2.2. Antibacterial Activities of Cannabinoids against Pathogens in the WHO’s Priority List
Cannabinoids and
C. sativa extracts have substantial activity against several resistant bacteria in the WHO’s current priority list (
Table 1). All major cannabinoids, including cannabidiol (CBD), THC, cannabigerol (CBG), cannabichromene (CBC), cannabinol (CBN), their derivatives like cannabidiolic acid (CBDA), cannabichromenic acid (CBCA), and even extracts and EOs, inhibit MRSA including the epidemic-causing EMRSA 15 and EMRSA 16. Methicillin-resistant Staphylococcus aureus (MRSA) are resistant to all known beta-lactam antibiotics
[41], and even to linezolid, daptomycin and vancomycin
[42]. Extensive work has been published recently by Farha et al., enlightening the antibiotic potency of major cannabinoids against MRSA regarding their efficacy to inhibit biofilms and persister cells
[43]. Biofilms represent a subpopulation of bacteria that secure themselves against adverse situations, and persister cells, which are dormant and non-dividing, are common sources of antibiotic tolerance to MRSA
[44][45]. When a biofilm forms, bacterial cells acquire 10–1000 times more resistance to antibiotics
[46]. Biofilms and persisters of MRSA are considered important virulence factors, especially when formed on necrotic tissues and medical devices
[43]. All five major cannabinoids can obstruct the formation of biofilms, destroy preformed biofilms and eradicate stationary phase cells of MRSA. MRSA persisters, which are highly resistant to gentamicin, ciprofloxacin, and vancomycin
[47] can be killed by cannabinoids, and notably by CBG, at a concentration of 5 µg/mL
[43], whereas oxacillin and vancomycin are ineffective
[48]. The MIC
90 of CBG against MRSA strains is favorable compared to conventional antibiotics
[43]. The efficacy of CBG against biofilms and persisters of MRSA was found to be MIC 2 µg/mL in vivo, in a murine systemic infection model. CBG was found to be hemolytic at only 32 µg/mL, many-fold higher than MIC
[43].
Table 1. Activity of cannabinoids and C. sativa against the resistant pathogens enlisted in WHO’s current priority list.
Pathogen |
Compound/Extract/EO |
Activity |
Reference Antibiotic |
Ref |
Antibiotic |
Activity |
Gram+ve |
|
|
|
|
|
Enterococcus faecium |
EO, α-humulene, α-pinene, β-pinene, myrcene |
MIC 0.75–1.87 (%v/v) MBC 1.39–2.83 (%v/v) |
|
|
[49] |
E. faecium |
EO, α-humulene, α-pinene, β-pinene, myrcene |
MIC 1–4 µg/mL |
Ciprofloxacin |
MIC 8 µg/mL |
[50] |
EMRSA 15 and EMRSA 16 |
CBD, THC, CBG, CBC, CBN |
MIC 0.5–2.0 µg/mL |
|
|
[51] |
MRSA |
4-acetoxy-2-geranyl-5-hydroxy-3-n-pentylphenol and 8-hydroxycannabinolic acid A |
IC50 6.7 µM |
Ciprofloxacin |
IC50 0.4 µM |
[52] |
MRSA |
CVDVM |
MIC 15.6 µM |
|
|
[53] |
MRSA |
CBCA |
MIC 3.9 µM |
|
|
[53] |
MRSA |
CBD |
MIC 1 µg/mL |
Tobramycin, Meropenem, Ofloxacin |
MIC 1, 16, 64 µg/mL (respectively) |
[54] |
MRSA |
CBD |
MBEC 2–4 µg/mL |
|
|
[55] |
MRSA |
CBD analogs |
MIC 0.25–64.0 µg/mL |
Vancomycin, Daptomycin, Mupirocin |
MIC 0.125–2.0 µg/mL |
[55] |
MRSA |
CBD, CBN, CBC, CBDV and Δ1 & 9-THC |
IC50 5.8–10.6 µM |
Ciprofloxacin |
IC50 9.33 µM |
[56] |
MRSA |
CBDA |
MIC 4 µg/mL |
Tobramycin, Meropenem, Ofloxacin |
MIC 1, 16, 64 µg/mL (respectively) |
[54] |
MRSA |
CBG |
MIC 2 µg/mL and MBEC 4 µg/mL |
|
|
[43] |
MRSA |
EO |
IC50 0.82–4.22 µg/mL |
|
|
[57] |
MRSA, VISA, VRSA, E. faecium |
CBD |
MIC 1–2 µg/mL |
Vancomycin, Daptomycin, Trimethoprim, Mupirocin, Clindamycin |
