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Genetics of cystic fibrosis
- Most common in Caucasian population
- Most common mutation is deltaF508
- Autosomal recessive trait (if both parents are carriers, 25% chance of child not having the gene, 25% chance of child having the disease, 50% chance of child being carrier)
Pathophysiology of cystic fibrosis
Defect in CFTR chloride channel results in decreased chloride secretion and increased sodium absorption (decr H20 secretion) - leads to altered viscosity of fluid excreted by exocrine glands and mucosal obstruction
Common clinical manifestations of CF
- Resp system: airway obstruction, chronic airway colonization/infx, chronic cough/sputum production, acute exacerbations, decreased exercise tolerance, digital clubbing, barrel chest, sinusitis
- GI system: pancreatic insufficiency leading to malabsorption and maldigestion, failure to thrive, vitamin deficiencies, recurrent pancreatitis, meconium ileus, distal intestinal obstruction syndrome, hepatobiliary disease, hypoproteinemia, CF related diabetes
- Salt loss thru salty sweat
- Late maturation - delayed puberty
- menstrual irregularities
Treatment strategies for respiratory problems in CF
- Airway clearance - chest physiotherapy, high-frequency chest compression vest QD to BID
- Mucolytics (Dornase alfa, hypertonic saline for inhalation pretreated with bronchodilator, N-acetylcysteine)
- LABA in pts with wheezing/dyspnea who benefit from albuterol
- Montelukast, antihistamines, intranasal steroids in pts with reactive airways or rhinitis
- PO corticosteroids NOT recommended for maintenance
- Antiinflammatory treatment - Azithromycin (3d/wk), high-dose ibuprofen, inhaled corticosteroid
Treatment strategies for GI problems in CF
- Pancreatic enzyme replacement -
- decr stool freq, incr stool quality, weight gain
- contains lipase, amylase, protease
- Enteric coated - capsules can be opened and mixed with acidic foods (but not in bottles)
- Infants - can mix with applesauce or rice cereal and give milk after - make sure no particles are left in mouth after - can cause ulcers
- Generics have dissolution probs - don't use
- Different brands are not bioequiv
- 1500-2000 units lipase/120 ml milk or 500-1000 units lipase/kg/meal
- Fat soluble vitamin supplementation
- Appetite stimulants
- Ursodiol to slow progression of liver disease
- PEG (miralax) for distal intestinal obstruction syndrome
Which antibiotics may be desirable to use in a CF pt with known P. aeruginosa colonization for respiratory exacerbation?
- Oral or IV Fluoroquinolones (cipro or levofloxacin) - good for outpt treatment of mild resp exacerbation - not good for long-term d/t resistance which happens quickly with FQ monotx
- IV antipseudomonal beta-lactams (piperacillin, pip/tazo, ceftazidime, cefepime, imipenem, meropenem, aztreonam)
- IV aminoglycosides (tobramycin, gentamicin, amikacin)
- Combos for more severe exacerbations - IV antipseudomonal beta lactam plus IV AG (e.g. ceftazidime + tobramycin) - combos promote less resistance and may provide synergy
What antibiotic is used in CF for anti-inflammatory treatment and how is it used?
Azithromycin - taken 3x/wk
What inhaled antimicrobial is used chronically in CF and why?
- tobramycin - it can suppress bacterial overgrowth of P. aeruginosa
- Used on a 28d on/28d off schedule
- leads to improved lung fxn, reduced microbes in sputum and fewer hospitalizations for IV abx
Inhaled aztreonam was recently approved for pts > or = 7 yoa (given tid)
What abx are used in CF pts for S. aureus?
- 1st or 2nd gen cephs
What antibiotics are used to treat H. influenzae infx in CF pts?
What antibiotics are used to treat S. maltophilia in CF pts?
What pharmacokinetic considerations are important to take into account with CF patients?
CF pts have higher volumes of distribution and enhanced total body clearance of many abx to use higher doses more frequently