Duloxetine is a selective serotonin reuptake inhibitor (SSRI) medication used to treat depression, generalized anxiety disorder, fibromyalgia, diabetic peripheral neuropathy, chronic musculoskeletal pain and overactive bladder syndrome. In some countries it is available only with a physician's prescription. A therapeutic duloxetine dose usually ranges from 40 to 120 milligrams (mg) total per day, taken in divided doses twice a day or once per day for the entire amount. A sufficient duloxetine dose is one that adequately treats the patient's symptoms while avoiding — if possible — most side effects. The specific dosage amount that accomplishes both these ends is dependent upon the patient's diagnosis, weight, age, sex, lifestyle, medical history and current drug regime.
The disease being treated is the first factor considered when determining an adequate and appropriate duloxetine dose. For treatment of depression, the medication is usually initially taken twice per day for a total of 40 mg. The dosage might be increased depending upon depressive symptoms and side effects, if present. When treating anxiety, fibromyalgia, chronic muscle pain or diabetic peripheral neuropathy, the beginning adult dosage is usually 60 mg per day taken at one time. A duloxetine dose of greater than 120 mg per day is unusual and not recommended.
The patient's weight, age and sex are also considered when determining the appropriate dosage of this medication. A general rule of thumb is that underweight patients should be started on a lower duloxetine dose than overweight or obese patients. Administering this medication to the elderly also requires that the lowest possible dose be used to reach therapeutic effects as this population often has a higher incidence of problematic side effects. A patient's lifestyle — working or retired, active or sedentary — may determine whether a side effect such as low blood pressure, dizziness or blurred vision is incapacitating or merely inconvenient.
The patient's medical history and current drug regime should also be taken into account when determining a sufficient duloxetine dose. A history of alcohol abuse, hypertension, liver or kidney disease may necessitate lower doses of duloxetine or even consideration of an alternative medication. Starting duloxetine within two weeks of having used monoamine oxidase (MAO) inhibitor drugs such as isocarboxazid, phenelzine, selegiline or traylcypromine is contraindicated. Additionally, patients should not begin duloxetine if they currently take linezolid, lithium, tryptophan, tramadol, sumatriptan, zolmitriptan or rizatriptan to avoid life-threatening interactions. Even common medications, supplements or compounds such as St. John's wort, acetaminophen and caffeine can interfere with metabolism and excretion of duloxetine and should therefore be avoided.