Absorption and Bioavailability — MCQs

10 questions

Volume of distribution of a drug is 500 ml and target concentration of drug in blood is 5 g/L. 20% of administered drug is reached to systemic circulation. What will be the loading dose of that drug -

Which of the following factors influences the duration of action of a drug?

Which route of administration undergoes the maximum first pass metabolism?

Which of the following describes the first-pass metabolism?

Through which of the following means of transport is folic acid absorbed in the proximal jejunum?

Lidocaine is used in a loading dose for the treatment of arrhythmias. The loading dose of this drug depends upon which of the following factors?

Which of the following is NOT an advantage of amoxicillin over ampicillin?

Which vitamin increases the absorption of iron?

Calcium absorption is hampered by

Q10

When alcohol is consumed with aerated soft drinks -

Absorption and Bioavailability Indian Medical PG Practice Questions and MCQs

Question 1: Volume of distribution of a drug is 500 ml and target concentration of drug in blood is 5 g/L. 20% of administered drug is reached to systemic circulation. What will be the loading dose of that drug -

A. 1 gm
B. 5 gm
C. 25 gm
D. 12.5 gm (Correct Answer)

Explanation: ***12.5 gm*** - The formula for loading dose (LD) is: LD = (Target Concentration × Volume of Distribution) / Bioavailability. - Given: Target Concentration = 5 g/L, Volume of Distribution = 500 mL = 0.5 L, Bioavailability = 20% = 0.2. - So, LD = (5 g/L × 0.5 L) / 0.2 = 2.5 g / 0.2 = **12.5 g**. *1 gm* - This value would be obtained if the target concentration was 2 g/L with 100% bioavailability, or if the calculation incorrectly handled the volume or bioavailability factor. - It does not account for the specified **bioavailability of 20%** or the given target concentration and volume of distribution. *5 gm* - This result would be obtained if the bioavailability was assumed to be 50% (LD = 2.5 g / 0.5 = 5 g), or if the volume of distribution was incorrectly used in the calculation. - This option does not correctly factor in the **20% bioavailability** of the administered drug. *25 gm* - This value would result from mistakes such as dividing by bioavailability of 10% instead of 20% (LD = 2.5 g / 0.1 = 25 g), or by multiplying bioavailability instead of dividing by it. - This answer significantly **overestimates** the required dose, which could lead to drug toxicity.

Question 2: Which of the following factors influences the duration of action of a drug?

A. Bioavailability
B. Clearance
C. Rate of elimination
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - **Clearance** and **rate of elimination** are the primary determinants of how long a drug stays in the body at therapeutic levels, thus directly influencing its duration of action. - **Bioavailability** affects the intensity and onset but can influence the perceived duration if subtherapeutic concentrations are achieved. - The interplay of these pharmacokinetic parameters ultimately determines the drug's therapeutic window and frequency of dosing. *Clearance* - **Clearance** is the rate at which the active drug is removed from the body, primarily by the kidneys and liver. - A higher clearance generally leads to a shorter elimination half-life and a **shorter duration of action**, as the drug is removed more quickly from the systemic circulation. *Rate of elimination* - The **rate of elimination** directly dictates how quickly the concentration of a drug in the body decreases over time. - A faster elimination rate (shorter half-life) means the drug's effects will wear off sooner, resulting in a **shorter duration of action**. - This is quantified by the elimination rate constant (Kel) and half-life (t½). *Bioavailability* - **Bioavailability** refers to the fraction of an administered dose of unchanged drug that reaches the systemic circulation. - While bioavailability primarily affects the **peak concentration (Cmax)** and **intensity** of drug effect, it can indirectly influence duration. - If bioavailability is very low, therapeutic concentrations may not be sustained long enough, effectively shortening the **clinically relevant duration of action**. - However, two drugs with identical elimination rates but different bioavailabilities will have the same elimination half-life and similar duration at therapeutic doses.

Question 3: Which route of administration undergoes the maximum first pass metabolism?

A. Intra-arterial
B. Rectal
C. Oral (Correct Answer)
D. Intravenous

Explanation: ***Oral*** - Drugs administered orally are absorbed from the **gastrointestinal tract** and transported via the **portal vein** directly to the liver, where they undergo significant **first-pass metabolism** before reaching systemic circulation. - This hepatic metabolism can drastically reduce the **bioavailability** of the drug, requiring higher doses or alternative administration routes. *Intra-arterial* - This route delivers drugs directly into an **artery** supplying a target tissue or organ, largely bypassing systemic circulation and initial hepatic metabolism. - It is used for localized effects, such as **chemotherapy** for specific tumors, minimizing systemic exposure. *Rectal* - While a portion of rectally administered drugs may bypass the portal circulation by entering the **inferior and middle rectal veins**, a significant amount can still be absorbed into the superior rectal vein, which drains into the portal system. - This means rectal administration offers only **partial avoidance** of first-pass metabolism, making it less complete than IV or intra-arterial routes for bypassing the liver altogether. *Intravenous* - Drugs administered intravenously are delivered directly into the **systemic circulation**, completely bypassing the gastrointestinal tract and the liver's first-pass metabolism. - This route ensures **100% bioavailability** and rapid onset of action, as the drug immediately reaches its target.

