Melatonin Other names: N-acetyl-5-methoxytryptamine Pineal Hormone

CYP1A2 inducers such as carbamazepine and rifampicin may give rise to reduced plasma concentrations of melatonin.

CYP1A2 inhibitors such as quinolones may give rise to increased melatonin exposure.

Alcohol should not be taken with melatonin, because it reduces the effectiveness of melatonin on sleep.

Caution should be exercised in patients on oestrogens (e.g. contraceptive or hormone replacement therapy), which increase melatonin levels by inhibiting its metabolism by CYP1A1 and CYP1A2.

Melatonin may enhance the sedative properties of benzodiazepines and non-benzodiazepine hypnotics, such as zaleplon, zolpidem and zopiclone. In a clinical trial, there was clear evidence for a transitory pharmacodynamic interaction between melatonin and zolpidem one hour following co-dosing. Concomitant administration resulted in increased impairment of attention, memory and co-ordination compared to zolpidem alone.

Caution should be exercised in patients on cimetidine a CYP2D inhibitor, which increases plasma melatonin levels, by inhibiting its metabolism.

Caution should be exercised in patients on fluvoxamine, which increases melatonin levels (by 17-fold higher AUC and a 12-fold higher serum C_max) by inhibiting its metabolism by hepatic cytochrome P450 (CYP) isozymes CYP1A2 and CYP2C19. The combination should be avoided.

Melatonin has been co-administered in studies with thioridazine and imipramine, active substances which affect the central nervous system. No clinically significant pharmacokinetic interactions were found in each case. However, melatonin co-administration resulted in increased feelings of tranquility and difficulty in performing tasks compared to imipramine alone, and increased feelings of “muzzy-headedness” compared to thioridazine alone.

Cigarette smoking may decrease melatonin levels due to induction of CYP1A2.

For melatonin, no clinical data on exposed pregnancies are available. Animal studies do not indicate direct or indirect harmful effects with respect to pregnancy, embryonal/foetal development, parturition or postnatal development. In view of the lack of clinical data, use in pregnant women and by women intending to become pregnant is not recommended.

Endogenous melatonin was measured in human breast milk thus exogenous melatonin is probably secreted into human milk. There are data in animal models including rodents, sheep, bovine and primates that indicate maternal transfer of melatonin to the foetus via the placenta or in the milk. Therefore, breast-feeding is not recommended in women under treatment with melatonin.

Melatonin has moderate influence on the ability to drive and use machines. Melatonin may cause drowsiness, therefore the product should be used with caution if the effects of drowsiness are likely to be associated with a risk to safety.

Summary of the safety profile

In clinical trials (in which a total of 1,931 patients were taking melatonin and 1,642 patients were taking placebo), 48.8% of patients receiving melatonin reported an adverse reaction compared with 37.8% taking placebo. Comparing the rate of patients with adverse reactions per 100 patient weeks, the rate was higher for placebo than melatonin (5,743 – placebo vs. 3,013 – melatonin). The most common adverse reactions were headache, nasopharyngitis, back pain, and arthralgia, which were common, by MedDRA definition, in both the melatonin and placebo treated groups.

List of adverse reactions

The following adverse reactions were reported in clinical trials and from post-marketing spontaneous reporting. In clinical trials a total of 9.5% of patients receiving melatonin reported an adverse reaction compared with 7.4% of patients taking placebo. Only those adverse reactions reported during clinical trials occurring in patients at an equivalent or greater rate than placebo have been included below.

Within each frequency grouping, undesirable effects are presented in order of decreasing seriousness.

Very common (≥1/10); Common (≥1/100 to <1/10); Uncommon (≥1/1,000 to <1/100); Rare (≥1/10,000 to <1/1,000); Very rare (<1/10,000); Not known (cannot be established from the available data).

Infections and infestations

Rare: Herpes zoster

Blood and lymphatic system disorders

Rare: Leukopenia, thrombocytopenia

Immune system disorders

Not known: Hyper-sensitivity reaction

Metabolism and nutrition disorders

Rare: Hypertriglyceridaemia, hypocalcaemia, hyponatraemia

Psychiatric disorders

Uncommon: Irritability, nervousness, restlessness, insomnia, abnormal dreams, nightmares, anxiety

Rare: Mood altered, aggression, agitation, crying, stress symptoms, disorientation, early morning awakening, libido increased, depressed mood, depression

Nervous system disorders

Uncommon: Migraine, headache, lethargy, psychomotor hyperactivity, dizziness, somnolence

Rare: Syncope, memory impairment, disturbance in attention, dreamy state, restless legs syndrome, poor quality sleep, paraesthesia

Eye disorders

Rare: Visual acuity reduced, vision blurred, lacrimation increased

Ear and labyrinth disorders

Rare: Vertigo positional, vertigo

Cardiac disorders

Rare: Angina pectoris, palpitations

Vascular disorders

Uncommon: Hypertension

Rare: Hot flush

Gastrointestinal disorders

Uncommon: Abdominal pain, abdominal pain upper, dyspepsia, mouth ulceration, dry mouth, nausea

Rare: Gastro-oesophageal reflux disease, gastrointestinal disorder, oral mucosal blistering, tongue ulceration, gastrointestinal upset, vomiting, bowel sounds abnormal, flatulence, salivary hypersecretion, halitosis, abdominal discomfort, gastric disorder, gastritis

Hepatobiliary disorders

Uncommon: Hyperbilirubinaemia

Skin and subcutaneous tissue disorders

Uncommon: Dermatitis, night sweats, pruritus, rash, pruritus generalised, dry skin

Rare: Eczema, erythema, hand dermatitis, psoriasis, rash generalised, rash pruritic, nail disorder

Not known: Angioedema, oedema of mouth, tongue oedema

Musculoskeletal and connective tissue disorders

Uncommon: Pain in extremity

Rare: Arthritis, muscle spasms, neck pain, night cramps

Renal and urinary disorders

Uncommon: Glycosuria, proteinuria

Rare: Polyuria, haematuria, nocturia

Reproductive system and breast disorders

Uncommon: Menopausal symptoms

Rare: Priapism, prostatitis

Not known: Galactorrhoea

General disorders and administration site conditions

Uncommon: Asthenia, chest pain

Rare: Fatigue, pain, thirst

Investigations

Uncommon: Liver function test abnormal, weight increased

Rare: Hepatic enzyme increased, blood electrolyes abnormal, laboratory test abnormal