Comment on: Serotonin syndrome due to co-administration of linezolid and venlafaxine

Synthesis and structure–activity relationship of 7-(substituted)-aminomethyl-4-quinolone-3-carboxylic acid derivatives

Gram-positive organisms have re-emerged as the major hospital pathogens, which make the unmet medical needs for antibacterial therapy even worse. In searching for potent agents against Gram-positive pathogens, novel 7-(substituted)-aminomethyl-quinolone-3-carboxylic acids were designed, synthesized, and evaluated for their antibacterial activities in vitro. Many 7-monoarylaminomethyl derivatives exhibited high potency against Gram-positive organisms compared to reference agents: vancomycin and pazufloxacin. Additionally, a few 7-monoalkylaminomethyl derivatives exhibited good activities against both Gram-positive and Gram-negative organisms.

Mild serotonin syndrome associated with concurrent linezolid and fluoxetine

PURPOSE

A case of serotonin syndrome that developed during concurrent linezolid and fluoxetine is presented.

SUMMARY

A 23-year-old white male patient was originally admitted to receive intravenous chemotherapy for acute myelogenous leukemia. He had a history of intravenous amphetamine abuse, hepatitis B virus infection, hepatitis C virus infection, depression, and bipolar disorder. The patient's routine medications before admission included methadone, fluoxetine, voriconazole, transdermal nicotine patch, lorazepam, and quetiapine. The patient developed persistent neutropenia and complications from chemotherapy, including mild mucositis. Despite treatment with levofloxacin, acyclovir, and voriconazole, the patient developed high fevers. Levofloxacin was discontinued and aztreonam and vancomycin were started. After a blood culture revealed that the bacteria were likely vancomycin resistant, vancomycin was discontinued and linezolid was initiated. Nine hours later, the patient began complaining of severe pain in his abdomen. After a total of four doses of linezolid, the patient reported further discomfort. Two days after linezolid initiation, a health care team member identified the interaction between fluoxetine and linezolid as the cause of the patient's symptoms, and linezolid was discontinued. All symptoms resolved within 48 hours. While resolution generally occurs within 24-48 hours after discontinuing the offending agent, the time to resolution may be delayed if the agent has a long half-life or active metabolites, in which case admission to an intensive care unit is recommended. Cyproheptadine and chlorpromazine may also be used to treat symptoms.

CONCLUSION

Serotonin syndrome developed in a patient taking concurrent linezolid and fluoxetine.

Tricyclic antidepressant pharmacology and therapeutic drug interactions updated

New data on the pharmacology of tricyclic antidepressants (TCAs), their affinities for human cloned CNS receptors and their cytochrome P450 enzyme inhibition profiles, allow improved deductions concerning their effects and interactions and indicate which of the TCAs are the most useful. The relative toxicity of TCAs continues to be more precisely defined, as do TCA interactions with selective serotonin reuptake inhibitors (SSRIs). TCA interactions with monoamine oxidase inhibitors (MAOIs) have been, historically, an uncertain and difficult question, but are now well understood, although this is not reflected in the literature. The data indicate that nortriptyline and desipramine have the most pharmacologically desirable characteristics as noradrenaline reuptake inhibitors (NRIs), and as drugs with few interactions that are also safe when coadministered with either MAOIs or SSRIs. Clomipramine is the only available antidepressant drug that has good evidence of clinically relevant serotonin and noradrenaline reuptake inhibition (SNRI). These data assist drug selection for monotherapy and combination therapy and predict reliably how and why pharmacodynamic and pharmacokinetic interactions occur. In comparison, two newer drugs proposed to have SNRI properties, duloxetine and venlafaxine, may have insufficient NRI potency to be effective SNRIs. Combinations such as sertraline and nortriptyline may therefore offer advantages over drugs like venlafaxine that have fixed ratios of SRI/NRI effects that are not ideal. However, no TCA/SSRI combination is sufficiently safe to be universally applicable without expert knowledge. Standard texts (e.g. the British National Formulary) and treatment guidelines would benefit by taking account of these new data and understandings.

