Page 1181 - Basic _ Clinical Pharmacology ( PDFDrive )

CHAPTER 66 Important Drug Interactions & Their Mechanisms 1167

TABLE 66–1 Important drug interactions.

Drug or Properties Promoting
Drug Group Drug Interaction Clinically Documented Interactions
HMG-CoA Gemfibrozil: [NP] Increased plasma lovastatin and simvastatin and increased risk of
reductase myopathy.
inhibitors
(statins) (cont.) Kinase inhibitors: [P] Decreased metabolism of atorvastatin, lovastatin, and simvastatin
by ceritinib, dasatinib, imatinib, idelalisib, and lapatinib.
Macrolide antibiotics: [P] Clarithromycin and erythromycin inhibit the elimination of
statins.
Nefazodone: [NP] Decreased atorvastatin, lovastatin, and simvastatin metabolism.
Phenytoin: [P] Increased atorvastatin, lovastatin, and simvastatin metabolism.
Rifampin: [P] Increased atorvastatin, lovastatin, and simvastatin metabolism.
St. John’s wort: [NP] Increased atorvastatin, lovastatin, and simvastatin metabolism.
See also Azole antifungals; Calcium channel blockers; Cyclosporine.
Iron Binds with drugs in gastrointestinal Methyldopa: [NE] Decreased methyldopa absorption.
tract, reducing absorption.
Mycophenolate: [P] Decreased mycophenolate absorption.
Quinolones: [P] Decreased absorption of ciprofloxacin and other quinolones.
Tetracyclines: [P] Decreased absorption of tetracyclines; decreased efficacy of iron.
Thyroid hormones: [P] Decreased thyroxine absorption.
See also Antacids.
Levodopa Levodopa degraded in gut prior to Clonidine: [NE] Inhibited antiparkinsonism effect.
reaching sites of absorption. Agents
that alter gastrointestinal motility Haloperidol: [NP] Inhibited antiparkinsonism effect.
may alter degree of intraluminal Metoclopramide: [NP] Inhibited antiparkinsonism effect.
degradation. Antiparkinsonism
effect of levodopa susceptible to Monoamine oxidase inhibitors (MAOIs): [P] Hypertensive reaction (carbidopa
inhibition by other drugs. prevents the interaction).
Papaverine: [NE] Inhibited antiparkinsonism effect.
Phenothiazines: [P] Inhibited antiparkinsonism effect.
Phenytoin: [NE] Inhibited antiparkinsonism effect.
Pyridoxine: [P] Inhibited antiparkinsonism effect (carbidopa prevents the
interaction).
Lithium Renal lithium excretion sensitive ACE inhibitors (ACEIs): [NE] Reduce renal clearance of lithium; increase lithium
to changes in sodium balance. effect.
(Sodium depletion tends to cause
lithium retention.) Susceptible to Angiotensin II receptor blockers (ARBs): [NE] Reduce renal clearance of lithium;
drugs enhancing central nervous increase lithium effect.
system lithium toxicity. Diuretics (especially thiazides): [P] Decreased excretion of lithium; furosemide
may be less likely to produce this effect than thiazide diuretics.
Haloperidol: [NP] Occasional cases of neurotoxicity in manic patients, especially with
large doses of one or both drugs.
Methyldopa: [NE] Increased likelihood of central nervous system lithium toxicity.
Nonsteroidal anti-inflammatory drugs (NSAIDs): [NE] Reduced renal lithium
excretion (except sulindac and salicylates).
Theophylline: [P] Increased renal excretion of lithium; reduced lithium effect.
E, Expected; HP, Highly predictable. Interaction occurs in almost all patients receiving the interacting combination; P, Predictable. Interaction occurs in most patients receiving the
combination; NP, Not predictable. Interaction occurs only in some patients receiving the combination; NE, Not established. Insufficient data available on which to base estimate
of predictability.
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