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Question
Consider the following antacids:
Show that antacid $\mathbf{X}$ is more effective, per tablet, than antacid $\mathbf{Y}$.
▶️Answer/Explanation
Markscheme
same reactant mole ratio «in both equations»
OR
$$
\begin{aligned}
& \mathrm{Mg}(\mathrm{OH})_2(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) \ll \rightarrow \mathrm{MgCl}_2(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}(1) » \text { AND } \\
& \mathrm{CaCO}_3(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) « \rightarrow \mathrm{CaCl}_2(\mathrm{aq})+\mathrm{H}_2 \mathrm{O}(1)+\mathrm{CO}_2(\mathrm{~g}) » \\
& \mathrm{Mg}^n(\mathrm{OH})_2=\ll \frac{0.200}{58.32}=» 3.43 \times 10^{-3} \text { «mol» AND } \\
& \mathrm{CaCO}_n=« \frac{0.220}{100.09}=» 2.20 \times 10^{-3} \text { 《mol» }
\end{aligned}
$$
«tablet of» X neutralizes $6.86 \times 10^{-3}$ «mol» $\mathrm{HCl} \boldsymbol{A N D}$ «tablet of» Y neutralizes $4.40 \times 10^{-3}$ «mol» $\mathrm{HCl}$ Award [3] for correct final statement AND values in M3.
Question
\text { Aspirin is formed by reacting salicylic acid with ethanoic anhydride. The structure of aspirin is given in section } 37 \text { of the data booklet. }
b. Aspirin crystals are rinsed with water after recrystallization to remove impurities.
Suggest why cold water is used.
c. The solubility of aspirin is increased by converting it to an ionic form. Draw the structure of the ionic form of aspirin.
d. Comment on the risk of overdose when taking aspirin as an analgesic, referring to the following values, for a person weighing $70 \mathrm{~kg}$ :
Minimum therapeutic dose $=0.5 \mathrm{~g}$
Estimated minimum lethal dose $=15 \mathrm{~g}$
▶️Answer/Explanation
Markscheme
Accept full OR condensed structural formula.
b. to avoid dissolving the crystals/aspirin
c
Accept a positive metal ion next to the $\mathrm{COO}^{-}$such as ” $\mathrm{Na}^{+} / \mathrm{K}^{+}$”.
Accept “-ONa/- OK” without showing the charges.
Accept notations such as “RCOO”” OR “RCOONa” OR “RCOOK” but not “RO-” OR “RON a” OR “ROK”.
d. low/medium risk «of overdosing» $A N D$ «estimated» lethal dose is 30 times/much larger than therapeutic dose OR
30 times the dose results in chance of dying
Accept “30 and low/medium risk due to large therapeutic index”.
Do not accept “low/medium risk AND large therapeutic window”.
Do not accept “30 times the dose” alone for the mark.
Question
This question is about antiviral drugs.
Oseltamivir, used for the treatment of severe flu, is inactive until converted in the liver to its active carboxylate form.
a(i)Draw a circle around the functional group that can be converted to the carboxylate by hydrolysis.
a(ii)Suggest a reason for using a phosphate salt of oseltamivir in oral tablets.
b. Anti-HIV drugs, such as zidovudine, often become less effective over time.
Explain the development of resistant virus strains in the presence of antiviral drugs.
▶️Answer/Explanation
Markscheme
a(i)
Note: Accept circles that include the alkyl side chain.
a(ii)more soluble «in water» $
b. viruses undergo «rapid» mutation $
mutation causes a change in viral protein
OR
Note: Accept “rapid reproduction “allows resistant viruses to multiply»”.
Question
Medicines and drugs are tested for effectiveness and safety.
a. Distinguish between therapeutic window and therapeutic index in humans.
Therapeutic window:
Therapeutic index:
$\mathrm{b}(\mathrm{i})$ State one advantage of using morphine as an analgesic.
$\mathrm{b}$ (ii Explain why diamorphine (heroin) is more potent than morphine using section 37 of the data booklet.
▶️Answer/Explanation
Markscheme
a. Therapeutic window:
range of dosage «over which a drug» provides the therapeutic/desired effect without causing adverse/toxic effects [ $\checkmark$ ]
Therapeutic index:
toxic dose of drug for $50 \%$ of population divided by minimum effective dose for $50 \%$ of population
OR
$\frac{\mathrm{TD} 50}{\mathrm{ED} 50}[\boldsymbol{\sim}]$
Note: M1 may be scored from a correctly labelled diagram.
