Pharmacology

(Back to Article Index)

Introduction

The term "pharmacology" refers to the study of drugs and their effects on body systems. A drug is defined as any chemical that effects living processes (the administration of drugs in the pre-hospital setting is what separates the basic emergency provider from the advanced provider). Due to the dynamic nature of emergency medicine, keeping current on your knowledge and skills in relation to drug administration is not going to be an easy task. New drugs are constantly being developed and old drugs are constantly being re-evaluated as new information on their actions are being discovered.

The use of drugs to treat patients with various complaints is an ancient practice dating back to primitive times. There is written evidence that ancient Egyptians had knowledge of pharmacology. The Ebers Papyrus writings refer to such remedies as oil, wine, opium, resins, turpentine, yeast, lead, and soda. These types of remedies were used mostly by trial and error to determine the dosage and effects on the living. One example of a primitive drug that was widely used is "purple foxglove". It was first used in as early as 1250 A.D. as a diuretic to treat edema. This condition was known as "dropsy" in early history. It's effects on the heart were not discovered until around 1800. Digitalis is the active ingredient in purple foxglove. Digitalis is widely prescribed for heart conditions today.

Drug Sources

  • Plants - Many drugs, such as digitalis, morphine, and atropine, are extracted from plants.
  • Animals - Animals (including humans) are another source for drugs such as epinephrine, insulin, and other hormones.
  • Inorganic Sources - This is a source for minerals such as iron, sodium bicarbonate, and calcium chloride.
  • Synthetic - Many drugs are man-made in the laboratory, or synthetic, such as lidocaine, diazepam, and many, many others.

Drug Names

Chemical Name

Usually the chemical name is the first of as many as four names assigned to a drug. The chemical name is an exact description of the chemical makeup of the drug. It describes the molecular structure. This is generally only used by chemists and lab personnel involved in the development of the particular drug.

Generic Name

The generic name is the official name given the drug by the United States Adopted Name Council. This name is completely independent of the manufacturer and often relates to the chemical name in some fashion.

Trade Name

This is also known as the brand name or proprietary name and is the name given to the drug by the manufacturer. For this reason a drug may have several trade names because it is produced by more than one company, it may only have one generic name.

Official Name

The official name of a drug is followed by USP (United States Pharmacopeia) or NF (National Formulary) which denotes its listing in official publications. Many times the official name and the generic name are the same minus the USP or NF.

Let's look at an example of a drug and its various names:

Chemical name - ethyl 1-methyl-4-phenylisonipecotate hydrochloride

Generic name - meperidine hydrochloride

Trade name - Demerol Hydrochloride

Official name - meperidine hydrochloride, USP

Many drugs are commonly referred to by their trade names and easily recognized as such. Drugs such as Narcan, Lasix, and Valium are well known and easily recognized by health care professionals by the trade names. It can be confusing, though, when using trade names and it is usually a good idea to refer to drugs by their generic name.

Drug Forms

Liquids

Drug preparations for oral use are often found in liquid form. The following are various liquid preparations.

  • Solutions - The term 'solution' refers to a preparation of a substance dissolved in a liquid. The solution may be in water, syrup, or another type of liquid. Examples are 5% Dextrose in Water, Normal Saline, and Lactated Ringer's.
  • Tinctures - The term 'tincture' refers to a preparation in which the drug was extracted from the source using alcohol. Tincture of iodine is an example. The tincture will usually contain some alcohol in dilute form.
  • Suspensions - This form of liquid preparation requires agitation of the contents because the components tend to separate with time and settle to the bottom of the container. They remain suspended after you shake the container, then they settle to the bottom. Activated charcoal and antibiotic preparations are examples.
  • Spirits - These solutions contain chemicals which will vaporize quickly and are usually dissolved in alcohol. Spirits of ammonia (ammonia inhalants) is an example.
  • Emulsions - These are preparations which contain an oily substance mixed with a solvent that does not dissolve the oil. Vinegar and oil salad dressing is similar in makeup. If the mixture is agitated, it forms globs of oil and these globs float in the solvent.
  • Elixirs - These are preparations which contain the active drug in a an alcohol solvent. Frequently an elixir will also contain an artificial flavoring such as cherry or grape. Tylenol elixir is an example.
  • Syrups - Syrups are used to enhance the flavor of a drug. Cough syrups are a good example.

