Pharmacology Flashcards
Define
- Pharmacodynamics
- Pharmacokinetics
- What the drug does to the body
- What the body does to the drug
What are the 4 main types of Cellular targets ??
- Ion channels (agonist/ antagonist)
{eg. local anaesthetics (works on voltage gated Na+ channels)} - G protein coupled receptors (produce action through 2nd messengers such as cAMP) eg. Adrenoreceptors
- Tyrosine Kinase receptors (eg. Insulin)
- Nuclear receptors (located within nucleus & drug MUST be Lipid soluble) eg. Prednisolone, levothyroxine
Types of Antagonists ??
Competitive (binds to the same site of the agonist==> prevents agonist from binding)
Non- competitive (Antagonist occupies another site==> this causes conformational change in binding site of agonist)
What is Efficacy ??
-Maximal effect a drug can produce (intrinsic activity)- represented by ‘y-value’ (Vmax)
increase in y-value= increase Vmax= Increase Efficacy
- Efficacious drugs can have high/low Potency
What is Potency ??
Amount of drug needed for a given effect - represented by x-value (EC50)
- Left shift= decrease EC50= Increase potency= lower drug needed
- Unrelated to Efficacy ie. Potent drugs can have high or low efficacy
What is Zero-order elimination ??
“Metabolism INDEPENDENT of conc. of drug”
Rate of elimination is constant regardless of Cp (Constant amount of drug eliminated per unit time)
{Due to Saturation of Met. processes}
- Cp decreases LINEARLY with time
eg- Phenytoin, Ethanol & Aspirin (Salicylates), Heparin
PEA H
What is 1st order elimination ??
Elimination is directly proportional to Drug conc. (constant amount of drug eliminated per unit time)
- Cp decreases EXPONENTIALLY with time
- Applies to most drugs
Give eg. for
- Capacity limited elimination
- Flow limited elimination
- Zero-order elimination (PEA H drugs)
- First-order elimination
In how many phases are drug eliminated ??
Phase 1 & Phase 2 (occurs in LIVER)
- Geriatric pts. lose Phase 1 first
- Slow acetylators ==> decreased rate of metabolism == increase S/E
Hallmark of Phase 1 ??
- Lipophilic drugs undergo phase 1
- CYP450 predominance
- has 3 steps (REDUCTION, OXIDATION, HYDROLYSIS)
- Leads to the formation of Toxic Metabolites { Slightly polar metabolite (active or inactive) & ROS metabolites}
Hallmark of Phase 2 ??
- Polar drugs (H2O soluble) undergo phase 2
- 4 steps (METHYLATION, GLUCURONIDATION, ACETYLATION, SULFATION)
- Inactive Metabolites {Very polar, hydrophillic metabolite produced (EXCEPT Acetylated metabolites)}
- Excretion: Serum (urine, sweat), Bile (stools)
Name the drugs which act on Serotonin receptors (Agonists & Antagonists)
- 5-HTr (+) used in Migraine (ACUTE Rx.) eg. Sumatriptan, Ergotamine [partial (+)]
- 5-HTr (-) used in Migraine (PROPHYLAXIS) eg.- Pizotifen [5-HT2 r (-) used in migraine prophylaxis]
Anti-diarrhoeal drug used in Carcinoid synd. ??
CYPROHEPTAHDINE [5-HT2 r (-)]
MoA of Ondansetron ??
5-HT3 r (-) used as Anti-emetic
What should we monitor in pts. on Statins ??
LFT (Baseline, at 3 months & at 12 months)
What should we monitor in pts. on Amiodarone ??
LFT, TFT, U&E, CXR - PRIOR to Rx.
LFT & TFT every 6 months
What should we monitor in pts. on Digoxin ??
ECG, U&E at least 6 hrs. post-dose
What should we monitor in pts. on MTX ??
FBC, LFT & U&E
- Prior to Rx.
- Weekly until Rx. stabilised
- Every 2 to 3 months after stabilizing
What should we monitor in pts. on Azathioprine ??
- FBC, LFT before Rx.
- FBC weekly for the 1st 4 wks.
- FBC, LFT every 3 months
Lithium Monitoring ??
Lithium levels
- T range : 0.4 to 1.0 mmol/l
- 12 hrs. post-dose
- Weekly until stabilized
- 3 monthly after stabilizing
TFT, U&E before Rx. & Every 6 months
What should we monitor in pts. on Sodium Valprote ??
- LFT, FBC before Rx.
- LFT “PERIODICALLY” during 1st 6 months
What should we monitor in pts. on Glitazones ??
LFT
- Prior Rx.
- ‘Regularly’ during Rx.
For which drugs do we check the Trough levels immediately before Rx.
Ciclosporin
Phenytoin (checked before dose ONLY if
- Dose adjustment done
- Suspected TOXICITY
- NON-ADHERENCE detected
Which drugs have a narrow Therapeutic Index (TI) ??
“Warning These Drugs Are Lethal”
- Warfarin
- Theophilline
- Digoxin
- Anti-epileptics
- Lithium