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State Medical Faculty Diploma in Pharmacy Final Exam study materials
State Medical Faculty Diploma in Pharmacy Final Exam study resources

State Medical Faculty Diploma in Pharmacy Final Exam practice questions

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Question 1Pharmaceutics

Which dosage form is designed to release drug at a controlled rate over an extended period after oral administration?

  1. Effervescent tablet
  2. Sustained-release tablet Correct answer.
  3. Sublingual tablet
  4. Dispersible tablet

Explanation

Sustained-release tablets are formulated with polymers or matrices that slow dissolution and diffusion so that plasma concentrations are maintained over many hours, reducing dosing frequency. Other tablets listed are designed for rapid disintegration or rapid absorption rather than prolonged release.

Question 2Pharmaceutics

In the wet granulation process, which excipient is added to the powder blend to promote formation of granules?

  1. Lubricant
  2. Glidant
  3. Binder Correct answer.
  4. Disintegrant

Explanation

A binder is dissolved or dispersed in the granulating liquid and, on drying, forms bridges between particles that hold the granules together. Lubricants, disintegrants and glidants serve different functions in compression and disintegration.

Question 3Pharmaceutics

Which route of administration completely avoids first-pass hepatic metabolism?

  1. Rectal
  2. Intravenous Correct answer.
  3. Oral
  4. Buccal

Explanation

Intravenous administration delivers drug directly into the systemic circulation, so no absorption step or hepatic first-pass extraction occurs. Oral, rectal and buccal routes involve absorption into portal or systemic blood where first-pass effects can reduce bioavailability.

Question 4Pharmaceutics

Which pharmacopoeial test measures the uniformity of drug content among individual tablets?

  1. Content uniformity Correct answer.
  2. Hardness test
  3. Friability test
  4. Uniformity of weight

Explanation

Content uniformity assays the amount of active ingredient in individual tablets to confirm each unit contains a consistent dose. Weight uniformity only assumes uniform drug distribution, while friability and hardness assess mechanical properties.

Question 5Pharmaceutics

Which type of emulsion results when water is dispersed as droplets in a continuous oil phase?

  1. Water-in-oil emulsion Correct answer.
  2. Microemulsion
  3. Oil-in-water emulsion
  4. Multiple emulsion

Explanation

In a water-in-oil emulsion the dispersed phase is water and the continuous phase is oil, giving a greasy, non-washable feel. The naming convention places the dispersed phase first.

Question 6Pharmaceutics

Which agent is used to reduce the surface tension between two immiscible liquids in an emulsion?

  1. Antioxidant
  2. Emulsifier Correct answer.
  3. Preservative
  4. Buffer

Explanation

Emulsifiers are surface-active agents that adsorb at the oil-water interface, lowering interfacial tension and forming a film that prevents droplet coalescence. Preservatives, antioxidants and buffers address microbial growth, oxidation and pH respectively.

Question 7Pharmaceutics

Which unit operation is used to reduce the particle size of a solid by impact and attrition in a rotating drum?

  1. Sieving
  2. Filtration
  3. Centrifugation
  4. Ball milling Correct answer.

Explanation

A ball mill contains grinding media that tumble and cascade inside a rotating drum, fracturing particles by impact and attrition. Sieving classifies particles by size, while filtration and centrifugation separate phases.

Question 8Pharmaceutics

Which statement best explains why a drug given as an intravenous bolus shows a very short distribution phase in a one-compartment model?

  1. The drug is extensively bound to plasma proteins
  2. The drug is excreted unchanged by the kidneys
  3. The drug undergoes saturable hepatic metabolism
  4. Absorption is instantaneous and the drug mixes rapidly in a single kinetic space Correct answer.

Explanation

A one-compartment model assumes the body behaves as a single well-mixed kinetic space, and an intravenous bolus introduces drug directly into that space without an absorption step. Protein binding, metabolism and renal excretion affect clearance or volume but not the assumption of instantaneous mixing.

