Pediatric Drug Formulations

ABSTRACT
Children differ from adults in many aspects of pharmacotherapy, including
capabilities for drug administration, medicine-related toxicity, and taste
preferences. It is essential that pediatric medicines are formulated to best suit a
child’s age, size, physiologic condition, and treatment requirements. To ensure
adequate treatment of all children, different routes of administration, dosage
forms, and strengths may be required. Many existing formulations are not
suitable for children, which often leads to off-label and unlicensed use of adult
medicines. New regulations, additional funding opportunities, and innovative
collaborative research initiatives have resulted in some recent progress in the
development of pediatric formulations. These advances include a paradigm shift
toward oral solid formulations and a focus on novel preparations, including
flexible, dispersible, and multiparticulate oral solid dosage forms. Such
developments have enabled greater dose flexibility, easier administration, and
better acceptance of drug formulations in children. However, new pediatric
formulations address only a small part of all therapeutic needs in children;
moreover, they are not always available. Five key issues need to be addressed to
stimulate the further development of better medicines for children: (1) the
continued prioritization of unmet formulation needs, particularly drug delivery
in neonates and treatment gaps in pediatric cancers and childhood diseases in
developing countries; (2) a better use of existing data to facilitate pediatric
formulation development; (3) innovative technologies in adults that can be used
to develop new pediatric formulations; (4) clinical feedback and practice-based
evidence on the impact of novel formulations; and (5) improved access to new
pediatric formulations.
Abbreviation:
WHO — World Health Organization
Drug formulations used in pediatric pharmacotherapy should be adapted to children’s
needs to suit their age, size, physiologic condition, and treatment requirements.1,2
Such pediatric medicines are key to achieving safe and accurate dose administration,
reducing the risk of medication errors, enhancing medication adherence, and
improving therapeutic outcomes in children.3,4
The use of inadequate drug formulations in children may pose problems not seen in
adults, such as difficulty in swallowing conventionally sized tablets, safety issues
with certain excipients that are acceptable in adult formulations, and adherence
problems with unpalatable medicines.1,5 These issues have led to tragedies in the
past, and they exist partly because only a small fraction of all marketed drugs are
available in formulations that are age appropriate.6–12 As a result, many adult
medicines are used off-label in children, a practice that carries additional health and
environmental risks.13–15
To strengthen the development of pediatric drug formulations, new legislation was
introduced in the United States and Europe, and efforts for global collaboration were
made by the World Health Organization (WHO).16–20 A number of innovative
pediatric formulations have followed, but their actual effect on pediatric drug
approvals remains to be seen, as clinical trials and marketing authorization take a
substantial amount of time.21–24
To optimize pharmacotherapy in children, it is important for clinicians to understand
the background of the aforementioned problems as well as to gain insight into the
challenges, developments, and potential solutions. The aim of the present review was
to describe why there is a specific need for pediatric drug formulations and to
illustrate the clinical consequences of the absence of suitable medicines for children.
We will discuss the progress achieved so far and determine additional steps required
to improve the development and availability of pediatric drug formulations.

