If given concurrently with theophylline, which drug needs to be administered at a reduced dose?

When theophylline is administered alongside certain drugs, it is crucial to consider potential interactions that can affect theophylline's metabolism. Enrofloxacin is known to inhibit the enzyme cytochrome P450 1A2, which is involved in the metabolism of theophylline. This inhibition can lead to increased plasma levels of theophylline, potentially resulting in toxicity. Therefore, when dogs receive both theophylline and enrofloxacin, the dose of theophylline must be reduced to prevent adverse effects associated with elevated concentrations.

The other drugs listed do not have the same significant interaction with theophylline and its metabolic pathways. Doxycycline, clindamycin, and phenobarbital do not require dose adjustments when given with theophylline, making them less critical in this context. Thus, enrofloxacin is the drug that necessitates a reduced dosage of theophylline to ensure safety and efficacy during concurrent administration.