Question 9Pharmaceutics

A tablet formulation shows poor powder flow and inconsistent die filling. Which excipient should be added to improve flow?

  1. Colloidal silicon dioxide Correct answer.
  2. Microcrystalline cellulose
  3. Sodium starch glycolate
  4. Magnesium stearate

Explanation

Colloidal silicon dioxide is a glidant that coats particle surfaces and reduces interparticle friction, improving flow. Sodium starch glycolate is a superdisintegrant, magnesium stearate is a lubricant, and microcrystalline cellulose is a diluent-binder.

Question 10Pharmaceutics

A pharmacist needs a sterile, pyrogen-free preparation for a patient who cannot tolerate large fluid volumes. Which formulation strategy is most appropriate?

  1. A concentrated aqueous solution given by slow intravenous infusion Correct answer.
  2. An intramuscular depot suspension
  3. A large-volume intravenous infusion
  4. An oral solution

Explanation

A concentrated sterile solution administered as a small volume by slow infusion limits the fluid load while remaining sterile and pyrogen-free. Large-volume infusions would overload the patient, depot injections are not for immediate systemic delivery, and oral solutions are unsuitable if the patient cannot take oral medicines.

Question 11Pharmaceutics

A drug has a half-life of 6 hours. Approximately how long will it take to reach steady state during constant-rate intravenous infusion?

  1. 24 hours Correct answer.
  2. 12 hours
  3. 48 hours
  4. 6 hours

Explanation

Steady state is generally reached after about four to five half-lives. For a half-life of 6 hours, four half-lives equal 24 hours, which is a reasonable estimate of the time to steady state.

Question 12Pharmaceutics

Which factor most directly increases the bioavailability of a poorly water-soluble drug formulated as a solid dispersion?

  1. Reduced particle size and amorphous drug dispersion Correct answer.
  2. Increased crystallinity of the drug
  3. Increased lubricant concentration
  4. Increased tablet hardness

Explanation

Solid dispersions disperse drug in an amorphous polymer matrix, often with reduced particle size, which increases surface area and apparent solubility. Increased crystallinity lowers dissolution rate, while hardness and lubricant levels do not enhance solubility.

Question 13Pharmaceutics

A suspension settles slowly but forms a hard cake that cannot be redispersed. Which formulation change is most likely to improve redispersibility?

  1. Increasing the particle size of the drug
  2. Reducing the viscosity of the continuous phase
  3. Increasing the dispersed-phase concentration
  4. Adding a flocculating agent to produce controlled flocculation Correct answer.

Explanation

Controlled flocculation produces loose aggregates held by weak van der Waals forces, which settle rapidly but redisperse easily on shaking. Deflocculated systems settle slowly but form hard, irreversible cakes.

Question 14Pharmaceutics

Which statement correctly describes the mechanism of action of a disintegrant such as croscarmellose sodium?

  1. It swells on contact with water and creates disruptive pressure within the tablet Correct answer.
  2. It reduces friction between the tablet and the die wall
  3. It coats particles to improve flow
  4. It dissolves to form a viscous gel that binds particles

Explanation

Croscarmellose sodium is a superdisintegrant that wicks water into the tablet and swells rapidly, generating internal pressure that breaks the tablet into granules. Binders, lubricants and glidants act by different mechanisms.

Question 15Pharmaceutics

In an aseptic filling operation, which practice best reduces the risk of microbial contamination of a sterile product?

  1. Storing vials in the filling room before sterilisation
  2. Performing filling in a Grade A laminar airflow zone within a Grade B background Correct answer.
  3. Increasing personnel movement in the cleanroom
  4. Using non-sterile filters for the product solution

Explanation

Aseptic filling requires a Grade A unidirectional airflow zone, typically within a Grade B background, to protect the exposed product from particulate and microbial contamination. Sterilising filters, minimising personnel movement and sterilising components are also essential controls.

Question 16Pharmaceutics

Which biopharmaceutical property is most important when selecting a drug candidate for a transdermal patch?

