Medical Pharmacology: Chapter 38 — Antiparasitic Drugs -- Module 4 — Ectoparasiticides and Special Populations

Chapter 38 — Antiparasitic Drugs — Module 4 — Ectoparasiticides and Special Populations

1. Pyrethroids are divided into Type I compounds (lacking an alpha-cyano group, such as permethrin) and Type II compounds (possessing an alpha-cyano substituent, such as deltamethrin and cypermethrin). In a high-dose poisoning, which clinical picture is characteristic of Type II pyrethroid toxicity, distinguishing it from Type I?

A) Pure muscarinic crisis with bradycardia, miosis, and copious bronchial secretions
B) Flaccid paralysis with absent reflexes and no involuntary movements
C) Choreoathetosis and hypersalivation, in contrast to the fine tremors and hyperexcitability typical of Type I compounds
D) Isolated hepatic failure without any neurological signs
E) An anticholinergic syndrome with dry skin, mydriasis, and urinary retention

ANSWER: C

Rationale:

Both pyrethroid subclasses prolong sodium-channel opening, but their high-dose neurotoxic syndromes differ. Type II compounds (alpha-cyano group: deltamethrin, cypermethrin, lambda-cyhalothrin) cause persistent membrane depolarization, producing choreoathetosis (writhing involuntary movements) and hypersalivation. Type I compounds (no alpha-cyano group: permethrin) cause repetitive firing that manifests as fine tremors, incoordination, and hypersensitivity to stimuli. Recognizing the alpha-cyano structural distinction predicts the toxidrome.

Option A: Option A is incorrect: a pure muscarinic crisis describes organophosphate (for example, malathion) cholinergic toxicity, not pyrethroid poisoning, which does not act through acetylcholinesterase.
Option B: Option B is incorrect: pyrethroid toxicity produces hyperexcitation (tremor or choreoathetosis), not flaccid paralysis with absent involuntary movements.
Option D: Option D is incorrect: pyrethroid toxicity is principally neurological; isolated hepatic failure without neurological signs is not the Type II picture.
Option E: Option E is incorrect: pyrethroids do not produce an anticholinergic (antimuscarinic) syndrome; dry skin, mydriasis, and urinary retention are not features of pyrethroid toxicity.

2. Over-the-counter head lice shampoos combine natural pyrethrins with piperonyl butoxide. What is the role of piperonyl butoxide, and does it restore efficacy against kdr-resistant lice?

A) It inhibits the louse esterase enzymes that would otherwise degrade pyrethrins, thereby potentiating pyrethrin activity, but it does not overcome target-site (kdr) resistance
B) It is itself a potent pyrethroid that kills lice by an independent sodium-channel action
C) It mutates the louse sodium channel back to a drug-sensitive state, reversing kdr resistance
D) It blocks acetylcholinesterase, adding an organophosphate-like mechanism to the product
E) It is an inert dye added only to color the shampoo, with no pharmacological role

ANSWER: A

Rationale:

Piperonyl butoxide is a synergist, not an insecticide in its own right. It inhibits the esterase (and related oxidative) enzymes that lice use to metabolize and inactivate pyrethrins, so more active pyrethrin reaches the target and activity is potentiated. However, because kdr is a target-site (sodium-channel) mutation rather than a metabolic one, inhibiting metabolic breakdown does nothing to restore binding; pyrethrin-piperonyl butoxide products remain less effective than permethrin against kdr-resistant lice.

Option B: Option B is incorrect: piperonyl butoxide is a metabolic synergist with no independent sodium-channel insecticidal action of its own.
Option C: Option C is incorrect: piperonyl butoxide does not alter the louse genome or reverse the kdr mutation; the resistant channel remains resistant.
Option D: Option D is incorrect: piperonyl butoxide does not inhibit acetylcholinesterase; that is the malathion (organophosphate) mechanism.
Option E: Option E is incorrect: piperonyl butoxide is pharmacologically active as a synergist, not an inert coloring agent.

3. Pyrethroids act on sodium channels that exist in both insects and mammals, yet they are far more toxic to the parasite than to the human host. What best explains this selective toxicity?

