Pharmacology Flashcards

Question

what are the advantages of topical drug therapy

Answer 1

ADVANTAGES ↓ systemic side effects- Useful if swallowing difficulties Onset of action may be quicker Compliance

Answer 2

Compliance? Physical difficulties? Reactions at site Staining of clothing Delayed onset of action-relys on skin intergrity e.g. hydrated Misconception that topical = safe

Answer 3

Half life is the time required to reduce the (drug) plasma concentration to half of its original value Also refered to as t ½ Can vary from drug to drug and from person to person Does not depend on dose / dose frequency Use to calculate dosage frequency / time to ‘steady state’

Answer 4

Bioavailability is the fraction of the administered dose that reaches the systemic circulation of the patient- fraction of the drug we give that reaches systemic circulation – e.g. by iv injection = 100 percent Affected by: Dosage form Dissolution and absorption of drug Route of administration Stability of the drug in the GI tract (if oral route) Extent of drug metabolism before reaching systemic circulation Presence of food/drugs in GI tract

Answer 5

Half-life is the time taken for the concentration of the drug in the blood to fall by half

Answer 6

Generally a drug with a short half-life is given more frequently E.g. paracetamol t ½ = 2 – 4 hours Usual dose? - 1g every 4 to 6 hours to maintain effective pharmcodynamic effect from paracetamol;

Answer 7

Generally a drug with a long half-life is given less frequently E.g. warfarin t ½ = 24 hours Usual frequency? - Given once daily

Answer 8

How do we need tp change doses if we are going from iv route to oral route Bioavailability when changing from IV to oral route of administration e..g propanol iv 100% oral 30 to 40% \

Answer 9

4 process Absorptiion Dstribution Metabolism Eliminarion

Answer 10

Most medicines are given orally and they must pass through the semi-permeable (lipid) membrane of the gut before reaching the systemic circulation (blood stream). – risk of loss of molecules – what yo put in ihg tnot be available for pharmacodynamic reaction Absorption can be affected by many factors – including the route in which the medicine is given but is generally proportional to the lipid solubility of the medicine. – main barrier to absorption = has pt used meds and have they used it in the right way Therefore, the absorption of non-ionised molecules is favoured as these are far more lipid soluble. A medicine given by intravenous injection is put straight in to the blood stream and is therefore rapidly distributed to tissues

Answer 11

Concordance ********* Food / Drink Formulation Blood flow- e.g. diabetes Route of administration Lack of specific receptor needed for absorption Gastric emptying- drug on empty stomach – drug is dormant GI motility Inactivation of drug in gut or liver Pre-existing medical conditions Drug interactions

Answer 12

required to distribute the medicine to body tissues Process where drug moves away from site of absorption to other areas of the body Each drug is uniquely distributed in the body, some go into the fat (lipid) and others remain in the extracellular fluid Drugs are found remotely from the desired site of action which can account for some side effects Major barriers to distribution: Cell membranes Capillaries Blood Brain Barrier- thick lipid barrier

Answer 13

Plasma protein binding Competition for protein binding sites (distribution may rely heavily on plasma protein binding) NB Bound drug– inactive / free drug – active- protein acts as a drug carrier – makes the drug inactive because using energy to adhere to protein when it reaches site of action drug is active – if drug becomes dsrbuted wrongly can become active in wrong places Regional blood flow - Reduced blood flow e.g. Diabetics Lipid solubility - Blood/brain barrier – generally if increased lipid solubility then increased penetration Disease - Liver disease can cause low plasma protein levels. Renal disease causes high blood urea levels

Answer 14

The liver is the main site of drug metabolism. However, the gastrointestinal system and the lungs have considerable metabolic activity. The primary aim of drug metabolism is to render a molecule as water soluble as possible so that it can be eliminated from the body by the kidneys. Metabolites tend to be less active than the parent compound although some, termed ‘active metabolites’ may be more potent if the parent compound was administered as a ‘pro-drug’ (an inactive compound on administration which is activated by metabolism).

Answer 15

Compounds given orally are primarily absorbed in the small intestine and enter the portal system which takes the drug molecule to the liver before effective distribution to body tissues. If the result of this first pass metabolism is an ineffective compound, then the medicines is not therapeutically viable by the oral route

Answer 16

Genetic factors e.g acetylation status – breakdown meachanism in liver = acetylation (‘fast- break down meds to quick /slow- risk of accumalatig meds metaboliser’) Age Impaired or immature hepatic enzyme activity Elderly- may metabolise less effectively Children < 6 months (especially premature babies) Other drugs hepatic enzyme inducers- quickens metabolism in liver hepatic enzyme inhibitors- slows down metabolism could result in accumulation of medication

Answer 17

Many compounds are primarily excreted by the kidneys. Water soluble compounds appearing in the glomerular filtrate will be eliminated in urine whereas lipid soluble compounds will be reabsorbed by passive diffusion in to the renal tubules. Some compounds are concentrated in bile and excreted in to the intestine where they may be re-absorbed (enterohepatic re-circulation-can increase the persistence of the drug in the body) or eliminated in faeces. Other routes of elimination include sweat, tears, genital secretions and breast milk

Answer 18

Kidney function declines with age – drop In filtration rate in the kidneys

Answer 19

How drugs work when they reach their site of action

Answer 20

Drugs may act on: One of the components of the cell One of the critical chemical pathways of the cell Transport mechanisms allowing chemicals into and outside of cells Chemical messaging systems between cells DNA / RNA replication

Answer 21

drugs can damage cell walls

Answer 22

Some antibiotics damage the bacterial cell wall Cell becomes leaky and dies and therefore as bavteria usually proliferate to creates infection stops bacteria from proliferating Example: penicillin

Answer 23

Cells need to transport molecules into and out of the cell Some molecules can pass through according to: Size Smaller the better Electric charge Less highly charged the better Polarity

Answer 24

By giving the molecule polartity it forces the molecule through the cell membrane even though it is to big

Answer 25

Osmosis is the passage of solvent such as water through a semi-permeable membrane from a less concentrated solution into a more concentrated one ie.spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides).