Sunday, January 15, 2006

pharmacokinetics

(see Table 10, 11) Pharmacokinetics is the action of drugs in the body over a period of time. Drugs administered orally are absorbed into the blood, distributed by circulation throughout the body and eliminated by detoxification in the liver and by excretion in the urine and bile. Drugs administered topically exert a local effect, although absorption into the blood stream may lead to an intended distant action, such as with nitroglycerin, or with an unintended action, as with systemic absorption of atropine. Parental administration (injection) bypasses gastrointestinal absorption, to be absorbed into the circulation.
Most drugs are absorbed from the gastrointestinal tract. They are usually given in tablet or capsule form, their solubility and rate of dissolution will affect absorption. Other factors that influence gastrointestinal absorption include the structure of the absorptive surface and the metabolic activity of the absorptive cells.
Age changes in gastrointestinal function influences the rate and completeness of drug absorption. Diminished gastric secretion may retard dissolving of tablets, the higher pH may reduce the solubility and absorption of some drugs such as tetracycline and reduce the effectiveness of others such as penicillin. Age-related changes that may impair drug absorption include delayed gastric emptying and reduced gastrointestinal blood flow. The reported effects of aging on gastric emptying time are conflicting. Absorption is affected by drugs that alter the rate of gastric emptying. Many drugs prescribed for the elderly either accelerate or retard gastric emptying. Anticholinergic agents (agents that block the passage of nerve impulses) such as paracetamol/acetaminophen, sulfamethiazole, and riboflavin retard gastric emptying and the delivery of drugs to the upper small intestine where most absorption occurs. Conversely, metoclopramide stimulates upper gastrointestinal motility, accelerating the absorptions of paracetamol/acetaminophen, tetracycline, lithium carbonate, and levodopa. Digoxin absorption from the upper gastrointestinal tract depends upon the form in which digoxin is administered.
Some drugs are better absorbed when given together with drugs that reduce gastrointestinal motility, allowing longer contact with the absorptive surface. When multiple drugs are used, reduced absorption due to binding or inactivation may occur: antacids decrease absorption of digoxin, salicylates, and tetracycline; cholestyramine binds oral anticoagulants, cardiac glycosides, and thyroid preparations.
When drugs are given with food the possibility of food-drug interaction exists: tea and orange juice respectively decrease and increase the absorption of iron, and acidic fruit juices and carbonated beverages inactivate many drugs, such as penicillin, and mineral oil containing laxatives causes malabsorption of fat soluble vitamins.
Brocklehurst, J. C. Textbook of Geriatric Medicine and Gerontology. New York: Churchhill Livingstone, 1985.

1 Comments:

Blogger dark_one said...

My name is Jason Gorman and I am 45 years old. My wife was taking 1200mg of Lithium Carbonate daily prescribed by the doctor for over two years. During this time no lab work was ever ordered. It built up in her system over a period of time. She was taken to the ER where she almost died. Her pulse was down to 31 and her blood pressure as low as 43 over 17. She under went kidney dialysis continuously for over 30 hours in ICU. She spent a total of 5 days in the hospital. I strongly recommend against taking Lithium. At least have periodic Lab Work done. Also if you do take this medication look up the side effects on the internet.

My wife has experienced some of these side effects-
Dizziness, Vomiting, Diarrhea, Confusion, Tremors, Muscle Weakness, Loss of Bladder Control, Inability to talk

I hope this information will be useful to others,
Jason Gorman

Lithium-Carbonate Side Effects

1:09 AM  

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