Solids

  • Pills - We are all familiar with the pill form of a drug. The pill is formed to make the drug easy to swallow and coatings improve the taste.
  • Powders - Powders are not used as much today as in the past. The powder form of a drug, such as aspirin, can be dissolved in water or placed directly in the mouth and washed down with a liquid.
  • Capsules - A capsule is a gelatin container for a powdered drug, this makes the powder more pleasant going down, the gelatin melts away in the stomach and releases the medication.
  • Tablets - There is very little difference between a tablet and a pill. The tablet is formed by compressing the drug into an easy to swallow size. One difference is that a tablet generally has no coating. Baby aspirin is in tablet form.
  • Troches or Lozenges - This is a type of tablet or pill that is designed to dissolve in the mouth rather than in the stomach, such as a medication used to treat a sore throat.
  • Suppositories - This type of medication is formed to remain a solid at room temperature, then when placed in the body, usually in the vagina or rectum, the body heat dissolves the preparation and it is absorbed through the tissue lining the mucous membrane. Tylenol is found in suppository form.

Parenteral

The parenteral route refers to any route other than through the digestive tract. Parenteral drugs are usually in liquid form and are stored in various types of containers such as:

  • Ampules - This is a sterile container designed to carry one or possibly two patient doses. The container is made of glass and the top portion is designed to be broken off easily so the drug can be drawn into a syringe. The ampule should be discarded in a sharps container.
  • Vials - These are glass containers with a rubber stopper arrangement on the top in which a syringe with a needle on it is pushed through the rubber in order to draw the mixture into the syringe. The preparation may be in liquid or powder form. The powder form of medication would of course require a liquid to be injected first, then agitated to dissolve the powder prior to drawing the medication into the syringe.
  • Cartridge or Tubex - These are commercially prepared, pre-filled cartridges or syringes that are designed for speedier delivery of the drug intravenously or intramuscularly. They generally contain a single dose and are designed for use with a specific type of syringe that accepts the cartridge it was designed for.

Pharmacokinetics

Definition

The term 'pharmacokinetics' refers to the study of drugs and how they enter the body, how they reach their intended target, how they are transformed by the body, and how they are eventually eliminated by the body.

Factors that Influence Pharmacokinetics

Every drug will have its own specific characteristics which determine its rate of absorption, distribution, metabolism (biotransformation), and excretion.

Absorption

The action that a drug will have on the body is dependent upon the rate and degree of absorption. Molecules pass through single layers of tissue easier than through multiple layers. This is why absorption by the gastrointestinal tract is faster than transdermally. The rate and degree of absorption is dependent upon the site of administration, dosage, the form of the administered drug, solubility of the drug, pH, blood flow to the site of administration, and the mechanisms involved in absorption which are diffusion, osmosis, and filtration.

Distribution

This term refers to the process by which the drug finds its way to its intended site of action. Some factors that affect distribution are cardiac function, physiologic barriers such as the blood-brain barrier or the placental barrier, and drug storage reservoirs.

Drug storage reservoirs are found in two forms: plasma proteins and tissue binding. The determining factor in the drugs binding capacity are the chemical-physical properties of the drug.

Biotransformation and Elimination

Drugs can be eliminated from the body either in their original form or as a metabolite. The kidneys, liver, digestive tract, and the lungs play a role in elimination as do the mammary glands, sweat glands, and salivary glands to a small degree. Rates of elimination depend on several factors such as the type of medication and the state of a person's health. The process of eliminating a drug by metabolizing it is also known as 'biotransformation'. Biotransformation is when a drug is converted into a product that is easily eliminated by the body. The aforementioned organs and body systems aid in the elimination of drugs through biotransformation. Infants and older adults have a tougher time eliminating drugs from their systems. In the infant, the organs are not fully developed, and in the older patient they are not working at peak efficiency any longer.

Pharmacodynamics

Definition

Pharmacodynamics is defined as the study of the effects of drugs on living tissues.

