Anti- Parasitic Drugs Flashcards
Macroscopic parasites
taenia species (tapeworms), enterobius (pinworm), pediculus (head louse)
Microscopic parasites
Entamoeba (amebiasis), giardia (beaver fever), trichomonas, plasmodium (malaria)
Beef tapeworm
Taenia saginata
Pork tapeworm
Taenia solium
Life cycle of Taenia species
Humans ingest undercooked meat → attaches to intestine → becomes adult → eggs get into feces → cattle or pigs ingest contaminated vegetation → oncospheres get into musculature and stay there
Structures at anterior end of tapeworm
Hooks and suckers
Cestocidal drugs
Praziquantel, niclosamide
Praziquantel mechanism
Binds outer layer of parasite and produces vacuoles, which causes an influx of calcium and muscle contraction → paralysis, dislodgement, death
Pk of praziquantel
High bioavailability orally
Clinical uses of praziquantel
Drug of choice against cestode infections, given in a single oral dose but cannot chew due to bitter taste
Adverse reactions to praziquantel
Mild nausea, headache, abdominal discomfort
Niclosamide mechanism
Inhibits ATP production and rapidly kills scolex and segments of adult tapeworms
Pk of niclosamide
Minimally absorbed from gi tract (good thing)
Clinical uses of niclosamide
Second choice for taenia species, given as a single oral done but is cheaper and accessible
Adverse reactions of niclosamide
Rare; nausea, vomiting, diarrhea
Prevention of tapeworm reinfection
Fully cook meat
Life cycle of enterobius vermicularis
Humans ingest eggs → larvae in si → adults in caecum → migrate to perianal region at night to lay eggs → eggs mature in 4-6 hours → ingested again
Clinical presentation of enterobius vermicularis
School-aged, asymptomatic, itching causes irritability, incontinence, weight loss
Minimizing enterobius infection
Personal hygiene, clean bedrooms, bed linen and night clothes changed frequently
Drugs for enterobius vermicularis
Mebendazole, pyrantel
Mebendazole pk
Given orally and minimally absorbed
Mebendazole mechanism
Binds beta tubulin so microtubules can’t polymerize → inhibits motility, glucose uptake, and division so parasite is slowly killed and expelled in feces
When you should not give mebendazole
When pt has diarrhea because quicker transit time means lower efficacy
Clinical uses of mebendazole
Pinworms - treat twice @2week intervals
Adverse reactions of mebendazole
Short-term is basically free of adverse effects, but is teratogenic
Pyrantel pk
Poorly absorbed from gi tract
Pyrantel mechanism
Acts at neuromuscular junction on nicotinic receptors to cause release of ACh and inhibition of AChE → paralysis → expulsion
Pyrantel clinical uses
Pinworms but narrower spectrum, treat twice @ 2 week interval
Adverse reactions of pyrantel
Mild nausea, vomiting, diarrhea
Life cycle of pediculus capitis
Stay on head and feed on human blood; go from egg to 1st nymph in 8-9 days and egg to adult in 18-21 days
Clinical presentation of pediculus capitis
Itchy head, most easily seen behind ears or back of neck
Transmission of pediculus capitis
Mainly direct head-to-head contact
Drugs for pediculus capitis
Permethrin and malathion
Permethrin mechanism
Keeps voltage-gated sodium channels open, which causes depolarization and paralysis
Pk of permethrin
Minimally absorbed through skin, rapidly inactivated in liver, high prevalence of resistance
Malathion mechanism
Irreversibly inhibits AChE —>paralysis
Adverse reactions of permethrin and malathion
Itching or burning of scalp that can persist for days after lice are killed
Principles of pediculus capitis treatment
They don’t kill eggs, retreat at 9-10 day intervals, treat bedmates at same time, treat household, manually remove nits after treatment
Protozoa
Eukaryotes with similar metabolic processes to the host, antiprotozoal drugs may cause significant toxicity
Entamoeba histolytica
Parasite that causes amebiasis
Amebiasis
Disease caused by E. Histolytica
Life cycle of E histolytica
Ingested by humans → cysts released in si and become trophozoites → turn back into cysts after replication → excreted in feces
Outcomes of amebiasis
Asymptomatic colonization in colon, invasive amoebic colitis, liver abscess, ameboma
Categories of amebicidal drugs
Luminal amebicides, systemic amebicides, mixed amebicides
Luminal amebicides
Used if you only have cysts and trophozoites it the bowel lumen (asymptomatic)
Systemic amebicides
Used if you have parasites in the intestinal wall and liver, but do not killed trophozoites or cysts in lumen