Question 4: Which of the following describes the first-pass metabolism?

A. Drug given orally is metabolized by the liver before entering the circulation. (Correct Answer)
B. Drug given intravenously bypasses the liver initially.
C. Gastric acids primarily affect the stability of drugs.
D. Absorption of a drug occurs in the intestines.

Explanation: ***Drug given orally is metabolized by the liver before entering the circulation.*** - **First-pass metabolism**, also known as **presystemic metabolism**, refers to the phenomenon where a drug is extensively metabolized in the **gastrointestinal tract** and **liver** before it reaches systemic circulation. - This process significantly reduces the **bioavailability** of orally administered drugs, as a substantial portion of the drug is inactivated or converted to metabolites before it can exert its therapeutic effect. *Drug given intravenously bypasses the liver initially.* - While intravenous (IV) administration does bypass **first-pass metabolism** in the liver and gastrointestinal tract, this statement describes what happens with IV drugs, not the first-pass metabolism itself. - IV drugs enter the **systemic circulation** directly, achieving 100% bioavailability, unlike orally administered drugs affected by first-pass metabolism. *Gastric acids primarily affect the stability of drugs.* - **Gastric acids** primarily affect the **chemical stability** and degradation of certain drugs, but this is a separate phenomenon from first-pass metabolism. - While acid degradation can reduce drug absorption, first-pass effect specifically refers to metabolic transformation in the gut wall and liver. *Absorption of a drug occurs in the intestines.* - The **small intestine** is indeed the primary site for drug absorption due to its large surface area and rich blood supply. - However, this statement describes **drug absorption** in general, not specifically the process of first-pass metabolism, which occurs *after* absorption and involves metabolism before systemic circulation.

Question 5: Through which of the following means of transport is folic acid absorbed in the proximal jejunum?

A. Facilitated diffusion
B. Both active and passive transport (Correct Answer)
C. Active transport
D. Passive transport

Explanation: ***Both active and passive transport*** - **Folic acid** absorption in the **proximal jejunum** occurs through **both active and passive mechanisms**. - At **low physiological concentrations**, an **active carrier-mediated transport** system is primarily responsible, while at **higher concentrations** (e.g., from supplements), **passive diffusion** also plays a significant role. *Facilitated diffusion* - While a type of passive transport, **facilitated diffusion** alone does not fully encompass the entirety of folic acid absorption, especially at low concentrations. - It relies on a **concentration gradient** and **carrier proteins** but does not require metabolic energy. *Active transport* - **Active transport** is crucial for absorbing folic acid when its concentration is low in the gut lumen. - This process requires **energy** and specific **carrier proteins**, like the **reduced folate carrier (RFC)**, to transport folate against a concentration gradient. *Passive transport* - **Passive transport**, specifically **simple diffusion**, contributes to folic acid absorption but primarily at **high lumen concentrations**, such as after taking large doses of supplements. - It occurs down a **concentration gradient** and does not require energy or specific carriers.

Question 6: Lidocaine is used in a loading dose for the treatment of arrhythmias. The loading dose of this drug depends upon which of the following factors?

A. Clearance
B. Volume of distribution (Correct Answer)
C. Half-life
D. Bioavailability
E. Elimination rate constant

Explanation: ***Volume of distribution*** - The **loading dose** of a drug is primarily determined by its **volume of distribution (Vd)** and the **target plasma concentration**. - A larger **Vd** means the drug distributes widely into tissues, requiring a larger loading dose to achieve the desired concentration in the central compartment. *Clearance* - **Clearance** dictates the **maintenance dose** needed to sustain a steady-state concentration once the loading dose has been administered. - It reflects the rate at which the drug is eliminated from the body, not how much is initially needed to fill the distribution volume. *Half-life* - **Half-life** determines the **time required to reach steady-state** and the **dosing interval** for maintaining therapeutic concentrations. - While related to clearance and Vd, it does not directly determine the magnitude of the initial loading dose itself. *Bioavailability* - **Bioavailability** is the fraction of administered drug that reaches the systemic circulation in an unchanged form. - It influences the oral dose required to achieve a certain plasma concentration, but the concept of loading dose is typically considered for the intravenous route where bioavailability is 100%. *Elimination rate constant* - The **elimination rate constant (ke)** describes the rate of drug elimination and is related to clearance and volume of distribution (ke = Cl/Vd). - Like clearance, it determines the **maintenance dose** and dosing frequency, not the initial loading dose required to achieve therapeutic levels.

Question 7: Which of the following is NOT an advantage of amoxicillin over ampicillin?