A) Mammals entirely lack the voltage-gated sodium channel that pyrethroids bind
B) Pyrethroids cannot be absorbed across mammalian cell membranes at all
C) Mammalian sodium channels are structurally identical to insect channels, so selectivity comes only from dose
D) Pyrethroids are converted in mammals into a more toxic metabolite, paradoxically sparing insects
E) Pyrethroid-bound channels recover much faster at the higher body temperature of mammals, and mammals rapidly metabolize pyrethroids via esterases and cytochrome P450 enzymes, both of which limit systemic toxicity

ANSWER: E

Rationale:

Selectivity is pharmacokinetic and biophysical rather than absolute. Pyrethroid-bound sodium channels recover from the prolonged-open state much more slowly at the cooler temperatures of invertebrates, whereas the higher core temperature of mammals accelerates channel recovery and blunts the effect. In addition, mammals rapidly inactivate pyrethroids through esterase and cytochrome P450 (CYP450) metabolism, so systemic levels stay low at therapeutic topical doses. Together these give the wide mammalian safety margin.

Option A: Option A is incorrect: mammals do possess voltage-gated sodium channels that pyrethroids can bind; selectivity is not due to the target being absent.
Option B: Option B is incorrect: pyrethroids can cross mammalian membranes (dermal absorption is low but not zero); the protection is metabolism and temperature, not an inability to be absorbed.
Option C: Option C is incorrect: insect and mammalian channels are not identical, and selectivity is not explained by dose alone.
Option D: Option D is incorrect: mammalian metabolism inactivates pyrethroids rather than converting them to a more toxic species; there is no insect-sparing toxic metabolite.

4. Knockdown resistance (kdr) in lice arises from point mutations such as T929I and L932F in the voltage-gated sodium channel. Some louse populations show an even higher level of pyrethroid resistance. What underlies this enhanced "super-kdr" phenotype?

A) Loss of the sodium channel gene entirely, so pyrethroids have no target
B) An additional mutation, typically at position 918, layered onto the existing kdr mutations, conferring a higher level of resistance than kdr alone
C) Increased esterase metabolism of the pyrethroid, with no change in the channel
D) A switch from sodium channels to potassium channels in the louse axon
E) Acquisition of a drug-efflux pump that exports the pyrethroid from neurons

ANSWER: B

Rationale:

Super-kdr describes a higher-grade target-site resistance produced when an additional sodium-channel mutation, characteristically at position 918, is present together with the standard kdr mutations (such as T929I/L932F). The extra change further reduces pyrethroid binding affinity, raising the resistance level beyond that conferred by kdr mutations alone. It remains a target-site mechanism, so it confers cross-resistance across the pyrethroid class.

Option A: Option A is incorrect: the channel gene is not deleted; super-kdr is a point-mutation enhancement of an existing channel, which still functions electrophysiologically.
Option C: Option C is incorrect: increased esterase metabolism is a separate (metabolic) resistance route; super-kdr is defined by an additional channel mutation, not by metabolism.
Option D: Option D is incorrect: lice do not replace sodium channels with potassium channels; the axonal sodium channel remains the target, just mutated.
Option E: Option E is incorrect: a drug-efflux pump is a different resistance strategy; super-kdr specifically denotes the position-918 channel mutation added to kdr.

5. Permethrin has a wide safety margin in humans, but there is one mammalian species in which it causes severe, often fatal neurotoxicity, such that veterinary products for one species must never be applied to it. Which species, and why?

A) Dogs, because dogs lack any cytochrome P450 enzymes
B) Horses, because of an unusually permeable skin barrier
C) Rabbits, because they hyperabsorb permethrin through the gut
D) Cats, because they metabolize permethrin very slowly (deficient glucuronidation), allowing toxic accumulation and severe neurotoxicity
E) Cattle, because rumen bacteria convert permethrin into a neurotoxin

ANSWER: D

Rationale:

Cats are uniquely vulnerable to permethrin toxicity because their hepatic metabolism of the compound is markedly slow (cats have limited glucuronidation capacity), so permethrin accumulates to neurotoxic levels rather than being cleared rapidly as in other mammals. Applying concentrated canine permethrin products to cats causes severe, sometimes fatal neurotoxicity (tremors, seizures), so permethrin should never be used in this species. This is the same rapid-metabolism principle that protects humans, failing in the cat.

Option A: Option A is incorrect: dogs tolerate permethrin well and do possess cytochrome P450 enzymes; they are not the sensitive species.
Option B: Option B is incorrect: the feline problem is slow metabolism, not skin permeability, and horses are not the classically sensitive species.
Option C: Option C is incorrect: the characteristic toxicity is in cats due to slow hepatic metabolism, not gut hyperabsorption in rabbits.
Option E: Option E is incorrect: the toxicity is not due to ruminal conversion in cattle; it is the cat's slow hepatic metabolism that is responsible.

