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Drug Cycle Project - choose a drug and apply it
3
The Drug Cycle of Synthroid (levothyroxine)
By: Paige Strole
The 1st Step!
Absorption
Medicines are absorbed when they travel from the site of administration into the body's circulation. For example Synthroid (levothyroxine) is taken in the form of tablets. Therefore this medication taken by mouth is shuttled via a special blood vessel leading from the digestive tract to the liver, where a large amount of the medicine is broken down. Scientists have looked into the absorption of this drug and have discovered that taking an acidic substance simultaneously may enhance the absorption.
Where Does it Go?
The majority of the Synthroid dose is absorbed from the jejunum and upper ileum
Where Does it Go?
Distribution
Distribution
Once a drug gets absorbed, the next stage of ADME is D, for distribution. Most often, the bloodstream is the vehicle for carrying medicines throughout the body. During this step, side effects can occur when a drug has an effect at a site other than its target. Levothyroxine has a limited volume of distribution, which has been reported to be 11.6 litres (L) in euthyroid volunteers and 14.7 L in primary hypothyroid subjects. This is approximately equivalent to the extracellular fluid volume of the body. All though all of this pharmacokinetics may seem scary essentially this information is saying is that this medication has small amount of distribution within the body and the amount distributed is the same amount as the body water outside cells. Other factors that can influence distribution include protein and fat molecules in the blood that can put drug molecules out of commission by latching onto them.
Distribution Graphic!
- Drug is distributed into most body tissues and fluids.
- The highest levels are found in the liver and kidneys; 99% is protein-bound.
Graphic!
Metabolism
Metabolism
After a medicine has been distributed throughout the body and has done its job, the drug is broken down, or metabolized, the M in ADME. Everything that enters the bloodstream — whether swallowed, injected, inhaled or absorbed through the skin — is carried to the body's chemical processing plant, the liver. There, substances are chemically pummeled, twisted, cut apart, stuck together and transformed by proteins called enzymes. These enzymes are used to break down the drugs. For example levothryoxine is deiodinated. This reaction is the removal of iodine by deiodinase enzyme. Levothryoxide is metabolized in peripheral tissues, primarily in the liver, kidneys, and intestines. About 85% of metabolized levothyroxine is deiodinated.
Steps to Metabolism!
The rate of drug metabolism varies widely between individuals, influenced by genetic and environmental factors. This is the major reason for inter-individual differences in the plasma concentration of some drugs after a standard dose, which leads to wide variation in drug response.
The Steps!
Excretion
Excretion
The now-inactive drug undergoes the final stage of its time in the body, excretion, the E in ADME. This removal happens via the urine or feces. The daily turnover rate for T4 is approximately 10 % while it is approximately 50–70 % for T3, with a slightly faster turnover rate in normal volunteers compared with patients with primary hypothyroidism (both T3 and T4 are metabolic hormones including iodine-containing thyroxine-T4 and triiodothyroxine-T3). Fecal excretion eliminates 20% to 40% of levothyroxine. Half-life is 6 to 7 days.