Accept “difference between ED50/minimum effective/therapeutic dose “for 50\% of population” AND TD50/toxic dose “for 50\% of population»” for M1.
Do not accept reference to lethal dose used in therapeutic index in animal studies.
b(i)blocks pain impulses/binds with «opioid» receptors in brain/CNS
OR
effective against strong pain
OR
sedate patients to reduce trauma $[\boldsymbol{U}$
Note: Accept “effective against pain after surgery/cancerffollowing serious injury”.
Accept “relieves anxiety/stress associated with severe/terminal illness”.
b(ii)morphine has «two» hydroxyl groups $A N D$ diamorphine has «two» ester/ethanoate/acetate groups
OR
molecule of diamorphine is less polar than morphine
OR
groups in morphine are replaced with less polar/non-polar groups in diamorphine [ $\checkmark$ ]
«less polar molecules» cross the blood-brain barrier faster/more easily
OR
diamorphine is more soluble in non-polar environment of CNS/central nervous system than morphine [ $\checkmark$ ]
Note: Accept “alcohol/hydroxy” for “hydroxyl” but not “hydroxide”.
Accept “fats” for “lipid”.
Accept “heroin” for “diamorphine”.
Question
The structure of penicillin is shown in section 37 of the data booklet.
a. State the internal bond angles in the $\beta$-lactam ring and the expected bond angles for the same atoms in an open structure.
b. Explain how the open $\beta$-lactam ring kills bacteria.
c. Outline one effect of over-prescription of penicilin.
d. State how the structure of penicillin can be changed to combat this effect.
e. Suggest why human cells are not affected by penicillin.
▶️Answer/Explanation
Markscheme
a.
Accept “109”.
b. «irreversibly» binds/bonds to enzyme/transpeptidase
OR
inhibits enzyme/transpeptidase «in bacteria» that produces cell walls
OR
prevents cross-linking of bacterial cell walls
cells absorb water $\boldsymbol{A N D}$ burst
OR
cells cannot reproduce
Accept “reacts with” for “bonds to” for M1.
Do not accept “cell membrane” for “cell wall” for M1.
Accept “cells burst due to osmotic pressure” for M2.
Accept “bacteria” for “cells” for M2.
c. Any one of:
leads to «bacterial» resistance «to antibiotics»
OR
makes antibiotics less effective
OR
increased side effects due to larger dosages/over time
increases proportion of resistant bacteria
destroys useful/beneficial bacteria
OR
destroyed bacteria replaced by more harmful bacteria
resistant bacteria pass on their mutation to next generation damage to ecosystems
Accept “superbugs such as MRSA develop” but superbug must be identified.
Accept “immune” for resistant but do not accept “tolerance”
d. «modify» side-chain
Accept ” “modify» R”.
e. no cell walls
OR
humans do not have transpeptidase
Question
Opiates are strong analgesics.
a. Explain why diamorphine (heroin) crosses the blood-brain barrier more easily than morphine.
[2]
b. Outline the meaning of the bioavailability of a drug.
[1]
▶️Answer/Explanation
Markscheme
a. blood-brain barrier is hydrophobic/non-polar/made of lipids
morphine has hydroxyl/OH «groups»/is more polar AND diamorphine has ester/ethanoate/ $\mathrm{OCOCH}_3 /$ acetate «groups»/is less polar/is lipid soluble
Accept “fats” for “lipid”.
Accept “alcohol/hydroxy” for “hydroxyl” but not “hydroxide”.
Accept “non-polar” for “less polar” in M2.
b. fraction/proportion/percentage of «administered dosage» enters blood/plasma/circulation
Accept “fraction/proportion/percentage of “administered dosage» that reaches target “part of human body»”.
Question
Medicines and drugs alter the physiological state of the body including consciousness and coordination.
Explain the meaning of the following terms:
State one other effect of medicines and drugs on the body.
therapeutic window.
tolerance.
Outline the major stages in the development of a new drug.
▶️Answer/Explanation
Markscheme
alters incoming sensory sensations / alters mood or emotions;
the range over which a drug can be safely administered / \({\text{T.I}} = \frac{{{\text{LD50}}}}{{{\text{ED50}}}}\) / ratio of the lethal dose for 50%population and the effective dose for 50% of population;
person needs to take ever larger quantities of a drug to gain the original effect;
drug is isolated from existing species / synthesized in the laboratory;
tested on animals to establish LD50;
tested on humans and half/some of the group is given a placebo;
Examiners report
[N/A]
Many candidates had difficulty explaining the term therapeutic window. Frequently they thought it referred to the time the drug was active in the body rather than an issue of dosage.