Terminology

  • Mechanism of Action - This is the way that the drug produces its desired effect
  • Drug Receptor - These are proteins found on the surface of cell membranes. A good way to help you visualize the receptor action is to think of the receptor as a lock and the drug as a key. The drug that holds the best fit for the lock will produce the best response. Where and how the drug acts in the body is determined by the localization of the receptor and the concentration of the drug to which the receptor is exposed.
  • Agonist - This is a term for a drug that binds to a receptor and causes a physiological response such as a change in cellular function.
  • Antagonist - This is when the drug has the ability to bind to a receptor site but does not cause a specific reaction. The antagonist often has an easier time binding to the receptor which in turn blocks the action of the agonist drug.
  • Bolus - A single, often large, dose of a medication given intravenously.
  • Indications - The most common uses for that drug or circumstances for which a drug may be useful.
  • Contraindications - The circumstances under which a drug should not be used.
  • Side Effects - Any actions or effects other than those desired.
  • Precautions - Situations in which a drug may be dangerous to the patient or when the dosage or technique of administration should be modified.
  • Beta Receptor - There are two types of beta receptors: the beta1 receptor and the beta2 receptor. Beta1 receptors are found primarily in the muscle of the heart and kidneys. Beta2 receptors are found primarily in the lungs, blood vessels, eyes, salivary glands, bronchioles, stomach, liver, pancreas, skeletal muscle, and other sites.
  • Beta Blocker - A beta-blocker is a drug that blocks a beta receptor. Certain chemicals released by the body (neurotransmitters) induce a sympathetic response by binding to beta receptors. A beta blocker blocks the beta receptor and therefore does not allow the sympathetic response that a beta chemical produces.
  • Therapeutic Threshold - This is the minimum concentration of a drug that is required to produce the desired response.
  • Affinity - The tendency of a drug to bind to a specific receptor site. An example would be: some drugs have an affinity for beta receptor sites; others have an affinity for alpha sites.
  • Efficacy - This refers to the drugs ability to initiate a biologic response after binding to the receptor site. Doses of a drug that reach therapeutic levels have a higher probability of efficacy than lower doses of the same drug.
  • Half-life - This is the amount of time it takes to reduce the concentration of a drug in the blood stream due to biotransformation or elimination by 50%.

Drug Actions

  • Addictive - This drug action causes the user to become physiologically or psychologically dependent on the drug which causes the user to crave the addictive drug leading to overuse and abuse.
  • Antagonistic - This is when two or more drugs act upon each and negate the desired effects of the individual drugs. Naloxone is an antagonistic drug which reduces the effects of certain narcotic drugs on the patient.
  • Cumulative - This action occurs when a drug is given in several doses which causes an increase in the action of the drug. This repeated dosing may reach toxic levels.
  • Depressant - A depressant drug causes a decrease in activity or bodily function.
  • Stimulant - A stimulant drug causes an increase in activity or bodily function.
  • Habituation - Similar to addiction in that habituation is a physical or psychological dependence on a certain type of drug following repeated use.
  • Hypersensitivity - When a hypersensitive reaction occurs, there is often an exaggerated immune response to the drug. This is similar to an allergic reaction to a foreign substance encountered by the body.
  • Idiosyncrasy - An idiosyncrasy is a reaction that is considered abnormal, unusual, or different than normally expected.
  • Potentiation - This is when one drug enhances the effects of another drug. Alcohol mixed with barbiturates are a good example.
  • Synergism - This is when two drugs combined have a much greater action than the effects of either drug alone.
  • Therapeutic action - This is the intended action of the given drug and occurs when the drug is taken in its prescribed dose and route.
  • Tolerance - This is when a person takes a specific drug for an extended period of time, the patient develops a tolerance for the drug and needs to take larger doses to achieve the therapeutic effect.
  • Untoward Reaction - This is simply the harmful side effect of a particular drug, the unwanted effects.

Routes of Administration

Enteral

This route of drug administration refers to the introduction of the drug along any part of the gastrointestinal tract. These areas include the following:

  • Oral
  • Buccal (inside the cheek)
  • Sublingual (under the tongue)
  • Rectal
  • Nasogastric

Typically the oral route is the easiest and perhaps the safest enteral route. It is certainly the most common route in the hospital setting but not in the pre-hospital setting. There is a slow rate of absorption when using this route making it an unpopular route in the emergency setting. Another reason for its lack of use in the field is that the oral form of drug administration often requires water or some other liquid to help swallow the drug, this is not recommended for patients with an altered level of consciousness or problems such as airway compromise. Examples of pre-hospital medications given by the enteral route are nitroglycerin, nifedipine, activated charcoal, and oral glucose.

