Course content. Chemotherapeutic agents

Transcription

1 Course content 1 Chemotherapeutic agents Mechanism of actions Indications Contraindications/Cautions Drug interactions Side-effects/Adverse reactions Dosage regimen (occasionally)

2 Reference Books 2 Pharmacology by Rang, Dale, Ritter, Gardner Clinical Pharmacology textbooks British National Formulary (BNF)

3 3 Antifungal agents

4 4 Most fungi are commensals or live in the environment. But increasing incidence and severity of human fungal infections Fungal infections are termed mycoses and in Generally can be divided into: 1) Superficial infections 2) Cutaneous infections 3) Sub-cutaneous infections 4) Systemic infections

5 FUNGAL INFECTIONS 5 candidiasis blastomycosis histoplasmosis ringworm mucorymycosis

6 Factors increasing incidence and severity of human fungal infections 6 Widespread use of broad-spectrum antibiotics (antimicrobial drugs) Reduced immune responses caused by AIDS Use of immunosuppressant drugs Administration of anticancer drugs (cancer chemotherapy) Chronic use of steroids (spreading of an infection)

7 FUNGAL INFECTIONS 7 Fungal infections. are usually more difficult to treat than bacterial infections Fungal organisms grow slowly Fungal infections often occur in tissues that are poorly penetrated by antimicrobial agents Eg: devitalized or avascular tissues

8 ANTIFUNGAL AGENTS 8 The Azoles Griseofulvin Flucytosine The polyenes Echinocandin antifungals (new)

9 9 I. Antifungals damaging permeability of the cell membrane Imidazoles: Bifonazole, Clotrimazole, Econazole, Ketoconazole, Miconazole Triazoles: Fluconazole, Itraconazole, Voriconazole Allylamines: Terbinafine, Naftifine Morpholines: Amorolfine Thiocarbamates: Tolciclate, Tolnaftate Substituted pyridones: Ciclopirox Polyene antibiotics: Amphotericin B, Nystatin

10 10 II. Antifungals inhibiting cell wall synthesis Echinocandins: Caspofungin, anidulafungin and micafungin III. Antifungals inhibiting synthesis of nucleic acids Flucytosine Griseofulvin?????

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12 AZOLES 12 Comprise the imidazoles and triazoles

13 13 Imidazoles: Miconazole Ketoconazole Clotrimazole Fenticonazole Isoconazole Sertaconazole Bifonazole Butoconazole Econazole Tioconazole Oxiconazole Sulconazole Triazoles: Fluconazole Itraconazole Ravuconazole Posaconazole Voriconazole

14 Mechanism of action Azoles inhibit the enzyme cytochrome P450 14αdemethylase. This enzyme converts lanosterol to ergosterol, and is required in fungal cell membrane synthesis 14

15 Azoles 15 Reduced fungal membrane ergosterol concentrations result in damaged, leaky cell membranes Azoles inhibiting cytochrome P450 enzymes (inhibits biosynthesis of adrenal and gonadal steroid hormones) The toxicity of these drugs depends on their relative affinities for mammalian and fungal cytochrome P450 enzymes. The triazoles tend to have fewer side effects, better absorption, better drug distribution in body tissues, and fewer drug interactions.

16 KETOCONAZOLE 16 Spectrum of activity includes Candida species Coccidioides immitis Cryptococcus neoformans * Dermatophytes & Pityriasis versicolor

17 Pharmacokinetics 17 An acid environment is necessary for ketoconazole absorption Administration of food with ketoconazole appears to increase absorption due possibly to: 1) increased bile secretions 2) delayed gastric emptying Does not cross the intact blood-brain barrier except in meningitis. Urinary concentrations of ketoconazole are usually low, but vaginal and vaginal tissue concentrations correlate with those in serum.

