1School of Allied Health Sciences, Sharda University, Knowledge Park III, Greater Noida 201306, UP. India, 2*Department of Pharmaceutical Technology, School of Health Science, NSHM Knowledge Campus, Kolkata 700053, W. B., India
Email: [email protected]
Received: 08 Nov 2021, Revised and Accepted: 12 Jan 2022
According to World Health Organization, WHO, antibiotic resistance is one of the biggest threats to global health, food security and development today. The means of delivering antibiotics to treat several brain infections, especially meningitis and encephalitis, have been inherently difficult, due to the presence of highly protective physiological barriers, mainly the blood-brain barrier (BBB), cerebrospinal fluid (CSF) that impairs the efficacy and bioavailability of antibiotics from reaching the susceptive organism. Many attempts have been made to optimize the therapeutic prognosis of such infections through the parenteral and intrathecal route of administration. These alternative routes have incited inadequate efficacy along with associated adverse effects. However, scientists have now considered the intranasal route (non-invasive) as a breakthrough to such inherent challenges. Moreover, several in vivo and ex vivo studies suggested evidence of the effectiveness of nose-to-brain delivery in treating bacterial and viral infections, thereby limiting the chance of antibiotic resistance. Targeting the multidrug resistance gram-positive and negative bacterias, a study was reported using nanoemulsion of Syzygiumaromaticum and Thymus vulgaris essential oils via the intranasal route. The result indicated the maximum inhibition of multi-drug resistance bacterias upon intranasal administration. Therefore, this study focuses to highlight the potential of intranasal delivery in the optimization of CNS infections and the prevention of antibiotic resistance.
Keywords: Antibiotic-resistance, Brain infection, Physiological barriers, Nose-to-brain delivery, Intranasal delivery
© 2022 The Authors. Published by Innovare Academic Sciences Pvt Ltd. This is an open-access article under the CC BY license (https://creativecommons.org/licenses/by/4.0/)
DOI: https://dx.doi.org/10.22159/ijcpr.2022v14i2.1559 Journal homepage: https://innovareacademics.in/journals/index.php/ijcpr
Infections caused by various species of bacteria, viruses, fungus, and other parasitescan be terminal infections if they happen to affect Central Nervous Systems (CNS). Meningitis is one such infections and refers to the inflammation of “membranes that surround the brain and spinal cord” (meninges); the inflammation can be caused by infections, adverse effects of certain drugs or autoimmune disease . Meningitis instigated by bacteria is termed as bacterial meningitis, and it is rare and the most fatal type . Other types include Pneumococcal, Meningococcal, Haemophilus influenza, Viral, and non-infectious meningitis that is caused by autoimmune disorders and adverse effect of certain medication, among others. Moreover, most fetal bacterial meningitis is caused by Listeria and E. coli species [3, 4]. Besides, encephalitis (inflammation of the brain) is commonly caused by herpes simplex types 1 and 2 viruses, as well as arboviruses, that often transmit from mosquito and other biting insects. However, encephalitis cases are rarely diagnosed among infected persons; about 60% of the case remain undetected. The prevalence rate of 2:1,000,000 per year in USA . Understanding the pathophysiology CNS related infections is very essential for imporoving their clinical prognosis, most importantly, through overcoming their inherent resistance to antibiotic.
Besides, the World Health Organization reported the progressive increment in antibiotic misuse and subsequent resistance that result in a high mortality rate to about 700,000-per year worldwide in addition to the economic burden it causes [2, 5]. However, the irrational use of conventional antibiotics is the most contributing factor to antibiotic resistance . Moreover, targeting brain infections with antibiotics remains inherently challenging , because many of these conventional antibiotics show extremely low oral bioavailability, frequent administration, patient noncompliance, cost of medication, and poor prognosis . Besides, CNS-related infections attributes to high morbidity and mortality rate even in developed countries like England, USA, Russia, and France. However, the Blood-brain barrier BBB is a highly protective barrier that serves as the rate-limiting strep for the drugs, including antibiotics to reach optimal bioavailability and target the specific site of action in the brain . M. Fung, et al., reported that BBB limited the permeation of approximately 98% of drugs from reaching their desired site of actions . Therefore, scientists have studied many techniques to maximize the bioavailability of such drugs by bypassing the hindrance of BBB . Amongst, Invasive (carrier-mediated) delivery was suggested earlier to as an option for targeting brain infections, but its clinical applications are limited by lack of safety, cost and many inconveniences; alternatively, noninvasive (intranasal) administration of the drugs is now the best techniques to bypass BBB and target brain infections and other related disorders. Nevertheless, Many in vivo and ex vivo studies have also shown that nose-to-brain delivery is effective in the treatment of bacterial and viral infections and has reduced antibiotic resistance. Therefore, this research is focused on the potential of intranasal delivery optimization for CNS infection subsequent prevention of antibiotic resistance.
