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Drug Distribution

Drug Distribution. Prepared by Prof.Abdulkader.H.El Daibani. Drug Distribution. Drug Distribution: After absorption, drug is distributed through body compartments (plasma"3L “ ,E.C.F"15L" and total body water T.B.W"40L". Drug Distribution. Volume of distribution (Vd):

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Drug Distribution

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  1. Drug Distribution Prepared by Prof.Abdulkader.H.El Daibani

  2. Drug Distribution Drug Distribution: • After absorption, drug is distributed through body compartments (plasma"3L“ ,E.C.F"15L" and total body water T.B.W"40L".

  3. Drug Distribution Volume of distribution (Vd): • Volume of fluid in which the drug appears to distribute with a conc. equal to that in plasma (Vd not real value). • Vd= Dose (mg)/Plasma conc.(mg/ml) at zero time (Co).

  4. Drug Distribution • If Vd=3L "then drug confined to blood e.g. warfarine, aspirin. • If Vd=15L "drug confined to E.C.F e.g. maninitol "osmotic diuretic". • if Vd=40L "drug distributed to TBF e.g. ethanol.

  5. Drug Distribution • If Vd>40L, the drug is distributed at extravascular sites or intracellular proteins or stored in adipose tissue "tissue localizion " e.g mepridine"pethidine"cpz 1500L, propofol 4000L and diazepam 820L.

  6. Drug Distribution DrugSite of disposition • Calcium, fluoride Bone and teeth and tetracycline • Iodine Thyroid gland • Chloroquine Liver and retina

  7. Drug Distribution • Dialysis is useful for drugs with low Vd e.g. salicylates but not for drug with large Vd. Drug plasma protein binding • % of total drug blood which is bound to plasma proteins. • [PD] ↔ [D]+[P]. Bound

  8. Drug Distribution Characteristics of P.P.B (plasma protein binding) 1) Reversible. 2)Not specific" more than one drug can compete for some site". 3) Bound drug is inactive and act as a reservoir and prolong duration t 1/2. 4)Free fraction is active and subject to metabolism and excretion.

  9. Drug Distribution • Drugs mainly bind to albumine, aspirin, warfarine but basic drugs also bind α acid glycoprotein e.g. Lidocaine, propranolol, imipramine. • Drug interaction may result from displacement of adrug bound to plasma • Proteins by another drug with more affinity of binding sites-this becomes clinically imp. of: 1)if more than 95% of drug is bound to plasma proteins. 2)Bound drug has low Vd. 3)Bound drug has low T.I (TE50/ED50). e.g. warfarine is displaced by aspirin→ ↑ plasma conc. of warfarin→ hemorrhage so aspirin is contraindicated with warfarin.

  10. Drug Distribution B.B.B.( Blood brain barrier) • No pores between endothelial cells of capillaries and endothelial cells have tight junction (slide), so only lipid soluble drugs can cross B.B.B. • e.g. general anesthesia, BD, other opioids and other C.N.S depressants L-Dopa (but not DA) treatment of parkinsonism INH, Rifampin but not streptomycin. • Inflammation as in bacterial meningitis increase permeability of B.B.B. e.g. to penicillin which is usually doesn't cross B.B.B.

  11. Drug Distribution Placental barrier • Lipid soluble drugs can cross the placenta. • Some drugs may cause congenital abnormalities if given early in pregnancy. • Thalidomide (sedative and hypnotic) :3-10 weeks of pregnancy phoceomelia (seal extremities). • Anticancer drugs 3-10 weeks teratogenic some drugs may cause adverse effects if given to mother just before delivery. • Morphine → Respiratory depression "asphyxia neonatorum" • Warfarin → hemorrhage • Tetracycline → bone deformity and permanent discoloration of teeth.

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