18 KETOCONAZOLE 18 Metabolized through oxidation, dealkylation, aromatic hydroxylation. Excreted into the bile, faeces and the urine Bile Faeces Urine

19 Side effects 19 Impotence Gynaecomastia Reduced sperm count Decreased libido Hepatotoxicity Nausea/vomiting Pruritis Dizziness Photophobia

20 Contraindications/Precautions 20 Achlorhydria Hypochlorhydria Alcoholism Breast-feeding Children Hepatic disease Pregnancy

21 Drug interactions 21 Antacids H 2 blockers Omeprazole Isoniazid Corticosteroids Ethanol Phenytoin Rifampicin Astemizole Amphotericin B

22 Miconazole, Econazole, Clotrimazole 22 Bioavailability is low when administered orally Usually used topically.

23 Fluconazole 23 Does not require an acidic environment, as does ketoconazole, for GI absorption. About 80 to 90% absorbed from GIT. Thet 1/2 of the drug is 27 to 37 h, permitting once-daily dosing in patients with normal renal function. Only 11% of the circulating drug is bound to plasma proteins.

24 Fluconazole 24 The drug penetrates widely into most body tissues eg CSF therefore effective for treating fungal meningitis. About 80% of the drug is excreted unchanged in the urine. Dosage reductions are required in the presence of renal insufficiency. Alopecia and hepatic necrosis have been reported as adverse effects

25 Itraconazole 25 Lipophilic and water insoluble Requires a low gastric ph for absorption. Oral bioavailability is variable (20 to 60%). It is highly protein bound (99%) Metabolized in the liver and excreted into the bile. Useful in the treatment of disseminated histoplasmosis in AIDS, nonmeningeal blastomycosis and sporotrichosis

26 Itraconazole 26 Contraindicated in conditions of hepatic and renal impairment, pregnancy and breastfeeding mothers Side effects include nausea, abdominal pain and rash. Flatulence, constipation, menstrual disorders and alopecia may occur.

27 GRISEOFULVIN 27 Fermentation product of Penicillium griseofulvum Mode of action not exactly understood but involves nucleic acid synthesis and cell mitosis Dermatophyte infections of the skin, scalp, hair and nails Infections where susceptible strains of Trichophyton, Microsporum and Epidermaphyte are implicated. Griseofulvin also is deposited in keratin cells on the surface of the skin making it difficult for fungus to invade the skin and other tissues

28 Pharmacokinetics 28 Well absorbed after oral administration. Presence of fat in the diet appears increase absorption of griseofulvin Metabolized in the liver and then excreted in urine

29 Drug Interactions 29 Barbiturates ( e.g. Phenobarbitone) Warfarin Oestrogen Progesterone preparations

30 Toxicity and Side Effects 30 Headache Abdominal discomfort Rashes Fatigue, Dizziness (enhance effect of alcohol) Confusion and impaired co-ordination

31 POLYENE ANTIFUNGALS 31 Amphotericin B Mechanism of Action: Destroys the integrity of cellular membrane of susceptible organism by binding to ergosterol Active against most fungi and yeast Treatment of systemic fungal infections. Not absorbed from the gut Given by IV infusion

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33 Toxic Effects 33 Anorexia, Nausea, Vomiting, diarrhoea, epigastric pain Headache, Muscle and Joint pain Disturbances in renal and liver functions Neurological and blood disorders

34 Clinical Uses 34 Drug of choice in most systemic mycoses Candidiasis Cryptococcosis Aspergillosis Mucormycosis.

35 Nystatin Produced from Streptomyces noursei 35 Active against Candida albicans infections of skin and mucous membranes Not absorbed when given by mouth Its activity is affected by long exposure to light, and heat

36 Side Effects 36 Nausea Vomiting and Diarrhoea (at high doses) Oral irritation Rashes (topical and vaginal forms)

37 Flucytosine (5-flucytosine, 5-FC) 37 Fluorinated purimidine related to fluouracil and floxuridine An analogue of cytosine that was originally synthesized for possible use as an antineoplastic agent. 5-FC is converted to 5-fluorouracil inside the cell by the fungal enzyme cytosine deaminase. The active metabolite 5-fluorouracil interferes with fungal DNA synthesis by inhibiting thymidylate synthetase. Incorporation of these metabolites into fungal RNA inhibits protein synthesis. Indicated for :Crytococcus neoformans (Crytococcal), Candida infections (UTI s) and Torulopsis glabrata

