Basic Concepts of Pharmacology

Jan Bazner-Chandler

CPNP, CNS, MSN, RN

Cellular Physiology

What does a cell do? Exchange material Obtain energy from nutrients Synthesize hormones, neurotransmitters,

enzymes, structural proteins and other complex molecules

Duplicate themselves

Pharmacokinetics

Drugs movement through the body to reach sites of action, metabolism and excretions

Drug Transport

What does this have to do with drug administration?

Drugs must reach and interact with or cross the cell membrane to stimulate or inhibit cellular function

Key Concepts

Absorption Distribution Metabolism Excretion Serum Drug Levels Serum Half-life

Oral Drugs

Dosage is determined by how much of the drug is required to be taken by mouth to given the desired affect.

Bioavailability – portion of the drug that reaches the systemic circulation

Oral Drugs

Drug needs to be taken orally – pill v liquid – size of pill – make up of pill

Time in the stomach – is the stomach empty – full – does it make a difference on how drug is absorbed

Small intestine – large surface area for absorption of nutrients and minerals

Amoxicillin Suspension

Amoxicillin Chewable Tablets

Amoxicillin Tablets

What else might influence oral drug absorption? Food in stomach Certain juices – grapefruit juice Milk – binds with molecules of some drugs so

that the drug is never absorbed Orange juice – enhances absorption of iron

taken orally The coating on the tablet: chewable, enteric

coated (breakdown occurs in small intestine), slow release capsules

IM and Sub-Q

IM – intramuscular – into a muscle group – pain medications / antibiotics / vaccinations

Sub-Q – into subcutaneous tissue – (Coumadin / heparin / Lovenox) (TB test)

Subcutaneous Injection

Intramuscular or IM

Local Administration

Adhesive patches – pain control, nitroglycerine patches, hormones, birth control patches, nicotine patches

Topical application – sunscreen, antibiotic ointments, cortisone

Eye, ear, nose drops Vaginal or rectal (PR)

Nitroglycerine Ointment

Nitroglycerine Patch

Eye Drops or Eye Ointment

Ear Drops

Rectal Suppositories

Rectal Suppositories

Excellent route of administration of medications for the client that is: Vomiting / nausea Refuses to take medication PO Difficulty swallowing a medication Infants – fever or pain medications

Inhaled

Asthmatic drugs Anesthetics

Distribution

Transportation of drug molecules within the body

Drug needs to be carried to the site of the action Need blood to circulate the drug Heart, liver, kidneys

Key Concepts of Distribution

Protein binding – drug molecules need to get from the blood plasma into the cell

Protein binding allows part of the drug to be stored and released as needed

Some of the drug is stored in muscle, fat and other body tissues and is gradually released into the plasma

Just how does the drug get into the cell? Drug must pass though the capillary wall Blood brain barrier – very effective in keeping

drugs from getting into the central nervous system or CNS – limits movement of drug molecules into brain tissue

Blood Brain Barrier

This is especially important when treating infections of the brain such as meningitis, encephalitis, or brain abscess

Medications must be able to penetrate the blood brain barrier

Medications usually given intravenous

Three ways to get in!

Direct penetration of the membrane Protein channels Carrier proteins

# 1 Lipid Soluble Drugs

Lipid soluble drugs are able to dissolve in the lipid layer of the cell membrane

No energy expended by the cell Passive diffusion

Oral tablets or capsules must be water soluble to dissolve in fluids of the stomach and small intestine

# 2 Protein Channels

Most drug molecules are to big to pass in to the cell via the channels – small ions such as sodium and potassium use the protein channels but their movement is regulated by gating mechanisms – only small amounts allowed

# 3 Carrier Proteins

Molecule needs to bind with a protein that will transport it from one side of the cell membrane to another – a drugs structure determines which carrier will transfer it.

Metabolism

Method by which the drugs are inactivated or biotransformed by the body Active drugs contain metabolites that are excreted

– skin, urine, stool Most drugs metabolized in the liver by

cytochrome P450 (CYP)

What can stop this process?

Enzyme inhibition Other drugs Combination drugs Liver disease Impaired blood circulation in person with heart

disease Infant with immature livers Malnourished people or those on low-protein diets

An important concept!

First-pass effect – some drugs are extensively metabolized or broken down in the liver and only a part of the drug is released into the systemic circulation

This is why dosage is important – how much drug needs to be taken in to give the desired effect and how often does it need to be taken

Excretion

Refers to the elimination of the drug from the body

Requires adequate functioning of the circulatory system and organs of excretion Kidneys Bowels Lungs Skin

Laboratory Values

Laboratory values reflecting function of liver and kidneys need to be looked at. BUN and Creatinine – kidney function LFT or liver function tests:

ALT – alamine aminotransferase (elevated in hepatitis) AST or SGOT– aspartate aminotransferase – elevated

in liver disease ALP – elevated in biliary tract disease Bilirubin levels – infants – gallstones in adults

Serum Drug Levels

Laboratory measurement of the amount of drug in the blood at a particular time

A minimum effective concentration (MEC) must be present before a drug exerts its action on a cell.

Toxic Levels

Excessive level of a drug in the body Single large dose Repeated small doses Slow metabolism which allows drug to accumulate

in the body Slow excretion from the body by the kidneys or

gastrointestinal tract

Yes, laboratory values are important! Serum drug levels indicate the onset, peak

and duration of the drug action

Do we do serum drug levels for all drugs? No When do we need them?