6. Benzyl benzoate 25% lotion kills the scabies mite by acting on a receptor that has no counterpart in mammals, which contributes to its selectivity. Which receptor system does it disrupt?

A) Octopamine receptor signaling, an invertebrate-specific neurotransmitter system absent in mammals, causing mite hyperexcitation and death
B) The mammalian beta-2 adrenergic receptor, shared between host and parasite
C) The voltage-gated sodium channel, identical to the permethrin target
D) Acetylcholinesterase, identical to the malathion target
E) The host histamine H1 receptor, blocking the itch reflex

ANSWER: A

Rationale:

Benzyl benzoate acts by disrupting octopamine receptor signaling in the mite. Octopamine is an invertebrate neurotransmitter (functionally analogous to noradrenaline) with no receptor counterpart in mammals, so interfering with it selectively poisons the parasite while sparing the human host. The result is hyperexcitation and death of the mite.

Option B: Option B is incorrect: benzyl benzoate does not act on mammalian beta-2 adrenergic receptors; its target is the invertebrate octopamine system.
Option C: Option C is incorrect: the sodium channel is the pyrethroid (permethrin) target, not the benzyl benzoate target.
Option D: Option D is incorrect: acetylcholinesterase is the malathion target; benzyl benzoate does not inhibit that enzyme.
Option E: Option E is incorrect: benzyl benzoate is scabicidal through the mite octopamine system, not by blocking the host H1 histamine receptor.

7. A key reason crusted scabies drives institutional outbreaks is the parasite's environmental persistence. Compared with common scabies, how long does the mite survive off the host in crusted scabies, and what is the practical implication?

A) About 1 hour off the host, so environmental decontamination is unnecessary
B) The same 24 to 36 hours as common scabies, so no special environmental measures are needed
C) Up to about 72 hours off the host, compared with roughly 24 to 36 hours in common scabies, so more aggressive environmental decontamination of bedding, clothing, and furniture is required
D) Up to several weeks off the host, making the environment permanently uninhabitable
E) The mite cannot survive off the host at all, so only the patient must be treated

ANSWER: C

Rationale:

In crusted scabies the mite can survive off the host for up to about 72 hours, compared with roughly 24 to 36 hours in common scabies. Combined with the enormous mite burden in crusted disease, this longer environmental survival means bedding, clothing, and furniture can remain infested and reseed the patient or spread to others, so aggressive environmental decontamination and contact precautions are required alongside drug treatment.

Option A: Option A is incorrect: the mite survives far longer than an hour, and environmental decontamination is in fact essential in crusted scabies.
Option B: Option B is incorrect: survival in crusted scabies (up to 72 hours) exceeds that of common scabies, and special environmental measures are needed.
Option D: Option D is incorrect: survival is on the order of days (up to about 72 hours), not weeks, and the environment is not rendered permanently uninhabitable.
Option E: Option E is incorrect: the mite does survive off the host, so treating the patient alone without environmental measures is inadequate.

8. Permethrin 1% rinse for head lice requires a mandatory second application about a week after the first, whereas spinosad 0.9% suspension is usually effective after a single application. What property of spinosad accounts for this difference?

A) Spinosad is applied for 8 to 12 hours rather than 10 minutes, killing everything in one prolonged exposure
B) Spinosad is ovicidal (it kills the eggs as well as the live lice), so newly hatched lice are not left behind to require a second treatment, unlike permethrin which is not reliably ovicidal
C) Spinosad permanently sterilizes the scalp so lice can never return
D) Spinosad remains active in the hair for several months, unlike any other agent
E) Spinosad is taken orally, so a topical second dose is irrelevant

ANSWER: B

Rationale:

Permethrin reliably kills live lice but is not dependably ovicidal, so a second application about a week later is required to kill lice that hatch from surviving eggs. Spinosad has both pediculicidal and ovicidal activity, killing eggs as well as adults, so it generally clears the infestation in a single application without a mandatory repeat. This egg-killing property is the operative difference.

Option A: Option A is incorrect: spinosad is applied for about 10 minutes, not 8 to 12 hours; the single-application advantage comes from ovicidal activity, not a longer contact time.
Option C: Option C is incorrect: spinosad does not permanently sterilize the scalp; reinfestation remains possible from new exposure.
Option D: Option D is incorrect: prolonged residual activity over months describes malathion's hair-binding effect, not the basis for spinosad's single-dose efficacy, which is its ovicidal action.
Option E: Option E is incorrect: spinosad 0.9% is a topical suspension, not an oral drug; its single-application efficacy is due to killing eggs.

