Antimicrobials; antibacterials, antifungals, antiprotozoans, antivirals, and antihelminthics 6

Transcription

1 Antimicrobials; antibacterials, antifungals, antiprotozoans, antivirals, and antihelminthics 6

2 Inhibition of Ergosterol Synthesis Azoles Miconazole Triazoles Allylamines For azole-resistant infections Figure 20.15

3 Inhibition of Ergosterol Synthesis Azoles; widely used as antifungals Imidazole; first azole (clotrimazole, miconazole), Miconazole, clotrimazole; non-prescriptional for topical agents against cutaneous mycoses (athlete s foot, vaginal yeast infection), Ketoconazole; broad spectrum, for systemic fungal infections (oral administration, less toxic than amphotericin B), also used as topical ointments for dermatomycoses, occasional liver damage Triazoles; diminished the use of ketoconazoles Voriconazole; promising new broad spectrum antifungal, replacing amphotericin B for systemic mycoses, special advantage in aspergillosis of the CNS (penetrate BBB) Fluconazole itraconazole; less toxic, more soluble (easier administration & more effective for systemic mycoses)

4 Cryptococcus neoformans Meningitis Also called cryptococcosis Soil fungus associated with pigeon and chicken droppings Transmitted by the respiratory route; spreads through blood to the CNS Mortality up to 30% Treatment: Amphotericin B and flucytosine

5 Inhibition of Ergosterol Synthesis Allylamines; recently developed. Inhibit ergosterol biosynthesis in a manner that is functionally distinct Pharmaceutically important allylamines: Terbinafine, flunarizine, and naftifine. Terbinafine & naftifine; acts to fight common fungus causing infections such as athlete's foot, jock itch, and ringworm. Frequently used for the resistance against azole-type antifungals. Terbinafine hydrochloride: known as the trade name, Lamisil, developed by Novartis. Synthetic antifungal allylamine. Highly hydrophobic in nature and tends to accumulate in skin, nails, and fatty tissues. Flunarizine: aids in the relief of migraines. Terbinafine

6 Inhibition of Cell Wall Synthesis Primary target; β-glucan Echinocandins Inhibit synthesis of β-glucan. Caspofungin (Cancidas); commercially available, used against Aspergillus, Candida & Pneumocystis. Especially valuable for persons with whose immune system is compromised.

7 Inhibition of Nucleic Acids Flucytocine Cytosine analog interferes with RNA synthesis. Fungus can convert flucytocine into 5-fluorouracil which is incorporated into RNA and eventually disrupts protein synthesis (Mammalian lack this function). Narrow spectrum, toxic to kidneys & bone marrow Pentamidine isethionate Anti-Pneumocystis that causes Pneumocystis pneumonia, a frequent complication of AIDS Also useful in treating several protozoan-caused tropical diseases may bind DNA Pentamidine

8 Other Antifungal Drugs Griseofulvin; active against superficial dermatomycoses on hairs (Tinea) & nails, despite its oral route for administration. Bind to keratin in skin, hair follicles & nails, and block microtubule assembly (block mitosis) Tolnaftate; an alternative to miconazole as topical agent for athlete s foot. Action unknown Undecylenic acid; fatty acid. anti-fungal activity against athlete s foot. Not as effective as tolnaftate or imidazoles Undecylenic acid Griseofulvin Tolnaftate

9 Antiprotozoan Drugs Anti-malaria drugs Quinine old drug against malaria from Peruvian cinchona tree. Traditionally known as an effective muscle relaxant and control shivering symptom of malaria. Jesuit powder. Chloroquine replace quinine. Most widely used and cheapest. Inhibits DNA synthesis Develop resistance Mefloquinine (Lariam) recommended for resistance to chloroquine. Psychiatric side effect (hallucinations) Figure 12.17b

10 quinine chloroquine mefloquine atovaquone proguanil

11 Malarone (Malanil): commercially available from GlaxoSmithKline since 2000 A combination of atovaquone and proguanil For chloroquine-resistant Atovaquone selectively inhibits the electron transport chain of parasites. High natural frequency of cytochrome b mutants leads to a high failure rate if atovaquone is used alone to treat malaria. Proguanil, via its metabolite cycloguanil, functions as a dihydrofolate reductase inhibitor, halting parasitic deoxythymidilate synthesis, and also acts as a mitochondrial sensitizer to synergize with atovaquone. Has far fewer side effects than older malaria drugs. While some people experience side effects, such as coughing, diarrhea, dizziness, headache, loss of appetite, mouth sores, nausea, stomach pain, vomiting, or weakness, the majority have none or few of these. However, not licensed for use in children weighing 10 kg or less. The pediatric tablets are not used in malaria treatment, but are used for prophylaxis.

12 Antiprotozoan Drugs Artemisinin and artemisinin-based combination therapies (ACTs) becoming principal treatment of malaria. Artesunate (not licensed ub US) and artemether Traditional Chinese medicine (long used for controlling fever). Isolated from the plant Artemisia annua, sweet wormwood, an herb. A precursor can be produced using genetically engineered yeast. Act by klling the asexual stages of Plasmodium spp. In blood Also affect the sexual stages that transmit the infection by mosquitoes More expensive than chloroquine a problem of counterfeit (minimal amount of genuine drug to evade simple tests accelerate development of resistance) Artesunate Nobel prize in 2015 Artemether Artemisinin

13 Antiprotozoan Drugs Other antiprotozoan drugs Quinacrine anti-giardiasis Diiodohydroxyquin (iodoquinol); important drug against amoebic diseases. Dosage control is very important because of optic nerve damage. Unknown mechanism Metronidazole (Flagyl) widely used antiprotozoan drug Against vaginitis (Trichomonas vaginalis), giardiasis, ameobic dysentery (Entamoeba), by interfering with anaerobic metabolism Also against obligately anaerobic bacteria (Clostridium) Damages DNA Metronidazole

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15 Tinidazole (Fasigyn) similar with metronidazole, recently aproved, Effective against giardiasis, amebiasis, trichomoniasis Nitazoxanide synthetic nitrothiazolyl-salicylamide derivative and an antiprotozoan agent. diarrhea (Cryptosporidium hominis), giardiasis, amebiasis. Also effective against helminths & some anaerobic bacteria Interferes with metabolism of anaerobes Anti-viral trial; activity against influenza A virus in vitro and currently in Phase II clinical trials for the treatment of hepatitis C in combination with peginterferon alfa-2a and ribavirin Tinidazole Nitazoxanide