Drugs with narrow margin of safety (digoxin, aminoglycoside antibiotics, lithium)

To check to see if the drug is at therapeutic levels – seizure medications

When drug overdose is suspected

Important concept!

Serum half-life or elimination half-life is the time it takes the serum concentration of the drug to reach 50% A drug with a short half-life requires more frequent

administration A drug with a long half-life requires less frequent

administration

Why is this important?

Half-life determines how often a drug is given Daily in the morning At bedtime Q.I.D - four times a day T.I.D – three times a day Q4 hours – every four hours Q 12 hours – 9 am and 9 pm

Pharmacodynamics

Drug actions on target cells and resulting cellular biochemical reaction of in simple terms “What the drug does to the body”.

Receptor Theory

Most drugs exert their effects by chemically biding with receptors at the cellular level.

Receptors are proteins located on the surfaces of cell membranes within the cells

What do the receptors do?

The receptors are often described as the lock into which the drug molecule fits as a key.

All body cells do not respond to all drugs even when all the cells are exposed to the drug.

More is not better!

Number of receptors site available will effect drug action so giving a higher dose does not necessarily produce additional pharmacological effects.

Variables that effect drug action Dosage of the drug refers to frequency, size,

and number of doses Ibuprofen (generic) or Advil (trade name) Dosage = 250 mg per tablet Tablets are enteric coated Children over 12 years or adults take 1 to 2 tablet

every 4 to 6 hours Not to exceed 6 tablets in 24 hours unless

prescribed by a doctor

Drug Dosing

Often the first dose is higher in an effort to bring the therapeutic blood serum levels up quicker

Route

Route of administration does affect drug action and client response IV the best for rapid response – drug put directly

into the blood stream IM in 10 to 15 minutes as it is absorbed into the

blood stream through the muscle Topical application of a drug depends on where

applied – skin (condition of skin), sublingual (under the tongue), patch etc

Drug – Diet interaction

Food can slow absorption Food substances can react with certain drugs How to give medication is information

provided in you drug manual

Drug – Drug Interaction

Some drugs taken together will enhance each other Tylenol with codeine

Some drugs taken together will interfere with another drugs actions

Some drugs are given to decrease or reverse the toxic effects of a drug Narcotic antidote is naloxone

Client Variables

Age Body weight Gender Ethnicity Co-existing medical conditions

Drug Tolerance

Body becomes accustomed to drug over period of time

Adverse Effects

Undesired response Allergic reaction Drowsiness Nausea / vomiting / GI upset Liver or kidney damage Fevers Drug dependency Cancinogenicity – ability to cause cancer Teratogenicity – cause damage to fetus

Administering Medications

Five rights Right drug Right dose Right client Right route Right time

Know your drug

Clients expect you to be knowledgeable You gain this knowledge be looking up

medications Drug hand book PDA Pharmacist

Legal Responsibilities

The nurse is responsible for safe and accurate administration having sufficient drug knowledge to recognize and

question erroneous orders actions delegated to other persons – LVN cannot

give IV meds monitor clients response to a medication following safe practices – the five rights

Medication Errors

44,000 to 98,000 deaths occur each year in the USA because of medical errors

JCAHO has set standards that hospitals must follow to decrease medication errors Computerized systems Bar coding of medications Patient identification system

Medication Systems

Each facility has a system for administering medication

Be familiar with this process Need to learn at each new facility Basics of medication administration

guidelines should always be observed

Medication Orders

Full name of client Generic or trade name of drug Dose, route, frequency Date, time and signature of provider The nurse will need to look up the medication

ordered to know it’s classification, safe dose, action, how to administer, and side effects

The nurse should know why the medication is ordered

Need to Memorize

Systems of measures Table 3-3 Equivalents

Metric System

Meter is used for linear measure, gram for weight and liter for volume

Apothecary System

Grains, minims, drams, ounces, pounds, pints, and quarts

Household measures

Drops, teaspoons, tablespoons and cups Important since this is often how people take

medications

Units

mEq – drugs ordered in number of units per dose Insulin heparin

Milliliters

mL = milliliter. This is a VOLUME measurement. it is 1/1000 of a liter. when talking about water or similar liquids, it is equivalent to one cubic centimeter.

Cubic Centimeter

cc = cubic centimeter. This is also a VOLUME measurement. Most syringes measure their capacity in cc's. If you have a 5cc syringe, it will hold ~5mL of liquid in it.

mL and cc’s

1 mL = 1cc 1 cc = 15 to 16 minims 1 cc = 15 to 16 drops

Fluids are generally written in cc’s to standardize the abbreviation – you may see mL’s written but this abbreviation is being eliminated

cc’s and household measures

5 cc = 1 tsp (teaspoon) 15 cc = 1 tbs (tablespoon) 30 cc = 1 oz (ounce) = 2 tablespoons 240 cc = 8 oz or 1 cup

Milligrams

mg = milligram. This is a WEIGHT measurement. It is 1/1000 of a gram. the amount of chemical substance is often measured in milligrams. For injectable solutions, this will be reported as a concentration of weight to volume, such as mg/ml (milligrams per milliliter).