Organic anion transporting polypeptide (OATP)

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The information presented here is NOT A COMPLETE LIST of OATP inducers, inhibitors, and substrates
Not all drug interactions are clinically significant. Potential drug interactions should be researched, and medication changes should only be made after consulting a health professional.

CYP - Cytochrome P450

OATP - Organic anion transporting polypeptide

Substrate - a drug that is metabolized by a certain enzyme is a substrate of that enzyme

OATP is sometimes referred to by its gene name, "SLCO - 1A2, 1B1, 1B3, ..."
OATP is a family of transport molecules located in cell membranes (not to be confused with OAT1, OAT2, OAT3, etc. which are another family of transporters)
OATP molecules transport drugs from the bloodstream into cells (influx) so that they can be metabolized. OATP molecules transport drugs that have a negative charge (anions).
Currently, eleven different OATPs have been discovered
Two of the polypeptides (OATP1B1, OATP1B3) have been studied extensively, and two (OATP2B1, OATP1A2) have very limited data. The other polypeptides are not well characterized.

Inducers - increase the activity of OATP (no OATP inducers have been discovered)
Inhibitors - block the action of OATP
When OATP inhibitors are taken with other medications that are transported by OATP, they can alter the elimination of that medication
Drugs may be transported by OATP and also inhibit it at the same time

If two drugs are transported by OATP, they may "compete" for it, and this can alter the elimination of one or both of the drugs

When a person is taking three or more drugs, the potential for compounded interactions exists

Drug A is metabolized by CYP2D6, and it is transported by OATP
Drug B inhibits CYP2D6. Drug C inhibits OATP.
When Drug A is taken with Drug B, its elimination is partially decreased, but it is not significant
When Drug A is taken with Drug B and Drug C, its elimination is decreased substantially and the interaction becomes significant

OATP is coded for by a gene called SLCO
Since individuals vary in their genetic makeup, their SLCO gene may vary also
Some people have SLCO genes that produce OATP molecules that are less effective
Genetic variations in the SLCO gene can affect how an individual eliminates a drug

Information on drug interactions can be difficult to assimilate
Certain drug interactions and metabolic pathways are well-documented while many are not

When a new drug is being developed, the FDA requires that it be tested for drug interactions with a small number of medications that are known to have significant interactions
Obviously, there is no way to test a medication in every possible drug combination that may occur. This means most drugs come to market with incomplete drug interaction profiles.
After a medication is prescribed to a large number of people, other drug interactions are inevitably discovered

Much of the research involving drug metabolism and drug interactions occurs in vitro meaning in a lab, or outside of the human body
Animal models and cell cultures are often used to test drugs for metabolic pathways and interactions
Findings from in vitro experiments do not always translate into what actually happens in the human body (in vivo)

Drug metabolism is an evolving field of medicine and pharmacology
Researchers are just beginning to understand all the different systems that are involved in how the body metabolizes and eliminates drugs
Cell transport systems (ex. p-glycoprotein, OAT, etc.) are a relatively new area of pharmacology and information about how these systems affect drug elimination is evolving

Not all drug interactions are known or can be predicted
Good information on possible drug interactions may not be available
Not all drug interactions are significant
Always consult your physician or pharmacist before changing your medication if you are concerned about a possible drug interaction

ORGANIC ANION TRANSPORTING POLYPEPTIDE (OATP)