Drug Interactions

Question 1

Levodopa

Answer 1

Pyridoxine (vit. B6)» inc. levodopa breakdown
MAOI» hypertensive crisis
Antipsychotics: dopamine antagonists

Question 2

Donepezil, galantamine, tacrine

Answer 2

Higher toxicity with CYP inhibitors: paroxetine, fluoxetine, erythromycin, prednisone, grapefruit juice)
Reduced effect with CYP inducers: carbamazepine, phenytoin, rifampin

Question 3

Gabapentin

Answer 3

Al, Mg, Ca antacid» dec. bioavailability

Question 4

SSRI

Answer 4

MAOI» serotonin syndrome: hyperthermia, muscle rigidity, sweating, myoclonus
Drugs metabolized wz CYP (careful wz paroxetine, fluoxetine)

Question 5

Repaglinide (GlucoNorm)

Answer 5

Gemifibrozil (increase repaglinide conc.)

Gemifibrozil is lipid lowering agent

Question 6

Metformin

Answer 6

Alcohol potentiates hypoglycemic effect

Question 7

Varenicline (Champix)

Answer 7

Insulin, NRT, Warfarin, Theophyline

Question 8

Sulfonylurea

Answer 8

Reduce effect:
Atypical antipsychotics, corticosteroids, diuretics, niacin, phenothiazine, sympathomimetic

Increase effect:
Allopurinol, azole antifungals, chloramphenicol, clarithromycin, MAOI, probenecid, salicylate, sulfonamide

Question 9

DPP-4 inhibitors

Answer 9

CYP450 inhibitors&raquo_space; inc. action

Question 10

Levothyroxine

Answer 10

Food, Ca, Al antacids, sucralfate, cholestyramine, colestipol&raquo_space; reduce its absorption
CYP inducers, inhibitors

Question 11

Zafirlukast (Accolate)

Answer 11

CYP inhibitors, inducers
ASA increase its levels
Potentiates effect of warfarin

Question 12

Oral contraceptives

Answer 12

CYP inducers: phenytoin, carbamazepine, rifampin كتر التكرار
Topiramate
Antibiotics, griseofulvin (antifungals)

Question 13

Digoxin

Answer 13

• BB, CCB, amiodarone, propfenone, quinidine&raquo_space; reduce digoxin dose by 25-50%
• amiodarone, propafenone, quinidine, verapamil, erythromycin, clarithromycin, tetracycline, itraconazole, cyclosporine, ritonavir: increase digoxin levels
• antacids, cholestyramine, colestipol, sulfasalazine, neomycin, rifampin, St. John wort: decrease digoxin levels

Question 14

BB

Answer 14

Digoxin, amiodarone, CCB» reduce dose by 25-50%

Hypoglycemic agents

Question 15

Montelukast

Answer 15

CYP inducers reduce its level

E.g. Carbamazepine, rifampin, phenytoin, phenobarbital

Question 16

Fexofenadine

Answer 16

Al, Mg antacids, fruit juices: reduce its bioavailability