Concept of antibiotic resistance
Antibiotic resistance occurs as germs such as bacteria and fungi can kill the medicines meant for their destruction. It means the germs are not destroyed and are still rising. Antibiotic-resistant germ-caused infections are difficult to treat and sometimes impossible. In most cases, infections resistant to antibiotics need prolonged hospital stays, extra medical visits, and expensive and harmful alternatives. Antibiotic resistance does not mean the body becomes antibiotic-resistant; it is because the bacteria become antibiotic-resistant. Antibiotic resistance can affect individuals and the medical, veterinary, and agricultural industries at any point in life and is one of the worst public health issues on the planet. In the U. S., at least 2.8 million people are infected with antibiotic-resistant bacteria or fungi per year, resulting in more than 35,000 deaths . Nobody can avoid the risk of resistive infections completely, but some people are at higher risk than others (e. g. people with chronic diseases). If antibiotics become less effective, we lose the ability to treat infection and control threats to public health [13, 14]. The ability to battle antibiotic infections, including joint replacements, Organ transplants, cancer treatments, and chronic disorders such as diabetes, asthma, and rheumatoid arthritis, are contingent upon several developments in medicines. The way it prescribes and uses antibiotics needs to change in the world urgently . Despite the improvement in behavior, antibiotic resistance is still a major problem even though new drug drugs are created. Changes in behavior will also include steps to reduce the spread of diseases through vaccination, washing of hands, healthier sex, and nutritious food .
Antibiotic tolerance and resistance have become global threats. New pathways for resistance are being developed and distributed globally, which challenge our ability to treat common infectious diseases [17, 18]. The growing number of infections, such as pneumonia, tuberculosis, blood poisoning, gonorrhea, and food diseases, are becoming more, more difficult, and often impossible to treat because antibiotics are less effective. Where antibiotic products may be obtained without a prescription for human or animal use, resistance grows and spreads further. Furthermore, antibiotics are frequently over-prescribed by and over-used by health workers and veterinarians in countries without formal care guidelines. Before immediate action, we are moving into a post-antibiotic age, where common infections and minor injuries will kill once again [19, 20].
Mechanism of intranasal delivery of antibiotics to 'brain infections
In general, the nose-to-brain delivery mechanism is not clearly understood . The large surface area and high vascularization  and anatomical features of nasal epithelial tissues ease the permeation of molecules to CNS through different pathways . Furthermore, the anatomy and physiology of the intranasal route provide insight on its possibility to be a breakthrough in brain delivery targeting. Thanks to the presence of olfactory and trigeminal pathways . The olfactory region is the most essential means for nose-to-brain delivery of drugs; therefore, it was discovered to be the "portal for drug resistance" However, this complex process involves the interactions between the nasal mucosa, lymphatic plexus, perineural sheaths, in subarachnoid space [25, 26]. The drug delivery through the intranasal route is given by three main pathways, namely, intracellular diffusion, paracellular transportation, and receptor-mediated or trans/endo-cytosis, a schematic representation of the same is done in Fig. 1. High lipophilicity and low molecular weight of the drug is a major prerequisite for its absorption through these pathways [27, 28]. Besides, the trigeminal nerve is an important pathway that connected the olfactory, respiratory epithelium, and CNS in the pons. Moreover, its short terminal branch in the olfactory bulbs (chemosensory zone) is very important for brain targeting, because it is where the highest drug concentration observes in CNS [29-31]]. The Ekberg et al., the study highlighted the mechanism of brain infection by Burkholderiapseudomallei bacteria via the pathway of the trigeminal nerve, and this proved the greater possibility of targeting brain infections with antibiotic drugs via the same route . Nanosized and small molecules are many upper advantages to pass BBB limitation through carrier-mediated transportation, the molecule of molecular weight of<400 Da and hydrogen bonds<8, possessed high preference of free diffusing through lipid-mediated carriers across BBB to the brain [33, 34]. Therefore, employing the concept of nanotechnology will also be essential for drug absorption in all drug delivery systems including nose-to-brain. More so, these concepts have been understudying by the scientist and several clinical trials are on-going while some antibiotics for intranasal delivery to CNS have been approved.
