SPH Block IV: Tox 1-5

Created by wagnekat 

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Selective toxicology, Dr. Keenan

amoxicillin

-PCN family
-inhibits synthesis of bacterial cell walls by inhibitings cross-linkage between peptidoglycan polymer chains that make up the cell walls of both gram + & -
-inhibits cell wall synthesis; acids (-); orally active.
-procaine PG and benzathine PG are repository forms with slow abs.
-PenV is orally active as Na+ or K+ salt - risk of hypo and hyper kalemia respectively

Chloramphenicol

-binds large ribosomal subunit and directly interferes with substrate binding, blocks protein production, bacteriostatic
-large Vd
-crosses BBB, accumulates in CNS
-not used in the US due to AEs of aplastic and erythrocytic anemias and others

ciprofloxacin

-inhibits DNA gyrase (type II topoisomerase), inhibiting cell division
-quinolone
-active against both gram + & -
-orally active, well absorbed into most hard-to-access areas but NOT CNS (urinary tract, reproductive, bone)
-tx for UTIs, prostate, bone infections
-affects mammalian cell replication also

cisplantin

-crosslinks DNA (alkylating agent)
-cell cycle phase nonspecific
-administered IV short term

clarithromycin

-macrolide
-binds small ribosomal subunit, inhibits peptide bond formation
-more effective against gram -

clavulanic acid

-beta-lactamase inhibitor
-usu combined w/ PCN abx to overcome antibiotic resistance (restore activity of beta-lactam ring
-suicide inhibitor, covalently binds active site

cyclophosphamide

-Crosslinks DNA irreversibly
-prodrug, converted by P450 dependent pathway to active phosphoramide mustard. This metabolite only forms in cells with low ALDH levels.
-tx of lymphomas, leukemia and solid tumors
-orally active unlike most alkylating agents due to P450 metabolism
-causes marked and persistent cholinesterase activity.

doxrubicin

-intercalates DNA
-also stabilizes topoisomerase II complex after it has broken the DNA chain for replication (DNA can't be "resealed")
-substrate for oxidative metabolism and superozide radical production
-cell cycle nonspecific
-administered IV, often in combo w/ other agents
-aka "Adriamycin"
-etabolized by P450 into active and inactive metabolites. .

doxycycline

-reversibly binds 30S ribosome and inhibits transpeptidation
-hepatic metabolism, significant enterohepatic recirculation
-relatively long acting
-can produce photosensitivity

erythromycin

-macrolide, binds 50S ribosome subunit
-easily inactivated by gastric acid, therefore all oral formulations have enteric coating
-good alternative to PCN
-major AE diarrhea

etoposide

-inhibits topoisomerase II, promotes cellular apoptosis (ca tx)
-late S & G2 phase specific

fluorouracil (5-FU)

-Metabolic inhibitor
-converted to 5-FdUMP which inhibits thymidylate synthase. RNA/protein synthesis not affected. Results in unbalanced cell growth
-S-phase specific
-given IV (poor oral bioavailability due to first pass met)

gentamicin and tobramycin
(aminoglycosides)

-binds small ribosomal subunit (AG)
-mostly effective against gram (-) aerobic bugs (uptake is O2 dependent)
-IV, IM, topical (not orally active, not absorbed)
-ototoxic

trastuzumab (Herceptin)

-McAb that binds HER2/neu receptor, down-regulates expression and arrests cell cycle
-tx for breast cancer.

imatinib

-inhibitor of TK enzymes, binds near ATP binding site of enzyme locking it in a closed or self-inhibited conformation,
-aka "Gleevac"
-tx CML

leucovorin (folinic acid)

-derivative of THF, vitamin activity equivalent to FA but does not require DHFR for conversion. Allows purine/pyrimidine synthesis in the presence of dihydrofolate reductase inhibition (for ca tx), so some normal DNA replication and RNA transcription processes can proceed.
-"rescue"

mechlorethamine and cyclophosphamide

-alkylating agent (crosslinks DNA)

methotrexate

-inhibits DHFR (converts DHF to active THF), decreases T and purine NT levels.
-S-Phase specific
- variable oral absorption, active uptake into cells, intrathacal for CNS treatment
-lethal at high doses requiring antidotal therapy using folinic acid and leucovorin. Intratheral for CNS treatment
-RENAL EXCRETION - may require dose adjustment.

paclitaxel (Taxol)

-Prevents mitotic spindle assembly, chromosome segregation & cell division. Stabilizes microtubule polymer and protects it from disassembly, leads to a mitotic block and apoptosis.
-sed for breast, ovarian and lung cancer.

PCN G & V

-inhibits bacterial cell wall synthesis
-usu tx for gram +
-freq hypersensitivity

strontium-89

-Beta emitter, IV treatment of bone metastases.

sulfamethoxazole

-Competitive antagonists of PABA synthesis, reduces precursors for DNA synthesis
-high PPB (80-90%)
-Administered 1:5 with trimethoprim (TMP/SMX) resulting in 1:20 plasma concentration due to larger Vd of TMP and low PPB
-can displace bilirubin binding in neonates = hyperbilirubinemia
-potentites actions of pheyntion and warfarin.

tamoxifen

-estrogen receptor antagonist in breast, in other tissues may act as an agonist
-causes cells to remain in the G0/G1
-prodrug, metabolized by CYP2D6/3A4
-tx for estrogen-related ca

tobramycin

-binds the small ribosomal subunit (AG)
-renal, ototoxicity

trimethoprim

-competitively inhibits DHFR (DHF --> THF) reduces precursors for synthesis of DNA, RNA, thymidylates, and protein
-BASIC drug, accumulates in acidic fluids of prostate (ion trapping) but due to duration of tx required for effect prostate infections more commonly treated w/ quinolones
-Administered 1:5 with sulfamethoxazole resulting in 1:20 plasma concentration (TMP/SMX) due to larger Vd of TMP and low PPB

vinblastine

-disrupts microtubule assembly, disrupting mitotic spindle
-M phase specific
--different spectrum of clinical activity and toxicity compared to vincristine
-AEs include n/v bone marrow suppression, alopecia

vincristine

-Binds to tubulin dimers, inhibiting assembly of microtubule structures
-M phase specific
-different spectrum of clinical activity and toxicity compared to vinblastine
-main dose limitation is neurotoxicity

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