I found an excellent explanation of metabolism of drugs, and this explains why people who are more active metabolize warfarin faster and generally require a higher dose than others.
When you're active, you're pumping your blood through your body faster, thus going through the liver more times. (See below about enzymes.) This was written by
Pharmacy Author: Omudhome Ogbru, Pharm.D.
Medical Editor: Jay Marks, M.D.
http://www.medicinenet.com/script/main/art.asp?articlekey=19912
Change in drug metabolism and elimination
Most drugs are eliminated through the kidney in either an unchanged form or as a by-product that results from the metabolism (alteration) of the drug by the liver. Therefore, the kidney and the liver are very important sites of potential drug interactions. Some drugs are able to reduce or increase the metabolism of other drugs by the liver or their elimination by the kidney.
Metabolism of drugs is the process through which the body converts (alters or modifies) drugs into forms that are easier for the body to eliminate through the kidneys. (This process also converts drugs that are given in inactive forms into active forms that actually produce the desired effect.) Most drug metabolism takes place in the liver, but other organs also may play a role (e.g., the kidneys). The cytochrome P450 enzymes are a group of enzymes in the liver that are responsible for the metabolism of most drugs. They are, therefore, often involved in drug interactions. Drugs and certain types of food may increase or decrease the activity of these enzymes and therefore affect the concentration of drugs that are metabolized by these enzymes. An increase in the activity of these enzymes leads to a decrease in the concentration and effect of an administered drug. Conversely, a decrease in enzyme activity leads to an increase in drug concentration and effect.
When you're active, you're pumping your blood through your body faster, thus going through the liver more times. (See below about enzymes.) This was written by
Pharmacy Author: Omudhome Ogbru, Pharm.D.
Medical Editor: Jay Marks, M.D.
http://www.medicinenet.com/script/main/art.asp?articlekey=19912
Change in drug metabolism and elimination
Most drugs are eliminated through the kidney in either an unchanged form or as a by-product that results from the metabolism (alteration) of the drug by the liver. Therefore, the kidney and the liver are very important sites of potential drug interactions. Some drugs are able to reduce or increase the metabolism of other drugs by the liver or their elimination by the kidney.
Metabolism of drugs is the process through which the body converts (alters or modifies) drugs into forms that are easier for the body to eliminate through the kidneys. (This process also converts drugs that are given in inactive forms into active forms that actually produce the desired effect.) Most drug metabolism takes place in the liver, but other organs also may play a role (e.g., the kidneys). The cytochrome P450 enzymes are a group of enzymes in the liver that are responsible for the metabolism of most drugs. They are, therefore, often involved in drug interactions. Drugs and certain types of food may increase or decrease the activity of these enzymes and therefore affect the concentration of drugs that are metabolized by these enzymes. An increase in the activity of these enzymes leads to a decrease in the concentration and effect of an administered drug. Conversely, a decrease in enzyme activity leads to an increase in drug concentration and effect.
