Rationale for use of azithromycin in neonates

Another potential drug, azithromycin, has anti-infective action against microbes including Ureaplasma in older age groups and also has potent anti-inflammatory actions utilised in many conditions including respiratory diseases such as cystic fibrosis.21,–,23 Azithromycin is actively concentrated within alveolar macrophages and thus is attractive to treat pulmonary conditions.24 If Ureaplasma colonisation is on the causal pathway to the development of CLD, then azithromycin may reduce the incidence of CLD in combination with its anti-inflammatory effects.

Proof-of-mechanism for azithromycin as a treatment for Ureaplasma in the newborn is suggested by work such as that of Sadowsky who injected U parvum into the amniotic fluid of a rhesus monkey.25 Azithromycin was administered to mothers at a dose of 12.5 mg/kg/12 hourly for 10 days. It eradicated the Ureaplasma from the amniotic fluid with significantly decreased pneumonitis.25 However, macrolides in pregnant women have not shown an alteration in maternal outcomes.26 27 Antenatal exposure to erythromycin close to birth improved some neonatal outcomes in the ORACLE trial.28 29 Antenatal exposure to azithromycin in the second trimester was not associated with any differences in outcomes in the APPLE trial.30 Postnatal azithromycin needs further evaluation in an adequately powered clinical trial.

Since pulmonary inflammation is thought to play an important role in the development of CLD and azithromycin is thought to modify inflammation, Ballard et al performed a pilot double-blind, randomised, placebo controlled trial which specifically excluded neonates colonised by Ureaplasma.31 Infants (birth weight ≤1000 g) were randomised to treatment or placebo within 12 h of beginning intermittent mandatory ventilation and within 72 h of birth. The treatment group received azithromycin 10 mg/kg/day for 7 days followed by 5 mg/kg/day until the infant no longer required mechanical ventilation or supplemental oxygen, to a maximum of 6 weeks. Mortality, incidence of CLD and other morbidities were not significantly different between groups. Postnatal steroid use was significantly less in the treatment group (31%, 6/19) versus the placebo group (62%, 10/16) (p=0.05) as was the duration of mechanical ventilation (median 13 days (range 1–47 days) vs 35 days (range 1–112 days)) (p=0.02). Importantly, the study did not report any significant adverse effects of the use of azithromycin for up to 6 weeks. In a subsequent study, Ballard and colleagues randomised 211 neonates with birth weight <1250 g to azithromycin or placebo irrespective of colonisation status32 and reported an improvement in CLD rates in Ureaplasma colonised infants with wide confidence intervals. Ballard's work indicates that azithromycin may affect surrogate outcomes, provides proof-of-concept for the anti-inflammatory effects of azithromycin in preterm neonates and demonstrates the tolerability of azithromycin in the target population.31 This extends the proof-of-concept to a group comprising Ureaplasma colonised and non-colonised neonates.

Clearly, at least one sufficiently powered randomised controlled trial is needed to address the role of azithromycin in preterm neonates and would have support from the neonatal community.33 However, before a large randomised controlled trial can be conducted, a number of decisions need to be taken so that a large trial has the best chance of giving a clear answer.

Which formulation should be used?

The development of an age-appropriate formulation is central to the paediatric investigation plans introduced under the EU regulation. The plans are guided by a reflection paper: Formulations of Choice for the Paediatric Population.34 To ensure an appropriate formulation, it is necessary to consider excipients, the optimal concentration of the formulation, the required characteristics of infusions pumps and procedures according to the concentration of the formulation and the local tolerance and toxicity of the presentation.

What is the role of animal work in the development plan?

Animal work, often labelled as preclinical work, needs to be considered for drug licensing in the EU.35 Preclinical testing of drugs for paediatric indications is likely to focus on developmental toxicity and short- and long-term safety. This is different from studies designed to elucidate the mechanism and test proof-of-concept.24 25 The tests performed often include physiological tests, psychomotor development, learning and memory, and a dose ranging pilot study. However, these may not be required for azithromycin as it is already on the market.

Which dosage regimen?

A wrong dose will not work! Before use in any trials, it is essential to establish an appropriate dose. Pharmacokinetics (PK; ie, how the body handles the drug) specifically for neonates are essential.36 The value of examining drug disposition in neonates is illustrated by a recent report of PK in neonates of metronidazole which found that differences in clearance according to GA indicated that different optimal dosage regimens are required at different GAs.37

With respect to azithromycin, there are two steps to consider: delivery and efficacy. Delivery will depend on a similar time–concentration curve as in older age groups. This is summarised by the area under the time–concentration curve (AUC). For children aged 0.5–16 years, the AUC did not differ with age for a single dose of 10 mg/kg.38 In contrast, the pilot PK data which are available in extremely preterm neonates, suggest that the AUC is markedly greater than in older age groups. This reflects the less extensive clearance of azithromycin and also a smaller volume of distribution.39 The net effect of these effects can only be determined empirically.

In refining the PK model before a large trial, a balance must be struck between safety and benefit. Under the European regulation, the European Medicines Agency (EMEA) has set up a Paediatric Committee to balance the scientific and patient welfare issues in paediatric drug development.

Should we treat infection or inflammation?

Azithromycin has both anti-infective and anti-inflammatory effects. If a trial is chosen to effect both actions, then duration of treatment needs to be optimised to cover both. The data available to inform this decision are:

1. Pulmonary inflammation is present early in life and does not settle within 3–7 days of age.40 41

2. Most previous studies using macrolides to eradicate Ureaplasma have used 7–14 days of treatment. Ballard's trials continued azithromycin therapy for up to 6 weeks.31 32

3. Hassan et al found that a single dose of 10 mg/kg of azithromycin did not affect inflammatory markers.39

4. Prolonged antibiotic exposure is likely to have adverse consequences.

Many clinicians would find it difficult to justify continuing antibiotics for the length of time used by Ballard et al because of the risk of selecting for resistant strains and of potential adverse effects. Caution is advised by the retrospective cohort study of 5693 neonates born at less than 1000 g42 which showed that increasing duration of empiric antibiotics, started within 3 days of birth among babies with negative blood cultures, was associated with increasing risk of necrotising enterocolitis and death.