MIC 0.125 to >64 µg/mL |
[55] |
Streptococcus pneumoniae |
CBD |
MIC 1–4 µg/mL |
Vancomycin, Daptomycin, Trimethoprim, Mupirocin, Clindamycin |
MIC 0.25 to >64 µg/mL |
[55] |
VRE |
CBCA |
MIC 7.8 µM |
|
|
[53] |
Gram -ve |
|
|
|
|
|
Escherichia coli |
Aqueous extract |
MIC 7.14 mg/mL |
Ciprofloxacin |
MIC < 0.12 mg/mL |
[58] |
E. coli |
N-p-trans-coumaroyl-tyramine |
IC50 0.8 µg/mL |
Ciprofloxacin |
IC50 0.01 µg/mL |
[59] |
E. coli |
Seed extract |
MIC 25 µg/mL |
|
|
[60] |
E. coli and Salmonella typhimurium |
Seed extract |
Growth inhibition at 1 mg/mL |
|
|
[61] |
E. coli, and Pseudomonas aeruginosa |
EO |
MIC 1.2 mg/mL |
|
MIC 0.062–1.0 mg/mL |
[62] |
Enterobacter aerogenes |
Seed extract |
MIC 2.5 mg/mL |
|
|
[61] |
Neisseria gonorrhoeae |
CBD |
MIC 1–2 µg/mL |
Vancomycin, Levofloxacin, Meropenem, Gentamicin |
MIC 0.002–4.0 µg/mL |
[55] |
N. gonorrhoeae |
CBD analogs |
MIC 0.03–16.0 µg/mL |
Mupirocin Colistin |
MIC 1–32 µg/mL |
[55] |
P. aeruginosa |
Aqueous extract |
MIC 7.14 mg/mL |
Ciprofloxacin |
MIC 1.23 mg/mL |
[58] |
P. aeruginosa |
Whole plant extract |
MIC 12.5 µg/mL |
|
|
[60] |
The rapid bactericidal activity of CBD was observed (<3 h) at 2 µg/mL
[55], and the effect resembled that of the natural nonionic detergents, saponins
[54]. CBD and CBDA showed no toxicity to human keratinocyte cells at up to seven and four-fold higher concentration of their respective MIC against MRSA (
Table 1)
[54]. CBD could potentiate bacitracin activity, reducing its MIC 64-fold against resistant bacteria, including MRSA
[63]. The combination affected morphological changes of the pathogen, impaired cell division and induced membrane irregularities. No synergistic or antagonist effect was seen on MRSA resulting from CBD with conventional antibiotics including vancomycin, methicillin, clindamycin, tobramycin, teicoplanin, ofloxacin and meropenem
[54]. Because of the hydrophobic nature of CBD, it cannot attack enough of the bacterial membrane to enhance the uptake of antibiotic drugs and does not interfere the mechanism of action of last-resort antibiotics.
In an in vivo study, CBCA showed more potent and faster bactericidal activity than vancomycin with lower a toxicity level to the mammalian cell lines A549 and HepG2. CBCA and cannabidivarin methyl ester (CBDVM) rendered minimum toxicity concentration (MTC), greater than 100 µM on both cell lines, which is far higher than their respective MIC against MRSA (
Table 1). Additionally, compared to vancomycin, the compound exhibited more biocidal activity with higher a bacterial load. Rapid bactericidal activity of CBCA could reduce treatment time and provide less opportunity for emergence of bacterial resistance. A time-kill assay showed considerable reduction of CBCA activity after 8 h of exposition to MRSA. The activity of CBCA was observed against both the exponential and stationary phases of MRSA and was independent of their cellular metabolism
[53]. The killing activity of many antibiotics is attributed to their effect on dividing bacteria cells, which is crucially interrupted by the stationary phase of MRSA, resulting in higher morbidity in nosocomial infections
[64]. Synergistic effects of phytocannabinoids and terpenoids are reported in the treatment of infections related to MRSA and fungi
[65]. The penetration of bacteria cell membranes differs among cannabinoids, which results in the non-identical effects of these compounds
[54].
