Pharmacokinetics
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Pharmacokinetics

Pharmacokinetics is what the body does to and with a drug. In both Western and Chinese medicine, the therapeutic response to; as well as paradoxical, cumulative, toxic, allergic, or dependency reactions to drugs and herbs are often due to how the drug or herb is:

  • absorbed from the GI tract
  • distributed to blood and tissues
  • biotransformed (metabolism)
  • excreted via the kidney, liver, lungs and skin

However, pharmacokinetics is not so much of a concern with herbs because human physiology has evolved in harmony with natural substances. Developing over eons, the correct enzymatic pathways of absorption, distribution, metabolism and excretion etc. to deal with what ever nature has in store. This means they are bio-compatible. Whereas, pharmaceuticals are new and foreign substances, which the body has not had time to adapt/ evolve into handling well. The caveat is that plants are made into medicinals (tinctures, essential oils, extracts) which represent the pharmaceutical level of use, which requires more knowledge, skill, and precautions (
Floracopiea)

The other consideration is that each individual has a genetic make-up (genotype & phenotype) that determines how their bodies will react. This is why some people have allergies and sensitivities that others do not, as well as susceptibility to certain diseases. Chinese herbs are prescribed based on many factors, including this constitutional uniqueness. In other words, Chinese medicine already has some principles upon which to determine if a person can or can not handle herbal therapy, and/or certain individual herbs at a particular time. 

In Western pharmacy, it is known that the pharmacokinetics of drugs is very much affected by age, race & gender. As well as body mass index, disease, activity level, dehydration & malnutrition, genetics, and drug-drug interactions. These factors determine when and how an intentionally therapeutic substance becomes an unintentionally toxic substance to an individual. For example:

Gender
According to Soldin & Mattison (2013) women experience more adverse events from drugs compared to men, due to:
  • Differences in gastric fluid acidity, and gut transit time.
  • Differences in body indices (e.g. total body water, blood volume, total body mass, and adipose tissue distribution).
  • The effect of estrogen and progesterone on hepatic enzyme activity, which can increase or decrease drug elimination.

Age
The Beer’s Criteria, from the American Geriatric Society (2012) is a tool that assists providers in “reviewing and grading the evidence for the drugs to avoid in the elderly”. For example, the clearance of antihistamines is reduced with advanced age. Tolerance can develop when antihistamines are used as sleep aides. In the elderly, there is greater risk of anticholinergic effects of antihistamnes (confusion, dry mouth, constipation), and toxicity (American Geriatric Society, 2012). Geriatric patients are at risk for accumulation of lipophilic drugs because of a lower muscle-to-fat ratio. Lower albumin levels due to poor nutrition make them susceptible to the toxicity of highly protein-bound drugs (e.g. coumadin), and acidic drugs (e.g. aspirin).

Race
Johnson (2000) demonstrated that hepatic (first-pass) metabolism, when a drug is inactivated by the liver, is commonly influenced by ethnic differences. But there is wide and unpredictable variation. Drugs that undergo gastrointestinal metabolism and /or drugs that are highly protein bound were also susceptible to alterations in pharmacokinetics by race and ethnicity.
 
INTEGRATIVE MEDICINE TIP: There are a few Chinese herbs that practitioners are careful with due to herbal pharmacokinetics. For example Du Zhong is avoided in those with latex allergies. Certain herbs are avoided if a person is allergic to iodine and shellfish. And powdered herbs (granulars) can contain a preservative that can cause allergic reaction in those who have sulfa allergies. All herbs are used with caution, if at all, if someone is on coumadin. A person my just have an aversion to using herbal substances that contain animal products such as a the very beneficial Lu Rong ( Deer horn antler); tortoise shell; or bone broth soup which is a jing tonic.


References
American Geriatric Society (2012). The American Geriatrics Society 2012 Beers Criteria Update
     Expert Panel. DOI: 10.1111/j.1532-5415.2012.03923.x
Edmunds, Winterton and Mayhew, Stewart (2013). Pharmacology for the primary care provider (4th
     ed.). St. Louis, MO: Elsevier Mosby.
Johnson, J. (2000). Predictability of the effects of race or ethnicity on pharmacokinetics of
     drugs. International Journal of Clinical Pharmacology 38(2), 53-60. 
Soldin, O & Mattison, D. (2013).  Sex differences in pharmacokinetics and pharmacodynamics. Clinical
     Pharmacokinetics. doi:  10.2165/00003088-200948030-00001. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3644551/







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