© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Fundamentals of Pharmacology for Veterinary Technicians Chapter 3 Therapeutic Range and Routes of Administration

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. The Therapeutic Range All drugs should be considered potential poisons and should be dispensed and given with great care The therapeutic range of a drug is the drug concentration in the body that produces the desired effect in the animal with minimal or no signs of toxicity

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Keeping Drugs in the Therapeutic Range Three major drug factors keep drugs in their therapeutic range: –Route of administration –Drug dose –Dosage interval

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Route of Administration Parenteral drugs are given by a route other than the gastrointestinal tract Nonparenteral drugs are given through the gastrointestinal tract Factors that affect the route of drug administration include: –Drug causes one effect when given parenterally and another nonparenterally –Water-insoluble drugs can be given IM, but not IV –Some drugs are destroyed by stomach acid and cannot be given orally

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Injectable Routes of Administration Injectable routes are parenteral Most common injectable administration routes are IV, IM, and SQ Drugs given by injectable administration routes may be aqueous solutions or emulsions (mixtures of two immiscible liquids)

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Injectable Routes of Administration (IV) Drugs given IV have rapid onset of action, higher initial body levels of drug, and shorter duration of activity IV injection techniques include bolus administration, intermittent therapy, and infusion of fluid In most cases, IV drugs should be given slowly All air bubbles must be removed from the drug before administration to avoid causing air emboli and tissue damage

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Injectable Routes of Administration (IM) Drugs given IM have relatively rapid onset of action and longer duration of activity than IV drugs Absorption rate depends on drug formulation IM-injectable drugs may be in a substance that delays absorption; these are referred to as repository or depot preparations IM drugs can be in aqueous solutions or suspensions –Solutions are clear liquids that contain one or more solvents and one or more solutes –Suspensions are liquid preparations that contain solid drug particles suspended in a suitable medium

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Injectable Routes of Administration (SQ) Drugs given SQ have slower onset of action and longer duration of activity than IV and IM drugs Absorption rate may be altered by the vehicle in the preparation Larger amounts of solutions can be given SQ; amount given should be based on animal species involved Pellets can also be implanted into the subcutaneous space The rate of absorption of SQ fluid can be manipulated by temperature –Applying heat to the area increases the rate of absorption –Applying cold to the area decreases the rate of absorption

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Other Parenteral Administration Routes Inhalation administration introduces drug to the animal by having it breathe the drug into the lungs –Particles diffuse across the alveolar membrane Topical medication goes on the surface of skin or mucous membrane –Forms of topical medication are summarized in Table 3-2 Other parenteral administration routes are listed in Table 3-1

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Nonparenteral Administration Routes Oral administration delivers the drug directly to the animal’s gastrointestinal tract Before entering the bloodstream, an oral drug must be released from the dose form, transported across the GI tract, and passed through the liver Oral drugs usually have slower onset of action, longer duration of activity, and absorption rates that may be affected by the type of digestive tract and/or GI disease Oral drugs may be tablets, capsules, boluses, powders, solutions, suspensions, or emulsions

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Drug Dose The dose of a drug is the amount of drug administered at one time to achieve the desired effect (can be in mL, cc, mg, g, tablets, etc.) Loading dose: initial dose of drug given to get the drug concentration up to the therapeutic range in a very short period of time Maintenance dose: dose of drug that maintains or keeps the drug in the therapeutic range Total daily dose: total amount of drug delivered in 24 hours

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Drug Dosage The dosage of a drug is the amount of drug per animal species’ body weight or measure –Examples include mg/kg or g/lb Dosage interval: how frequently the dosage is given –Examples include BID or TID Dosage regimen: dosage interval and the dosage together –Examples include 30 mg/kg TID and 5 g/lb BID

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Drug Toxicity Drug toxicity may be due to human error and/or accident Drug toxicity may be related to side effects of the drug Examples of drug toxicities: –Outright overdose –Relative overdose –Side effects –Accidental exposure –Interaction with other drugs –Incorrect treatment

© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Counteracting Drug Toxicities Veterinary staff must act quickly to counteract any problems caused by drug treatment Some ways to treat drug toxicities: –Removal of the offending drug –Enhancing drug removal by the animal –Counteracting with an antidote –Providing symptomatic care or nursing care until the toxicity signs have diminished