9. A clinician counseling a patient about malathion 0.5% lotion for head lice should include two practical points specific to this agent. Which pairing is correct?

A) It must be kept refrigerated, and it stains the hair permanently green
B) It requires intravenous loading, and it turns urine orange
C) It must be combined with oral antibiotics, and it causes photosensitivity rash
D) It should be rinsed off within 5 minutes, and it requires three applications per day
E) It is flammable while on the hair, so the patient must avoid open flames, cigarettes, and hair dryers during application and drying, and it has a residual effect on the hair of about 6 weeks so routine early reapplication is not needed

ANSWER: E

Rationale:

Two malathion-specific counseling points matter. First, the lotion is flammable while on the hair, so patients must avoid open flames, lit cigarettes, and hair dryers during application and the drying period to prevent burns. Second, malathion binds to the hair shaft and exerts a residual effect for approximately 6 weeks, so reapplication within that window is generally not required for recurrence. Both points reflect properties unique to this organophosphate lotion.

Option A: Option A is incorrect: malathion does not require refrigeration and does not permanently dye the hair green.
Option B: Option B is incorrect: malathion is a topical lotion, not an intravenous drug, and it does not characteristically turn urine orange.
Option C: Option C is incorrect: malathion is not routinely combined with oral antibiotics, and photosensitivity rash is not its hallmark counseling issue.
Option D: Option D is incorrect: malathion is left on dry hair for 8 to 12 hours, not rinsed within 5 minutes, and it is not dosed three times daily.

10. Ivermectin is normally safe in the human central nervous system because it is kept out of the brain. Under what circumstances does ivermectin cause central nervous system toxicity at standard doses?

A) Whenever it is taken with food, which forces it into the brain
B) Only in patients with normal blood-brain barrier function and no other medications
C) Routinely in all adults, which is why it is rarely used
D) When the blood-brain barrier is compromised or the P-glycoprotein efflux pump that normally exports ivermectin from the brain is inhibited (for example by ritonavir or verapamil) or genetically deficient
E) Only when given intravenously, which is the standard route

ANSWER: D

Rationale:

Ivermectin is normally excluded from the central nervous system (CNS) by P-glycoprotein (P-gp), an efflux transporter at the blood-brain barrier (BBB) that pumps the drug back out of the brain. CNS toxicity at standard doses therefore occurs when this protection fails: a compromised BBB, pharmacologic inhibition of P-gp by drugs such as ritonavir or verapamil, or rare loss-of-function variants of the transporter (MDR1). Recognizing P-gp inhibitor co-administration is the key safety consideration.

Option A: Option A is incorrect: taking ivermectin with food increases its absorption but does not drive it across an intact, P-gp-protected blood-brain barrier into the brain.
Option B: Option B is incorrect: with a normal blood-brain barrier and no interacting drugs, ivermectin is kept out of the CNS, so toxicity is not expected under those conditions.
Option C: Option C is incorrect: ivermectin does not routinely cause CNS toxicity in all adults; it is widely and safely used.
Option E: Option E is incorrect: ivermectin for these indications is given orally, not intravenously, and CNS toxicity is tied to barrier/efflux failure, not to an intravenous route.

11. A patient is started on a prolonged course of albendazole for neurocysticercosis. Which adverse effect and monitoring plan is most appropriate for extended albendazole therapy?

A) Transaminase (liver enzyme) elevation occurs in roughly 10 to 17 percent of patients, so liver function tests and a complete blood count are monitored about every 2 weeks during each treatment cycle
B) Irreversible deafness in most patients, monitored with weekly audiograms
C) Acute renal failure in the majority, monitored with daily creatinine for the first month
D) Severe hyperkalemia, monitored with continuous cardiac telemetry
E) No adverse effects of any kind, so no laboratory monitoring is required

ANSWER: A

Rationale:

Prolonged albendazole (as used for neurocysticercosis, echinococcosis, or visceral larva migrans) causes transaminase elevation in approximately 10 to 17 percent of patients; most elevations are mild to moderate and reverse with dose reduction or discontinuation. A minority also develop bone marrow suppression (leukopenia, thrombocytopenia). Accordingly, liver function tests (LFTs) and a complete blood count (CBC) are checked about every 2 weeks during each extended treatment cycle.