  1. Rapid hepatic clearance
  2. High oral bioavailability
  3. Low molecular weight with adequate lipophilicity Correct answer.
  4. High molecular weight and high polarity

Explanation

Transdermal delivery favours drugs with low molecular weight (generally below about 500 Da) and balanced lipophilicity so they can partition into and diffuse through the stratum corneum. High molecular weight and high polarity limit permeation.

Question 17Pharmaceutics

A patient on a narrow-therapeutic-index drug shows signs of toxicity. Which pharmacokinetic parameter should be measured to guide dose adjustment?

  1. Tablet hardness
  2. Angle of repose
  3. Plasma drug concentration Correct answer.
  4. Disintegration time

Explanation

For narrow-therapeutic-index drugs, plasma concentration monitoring allows individualisation of dose to keep levels within the therapeutic range. Hardness, disintegration and angle of repose are formulation or manufacturing parameters, not patient-specific pharmacokinetic measures.

Question 18Pharmaceutics

Which process is responsible for the degradation of a drug by reaction with oxygen, and how is it usually prevented in a liquid formulation?

  1. Photolysis; prevented by adding a buffer
  2. Hydrolysis; prevented by adding water
  3. Racemisation; prevented by adding a preservative
  4. Oxidation; prevented by adding an antioxidant and chelating agent Correct answer.

Explanation

Oxidation involves loss of electrons from the drug, often catalysed by trace metals, and is controlled by antioxidants and chelating agents such as edetate. Hydrolysis involves water, photolysis involves light, and racemisation involves loss of stereochemical integrity.

Question 19Pharmaceutics

Which equation relates the rate of drug release from a matrix tablet to the square root of time for diffusion-controlled systems?

  1. Higuchi equation Correct answer.
  2. Michaelis-Menten equation
  3. Zero-order equation
  4. First-order equation

Explanation

The Higuchi model describes release from a matrix as proportional to the square root of time, reflecting diffusion through a progressively thicker depleted layer. Zero-order and first-order models describe constant and concentration-dependent release, while Michaelis-Menten describes saturable enzyme kinetics.

Question 20Pharmaceutics

A pharmacist must prepare a sterile ophthalmic solution. Which property is most critical to ensure patient safety?

  1. Isotonicity with tear fluid
  2. Viscosity matching that of tears
  3. Sterility and freedom from particulate matter Correct answer.
  4. Colour of the solution

Explanation

Ophthalmic solutions must be sterile and free from particulate matter because the eye is a sensitive, poorly defended site where contamination can cause infection or injury. Isotonicity improves comfort but is secondary to sterility, and viscosity and colour are not safety-critical.

Question 21Pharmaceutics

Which manufacturing factor is most likely to cause capping of tablets during compression?

  1. Presence of a glidant
  2. Excessive fines in the granulation and air entrapment Correct answer.
  3. Use of a superdisintegrant
  4. Low compression force

Explanation

Capping occurs when the top of the tablet separates during or after compression, often because air trapped in the granulation or excessive fines prevents proper bonding. Reducing fines, optimising moisture and slowing the turret speed help prevent it.

Question 22Pharmaceutics

A drug follows first-order elimination with a half-life of 8 hours and a volume of distribution of 40 L. What is the approximate clearance?

  1. 0.87 L/h
  2. 3.47 L/h Correct answer.
  3. 5.55 L/h
  4. 11.1 L/h

Explanation

Clearance equals the elimination rate constant multiplied by volume of distribution. The rate constant is 0.693 divided by 8 hours, about 0.0866 per hour; multiplied by 40 L gives approximately 3.47 L/h.

Question 23Pharmaceutics

A formulation contains a drug that is unstable at gastric pH and is intended for systemic action. Which strategy best protects the drug while allowing absorption?