THE NECESSITY OF PEDIATRIC DRUG FORMULATIONS

Diversity in Children
It has been well established that children are not small adults but rather a distinct and
heterogeneous patient group with regard to pharmacotherapy.25 They often exhibit a
different response to both active substance and excipients.26 Children present a
continuum of growth and developmental phases as a result of their rapid growth,
maturation of the body composition, and physiologic and cognitive changes during
childhood.
Children differ from adults in many aspects of pharmacokinetics and
pharmacodynamics, potential routes of administration, medicine-related toxicity, and
taste preferences.3,25 Important pharmacokinetic differences between children and
adults include the rate of gastric emptying and pH, gastrointestinal permeability, and
the surface area available for drug absorption. Dissimilarities have also been reported
in drug metabolism, transporter expression, biliary function, and renal clearance,
resulting in differences in drug disposition and elimination.27,28 The largest deviation
from adult pharmacokinetics is observed in the first 12 to 18 months, when organ
functions are developing.29,30 In older children and adolescents, the pharmacokinetic
parameters approach adult values and are thus easier to predict.26,31–33 The effect of
age on pharmacokinetics leads to different dosing requirements for different age
groups. From birth to adulthood, the body size and weight of an average child
increases up to 20-fold, and the magnitude of dose variation administered throughout
childhood may be 100-fold.5 More dramatically, premature neonates admitted to the
hospital can weigh as little as 500 g, further highlighting the need for dose
variability.29,30 Maturation processes in children are not linear, and therefore doses in
certain age subsets may be lower, identical to, or higher than in adults, depending on
a drug’s metabolic pathway.32,34,35
Due to this extensive variability in children, there is an obvious need for drug
formulations tailored to children in all the target age groups. The International
Conference of Harmonisation divides childhood into 5 age groups related to the
developmental stages, derived from the physiologic and pharmacokinetic differences
mentioned earlier.28 These groups (with age ranges) are: preterm newborn infants;
term newborn infants (0–27 days); infants and toddlers (1–23 months); children (2–
11 years); and adolescents (12–16 years in the United States or 12–18 years in the
European Union).5,36
The European Committee for Medicinal Products for Human Use further subdivides
the age group “children” (2–11 years) into “preschool children” (2–5 years), and
“school children” (6–11 years) to more precisely reflect the children’s ability to
accept and use different dosage forms.5 However, the classification of the pediatric
population into age categories is to some extent arbitrary because children of the
same chronologic age may still develop at different rates.28
Age-Related Adherence to Pediatric Drug Formulations
Formulation acceptability and preferences facilitate medication adherence in
children, and they are important factors in achieving the intended treatment
outcomes. Formulation acceptability differs across age groups as children gradually
develop their cognitive and motor skills, and improve their ability to swallow
medications. At certain ages, the dependence on caregivers also plays a role in the
administration of pediatric dosage forms.1 Pain, discomfort, and an unnecessary
burden on children and/or caregivers during drug administration should be
minimized to assure adequate medication adherence. In older children and
adolescents, lifestyle and peer pressure may also influence medication adherence and
possible preferences for particular formulations.
Taste attributes may be critical to ensure acceptable adherence to pediatric oral
formulations. Because children have a low tolerance for disagreeable taste, the use of
tasteless or palatable medicines can minimize the loss of medication from spillage
and/or spitting.14,37,38 Taste preferences may differ between children and adults, as
children prefer sweet and salty flavors, and dislike bitter and peppermint taste. These
findings suggest that taste assessment should involve children early in the drug
formulation development.35,38,39 Children’s communication about taste perceptions
can be facilitated by using age-appropriate methods, scales, and measures.40
Alternative taste-screening methods may include adult taste panels with validated
design for data transferability or predictive electrochemical sensor systems (so called
“electronic tongues”).41,42
CLINICAL CONSEQUENCES OF THE ABSENCE OF SUITABLE PEDIATRIC DRUG
FORMULATIONS
Potential Limitations of Pediatric Drug Formulations
Historically, the failure to appreciate the developmental changes in children has led
to many adverse outcomes in clinical practice. Examples include infant deaths from
choking on albendazole tablets, the lethal use of benzyl alcohol or diethylene glycol
in sulfanilamide elixirs, and electrolyte imbalances caused by high contents of
sodium or potassium in parenteral formulations.6–9
To prevent such tragedies and ensure adequate treatment of children of all ages,
different routes of administration, dosage forms, and strengths are often needed for
the same active substance.1 Table 1 illustrates the specific purposes, potential
strengths, and weaknesses of various routes of administration and dosage forms for
pediatric use.1,2,5,43–47 As in adults, the oral route is the predominant route of
administration in children.1,2,43 Alternative nonoral routes of administration include
rectal, dermal, nasal, pulmonary, and ocular routes.1,2