Many candidates had difficulty explaining the term therapeutic window. Frequently they thought it referred to the time the drug was active in the body rather than an issue of dosage. They fared better with explaining the terms tolerance and the placebo effect.
Candidates had more difficulty providing specific information about the drug development process, especially with respect to animal testing and human testing. Candidates needed to use accurate chemical terms when outlining the major stages in the development of a new drug.
Question
Discuss the term therapeutic window. Your answer should include its meaning, a quantitative description and an explanation of wide and narrow therapeutic windows.
▶️Answer/Explanation
Markscheme
measure of the relative margin of safety of a drug (for a particular treatment for a typical population) / measure for safe effective treatment;
\(\frac{{{\text{lethal dose (L}}{{\text{D}}_{{\text{50}}}}{\text{)}}}}{{{\text{therapeutic or effective dose (E}}{{\text{D}}_{{\text{50}}}}{\text{)}}}}\) /
ratio of the lethal dose \({\text{(L}}{{\text{D}}_{{\text{50}}}}{\text{)}}\) to the therapeutic or effective dose \({\text{(E}}{{\text{D}}_{{\text{50}}}}{\text{)}}\) / the range of dosage of a drug/its concentration in a bodily system/blood;
Definition of LD50 and ED50 not required for mark.
wide therapeutic window exists for small effective dose and larger lethal dose / toxicity occurs at much higher concentrations than for successful treatment / a big difference between effective and lethal dose / drugs with wide therapeutic window are safer;
narrow therapeutic window requires small doses as lethal dose is not large / OWTTE;
Examiners report
Most candidates gave the description of a therapeutic window, but it was clear that many candidates did not really understand what it means and some confused wide and narrow therapeutic window with wide and narrow spectrum antibiotics.
Question
Explain the meaning of the terms:
The effectiveness of a drug depends on the method of administration.
side-effect
therapeutic window
One method of injecting drugs into the body results in the drug having a very rapid effect. State the method and explain its rapid action.
List the two other methods which can be used to inject drugs into the body.
Identify the method of administration used to treat respiratory diseases such as asthma.
▶️Answer/Explanation
Markscheme
an effect produced in addition to the one intended / unwanted/undesired effect;
range of a drugs concentration (in blood) between effective/\({\text{E}}{{\text{D}}_{{\text{50}}}}\) and toxic levels/\({\text{L}}{{\text{D}}_{{\text{50}}}}\) / (Therapeutic Index) = \({\text{L}}{{\text{D}}_{{\text{50}}}}\) / \({\text{E}}{{\text{D}}_{{\text{50}}}}\);
Do not accept “difference of drug concentration”.
intravenous / into veins;
transported/pumped via blood (to various parts of body);
intramuscular/intermuscular/into muscles and subcutaneous/into fat;
Allow [1] if all three methods are stated in (b) (i) and (ii) but not in correct place.
inhalation/breathing it in;
Examiners report
This was generally very well answered, with no serious errors.
Question
Aspirin, paracetamol (acetaminophen), morphine and diamorphine (heroin) are all pain killers. Their structures are given in Table 20 of the Data Booklet.
Aspirin is thought to interfere with the production of prostaglandins. Explain how this produces an analgesic effect.
Explain how morphine can prevent pain.
Paracetamol (acetaminophen) is generally considered to be safe to use as an analgesic in small doses. Other than the possibility of death, outline the problems associated with taking larger doses of paracetamol.
State one important use for aspirin other than the relief of pain and fever.
Explain what is meant by the term tolerance and suggest why this is a particular problem for heroin users.
▶️Answer/Explanation
Markscheme
prostaglandins are involved in the transmission of pain impulses (to the brain) / OWTTE;
morphine (temporarily) bonds to/inhibits receptor sites in the brain (without depressing central nervous system) / OWTTE;
causes blood disorders;
causes damage to kidney;
causes damage to liver;
causes damage to brain;
preventing (recurrence of) heart attacks/strokes / reduces blood clotting / thins the blood / anti-inflammatory;
tolerance: more of the drug needs to be taken to achieve the initial effect / OWTTE;
in order to achieve the desired effect heroin users may reach/exceed the lethal dose / heroin users are more likely to commit crimes to pay for gradually increasing doses of the drug / OWTTE;
Examiners report
This question was generally answered very well compared with other sections of the paper. In part (a) most candidates knew that prostaglandins is involved in the transmission of pain impulses to the brain.
