Continued Actions of Drugs

Subcutaneous and Intramuscular Injections •Subcutaneous injection injection under the skin also known as "skin popping" if the material injected is extremely irritating to the tissue, the skin around the site of injection might die and be shed intramuscular injection absorption is more rapid from intramuscular injection than from Subcutaneous injection because of the greater blood supply in muscles *alasorption of drugs is most rapid when the injection is into the deltoid muscle of the arm and least rapid when the injection is in the buttock - larger volumes of material can be deposited in a muscle Inhalation • efficient way of delivering a drug • onset of drug effects is rapid because the capillary walls are accessible in the lungs, and the drug thus enters the blood quickly produces more rapid effects for psychoactive drugs than intravenous administration blood from the lungs, which contains the drug, moves directly to the brain Transport in the Blood drug molecules attach to protein molecules most common protein involved albumin inactive in this state and cannot leave the blood protected from inactivation by enzymes • free or unbound drug molecules can move to sites of action in the body release of protein-bound drug occurs to maintain the proportion of bound to free molecules drugs vary in their affinity for binding with plasma proteins 'a drug with affinity will displace a drug with low affinity, and thus, the drug with low affinity exists in the unbound form * increase in the unbound drug concentration helps move the drug out of the bloodstream to the sites of action faster Blood-Brain Barrier • in general, only small lipophilic molecules enter the brain heroin is more lipophilic than morphine, and thus, it is more potent • albout 85% of brain Capillaries are covered with glial cells, and there is little extracellular Space next to the blood vessel walls -active transport Systems may be needed to move chemicals in and out of the brain Cerebral trauma can impair the blood-brain barrier and permit agents to enter that. normally would be excluded Mechanisms of Drug Action • effects on all neurons "drugs act on the semipermeable membrane of neurons * alter the electrical characteristics of the neuron by influencing its permeability • effects on specific neurotransmitter Systems "drugs may aher the availability of a neurotransmitter by changing the transmitter Chemicals rate of: Synthesis * metabolism * release from storage vesicies. * reuptake into the releasing neuron "drugs may activate or prevent the activation of a receptor Drug Interactions *all depressant drugs, accond, and all narcotics tend to slow down the respiration rate Combining any of these drugs can result in respiratory depression. Combining Stimulants and depressants Complicated interactions occur ex: combination of an upper, or methamphetamine, and a downer, or acconol *methamphetamine lessens alcohol-related performance disruptions *alcohol lessens methamphetamine-related sleep disruptions * produces greater increases in heart rate and eupnaria Drug Deactivation • a drug ceases to have an effect when it is excreted unchanged from the body or is Chemically changed Common way is for enzymes in the liver to act on the Chemical Structure drug molecules tす change their enzyme induction "when the body's cells detect the presence of a foreign drug, they produce more of the enzyme that breaks down that molecules CYP 450 family, the most important drug-metabolizing liver enzymes, is specialized to inactive various general foreign chemicals ingested -important for: * tolerance to a particular drug * interactions with other drugs broken down by the same enzyme increased rate of metabolism may atter the effectiveness of a previously effective drug dose many drugs have active metabolites that produce effects similar to those of the origincl drug and prolong the effects considerably - ex: marijuana and diazepam, or valium prodrugs are being developed inactive in original form and active only when attered by liver enzymes Tolerance and Withdrawal Symptoms • drug disposition, or pharmacokinetic, folerance -increased metabolism or excretion reduces the effect of the subsequent dose •may relate to enzyme activity or the alteration of the pH of the urine behavioral tolerance -drug continues to have the same biochemical effect but with a reduced effect on behavior *reduced behavioral effect is a result of a drug user leaming to compensate pharmacodynamic tolerance leads to a reduced effectiveness of the drug Causes withdrawal Symptoms