home > drugs a-z list > tobradex st (tobramycin / dexamethasone ophthalmic suspension 0.3%/0.05%) drug center > tobradex st (tobramycin / dexamethasone ophthalmic suspension 0.3%/0.05%) drug - clinical pharmacology

Mechanism of Action

Dexamethasone is a potent corticoid. Corticoids suppress the inflammatory response to a variety of agents and they can delay or slow healing. Since corticoids may inhibit the body's defense mechanism against infection, a concomitant antimicrobial drug may be used when this inhibition is considered to be clinically significant.

Tobramycin is an antibacterial drug. It inhibits the growth of bacteria by inhibiting protein synthesis. Tobramycin is included in this combination product to provide action against susceptible bacteria.

Pharmacokinetics

In a multi-center, double-masked, parallel-group, randomized, single-dose pharmacokinetic study in male and female cataract surgery patients, mean dexamethasone concentrations following administration of TOBRADEX ST (tobramycin / dexamethasone ophthalmic suspension 0.3%/0.05%) were similar to dexamethasone concentrations following administration of TOBRADEX (tobramycin /dexamethasone ophthalmic suspension) 0.3%/0.1%. Aqueous humor concentrations reached a mean peak of 33.7 ng/mL 2 hours following single-dose administration of TOBRADEX ST (tobramycin / dexamethasone ophthalmic suspension 0.3%/0.05%) .

No data are available on the extent of systemic absorption of dexamethasone or tobramycin from TOBRADEX ST (tobramycin / dexamethasone ophthalmic suspension 0.3%/0.05%) ophthalmic suspension. Following multiple-dose (QID for 2 days) bilateral ocular administration of TOBRADEX (Tobramycin 0.3%/Dexamethasone 0.1% ophthalmic suspension) in healthy male and female volunteers, peak plasma concentrations of dexamethasone were less than 1 ng/mL and occurred within 2 hours post-dose across all subjects.

Microbiology

The antibiotic component (tobramycin) in the combination is included to provide action against susceptible bacteria. In vitro studies have demonstrated that tobramycin is active against susceptible isolates of the following bacteria: Staphylococcus aureus (includes penicillin-resistant isolates), Staphylococcus epidermidis (includes penicillin-resistant isolates), Streptococci, including some Group A other beta-hemolytic species, some nonhemolytic species, and some Streptococcus pneumoniae. Acinetobacter calcoaceticus, Enterobacter aerogenes, Escherichia coli, Haemophilus influenzae, Haemophilus aegypticus, Klebsiella pneumoniae, Moraxella lacunata, Morganella morganii, Neisseria perflava, Neisseria sicca, Proteus mirabilis, Proteus vulgaris, Pseudomonas aeruginosa.

In vitro bacterial studies demonstrate that in some cases bacteria resistant to gentamicin are susceptible to tobramycin.

Last reviewed on RxList: 9/7/2010
This monograph has been modified to include the generic and brand name in many instances.