Parenteral

This refers to administration of a drug by any route other than the GI tract. It includes the following routes:

  • Intradermal - This is where the drug is injected into the dermal layer of the skin.
  • Transdermal - This method is used when slow absorption is desirable. The term means 'across the skin'. Patches are a customary method of transdermal medication delivery.
  • Subcutaneous - The injection is given beneath the skin into the connective tissue or fatty area immediately below the dermis. This route is generally used for small volume injections of 0.5 mL or less. This provides a slow absorption rate and a prolonged effect.
  • Intramuscular - This injection is given into the skeletal muscle mand usually provides for a faster absorption rate than subcutaneous injection due to the richness of blood vessels in this area.
  • Intravenous - An injection given directly into the bloodstream through a vein. This bypasses the absorption process providing a nearly immediate effect. Different drugs require different rates of injection to avoid causing an adverse reaction.
  • Endotracheal - This is when the drug is given down an endotracheal tube following successful endotracheal intubation. It is primarily used to administer drugs that preferably would be administered intravenously but intravenous access has not yet been established. There are very few drugs that can be administered in this fashion such as naloxone, epinephrine, atropine, and lidocaine. The absorption rate of the lungs is comparable to that of the intravenous route due to the large surface area and large number of alveolar sacs in the lungs. Drugs delivered in this fashion need to have the usual intravenous dosage increased by 2 - 2.5 times the normal amount, diluted in 10 mL of normal saline.
  • Intraosseous - This is when the drug is administered directly into the bone marrow of the patient. This route has an absorption rate comparable to the intravenous route and the drug is absorbed through the medullary cavity of the bone. There are numerous venous outlets from the long bones of the body and the drug can enter the central circulation via these routes. IO administration is usually reserved for pediatric patients but can be performed in adults if found necessary. The process of establishing IV access by this route was widely used in the 1950's and is gaining in popularity again. It should only be used in serious emergencies when no other IV access is available and is for short term use. Drugs that are known to be effective by the IO route are atropine, Decadron, dopamine, dobutamine, epinephrine, and sodium bicarbonate. IV fluids and whole blood can be given via this route successfully as well as drugs.
  • Inhalational - The respiratory system offers an enormous amount of absorption surface making it a viable route for drug administration. Drugs given by this route can have both local and systemic effects. The inhalational medications are usually given for respiratory ailments. They are usually delivered by having the patient inhale a fine mist or spray. Adjuncts such as a nebulizer or metered dose inhaler are common forms of administration. The effect of the drug taken in this manner is almost instantaneous.

Essential Drug Safety Information

Safety

The business of pre-hospital care inherently provides us with many distractions and stressful situations. There is often intense pressure to perform quickly. There is often a crowd of responders as well as non-responders adding to the confusion. These components make it necessary for you to develop safe habits.

Avoid Distractions

Once you have decided that your patient is in need of a drug, it is your responsibility to deliver it safely. Concentrate on the five rights of drug administration and don't allow the confusion and noise to become a distraction.

Any time you take your focus away from the drug that you have decided to administer, recheck the drug label, dosage and expiration date, especially if you have let go of it and set it down somewhere.

The Five Rights

  • Right Patient - This is not as big a problem for the pre-hospital provider as it can be in the hospital setting, but you still need to be sure that this patient is the right candidate for the drug about to be administered. If you are receiving orders from your medical director to give a drug it is imperative that you supply him with as much pertinent information as you can so he can make the correct decision regarding drug dosage and administration. If you suspect that you have been given the wrong orders or something just doesn't sound right, then you should question the order and clarify it with the medical director.
  • Right Dose - You need to be sure that your drug calculations and preparation is accurate. Most drugs we use in the field are pre-measured in single dose packaging, but there are times when you will have to give half doses or possibly double doses depending on the type of patient you encounter. Use reference materials and field guides when possible. Try to be as accurate as possible when determining the patient's weight (in kilograms) if that is a factor. Most adult dosages are easily remembered by the practicing paramedic, but when it comes to pediatric dosages you will likely need to refer to a chart or field guide to help you. There is no shame in looking it up to get it right.
  • Right Drug - To ensure that you are about to give the right drug you need to check the label of the drug and compare it with the orders or protocols you are working under. It is easy to become complacent and too familiar with the arrangements of the drugs carried on the unit. Always check the label prior to administering the drug. This becomes perhaps even more important in the wee hours of the morning. Check the label for the name of the drug, the expiration date, and the concentration. Compare the container with the box, making sure that what was in the box is what was supposed to be in the box. Check the label when you remove the drug from the box, prior to preparing the dose, and once again prior to administration. This triple check will prevent serious mistakes from occurring at three in the morning. Never administer an unlabeled drug unless you have personally prepared the drug just prior to administration.
  • Right Route - Drug actions are affected by the route in which the drug is administered. Different routes require different doses to reach the therapeutic level. Be sure to check the dose and concentration of the chosen drug and be sure you are giving it via the correct route.
  • Right Time - Giving the correct drug at the correct time is very important if the drug is to have the greatest benefit to the patient. Some emergency situations require that a drug be given immediately to correct life-threatening problems, other drugs need to be administered at various time intervals to achieve the desired effect. The right time also refers to piggyback administration. The drug needs to be administered at the proper rate over the proper time period to achieve the desired effect. Giving some drugs too fast or too slow can change the effects the drug will have on the patient, sometimes leading to disastrous results. A dopamine bolus, for instance, may be lethal to a patient.

