Bioavailability

Bioavail­abil­ity Defined

Bioavail­abil­ity is a term heard often when dis­cussing med­ica­tion.  Do con­sumers know what it means??

For a med­ica­tion to be use­ful for the patient, it needs to be bioavail­able for the body to use.  In another way, when you take a tablet the med­i­cine in that tablet needs to be able to get out of the diges­tive sys­tem and into the blood stream.  There are two fac­tors that affect bioavail­abil­ity:
•    Sol­u­bil­ity of the drug in diges­tive flu­ids
•    Per­me­abil­ity of the drug.  How eas­ily does the drug pass through the diges­tive lin­ing into the blood stream.

A drug that is very sol­u­ble in the diges­tive sys­tem usu­ally has a high bioavail­abil­ity.  A drug that is highly per­me­able has a high bioavail­abil­ity.  There is a clas­si­fi­ca­tion sys­tem that describes bioavail­abil­ity pic­to­ri­ally.  The pic­ture below describes the BCS (Bio­phar­ma­ceu­tics Clas­si­fi­ca­tion Sys­tem).  Each drug mol­e­cule can be clas­si­fied as Class I, II, III or IV.  Class I drugs are usu­ally very easy to for­mu­late into a med­ica­tion.  Many of the drugs in devel­op­ment today are Class II or IV.  These drugs are very dif­fi­cult to for­mu­late because they are very insol­u­ble or do not per­me­ate diges­tive lin­ing.  In the phar­ma­ceu­ti­cal for­mu­la­tion busi­ness, those com­pounds are nick­named “brick-dust”, some­thing that isn’t going anywhere.

For more infor­ma­tion, please see the following.

FDA:  http://www.fda.gov/AboutFDA/CentersOffices/CDER/ucm128219.htm
Wikipedia:  http://en.wikipedia.org/wiki/Biopharmaceutics_Classification_System

Bioavail­abilty of nutri­tional sup­ple­ments is also stud­ied.  There are a vast num­ber of metal based nutri­ents that a per­son needs in trace quan­ti­ties to sur­vive.   Did you know that your body con­tains 3.5 grams of iron and 2.5 grams of zinc?  Here is a short list of some of the impor­tant trace met­als and their role.
•    Iron — blood func­tion
•    Cop­per — elec­tron and oxy­gen trans­port
•    Zinc — antiox­i­dant and immune sys­tem prop­er­ties (proposed!)

Food For­ti­fi­ca­tion ver­sus Nutri­tional Sup­ple­men­ta­tion

Food is for­ti­fied with trace ele­ments so defi­cien­cies in the pop­u­la­tion are reduced.  Cereal is for­ti­fied.  Read the Nutri­tion Facts on the clos­est box of cereal.  In addi­tion to added vit­a­mins you’ll see “zinc (zinc oxide)”.  Zinc oxide is very inex­pen­sive and very sta­ble; a good can­di­date for food for­ti­fi­ca­tion.  It does, how­ever, have fairly poor bioavail­abil­ity.  Luck­ily, you don’t need a lot of zinc daily.  The USRDA for zinc is 8 mg to 11 mg.

Nutri­tional sup­ple­ments are designed to com­pen­sate for low bioavail­abil­ity by uti­liz­ing a metal con­tain­ing organic chem­i­cal for bet­ter bioavail­abil­ity.  An exam­ple is zinc picol­i­nate.  Zinc picol­i­nate is con­sid­er­ably more bioavail­able than zinc oxide; it is also more expen­sive hence its use in nutri­tional sup­ple­ments. (Bar­rie, SA, Wright, JV, Piz­zorno, E, Kut­ter, and Bar­ron, E  Com­par­a­tive absorp­tion of Zinc Picol­i­nate, Zinc Cit­rate and Zinc Glu­conate in Humans.  Agents and Actions.  21 1/2 (1987)

Please, if you are con­sid­er­ing tak­ing a nutri­tional sup­ple­ment in addi­tion to your nor­mal daily diet TALK WITH YOUR DOCTOR.  Exces­sive intake of most any­thing can be very bad.  Too much zinc, for exam­ple, “Zinc tox­i­c­ity can occur in both acute and chronic forms. Acute adverse effects of high zinc intake include nau­sea, vom­it­ing, loss of appetite, abdom­i­nal cramps, diar­rhea, and headaches.”

For more infor­ma­tion on Zinc sup­ple­men­ta­tion: The Office of Dietary Sup­ple­ments, National Insti­tute of Health.

© Grove Ridge Con­sult­ing, 2011