The Chronic Hypersensitivity Pneumonitis (HP), is an inflammatory disease who has an evolution to develop progressive interstitial fibrosis, who cause the death of the patient. Actually HP has been treated with Prednisone and occasionally with Azathioprine, but unfortunately the treatment with these drugs have not an effective result to treat the interstitial fibrosis.

Pirfenidone has been studied over the world for the treatment of Fibrotic diseases, with positive results, and due to the Pirfenidone mechanism of action has anti-inflammatory and anti-fibrotic properties, the investigators propose to evaluate the addition of Pirfenidone to the actual treatment with Prednisone and Azathioprine in the treatment of patients with Pulmonary Fibrosis secondary to a Chronic Hypersensitivity Pneumonitis.

The Chronic Hypersensitivity Pneumonitis (HP), is a complex syndrome due to a exaggerated immune response caused by inhalation of foreign substances, such as molds, dusts, and organic particles, causing alveoli inflammation and in the chronic forms the disease has high rate of mortality, due to the big number of patients who develop progressive interstitial fibrosis and eventually they curse with respiratory insufficiency who cause the death of the patient.

Pirfenidone has been studied over the world for the treatment of Idiophatic Pulmonary Fibrosis (IPF), disease who constitute the most aggressive of the fibrotic diseases of the lung. Additionally Pirfenidone has been showed potential results in the treatment of fibrotic diseases in other organs, as Liver, Kidney, Hearth, etc. Pirfenidone has been described as a modulator of the fibrotic process due to his action over TGF-beta and MMP´s and also has into-inflammatory actions acting over TNF-alfa and IL-1 and IL-6.

Actually HP has been treated with Prednisone and occasionally with Azathioprine, but a high number of patients will develop irreversibly to a interstitial fibrosis with pulmonary parenchyma destruction. Unfortunately the investigators have not an effective treatment for this cases. Due to the positive results obtained with Pirfenidone in the treatment of IPF and other kind of organ fibrosis, the investigators propose to evaluate the addition of Pirfenidone to the treatment with Prednisone and Azathioprine in the treatment of patients with Pulmonary Fibrosis secondary to a Chronic Hypersensitivity Pneumonitis.

Inclusion Criteria:

• Chronic Hypersensitivity pneumonitis with recent diagnosis confirmed by HRT with or without biopsy
• Acceptation with signed informed consent

Exclusion Criteria:

• No confirmed diagnosis
• Patients with peptic ulcer
• Pregnancy or breast feeding period
• Clinical signs of active infection
• History of severe Hepatic disease
• History of severe Kidney disease, who requires some kind of dialysis
• History of inestable cardiopathy
• History of alcohol or drugs abuse
• Bronchial hyperactivity or History of asthma or EPOC
• Smoking habit 3 months before the starting or patient who decline suspend the smoking habit during the study
• Patient with impossibility to make spirometry or who can not walk
• Use of Immunosuppressants, cytotoxic agents, cytosine modulators or receptor antagonist, fluvoxamine or daily use of sildenafil.
• Patients who not accept sign the informed consent