In vitro studies
F. Ronald et al., targeted the multidrug resistance gram-positive and negative bacterias with nanoemulsion of Syzygiumaromaticum and Thymus vulgaris essential oils using the intranasal route. The result indicated the maximum inhibition of multi-drug resistance bacteria upon intranasal administration . P. Manda et al., delivered cefotaxime to treat brain infection through the intranasal route and the Pharmacokinetic investigation shows high bioavailability of the cefotaxime in the brain by administration intranasally . Nano-aerosol of AmB has shown higher bioavailability than oral, parenteral, and intrathecal [37, 38]. S. T. Lim et al. demonstrated a comparative in vitro study between intravenous and intranasal administration of Gentamicin antibiotics. The study result indicated the intranasally administered Gentamicin attained high bioavailability as compared to the intravenous route .
In vivo studies
Petra J. et al., induced meningitis using Streptococcus pneumonia on a murine model and demonstrated the efficiency of intranasal administration as a gold standard for the treatment of brain infection in humans .
Sakane et al. evaluated the bioavailability of cephalexin antibiotic using in vitro experiment on a rat model, and the study revealed the drug to have reach maximum safety concentration within 30 min, even though cephalexin was known to have poor bioavailability to CSF due to itslimited permeation to BBB when administered via other routes. The study concluded that the
bioavailabilityof cephalexin upon nasal administration is 166-fold higher than that of other routes . D. Inoue et al. reported the administration of norfloxacin via the intranasal route increases its absorption rate. However, the study found the change in mucociliary clearance to have affected the bioavailability of norfloxacin after in vivo demonstration on Male Wistar rats. Therefore, the nose-to-brain delivery system can be the route of choice for delivering antibiotics like norfloxacin for targeting brain infections . Joana S. et al. evaluated and compared the efficacy of levofloxacin upon intravenous and intranasal administration to healthy adult male.
Wistar rats. The in vivo pharmacokinetic examination reveals that intranasally, the levofloxacin attained a high concentration at a lower dose of 0.24 mg/kg while the intravenous route that shows the same concentration at the higher dose .
Fig. 1: Mechanism of intranasal delivery of antibiotics to 'brain infections'
Challenges and future perspectives
Bacterial infections are causing serious concern around the globe . Owing to the global emergence of multidrug-resistant (MDR) bacterial pathogens, the efficacy of traditional antibiotics is decreasing. This cycle appears to be mainly triggered by indiscriminate and excessive use of antibiotics in non-infected patients and the food industry. New types of antibiotics with specific behavior against MDR pathogens need to be established urgently [44, 45]. Besides, due to the existence of highly protective physiological barriers, primarily BBB, CSF, which inhibited the effectiveness and bioavailability of antibiotics from reaching susceptible species, the means for delivery of antibiotics to treat many brain infections, particularly meningitis and encephalitis, have been difficult. There have been several efforts to improve the therapeutic prognosis of these infections, and insufficiency along the associated adverse effects is seen via a parenteral and intrathecal route of administration . However, the clinical benefits of intranasal delivery were limited because of the effect of mucociliary clearance, enzymatic degradation of proteins, and peptides these limitations need to be addressed to optimize the clinical efficiency of intranasal delivery [47, 48]. Therefore, advanced research in this field is highly recommended.
The menace of antibiotic resistance could be overcome through formulating intranasal antibiotics since the route is capable of bypassing the hindrance effect of the main physiological blood-brain barrier. However, brain infections can optimally be targeted, therefore, the clinical prognosis of deleterious CNS infections like meningitis, encephalopathy could effectively be improved.
MDR: Multidrug-resistant, BBB: Blood brain barrier, BTB: Blood tumour barrier, CSF: Cerebrospinal fluid, CNS: Central Nervous System
The authors would like to acknowledge the contribution of their co-authors
This work did not receive any funding in cash or kind
Meningitis and encephalitis fact sheet | National institute of neurological disorders and stroke, (n.d.). Available from: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Meningitis-and-Encephalitis-Fact-Sheet. [Last accessed on 27 Aug 2020]
Diekema DJ, Richter SS, Heilmann KP, Dohrn CL, Riahi F, Tendolkar S, McDanel JS, Doern GV. Continued emergence of USA300 methicillin-resistant Staphylococcus aureus in the United States: results from a nationwide surveillance study. Infect Control Hosp Epidemiol. 2014 Mar 1;35(3):285-92. doi: 10.1086/675283, PMID 24521595.