In contrast to pure active compounds,
C. sativa extracts and EOs sometimes have even greater activity against resistant pathogens as a result of probable synergism. Drug-resistant clinical isolates, including MRSA, vancomycin-resistant Staphylococcus aureus (VRSA) and vancomycin-intermediate Staphylococcus aureus (VISA) demonstrated susceptibility to alcoholic
C. sativa extracts
[66][67]. A profound inhibitory efficacy was achieved when an ethanolic extract of
C. sativa leaves was combined with a Thuja orientalis leaf extract in a 1:1 ratio. The synergism was obtained due to the antibacterial effect of the phenolic compounds quercetin, gallic acid and catechin present in the leaf extract
[66].
Gram-negative organisms generally exhibit more resistance to antibiotics due to their distinctive structure. They are dominant killers in intensive care units showing resistance to wide-spectrum antibiotics including third-generation cephalosporins and carbapenems
[68]. They differ in structure from GPB since they have an outer membrane containing lipopolysaccharide (LPS)/endotoxin, which provides the pathogen intrinsic resistance against antibacterial agents
[69]. This acts as an important barrier and provides protection by resisting the penetration of toxic antibiotics and innate host immune molecules
[70].
However, GNB, whose outer membrane is permeable, are susceptible to cannabinoids
[43]. All the five major cannabinoids showed synergism against clinically isolated multidrug-resistant GNB, including Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Escherichia coli when used with polymyxin B at sublethal concentration
[43][55]. The activity against
K. pneumoniae was increased for EO exhibiting full synergism with addition of ciprofloxacin
[62]. Naringenin with EO was found to be bactericidal against drug resistant Helicobacter pylori
[71]. Aqueous and solvent extracts of leaf, stem and roots also displayed substantial activity against
K. pneumoniae,
A. baumannii and Haemophilus influenzae
[72].
CBD has strong inhibitory efficacy on release of membrane vesicles (MV) from
E. coli VCS257 and can boost bactericidal power of vancomycin against
E. coli, to which it shows resistance
[73]. MVs are nanosized spheres composed of lipid membranes derived from the outer membrane of bacteria that can cause an extra layer of protection against antibiotics
[74][75]. EO exhibits synergistic effect against
E. coli, and
P. aeruginosa in combination with ciprofloxacin
[62].
P. aeruginosa is resistant to antibiotics including beta-lactams, aminoglycosides and quinolones
[76]. The efficacy of solvent extracts of
C. sativa against
P. aeruginosa in terms of inhibitory zone is comparable with gentamicin
[60], ampicillin
[77] and ciprofloxacin
[62]. Notably, the level of sensitivity of the extracts in qualitative tests is not equipollent since their polarity and solubility change their diffusivity through media
[78][79]. However, in many other investigations, the activity of
C. sativa was shown against
P. aeruginosa [72][80][81][82][83][84],
E. coli [72][60][77][81][85][86][87][88][89][90][91], Salmonella species
[85][89][92][93], Shigella species
[85][91],
K. pneumoniae [91],
Acinetobacter calcoaceticus [88],
Morganella morganii [72] and
Serratia marcescens [93].
The ability of cannabinoids to modulate physiological and pathophysiological activities can hinder bacterial conjugation by targeting plasmid DNA
[94]. Conjugation is one of the major processes of acquiring antibiotic resistance and involves replication and transfer of an extra piece of bacterial DNA plasmid into a recipient bacterium
[95]. Plasmids contain genes to express resistance to antibiotics. Δ
9-THC, CBN and CBD impaired plasmid transfer activity near to zero for pKM 101 and TP 114
[94]. Tetrahydrocannabinolic acid (THCA) reduced plasmid curing activity by 30% in
E. coli K12 F’lac strain
[96]. Plasmid curing is a process by which the plasmid is eliminated, and the bacteria become susceptible. THCA and some cannabispiro compounds were inhibited transformation of plasmid DNA (pBR322), elimination (F’lac) and transfer (R144) of plasmid from
E. coli to E. coli, and even killing plasmid carrying bacteria despite possessing a higher MIC value
[97].
