Drug Excretion, Bioavailability, Bioequivalence And Drug Interaction Flashcards
Organs of excretion
Kidney(urine), tongue( saliva), skin(sweat), breast( breast milk), lungs(breath), rectum/intestine (bile/faeces) , eye( tears) and lastly through hair
Example of drugs passed through large intestine/ rectum
Vancomycin $ vincristine
What type of drugs are excreted in the tongue and what is the PH of the saliva
Basic drugs
Ph 5.8-8.4
Examples of drugs excreted through the tongue
Phenytoin, diazepam, theophylline, caffeine and lithium
What type of transport does the saliva use to excrete drugs
Passive diffusion across the cells of the salivary glands and oral epithelium
Examples of drugs the eye excretes
Cytarabine
What type of transport does the eye use to excrete drugs
Passive transport of lipophilic non protein bound and unionized molecules from plasma across the eccrine and lacrimal glands
Examples of drugs are excreted by the lungs
Mainly anaesthetics
Examples of drugs that are excreted by the skin
Antipyrine, alchol, benzoic acid, salycitic acid, lead and mercury, cocaine
What type of drugs are excreted by the breast’s
Most drugs e.g aspirin
Examples of drugs excreted by the hair
Phenobarbital, methamphetamine, methoxyphenamine
What is the most important organ involved in eliminating drugs and their metabolites
Kidneys via their functional unit
(Nephron: glomerulus + tubules)
Renal excretion =
Glomerular filtration - tubular reabsorption + tubular secretion
Tubular secretion
Carrier mediated, independent of size not protein binding
EXCRETES MOST DRUGS (80%)
Where does tubular secretion occur
Occurs at both the proximal and distal convulated tubules
What type of drugs are not excreted by glomerular filtration
Drugs with high molecular weight like heparin, high molecular weight plasma proteins like albumin(68000) and highly protein bound drugs such as warfarin(98%)
Glomerular filtration filters small molecules ( <20,000) such as what
Water, Sugar, salt, Unbound drugs via pores at the base of the glomerulus
Tubular reabsorption
Occurs by passive diffusion from the tubules into the peritubular capillaries, requires lipid solubility
What is renal clearance
It can be defined as the volume of plasma containing the amount of substance that is excreted by the urine per unit time
Formula for renal clearance
CLr= Cu/Cp X Vu
List the 2 types of half life
1) Biological half life
2) plasma half life
Define biological half life
It is the time taken for a substance to lose half of its physiological, pharmacological and radioactive activity
Define plasma t1/2
Time taken for a drug to lose half of its plasma concentration
Plasma half life depends on what
Rate of excretion and metabolism of the drug
List the factors affecting drug excretion
Lipid solubility
PH
Enterohepatic cycling
Particle size
Protein binding
Drug interaction
Renal disease
List the basic drugs
Quinine
Probenecid
Morphine
Histamine
Serotonin
Dopamine
Pethidine
List the acidic drugs
Aspirin
Penicillin
Methotrexate
Indomethacin
Frusemide
Thiazide diuretics
List drugs that undergo enterohepatic cycling
Tetracycline, Chloramphenicol, Flurbiprofen, leflunomide, colchicine, digitoxin, phenytoin and oestradiol
Give an example how drug interaction can affect drug excretion
Probenecid inhibits excretion of penicillin by competing with it for tubular secretion at the proximal tubule thereby prolonging its action
Normal GFR range
Kidney disease range
Kidney failure range
100-130
Kidney disease < 60
Kidney failure <15 ml/min
List the substances that alkalize urine
Sodium bicarbonate, acetazolamide, potassium citrate
List the substances that acidify urine
Ammonium chloride, sodium phosphate, potassium phosphate