Infections of the nervous system, (n.d.). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3401822/. [Last accessed on 27 Aug 2020]
Rushing EJ, Burns DK. Infections of the nervous system. Neuroimaging Clin N Am. 2001;11(1):1-13. doi: 10.1016/j.nic.2011.07.012. PMID 11331225.
Kourtis AP, Hatfield K, Baggs J, Mu Y, See I, Epson E, Nadle J, Kainer MA, Dumyati G, Petit S, Ray SM, Emerging Infections Program MRSA author group, Ham D, Capers C, Ewing H, Coffin N, McDonald LC, Jernigan J, Cardo D. Vital signs: epidemiology and recent trends in methicillin-resistant and in methicillin-susceptible staphylococcus aureus bloodstream infections-United States. MMWR Morb Mortal Wkly Rep. 2019 Mar 8;68(9):214-9. doi: 10.15585/mmwr.mm6809e1, PMID 30845118.
Ghosh C, Sarkar P, Issa R, Haldar J. Alternatives to conventional antibiotics in the era of antimicrobial resistance. Trends Microbiol. 2019 Apr 1;27(4):323-38. doi: 10.1016/j.tim.2018.12.010, PMID 30683453.
Daum RS, Spellberg B. Progress toward a staphylococcus aureus vaccine. Clin Infect Dis. 2012 Feb 15;54(4):560-7. doi: 10.1093/cid/cir828, PMID 22186773.
Livorsi DJ, Chorazy ML, Schweizer ML, Balkenende EC, Blevins AE, Nair R, Samore MH, Nelson RE, Khader K, Perencevich EN. A systematic review of the epidemiology of carbapenem-resistant enterobacteriaceae in the United States. Antimicrob Resist Infect Control. 2018 Apr 24;7:55. doi: 10.1186/s13756-018-0346-9, PMID 29719718.
Chaud MV, Rios AC, dos Santos CA, de Barros CT, de Souza JF, Alves TFR. Nanostructure self-assembly for direct nose-to-brain drug delivery: a novel approach for cryptococcal meningitis. Nanomycotoxicology. 2020:449-80.
Das M. Does the targeted delivery of theranostic carbon nanotubes have potential as a valid anticancer strategy? Ther Deliv. 2014;5(1):1-5. doi: 10.4155/tde.13.123, PMID 24341809.
Hanson LR, Frey WH. Intranasal delivery bypasses the blood–brain barrier to target therapeutic agents to the central nervous system and treat neurodegenerative disease. BMC Neurosci. 2008;9.
WHO. Global priority list of antibiotic-resistant bat ceria to guide research, discovery, and development of new antibiotics. WHO; 2017.
Munita JM, Arias CA. Mechanisms of antibiotic resistance. Microbiol Spectr. 2016 Apr;4(2):VMBF-0016. doi: 10.1128/microbiolspec.VMBF-0016-2015, PMID 27227291.
CDC. About antimicrobial resistance | antibiotic/antimicrobial resistance | CDC, Cdc Ncezid Dhqp; 2017.
Normark BH, Normark S. Evolution and spread of antibiotic resistance. J Intern Med. 2002 Aug 1;252(2):91-106. doi: 10.1046/j.1365-2796.2002.01026.x, PMID 12190884.
CDC. Antibiotic resistance threats in the United States. Current; 2013.
Brauner A, Fridman O, Gefen O, Balaban NQ. Distinguishing between resistance, tolerance and persistence to antibiotic treatment. Nat Rev Microbiol. 2016;14(5):320-30. doi: 10.1038/nrmicro.2016.34, PMID 27080241.
Hall CW, Mah TF. Molecular mechanisms of biofilm-based antibiotic resistance and tolerance in pathogenic bacteria. FEMS Microbiol Rev. 2017 May 1;41(3):276-301. doi: 10.1093/femsre/fux010, PMID 28369412.