In part (b) there was some confusion between signals and receptors when describing how morphine can prevent pain.
In part (c) most candidates could outline problems associated with larger doses of paracetamol (acetaminophen), although some candidates confused aspirin and paracetamol and incorrectly referred to Reye’s syndrome or stomach bleeding.
Most candidates stated a use for aspirin other than relief of pain or fever in part (d).
In part (f) most candidates successfully stated the meaning of tolerance and suggested why it is a particular problem for heroin users.
Question
Aspirin and paracetamol (acetaminophen) are mild analgesics.
Morphine is a strong analgesic which is administered parenterally.
Explain why it is dangerous to take aspirin when ethanol has also been consumed.
State the meaning of the term parenteral.
Explain how a strong analgesic such as morphine prevents pain.
The structures of morphine and diamorphine (heroin) are shown in Table 20 of the Data Booklet. State the name of a functional group present in diamorphine (heroin) but not in morphine.
▶️Answer/Explanation
Markscheme
increased risk of stomach bleeding;
administered by injection;
(temporarily) bond to receptor sites in the brain/CNS;
prevent the transmission of pain impulses;
ester;
Examiners report
Most candidates were very familiar with analgesics and the synergistic effect of ethanol and aspirin.
Many of the weaker candidates thought that parenteral administration of morphine required supervision by parents or authorities. Assessment statement D.1.3 outlines the meaning of this technique.
Many candidates gave good descriptions of how morphine prevents pain.
[N/A]
Question
During drug development, trials are conducted to determine the therapeutic window.
Explain the meaning of the term therapeutic window and discuss its importance in drug administration.
▶️Answer/Explanation
Markscheme
if concentration is too high it will have harmful side effects / determination of the lethal dose (to 50% of the population) / OWTTE;
if concentration is too low it has little or no beneficial effect / determination of the effective dose / dose which has a noticeable effect (on 50% of the population) / OWTTE;
therapeutic window is the range between these doses / range over which a drug can be safely administered / ratio of \({\text{L}}{{\text{D}}_{50}}\): \({\text{E}}{{\text{D}}_{50}}\);
for minor ailments a larger window is desirable, for serious conditions a smaller window may be acceptable / OWTTE;
(therapeutic window) depends on the drug/age/sex/weight;
a small therapeutic window means that an overdose is a high risk / OWTTE;
Examiners report
Many candidates clearly had an understanding of therapeutic window and placebos but failed to score full marks as insufficient details were given.
Question
Medicines and drugs are natural or synthetic substances used for their effects on the body.
List two general effects of medicines and drugs on the functioning of the body.
▶️Answer/Explanation
Markscheme
Any two for [1]
alter physiological state/consciousness/activity level/coordination
alter incoming sensory sensations
alter mood/emotions
Examiners report
The general effects of medicines and drugs on the functioning of the human body were generally very well answered.
Question
Drugs are most commonly taken orally.
Drugs are most commonly taken orally.
(a) State one advantage and one disadvantage of this.
Advantage:
Disadvantage:
List three methods, other than orally, that can be used for the administration of a drug.
▶️Answer/Explanation
Markscheme
Advantage:
easily taken/convenient / no specialist equipment needed;
Disadvantage:
stomach acid reacts with drugs / slow effect / only small fraction of drug absorbed / vomiting / requires conscious patient / harm digestive system/can cause stomach bleeding;
inhalation
parenteral / by injection / intravenous / intramuscular / subcutaneous
rectal
skin patches
eye/ear/nose drops
topical
Award [2] for all 3 correct, [1] for 2 correct, [0] for 1 correct.
Question
Creating a new pharmaceutical product is a long and complex process. Outline the main stages of this process in the correct order.
There are various ways to administer drugs to a patient. One of the common methods, parenteral, is also known as injection. State and describe two other methods of administering drugs.
The efficiency of certain drugs is strongly dependent on the frequency and regularity of their administration. Explain the importance of patient compliance when the patient is treated with antibacterials.
