to treatment discontinuation occurred within in the first year.

Adverse Reactions in Pediatric Patients with Heterozygous Familial Hypercholesterolemia

In a 48-week clinical study in pediatric patients 10 years of age and older (43% female, 97.7% Caucasians, 1.7% Hispanics, 0.6% Multiracial) with HeFH (n=175), treated with placebo or simvastatin (10 - 40 mg daily), the most common adverse reactions were upper respiratory infection, headache, abdominal pain, and nausea [see USE IN SPECIFIC POPULATIONS (8.4) AND CLINICAL STUDIES (14)].

The following adverse reactions have been identified during post-approval use of simvastatin. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Body as whole 

fever, chills, malaise, asthenia

Blood and Lymphatic System Disorders

anemia, thrombocytopenia, leukopenia, hemolytic anemia, positive ANA, ESR increase, eosinophilia

Gastrointestinal Disorders

pancreatitis, vomiting

Hepatic and Pancreatic Disorders 

hepatitis/jaundice, fatal and non-fatal hepatic failure

Immune System Disorders 

hypersensitivity syndrome including: anaphylaxis, angioedema, lupus erythematous-like syndrome, dermatomyositis, vasculitis

Musculoskeletal and Connective Tissue Disorders

muscle cramps, immune-mediated necrotizing myopathy, polymyalgia rheumatica, arthritis

Nervous System Disorders 

dizziness, depression, paresthesia, peripheral neuropathy. Rare reports of cognitive impairment (e.g., memory loss, forgetfulness, amnesia, memory impairment, confusion) associated with statin use. Cognitive impairment was generally nonserious, and reversible upon statin discontinuation, with variable times to symptom onset (1 day to years) and symptom resolution (median of 3 weeks). There have been rare reports of new-onset or exacerbation of myasthenia gravis, including ocular myasthenia, and reports of recurrence when the same or a different statin was administered.

Skin and Subcutaneous Tissue Disorders 

pruritus, alopecia, a variety of skin changes (e.g., nodules, discoloration, dryness of skin/mucous membranes, changes to hair/nails), purpura, lichen planus, urticaria, photosensitivity, flushing, toxic epidermal necrolysis, erythema multiforme, including Stevens-Johnson syndrome

Respiratory and Thoracic 

interstitial lung disease, dyspnea

Reproductive System Disorders 

erectile dysfunction

Simvastatin is a substrate of CYP3A4 and of the transport protein OATP1B1. Simvastatin exposure can be significantly increased with concomitant administration of inhibitors of CYP3A4 and OATP1B1. Table 2 includes a list of drugs that increase the risk of myopathy and rhabdomyolysis when used concomitantly with simvastatin and instructions for preventing or managing them [see WARNINGS AND PRECAUTIONS (5.1) AND CLINICAL PHARMACOLOGY (12.3)].

Table 3 presents Simvastatin's effect on other drugs and instructions for preventing or managing them.

Risk Summary

Discontinue simvastatin when pregnancy is recognized. Alternatively, consider the ongoing therapeutic needs of the individual patient.

Simvastatin decreases synthesis of cholesterol and possibly other biologically active substances derived from cholesterol; therefore, simvastatin may cause fetal harm when administered to pregnant patients based on the mechanism of action [see CLINICAL PHARMACOLOGY (12.1)]. In addition, treatment of hyperlipidemia is not generally necessary during pregnancy. Atherosclerosis is a chronic process and the discontinuation of lipid-lowering drugs during pregnancy should have little impact on the outcome of long-term therapy of primary hyperlipidemia for most patients.

Available data from case series and prospective and retrospective observational cohort studies over decades of use with statins in pregnant women have not identified a drug-associated risk of major congenital malformations. Published data from prospective and retrospective observational cohort studies with simvastatin use in pregnant women are insufficient to determine if there is a drug-associated risk of miscarriage (see Data).

In animal reproduction studies, no adverse developmental effects were observed in pregnant rats or rabbits orally administered simvastatin during the period of organogenesis at doses that resulted in 2.5 and 2 times, respectively, the human exposure at the maximum recommended human dosage of 80 mg/day, based on body surface area (mg/m²) (see DATA).

The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.

