Drug interactions

Question 1

Pharmacokinetic interaction

Answer 1

delivery of object drug to its site of action is altered by precipitant drug

Question 2

Pharmacodynamic interaction

Answer 2

the response of the object drug is modified by the precipitant drug without changes in drug concentrations

Question 3

pharmaceutic interactions

Answer 3

physical and chemical incompatibilities

Question 4

Drugs that SLOW gastric emtying

Answer 4

Opiate anagesics, antimuscarinics (atropine), tricyclic antidepressants (antimuscarinic side effects).

Question 5

In general, what is the effect of an antacid on the absorption of an acidic drug? A basic drug?

Answer 5

Less acidic stomach contents means more acidic drug will be in its ionised form, therefore will be absorbed slower. If the drug is basic, less will be ionized and more absorbed faster. EtOH has opposite effects.

Note: most absorption is in intestine, so absorption in stomach is not super clinically relevant.

Question 6

In general, what is the effect of an antacid on the absorption of an acidic drug? A basic drug?

Answer 6

Less acidic stomach contents means more acidic drug will be in its ionised form, therefore will be absorbed slower. If the drug is basic, less will be ionized and more absorbed faster. EtOH has opposite effects.

Note: most absorption is in intestine, so absorption in stomach is not super clinically relevant.

Question 7

Tetracyclines and polyvalent cations

Answer 7

Tetracyclines chelate cations- effect is greatly reduced availability of tetracycline. Solution: administer min 2hrs apart.

Question 8

Cholestyramine

Answer 8

Basic anion exchange resin will bind to ANY acidic drug that is coadministered.

Question 9

Cholestyramine

Answer 9

Basic anion exchange resin will bind to ANY acidic drug that is coadministered.

Question 10

What are some p450 inducers?

Answer 10

Rifampicin, ethanol, phenytoin

Question 11

What are som p450 inhibitors?

Answer 11

Azoles, grapefruit juice, cimetidine

Question 12

How does induction work and how long does it take?

Answer 12

Via transcriptional upregulation of CYP gene. Requires days-2 weeks to peak. Requires 1+ week to return to baseline. Excdeption is EtOH- faster induction.

Question 13

What are some pharmacodynamic interactions?

Answer 13

NSAIDs-antihypertensives (opposite effectsw on Na and water retention)

Question 14

What are some pharmacodynamic interactions?

Answer 14

NSAIDs-antihypertensives (opposite effectsw on Na and water retention)
Naloxone-opiates
MAOI-SSRI, Linezolid-SSRI- Additive seritonergic effects. fatal
Beta-blocker-theophylline- antagonized bronchodilation of theophylline