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39 Pharmacokinetics 39 Rapidly and well absorbed in GI tract Widely distributed in the body Minimally bound to proteins Approximately 80% excreted in the urine (unchanged) Half-life 3-6 hours

40 Side Effects 40 Leukopenia Thrombocytopenia Rash Nausea and vomiting diarrhoea. Severe enterocolitis Confusion, headache, sedation

41 Drug Interactions 41 Amphotericin Cytotoxics

42 Allylamines 42 Reversible noncompetitive inhibitors of the fungal enzyme squalene epoxidase, which converts squalene to lanosterol. These agents exhibit fungicidal activity against dermatophytesand fungistatic activity against yeasts. Naftifine is available for topical use only in the treatment of cutaneous dermatophyte and Candida infections.

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44 Terbinafine 44 Dermatophyte infections of the nails and ringworm infections Available for topical and systemic use Lipophilic and highly binds to plasma protiens Cautions Hepatic and renal impairment Pregnancy Breast feeding

45 Drug interactions 45 Rifampicin Cimetidine Famotidine

46 Side effects 46 Abdominal discomfort Anorexia Urticaria rash Taste disturbance Photosensitivity

47 ECHINOCANDIN ANTIFUNGALS Mode of action: inhibit ß-(1,3) glucan synthesis, damaging fungal cell walls 47 no drug target in mammalian cells Rapidly fungicidal against most Candida spp. Fungistatic against Aspergillus spp. Active against cyst form of Pneumocystis carinii.

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49 Caspofungin 49 Pharmacokinetics Administration: IV 96% plasma protein bound Predominantly hepatic metabolism (hydrolysis and N-acetylation). Distribution: urinary concentration low, CSF concentration expected to be low

50 Adverse effects 50 Fever Hepatotoxicity raised transaminases common in patients receiving caspofungin hepatic necrosis in animals given large doses (5-8 mg/kg) Headache Phlebitis Rash (infrequent) Haemolysis may occur but clinically significant haemolysis is rare

51 Drug interactions 51 Slight increases in clearance with coadminstration of: phenytoin carbamazepine dexamethasone efavirenz, nelfinavir, nevirapine Rifampicin - concentrations of both drugs increased Tacrolimus - concentration of tacrolimus decreased by ~20% Cyclosporin - increased caspofungin plasma concentration

52 Micafungin Pharmacokinetics Administration: IV 99.8% plasma protein bound 52 Predominantly hepatic metabolism (hydrolysis and N-acetylation). Hepatic uptake slow, leading to long terminal half-life of h also adrenal and splenic metabolism cannot be dialysed Distribution: urinary concentration low, CSF concentration is low

53 Clinical use 53 Invasive aspergillosis Drug interactions No interactions reported

54 Adverse effects 54 Phlebitis Abnormal liver function tests Rash (infrequent ) Headache Fever uncommon Clinically significant haemolysis rare

55 Pyridones 55 Ciclopirox olamine is a pyridone derivative Use for the treatment of cutaneous dermatophyte infections, cutaneous C. albicans infections and tinea versicolor caused by Malassezia furfur. Mode of action: It interferes with fungal growth by inhibiting macromolecule synthesis (blocks amino acid synthesis)

56 Thiocarbamates 56 Tolnaftate effective in the treatment of dermatophyte infections and tinea. Mechanism of action : not clear however, it is believed to inhibit squalene epoxidase,

57 Haloprogin 57 Haloprogin is a halogenated phenolic ether administered topically for dermotaphytic (tinea)infections. Mechanism of action is unknown, but it is thought to be via inhibition of oxygen uptake and disruption of yeast membrane structure and function

58 Thanks for your attention 58