Apart from phytocannabinoids, some endocannabinoids (EC) and endocannabinoid-like (EC-like) natural endogenous compounds have good potency against MRSA biofilms. Anamide and arachidonoyl serine, an EC and EC-like natural endogenous compound respectively, did not kill the bacteria in vitro, but inhibited biofilm formation and preformed biofilms of MRSA, altered biofilm-associated virulence factors, and could modify MRSA cell surface characteristics
[98]. The compounds also exhibited synergy with different antibiotics including ampicillin, methicillin and gentamicin under both planktonic growth conditions and biofilm formation
[99]. Besides, their combination with methicillin impaired slime formation of MRSA
[99]. The slime layer is not easily be washed off and can be expressed as a virulence factor
[100][101].
2.3. Antibacterial Activities of Cannabinoids against Pathogenic Bacteria Not on the WHO Priority List
C. sativa has broad-spectrum antibacterial efficacy against a number of pathogenic bacteria (Table 2) that are not listed in WHO’s current priority list.
Table 2. Activity of cannabinoids and C. sativa against pathogens other than those on the WHO’s priority list (* collected from foods or food environments).
Pathogen |
Compound/Extract/EO |
Activity |
Reference Antibiotic |
Ref |
Antibiotic |
Activity |
Gram+ve |
|
|
|
|
|
Bacillus subtilis and Staphylococcus aureus |
Leaf extract |
MIC 1.56 mg/mL |
|
|
[90] |
B. subtilis, S. aureus and Micrococcus luteus |
EO |
MIC 1.2–4.7 mg/mL |
Ciprofloxacin |
MIC 0.015–0.031 mg/mL |
[62] |
B. subtilis, S. aureus, Mycobacterium smegmatis |
CBC, its homologs and isomers |
MIC 0.39–3.12 µg/mL |
|
|
[102] |
Clostridium species *, Enterococcus hirae *, Streptococcus salivarius * |
EO, α-humulene, α-pinene, β-pinene, myrcene |
MIC ≥ 0.8 (%v/v) |
|
|
[49] |
Enterococcus *, Staphylococcus *, and Bacillus species * |
EO |
MIC ≥ 0.5 µg/mL |
Ampicillin, Ciprofloxacin |
MIC ≥ 0.25 µg/mL |
[50] |
Listeria monocytogenes strains * |
EO |
MIC/MBC 2.5–5.0 μL/mL |
|
|
[103] |
L. monocytogenes * |
EO |
MIC ≥ 1 µg/mL |
Ampicillin |
MIC ≥ 0.25 µg/mL |
[50] |
L. monocytogenes * |
EO, α-pinene, Myrcene |
MBC ≥ 1024 µg/mL |
|
|
[104] |
Lancefield Group A Streptococcus sp. |
Leaf extract |
MIC 20 mg/mL MBC 30 mg/mL |
|
|
[105] |
MRSA biofilms * |
Seed extract |
MIC 1 mg/mL |
|
|
[61] |
MSSA |
CBCA |
MIC 7.8 µM |
|
|
[53] |
MSSA, VISE, Staphylococcus epidermidis, Staphylococcus pyogenes, Enterococcus faecalis, Cutibacterium acnes, Clostridioides difficile |
CBD |
MIC 0.5–4.0 µg/mL |
Vancomycin, Daptomycin, Trimethoprim, Mupirocin, Clindamycin, Levofloxacin, Meropenem, Gentamicin, Erythromycin, Tetracycline, Mupirocin |
MIC 0.03–64.0 µg/mL |
[55] |
Mycobacterium intracellulare |
CBG |
IC50 15 µg/mL |
|
|
[106] |
S. aureus |
4-acetoxy-2-geranyl-5-hydroxy-3-n-pentylphenol, 8-hydroxycannabinolic acid A |
IC50 3.5 µM |
Ciprofloxacin |
IC50 0.4 µM |
[52] |
S. aureus |
Aqueous extract |
MIC 3.57 mg/mL |
Ciprofloxacin |
MIC 0.62 µg/mL |
[58] |
S. aureus |
Methanol extract |
MIC 25 µg/mL |
|
|
[60] |
S. aureus (including multi drug resistant S. aureus 104) |
EO |
MIC 8 mg/mL |
|
|
[71] |
S. aureus (mature and pre-formed biofilms) |
EO |
MBEC 24 mg/mL |
|
|
[71] |
S. aureus and E. faecalis |
Seed extract |
MIC 1 mg/mL |
|
|
[61] |
S. aureus biofilm * |
EO |
MIC 0.5 mg/mL |
|
|
[61] |
S. aureus planktonic cells * |
EO |
MIC 1 mg/mL |
|
|
[61] |
S. aureus * |
EO |