  1. Use of a flavouring agent
  2. Enteric coating of the tablet Correct answer.
  3. Compression at higher hardness
  4. Addition of a superdisintegrant

Explanation

An enteric coating resists dissolution in gastric acid and dissolves in the higher pH of the small intestine, protecting acid-labile drugs until they reach an absorptive region. Disintegrants, flavours and hardness do not protect against gastric degradation.

Question 24Pharmaceutics

During stability testing, a liquid formulation shows a first-order degradation with a rate constant of 0.02 per month. What is the approximate shelf life (t90) at which 10% of the drug has degraded?

  1. 11 months
  2. 50 months
  3. 5.3 months Correct answer.
  4. 0.53 months

Explanation

For first-order degradation, the time for 10% loss is 0.105 divided by the rate constant. Dividing 0.105 by 0.02 per month gives approximately 5.3 months, which is the t90 shelf life.

Question 25Pharmaceutics

A poorly soluble weak base is formulated as a salt to improve dissolution. Which principle explains the improvement?

  1. The salt form increases aqueous solubility and dissolution rate at intestinal pH Correct answer.
  2. The salt form prevents all metabolism
  3. The salt form increases the partition coefficient into lipids
  4. The salt form reduces the drug's molecular weight

Explanation

Salt formation increases the aqueous solubility of weakly basic or acidic drugs, raising the concentration gradient that drives dissolution according to the Noyes-Whitney relationship. It does not necessarily increase lipophilicity, reduce molecular weight or block metabolism.

Question 26Pharmaceutics

Which type of excipient is included in a tablet formulation to prevent sticking of the granules to the punch faces during compression?

  1. An antiadherent such as magnesium stearate Correct answer.
  2. A binder such as povidone
  3. A glidant such as colloidal silicon dioxide
  4. A disintegrant such as starch

Explanation

Antiadherents reduce adhesion between the compressed powder and the metal surfaces of punches and dies, so material does not stick and tear the tablet surface. Magnesium stearate is the classic example, acting at the interface rather than within the granule structure. Binders, disintegrants, and glidants serve different mechanical functions and do not primarily prevent punch sticking.

Question 27Pharmaceutics

Which type of emulsion is formed when water is the continuous phase and oil is dispersed as droplets?

  1. An oil-in-water emulsion
  2. An anhydrous ointment base
  3. A multiple water-in-oil-in-water emulsion
  4. A water-in-oil emulsion Correct answer.

Explanation

Emulsion type is named by the dispersed phase first and the continuous phase second, so a system with oil droplets dispersed in water is an oil-in-water emulsion. In the reverse case, water droplets dispersed in oil give a water-in-oil emulsion. The continuous phase determines the external feel and dilution behavior of the product.

Question 28Pharmaceutics

Which statement describes the purpose of the leak test performed on sealed ampoules after filling?

  1. It confirms that the fill volume meets the labeled amount.
  2. It detects containers with incomplete seals that could admit microorganisms. Correct answer.
  3. It measures the pH of the solution inside each container.
  4. It verifies that the sterilization cycle reached the required temperature.

Explanation

A leak test exposes sealed ampoules to a dye or vacuum so that any container with a defective seal draws in colored liquid or shows pressure loss. Its purpose is to identify packages that could allow microbial ingress and contaminate a sterile product. Fill volume, sterilization efficacy, and pH are assessed by separate tests.

Question 29Pharmaceutics

A pharmacist prepares a solution of a weak acid drug and adjusts the pH well below its pKa. What effect does this have on the proportion of drug that is ionized?

  1. The proportion ionized increases because more hydrogen ions are available.
  2. The proportion ionized stays constant because pH does not affect weak acids.
  3. The proportion ionized falls to zero because the drug precipitates completely.
  4. The proportion ionized decreases because the equilibrium shifts toward the un-ionized form. Correct answer.

Explanation

For a weak acid, lowering the pH below the pKa shifts the dissociation equilibrium toward the protonated, un-ionized species. The Henderson-Hasselbalch relationship shows that the ratio of ionized to un-ionized drug falls as hydrogen ion concentration rises. This principle is used to improve partitioning of acidic drugs across lipid membranes.

