Routes of Administration

Chapter 4 Pharmacokinetics Learning Objectives: 1. List the four main processes that make up pharmacokinetics. ● The four main processes that make up pharmacokinetics are absorption, distribution, metabolism, and excretion. Chapter 4 reading: Pharmacokinetics is the study of how drugs move throughout the body, including processes like absorption, distribution, metabolism, and excretion. Understanding pharmacokinetics is crucial in maximizing the benefits of drug therapy and minimizing harm. By applying this knowledge, healthcare professionals can make informed decisions regarding dosage, route of administration, and dosing schedule. Bullet points Routes of administration ● ● Oral administration: drugs are taken by mouth (per os) Intramuscular administration (IM): drugs are injected into a muscle Safety considerations ● ● ● Administering subcutaneous (SubQ) drugs intravenously (IV) can be fatal Concentrated solutions intended for IV use are dilute to prevent adverse effects Administering concentrated epinephrine IV can lead to severe hypertension and other complications Barriers to absorption ● ● ● After oral administration, drugs must cross the GI epithelium and the capillary wall In IM administration, the only barrier to absorption is the capillary wall Some drugs may be affected by PGP, a transporter that pumps certain drugs back into the intestine Absorption patterns ● ● ● Drugs administered IM can be rapidly or slowly absorbed Absorption rate is influenced by water solubility of the drug and blood flow to the injection site Multiple factors can influence absorption after oral administration, including solubility, pH, gastric emptying time, food in the gut, coadministration of other drugs, and special coatings on the drug preparation Advantages of IM administration ● ● Can be used for parenteral administration of poorly soluble drugs Can be used for depot preparations, where drug absorption occurs slowly over time Advantages of depot preparations and IM administration: ● ● VEIN Cycling HEART can release therapeutically effective amounts of penicillin for a month after a single IM injection Reduces the number of injections required during long-term therapy Disadvantages of IM administration: ● ● ● ● ● Discomfort and inconvenience Painful injections May cause local tissue injury and nerve damage if done improperly Cannot be used for patients receiving anticoagulant therapy Less convenient than oral administration Pharmacokinetics of subQ administration: ● ● Similar to IM administration No significant barriers to absorption Advantages of oral administration: ● ● ● ● ● ● Easy and convenient Preferred route for self-medication Safer than injection No risk for fluid overload, infection, or embolism Can be potentially reversible Safe for patients who cannot or will not take drugs orally Situations where oral administration is preferred: ● ● ● ● ● ● ● Emergencies that require rapid onset of drug action Situations where plasma drug levels must be tightly controlled Treatment with drugs that would be destroyed by gastric acidity, digestive enzymes, or hepatic enzymes if given orally Treatment with drugs that would cause severe local injury if administered by mouth Treating a systemic disorder with drugs that cannot cross membranes Treating conditions for which the prolonged effects of a depot preparation might be desirable Treating patients who cannot or will not take drugs orally Types of pharmaceutical preparations for oral administration: ● Various "packages" or formulations available Drug preparations ● ● ● Chemical equivalence: Preparations containing the same amount of the identical chemical compound (drug) Bioavailability: Preparations with the same rate and extent of drug absorption Variability in absorption: Oral therapy can lead to highly variable drug absorption, affecting concentration, onset, intensity, and duration of effects