[TABLE 1]
Potential Clinical Advantages and Disadvantages of Different Formulations and
Routes of Administration in Children1,2,5,43–47
The selection for clinical use is influenced by the limitations of each dosage form.
Oral solids are associated with the risk of choking or chewing and with limited dose
flexibility, whereas palatability and dose uniformity may be challenging for liquid
preparations.1,2,43,44 In addition, liquid forms raise issues regarding stability
(chemical, physical, or microbiological) and the requirement for clean water;
moreover, they can be bulky, impractical, and expensive to ship and store,
particularly in lower income countries with hot and humid climates.48,49
The use of nonoral routes of drug administration may be hampered by difficult
application, local irritation, fluid overload, electrolyte imbalance, or poor drug
acceptability (Table 1).1,2,5,43–47 In neonates, intravenous administration may lead to
volume overload. Moreover, measuring small dose volumes may cause large dosage
variations and errors.47 Similarly, age-appropriate dosing volumes are important to
ensure full dose ingestion for oral liquids.5
Another important concern in pediatric drug formulations are the excipients,
frequently used as preservatives, sweeteners, fillers, solvents, and coating and
coloring agents. Their selection for pediatric medicines is challenging because
neither the inactive ingredients guide list of the US Food and Drug Administration
nor the “generally regarded as safe” status has been validated for pediatric
use.3,29,30,50 Little is known about the safety of excipients in children, and accepted
daily and cumulative intakes of excipients have not been established. Anecdotal
evidence suggests an association between some excipients commonly used in adult
medicines and elevated toxicity and safety issues in children, especially neonates
(Table 2).3,6–9,26,50–60 A recent example is the administration of lopinavir/ritonavir
(Kaletra [Abbott Laboratories, Abbott Park, IL]) oral solution in premature newborns
who were exposed to the risk of ethanol and/or propylene glycol toxicity. This
situation resulted in a Food and Drug Administration drug safety communication and
a change in the drug label in 2011.61 A number of recent studies in NICUs revealed
systemic concentrations of excipients that were intolerable even in older age
groups.54,62,63
[TABLE 2]
Examples of Excipients With Elevated Toxicity and Safety Risks for (Preterm and
Term) Newborns and Infants <6 Months of Age7,8,53–60
The urgent need to understand these safety concerns has led to a collaborative effort
by the United States and the European Union to create a STEP (Safety and Toxicity
of Excipients for Pediatrics) database. Its aim is to improve systematic data
collection on excipient toxicity and tolerance in children.64–66 A similar initiative,
ESNEE (European Study of Neonatal Exposure to Excipients), has developed a
platform for the systematic assessment of excipients in neonates.67
Concerns Over Off-label and Unlicensed Use of Medicines in Children
Pediatric drug development is associated with numerous challenges, including
methodologic and ethical requirements for pediatric trials, high developmental costs,
and a small and fragmented market.3,4,50,68–71 As a result of these challenges, there
have only been limited research efforts to adapt medicines according to pediatric
needs. Thus, only one-third of all medicines approved by the European Medicines
Agency over the period of 1995 to 2005 were licensed for use in children.11,23,72
Higher but still unsatisfactory rates were reported in New Zealand (35%), Australia
(38%), and the United States (54%).23,73,74 The pediatric market has focused mostly
on only a limited number of therapeutic areas, such as antiinfectives, hormones, and
medicines for the respiratory and central nervous system.75 Meanwhile, there are
hardly any dermal preparations and medicines specifically aimed at younger age
groups for the cardiovascular system, sensory organs, and cancers.23 Moreover,
especially in younger children and neonates, even authorized pediatric medicines
may not always be age appropriate with respect to dosing, suitability of dosage
forms, and excipients.
This lack of pediatric formulations often leaves health care professionals no
alternative but to use adult medicines in an off-label or unlicensed manner. The trend
is widespread: in the European Union, 45% to 60% of all medicines are given to
children off-label. This trend is also true for 90% of medicines administered to
neonates and infants, particularly in PICUs.76 Not surprisingly, off-label use is
common for antiarrhythmics, antihypertensives, proton pump inhibitors, H2-receptor
antagonists, antiasthmatic agents, and some antidepressants.76 In the United States,
two-thirds of medicines used in pediatrics are off-label; worldwide, this proportion is
up to three-quarters.77
Risk Management of Compounding and Manipulation of Medicines for
Children
Alternative treatment options are often used to make unavailable drugs accessible for
children and/or to adjust drug doses according to individual patient needs. These
options include the modification of administration routes (eg, oral use of parenteral
formulations); manipulation of adult dosage forms (eg, diluting liquid formulations);
segmenting tablets and suppositories, cutting patches, and dispersing open capsules
or crushed tablets in water, liquid, or food; or extemporaneous dispensing (ie,
compounding medicines from ingredients within pharmacies).5,78
Administering medicines in this way is difficult and unsafe because limited data are
available to validate stability, bioavailability, pharmacokinetics, pharmacodynamics,
dosing accuracy, tolerability, and reproducibility.79–84 A documented example is the
crushing of Kaletra tablets for pediatric administration, which resulted in reduced
bioavailability and drug exposure in children.85 All these manipulations may
compromise drug efficacy and/or safety, as well as create risks for the environment
and individuals handling the dosage forms, particularly in the case of mutagen and
cytotoxic compounds.79–84
Producing a medicine by extemporaneous dispensing may be the only option for
some children to receive a certain medicine in a suitable dosage form. In such
situations, the risks can be reduced by applying sound quality assurance systems.
Pharmacists should ensure that good manufacturing principles are implemented,
adequate raw materials and formulae are used, and stability studies are validated and
conducted by certified laboratories. Moreover, because practices and guidelines for
extemporaneous formulations differ greatly among practitioners, there is an urgent
need for a standardization of commonly applied compounding practices.78,86 Existing
networks, resources, and guidelines should be stimulated to provide appropriate
information on the standards of practice for extemporaneous formulations.78,84
However, the available information may not always be easily transferable to a local
situation or may not be exclusively focused on children.87

