Tryptophan

Oral
Adjunct in treatment-resistant depression

Dose reduction may be needed.

Dose reduction may be needed.

History of eosinophilia-myalgia syndrome associated with tryptophan treatment.

May affect ability to drive or operate machinery. Monitor for suicidal thoughts or clinical worsening of depression during initial treatment period. Renal or hepatic impairment. Elderly.

Nausea (take after food to minimise nausea), headache, lightheadedness, drowsiness, eosinophilia-myalgia syndrome.

Symptoms: Drowsiness and vomiting. Management: Treatment is supportive.

Increased risk of serotonin syndrome with SSRI. Possible decrease in levodopa plasma levels with tryptophan.
Potentially Fatal: Increased risk of severe behavioural and neurological toxicity with MAOI, start with lower initial dose of tryptophan if needed.

Description:
Mechanism of Action: Tryptophan is an essential amino acid which is the precursor of serotonin. It may be used as an adjunctive therapy in treatment-resistant depression. It is sometimes administered with pyridoxine and ascorbic acid. Due to its association with eosinophilia-myalgia syndrome, the use of tryptophan as dietary supplements (e.g. for insomnia) is limited or restricted.
Pharmacokinetics:
Absorption: Readily absorbed from GI tract.
Distribution: Protein binding: Extensive, to plasma albumin.
Metabolism: By liver to metabolites e.g. hydroxytryptophan and kynurenine derivatives.
Excretion: Elimination half life (oral or IV L-tryptophan): 1-3 hr.

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