# Drugs for Cystic Fibrosis

> Cystic fibrosis drugs in MBBS Pharmacology: CFTR modulators, ivacaftor, elexacaftor, dornase alfa, hypertonic saline, pancrelipase and inhaled antibiotics.

- Canonical URL: https://prepelephant.com/topics/mbbs/pharmacology/drugs-cystic-fibrosis
- Exam / course: MBBS · Subject: Pharmacology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Drugs for Cystic Fibrosis", PrepElephant, https://prepelephant.com/topics/mbbs/pharmacology/drugs-cystic-fibrosis

## Direct answer

Cystic fibrosis pharmacology now runs on two pillars: CFTR modulators that repair the defective channel (ivacaftor the potentiator for gating mutations such as G551D, and elexacaftor-tezacaftor-ivacaftor, the triple combination transformative for F508del), and a lifelong airway-and-nutrition stack — dornase alfa to cleave extracellular DNA in sputum, hypertonic saline to hydrate mucus, inhaled tobramycin or aztreonam for Pseudomonas eradication, chronic azithromycin as an anti-inflammatory, and pancreatic enzyme replacement with fat-soluble vitamins. Indian practice leans heavily on the second pillar because modulator access is limited by cost and import, so the exam answer and the government-clinic answer still diverge.

## What you must remember

- **Ivacaftor:** CFTR potentiator holding the channel open longer; indicated for gating mutations class III (classic question: G551D), 150 mg twice daily with fat-containing food.
- **Correctors:** lumacaftor and tezacaftor improve F508del protein folding (class II processing defect); tezacaftor has fewer drug interactions and less chest tightness than lumacaftor.
- **Triple therapy:** elexacaftor-tezacaftor-ivacaftor, licensed for F508del (homozygous, and heterozygous with a second mutation), improved percent-predicted FEV1 by about 10 points and sweat chloride dramatically in trials — the benchmark result worth quoting.
- **Dornase alfa:** recombinant human DNase nebulised once daily; cleaves neutrophil-derived free DNA and lowers sputum viscosity; does nothing for mucin itself.
- **Hypertonic saline:** 3% to 7% nebulised (premedicate with a bronchodilator) draws water into mucus by osmosis and improves mucus clearance; cheap and fully available in India.
- **Inhaled antibiotics:** tobramycin inhalation solution 300 mg twice daily in alternating 28-day cycles, or inhaled aztreonam, for chronic Pseudomonas colonisation — inhaled delivery achieves high sputum levels with low systemic toxicity.
- **Azithromycin:** 250-500 mg thrice weekly as immunomodulatory maintenance in colonised patients, not for bacterial killing alone.
- **Nutrition:** pancrelipase (lipase 500-2,500 units/kg per meal for children, titrated) with every feed plus vitamins A, D, E and K; enzyme dose creeping upward suggests blocked bowel or non-adherence, not just disease progression.

## A diagnosis-to-prescription walk-through

Picture a 3-year-old with recurrent pneumonia, failure to thrive and a sweat chloride of 96 mmol/L, genotype F508del homozygous. Day one of treatment is not a modulator — it is airway clearance taught to the mother, dornase alfa after the morning physiotherapy session, and hypertonic saline before it. Pancreatic insufficiency is assumed with F508del: pancrelipase split across meals and snacks (half at the start, half mid-meal is one accepted pattern), fat-soluble vitamin supplementation, and salt replacement in Indian summers because cystic fibrosis children lose salt profusely in sweat. Sputum or cough swab surveillance follows quarterly; the first Pseudomonas growth triggers eradication with inhaled tobramycin or colistin plus an oral fluoroquinolone course, because delaying chronic colonisation preserves lung function. Only then does the counsellor discuss elexacaftor-tezacaftor-ivacaftor — effective for her genotype, but in India accessed largely through import at high cost or compassionate programmes; monthly monitoring of liver enzymes and an eye check for cataract (reported in children on modulators) is the follow-up routine taught in specialist centres.

## How the exam frames it

Questions rarely ask for a dose; they ask for mechanism-to-mutation matching. Know the classes: class I stops codons (no protein — eligible for read-through agents like ataluren in research), class II F508del misfolding (correctors plus potentiator), class III gating (potentiator alone), class IV conduction (variable modulator response). The examiner's trap is calling ivacaftor a "corrector" — it is strictly a potentiator, and giving it alone to F508del patients does little because little protein reaches the surface. A second trap is dornase alfa versus N-acetylcysteine: NAC cleaves disulphide bonds in mucus glycoproteins and has disappointed in cystic fibrosis, while dornase alfa targets DNA — free DNA from dead neutrophils is what makes cystic fibrosis sputum viscoelastic. Quote that sentence in a viva and the marks follow.

## Frequently asked questions

### Which CFTR mutation responds to ivacaftor alone?

Gating mutations such as G551D — ivacaftor potentiates channels already at the surface, so class III defects respond without a corrector.

### Why does dornase alfa specifically help cystic fibrosis sputum?

Cystic fibrosis airways are neutrophil-rich; free DNA from degenerating neutrophils is the major viscosity driver, and recombinant DNase cleaves it.

### Which combination is indicated for F508del homozygous patients?

Elexacaftor-tezacaftor-ivacaftor (triple therapy) is the current standard, replacing lumacaftor-ivacaftor on efficacy and tolerability.

### Why are antibiotics inhaled rather than oral in colonised patients?

### Are CFTR modulators freely available in India?

Access remains limited — largely imported, costly, and used in select centres or via compassionate-access programmes; airway and nutritional therapy remains the universal backbone, per current Indian practice.