▶️Answer/Explanation
Markscheme
drug design/discovery/screening/identifying lead compound;
preparation of analogues through combinatorial chemistry;
characterization of the new compound / in vitro testing / drug formulation/delivery/stability studies;
pre-clinical (toxicology and pharmacokinetics) tests / tests on animals/bacteria/cell cultures / LD50 / OWTTE;
clinical tests/tests on humans;
ED50 to show improvements over existing drugs / OWTTE;
Penalize for incorrect order once only.
oral – by mouth / swallowing pills/powders / drinking liquids/mixtures / OWTTE;
inhalation – administering drugs into respiratory tract / inhaling gases/vapours/sprays/powders;
rectal – introducing drugs into the rectum/colon via the anus / using suppositories/enemas;
transdermal – diffusion through the skin/skin patches/ointments/therapeutic baths;
Accept other methods/variations with appropriate descriptions.
Award [1 max] if only two correct names or two correct descriptions are given.
irregular/interrupted treatment allows more bacteria to survive (and mutate) / failure to complete full course / OWTTE;
surviving bacteria develop/pass on resistance (to the drug);
Do not accept superbugs.
Examiners report
Part (a) was generally well answered although a lot of candidates seem to think that ED50 is established on animals and a few, even more worryingly, linked LD50 with human trials!
In part (b), descriptions were often missing but in (c) most understood the importance of frequency and regularity of drug administration.
In part (b), descriptions were often missing but in (c) most understood the importance of frequency and regularity of drug administration.
Question
The therapeutic window is used as a measure of the safety of a drug. Define the term therapeutic window.
▶️Answer/Explanation
Markscheme
range of dosages/concentrations of drug able to treat disease successfully staying within safety limit/between therapeutic and toxic levels / OWTTE;
Accept LD50 over ED50.
Examiners report
This was answered well although few recognized the amide group in (a) (ii) and the therapeutic window was a little shaky. Many defined the therapeutic index which is not quite the same thing.
Question
Drug research and development is a lengthy and expensive process. Testing is required to determine the therapeutic window, tolerance and side-effects of a drug before it can be approved for use.
State the meaning of the term therapeutic window.
Suggest why a narrow therapeutic window may be a problem.
State the meaning of the term side-effects.
▶️Answer/Explanation
Markscheme
range of dosages/concentrations of drug (able to treat disease successfully) staying within safety limit / between effective/ED50 and toxic levels/LD50;
Do not accept definition of therapeutic index (ratio of LD50/TD50 to ED50).
Accept “lethal levels” for “toxic levels” even if laboratory animals are not referred to.
toxic levels are easily reached / effective dose not given for fear of reaching toxic level / close medical supervision required;
Accept “lethal levels” for “toxic levels”.
adverse effects of drug / physiological/psychological effect other than that for which the drug was prescribed / secondary (undesired) effects of drug / OWTTE;
Examiners report
Many candidates confused the definition of “therapeutic window” with “therapeutic index”. The nature of a narrow therapeutic window was also not well understood although the nature of side-effects was well articulated. The role of dimethicone as an anti-foaming agent was well understood overall. It was correctly identified as an anti-foaming agent where small bubbles are converted into larger ones and then released. This decreases “bloating” and increases rather than decreases “flatulence” which was seen quite often as a response in the use of dimethicone.
Question
Medicines have a variety of different effects on the body and act at the molecular level.
Morphine and codeine are strong analgesics. Their structures are given in section 37 of the data booklet.
Dose response curves are determined for each drug.
Outline the significance of range “a”.
Suggest the type of reaction used to convert morphine to codeine.
State and explain the action of opiates as painkillers.
▶️Answer/Explanation
Markscheme
«measures» therapeutic window/margin «of a drug»
OR
range of doses that produce a therapeutic effect without causing toxic effects
Accept “difference between ED50/minimum effective/therapeutic dose «for 50% of population» AND TD50 /toxic dose «for 50% of population»”.
Do not accept “therapeutic index”.
Do not accept “lethal/fatal dose” as this is not LD50.
[1 mark]
«nucleophilic» substitution/SN
Accept “methylation”.
[1 mark]
work directly on opioid/pain receptors «in brain»
suppress pain impulses in brain/CNS
resemble endorphins/enkephalins/natural chemical painkillers «produced in the brain and spinal cord»
Do not award mark for “resemble hormones”.
[2 marks]
Question
Aspirin is one of the most widely used drugs in the world.