Risk of serotonin syndrome with concomitant administration of linezolid and serotonin agonists

Linezolid, an antimicrobial used to treat resistant gram-positive bacteria, can inhibit monoamine oxidase, an enzyme that metabolizes serotonin and other biogenic amines. Inhibition of this enzyme can predispose patients who are concomitantly taking serotonin agonists to serotonin syndrome. Because of the potential of linezolid to inhibit monoamine oxidase, premarketing studies were conducted with drugs such as selective serotonin reuptake inhibitors. No cases of serotonin syndrome were recorded. After linezolid was released to the United States market, several case reports of serotonin syndrome emerged. A literature search revealed 13 cases of serotonin syndrome occurring with the concomitant use of linezolid and drugs possessing serotonergic properties. To direct clinical management of this potential drug interaction, we reviewed reports of serotonin syndrome to determine relevant drug interactions with linezolid and serotonergic drugs and to characterize similarities and differences in the reported cases. Clinicians should obtain complete drug histories to identify patients at risk, strictly monitor drug therapy including concomitant drugs, and receive education about this potential drug interaction and the symptoms of serotonin syndrome.

Monoamine oxidase inhibitors, opioid analgesics and serotonin toxicity

Toxicity resulting from excessive intra-synaptic serotonin, historically referred to as serotonin syndrome, is now understood to be an intra-synaptic serotonin concentration-related phenomenon. Recent research more clearly delineates serotonin toxicity as a discreet toxidrome characterized by clonus, hyper-reflexia, hyperthermia and agitation. Serotonergic side-effects occur with serotonergic drugs, and overdoses of serotonin re-uptake inhibitors (SRIs) frequently produce marked serotonergic side-effects, and in 15% of cases, moderate serotonergic toxicity, but not to a severe degree, which produces hyperthermia and risk of death. It is only combinations of serotonergic drugs acting by different mechanisms that are capable of raising intra-synaptic serotonin to a level that is life threatening. The combination that most commonly does this is a monoamine oxidase inhibitor (MAOI) drug combined with any SRI. There are a number of lesser-known drugs that are MAOIs, such as linezolid and moclobemide; and some opioid analgesics have serotonergic activity. These properties when combined can precipitate life threatening serotonin toxicity. Possibly preventable deaths are still occurring. Knowledge of the properties of these drugs will therefore help to ensure that problems can be avoided in most clinical situations, and treated appropriately (with 5-HT(2A) antagonists for severe cases) if they occur. The phenylpiperidine series opioids, pethidine (meperidine), tramadol, methadone and dextromethorphan and propoxyphene, appear to be weak serotonin re-uptake inhibitors and have all been involved in serotonin toxicity reactions with MAOIs (including some fatalities). Morphine, codeine, oxycodone and buprenorphine are known not to be SRIs, and do not precipitate serotonin toxicity with MAOIs.

Serotonin Toxicity Associated with Concomitant Use of Linezolid

OBJECTIVE:

To report 2 cases of serotonin toxicity (ST) associated with concomitant use of linezolid and serotonergic drugs and review previously published case reports.

CASE SUMMARIES:

Case 1. A 38-year-old white female with cystic fibrosis treated with venlafaxine 300 mg/day for one year was prescribed linezolid 600 mg intravenously every 12 hours for treatment of methicillin-resistant Staphylococcus aureus (MRSA) pulmonary infection. She displayed symptoms of ST 8 days after the introduction of linezolid. The venlafaxine dosage was decreased to 150 mg/day, and symptoms gradually abated over 36 hours. Case 2. A 37-year-old male with multiple myeloma received citalopram 40 mg/day and trazodone 150 mg/day for anxiety-related disorders. Linezolid treatment with 600 mg orally twice daily was instituted for MRSA cellulitis. The following day, the patient developed anxiety, panic attacks, tremors, tachycardia, and hypertension that persisted throughout linezolid treatment. Symptoms finally waned 5 days after linezolid treatment was stopped.

DISCUSSION:

The symptoms observed in our patients were consistent with Sternbach's criteria for ST. A review of published case reports showed a short time to onset of symptoms following the introduction of linezolid, generally within 1–3 days. Also of note is the use of relatively high dosages of serotonergic drugs. Use of the Naranjo probability scale indicated a possible relationship between the use of linezolid and the occurrence of ST in both cases.

CONCLUSIONS:

Clinicians should pay special attention to patients treated with serotonergic drugs, especially those receiving dosages in the higher end of the normal range who are prescribed linezolid, and consider tapering or reducing the dosage of serotonergic drugs for the duration of antibiotic therapy.