24 Questions
What is an important factor affecting drug absorption?
All of the above
Where are acidic drugs absorbed?
Stomach
What can alter the absorption rate of a drug?
All of the above
What is the primary elimination route for polar drugs?
Kidneys
What determines the distribution of a drug in the body?
Hydrophobicity
What is the volume of distribution (Vd) of a drug?
The ratio of total body store of drug to plasma concentration
Why do drugs with low Vd remain mostly in the plasma?
Because they are ionized and highly water-soluble
What is the significance of a high Vd for a drug?
The drug is highly lipid-soluble
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
What factor influences drug absorption through the GI tract?
Formulation of the drug
Which of the following mechanisms is involved in drug absorption through the GI tract?
Both active and passive transport mechanisms
What is the most common route of administration for drugs?
Oral administration
What affects the diffusion of a drug from the GI tract to the bloodstream?
Chemical structure of the drug
What is the primary mechanism of drug absorption through the GI tract?
Passive diffusion
Which of the following factors does not influence drug absorption through the GI tract?
Rate of elimination
What determines the rate of absorption of a drug through the GI tract?
All of the above
What is the characteristic of a drug with a high volume of distribution?
Low blood concentration and high tissue concentration
What is the effect of hepatic dysfunction on the drug Carbamazepine?
It may cause LFT to be checked frequently
What is the most serious side effect of Carbamazepine?
Leukopenia
What is the plasma concentration of Carbamazepine associated with hematologic dyscrasias and possible aplastic anemia?
Greater than 15 μg/mL
What is the characteristic of Ethosuximide?
It has rare and tolerable toxicities
What is the therapeutic index of Lithium?
0.8-1.2 mmol/L
What is the characteristic of Tricyclic Antidepressants (TCAs)?
They are highly protein-bound
What is the effect of high plasma concentration on the toxicity of Ethosuximide?
It has a rare and tolerable effect on the toxicity
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
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.
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