Question 30Pharmaceutics

A drug is to be formulated as a suppository for a patient who cannot swallow. Which property of the base most directly determines whether the drug is released rapidly after insertion?

  1. The refractive index of the base
  2. The color of the base after storage
  3. The density of the base at room temperature
  4. The melting point of the base and its ability to melt at body temperature Correct answer.

Explanation

Release from a suppository depends largely on the base melting or dissolving at rectal temperature, so a base with a melting point near 37 degrees Celsius liquefies and liberates the drug promptly. Bases that melt well above body temperature remain solid and release drug slowly. Color, density, and refractive index do not govern the melting-based release mechanism.

Question 31Pharmaceutics

A suspension for oral use is being designed to remain easily redispersible on shaking. Which approach best supports this goal?

  1. Adding a flocculating agent to produce loose aggregates of particles Correct answer.
  2. Reducing the viscosity of the continuous phase
  3. Increasing the particle size of the dispersed solid
  4. Using a vehicle in which the particles are completely insoluble and densely packed

Explanation

Controlled flocculation produces loose, easily broken aggregates that settle rapidly but redisperse readily with gentle shaking, avoiding hard caking. Deflocculated systems settle slowly but tend to form compact sediments that are difficult to resuspend. Particle size reduction and adequate viscosity also aid stability, but flocculation is the direct strategy for redispersibility.

Question 32Pharmaceutics

A manufacturer wants to convert a crystalline drug into an amorphous solid to enhance dissolution rate. Which statement best explains the underlying physical principle?

  1. The amorphous form has a higher melting point that increases thermodynamic driving force.
  2. The amorphous form has a smaller surface area than the crystalline form.
  3. The amorphous form has a higher apparent solubility because no crystal lattice must be disrupted during dissolution. Correct answer.
  4. The amorphous form contains more water of crystallization that accelerates dissolution.

Explanation

Dissolution of a crystal requires energy to break the lattice, so the crystalline form has lower apparent solubility than the amorphous form. The amorphous state lacks long-range order and therefore presents a higher apparent solubility and faster dissolution. This thermodynamic advantage is offset by a greater tendency toward recrystallization on storage.

Question 33Pharmaceutics

A compressed tablet shows a laminated top cap separating from the main body shortly after ejection from the die. Which change is most likely to reduce this defect?

  1. Adding more lubricant to increase ejection force requirements
  2. Increasing the compression force to eliminate all porosity
  3. Increasing the tablet thickness while keeping the same weight
  4. Reducing the amount of fines in the granulation and improving its flow Correct answer.

Explanation

Capping and lamination arise from entrapped air and elastic recovery when the compact is stressed unevenly during decompression. Reducing fines and improving granule flow gives more uniform die filling and a more homogeneous compact, lowering the risk of separation. Excessive force and excess lubricant tend to aggravate rather than correct the defect.

Question 34Pharmaceutics

During development of a hydrophilic matrix tablet, the polymer is found to hydrate too slowly, so the gel layer forms late and drug release is erratic. Which formulation change is most appropriate?

  1. Increasing the molecular weight of the matrix polymer
  2. Using a finer particle size grade of the polymer and increasing its proportion Correct answer.
  3. Adding a hydrophobic lubricant at a higher level
  4. Replacing the polymer with a higher-viscosity grade

Explanation

Hydration of a hydrophilic matrix begins at the particle surface, so a finer particle size increases the surface area available for water uptake and speeds gel formation. Increasing the polymer proportion also strengthens and advances the gel barrier. Higher molecular weight or higher viscosity grades hydrate more slowly and would worsen the problem.

Question 35Pharmaceutical Chemistry

Which functional group is present in the structure of paracetamol (acetaminophen)?

  1. Ester
  2. Sulfonamide
  3. Amide Correct answer.
  4. Carboxylic acid

Explanation

Paracetamol contains an N-acetyl group attached to an aromatic amine, which is an amide linkage, together with a phenolic hydroxyl group. The amide is the defining nitrogen-containing functional group of this molecule.