MacFadden DR, McGough SF, Fisman D, Santillana M, Brownstein JS. Antibiotic resistance increases with local temperature. Nat Clim Change. 2018 May 21;8(6):510-4. doi: 10.1038/s41558-018-0161-6, PMID 30369964.
Lima TB, Pinto MF, Ribeiro SM, de Lima LA, Viana JC, Gomes Junior N, Candido Ede S, Dias SC, Franco OL. Bacterial resistance mechanism: what proteomics can elucidate. FASEB J. 2013 Apr 1;27(4):1291-303. doi: 10.1096/fj.12-221127, PMID 23349550.
Psimadas D, Georgoulias P, Valotassiou V, Loudos G. Molecular nanomedicine towards cancer: ¹¹¹In-labeled nanoparticles. J Pharm Sci. 2012 Jul 1;101(7):2271-80. doi: 10.1002/jps.23146, PMID 22488174.
Djupesland PG, Messina JC, Mahmoud RA. The nasal approach to delivering treatment for brain diseases: an anatomic, physiologic, and delivery technology overview. Ther Deliv. 2014 Jun 1;5(6):709-33. doi: 10.4155/tde.14.41, PMID 25090283.
Thwala LN, Preat V, Csaba NS. Emerging delivery platforms for mucosal administration of biopharmaceuticals: a critical update on nasal, pulmonary and oral routes. Expert Opin Drug Deliv. 2017 Jan 1;14(1):23-36. doi: 10.1080/17425247.2016.1206074, PMID 27351299.
Talegaonkar S, Mishra PR. Intranasal delivery: an approach to bypass the blood brain barrier. Indian J Pharmacol. 2004;36(3):140-7.
Gizurarson S. Anatomical and histological factors affecting intranasal drug and vaccine delivery. Curr Drug Deliv. 2012;9(6):566-82. doi: 10.2174/156720112803529828, PMID 22788696.
Wen MM. Olfactory targeting through intranasal delivery of biopharmaceutical drugs to the brain: current development. Discov Med. 2011 Jun 1;11(61):497-503. PMID 21712015.
Crowe TP, Greenlee MHW, Kanthasamy AG, Hsu WH. Mechanism of intranasal drug delivery directly to the brain. Life Sci. 2018 Feb 1;195:44-52. doi: 10.1016/j.lfs.2017.12.025, PMID 29277310.
Rahisuddin SPK, Garg G, Salim M. Review on nasal drug delivery system with recent advancement. Int J Pharm Pharm Sci. 2011 Oct 15;3(2):6-11.
Banks WA, During MJ, Niehoff ML. Brain uptake of the glucagon-like Peptide-1 antagonist exendin(9-39) after intranasal administration. J Pharmacol Exp Ther. 2004;309(2):469-75. doi: 10.1124/jpet.103.063222, PMID 14724226.
Charlton ST, Whetstone J, Fayinka ST, Read KD, Illum L, Davis SS. Evaluation of direct transport pathways of glycine receptor antagonists and an angiotensin antagonist from the nasal cavity to the central nervous system in the rat model. Pharm Res. 2008 Jul;25(7):1531-43. doi: 10.1007/s11095-008-9550-2, PMID 18293062.
Dufes C, Olivier JC, Gaillard F, Gaillard A, Couet W, Muller JM. Brain delivery of vasoactive intestinal peptide (VIP) following nasal administration to rats. Int J Pharm. 2003 Apr 14;255(1-2):87-97. doi: 10.1016/s0378-5173(03)00039-5, PMID 12672605.
St John JA, Walkden H, Nazareth L, Beagley KW, Ulett GC, Batzloff MR, Beacham IR, Ekberg JAK. Burkholderia pseudomallei rapidly infects the brain stem and spinal cord via the trigeminal nerve after intranasal inoculation. Infect Immun. 2016 Sep;84(9):2681-8. doi: 10.1128/IAI.00361-16, PMID 27382023.
Pardridge WM, Boado RJ. Reengineering biopharmaceuticals for targeted delivery across the blood–brain barrier. Methods Enzymol. 2012;503:269-92. doi: 10.1016/B978-0-12-396962-0.00011-2, PMID 22230573.
Bhaskar S, Tian F, Stoeger T, Kreyling W, de la Fuente JM, Grazu V, Borm P, Estrada G, Ntziachristos V, Razansky D. Multifunctional nanocarriers for diagnostics, drug delivery and targeted treatment across blood–brain barrier: perspectives on tracking and neuroimaging. Part Fibre Toxicol. 2010 Mar 3;7:3. doi: 10.1186/1743-8977-7-3, PMID 20199661.
