Drug Interactions between chlorpheniramine / ephedrine / guaifenesin and nebivolol

MONITOR: Beta-blockers may antagonize the cardiostimulatory effects of ephedrine by blocking beta-1 adrenergic receptors in the heart. Parenteral ephedrine may be less effective in the treatment of shock and hypotension if the patient is receiving, or has recently received, a beta-blocking drug. In addition, peripheral vascular resistance may increase due to unopposed alpha-adrenergic effect of ephedrine in the presence of beta-blockade. Theoretically, the interaction may also occur with beta-blocker ophthalmic preparations, since they may be systemically absorbed and can produce clinically significant systemic effects even at low or undetectable plasma levels.

MANAGEMENT: Clinicians should be alert to the potential for diminished cardiac response when parenteral ephedrine is used in patients treated with beta-blockers, including ophthalmic formulations.

GENERALLY AVOID: Noncardioselective beta-blockers can antagonize the bronchodilating effects of ephedrine by blocking beta-2 adrenergic receptors in smooth muscles of the bronchial tree. The interaction is less likely to occur with cardioselective beta-blockers, which generally have little effect on beta-2 adrenergic receptors at therapeutic dosages. However, cardioselectivity is not absolute and may be lost with larger doses.

MANAGEMENT: Noncardioselective beta-blockers, including ophthalmic formulations, should generally be avoided in patients using ephedrine-containing preparations for bronchospastic diseases. If beta-blocker therapy is necessary, an agent with beta-1 selectivity (e.g., atenolol, metoprolol, betaxolol) is considered safer. However, caution is advised, especially with higher dosages of the beta-blocker.