MIC 1.25–5.0 µg/mL |
|
|
[103] |
S. aureus * |
EO |
MIC 1–4 µg/mL |
Ciprofloxacin |
MIC 0.5–16.0 µg/mL |
[50] |
S. aureus, S. epidermidis |
CBD, CBDA |
MIC 1–4 µg/mL |
Torbamycin, Meropenem, Ofloxacin |
MIC 0.06–0.5 µg/mL |
[54] |
SA-1199B (MDR), RN4220 (Macrolide-resistant), XU212 (Tetracycline-resistant) |
CBD, CBC, THC, CBG, CBN, Carboxylated versions, Abnormal cannabinoids |
MIC 0.5–4.0 µg/mL |
|
|
[51] |
Staphylococcus species |
THC, CBD |
MIC 1–5 µg/mL |
|
|
[107] |
Staphylococcus, Lactococcus and Bacillus species |
CBD, CBN, CBC, CBDV and Δ1 & 9-THC |
IC50 2.6–9.2 µM |
Ciprofloxacin |
IC50 0.003–2.4 µM |
[56] |
Gram-ve |
|
|
|
|
|
Moraxella catarrhalis, Neisseria meningitidis and Legionella pneumophila |
CBD |
MIC 0.25–1.0 µg/mL |
Vancomycin, Levofloxacin, Meropenem, Gentamicin |
MIC 0.03–32 µg/mL |
[55] |
Pectobacterium carotovorum subsp. carotovorum * |
EO, α-humulene, α-pinene, β-pinene, myrcene |
MIC ≥ 1.24 (%v/v) |
|
|
[49] |
Pseudomonas fluorescens and Xanthobacter flavus |
CBD, CBN, CBC, CBDV and Δ1 & 9-THC |
IC50 3.1–9.3 µM |
Ciprofloxacin |
IC50 0.15–2.3 µM |
[56] |
Pseudomonas species |
EO(s) and Terpenes |
MIC 1.05–1.97 (%v/v) |
|
|
[49] |
CBD has bacitracin activity, reducing its MIC 64-fold against Listeria monocytogenes and Enterococcus faecalis
[63]. It can increase the effectiveness of kanamycin against Staphylococcus aureus without affecting MV release
[73]. The EO exhibited bactericidal activity against clinically isolated methicillin-resistant Staphylococcus pseudintermedius (MRSP) from dogs suffering from pyoderma
[108]. A combination of ciprofloxacin with EO significantly decreased MIC against Bacillus subtilis,
S. aureus and
Micrococcus luteus due to partial and full synergism
[62]. The inhibition pattern of seed extract against
S. aureus biofilms is similar to that of vancomycin, and the efficacy was found to be dose-dependent
[109]. The bactericidal activity of solvent extracts against penicillin resistant
S. aureus was recorded by Kabelik
[18][110]. Acidic fractions are responsible for the antimicrobial properties of crude extract of leaves
[111]. Leaf extract out-performs chloramphenicol in terms of inhibition zone against the strep-throat-causing Lancefield Group A
Streptococcus sp., and its activity is comparable with penicillin and amoxicillin
[10], which are commercially used as beta-lactam antibiotics for strep-throat treatment.
Moreover, a considerable number of diffusion tests showed medium to higher activity against
S. aureus [60][77][80][83][85][86][88][91][93][111][112],
B. subtilis [60][88][89][91][93][111],
Bacillus cereus [86][89][93],
Bacillus pumilus [111],
E. faecalis [86][92][93][113],
Micrococcus flavus [111],
M. luteus [88][93],
Brevibacterium linens,
Brochothrix thermosphacta [88] and Methicillin-resistant coagulase-negative Staphylococci (MRCoNS)
[67]. The findings indicate that
C. sativa can be targeted as a natural source for developing antibacterial drugs.
Like other antibiotics, a plant’s secondary metabolites encounter a barrier at the outer membrane of GNB, and limited efficacy is observed
[114]. Nevertheless, many studies show
C. sativa having a moderate to large inhibitory zone for Yersinia enterocolitica
[88][92][113],
Vibrio cholerae [82], Citrobacter freundii CCM 7187
[93],
Erwinia carotovora [115],
Bordetella bronchioseptica,
Proteus vulgaris [111],
Aeromonas hydrophyla,
Beneckea natriegens, and
Flavobacterium suaveolens [88].