Data

Human Data:

A Medicaid cohort linkage study of 1152 statin-exposed pregnant women compared to 886,996 controls did not find a significant teratogenic effect from maternal use of statins in the first trimester of pregnancy, after adjusting for potential confounders – including maternal age, diabetes mellitus, hypertension, obesity, and alcohol and tobacco use – using propensity score-based methods. The relative risk of congenital malformations between the group with statin use and the group with no statin use in the first trimester was 1.07 (95% confidence interval 0.85 to 1.37) after controlling for confounders, particularly pre-existing diabetes mellitus. There were also no statistically significant increases in any of the organ-specific malformations assessed after accounting for confounders. In the majority of pregnancies, statin treatment was initiated prior to pregnancy and was discontinued at some point in the first trimester when pregnancy was identified. Study limitations include reliance on physician coding to define the presence of a malformation, lack of control for certain confounders such as body mass index, use of prescription dispensing as verification for the use of a statin, and lack of information on non-live births.

Animal Data:

Simvastatin was given to pregnant rats at doses of 6.25, 12.5 and 25 mg/kg/day (0.6 times, 1.3 times, and 2.5 times, respectively, the maximum recommended dosage of 80 mg/day when normalized to body surface area) from gestation days 6-17 and to pregnant rabbits from gestation days 6-18 at doses of 2.5, 5, and 10 mg/kg/day (0.5 times, 1 times, and 2 times, respectively, the maximum recommended dosage of 80 mg/day when normalized to body surface area). For both species, there was no evidence of maternal toxicity or embryolethality. In rats, mean fetal body weights in the 25 mg/kg/day group were decreased 5.4%. Similar fetal body weight effects were not observed in rabbits.

Simvastatin doses of 6.25, 12.5 and 25 mg/kg/day (0.6 times, 1.3 times, and 2.5 times, respectively, the maximum recommended dosage of 80 mg/day when normalized to body surface area) were given to pregnant rats from gestation day 15 to lactation day 21. Slight decreases in maternal body weight gain and pup postnatal day 0 weight were observed in the 25 mg/kg/day dose group. Mean body weight gain of pups during lactation was slightly decreased at doses ≥12.5 mg/kg/day. Post weaning weight, behavior, reproductive performance and fertility of the offspring were not affected at any dose tested.

Placental transfer of simvastatin was not evaluated in rats or rabbits. However, it has been shown that other drugs in this class cross the placenta.

Risk Summary

There is no information about the presence of simvastatin in human or animal milk, the effects of the drug on the breastfed infant or the effects of the drug on milk production. However, it has been shown that another drug in this class passes into human milk. Statins, including

simvastatin, decrease cholesterol synthesis and possibly the synthesis of other biologically active substances derived from cholesterol and may cause harm to the breastfed infant.

Because of the potential for serious adverse reactions in a breastfed infant, based on the mechanism of action, advise patients that breastfeeding is not recommended during treatment with simvastatin [see USE IN SPECIFIC POPULATIONS (8.1), CLINICAL PHARMACOLOGY (12.1)].

The safety and effectiveness of simvastatin as an adjunct to diet to reduce LDL-C have been established in pediatric patients 10 years of age and older with HeFH. Use of simvastatin for this indication is based on a double-blind, placebo-controlled clinical study in 175 pediatric patients (99 boys and 76 girls at least 1 year post-menarche) 10 years of age and older with HeFH. In this limited controlled study, there was no significant effect on growth or sexual maturation in the boys or girls, or on menstrual cycle length in girls.

The safety and effectiveness of simvastatin have not been established in pediatric patients younger than 10 years of age with HeFH or in pediatric patients with other types of hyperlipidemia (other than HeFH).

Of the total number of simvastatin-treated patients in clinical studies 1,021 (23%) patients, 5,366 (52%) patients, and 363 (15%) patients were ≥65 years old, respectively. In Study HPS, 615 (6%) patients were ≥75 years old [see CLINICAL STUDIES (14)]. In a clinical study of patients treated with simvastatin 80 mg daily, patients ≥65 years of age had an increased risk of myopathy, including rhabdomyolysis, compared to patients <65 years of age.

A pharmacokinetic study with simvastatin use showed the mean plasma level of total inhibitors to be approximately 45% higher in geriatric patients between 70-78 years of age compared with patients between 18-30 years of age [see CLINICAL PHARMACOLOGY (12.3)].