Option B: Option B is incorrect: irreversible deafness is not the characteristic albendazole toxicity; hepatotoxicity and marrow suppression are, and audiograms are not the monitoring tool.
Option C: Option C is incorrect: albendazole is not characteristically nephrotoxic in most patients; the monitored toxicities are hepatic and hematologic.
Option D: Option D is incorrect: severe hyperkalemia is not an albendazole effect; the relevant monitoring is LFTs and CBC, not telemetry for potassium.
Option E: Option E is incorrect: prolonged albendazole does have monitorable toxicities, so laboratory surveillance is required rather than omitted.

12. Benznidazole is used to treat Chagas disease (American trypanosomiasis) over a roughly 60-day course. Which monitoring schedule and toxicity profile fits this drug?

A) A single baseline test only, because benznidazole has no cumulative toxicity over the course
B) Daily thyroid function tests, because its dose-limiting toxicity is hypothyroidism
C) Complete blood count and liver function tests at about weeks 2, 4, and 8, because its dose-limiting toxicities include leukopenia and hepatotoxicity
D) Weekly bone density scans, because it causes rapid osteoporosis
E) Continuous glucose monitoring, because it commonly precipitates diabetic ketoacidosis

ANSWER: C

Rationale:

Benznidazole's dose-limiting toxicities over its prolonged (about 60-day) course include leukopenia (bone marrow suppression) and hepatotoxicity, along with dermatologic and peripheral nerve effects. Monitoring a complete blood count (CBC) and liver function tests (LFTs) at approximately weeks 2, 4, and 8 of treatment allows early detection of marrow suppression and hepatic injury so therapy can be adjusted or stopped.

Option A: Option A is incorrect: benznidazole does have cumulative toxicities over its long course, so a single baseline test is inadequate.
Option B: Option B is incorrect: the dose-limiting toxicity is marrow suppression and hepatotoxicity, not hypothyroidism, so thyroid testing is not the monitoring focus.
Option D: Option D is incorrect: benznidazole does not characteristically cause osteoporosis, and bone density scanning is not the relevant surveillance.
Option E: Option E is incorrect: benznidazole is not a recognized cause of diabetic ketoacidosis, so continuous glucose monitoring is not the indicated plan.

13. A patient stable on warfarin is prescribed metronidazole for a protozoal infection. What interaction should the clinician anticipate, and what is the mechanism?

A) Metronidazole reduces warfarin's effect, so the warfarin dose must be increased and the INR will fall
B) Metronidazole enhances warfarin's anticoagulant effect by inhibiting the liver enzyme (CYP2C9) that metabolizes the more active warfarin enantiomer, raising bleeding risk, so the INR must be monitored closely
C) There is no interaction, because warfarin and metronidazole use entirely separate pathways
D) Metronidazole physically binds warfarin in the gut, so simply separating the doses by 2 hours eliminates any concern
E) Metronidazole replaces warfarin at the vitamin K epoxide reductase enzyme, acting as a direct anticoagulant itself

ANSWER: B

Rationale:

Metronidazole inhibits cytochrome P450 2C9 (CYP2C9), the enzyme that metabolizes S-warfarin (the more potent enantiomer). Slowed metabolism raises warfarin levels and potentiates its anticoagulant effect, increasing the international normalized ratio (INR) and the risk of bleeding. The appropriate response is close INR monitoring (and dose adjustment as needed) when the two are combined.

Option A: Option A is incorrect: metronidazole increases rather than decreases warfarin's effect, so the INR rises and the dose typically needs reduction, not increase.
Option C: Option C is incorrect: there is a clinically important interaction; warfarin metabolism depends on CYP2C9, which metronidazole inhibits.
Option D: Option D is incorrect: the interaction is metabolic enzyme inhibition, not gut binding, so spacing the doses does not prevent it.
Option E: Option E is incorrect: metronidazole does not act at vitamin K epoxide reductase and is not itself an anticoagulant; it potentiates warfarin by inhibiting warfarin metabolism.

14. The older antimalarial halofantrine is now rarely used, in part because of a dangerous interaction with another antimalarial. Which combination is specifically hazardous, and why?

