Basic principles of pharmacology

19 Basic principles of pharmacology


Additive Effect:  Occurs when a second drug with properties similar to the first is added to produce an effect equal to the algebraic sum of the effects of the two individual drugs. Shorthand often used is 1 + 1 = 2.

Agonists:  Drugs such as dopamine that attach and activate specific receptors.

Antagonists:  Drugs such as naloxone (Narcan) that attach to a specific receptor and do not activate the receptor, but prevent an agonist or body chemical such as a neurotransmitter from stimulating the receptor.

Competitive Antagonist:  When the concentration of the antagonist is higher than the agonist concentration resulting in reversal or antagonism of the agonist. Examples include naloxone (Narcan) reversing fentanyl or flumazenil (Romazicon) reversing midazolam (Versed). Shorthand often used is 1 + 1 = 0.

Cross Tolerance:  Tolerance to a drug because of an existing tolerance to a similar drug. An example of cross tolerance is a patient who has developed a tolerance to morphine due to repeated administration will also require higher doses of all other opioids as well.

Efficacy of a Drug:  Refers to the maximum effect that can be produced by a drug.

Hyperreactivity:  An abnormal reaction to an unusually low dose of a drug. For example, patients with Addison disease, myxedema, or dystrophia myotonica have hyperreactivity to unusually low doses of barbiturates.

Hypersensitivity (Anaphylaxis):  A drug-induced antigen-antibody reaction. The particular hypersensitivity reaction can be either an immediate (anaphylactic) or a delayed reaction. Hypersensitivity reactions can occur with succinylcholine, antibiotics, and many other drugs that are administered in the PACU (see Chapter 18).

Hyporeactivity:  An indication that a person needs excessively large doses of a drug to obtain a therapeutic or desired effect.

Idiosyncrasy:  An adverse drug reaction that occurs in a small number of persons and has no correlation to dosage or of type of therapy. Postoperative liver dysfunction following halothane administration is an example.

Pharmacodynamics:  The study of the mechanisms of action of drugs and other biochemical and physiologic effects on the body.

Pharmacokinetics:  The study of the movement of drugs throughout the body, including the processes of absorption, distribution, biotransformation or metabolism, and excretion.

Potency of a Drug:  The dose necessary of a particular drug to produce a specific effect that is designated as the effective dose (ED). When that effect is achieved in a particular percentage of patients, it is quantified as ED50 for 50% of the patients and ED95 for 95% of the patients who show an effect to the drug.

Potentiation:  The enhancement of the action of one drug by a second drug that has no detectable action of its own. Shorthand commonly used is 1 + 0 = 3.

Receptors:  The portion on or in a cell, usually a protein complex, at which attachment of drugs leads to a physiologic response. The receptors are selective in that they recognize and bind only to specific pharmacologic or physiologic agents.

Synergistic Effect:  Addition of a second drug to a drug with properties similar to the first that results in an effect greater than the algebraic sum of the effects of the two individual drugs. Shorthand often used is 1 + 1 = 3.

Tachyphylaxis:  An acute drug tolerance—for example, succinylcholine administered by intravenous drip. Over time, a higher drip rate is needed to achieve the necessary response.

Tolerance:  A type of hyporeactivity that is acquired during chronic exposure to a drug in which unusually large doses are needed to reach a desired effect. A prime example is a person who has become dependent on opioids and needs larger than normal doses to elicit the desired therapeutic response.

A thorough understanding of the pharmacology of the drugs used in perianesthesia care is necessary to ensure the best outcomes in surgical patients. Anesthesia care continues to evolve, and the judicious use of a number of selective, potent drugs in various combinations represents the cornerstone of current practice. Consequently, a comprehensive review of the principles and concepts of pharmacology is presented in this chapter. The specific actions and uses of drugs related to perianesthesia care are discussed in the physiology chapters in Section II, as are the concepts of anesthetic agents in the chapters in Section III. The pharmacology of individual drugs can be best understood in relation to the physiologic functions they affect and their common clinical applications.

A significant portion of this chapter is dedicated to an overview of drug interactions, because modern anesthesia care requires balancing the administration of multiple drugs throughout the perianesthesia period. These drugs include anesthesia-related agents, the patient’s existing medications, including herbal agents, and other over-the-counter preparations.1 Clinically, at least 10% of the patients for perianesthesia are taking some form of herbal preparation.2 Consequently, knowledge of the principles of pharmacology becomes a meaningful and useful tool in the delivery of nursing care to the patient in the postanesthesia care unit (PACU).

Drug responses

Drugs are given via a chosen route of administration at a specific dose with the expectation of a desired response. Many factors affect the time of onset, the efficacy, and the duration of action of a particular drug. The perianesthesia nurse must be aware of the basic principles of drug actions within a biologic system. A review of the basic concepts of drug responses is presented, with particular emphasis on the patient in the PACU.

Pharmacokinetic actions

Pharmacokinetics is the pharmacology subspecialty that studies the absorption, distribution, metabolism, and elimination of a drug in the body. Consequently, pharmacokinetics can be viewed as what the body does to a drug after it is administered.

Systemic absorption by various routes of administration

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Nov 6, 2016 | Posted by in NURSING | Comments Off on Basic principles of pharmacology

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