Key Drug Interactions
·
Serotonin
syndrome
o Mental
status changes, agitation, diaphoresis, tachycardia, death
o monoamine
oxidase inhibitor (MAOI) - phenelzine or tranylcypromine sulfate
o dextromethorphan,
meperidine, and SSRI such as fluoxetine
o stop
fluoxetine 5 weeks before MAOI due to long half-life of metabolite
norfluoxetine
o wait
2 after MAOI ends and SSRI begins
·
Digoxin
and Quinidine
o Increase
in digoxin levels
o Quinidine
displaces digoxin from binding sites and leading to a decreased Vd of digoxin
o Quinidine
decreases renal and nonrenal excretion of digoxin
·
Sildenafil
and Isosorbide mononitrate
o Hypotension
due to sildenafil being a PDE5 inhibitor and nitrates increase cGMP
·
Potassium
(chloride, bicarbonate, citrate, acetate, gluconite, and iodide) and potassium sparing diuretics
(spironolactone, amiloride, triamterene)
o Leads
to hyperkalemia, cardiac failure, and death especially in patients in renal
impairment
·
Clonidine
and Propanolol
o Rebound
hypertension when suddenly stopping clonidine
o Clonidine
is a central alpha-2 adrenergic agonist that causes a decrease in NE
o Alpha-1
receptors then become sensitized because of less norepinephrine
o With
suddenly withdrawn a large increase in norepinephrine occurs leading to
vasoconstriction by the sensitized alpha1 receptors
o Body
cannot compensate because the beta-2 receptors are blocked
·
Warfarin
and NSAID (diflunisal, ketoprofen, piroxicam, sulindac, diclo-fenac, and
ketorolac)
o increase
the risk of GI bleeding
o acetaminophen
or nonacetylated salicylates (magnesium salicylate or salsalate) is an
alternative
·
Theophylline
and Ciprofloxacin
o Increase
in theophylline levels
o Theophylline
is metabolized by CYP1A2
o Ciprofloxacin,
clarithromycin, erythromycin, fluvoxamine, and cimetidine inhibit CYP1A2
o levofloxacin
or ofloxacin is an alternative
·
Pimozide
and Ketoconazole
o Prolong
QT interval and ventricular arrhythmias (torsades de pointes)
o Pimozide
is metabolized by CYP3A4
o Ketoconazole,
fluconazole inhibit CYP3A4
o Terbinafine
is safer
·
Methotrexate
and Probenecid or Penicillins or Salicylates
o Increase
methotrexate levels
o Probenecid
inhibits renal secretion
o methotrexate
toxicity include diarrhea, vomiting, diaphoresis, renal failure, and death
o alternatives
include acetaminophen not salicylates or NSAIDS (celecoxib okay, rofexcoxib NOT
okay)
·
Bromocriptine
and Pseudoephedrine
o peripheral
vasoconstriction, ventricular tachycardia, seizures, and possibly death
o Bromocriptine
dopamine agonist for Parkinson’s (first line therapy is bromocriptine or other
dopamine agonist such as ropinirole, pramipexole, or pergolide
o Avoid
all sympathomimetics with bromocriptine
Source:
http://www.pharmacytimes.com/publications/issue/2002/2002-11/2002-11-7010