PROGRESS IN DEVELOPING PEDIATRIC DRUG FORMULATIONS

New Frameworks for the Development of Pediatric Drug Formulations
To overcome the aforementioned challenges, a new pediatric regulatory environment
has been created to stimulate the development and availability of age-appropriate
medicines for children.16–19 The intended long-term aim is to integrate pediatric
needs into overall drug development, so that each new component is systematically
evaluated for its potential use in children. Initial progress has been made by
combining legal requirements with incentives for companies to test, authorize, and
formulate medicines for use in children. Over the past decade, the Best
Pharmaceuticals for Children Act and the Pediatric Research Equity Act in the
United States, and the Pediatric Regulation in the European Union, have fueled an
increasing number of pediatric clinical trials and innovations in pediatric drug
formulations.22,24
Nonetheless, therapeutic areas addressed by the industry seem to be more aligned
with adult drug development than with unmet public health needs in children.22,68,88,89
To guide the efforts toward significant therapeutic benefits for children, the US and
European Union government agencies have produced priority medicines lists,
highlighting areas with substantial off-label use in children and gaps in pediatric
data.90,91
Simultaneously, a WHO initiative (“Make Medicines Child Size”) has drawn
attention to the fact that the lack of medicines most acutely affects children living in
developing countries.20,92 A focus on the development of suitable dosage forms to
treat diseases of high burden in childhood in low-resource settings could greatly
reduce childhood morbidity and mortality.92 There have been comprehensive WHO
activities to improve access to and use of safe and appropriate pediatric medicines.
These activities include establishing a model list of essential medicines for children
and a list of priority life-saving medicines for women and children, developing
model formularies for children, updating childhood treatment recommendations, and
including pediatric medicines in the prequalification process.93–97
Furthermore, the present reward system has not proved to be an adequate incentive
for investment in off-patent drug research.69,89 This tendency may be linked to
prescription reimbursement rules that attach little value to old medicines, even if they
include new child-friendly formulations.69 To generate more interest in off-patent
medicines, new public funding opportunities in academia and small- and medium-
sized enterprises have been provided by both the US Eunice Kennedy Shriver
National Institute of Child Health and Human Development Pediatrics Formulation
Initiative and the EU's Seventh Framework Program for Research.98–100 However,
new technologies developed from these initiatives must be adopted by the industry
and marketed so they can realize their full potential.
There is also increased recognition that the selection of appropriate pediatric
formulations requires a risk/benefit analysis on a case-by-case basis.1,2 Taking into
consideration the heterogeneity of children and specific characteristics of each
dosage form (Table 1), the industry has recently proposed a composite assessment
tool to guide optimal formulation choices for individual patients.44 This structured
framework is based on 3 predetermined criteria for each drug formulation: product
efficacy and ease of use (eg, dose flexibility, drug acceptability, convenient handling,
correct use), patient safety (eg, bioavailability of active substances, safety of
excipients, medication stability, risk of medication errors) and patient access (eg,
product manufacturability, affordability, development, production speed).41 The
choice between alternatives is based on a quantitative scoring system for each
pharmaceutical formulation option.44 This individualized approach to optimal
formulations can also be replicated in clinical settings if the selection criteria include
relevant aspects of patient care.
Novel Oral Pediatric Formulations
Recent progress in pediatric drug development mostly concerns oral
formulations.22,101 Until recently, liquid formulations were preferred for younger
children because of their easy and simple dosing across age subgroups.5,10,102 In
2008, a WHO expert forum proposed a paradigm shift toward pediatric oral solids in
view of stability problems and the high transportation and storage costs involved in
liquid formulations.92 From then on, flexible oral solid dosage forms, such as
orodispersible tablets and/or tablets used to prepare oral liquid preparations suitable
for younger children, have become the recommended pediatric dosage forms
worldwide. In 2009, Coartem Dispersible (Novartis International AG, Basel,
Switzerland, and Medicines for Malaria) was launched to offer flexible artemisinin-
based combination therapy for children (5–35 kg) with a cure rate comparable to that
of the Coartem tablet.103,104
For oral medicines requiring precise dose measurement, a new flexible platform
technology was proposed to produce solid multiparticulate dosage forms (eg, mini-
tablets, pellets) and dosage forms dispersible in liquids or sprinkled on food.92 This
platform technology has the potential flexibility to construct fixed-dose combination
products, especially for chronic diseases such as HIV or tuberculosis.105–107 Table 3
illustrates some of the quality-certified, innovative oral pediatric dosage forms
brought to market, including much needed heat-stable formulations and fixed-dose
combination products for low-resource settings.97,104,108–116