It can be assumed that the bioactivity of
C. sativa extracts and EOs fundamentally come from compounds such as cannabinoids, phenolics and terpenes
[62][61][103]. The anntimicrobial profile of low-level THC content of
C. sativa (industrial hemp) is partially related to CBD
[50], CBDA
[109], phenolics including flavonoids, caffeoyltyramine, cannabisin and polyphenols
[58][61] and terpenes including α-pinene, α-humulene, β-pinene, β-caryophyllene, (E) caryophyllene, caryophyllene oxide and myrcene
[62][49][50][108][103][104].
3. Antifungal Activity
Both superficial and systemic fungal infections have increased due to the emergence of many immunological dysfunctions in people
[116]. The management of fungal infections suffers from the unavailability of drugs, toxicity, resistance and relapse of conditions
[117]. Therefore, finding new antifungal drugs to combat fungal infections is a priority. In agreement with the set threshold by Kuete and Dabur to ascribe the antimicrobial and antifungal properties of plant juices
[118][119],
C. sativa extract, EO and their phytoconstituents possess significant activity against a number of pathogenic fungi and algae (
Table 3).
Table 3. Activity of cannabinoids and C. sativa against fungi.
Pathogen |
Compound/Extract/EO |
Activity |
Reference Antibiotic |
Ref |
Antibiotic |
Activity |
Candida albicans |
Extract |
MIC 0.25 mg/mL |
|
|
[120] |
C. albicans |
Extract |
MIC 1.42 mg/mL |
Fluconazole |
MIC 2 mg/mL |
[58] |
C. albicans |
4-terpenyl cannabinolate |
MIC 8.5 µg/mL |
|
|
[121] |
C. albicans |
8-hydroxycannabinol |
IC50 4.6 µM |
Amphotericin B |
IC50 0.3 µM |
[52] |
C. albicans |
Cannabis and ginger blend |
MIC 4.69 mg/mL |
|
|
[122] |
C. albicans |
CBDV |
IC50 11.9 mM |
Nystatin |
IC50 1.50 mM |
[56] |
C. albicans |
CBNA |
IC50 8.5 µg/mL |
|
|
[121] |
Candida krusei |
Cannabinoids |
IC50 53.4–60.5 µM |
amphotericin B |
IC50 0.7 µM |
[52] |
Candida neoformans |
β-caryophyllene/oxide |
IC50 1.18–19.4 µg/mL |
|
|
[57] |
Candida species |
β-caryophyllene |
MIC 1.45–10.0 µg/mL |
|
|
[57] |
Plasmodium falciparum |
Cannabinoids |
IC50 4.0–6.7 µM |
Chloroquine |
IC50 0.1–0.5 µM |
[52] |
P. falciparum |
CBNA |
IC50 2.4–2.7 µg/mL |
|
|
[121] |
Trichophyton and Arthroderma species |
EO |
MIC 0.312–6.3 µg/mL |
Griseofulvin |
MIC 1.26 to >8.0 µg/mL |
[123] |
Candida albicans, a prevalent opportunistic pathogenic fungus to humans, which is resistant to fluconazole, exhibited higher susceptibility to
C. sativa extracts, EO and other compounds. Moreover, EO of
C. sativa has a full synergistic effect with fluconazole, resulting in a 16-fold reduction of MIC against
Candida spp.
[62].
C. albicans is part of a natural microflora that forms asymptomatic colonies on the skin and inside the body and can proliferate if the host has an immunosuppressed condition and cause superficial mucosal and dermal infections
[124][125]. Activity against
Candida species
[60][82][83][111][113] Fusarium spp.
[77],
Candida neoformans [82] and
Aspergillus [77][111][126] are documented. Antifungal activity is cultivar-dependent
[123] and also related to the active compounds’ chemical structures
[84]. The findings indicate that more intensive study on the fungicidal activity of
C. sativa phytoextracts is required for the treatment of fungal infections, especially for external use.