LEC 2: Drugs & the Body INCOMPLETE

Pharmacodynamics

• science dealing with interactions between the chemical components of living systems and the foreign chemicals, including drugs, that enter those systems.

• What the drug does to the body

1. To replace or act as substitutes for missing chemicals

2. To increase or stimulate certain cellular activities

3. To depress or slow cellular activities

4. To interfere with the functioning of foreign cells, such as invading microorganisms or neoplasm

4 ways drugs usually work

To replace or act as substitutes for missing chemicals

The following example exhibits what way drugs work:

Hypokalemic client (low K) needs to be given KCl which will replace the missing K

• K works directly on the smooth muscles of heart so if low K, slow heart beat

• If high K patient may have tachycardia with ECG disturbed

To increase or stimulate certain cellular activities

The following example exhibits what way drugs work:

• Ex: Client with constipation is given laxatives

To depress or slow cellular activity

The following example exhibits what way drugs work:

• Ex. Client with allergies given antihistamine

To interfere with functions of foreign cells

The following example exhibits what way drugs work:

• Antineoplasms (chemotherapeutic agents)

• Antibiotics

Receptor sites

• Specific areas on membranes where many drugs are thought to act

Agonists

What type of drug is exemplified

• Insulin acts as a key to a specific insulin receptor site so sugar can enter the cells

Antagonists

What type of drug is exemplified

• Monoamine oxidase inhibitor (MAOI) will metabolize the norepinephrine - usually patients with depression have increased norepinephrine so to prevent this need to block __ from its course —> results in relief from depression

Drug-Enzyme Interactions

• Phenomenon in which drugs also can cause their effects by interfering with the enzyme systems that act as catalysts for various chemical reactions.

Drug-Enzyme Interactions

What is exemplified;

• Heparin is an anticoagulant w/c works by stopping the clot (heparin prevents fibrinogen turning into fibrin —> no clot since can’t form clotting mesh)

Selective Toxicity

• Ability of drug to attack only those systems found in foreign cells

Selective Toxicity

What is exemplified:

• Antineoplastics destroy cancer cells AND healthy cells. However, there are certain meds that kill only malignant cells

• Penicillin only kills bacterial cells

Pharmacokinetics

• Involves the study of absorption, distribution, metabolism (biotransformation), and excretion of drugs.

• What the body does to the drug

Critical Concentration

• It is amount of drug that is needed to cause a therapeutic effect

Loading Dose

• Higher dose than that usually used for treatment to reach critical course

• ex: 2000 heparin given if before dialysis, 2000-1000-1000

• ex: IV starts as 1g then succeeding 500g

Therapeutic Index

• Ratio of blood conc at w/c a drug becomes toxic to the conc at w/c drug is effective

0.6-1.2

What is the therapeutic index of lithium?

Mood stabilizer for those with bipolar disorder (those experiencing mania and depression at the same time)

What does lithium usually function as?

Manic

In what phase is lithium usually given in?

Mania

If lithium <0.6 what will occur?

Toxicity

If lithium >1.2 what will occur?

1. Absorption

2. Distribution

3. Metabolism

4. Excretion

Phases of Pharamacokinetics

First Pass Effect

• When given oral medications 50 mg is given since the drug is still metabolized by the liver

• This is why oral doses are higher compared to IV

Half-Life

• During excretion

• If drug peaks (maximum therapeutic effects)

• Ex: px sugar is 302 and on sliding scale (order of doctor on pila insulin given to patient and inc by 2-200)