Alendronate


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Pharmacokinetics of Alendronate

Pharmacokinetics or the way in which drugs travel and metabolize throughout the body is important to prescribing physicians and patients. Pharmacokinetic calculations play a crucial role in the consideration of dosage requirements. Factors that affect the drug concentration after administration include: route of administration, genetic make-up, body size/weight, water and electrolyte imbalances, metabolic considerations and general overall medical condition of the person taking it.

Drug concentration is defined by the amount of a drug remaining in a measured amount of blood plasma normally measured in microgram units per liter. Mathematical modelsi are then used to determine concentration values. These values assist physicians in assessing potential drug interactions and toxicity implications before drug administration. There is a common acronym used by the pharmaceutical community known as L.A.D.M.E.

LIBERATION

Liberation is the release of medication. You may have noticed pill advertisements indicating enhanced performance in the way of extended release tablet forms. There are also delayed, or slow release versions available depending on what is recommended by your physician.

ABSORPTION

The properties of absorption are also determined by route of administration and the properties of the drugs themselves. In order to survive in its full integrity, the drug must be able to stand up to the digestive system. Additionally, unless given in an IV format, the drug must pass through several semi permeable membranes (think of a spongey type surface with many tiny holes) before it reaches the point of active circulation within the body. Once the drug is absorbed it is the distributed through the blood stream and then to the tissues.

DISTRIBUTION and HALF LIFE

Distribution is the how the drug flows through the body. Half-life is the amount of time for the drug concentration to be cut in half. This is determined by the amount of drug left in the plasma of the blood or equal to the amount of time after the dosage of the ingested drug is reduced by half.

*An example would be a drug with a doge of 100mg with a half- life of 15 minutes means that the half- life after the first initial dose would be 50 mg after 15 minutes, 25mg after 30 minutes (½ of the 50mg and time x 2) In pharmacokinetics, the half-life is also used to determine a measured amount of time for a drug to be completely out of the body. Typically, it is estimated that it takes 4-5 half-lives for a drug to be completely eliminated from the bloodstream.

METABOLISM and EXCRETION

Before the drug can be excreted, it first has to be metabolized. The metabolic process is made possible by two separate enzymes phases:

The first phase involves a series of chemical modifications of the drug by oxidation, reduction, and hydrolysis.

The second phase involves enzymes that serve in the conjugation of the drug so that it can be excreted by the urine or bile.

Drug excretion rate depends on the concentration volume in the blood plasma and is often referred to as the clearance rate. The excretory system is made up of the kidneys, ureters, bladder, and urethra, however, drugs can also be eliminated from the body by way of sweating, crying (tears), breathing, and saliva. In determining the length of time before a drug is completely out of the body, physicians refer to the drug's half-life. As the last part of the pharmacokinetic process, excretion completes the metabolic phase of eliminating the drug from the bloodstream.

 

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