Inherited disorders: Cystic fibrosis

Last updated: Tuesday, September 07, 2021

Cystic fibrosis (CF) is a disorder usually diagnosed at birth through newborn screening programmes. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene result in faulty production of the CFTR protein. This protein regulates the movement of chloride and bicarbonate ions and water across membranes. This means that secretions in certain parts of the body such as the lungs, pancreas and gut, become very thick and are difficult to clear. 

Life expectancy for people with CF has gradually been increasing with interventions such as physiotherapy and long-term antimicrobial prophylaxis. However the recent introduction of medicines that restore CFTR function (‘CFTR modulators’) has significantly improved the quality of life and health outcomes for some patients with CF.

Chronic respiratory complications

In patients with CF, mucous accumulates in the lungs which become infected by bacteria (most commonly Pseudomonas aeruginosa). Recurrent, intermittent infections occur and can become chronic, which may accelerate a decline in respiratory function. Most people who die of CF each year are young adults, and this is typically due to lung-related causes. Preventing chronic chest infection is a therefore key element in increasing survival. Airways clearance techniques such as physiotherapy help to reverse the build-up of mucous, and medicines such as inhaled dornase alfa or hypertonic saline reduce the viscosity of lung secretions. Acute infections are treated with inhaled antibiotics such as tobramycin or colistimethate sodium, and oral azithromycin has been given as a long-term oral prophylaxis.

Other complications

Damage to the pancreas results in its digestive enzymes not reaching the bowel in sufficient quantity, and this can give rise to malnutrition. In children this dietary deficiency can affect growth. Patients with CF take pancreatic enzyme supplements orally (pancreatin), and also need nutritional supplements to boost their calorific intake and to ensure they receive adequate fat-soluble vitamins. Some patients suffer from liver impairment, and older patients with CF can develop diabetes because of ongoing damage to the pancreas which may need to be treated pharmacologically.

Medicines optimisation

Patients with CF may handle medicines differently, but it's difficult to make generalisations. The absorption of medicines may be altered because of the effects that CF has on the gut. Some people need higher doses of medicines or more frequent dosing because CF may enhance drug clearance. At the same time, patients may be smaller than expected for their age and thinner, and generally have little body fat, and this affects volume of distribution. Many patients with CF are children and the special care with which medicines are generally used in this age group is discussed in the children tutorial.

Patients with CF may need medicines that are not commonly used in other patient groups, and so pharmacists have a particular role to ensure that prescribed regimens are safe and correct. The medicines concerned may be unlicensed, given via an unlicensed route, or be taken at larger than expected doses. 

Specialist cystic fibrosis pharmacists are experts at medicines optimisation in this group of patients, so you should try to contact one for advice before making a significant intervention.