The main factors affecting the establishment of a sufficient isoniazid dose are the indication for which it is being used and the weight of the patient being treated. Isoniazid is an antimycobacterial drug used mainly to treat tuberculosis (TB), in combination with other drugs, or as prophylaxis to prevent TB in people at risk. It is known by different trade names in different countries, according to manufacturer, and is available only by prescription in most countries.
Tuberculosis is a highly infectious disease which is spread from person to person in the air. Most commonly it affects the lungs but it can affect most parts of the body. It is an increasingly large problem, especially in developing countries and is commonly found as a co-infection in people with HIV. Symptoms may include night sweats, loss of weight, persistent coughing and fatigue. Should any of these symptoms be experienced, urgent medical advice should be sought.
The treatment of tuberculosis usually spans over six to twelve months, depending on a number of factors, including the site of the infection, whether it is a recurrence of the disease and the sensitivity of the causative organism. Resistance to some first line drugs, of which isoniazid is one, has been reported. Should tuberculosis be diagnosed, a sample, such as sputum, will be taken from the patient for sensitivity testing in the lab. This will allow the treating doctor to prescribe the correct combination of drugs.
When establishing the isoniazid dose to treat TB, the main factor the doctor will consider is the weight of the patient, as the dose is generally established on a per kilogram basis. Depending on the patient, ease of access to the clinic, and the severity of the disease, the isoniazid dose may be given as a daily dose or three times weekly. The per kilogram isoniazid dose prescribed will be bigger if it is given as a three times a week dose. The isoniazid dose for children is generally higher than the adult dose on a per kilogram scale.
The isoniazid dose for prophylaxis, or prevention of tuberculosis in those at risk may be established by weight, especially in children, or given as a standard dose of 300 mg daily to all adults. When using isoniazid for both treatment and prophylaxis, it is vital to complete the full course prescribed by the doctor, to prevent resistance. This may be between six and eighteen months.