Increasing dose regimen in children with reactions to ceftazidime

Mechanism for acute oral desensitization to antibiotics

BACKGROUND

Despite the widespread use of an acute oral desensitization procedure in patients with allergic reactions to a variety of antibiotics, the precise mechanism of this procedure is poorly understood.

OBJECTIVE

To investigate the mechanisms underlying acute oral desensitization to antibiotics.

METHODS

Using a murine model of active systemic anaphylaxis to penicillin V (Pen V), mice previously sensitized to Pen V were desensitized by oral feeding of Pen V. The dose was doubled every 15 min and five feedings were given. The achievement of acute oral desensitization was evaluated by induction of active systemic and active cutaneous anaphylaxis, and by measuring the plasma levels of platelet-activating factor and histamine. Antigen-specific serum IgE antibody (Ab) levels were determined by passive cutaneous anaphylaxis.

RESULTS

Mice fed more than 3 mg of cumulative dose of Pen V were completely protected from fatal systemic anaphylactic reaction and the desensitized state lasted approximately 1 h. Antigen-specific mast cell desensitization, but not hapten inhibition, consumption of IgE Abs, or depletion of mast cell mediators, occurred during acute oral desensitization.

CONCLUSIONS

Acute oral desensitization to Pen V occurred in the mice, and antigen-specific mast cell desensitization was associated with the underlying mechanism for oral desensitization.

The treatment of respiratory pseudomonas infection in cystic fibrosis: what drug and which way?

Pseudomonas aeruginosa is a non-capsulate and non-sporing gram-negative bacillus that most commonly affects the lower respiratory system in humans. Burkholderia (previously Pseudomonas) cepacia has emerged as an important respiratory pathogen in patients with cystic fibrosis (CF). The ability of P. aeruginosa to persist and multiply in moist environments and equipment, such as humidifiers in hospital wards, bathrooms, sinks and kitchens, maybe of importance in cross-infection. P. aeruginosa infections of the lower respiratory tract can range in severity from colonisation (without an immunological response) to a severe necrotising bronchopneumonia. Infection is seen in patients with CF and other chronic lung diseases such as non-CF bronchiectasis. In patients with CF, once P. aeruginosa is established in the airways it is almost impossible to eradicate, but prior to this, aggressive treatment can delay the development of chronic infection. 30 to 40% of the present paediatric population with CF will have chronic pseudomonal infection. B. cepacia has a particular predisposition to infect patients with CF and may be distinguished from P. aeruginosa by accelerated lung disease in about one- third of patients. Overwhelming septicaemia and necrotising pneumonia are well described (cepacia syndrome); events that are rare with P. aeruginosa. With the propensity for social cross-infection, segregation policies have been accepted as means of controlling outbreaks. A number of antipseudomonal agents are available. The most commonly used are the extended-spectrum penicillins, aminoglycosides, cephalosporins, fluoroquinolones, polymixins and the monobactams. An aminoglycoside with a beta-lactam penicillin is usually considered to be the first line treatment. No trial has shown any significant clinical advantage of any particular combination regimen over another. The emergence of resistance continues to be a concern. Pipericillin, piperacillin/tazobactam and meropenem have good but equivalent antibacterial activity against P. aeruginosa. However, B. cepacia is characterised by in vitro resistance to colistin (colomycin), aminoglycosides and ciprofloxacin but better susceptibility to ceftazidime. Nebulised delivery of antipseudomonal antibiotics is thought to prevent recurrent exacerbations, reduce antibiotic usage and maintain lung function, particularly in patients with CF. Colistin, tobramycin and gentamicin are currently the most commonly prescribed nebulised antibiotics. Much effort is directed at treating chronic P. aeruginosa infection but as chronic infection is seldom if ever eradicated when first established, prevention is preferable. Early intensive treatment for P. aeruginosa infection is advocated in order to maintain pulmonary function and postpone the onset of chronic P. aeruginosa infection.

Home intravenous antibiotic therapy: practical aspects in children

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