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Correct answer is (d) The volume of the body fluid in which the drug is getting dissolved

To EXPLAIN I WOULD say: Concentration of drug in plasma C is DIRECTLY proportional to the amount of drug in body X. The proportionality constant Vd has the unit of volume and is also CALLED the apparent volume of distribution. It is the volume of the body fluid into which a drug is dissolved.

Right CHOICE is (b) TISSUE volume, tissue/blood partition COEFFICIENT of drug

Explanation: The DISTRIBUTION of the drug in a tissue or organ depends upon the size of the tissue i.e. the volume of the tissue. And ALSO depends upon the tissue/blood partition coefficient of a drug.

The correct ANSWER is (b) False

Easiest explanation: Drugs having a molecular WEIGHT less than 1000 Dalton and moderate to high lipid solubility can pass through the PLACENTAL barrier. Thus, this MAKES the placental barrier less effective the blood-brain barrier.

The CORRECT choice is (d) Reversible transfer of drug between blood and EXTRAVASCULAR fluids and tissues

Easy EXPLANATION: Distribution is the reversible transfer of a drug between the blood and the extravascular fluids and tissues. The driving force for absorption is the concentration GRADIENT.

Right choice is (c) Cannot CROSS the blood-brain barrier

For explanation: The SELECTIVE PERMEABILITY of the lipid soluble moieties through the BBB does not allow several drugs to just pass the barrier. Parkinsonism cannot be treated by the administration of dopamine SINCE dopamine cannot cross the BBB.

The correct OPTION is (c) Difference between total body water and ECF volume

To elaborate: The INTRACELLULAR fluid volume can be determined by finding out the difference between the TBW and the ECF volume. The intracellular fluid volume is APPROXIMATELY 27 litres.

Right answer is (a) True

Best explanation: Yes the statement is true since disease states can alter drug-protein binding, alter perfusion of the drug into any organ, and alter the pH of some TISSUE. In MENINGITIS and ENCEPHALITIS polar antibiotics gain ACCESS to BBB which don’t happen to a HEALTHY person.

Correct OPTION is (d) Endothelial CELLS

Easiest explanation: The brain capillaries are made up of EPITHELIAL cells joined to one another by continuous tight intercellular junctions thereby MAKING the blood-brain barrier. These are highly SPECIALIZED capillaries which are much less permeable to water-soluble drugs.

Correct ANSWER is (d) Drug size more than 600 DALTON

Easy explanation: Drugs size of fewer than 50 Daltons can only pass the plasma membrane barrier. Lipophilic drugs of molecular weight 50-600 Dalton, POLARISED drugs of size GREATER than 50deltons can also pass the given membrane.

The correct option is (a) True

Best explanation: Concentration of drug in plasma C is directly proportional to the AMOUNT of drug in BODY X. The PROPORTIONALITY CONSTANT Vd has the unit of volume and is also called the APPARENT volume of distribution. It is the volume of the body fluid into which a drug is dissolved.

The correct choice is (d) The growth of the uterus, PLACENTA, and foetus increases the volume thus INCREASING DISTRIBUTION. And EVEN the BABY forms a separate compartment for a drug to get distributed

Explanation: Pregnancy leads to the growth of uterus, placenta, and foetus increases the volume thus increasing distribution. And even the baby forms a separate compartment for the drug to get distributed. The plasma and the ECF volume also increase.

Right option is (a) True

Explanation: Since the blood-brain BARRIER has a HIGH oil-water partition coefficient. THUS, the blood-brain barrier is a lipoidal barrier. A highly lipid SOLUBLE DRUG can easily pass the barrier.

Right CHOICE is (c) The volume of blood that flows per unit TIME per unit volume of tissue

To ELABORATE: Perfusion rate is DEFINED as the volume of blood that flows through the tissue per unit time per unit volume of the tissue. It is expressed in ml/min/ml of the tissue.

Correct answer is (b) The apparent volume of DISTRIBUTION is more than the true volume of distribution

Easy explanation: Drugs which binds selectively to extravascular tissues have an apparent volume of distribution is more than the true volume of distribution. The volume of distribution of these drugs is always GREATER than 42 litres or TOTAL body water volume. For EXAMPLE, chloroquine has volume distribution of approximately 15,000 litres.

The correct choice is (a) Fat and bone

To elaborate: High perfusion rate is SEEN in the organs such as lungs, KIDNEYS, adrenals, liver, heart, brain. The moderate perfusion rate is in MUSCLES and SKIN. LEAST perfusion rate is in fat and bones.