Some areas also include the Right Location, such as an SQ dose of Epinephrine not being administered via a finger or toe, but only deltoid area or quadriceps.

Read the Label & Compare to Orders

Typically, orders for giving medications include information such as the name of the drug, the dose, the administration route, and possibly the rate of administration. It would be ideal to be able to write the orders down so you could double check the orders prior to administration, and again after preparing the drug. Written protocols should be consulted if there is any question as to the dosage, route, rate, indications or contraindications. If the orders are given to you verbally you should always repeat the orders to verify them and avoid confusion.

You have the responsibility to question any orders which may seem inappropriate. Always check the label of the drug prior to administration for expiration date, concentration, clarity, discoloration, and signs of tampering. Anytime your focus has been shifted away from the drug you are about to administer it would be a very good idea to recheck the label to reconfirm that it is the drug you were intending to give before you were distracted.

Needles and Safety

It goes without saying that safety with needles is very important to you, your crew, the patient, and the public. It would be ideal to immediately discard the needle after use into an appropriate container without having the needle ever change hands. You should personally discard the needle immediately after use into a sharps container without handing it over to someone else. We have all seen inappropriate handling of needles in the field such as sticking them into the ground or some other object, or otherwise discarded in an unwise fashion. The bottom line is that we have a major responsibility to the people around us to treat needles in the proper manner. The various bloodborne diseases we encounter on a daily basis do not need any help from medics to continue to spread. You need to do your part to maintain a high degree of safety when dealing with "sharps".

Patient Monitoring

It is important to monitor the patient to whom we have administered drugs, not only for the expected effects of the particular drug but also any unwanted side effects or reactions. Keep in mind the different problems that are associated with various age groups. The pediatric patients and the geriatric patients will need special considerations when administering drugs.

Monitor the patients for patency of the IV, check the IV site for problems often. Verify initial placement of endotracheal tubes, and recheck placement of ET tubes at regular intervals. Monitor injection sites for adverse reactions.

Documentation

Documentation of drug administration serves two purposes, both clinical and legal. Recording the drug name, route of administration, dosage, site of administration, and any other pertinent information is very important. Documentation of reasons why you decided not to administer a drug following orders to do so would be very important. It may be a good practice to give reasons that you felt the need to administer the drug, the effects the drug seem to have had on the patient (expected and unexpected), or the reasons that you felt the drug was not indicated in this particular case. You never know which case may end up in court and how long it may take to get there. You need to document in such a way that you will be able to recall the events as clearly as possible.

Metric System

An understanding of the metric system is required to properly calculate drug dosages. The basic unit of measurement in the metric system of mass (a solid) is the gram (g or gm). As the gram is divided into smaller units, a prefix is given to the word "gram" to signify the unit of measurement and its relation to a gram. The gram is broken down into thousandths of a gram in this manner.

The basic unit of volume (liquid and gas) measurement in the metric system is the liter (L). As with the gram, liters are commonly divided into smaller amounts and given a prefix to compare the amount to a liter. Liters are also commonly divided by thousandths.

Metric Conversions

The following are common prefixes associated with the metric system and paramedic drug calculations for solids.

Kilo- A kilogram is equal to 1000 grams

Milli- A milligram (mg) is equal to .001 of a gram (a gram divided by 1000)

Micro- A microgram (mcg or µg)is equal to .001 of a milligram (milligram divided by 1000) or .000001 of a gram (a gram divided by 1,000,000 

The following are common prefixes found when dealing with liquid measurement in the metric system.

Milli- A milliliter is equal to .001 of a liter, so it is a liter divided by 1000

Micro- A microliter is equal to .001 of a milliliter, a milliliter divided by 1000 or a liter divided by 1,000,000 (not commonly used in drug calculations)

It is important to note that a cubic centimeter (cc) is the same as a milliliter (ml). There are units of measurement for quantities larger than kilograms and liters but the need for these units are not common.

Moving the Decimal Point

The easiest way to convert grams and liters into smaller units is to move the decimal point either right or left depending on whether you wish to increase or decrease the unit of measurement. The following is an example:

To convert 1.0 g to milligrams it is necessary to move the decimal place of 1.0 g to the left, three places. Moving the decimal point to the left makes the number smaller by 10 times for each time you move it.