Aspirin was synthesized from 2.65 g of salicylic acid (2-hydroxybenzoic acid) (Mr = 138.13) and 2.51 g of ethanoic anhydride (Mr = 102.10).
Calculate the amounts, in mol, of each reactant.
Calculate, in g, the theoretical yield of aspirin.
State two techniques which could be used to confirm the identity of aspirin.
State how aspirin can be converted to water-soluble aspirin.
Compare, giving a reason, the bioavailability of soluble aspirin with aspirin.
▶️Answer/Explanation
Markscheme
n(salicylic acid) = «\(\frac{{2.65{\text{ g}}}}{{138.13{\text{ g}}\,{\text{mo}}{{\text{l}}^{ – 1}}}}\)» 0.0192 «mol»
AND
n(ethanoic anhydride) = «\(\frac{{2.51{\text{ g}}}}{{102.10{\text{ g}}\,{\text{mo}}{{\text{l}}^{ – 1}}}}\)» 0.0246 «mol»
[1 mark]
«mass = 0.0192 mol x 180.17 g\(\,\)mol–1 =» 3.46 «g»
Award ECF mark only if limiting reagent determined in (i) has been used.
[1 mark]
Any two of:
melting point
mass spectrometry/MS
high-performance liquid chromatography/HPLC
NMR/nuclear magnetic resonance
X-ray crystallography
elemental analysis «for elemental percent composition»
Accept “spectroscopy” instead of “spectrometry” where mentioned but not “spectrum”.
Accept “infra-red spectroscopy/IR” OR “ultraviolet «-visible» spectroscopy/UV/UV-Vis”.
Do not accept “gas chromatography/GC”.
Accept “thin-layer chromatography/TLC” as an alternative to “HPLC”.
[2 marks]
react with NaOH
Accept “NaHCO3” or “Na2CO3” instead of “NaOH”.
Accept chemical equation OR name for reagent used.
[1 mark]
«marginally» higher AND increase rate of dispersion
OR
«marginally» higher AND increase absorption in mouth/stomach «mucosa»
OR
«approximately the» same AND ionic salt reacts with HCl/acid in stomach to produce aspirin again
Do not accept “«marginally» higher AND greater solubility in blood”.
[1 mark]
Question
The structures of oseltamivir (Tamiflu) and zanamivir (Relenza) are given in section 37 of the data booklet.
Compare and contrast the structures of oseltamivir and zanamivir, stating the names of functional groups.
Deduce the wavenumber of one absorbance seen in the IR spectrum of only one of the compounds, using section 26 of the data booklet.
Suggest one ethical consideration faced by medical researchers when developing medications.
▶️Answer/Explanation
Markscheme
One similarity:
both contain amido «group»
One difference:
oseltamivir contains ester «group» AND zanamivir does not
OR
oseltamivir contains amino «group» AND zanamivir does not «but contains a guanidino group»
OR
zanamivir contains carboxyl «group» AND oseltamivir does not
OR
zanamivir contains «several» hydroxyl «groups» AND oseltamivir does not
OR
oseltamivir contains ester «group» AND zanamivir contains carboxyl «group»
OR
oseltamivir contains ester «group» AND zanamivir contains «several» hydroxyl «groups»
Accept “both contain ether «group»” OR “both contain alkene/alkenyl «group»” OR “both contain carbonyl «group»” OR “both contain amino/amine «group»”. Latter cannot be given in combination with second difference alternative with respect to amino group.
Accept “amide/carboxamide/carbamoyl” for “amido”.
Accept “amine” for “amino”.
Accept “carboxylic acid” for “carboxyl”.
Accept “hydroxy/alcohol” for “hydroxyl”, but not “hydroxide”.
[2 marks]
1050–1410
OR
1620–1680
OR
1700–1750
OR
2500–3000
OR
3200–3600
OR
2850–3090
OR
3300–3500 «cm–1»
[1 mark]
«negative» side-effects of medication on patient/volunteers
OR
effects on environment «from all materials used and produced»
OR
potential for abuse
OR
drugs may be developed that are contrary to some religious doctrines
OR
animal testing
OR
risk to benefit ratio
OR
appropriate consent of patient volunteers
[1 mark]
Question
New drugs undergo thorough clinical trials before they are approved.
Outline the difference between the therapeutic index in animal studies and the therapeutic index in humans.
State the method of drug administration that gives the maximum bioavailability.