Question 36Pharmaceutical Chemistry

Aspirin is chemically classified as which type of compound?

  1. Benzodiazepine
  2. Phenothiazine
  3. Salicylate ester Correct answer.
  4. Barbiturate

Explanation

Aspirin is acetylsalicylic acid, in which the phenolic hydroxyl of salicylic acid is acetylated to form an ester. It therefore belongs to the salicylate ester class of analgesic agents.

Question 37Pharmaceutical Chemistry

Which analytical technique measures the absorption of infrared radiation to identify functional groups?

  1. Nephelometry
  2. Infrared spectroscopy Correct answer.
  3. Atomic absorption spectroscopy
  4. Flame photometry

Explanation

Infrared spectroscopy probes vibrational transitions of covalent bonds, giving characteristic absorption bands for functional groups such as carbonyl, hydroxyl and amine. The other techniques measure elemental absorption or light scattering rather than molecular vibrations.

Question 38Pharmaceutical Chemistry

The IUPAC name of the compound formed when the hydroxyl hydrogen of phenol is replaced by a methyl group is which of the following?

  1. Cresol
  2. Toluene
  3. Anisole Correct answer.
  4. Catechol

Explanation

Replacing the phenolic hydrogen with a methyl group converts phenol into methoxybenzene, whose common name is anisole. Toluene is methylbenzene, cresol is methylphenol, and catechol is dihydroxybenzene.

Question 39Pharmaceutical Chemistry

Which of the following is the pharmacopoeial limit test used to detect chloride impurity in pharmaceutical substances?

  1. Flame test with barium chloride
  2. Opalescence comparison with silver nitrate Correct answer.
  3. Precipitation with ammonium molybdate
  4. Colour reaction with diphenylcarbazone

Explanation

The chloride limit test precipitates silver chloride in dilute nitric acid and compares the resulting opalescence with a standard. This turbidity-based comparison quantifies the chloride impurity against a known reference.

Question 40Pharmaceutical Chemistry

Which of the following drugs is a prodrug that requires metabolic conversion to release its active component?

  1. Furosemide
  2. Enalapril Correct answer.
  3. Atenolol
  4. Metformin

Explanation

Enalapril is an ester prodrug that undergoes hepatic hydrolysis to enalaprilat, the active angiotensin-converting enzyme inhibitor. The esterification improves oral bioavailability before the active acid is liberated.

Question 41Pharmaceutical Chemistry

Which of the following is the correct definition of a buffer solution?

  1. A solution that resists pH change on addition of small amounts of acid or base Correct answer.
  2. A solution that conducts electricity without ionisation
  3. A solution whose pH is always exactly 7.0
  4. A solution that neutralises any amount of strong acid completely

Explanation

A buffer contains a weak acid and its conjugate base, or a weak base and its conjugate acid, and resists pH change when small amounts of acid or alkali are added. Its capacity is finite, so it cannot neutralise unlimited strong acid.

Question 42Pharmaceutical Chemistry

Which element is determined quantitatively in organic pharmaceutical compounds by the Kjeldahl method?

  1. Phosphorus
  2. Nitrogen Correct answer.
  3. Sulfur
  4. Chlorine

Explanation

The Kjeldahl method digests the sample with sulfuric acid to convert nitrogen into ammonium sulfate, which is then distilled with alkali and titrated. It is the standard nitrogen determination method for organic compounds.

Question 43Pharmaceutical Chemistry

Which of the following statements best describes the role of glucuronic acid conjugation in drug metabolism?

  1. It increases lipid solubility and tissue storage
  2. It converts the drug into a more toxic electrophile
  3. It increases water solubility and promotes urinary excretion Correct answer.
  4. It reduces molecular weight by removing functional groups

Explanation

Glucuronidation attaches glucuronic acid to a nucleophilic group on the drug, raising polarity and water solubility. The resulting conjugate is more readily excreted in bile or urine.

