Chapter 4

Chapter 4 - What Happens to the Drugs after Taken - Ways of administering drugs: 1. Oral Ingestion - Expected to disintegrate in the stomach and get absorbed in the bloodstream from the stomach or small intestine. Some drugs are designed not to dissolve in the bloodstream (aspirin) or some have to be taken with food (antibiotics) to avoid irritation of the stomach (internal bleeding). A disadvantage is sometime the drug is destroyed by the stomach acid before it is absorbed 2. Inhaled - Rapidly absorbed because of the number of blood vessels in the lungs and nasal region. Nasal decongestants shrink nasal membrane and some proteins can be inhaled in the form of an aerosol spray. Disadvantage: Possible drug induced irritation of the mucous membrane. 3. Paternal(Injected) - Hyperdermic injection into muscle, veins, beneath skin, etc. Advantage: Rapid access to bloodstream therefore rapid action, and can be stopped if necessary. Disadvantage: possible pain, need for sterility, and drug has to be in an injectable form which are more expensive than other forms 4. Body Orifices - Eye, ear and nose drops; dissolving tablets under tongue, buccal cavity between cheek and teeth(chewing tobacco) 5. Skin Application - Petroleum based creams (topical antibiotics) such as polysporin, oil in water emulsions, and some aerosol spray 6. Transdermal Skin Patches - Slow absorption into the bloodstream from a patch placed on some area of the body ex. Nicotine patches for nicotine withdrawal. Best for potent drugs which are taken for long periods of time. The drug must have significant solubility in oil and water to pass through the semipermeable membrane in the patch and the skin 7. Implantable Drug Delivery - Using pellets, reservoirs or pumps can be used to take drugs such as insulin, morphine, antibiotics, and contraceptives. Also include implanted drugs 8. Microsponges - For cosmetics, acne medication (benzoyl peroxide microsponge) - Fake drugs are hard to identify. Fake drugs often don’t contain active ingredient and have non- standard weights - Identifying features of a drug include colour and shape Tablet Treatments - Some foil wrapped to keep out moisture, almost all contain binders to hold the active ingredient together such as gelatine to ease swallowing. Sometimes enterically coated to dissolve in the small intestine rather than the stomach. Aspirin most common - Aspirin - Often enterically coated - Bayer advanced aspirin has smaller particles by a factor of ~10 making it act against pain faster since it dissolves 6x faster. Patients say pain relief starts after 16 minutes vs 100 minutes with normal aspirin. The increased surface area (smaller particle sizes) increases rates of chemical processes and reactions - Liquid Medications - (ex. cough syrup) Sometimes aqueous solutions so shelf life decreases and may have to refrigerate. Heat, light and oxygen can cause degradation - Pharmacokinetics - Study of the rates of change of drug concentrations in the body. Factors involved are: 1. Absorption - Starts in the “unloading area” called the capillary bed which is a network of tiny blood vessels in the lungs, stomach and intestines. Drugs can enter or leave the bloodstream via the capillary bed a. because the stomach juices are really acidic (pH 1-3) weak organic acids such as aspirin are easily absorbed but, basic molecules such as amines aren’t absorbed by stomach but instead usually absorbed by the small intestine b. Rich dairy products can inhibit antibiotics absorption 2. Distribution - After absorption delivers drug to other body fluids, cells, tissues or specific molecular targets in fluids. a. Body Tissue Targets - Muscle, fat, bone, and organs b. Molecular Targets within fluids - Some drugs target albumins and other blood proteins c. Barriers to Absorption - The blood-brain barrier. As a general rule fat soluble drugs penetrate this more easily than water soluble drugs. Drugs that easily penetrate the B-B barrier include tranquilizers, LSD, narcotics, marijuana and alcohol. (Oxidation products in alcohol cause a dysfunction of the B-B barrier and can increase the effects of other drugs) d. Of Fat Soluble Drugs - Non polar molecule that remain in the body longer than polar ones. Thus THC’s stay in the body for a long time. All vitamins except B and C are fat soluble e. Water dissolves polar molecules (salts, alcohols and