Renal impairment is a risk factor for myopathy and rhabdomyolysis. Monitor all patients with renal impairment for development of myopathy. In patients with severe renal impairment (CLcr 15 – 29 mL/min), the recommended starting dosage is simvastatin 5 mg once daily [see DOSAGE AND ADMINISTRATION (2.4), WARNINGS AND PRECAUTIONS (5.1)]. Simvastatin is not available in a 5 mg strength. Use another simvastatin product to initiate dosing in such patients.

Simvastatin is contraindicated in patients with acute liver failure or decompensated cirrhosis [see CONTRAINDICATIONS (4), WARNINGS AND PRECAUTIONS (5.3)].

In a clinical study in which patients at high risk of CVD were treated with simvastatin 40 mg/day (median follow-up 3.9 years), the incidence of myopathy was approximately 0.05% for non-Chinese patients (n=7367) compared with 0.24% for Chinese patients (n=5468). In this study, the incidence of myopathy for Chinese patients on simvastatin 40 mg/day or ezetimibe/simvastatin 10/40 mg/day coadministered with extended-release niacin 2 g/day was 1.24%.

Chinese patients may be at higher risk for myopathy, monitor these patients appropriately. Coadministration of simvastatin with lipid-modifying doses of niacin-containing products (≥1 g/day niacin) is not recommended in Chinese patients [see WARNINGS AND PRECAUTIONS (5.1), DRUG INTERACTIONS (7.1)].

Simvastatin is a prodrug and is hydrolyzed to its active β-hydroxyacid form, simvastatin acid, after administration. Simvastatin acid and its metabolites are inhibitors of HMG-CoA reductase, the rate-limiting enzyme that converts HMG-CoA to mevalonate, a precursor of cholesterol.

Inhibition of HMG-CoA reductase by simvastatin acid accelerates the expression of LDL-receptors, followed by the uptake of LDL-C from blood to the liver, leading to a decrease in plasma LDL-C and total cholesterol. Sustained inhibition of cholesterol synthesis in the liver also decreases levels of very-low-density lipoproteins. The maximum LDL-C reduction of simvastatin is usually achieved by 4 weeks and is maintained after that

Simvastatin is a lactone that is readily hydrolyzed in vivo to the corresponding β-hydroxyacid. Pharmacokinetics (PK) of simvastatin and its metabolites was originally characterized using inhibition of HMG-CoA reductase activity following base hydrolysis of plasma samples, as specific bioanalytical methods were not available. Inhibition of the enzyme activity (equivalent to the level of total inhibitors) represented the combination of activities in plasma following administration of simvastatin from both active (simvastatin acid and its metabolites) and latent forms (simvastatin and its metabolites) after conversion to the active forms in the presence of base.

Absorption

Following an oral dose of ¹⁴C-labeled simvastatin, plasma concentrations of total radioactivity (simvastatin plus ¹⁴C-metabolites) peaked at 4 hours and declined rapidly to about 10% of peak by 12 hours postdose. Since simvastatin undergoes extensive first-pass extraction in the liver, the availability of simvastatin to the general circulation is low (<5%). PK, assessed as area under the concentrations of total inhibitors –time curve, was apparently linear with doses up to 120 mg

Effect of Food:

The plasma profile of total inhibitors concentration was not affected when simvastatin was administered with low fat meal.

Distribution

Both simvastatin and its β-hydroxyacid metabolite are highly bound (approximately 95%) to human plasma proteins.

Elimination

Metabolism:

Simvastatin is metabolized by CYP3A4. The major active metabolites of simvastatin present in human plasma are simvastatin acid and its 6′-hydroxy, 6′-hydroxymethyl, and 6′-exomethylene derivatives. Peak plasma concentrations of both active and total inhibitors were attained within 1.3 to 2.4 hours postdose.

Excretion:

Following an oral dose of ¹⁴C-labeled simvastatin, 13% of the dose was excreted in urine and 60% in feces.

Specific Populations

Geriatric Patients:

In a study including 16 geriatric patients between 70 and 78 years of age who received simvastatin 40 mg/day, the mean plasma level of total inhibitors was increased approximately 45% compared with 18 patients between 18-30 years of age [see USE IN SPECIFIC POPULATIONS (8.5)].