A) Halofantrine after albendazole, because of additive hepatotoxicity
B) Halofantrine after permethrin, because of additive sodium-channel toxicity
C) Halofantrine after metronidazole, because of additive bleeding risk
D) Halofantrine after pyrimethamine, because of additive bone marrow suppression
E) Halofantrine after mefloquine, because both prolong the QTc interval and the combination can cause fatal QTc prolongation and torsades de pointes

ANSWER: E

Rationale:

Halofantrine markedly prolongs the QTc interval, and mefloquine also affects cardiac conduction. Giving halofantrine after mefloquine produces additive QTc prolongation that can precipitate torsades de pointes and sudden death. This dangerous cardiac interaction is a major reason halofantrine has fallen out of use; it should not follow mefloquine.

Option A: Option A is incorrect: the defining halofantrine hazard is cardiac QTc prolongation with mefloquine, not additive hepatotoxicity with albendazole.
Option B: Option B is incorrect: halofantrine toxicity is QTc prolongation, not a sodium-channel interaction with permethrin.
Option C: Option C is incorrect: the dangerous interaction is cardiac with mefloquine; additive bleeding with metronidazole is not the halofantrine concern.
Option D: Option D is incorrect: halofantrine's signature danger is QTc prolongation with mefloquine, not marrow suppression with pyrimethamine.

15. In neurocysticercosis, corticosteroids are often co-administered to control inflammation when parasites in the brain are killed. What interaction does this create with praziquantel, and why does it matter?

A) Corticosteroids raise praziquantel cerebrospinal fluid levels, increasing neurotoxicity, so praziquantel must be stopped
B) Corticosteroids have no effect on praziquantel levels in any compartment
C) Corticosteroids bind praziquantel in the gut and block its absorption entirely
D) Corticosteroids reduce praziquantel cerebrospinal fluid levels by roughly 50 percent, which can lower drug exposure at the site of the central nervous system parasites and must be accounted for
E) Corticosteroids convert praziquantel into an inactive antimalarial metabolite

ANSWER: D

Rationale:

Corticosteroids reduce praziquantel penetration into the cerebrospinal fluid (CSF) by approximately 50 percent. In neurocysticercosis this matters because it lowers praziquantel exposure precisely where the central nervous system parasites are, potentially reducing efficacy; clinicians must account for this when corticosteroids are used to manage the inflammatory response. (By contrast, corticosteroids increase benznidazole plasma levels, a separate interaction.)

Option A: Option A is incorrect: corticosteroids lower, not raise, praziquantel CSF levels, so the concern is reduced efficacy, not increased neurotoxicity requiring drug discontinuation.
Option B: Option B is incorrect: there is a clinically relevant effect; corticosteroids reduce praziquantel CSF concentrations by about half.
Option C: Option C is incorrect: the interaction is reduced CSF penetration, not complete blockade of gut absorption.
Option E: Option E is incorrect: corticosteroids do not transform praziquantel into an antimalarial metabolite; they reduce its CSF levels.

16. Quinine retains specific roles in malaria therapy despite the dominance of artemisinin combinations. Which statement about quinine's use and toxicity is correct?

A) Quinine is used only for uncomplicated malaria in healthy adults and is contraindicated in severe disease
B) Quinine is used for severe malaria and for first-trimester malaria, dosed around 10 mg/kg every 8 hours, and at toxic levels causes cinchonism (tinnitus, visual disturbance, altered mental status)
C) Quinine has no recognized toxicity and requires no dose limit
D) Quinine is a topical agent for scabies with no systemic antimalarial role
E) Quinine is given as a single lifelong dose and never causes QTc effects

ANSWER: B

Rationale:

Quinine remains important for severe malaria (given intravenously in hospital) and for first-trimester malaria when artemisinin-based therapy is not used, typically dosed around 10 mg/kg every 8 hours. Its characteristic toxicity at high levels is cinchonism, a cluster of tinnitus, visual disturbance, headache, and altered mental status; quinine and the related quinidine also cause dose-dependent QTc prolongation. These features define its clinical use and monitoring.

Option A: Option A is incorrect: quinine is in fact used for severe malaria and first-trimester malaria, so restricting it to uncomplicated disease and calling it contraindicated in severe disease is wrong.
Option C: Option C is incorrect: quinine has well-recognized toxicity (cinchonism, QTc prolongation), so the claim of no toxicity and no dose limit is false.
Option D: Option D is incorrect: quinine is a systemic antimalarial, not a topical scabicide.
Option E: Option E is incorrect: quinine is dosed repeatedly during a treatment course, not as a single lifelong dose, and it does cause QTc prolongation.