 

1.0 g divided by 10 would look like this: 0.1 g

1.0 g divided by 100 would look like this: 0.01 g

1.0 g divided by 1000 would look like this: 0.001 g

A gram divided by 1000 is equal to 1 mg. A milligram divided by 1000 is a microgram. To convert back to larger units, it is only necessary to move the decimal place back to the left again, to convert 1.0 mcg to milligrams simply move the decimal place to the right three times, and move it to the right six times to convert 1.0 mcg to grams Like this:

1.0 mcg = .001 mg

1.0 mcg = .000001 g 

Drug Calculations

There are many instances in which a paramedic will be required to perform drug dosage calculations in the pre-hospital setting. There are many different ways to perform these mathematical calculations. They all have certain components in common and certain types of information that are required in order to correctly calculate the required dose. The information required in most methods of calculation is as follows:

Desired Dose - It is important that you know the quantity of the medication or fluid that the medical orders call for. The orders for a drug will normally be expressed in either grams, milligrams, or micrograms. Sometimes the apothecary method of measurement is used and the order may be expressed in grains (not in common use).

Concentration of Drug on Hand - It is equally important to know what concentration the desired drug on hand is found in. The concentration should be stated on the label and is usually expressed in grams, milligrams, micrograms, or grains. It may be expressed a as 5 mg in 10 ml of saline meaning that there is 5 milligrams of the drug in 10 ml of fluid. The concentration may then be expressed as 0.5 mg/ml.

With these two pieces of information, you can accurately calculate the volume of a drug to be given to a patient. The standard math formula that utilizes these three pieces of information is as follows:

'Amount to give' = 'Desired dose' divided by 'Concentration'

To use this formula, plug in the known values and work the formula as in this example:

The orders you were given by a physician were to administer 60 mg of lidocaine to a patient by IV bolus. You find the drug supplied in a pre-filled syringe that contains 100 mg of lidocaine in 5 ml of saline.

Plug in the known values like this:

Desired dose = 60 mg

Concentration on hand = 100 mg per 5 ml

Amount to give = (60 mg) divided by (100 mg/5 ml)

Amount to give = (60 mg) times (5 ml/100 mg)

Amount to give = (60 mg) times (5 ml/100 mg) = (60 x 5)/100

= 300/100 = 3

This works out to 3 ml of the drug to be delivered to the patient to supply the correct amount of the drug.

This type of formula only works when the units of measurement are the same. You can't mix grams and milligrams (or liters and milliliters) in the same formula, for example. You would have to convert everything to either grams or milligrams (liters or milliliters). It doesn't matter which you use, they only need to be the same.

Variations

The same type of formula works if you need to figure an infusion rate.

'Infusion rate' = [ 'Desired dose' x 'Administration set' ] / 'Concentration' 

Let's say the doctor orders an infusion of drug X at 2 mg/minute. The doctor orders you to prepare a mixture of drug X at a concentration of 4 g in 1 liter of saline. The doctor wants you to use a 60 gtts/ml administration set to deliver the drug. Work the formula as follows:

Desired dose = 2 mg/min

Concentration = 4 g (4000 mg) in 1000 ml or 4 mg/ml

Infusion rate = [ Desired dose x Dosage ] / Concentration

? gtts/min = [ (2 mg/min) x (60 gtts/ml) ] / (4 mg/ml)

= (2 x 60) / 4 = 120/4

= 30 gtts/min

Many drugs are dosed according to weight and most pediatric dosages are according to weight. You will need to convert the patient's weight from pounds to kilograms. Simply divide the patient's weight in pounds by 2.2 to convert to kilograms.

For example, for a patient that weighs 165 pounds: 165/2.2 = 75.

So your patient that weighs 165 pounds weighs 75 kilograms.

Lidocaine is a common pre-hospital drug that is dosed according to weight. The normal dosage of lidocaine is 1 - 1.5 mg/kg. For a patient that weighs 220 pounds, first you convert to kilograms: 220/2.2 = 100 kg.

Then you plug the weight in the formula: 1 X 100 = 100 and 1.5 X 100 = 150.

For this patient you would administer 100 - 150 mg of lidocaine.

As mentioned earlier there are many different ways to calculate doses and you should find a way that you understand and are able to use at three o'clock in the morning, under pressure. That may be a bit tough to do but with a lot of practice you can do it!