▶️Answer/Explanation
Markscheme
in animal studies \(\frac{{{\text{LD50}}}}{{{\text{ED50}}}}\) AND in humans \(\frac{{{\text{TD50}}}}{{{\text{ED50}}}}\)
OR
in animal studies lethal dose/LD50 AND in humans toxic dose/TD50
intravenous/IV «injection»
OR
injection into the bloodstream
Question
Many drugs, including aspirin, penicillin, codeine and taxol, have been modified from compounds that occur naturally.
Aspirin is often taken to reduce pain, swelling or fever. State one other use of aspirin.
State what is meant by the bioavailability of a drug.
Outline how the bioavailability of aspirin may be increased.
Compare and contrast the IR spectrum of aspirin with that of salicylic acid, using section 26 of the data booklet.
Describe how penicillin combats bacterial infections.
Outline two consequences of prescribing antibiotics such as penicillin unnecessarily.
State how penicillins may be modified to increase their effectiveness.
Morphine and codeine are strong analgesics. Outline how strong analgesics function.
Suggest one reason why codeine is more widely used than morphine as an analgesic.
▶️Answer/Explanation
Markscheme
Any one of:
anticoagulant
lower risk of heart attack/strokes
prevent recurrence of heart attack/stroke
prevents cancer of colon/oesophagus/stomach
Accept “prevents/reduces blood clots” OR “blood thinner”.
[1 mark]
fraction/proportion/percentage «of administered dosage» that reaches target «part of human body»
OR
fraction/ proportion/percentage «of administered dosage» that reaches blood «plasma»/systemic circulation
Accept “the ability of the drug to be absorbed by the body” OR “the extent to which the drug is absorbed by the body”.
Do not accept “the amount/quantity of the drug absorbed”.
[1 mark]
«intravenous» injection/IV
Accept “parenterally”.
Accept “react with alkali/NaOH” OR “convert to ionic form/salt”.
[1 mark]
One absorption found in both spectra:
Any one of:
1050–1410 cm–1 «C–O in alcohols, esters, ethers»
1700–1750 cm–1 «C=O in carboxylic acids, esters»
2500–3000 cm–1 «O–H in carboxylic acids»
2850–3090 cm–1 «C–H in alkanes, alkenes, arenes»
One absorption found in only one of the spectra:
3200–3600 cm–1 «O–H in alcohols, phenols»
Award [1 max] if candidate states bonds (C=O in both, O–H in salicylic acid only) but doesn’t quote wavelength ranges.
Accept a second/additional absorption at 1700–1750 cm–1 from the C=O in ester.
[2 marks]
Any two of:
ring is «sterically» strained
OR
ring breaks up/opens/reacts «easily»
OR
amide/amido group «in ring» is «highly» reactive
«irreversibly» binds/bonds to enzyme/transpeptidase
OR
inhibits enzyme/transpeptidase «in bacteria» that produces cell walls
OR
prevents cross-linking of bacterial cell walls
cells absorb water AND burst
OR
cells cannot reproduce
Award [1 max] for “interferes with cell wall production”.
Do not accept “cell membrane” instead of “cell wall”.
[2 marks]
Any two of:
leads to «bacterial» resistance/proportion of resistant bacteria increases
OR
leads to penicillinase-producing bacteria
damage to/contamination of bodies of water/ecosystems
destroys useful/beneficial bacteria
destroyed bacteria replaced by more harmful bacteria
Accept “endocrine disruptor”.
Do not accept “increased cost of developing antibiotics”.
[2 marks]
modify side chain
[1 mark]
temporarily bind to/block/interfere with receptor sites in brain
OR
prevent transmission of pain impulses within CNS/central nervous system
[1 mark]
codeine has a wider therapeutic window
Accept “codeine has lower activity” OR “codeine has lower risk of overdose” OR “codeine is less potent” OR “codeine has less side-effects”.
Do not accept “lower abuse potential for codeine” OR “less addictive «than morphine»” OR “codeine has a lower bioavailability” OR “available without prescription” OR “cheaper”.
[1 mark]
Question
Drug testing is necessary to determine safe and effective doses.
Distinguish between the lethal dose (LD50) and the toxic dose (TD50).
▶️Answer/Explanation
Markscheme
LD50: amount/dose that kills 50% of the population
TD50: amount/dose that negatively affects/produces toxic effects in 50% of the population
Award [1 max] for “LD50 used in animal trials AND TD50 used in human studies”.
[2 marks]