Mixed amebicides
Drug of preference for sick pts; kill parasites in lumen, wall, and liver
Metronidazole pharmacokinetics
Given orally, readily absorbed, and extensively distributed; metabolized by mixed-function oxidase and glucuronylation in liver, all excreted in urine; clearance will decrease if impaired liver function
Metronidazole mechanism
Ferrodoxin-like, low-redox potential, electron transport proteins transfer electrons to nitro groups of metronidazole → cytotoxic products
Metronidazole adverse effects
Nausea, vomiting, headache, abdominal cramps, metallic taste, alcohol causes nausea and vomiting, avoided in pregnant/nursing women because mutagenic in bacteria
Clinical uses of metronidazole
Drug of choice for diarrhea/dysentery but not reliable for luminal parasites so have to be given with luminal amebicide
Iodoquinol uses
After treatment of symptomatic amebiasis and for asymptomatic infections; effective against luminal stages
Iodoquinol adverse effects
Rash, diarrhea, peripheral neuropathy, optic neuritis (avoid long-term use)
Treatment protocol for metastatic amebiasis
High dosage metronidazole followed by iodoquinol
Life cycle of Giardia lamblia
Ingested through contaminated food /water → get into intestine but do not invade → excreted in feces but only cysts survive in environment
Clinical signs of Giardia
Usually asymptomatic but can cause severe diarrhea
Drug of choice for Giardia
Metronidazole at low doses but do not treat asymptomatic infections
Trichomonas vaginalis residence
Female lower genital tract, male urethra and prostate; do not survive in external environment, do not have cyst form
Trichomoniasis
Common sexually transmitted disease
Clinical signs of trichomoniasis
Vaginal discharge, vulvar itching, urination discomfort, men usually asymptomatic but can have urethral discharge or burning sensation
Trichomoniasis treatment
Metronidazole, typically single dose unless resistant, systemic therapy preferred, always treat sexual partner
Most severe form of malaria
Plasmodium falciparum
Only parasites of malaria that cause clinical illness
Erythrocytic
Clinical signs of malaria
Headache, back and limb pain, anorexia, nausea, fever, chills, anemia
Cerebral malaria
Slowly lapse into coma with convulsions because parasitized RBCs block cerebral blood vessels
Plasmodium life cycle
Infected mosquito injects sporozoites into human → infect liver and multiply asexually as tissue schizonts → liver cells burst and release merozoites that infect red blood cells → merozoites reproduce asexually in red blood cells as blood schizonts → infected RBCs burst and release gametes → mosquito picks up gametes and produces sporozoites
Categories of malaria drugs
Tissue schizonticides, blood schizonticides, gametocides
Treatment of falciparum and malariae
Only need blood schizonticides
Treatment of vivax and ovale
Need tissue and blood schizonticides
Prevention of mosquito bites
Insect repellents, insecticides, appropriate clothing, bed nets with permethrin
Chloroquine clinical uses
Chemo prophylaxis if parasites are sensitive to it, treatment of chloroquine-sensitive falciparum
Chloroquine pk
Taken orally once/week, rapidly absorbed and distributed, is a blood schizonticide, metabolized by liver and excreted in urine
Chloroquine mechanism
Concentrates in food vacuole and prevents polymerization of heme into hemozoin, resulting in oxidative damage and lysis
Chloroquine resistance
Mutations in membrane transporter
Chloroquine adverse effects
Minimal at low doses, at high doses can get nausea, vomiting, blurred vision, but can take after meals to minimize
Mefloquine clinical uses
Chemoprophylaxis and treatment of chloroquine-resistant falciparum
Mefloquine resistance
Less common; associated with quinine and halofantrine resistance
Mefloquine pk
Given orally once/week, well absorbed and distributed, eliminated slowly, blood schizonticide
Mefloquine mechanism
Concentrated in parasite and may inhibit heme polymerization; final result is membrane damage
Mefloquine adverse reactions
Neuropsychiatric toxicity, nausea, vomiting, dizziness, sleep and behaviour disturbances
Doxycycline clinical lenses
Chemo prophylaxis of multidrug resistant falciparum, treatment of falciparum with quinidine or quinine
Doxycycline pk
Given daily orally, blood schizonticide
Doxycycline mechanism
Inhibits protein synthesis
Doxycycline adverse effects
Infrequent gi symptoms, photosensitivity