How and Why Drugs Work PPT Series 5A

Intended and Unintended Effects of Drugs Intended responses: Reason for using the drug Unintended responses: Side effects The main distinction between intended responses and side effects depends on the therapeutic objective. (what is the purpose of taking the drug) People make take drugs (misuse drugs) to experience the side effects (ex. drowsiness from antihistamines)

Common Side Effects of Drugs Nausea or vomiting Changes in mental alertness such as sedation or anxiety Dependence that compels people to continue using the drug in order to avoid withdrawal. Allergic reactions often experienced as labored breathing or rashes Changes in cardiovascular activity in heart rhythm and/or blood pressure. (see Figure 1, next slide for side effects with drugs of abuse)

Common Side Effects of Drug (continued)

Side Effects of Drugs – Risk, Cost, vs. Benefit Is the drug therapeutic or recreational? Are the therapeutic benefits of the drug greater than the risk of the drug? Does the benefit of the drug outweigh the potential amount of cost the drug may cause in side effects? Is the cost of not taking the medication greater than the alternative medical treatment?

Dose-Response All effects- both desired and unwanted – are related to the amount of drug administered. Many factors can affect the way an individual responds to a drug, including the following: Dose – Amount of the drug taken Potency – The amount of drug necessary to cause an effect Tolerance – Changes in the body that decrease response to a drug even though the dose remains the same

Dose-Response Curve (see Fig. 5-2, p.159) Because there is a relationship between the response to a drug and the quantity of the drug dose, dose-response curves can help determine therapeutic response of an individual. Figure 5.0.2: Dose–response curve for relieving a headache with ibuprofen in three users. User A is the most sensitive and has 100% headache relief at a dose of 400 milligrams. User B is the next most sensitive and experiences 50% headache relief with a 400-milligram dose. The least sensitive is user C: with a 400-milligram dose, user C has no relief from a headache.

Dose-Response Curve Many factors can contribute to the variability in drug response including: Tolerance following multiple dosing Body Size Enzymatic activity of the liver State of persons health How drug is administered, etc. Multiple interacting factors makes it difficult to accurately calculate the final drug effect for any given individual at any given time

Margin of Safety The margin of safety is determined by the difference between the amount of drug necessary to cause a therapeutic or recreational intended effect and the toxic unintended effect.

Margin of Safety The larger the margin of safety, the less likely that serious side effects will occur Drugs with narrow margins of safety pose a greater danger of adverse and toxic effects.

Potency vs. Toxicity Potency: The amount of drug necessary to cause an effect. The smaller the drug amount required to perform the desired therapy (or effect), the greater the potency. “Not your Dad’s Weed”

Potency vs. Toxicity Toxicity: The capacity of a drug to do damage or cause adverse effects in the body. A high potency drug has a greater capacity for toxicity. If physiological systems of the body are already compromised a smaller dose of a drug may prove toxic

Drug Interaction When initial drugs are present in the system, the drug’s effects may be altered (augmented or diminished) when additional drugs are ingested. The augmentation of the drug’s effects with the introduction of the additional drug is known as drug interaction. Drug interactions may create serious medical problems (ex. Depressants, plus alcohol, plus cold medications) Drug interaction may be categorized into three types: 1) Additive; 2) Antagonistic; and,3) Potentiative

Drug Interaction Additive effects Summation of effects of drugs taken concurrently (1+1=2) Example: Aspirin + Tylenol results in the analgesic (pain relief) effect being the sum of the two. Also, the analgesic effect would be the same if two doses of either aspirin or Tylenol were taken (two tablets of each) vs. one tablet of each.

Drug Interaction Antagonistic (inhibitory) effects One drug cancels or blocks effects of another drug. Example : Taking antihistamines to reduce nasal congestion (side effect = drowsiness), then consuming a mild stimulant (caffeine) to antagonize the side effects of the antihistamine. This practice can be dangerous. Example: Using alcohol (CNS depressant) to suppress the hyper stimulation of the CNS with cocaine ingestion may lead to sudden cardiac death (Effects of Cocaethylene)

Drug Interaction Potentiative effects Effect of a drug is enhanced by another drug or substance, whether the synthetic or naturally occurring. Thus, one drug prolongs or multiplies the effects of the other drug. Example: Combining alcohol with opioid drugs. Combining the two together depresses the CNS to an extent greater than the summative effect that would be expected.

See “Prescription for Abuse” p. 163, text. Table 1, Chapter 5: Many drugs and substances used will interact and possibly produce dangerous outcomes. Many drug abusers are polydrug (many drug) users who may be unaware of the dangers of drug combinations. See “Prescription for Abuse” p. 163, text. End of PPT 05A Series