Absorption of drugs - Pharmacokinetics

Absorption is the transport of drugs from the drug (oral, injection) into the bloodstream and then throughout the body, to which effect. Thus the absorption will depend on:

- Solubility of drugs. Drugs used in the form of an aqueous solution more readily absorbable form of oil, suspension or rigid.

- PH for absorption in place that affect the ionization and solubility of drugs.

- The concentration of the drug. Concentrations as high as rapidly absorbed.

- Circulation in the absorption: the more circuits, more rapidly absorbed.

- The area of the absorption. The lungs, intestinal mucosa large area, quickly absorbed.

Since the factors that showed the road taken the medication will have a great impact on the uptake.

Except intravenously, in the process of absorption into the circulation, part of the drug will be destroyed by the digestive enzymes, cells of the intestine, especially in the liver, which has an affinity for drugs . Part drugs were destroyed prior to the cycle called "first pass metabolism" (absorbed or metabolized by hepatic metabolism is often the first time since taking). The new section is circulated to promote pharmacological effects, called bioavailability (bioavailability) of drugs.

Following points through the usual route of administration à v characteristics of them.

Drug absorption from the gastrointestinal tract

The advantage is easy to use because of the natural sugar absorption.

The downside is that the digestive enzymes are destroyed or drug complexes with slow food absorption. Sometimes drugs stimulate gastrointestinal mucosa, causing ulcers

Absorbed through the oral mucosa: sublingual drug

Do drugs directly into circulation should not be destroyed gastric, hepatic metabolism is not the first time

drug

The drug will pass through the stomach and intestine with the following characteristics: thick ODA:

- There pH = 1- 3 should only absorb weak acid, less ionized, such as aspirin, phenylbutazone, barbiturates.

- Generally less mucosal absorption for less vascular, contains more cholesterol, while no longer the drug in the stomach.

- When hungry absorbed faster, but excitable * In the small intestine:

Where the absorption is mainly due to the absorption of very large area (> 40 m 2), the perfused much, pH increases to base (pH 6 to 8).

- Are less ionized but if little or no lipid soluble (Sulfaguanidine, streptomycin) is less absorbed.

- The drug carries amine 4 will be difficult to absorb strongly ionized, for example the type of Cura.

- The sulfate anion SO4- - unabsorbed: MgSO4, Na2SO4 only effective bleaching.

Rectal suppository

When not be administered orally (by vomiting, coma caused by, or in children) then put on medication labor ng anus. Digestive enzymes are not destroyed, about 50% of drug absorbed from the rectum will pass hepatic metabolism original subject.

The downside is not completely absorbed and can irritate the lining of the anus.

injections

- Subcutaneous injection: because many sensory nerve fibers to pain, less blood vessels to slow the absorption of drugs

- Intramuscular: to overcome the above disadvantages of two subcutaneous injections - some drugs can cause muscle necrosis as Ouabain, calcium chloride shall not be administered intramuscularly.

Intravenous injection: the drug is rapidly absorbed, completely, can be quickly adjusted dose. Use of aqueous injection or intramuscular irritating not to be less sensitive for intravascular blood dilution and injection drug faster if slow.

Soluble drugs, drug precipitate of blood components h ay dissolving drugs are not injected red blood vessels.

Topical

- Absorbed through the mucosa: drugs may apply, drip into the nasal mucosa, throat, vagina, bladder to the treatment site. Sometimes, due to rapid absorption, directly into the blood, do not be evil c enzymes destroyed in the process of absorption should still have systemic effects: ADH nasal inhalation powder; anesthetics (lidocaine, cocaine) applied topically, can be absorbed, causing systemic toxicity.

- Dermal: less drug can be absorbed through intact skin. The topical (ointment, youth c massage, plaster) agricultural work site antiseptic, antifungal, analgesic.

However, when skin lesions, infections, burns ... drug can be absorbed. Some fat-soluble toxins can be absorbed through the skin causing systemic toxicity (organophosphate pesticides, toxic industrial aniline).

Moisturizing ointment place (bandage), massage, use vasodilators in place, using the method of ion -

di (Iontophoresis) drugs are absorbed through the skin increases.

There are new forms of medication patches, releases the drug slowly and steadily over the skin, maintaining a stable dose reachable enough blood: scopolamin patches, estrogen, nitrites.

Caucasian infants and young children, with thin stratum corneum, permeability strong, easily irritated, so be cautious when using the restricted area of the ointment.

- Eye drops: mostly weights i work place. When drugs flowing through the tube tip - down rules for the nasal mucosa, the drug can be absorbed directly into the bloodstream, causing unwanted effects.

The other way

- Through lung gases and vaporized medicine can be absorbed through the alveolar epithelial cells, airway mucosa. Since a large area (80-100 m2) should be rapidly absorbed. This is the way the absorption and elimination of anesthetic vapor. The absorption depends on the concentration of anesthetic in the air inhaled, respiratory ventilation, the solubility of anesthetics in blood.

Some drugs can be used as a spray for topical treatment (asthma).

- Inject the spinal cord: usually injected into the subarachnoid space or epidural to numb the lower

(lower extremities, pelvis) with high density solution (hyperbaric solution) than CSF.

Pharmacokinetic parameters of absorption: bioavailability (F)

define

The bioavailability F (bioavailability) is the percentage of drugs in circulation was also active as the velocity and absorption (Cmax and Tmax expressed through) than the dose used. The bioavailability reflects absorption.

meaning

- When changing the excipients, the apothecary will change the solubility of the drug (active ingredient) and change of medication F. Thus, two types of cells ch ế same product can have two different bioavailability. The concept of bioequivalence (bioequivalence) used to compare the F of different dosage forms of the active ingredient 1: F1 / F2.

- When changing the chemical structure, can make changes F: Ampicillin with F = 50%

Amoxicillin (attach additional OH group) with F = 95%.

- The hepatic drug metabolism as the first, or transformed into circulation before (first pass metabolism) reduces the bioavailability of the drug. But sometimes because of the drug through the liver to be metabolized to active though oral bioavailability is low but the pharmacological effects are not bad intravenous injection. For example propranolol have oral bioavailability is 30% but it is metabolized in the liver to 4 - OH still active as propranolol propranolol.

- The F factor altering drug user:

Dietary changes the pH or gastrointestinal motility. . Age (children, elderly): change of the enzyme activity. . Medical conditions: constipation, diarrhea, liver failure.

Drug interactions: two drugs may dispute in which the absorption or alter the solubility, the separation of each other.