Tamsulosin drug interactions
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
List of drug interactions
Nifedipine, Atenolol, Enalapril
Warfarin
Digoxin and Theophylline
Furosemide
Cimetidine
Nifedipine, Atenolol, Enalapril
In three studies in hypertensive subjects (age range 47-79 years) whose blood pressure was
controlled with stable doses of Procardia XL®, atenolol, or enalapril for at least three months,
Tamsulosin capsules 0.4 mg for seven days followed by Tamsulosin capsules 0.8 mg for
another seven days (n=8 per study) resulted in no clinically significant effects on blood
pressure and pulse rate compared to placebo (n=4 per study). Therefore, dosage adjustments
are not necessary when Tamsulosin capsules are administered concomitantly with Procardia
XL®, atenolol, or enalapril. Return to top
Warfarin
A definitive drug-drug interaction study between tamsulosin HCl and warfarin was not
conducted. Results from limited in vitro and in vivo studies are inconclusive. Therefore,
caution should be exercised with concomitant administration of warfarin and FLOMAX
capsules. Return to top
Digoxin and Theophylline
In two studies in healthy volunteers (n=10 per study; age range 19-39 years) receiving
FLOMAX capsules 0.4 mg/day for two days, followed by Tamsulosin capsules 0.8 mg/day for
five to eight days, single intravenous doses of digoxin 0.5 mg or theophylline 5 mg/kg
resulted in no change in the pharmacokinetics of digoxin or theophylline. Therefore, dosage
adjustments are not necessary when a FLOMAX capsule is administered concomitantly with
digoxin or theophylline. Return to top
Furosemide
The pharmacokinetic and pharmacodynamic interaction between Tamsulosin capsules 0.8
mg/day (steady-state) and furosemide 20 mg intravenously (single dose) was evaluated in ten
healthy volunteers (age range 21-40 years). Tamsulosin capsules had no effect on the
pharmacodynamics (excretion of electrolytes) of furosemide. While furosemide produced an
11% to 12% reduction in tamsulosin HCl Cmax and AUC, these changes are expected to be
clinically insignificant and do not require adjustment of the FLOMAX capsules dosage. Return to top
Cimetidine
The effects of cimetidine at the highest recommended dose (400 mg every six hours for six
days) on the pharmacokinetics of a single Tamsulosin capsule 0.4 mg dose was investigated in
ten healthy volunteers (age range 21-38 years). Treatment with cimetidine resulted in a
significant decrease (26%) in the clearance of tamsulosin HCl which resulted in a moderate
increase in tamsulosin HCl AUC (44%). Therefore, Tamsulosin capsules should be used with
caution in combination with cimetidine, particularly at doses higher than 0.4 mg. Return to top
Adapted from the FDA Package Insert.