Pharmacology: Drug Absorption and Distribution

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Questions and Answers

What is an important factor affecting drug absorption?

Age

Pregnancy

Inflammation

All of the above (correct)

Where are acidic drugs absorbed?

Intestines

Liver

Kidneys

Stomach (correct)

What can alter the absorption rate of a drug?

Changes in pH

Co-administered drugs

Changes in intestinal motility

All of the above (correct)

What is the primary elimination route for polar drugs?

Kidneys Signup and view all the answers

What determines the distribution of a drug in the body?

Hydrophobicity Signup and view all the answers

What is the volume of distribution (Vd) of a drug?

The ratio of total body store of drug to plasma concentration Signup and view all the answers

Why do drugs with low Vd remain mostly in the plasma?

Because they are ionized and highly water-soluble Signup and view all the answers

What is the significance of a high Vd for a drug?

The drug is highly lipid-soluble Signup and view all the answers

What is the main purpose of Therapeutic Drug Monitoring (TDM)?

To ensure that a given drug dosage is within a range that produces maximal therapeutic benefit Signup and view all the answers

What factor influences drug absorption through the GI tract?

Formulation of the drug Signup and view all the answers

Which of the following mechanisms is involved in drug absorption through the GI tract?

Both active and passive transport mechanisms Signup and view all the answers

What is the most common route of administration for drugs?

Oral administration Signup and view all the answers

What affects the diffusion of a drug from the GI tract to the bloodstream?

Chemical structure of the drug Signup and view all the answers

What is the primary mechanism of drug absorption through the GI tract?

Passive diffusion Signup and view all the answers

Which of the following factors does not influence drug absorption through the GI tract?

Rate of elimination Signup and view all the answers

What determines the rate of absorption of a drug through the GI tract?

All of the above Signup and view all the answers

What is the characteristic of a drug with a high volume of distribution?

Low blood concentration and high tissue concentration Signup and view all the answers

What is the effect of hepatic dysfunction on the drug Carbamazepine?

It may cause LFT to be checked frequently Signup and view all the answers

What is the most serious side effect of Carbamazepine?

Leukopenia Signup and view all the answers

What is the plasma concentration of Carbamazepine associated with hematologic dyscrasias and possible aplastic anemia?

Greater than 15 μg/mL Signup and view all the answers

What is the characteristic of Ethosuximide?

It has rare and tolerable toxicities Signup and view all the answers

What is the therapeutic index of Lithium?

0.8-1.2 mmol/L Signup and view all the answers

What is the characteristic of Tricyclic Antidepressants (TCAs)?

They are highly protein-bound Signup and view all the answers

What is the effect of high plasma concentration on the toxicity of Ethosuximide?

It has a rare and tolerable effect on the toxicity Signup and view all the answers

Study Notes

Drug Absorption and Distribution

Acidic drugs are absorbed in the stomach, while basic drugs are absorbed in the intestines due to the pH differences
Many factors can alter absorption rates, including changes in intestinal motility, pH, inflammation, food, and co-administered drugs
Genetic variations, age, pregnancy, and pathologic conditions can also affect absorption

Drug Distribution

Hydrophobic (lipid-soluble) drugs can easily traverse cellular membranes and partition into lipid compartments
Polar but non-ionized drugs can cross cell membranes but do not sequester into lipid compartments
Ionized drugs diffuse out of the vasculature at a slow rate
Polar (water-soluble) drugs are primarily eliminated by the kidneys, while nonpolar (lipid-soluble) drugs are eliminated in feces and bile

Volume of Distribution (Vd)

Vd is an index that describes a drug's distribution characteristics
Vd is calculated as Vd = D/C, where D is the IV injected dose and C is the concentration in plasma
Drugs with low Vd are contained mostly in the plasma due to being ionized and highly water-soluble or highly protein-bound
Drugs with high Vd are mostly in tissues due to being hydrophobic and lipid-soluble

Therapeutic Drug Monitoring (TDM)

Definition: analysis, assessment, and evaluation of circulating concentrations of drugs in serum, plasma, or whole blood
Major purposes of TDM: ensure dosage produces maximal therapeutic benefit and identify when the drug is outside the therapeutic range

Routes of Administration

Intravenous (IV): injected directly into circulation
Intramuscular (IM): injected into muscle
Subcutaneous (SC): injected just under the skin
Transcutaneous: inhaled or absorbed through the skin
Suppository: rectal delivery
Oral Administration: by mouth

Factors Influencing Drug Levels

Route of Administration
Rate of Absorption
Distribution of drug within the body
Rate of Elimination

Antiepileptic and Psychoactive Drugs

Carbamazepine (Tegretol): treats various seizure disorders, but has serious toxic adverse effects
Ethosuximide (Zarontin): controls petit mal seizure, with rare and tolerable toxicities associated with high plasma concentrations
Lithium: treats manic depression, with a narrow therapeutic index and determination of serum lithium levels done by ion-selective electrode
Tricyclic Antidepressants (TCAs): treat depression and insomnia, with high protein binding and dose-dependent toxicity

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Description

This quiz covers the factors affecting drug absorption, including pH, intestinal motility, and co-administered drugs. It also explores drug distribution into interstitial and intracellular spaces.