Dosage

Dosage is the amount to be given at a time. It is the regulation of the frequency, size, and number of doses. Dosage is a major determinant of drug action and responses both therapeutic and adverse. This includes both the amount of drug and the frequency of administration.

Toxic doses are doses that produce signs and symptoms of toxicity while, lethal doses are the ones that cause death.

Route of Administration

This affects drug actions and response largely by influencing absorption and distribution.

Drug-Diet Interactions

Food slows absorption of oral drugs by slowing gastric emptying time and altering Gastrointestinal secretions and motility. This then makes the drugs to dissolve and deliver to absorptive sites more slowly. It can also form and insoluble drug-food complex.

Drug-Drug Interaction

The action of a particular drug may be increased or decreased by its interaction with another drug in the body.

1. Additive effect. It improves desirable properties of the drug.
2. Synergism or potentiation. Use of two or more agents that produce a pharmacological response greater than what would be expected by individual effects of each.
3. Interference. It inhibits the performance of the drug.
4. Displacement. It replaces the action of the drug.

1. Antidote
2. Non-absorbable compounds
3. Enzyme inducer
4. Increased excretion

Age

The effects of drugs are more pronounced in young children and elderly people. The drug action depends largely on age and developmental stage.
When pregnant, many drugs when absorbed cross the placenta and adversely affect the fetus.
Newborns generally handles drugs less efficiently than the older children or adult.
Older children metabolizes drug rapidly and handles drugs similarly to healthy adults.
Elderly adults have physiologic changes that may alter all pharmacokinetic processes. All their physiologic changes may slow excretion and promote accumulation of drugs in the body.

Body Weight

People greater than the average weight need a larger dose, provided that renal, hepatic, and cardiovascular functions are adequate and normal.

Sex

The influence is more pronounced during pregnancy and breast feeding.

Pathologic Conditions

The disease processes are capable of altering pharmacokinetic processes.

Psychologic Considerations

Influences individual response to drug administration. An example of this is the placebo effect or response, where the client is given an inert or sugar pill and is told that it would improve his condition. The client believes it and sometimes causes a therapeutic effect thus showing signs of improving health.

Additional Elements of the Receptor Theory of Drug Action include the following

1. Only drugs with an affinity for the affected tissues are able to interact with receptors and exert pharmacologic effects.
2. When a drug molecule chemically binds with a cell receptor, two types of pharmacologic effects may occur:
   • Agonism or agonist effect where it prevents stimulation of cell function.
   • Antagonism or antagonist effect where it prevents stimulation of cell function by natural body substances (neurotransmitters and hormones) or molecules of other drugs. The antagonist drug will occupy all receptor sites and prevent their interaction with other substances.
3. The number of receptor sites available to interact with drug molecules largely determines the extent of drug action.

Specific Mechanism of Drug Movement

In order to act or produce an effect, drugs must be able to reach tissue fluids surrounding responsive cells in adequate concentration.

1. Passive diffusion is the most common mechanism. It is the movement of a drug from an area of higher concentration to lower concentration.
2. Facilitated diffusion, where drug molecules combine with a carrier substances or enzymes of other protein.
3. Active transport is when the drug molecules are moved from an area of lower concentration to one of higher concentration. It requires both a carrier substance and the release of cellular energy

Drug movement and drug action are affected by drug’s ability to cross cell membranes. Cell membranes are complex structures composed of lipid and protein.

• Lipid-soluble drugs are drugs that cross the cell membrane by dissolving in a lipid layer. Most drugs are lipid-soluble.
• Water-soluble drugs cross cell membranes through pores or openings. Most lipid-soluble drugs are able to cross cell membranes more easily than water-soluble ones.

Two Types of Medication

• Local. This pertains to a particular or certain area of the body. Examples are creams, ointments and local anesthetics
• Systemic. Is absorbed into the blood stream and circulated to various parts of the body.

Sources of Drugs

• Plants. This yields pharmacologically active substance like alkaloids.
• Animals. Are hormones extracted from animals.
• Minerals. Sources provide iron and potassium preparation among others.
• Synthetic. Are artificially produced from chemical substances in laboratories. Semi-synthetic drugs are naturally occuring substances that have been chemically altered.

Drug Nomenclature is the scientific or systemic naming of the drugs. They are classified or grouped according to effects on particular body systems, therapeutic effect and the chemical characteristics.

A Prototype is a model or individual drug that represents classifications or groups of drugs. It is the standard with which other drugs are compared. The prototype drugs are extremely stable type of drugs. Usually, new drugs can be assigned to a group and compared with an established prototype.

Drugs and their Names

• Generic. Is related to the chemical or official name. It is independent of the manufacturer.
• Brand. The brand name is the trade name. it is designated and patented by the manufacturer.

Sources of Drug Information

• Pharmacology book. Is the best source of information for beginners. It describes the source of drugs in relation to therapeutic use and their effects. It gives an overview of drug classification and its effect on the human body.
• Drug reference book. Most helpful in relation to individual drugs.
• American Formulary Service
• AMA Drug Evaluation
• Prescription Drug Reference
• Journal or Articles. Describes drug usage in specific disease processes.