Pharmacology: Elimination and Pharmacokinetics Flashcards
What drugs demonstrate ‘zero order’ elimination?
Ethanol, phenytoin, aspirin
What does zero order kinetics imply?
That the rate of elimination of a drug is constant per unit time. If 5units of a medication are eliminated per unit of time, then the rate of elimination = 5 x [Drug]^0.
What does first order elimination imply?
That the rate of elimination of a drug is dependent on the serum concentration of the drug, but also that the % change with time is constant. (ergo, the T1/2 is constant). Rate = C x [Drug]^1.
What are the special types of drug elimination?
- Flow-dependent, 2. Capacity-dependent
Give an example of flow dependent elimination of a drug
The elimination of morphine is affected in low flow states such as heart failure.
Give an example of capacity mediated elimination
These drugs are strict adherents of Michaelis Menton kinetics and therefore show ‘saturation’ in that a high enough C will cause Vmax. When this happens, elimination is by zero order kinetics.
How and why might urine pH affect the excretion of a drug?
Drugs are either weak acids or weak bases. Alkalinization of the urine assists with the clearance of weak acids and vice versa.
Give examples of drugs that are weak acids?
Aspirin and phenobarbital
Give examples of drugs that are weak bases?
Amphetamines, phenylcycline, and quinidine.
What is the principle function of the liver in drug elimination?
Biotransformation- changing a lipophilic drug into a hydrophilic one so that it can be excreted in the urine.
What are the phase 1 reactions?
Reduction, oxidation, and hydrolysis
The cytochrome P450 system is involved in what stage of metabolism?
Phase 1
What are CYP P450 inducers?
Chronic EtOH, phenobarbital, rifampin, carbamazepine, griseofulvin, phenytoin
What are the CYP P450 inhibitors?
Isoniazid, erythromycin, cimetidine, grape-fruit juice, azoles, and ritonavir
What is the function of phase 2 reactions?
To make polar, inactive metabolites.
