L13 - optimising drug properties to ensure good oral bioavailability
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7 requirements for a good drug
• efficacy • chemical stability • solubility • suitable LogP value (around 1 to 3) • oral bioavailability (not essential) • appropriate pharmacokinetics • favourable safety profile
what does it mean by drugs need to have efficacy?
• Must give intended therapeutic effect • Appropriate size and structure to interact with target
what does it mean by drugs need to have chemical stability?
need to be stable over entire shelf life (not degraded by heat/light)
what does it mean by drugs need to be soluble?
drug needs to be in solution to be absorbed
what does it mean by drugs need to have a LogP value of 1 to 3?
needs lipophilicity
what does it mean by drugs need to have good oral bioavailability?
..
what does it mean by drugs need to have appropriate pharmacokinetics?
absorption, distribution, excretion, metabolism needs to be appropriate
what does it mean by drugs need to have a favourable safety profile?
don’t want toxic drug that makes patient ill
what is fick’s first law of diffusion?
J = A D K (Co - Ci) / h
what does everything stand for in the fick’s first law equation?
J = flux / rate of absorption of a drug A - membrane area D = diffusivity of drug in memb K = partition coefficient / lipophilicity of drug (Co - Ci) = concentration gradient (change in C) h = membrane thickness
key points about ficks first law
• Larger the particle, smaller the diffusivity, decreasing flux/ rate of absorption • Large conc gradient increases flux • Partition coefficient is lipophilicity of drug • Higher lipophilicity = greater absorption of drug • Describes drug diffusion ACROSS A MEMB • Applied to diffusion rate (flux) across whole • epithelium (considering A and h) • Properties of the drug are k, change in C and radius (MW)