The following represents the best responses based on drug metabolism, pharmacokinetics, species, diagnostic differentials, clinical and laboratory data, and other pertinent findings.
Correct ResponseCautionAcepromazine is a phenothiazine tranquilizer that antagonizes dopaminergic receptors, resulting in the desired goal of sedation. However, acepromazine antagonizes other receptors, including α1-adrenergic receptors, leading to the undesirable effects of vasodilation.1 Caution is thus indicated because trazodone is an α1-adrenergic antagonist (see Mechanism of Action).
Although use of acepromazine is of minimal risk to this otherwise healthy patient, when the drug is used in combination with trazodone, lower doses of acepromazine should be recommended to lessen the likelihood of hypotension during surgery.2
Correct ResponseSafeHydromorphone, a pure µ-opioid agonist used for analgesia, should be safe to administer concurrently with trazodone.
Correct ResponseSafePropofol is a γ-aminobutyric acid (GABA)-A neurotransmitter receptor agonist commonly used as a sedative and induction agent. Although propofol may induce vasodilation, it is metabolized quickly and thus should be safe to administer concurrently with trazodone.
Correct ResponseSafeIsoflurane is the most common inhalation agent used for maintenance of anesthesia in veterinary medicine. This drug has effects on GABA receptors, N-methyl-d-aspartate receptors, and glycine receptors. Isoflurane causes dose-dependent hypotension; however, because of its low lipid solubility, it is metabolized quickly and thus should be safe to administer to orthopedic surgical patients concurrently with trazodone.
Correct ResponseSafeCefazolin, a β-lactam antibiotic that leads to bacterial cell lysis, should be safe to administer concurrently with trazodone.
Correct ResponseCautionKetoconazole is an antifungal drug that also inhibits cytochrome P450 3A (CYP3A) metabolism of multiple drugs, including trazodone. By inhibiting this enzyme pathway, there is potential to increase trazodone plasma concentrations, which could result in serotonin syndrome. Therefore, CYP3A-inhibitor drugs should be used with caution in dogs receiving trazodone. Other CYP3A inhibitors commonly used in dogs include erythromycin, clarithromycin, and itraconazole.
Correct ResponseSafeMaropitant, a neurokinin-1 receptor antagonist, is commonly prescribed for its antiemetic effect in the perioperative period. Because it works on a different receptor than does trazodone, maropitant is considered safe to use concurrently.
Correct ResponseCautionMirtazapine is primarily used as an appetite stimulant and antiemetic. It is important to recognize that mirtazapine antagonizes several receptors, including serotonin receptor subtypes, with resultant increased serotonin levels. Because of the risk for serotonin syndrome, mirtazapine should be used with caution in dogs receiving trazodone.3,4
Correct ResponseCautionHydroxyzine, an antihistamine used for the treatment of allergies, is an antagonist of serotonin (5-hydroxytryptamine [5-HT]) receptors, specifically 5-HT2A. Because it may increase the risk for serotonin syndrome, hydroxyzine should be used with caution in dogs receiving trazodone.2,3
Correct ResponseCautionAmitriptyline is a tricyclic antidepressant and therefore should be used with caution in dogs receiving trazodone, as amitriptyline can increase serotonin concentrations, resulting in serotonin syndrome.2,3,5,6
Correct ResponseSafeOmeprazole is a proton pump inhibitor used for the treatment of GI ulcers. It is safe to use in dogs receiving trazodone.
Correct ResponseCautionTramadol is commonly prescribed for the potential analgesic effects provided by its parent compound and its metabolites as µ-receptor agonists. However, tramadol also inhibits the reuptake of serotonin and norepinephrine.7 Therefore, use of tramadol in dogs receiving trazodone could lead to increased concentrations of serotonin and resultant serotonin syndrome (see Mechanism of Action).3,8
Correct ResponseSafeCarprofen is an NSAID used to treat pain and inflammation. Several case studies reported no complications when trazodone was administered to dogs receiving NSAIDs for postoperative pain.2,5,8
Correct ResponseSafeTylenol #4 is acetaminophen with codeine. Acetaminophen has antipyretic and analgesic properties, and codeine is a pure µ-opioid agonist used for pain relief. Opioids may cause histamine release, resulting in hypotension. However, in an otherwise healthy dog, Tylenol #4 should be safe to administer with trazodone.
Correct ResponseSafeIvermectin is an antiparasitic agent that works on glutamate-gated chloride ion channels. It is also a GABA agonist. Ivermectin should be safe to administer with trazodone in this patient.
Do Not UseMonoamine oxidase inhibitors (MAOIs; eg, amitraz, isocarboxazid, phenelzine, selegiline, tranylcypromine) are antidepressants primarily prescribed for humans; they are infrequently used in dogs, but of the MAOIs that are used, selegiline is the most common. The main function of monoamine oxidase is to break down dopamine, norepinephrine, and serotonin. MAOIs work by blocking these enzymes, causing an increase in serotonin concentration and other neurotransmitters in the brain.2,3,7 Although MAOIs are not commonly used in dogs, it is important to know that concurrent use of trazodone and MAOIs is contraindicated because of the resultant increase in serotonin concentration and risk for serotonin syndrome.2,3,7
Correct ResponseSafeGabapentin is an anticonvulsant agent that is also used to treat neuropathic pain. Although its mechanism of action is not well understood, it is known to involve inhibition of the α2δ-1 subunit of voltage-gated calcium channels. Because gabapentin’s mechanism of action differs from that of trazodone, it is considered safe to use concurrently.2,9