Risk Factors For Simvastatin (Zocor®) Side Effects

SLCO1B1

All medications are processed in the liver. The SLCO1B1 gene provides instructions to tell the body how to make liver cell membrane transport proteins that influence how much simvastatin (Zocor®) is taken into the liver for processing. Variants in the SLCO1B1 gene may impair liver uptake activity, causing simvastatin (Zocor®) to build up in the body. If simvastatin (Zocor®) builds up in the body, serious side effects can occur.

Simvastatin (Zocor®) Drug Side Effects

One of the serious potential side effects of simvastatin (Zocor®) is myopathy (muscle weakness). Myopathy is most likely to occur in someone who has reduced or intermediate liver uptake activity (impaired ability to process simvastatin (Zocor®)) and is taking a 40 mg/day dose or higher of simvastatin (Zocor®).

Other side effects of simvastatin (Zocor®) include:

  • dizziness
  • fainting
  • fast or irregular heartbeat
  • fever or chills
  • difficulty breathing or swallowing
  • hoarseness
  • flushing
  • fatigue
  • dark colored urine
  • painful or burning urination
  • urinating less than usual or not at all
  • clay-colored stools
  • swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs
  • weight gain
  • nausea
  • upper stomach pain
  • loss of appetite
  • blisters, rash or hives
  • itching
  • jaundice (yellowing of skin or eyes)
  • sensitivity to light
  • memory loss/forgetfulness
  • confusion

Less serious side effects of simvastatin (Zocor®) may include:

  • headache
  • joint pain
  • mild muscle pain
  • constipation
  • stomach pain
  • indigestion
  • nausea
  • insomnia
  • cold symptoms (sneezing, stuffy nose, sore throat)

SLCO1B1 Gene Variants

There are four genetic variants in the SLCO1B1 gene that impact the way the body responds to simvastatin (Zocor®). Your response to simvastatin (Zocor®) is determined by your specific combination of genetic variants in the SLCO1B1 gene, not simply by the number of variants that you have. Each combination of genetic variants in or near a gene is called a "haplotype." There can be many different combinations of variants for each gene. To distinguish one combination of variants from another, scientists sometimes use a numbering system. For example: one combination of variants within the SLCO1B1 gene may be called "star 3", written as *3, while another combination is known as *1.

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How Haplotypes Are Inherited

Since we have two copies of each gene, one from our mother and one from our father, each person will have one combination of variants (called a haplotype) from each parent. When genetic testing is performed the results are noted as two numbers (each representing the haplotype from each parent), separated by a slash. For example, someone who inherited the combination of variants from their mother known as *3 and the combination known as *5 from their father would be a *3/*5 for the gene tested. Some people have combinations of variants that are rare and have not been studied or named. Sometimes, the genetic test that is performed cannot determine a person's result with certainty.

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The Impact of SLCO1B1 Gene Variants on Liver Uptake Activity

Different combinations of variants in the SLCO1B1 gene can be used to predict how a person will respond to simvastatin (Zocor®). A person's predicted liver uptake activity is based on the two SLCO1B1 haplotypes they inherited from their parents. The following table summarizes the possible liver uptake activity levels that are determined by variants in the SLCO1B1 gene.

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Are There Other Factors That Can Affect How I Respond to Simvastatin (Zocor®)?

Many factors affect how your body will respond to a medication. Non-genetic factors that affect your response to simvastatin (Zocor®) include interactions between different drugs you may be taking, interactions between drugs and your other health conditions (like liver or kidney disease), and interactions between drugs and your lifestyle.