The correct answer is (C) Lungs and kidney

The best I can explain: High perfusion rate is SEEN in the organs such as lungs, kidneys, adrenals, liver, heart, brain. Moderate perfusion rate is in muscles and skin. Least perfusion rate is in fat and BONES.

The correct choice is (d) Restricts the passage of DRUGS to SPERMATOCYTES and spermatids

For explanation I would say: Blood-TESTIS barrier is a tight JUNCTION between Sertoli CELLS located at the capillary endothelial level of the testis. It acts as the blood-testes barrier restricting drugs to spermatocytes and spermatids.

Correct answer is (b) 500-600 Dalton

The EXPLANATION is: Drugs with molecular weight less than 500-600 Daltons can easily cross the CAPILLARY membrane and diffuse into the EXTRACELLULAR INTERSTITIAL fluids. Molecular size, ionization constant, and lipophilicity control the penetration of drugs from the extracellular fluid to the cells.

The correct choice is (a) True

Best explanation: DRUGS of size less than 50 Dalton can pass the CELL membrane to reach intracellular fluid. Lipophilic drugs 50-600 Dalton and POLAR or ionized drugs of size less than 50 Dalton can pass the plasma membrane barrier.

Correct ANSWER is (b) Drugs bound to blood components

The explanation: All drugs ionized, unionized but with a MOLECULAR SIZE less than 600 Dalton can pass through the capillary endothelial into the interstitial fluid. Only drugs bound to the blood components are RESTRICTED because the molecular size BECOMES large.

The CORRECT choice is (C) Infants

To explain: The TOTAL body water is the net content of water present in intracellular and extracellular of an ANIMAL body. The total body water in the case of a HUMAN being is more in an infant’s body.

The correct choice is (c) Use of highly LIPOPHILIC drug only

Best explanation: Three different approaches that have been used to PROMOTE crossing the BBB is the use of permeation enhancers such as DMSO, osmotic disruption of the BBB by infusing internal carotid ARTERY with MANNITOL, Use of dihydropyridine redox system as drug CARRIERS to the brain.

Right answer is (c) INFANTS and elders

For EXPLANATION: Total fat CONTENT is the amount of fat in a person’s BODY. The total fat content is higher in infants and as well as elders.

Correct answer is (c) Drugs having a molecular weight less than 1000 Dalton and moderate to high lipid SOLUBILITY, analgesics, and antibiotics

The explanation is: Drugs having a molecular weight less than 1000deltons and drugs which are moderate to high LIPOPHILIC in nature can easily pass the placental barrier. For e.g. drugs such as ethanol, ANESTHETICS, steroids, NARCOTIC analgesics, and antibiotics, etc. can pass the placental barrier.

Right ANSWER is (a) The APPARENT volume of distribution is less than the true volume of distribution

For explanation: DRUGS which bind to plasma protein or other blood components such as that of warfarin, their apparent volume of distribution is less than the true volume of distribution. The volume of distribution of these drugs lies between blood volume and TOTAL body water volume.

Right answer is (d) Between the TISSUE layers

The explanation: The BODY WATER has 3 distinct COMPARTMENTS. The name of the compartments is vascular FLUID/ blood, extracellular fluid (excluding plasma), intracellular fluid (excluding blood cells).

Right ANSWER is (a) Infants

Explanation: Infants are newly BORN. Their BBB is poorly developed. The myelin content is LOW but the cerebral blood FLOW is very high. Thus LEADING to the high penetrating ability of the drugs into the brain of infants.

Right choice is (a) True

Best explanation: Factors altering the binding of the DRUG to the blood INCREASES the volume of distribution of the drug and the factors that influence drug binding to the EXTRAVASCULAR component decreases the volume of distribution. Other factors that influence the volume of distribution are changes in tissue perfusion, permeability, changes in PHYSICOCHEMICAL CHARACTERISTICS of the drug.

Correct OPTION is (B) False

For explanation I would say: The plasma volume can be determined by the USE of high molecular weight dyes or substances which can easily get bind to plasma ALBUMIN. TOTAL body water can be determined by heavy water or tritiated water and lipid soluble substances like antipyrine.

The correct CHOICE is (d) The high fatty acid level affect the binding of ACIDIC drugs

Easiest explanation: High fatty diet leads to an increase in fatty acids in the patients’ BLOOD. This affects the binding of acidic drugs to the PLASMA. Example drugs such as NSAIDs to ALBUMIN.

Right OPTION is (c) High adipose tissue take up most of the lipophilic drug

For explanation I would say: The high adipose tissue in the obese person take up a large FRACTION of the lipophilic drugs. THOUGH the perfusion through it is low. The high fatty acid levels in obese person ALTER the binding characteristics of acidic drugs.