Rinaldi F, Oliva A, Sabatino M, Imbriano A, Hanieh PN, Garzoli S, Mastroianni CM, De Angelis M, Miele MC, Arnaut M, Di Timoteo F, Marianecci C, Ragno R, Carafa M. Antimicrobial essential oil formulation: chitosan coated nanoemulsions for nose to brain delivery. Pharmaceutics. 2020 Jul 1;12(7):678. doi: 10.3390/pharmaceutics12070678, PMID 32709076.
Manda P, Hargett JK, Vaka SRK, Repka MA, Murthy SN. Delivery of cefotaxime to the brain via intranasal administration. Drug Dev Ind Pharm. 2011;37(11):1306-10. doi: 10.3109/03639045.2011.571696, PMID 21702731.
Usman F, Khalil R, Ul-Haq Z, Nakpheng T, Srichana T. Bioactivity, safety, and efficacy of amphotericin B nanomicellar aerosols using sodium deoxycholate sulfate as the lipid carrier. AAPS PharmSciTech. 2018 Jul 1;19(5):2077-86. doi: 10.1208/s12249-018-1013-4, PMID 29691753.
Gangadhar KN, Adhikari K, Srichana T. Synthesis and evaluation of sodium deoxycholate sulfate as a lipid drug carrier to enhance the solubility, stability and safety of an amphotericin B inhalation formulation. Int J Pharm. 2014 Aug 25;471(1-2):430-8. doi: 10.1016/j.ijpharm.2014.05.066, PMID 24907597.
Lim ST, Forbes B, Berry DJ, Martin GP, Brown MB. In vivo evaluation of novel hyaluronan/chitosan microparticulate delivery systems for the nasal delivery of gentamicin in rabbits. Int J Pharm. 2002 Jan 1;231(1):73-82. doi: 10.1016/s0378-5173(01)00873-0, PMID 11719016.
Zwijnenburg PJG, van der Poll T, Florquin S, van Deventer SJH, Roord JJ, van Furth AM. Experimental pneumococcal meningitis in mice: a model of intranasal infection. J Infect Dis. 2001 Apr 1;183(7):1143-6. doi: 10.1086/319271, PMID 11237845.
Sakane T, Akizuki M, Yoshida M, Yamashita S, Nadai T, Hashida M, Sezaki H. Transport of cephalexin to the cerebrospinal fluid directly from the nasal cavity. J Pharm Pharmacol. 1991 Jun 1;43(6):449-51. doi: 10.1111/j.2042-7158.1991.tb03510.x, PMID 1681064.
Sousa J, Alves G, Fortuna A, Falcao A. Intranasal delivery of topically-acting levofloxacin to rats: a proof-of-concept pharmacokinetic study. Pharm Res. 2017;34(11):2260-9. doi: 10.1007/s11095-017-2232-1, PMID 28748398.
Karunasagar I, Ryder J, Ababouch L, Balaban M. Minimising antimicrobial use in aquaculture and improving food safety. FAO Fish Aquac Proc. 2012.
Mitsakakis K, Kaman WE, Elshout G, Specht M, Hays JP. Challenges in identifying antibiotic resistance targets for point-of-care diagnostics in general practice. Future Microbiol. 2018;13(10):1157-64. doi: 10.2217/fmb-2018-0084, PMID 30113214.
O’Morain C, Montague S. Challenges to therapy in the future. Helicobacter. 2000;5Suppl 1:S23-6, discussion S27. doi: 10.1046/j.1523-5378.2000.0050s1023.x, PMID 10828751.
Putheti RR, Patil MC, Obire O. Nasal Drug delivery in pharmaceutical and biotechnology: present and future. Japan Science and Technology (Corporation); 2009.
Comfort C, Garrastazu G, Pozzoli M, Sonvico F. Opportunities and challenges for the nasal administration of nanoemulsions. Curr Top Med Chem. 2015;15(4):356-68. doi: 10.2174/1568026615666150108144655, PMID 25579345.
Yusuf H, Kett V. Current prospects and future challenges for nasal vaccine delivery. Hum Vaccin Immunother. 2017 Jan 13;13(1):34-45. doi: 10.1080/21645515.2016.1239668, PMID 27936348.