Pharm 2. Flashcards
Which types of drug pass through membranes most easily?
small, non charged
Why do most drugs need to be water soluble?
to be dissolved int eh gastrointestinal fluid or carried by plasma
What happens with protein bound drugs?
unable to cross capillary membrane
What helps decided the portion of ionized/non-ionized drugs?
pH
What type of drugs cannot diffuse across membranes?
ionized (charged)
Henderson-Hasselbach Equation
pH = pKa + log A-/HA
Weak acid drug
easily absorbed by GI tract - can be given as a pill to be swallowed
Weak base drug
weak absorption in GI tract, pill form not good (because charged in acid environment)
enteral
drug administration that uses a portion of GI tract
parenteral
drug administration that does not use the GI tract
enteral routes
oral, rectal, sublingual
parenteral routes
intravenous, intraarterial, intramuscular, subcutaneous, intrathecal, topical, inhalation
oral advantages
ease, safety, self-administration, cheap, prolonged absorption causing prolonged effect
oral disadvantages
absorption may be too slow, absorption often variable and unpredictable, drug may be too irritating, destroyed by gastric acid/enzymes, completely metabolized on first pass through liver - not available for comatose, vomiting patients
rectal advantages
useful for infants, comatose, vomiting patients; useful for foul-smelling distasteful drugs; useful for drugs destroyed in upper GI, avoids immediate metabolism by liver!, for local action in rectum
rectal disadvantages
nuisance, poor compliance, absorption may be erratic, incomplete, possibility of rectal irritation
sublingual advantages
by-passes liver when first absorbed, rapid absorption
sublingual disadvantages
drugs must be soluble in saliva, not too distasteful, have appropriate pKa for rapid absorption, tablets must be small
intravenous advantages
rapid effect, can watch response and titrate drugs!, all dose enters circulation, when oral route not available, for drugs given in large volume, for drugs too irritating when given IM or SC, for infusion and continuous monitoring, parenteral administration of hypertonic solutions possible
intravenous disadvantages
cost, skill, danger of infection, possible anaphylactic reaction, danger of embolus formation, danger of adverse cardiovascular effects if administration too rapid, pain
intraarterial advantages
administration of radiopaque material for visualization of circulatory tree, high concentration of drug going to local area when available
intraarterial disadvantages
same as IV: cost, skill, danger of infection, possible anaphylactic reaction, danger of embolus formation, danger of adverse cardiovascular effects if administration too rapid, pain
intramuscular advantages
when oral route not available, absorption less variable than oral, may be less painful than SC, absorption more rapid than SC, possibility of slowing absorption to prolong effect
intramuscular disadvantages
pain, sterile technique, possible local necrosis, lag period before effect onset, accident IV injection possible, not to be used after anticoagulant
subcutaneous advantages
absorption usually slower than after IM and effect more prolonged, same as IM: when oral route not available, absorption less variable than oral, may be less painful than SC, absorption more rapid than SC, possibility of slowing absorption to prolong effect
subcutaneous disadvantages
same as IM: pain, sterile technique, possible local necrosis, lag period before effect onset, accident IV injection possible, not to be used after anticoagulant
intrathecal advantages
(introduction of drug into cerebral spinal space): when local effect on CNS required
intrathecal disadvantages
skill, danger of spinal cord injury
topical advantages
for local action on or under skin/membrane, non invasive
topical disadvantages
difficulty of absorption through skin, danger of excessive absorption through membranes and systemic toxicity
inhalation advantages
rapid absorption for systemic action(lots of surface area in lung), high concentration attainable for local effect, self administration possible
inhalation disadvantages
possible excessive absorption and systemic toxicity, poor regulation of dosage, irritation of pulmonary
which administration of drugs has most free drug molecules in plasma?
IV
which administration of drugs has the most sustained plasma level?
oral
bioavailability
fraction of dose available for biologic action (oral drug administration has “first pass” effects - how much of drug actually reaches circulation)
how is bioavailability measured?
area under the curved for the oral dose form vs the intravenous dose form (AUC oral / AUC iv)
What can be a problem with generic drugs?
chemical equivalence does not necessarily equal biological equivalence!! (the generic might not have as much bioavailability)
What is the equation to predict plasma concentration of a drug?
Cp = Dose/Vd (volume of distribution)
How does the plasma concentration equation change if there are significant limitation in bioavailability?
Cp = (F x Dose) / Vd F = fraction absorbed
What is often the limiting step of for achieve a desired plasma level of a drug given orally?
dissolution
When is it esp. important to predict plasma concentration of a drug?
- drugs that are potent in small doses 2. drugs given for serious illnesses 3. changes in drug manufacturer
What factors affect absorption of enteral drugs?
form of drug, food in stomach, illness, blood flow to GI
What is the order of fastest absorbed enteral drugs?
solution > suspension > capsule > tablet > timed release
Why is blood flow important to consider in speed of absorption of enteral drugs?
if someone is in shock, they won’t have blood flow to GI tract thus no absorption. you want to avoid orally given pills when someone is in shock
What factors affect absorption of parenteral drugs?
blood flow (need blood flow to area of administration), heat, cold, illness, form of drug
What is the predominant influence of the absorption of parenteral drugs?
blood flow
How does heat/cold affect absorption of parenteral drugs?
cold slows absorption of toxins/drugs while heat increases absorption and muscle activity