[TABLE 3]
Examples of Recently Marketed/Prequalified Novel Oral Drug Formulations for
Children97,104,108–116
Current surveys reveal that novel oral solids may be used in children at an earlier age
than previously anticipated.5,117,118 Initially, in 2009, Thomson et al119 demonstrated
that 46% of 2-year-old children and 86% of 5-year-old children could swallow
innovative 3-mm mini-tablets without choking or aspiration. The age limit was
further decreased in an exploratory study which demonstrated that children aged 6 to
12 months were capable of swallowing uncoated, drug-free, 2-mm mini-tablets and
accepted them better than sweet liquid formulations.120,121 For infants aged <2 years,
a new promising development is the orally disintegrating mini-tablet, which
combines mini-tablets and fast-dissolving dosage forms.111
A complementary research area is the development of pediatric dosing devices,
which facilitate the accurate and consistent administration of oral pediatric
formulations.1,122 New devices generally assist the oral delivery of liquids to small
children by using modified feeding bottles and pacifiers with medicines placed in a
reservoir, help improve the palatability of oral solutions by using a dose-sipping
technology, or help increase product stability by using a pulp-spoon with a single dry
dose of medicine (see Table 4 for more detailed examples).3,116,122

[TABLE 4]

FUTURE STEPS
The ideal pediatric formulation should have flexible dosage increments and minimal
excipients, be palatable, safe and easy to administer, and be stable with regard to
light, humidity, and heat. Nevertheless, a significant number of drug formulations are
unsuitable for children, which leads to unsafe off-label and unlicensed use of adult
medicines. Recent initiatives promoting pediatric drug development have made some
initial progress in the neglected area of pediatric formulations. Most efforts have
focused on age-appropriate oral solid preparations, which enable dose flexibility,
easier administration, and better acceptance in children. Despite these advances, the
new pediatric formulations are still only a small part of the full therapeutic arsenal
needed to serve all pediatric patients.
The following 5 priorities have been identified as critical for the further development
of appropriate pediatric formulations. The first key issue is the continuous
prioritization process that focuses on unmet public health issues and ensures that
drug development aligns with the true clinical needs in children. Special attention
should be paid to innovations that improve drug delivery in neonates, fill treatment
gaps in pediatric cancers, and treat diseases of high burden in developing
countries.49,90,91,94,123
Second, better use of existing data are required to facilitate pediatric drug
development. Some innovative scenarios under investigation include preliminary
“enabling” formulations that bridge existing adult formulations and potential
pediatric market formulations, adjustments of adult in vitro gastrointestinal models to
study drug bioavailability in children, and refined criteria for the extrapolation of
adult efficacy data to the pediatric population.124–126
Third, future research on pediatric formulations could potentially benefit from
existing or innovative technologies under development in adults.127 Novel
experimental treatments of adult cancers, infections, and asthma have used
nanoparticle-targeted therapy, novel smart polymer-based drug delivery systems,
new chemical entities (eg, dendrimers), and remote triggering devices. These
treatments may have significant applications in children, and the identification of
appropriate animal models for pediatric preclinical studies should be a research
priority.128–130
Fourth, ongoing technologic advances need to be accompanied by relevant patient
outcome studies and clinical feedback on efficacy, safety, patient acceptability,
preferences, and adherence regarding new formulations; currently, such studies and
feedback are lacking.131 Practice-based evidence on the impact of novel
formulations, generated by health care professionals and caregivers, could provide
further support for the development of pediatric medicines with clear clinical
advantages.
The fifth priority concerns finance. Because innovative technologies are costly, the
ultimate challenge is to make these new pediatric formulations available on the
market and in daily practice.22,89,132 Their commercial viability might be improved by
an increased market size (eg, global scale, inclusion of geriatric patients and adults
with swallowing difficulties); new incentive schemes (particularly for off-patent
drugs), such as limited exclusivity and premiums, funding, and tax breaks; and
public–private partnerships that support the development of orphan drugs and other
less profitable niches.69,98–100
In sum, to reach these goals, it is essential that there is a committed collaboration
between stakeholders that extends across disciplines and geographic regions.
Moreover, this collaboration should have the innovative potential to further shape the
pediatric drug development agenda and thus to close the adult–child medicine gap.

ACKNOWLEDGMENT
We acknowledge Dr Richard Laing (WHO) for his advice on the progress analysis
and recommendations for improving pediatric drug formulations.