Term
| What is the Henderson-Hasselbach equation? |
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Definition
LOG (protonated/unprotonated) = pKa-pH
For example, if the pKa of aspirin is 3.5 and the pH of the stomach is 1.5, what percent of the aspirin will be in the protonated form?
pKa-pH = 2, so protonated/unprotonated= 100, therefore approximately 99% of the aspirin will be in the protonated form. When an acidic drug like aspirin is in its protonated form, it is uncharged and can diffuse across the gut walls. |
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Term
| Why might a drug given orally have a low bioavailability? |
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Definition
Large first pass effect,
acidic stomach ENVR |
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Term
| How is a subcutaneous or intramuscular injection absorbed? |
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Definition
through bulk-flow transfer, which depends on the local blood flow and the drug solubility.
can be hastened by warming or rubbing the injection site |
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Term
What is the Volume of Distribution?
state the equation |
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Definition
the volume required to hold total amt of drug in body at the same concentration it is found in the plasma.
Vd= (D*F)/Co
D= dose/amt of drug
F= bioavailability
Co= plasma concentration |
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Term
| What are phase I reactions? |
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Definition
Oxidations, Reductions, Hydrolysis
Phase I reactions involve the unmasking or introduction of a polar group, thereby making the drug more water soluble |
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Term
| What are phase II reactions? |
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Definition
Conjugation reactions:
glucuronidation
acetylation
methylation
sulfation
the covalent attachment of small polar molecules |
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Term
| What enzyme catalyzes glucuronidations? |
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Definition
| UDP glucuronosyltransferase in the liver |
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Term
| What drugs induce the CYP450 system? |
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Definition
Barbiturates
Rifampicin
Phenytoin
Carbamazepine
Induction of the p450 system may severely limit the effectiveness of other drugs that are extensively metabolized through this system by hastening their inactivation |
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Term
| What CYP450 enzyme is a factor in the metabolism of 50% of all drugs? |
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Definition
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Term
| What drugs inhibit the CYP450 system? |
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Definition
Cimetidine
SSRIs
Omeprazole
These may cause an otherwise normal dose of another drug to become toxic. |
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Term
| What are microsomal enzymes? |
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Definition
microsomal enzymes are found on the SER; they are the mixed function oxidases:
1) CYP450 enzymes
2) Monooxygenases
they act only on LIPID SOLUBLE COMPOUNDS |
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Term
| what is(are) the equation(s) for drug half-life |
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Definition
t1/2= 0.693/ke
t1/2= (0.693*Vd) / CL
(because ke= CL/Vd) |
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Term
| What are the formulas for clearance? |
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Definition
CL= (0.693*Vd) / t1/2
CL= DoseRate/Css |
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Term
| What are the formulas for plasma concentration at steady state? |
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Definition
(Dose*F) / T = Css*CL (aka: Css=Dose rate/CL)
Css= (Dose*F) / (T*ke*Vd)
Css= (Dose*F*t1/2) / (T*0.693*Vd) |
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Term
| What is the equation for dosing rate? |
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Definition
DR= (Dose*F) / T
where T is the dosing interval |
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Term
| How long does it take for a drug to be eliminated after administration? |
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Definition
four half lives
*also takes 4 half lives for a drug to reach a steady state while being administered |
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Term
| What is the equation for loading dose? |
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Definition
LD= (Css * Vd) / F
where Css is the desired plasma steady state concentration |
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