A. Spectrum includes H. influenzae & Shigella (Correct Answer)
B. Incidence of diarrhea is lower
C. Food does not interfere with its absorption
D. Better bioavailability & faster action

Explanation: ***Spectrum includes H. influenzae & Shigella*** - Amoxicillin and ampicillin both have a similar spectrum of activity against *Haemophilus influenzae* and *Shigella* species. Neither drug possesses a distinct advantage over the other in this regard for these specific pathogens. - Therefore, stating that amoxicillin's spectrum *includes* these bacteria as an advantage over ampicillin implies a unique characteristic, which is incorrect. *Better bioavailability & faster action* - **Amoxicillin** has superior oral **bioavailability** compared to ampicillin, leading to higher and more consistent blood levels. - This improved absorption often translates to a **faster onset of action** and allows for less frequent dosing. *Incidence of diarrhea is lower* - **Amoxicillin** is associated with a **lower incidence of diarrhea** and other gastrointestinal side effects compared to ampicillin. - This is partly due to its better absorption, meaning less unabsorbed drug reaches the colon to disrupt normal flora. *Food does not interfere with its absorption* - The absorption of **amoxicillin is largely unaffected by food**, allowing it to be taken without regard to meals. - In contrast, ampicillin's absorption can be significantly reduced when taken with food, making amoxicillin more convenient.

Question 8: Which vitamin increases the absorption of iron?

A. Riboflavin
B. Vitamin A
C. Thiamin
D. Vitamin C (Correct Answer)

Explanation: ***Vitamin C*** - **Ascorbic acid** (Vitamin C) acts as a reducing agent, converting ferric iron (Fe3+) in the diet to ferrous iron (Fe2+), which is more soluble and readily absorbed in the duodenum. - It also counteracts the effects of absorption inhibitors like phytates and polyphenols found in plant-based foods, further enhancing **non-heme iron absorption**. *Riboflavin* - **Riboflavin** (Vitamin B2) is crucial for various metabolic processes, including red blood cell production, but it does not directly enhance iron absorption. - Deficiency can lead to anemia, but this is due to impaired red blood cell synthesis, not altered iron uptake. *Vitamin A* - **Vitamin A** plays a role in the mobilization of iron stores and erythrocyte differentiation, and deficiency can exacerbate iron deficiency anemia. - However, it does not directly increase the absorption of dietary iron from the gut. *Thiamin* - **Thiamin** (Vitamin B1) is essential for carbohydrate metabolism and nerve function. - It has no known direct role in the absorption or metabolism of iron.

Question 9: Calcium absorption is hampered by

A. Protein
B. Lactose
C. Acid
D. Phytates (Correct Answer)

Explanation: ***Phytates*** - **Phytates** (phytic acid) found in whole grains, legumes, nuts, and seeds bind to calcium, forming an insoluble complex that significantly **reduces its absorption** in the intestines. - This binding prevents the free calcium ions from crossing the intestinal wall into the bloodstream. *Protein* - **Protein** generally *enhances* calcium absorption, especially when consumed in moderate amounts, as some amino acids can form soluble calcium complexes. - However, very high protein intake, particularly from animal sources, *may* slightly increase urinary calcium excretion in the long term, but it does not directly hamper intestinal absorption. *Lactose* - **Lactose**, a sugar found in milk, is known to *enhance* calcium absorption. - It does so by creating a more acidic environment in the small intestine and by forming soluble complexes with calcium, making it more bioavailable. *Acid* - **Stomach acid** (hydrochloric acid) is crucial for calcium absorption as it helps to solubilize calcium salts from food. - A *reduced* acidic environment, such as from antacid use or certain medical conditions, would hamper calcium absorption, but acid itself is beneficial.

Question 10: When alcohol is consumed with aerated soft drinks -

A. Effect is enhanced
B. To reduce hangover risk
C. Absorption is faster, increasing intoxication risk (Correct Answer)
D. None of the options

Explanation: ***Absorption is faster, increasing intoxication risk*** - The carbonation in aerated soft drinks speeds up the absorption of alcohol into the bloodstream. - This **faster absorption** leads to a more rapid increase in blood alcohol concentration and can intensify the effects of alcohol, thereby increasing the risk of intoxication. *Effect is enhanced* - While the **effect** might seem to be enhanced due to quicker onset, this option doesn't fully explain the physiological mechanism. - The primary reason for the perceived enhancement is the **accelerated absorption**, not a direct potentiation of alcohol's action. *To reduce hangover risk* - Mixing alcohol with aerated drinks generally **does not reduce hangover risk**; in fact, the rapid absorption can sometimes worsen dehydration and lead to a more severe hangover. - Hangovers are primarily caused by dehydration, acetaldehyde buildup, and other congeners, which are not mitigated by carbonated mixers. *None of the options* - This option is incorrect because the statement about **faster absorption leading to increased intoxication risk** is a well-established physiological effect.

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free