Page 1180 - Basic _ Clinical Pharmacology ( PDFDrive )

1166 SECTION X Special Topics

TABLE 66–1 Important drug interactions.

Drug or Properties Promoting
Drug Group Drug Interaction Clinically Documented Interactions
Disulfiram Inhibits CYP2C9. Inhibits aldehyde Benzodiazepines: [P] Decreased metabolism of chlordiazepoxide and diazepam but
dehydrogenase. not lorazepam and oxazepam.
Metronidazole: [NE] Confusion and psychoses reported in patients receiving this
combination; mechanisms unknown.
Phenytoin: [P] Decreased phenytoin metabolism.
See also Alcohol; Anticoagulants, oral.
Estrogens Estrogen metabolism (CYP3A4) Ampicillin: [NP] Interruption of enterohepatic circulation of estrogen; possible reduction
susceptible to induction and in oral contraceptive efficacy. Some other oral antibiotics may have a similar effect.
inhibition. Enterohepatic circulation
of estrogen may be interrupted by Bexarotene: [P] Increased estrogen metabolism, possible reduction in oral
alteration in bowel flora (eg, due to contraceptive efficacy.
antibiotics). Bosentan: [NP] Enzyme induction leading to reduced estrogen effect.
Corticosteroids: [P] Decreased metabolism of corticosteroids leading to increased
corticosteroid effect. Dexamethasone may increase estrogen metabolism.
Efavirenz: [P] Increased estrogen metabolism, possible reduction in oral contraceptive
efficacy.
Griseofulvin: [NP] Increased estrogen metabolism, possible reduction in oral
contraceptive efficacy.
Nelfinavir: [P] Increased estrogen metabolism, possible reduction in oral contraceptive
efficacy.
Nevirapine: [NP] Increased estrogen metabolism, possible reduction in oral
contraceptive efficacy.
Phenytoin: [P] Increased estrogen metabolism; possible reduction in oral
contraceptive efficacy.
Primidone: [P] Increased estrogen metabolism; possible reduction in oral
contraceptive efficacy.
Rifabutin: [P] Increased estrogen metabolism; possible reduction in oral contraceptive
efficacy.
Rifampin: [P] Increased estrogen metabolism; possible reduction in oral contraceptive
efficacy.
St. John’s wort: [P] Increased estrogen metabolism; possible reduction in oral
contraceptive efficacy.
See also Barbiturates; Carbamazepine.
HMG-CoA Lovastatin, simvastatin, and, to Amiodarone: [NP] Decreased atorvastatin, lovastatin, and simvastatin metabolism.
reductase a lesser extent, atorvastatin are Expect similar interactions with dronedarone.
inhibitors susceptible to CYP3A4 inhibitors
(statins) and inducers; additive risk with Antivirals: [P] Amprenavir, atazanavir, boceprevir, darunavir, delavirdine,
other drugs that can cause fosamprenavir, indinavir, nelfinavir, ritonavir, saquinavir, simeprevir, and telaprevir
myopathy. inhibit the metabolism of atorvastatin, lovastatin, and simvastatin.
Bosentan: [P] Increased atorvastatin, lovastatin, and simvastatin metabolism.
Carbamazepine: [P] Increased atorvastatin, lovastatin, and simvastatin metabolism.
Clofibrate: [NP] Increased risk of myopathy.
Cobicistat: [P] Decreased metabolism of atorvastatin, lovastatin, and simvastatin.
Conivaptan: [P] Decreased metabolism of atorvastatin, lovastatin, and simvastatin.
Cyclosporine: [P] Decreased atorvastatin, lovastatin, rosuvastatin, pitavastatin, and
simvastatin elimination.
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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