Question 44Pharmaceutical Chemistry

Which of the following structural features is responsible for the acidic character of sulfonamide drugs?

  1. The aromatic amino group in the para position
  2. The hydrogen atom on the sulfonamide nitrogen Correct answer.
  3. The secondary alcohol in the side chain
  4. The methyl substituent on the isoxazole ring

Explanation

The N-H proton of the sulfonamide group is sufficiently acidic to form a water-soluble sodium salt because the adjacent sulfonyl group strongly withdraws electrons. This property allows formulation of soluble sulfonamide salts.

Question 45Pharmaceutical Chemistry

Which of the following is the primary pharmacopoeial assay method for determining the content of a primary aromatic amine by diazotisation?

  1. Complexometric titration with EDTA
  2. Non-aqueous titration with perchloric acid
  3. Sodium nitrite titration in acidic medium Correct answer.
  4. Iodimetric titration in alkaline medium

Explanation

Primary aromatic amines are assayed by titration with sodium nitrite in hydrochloric acid at low temperature, forming a diazonium salt. Starch-iodide paper or an electrometric endpoint detects excess nitrous acid.

Question 46Pharmaceutical Chemistry

Which of the following chromatographic techniques separates molecules primarily on the basis of size?

  1. Affinity chromatography
  2. Reversed-phase chromatography
  3. Size-exclusion chromatography Correct answer.
  4. Ion-exchange chromatography

Explanation

Size-exclusion chromatography uses a porous stationary phase in which smaller molecules penetrate the pores and are retarded, while larger molecules elute earlier. Separation depends on molecular size and shape.

Question 47Pharmaceutical Chemistry

A drug has a pKa of 7.4 and is a weak base. At physiological pH 7.4, which fraction is present in the ionised form?

  1. About 100 percent
  2. About 10 percent
  3. About 50 percent Correct answer.
  4. About 90 percent

Explanation

For a weak base, when the pH equals the pKa of the conjugate acid, the Henderson-Hasselbalch relationship gives equal concentrations of ionised and un-ionised species. Therefore approximately half the molecules are ionised at that pH.

Question 48Pharmaceutical Chemistry

Which of the following oxidation reactions is used in the pharmacopoeial assay of ferrous sulfate?

  1. Titration with silver nitrate using potassium chromate
  2. Titration with ceric ammonium sulfate using ferroin indicator Correct answer.
  3. Titration with disodium edetate using murexide
  4. Titration with sodium hydroxide using phenolphthalein

Explanation

Ferrous sulfate is assayed by oxidation of iron(II) to iron(III) with ceric ammonium sulfate, with ferroin serving as the redox indicator. The oxidising titrant gives a sharp colour change at the endpoint.

Question 49Pharmaceutical Chemistry

Which of the following statements about the relationship between lipophilicity and drug absorption is most accurate?

  1. Highly hydrophilic drugs cross lipid bilayers most rapidly
  2. Lipophilicity has no influence on passive diffusion across membranes
  3. Increasing lipophilicity always increases both permeation and aqueous solubility
  4. Increasing lipophilicity generally increases membrane permeation until aqueous solubility becomes limiting Correct answer.

Explanation

Passive diffusion requires the drug to partition into the lipid bilayer, so moderate lipophilicity favours permeation. Beyond an optimum, poor aqueous solubility limits dissolution and absorption, giving a parabolic relationship.

Question 50Pharmaceutical Chemistry

Which of the following is the principal reason for coating an enteric dosage form?

  1. To accelerate disintegration in the stomach
  2. To improve taste masking in the mouth
  3. To prevent drug release in the acidic gastric environment Correct answer.
  4. To provide sustained release over 24 hours

Explanation

Enteric polymers are insoluble in gastric acid and dissolve at the higher pH of the intestine, protecting acid-labile drugs or the gastric mucosa. The coating therefore delays release until the dosage form leaves the stomach.