Drug Interaction Studies

Simvastatin acid is a substrate of the transport protein OATP1B1. Concomitant administration of inhibitors of the transport protein OATP1B1 and/or CYP3A4 may lead to increased exposure of simvastatin acid. Cyclosporine has been shown to increase the AUC of statins; although the mechanism is not fully understood, the increase in AUC for simvastatin acid is presumably due, in part, to inhibition of CYP3A4 and/or OATP1B1 [see DRUG INTERACTIONS (7)].

Table 4 displays the effect of coadministered drugs or grapefruit juice on simvastatin systemic exposure [see DRUG INTERACTIONS (7)].

Simvastatin's Effect on the Pharmacokinetics of Other Drugs:

In a study of 12 healthy volunteers, simvastatin at the 80-mg dose had no effect on the metabolism of the probe cytochrome P450 isoform 3A4 (CYP3A4) substrates midazolam and erythromycin. Simvastatin is not an inhibitor of CYP3A4 and is not expected to affect the plasma levels of other drugs metabolized by CYP3A4.

Coadministration of simvastatin (40 mg QD for 10 days) resulted in an increase in the maximum mean levels of cardioactive digoxin (given as a single 0.4 mg dose on day 10) by approximately 0.3 ng/mL [see DRUG INTERACTIONS (7.2)].

In a 72-week carcinogenicity study, mice were administered daily doses of simvastatin of 25, 100, and 400 mg/kg body weight, which resulted in mean plasma drug levels approximately 1, 4, and 8 times higher than the mean human plasma drug level, respectively (as total inhibitory activity based on AUC) after an 80-mg oral dose. Liver carcinomas were significantly increased in high-dose females and mid- and high-dose males with a maximum incidence of 90% in males. The incidence of adenomas of the liver was significantly increased in mid- and high-dose females. Drug treatment also significantly increased the incidence of lung adenomas in mid- and high-dose males and females. Adenomas of the Harderian gland (a gland of the eye of rodents) were significantly higher in high-dose mice than in controls. No evidence of a tumorigenic effect was observed at 25 mg/kg/day.

In a separate 92-week carcinogenicity study in mice at doses up to 25 mg/kg/day, no evidence of a tumorigenic effect was observed (mean plasma drug levels were 1 times higher than humans given 80 mg simvastatin as measured by AUC).

In a two-year study in rats at 25 mg/kg/day, there was a statistically significant increase in the incidence of thyroid follicular adenomas in female rats exposed to approximately 11 times higher levels of simvastatin than in humans given 80 mg simvastatin (as measured by AUC).

A second two-year rat carcinogenicity study with doses of 50 and 100 mg/kg/day produced hepatocellular adenomas and carcinomas (in female rats at both doses and in males at 100 mg/kg/day). Thyroid follicular cell adenomas were increased in males and females at both doses; thyroid follicular cell carcinomas were increased in females at 100 mg/kg/day. The increased incidence of thyroid neoplasms appears to be consistent with findings from other statins. These treatment levels represented plasma drug levels (AUC) of approximately 7 and 15 times (males) and 22 and 25 times (females) the mean human plasma drug exposure after an 80 milligram daily dose.

No evidence of mutagenicity was observed in a microbial mutagenicity (Ames) test with or without rat or mouse liver metabolic activation. In addition, no evidence of damage to genetic material was noted in an in vitro alkaline elution assay using rat hepatocytes, a V-79 mammalian cell forward mutation study, an in vitro chromosome aberration study in CHO cells, or an in vivo chromosomal aberration assay in mouse bone marrow.

There was decreased fertility in male rats treated with simvastatin for 34 weeks at 25 mg/kg body weight (4 times the maximum human exposure level, based on AUC, in patients receiving 80 mg/day); however, this effect was not observed during a subsequent fertility study in which simvastatin was administered at this same dose level to male rats for 11 weeks (the entire cycle of spermatogenesis including epididymal maturation). No microscopic changes were observed in the testes of rats from either study. At 180 mg/kg/day, (which produces exposure levels 22 times higher than those in humans taking 80 mg/day based on surface area, mg/m²), seminiferous tubule degeneration (necrosis and loss of spermatogenic epithelium) was observed. In dogs, there was drug-related testicular atrophy, decreased spermatogenesis, spermatocytic degeneration and giant cell formation at 10 mg/kg/day, (approximately 2 times the human exposure, based on AUC, at 80 mg/day). The clinical significance of these findings is unclear.