What inclusion criteria should we use?

It is important to include preterm infants at high risk of developing CLD, particularly those who are receiving respiratory support at birth. It is difficult to recruit immediately after birth. Inclusion of infants at highest risk of developing CLD, that is, with a GA of 28 weeks or less, receiving respiratory support within 12 h of birth and recruited within 48 h of birth (with first dose administered within 72 h of birth) would seem reasonable. Those infants who may develop respiratory disease due to underlying conditions such as congenital, surgical or cardiac anomalies may be reasonably excluded.

Which microbiological assessments should be done?

It would be crucial to account for pulmonary colonisation by Ureaplasma among the secondary, explanatory outcomes. A nasogastric tube is almost always inserted within the first few hours of age in such babies and thus provides an ideal sample to reflect the antenatal environment, with tracheal or nasopharyngeal aspirates for reflection of the postnatal environment.43 44 This should permit secondary analysis of the effect of colonisation status on outcome and identify the prevalence of Ureaplasma antibiotic resistance.45 46 Follow-up sampling to test for treatment cure is essential but may be limited by sample availability. Standard practice for test-of-cure is to examine whether the antimicrobial has been effective three half-lives after treatment stops.

Which end points?

Any chosen end points should have clinical relevance, should be reproducible and include both respiratory and non-respiratory secondary end points. One option is to use a combined outcome (death or CLD), another option is to use a single outcome (CLD) and use survival analysis to adjust for death. Death may be unrelated to CLD, so that a combined outcome may underestimate the difference that is due to the trial medication. On the other hand, death may be related to CLD, in which case a composite outcome would be a conservative approach. Secondary end points should include length of oxygen dependency, hospital stay and respiratory support with intubated or non-invasive mechanical ventilation (including continuous positive airway pressure), drug usage including postnatal corticosteroids and antibiotics, infection rates, intraventricular haemorrhage, necrotising enterocolitis and retinopathy of prematurity. For the diagnosis of CLD, it is important to use a standardised physiological end point, as recommended by the National Institutes of Health consensus47 or a physiological test.48 49

It is important to follow-up after discharge. CLD at 36 weeks is an important outcome that reflects hospital costs and predicts subsequent events, so it is a reasonable outcome to use to assess efficacy. Outcomes to 2 years, for example, are important to assess safety and provide preliminary evidence of effectiveness.

What should the sample size be for large clinical trials?

Issues to consider include rates of CLD/death. It may be advantageous to take account of the proportion of participants who have Ureaplasma colonisation but may not be available within the treatment window. The effect of colonisation may best be considered as a prespecified secondary analysis. Uncertainties in sample size often remain. As an estimate, between 650 and 700 preterm infants of 28 weeks or less gestation are likely to be required in an adequately powered randomised controlled trial, which clearly may need modification when colonisation by pulmonary Ureaplasma is factored into the calculations. Prior to protocol finalisation, sample size and power can be modelled in light of the PK study, a feasibility survey among participating centres and the available literature. A range of analyses is required. The fundamental interpretation of trials for superiority should be based on an intention-to-treat analysis. This evaluation will need to be supplemented by per protocol analyses and analyses of microbiologically evaluable participants.

How should safety be assessed?

Safety assessments are central to drug development. The choice of safety assessments and their timing should be based on risk assessment which includes the known safety issues with azithromycin and the characteristics of the target population (comorbidity is high among babies born at less than 29 weeks gestation and should not be ascribed to azithromycin unless there is clear evidence of this).

Should we aim for a marketing authorisation?

A marketing authorisation provides assurance that pharmaceutical quality, safety and efficacy have been assessed by independent experts, and dosage and interactions considered. Conventional peer review is not sufficient to meet these needs.50 Marketing authorisation holders have a range of duties to monitor the usage of each authorised medicine and maintain standards, including postmarketing surveillance. In the absence of a marketing authorisation, a range of individual prescribers each has responsibility for off-label use, which would make it very difficult to develop and maintain a safety registry; pharmacists carry out a lot of work behind the scenes to support off-label medicines. A marketing authorisation provides an income stream that increases the justification for manufacturers to invest in a medicine and provides protection for that investment. If the market is large enough, a marketing authorisation will be the optimal way for neonatal drug development in the future.

Drug development costs

The costs of developing a drug for use in children are significant. The majority of the costs incurred in clinical drug development relate to management of clinical trials and to data collection in clinical trials. Estimates of the costs to address a ‘written request’ leading to changes in the marketing authorisation relating to children by the American Food and Drugs Administration vary between US$5.3 million for a programme involving a single trial of efficacy in 151 children with refractory tumours and US$50 million for a programme involving two PK studies, seven efficacy studies and 926 children with depression.51 Azithromycin to prevent CLD by treating Ureaplasma was placed on the EMEA's list of priority off-patent medicines and the authors have successfully secured funds from the European Commission's Framework Programme 7.

What should the drug development plan look like?

One approach is illustrated in figure 1. This represents a balance between timely research and filling in gaps in knowledge.

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Figure 1

Sample drug development plan. DSMB, data and safety monitoring board; PD, pharmacodynamics; PK, pharmacokinetics; SUSAR suspected unexpected serious adverse reaction.