Combination Antifungal Therapy

Melissa D. Johnson; Conan MacDougall; Luis Ostrosky-Zeichner; John R. Perfect; John H. Rex

doi:10.1128/AAC.48.3.693-715.2004

DOI: 10.1128/AAC.48.3.693-715.2004

Article Figures & Data

Tables

TABLE 1.

Consensus terminology for describing results of combination testing^a

Category	Terminology for indicated conditions
Category	Both agents are active alone; additive effects model is presumed	Both agents are active alone; multiplicative effects model is presumed	One agent is active alone; the other is not	Neither agent is active alone
Combination result is better than expected	Loewe synergism	Bliss synergism	Synergism	Coalism
Combination result is as expected	Loewe additivity	Bliss independence	Inertism	Inertism
Combination result is worse than expected	Loewe antagonism	Bliss antagonism	Antagonism

↵ a The terminology shown is that proposed by Greco et al. (79) following a consensus conference occurring in Sarriselka, Finland. Models based on the additive interaction concept first proposed by Loewe and Muischnek (111) follow the intuitive result in which a drug combined with itself produces a linear sum of effects. That is, 1 μg/ml plus 1 μg/ml gives the effect of 2 μg/ml and this result is neither synergistic nor antagonistic. Models based on the multiplicative interaction concept first proposed by Bliss (26) follow a probabilistic model in which the two agents truly act independently as determined on the basis of their separate probabilities of effect. If 1 μg/ml permits 40% of the target organism to survive, then 1 + 1 = 2 μg/ml should permit only 40% × 40% = 16% survival. As reviewed in detail by Greco et al. (79), both models have strengths and weaknesses but Loewe additivity-based models more often seem appropriate for combinations of antimicrobial agents.

TABLE 2.

Technical and analytical issues associated with different model systems for studying combination antifungal therapy

Category	Characteristic
Category	In vitro studies	Animal models	Clinical trials
Strengths	Easily repeated across a wide variety of drug concentrations	Studies can be done with homogeneous hosts	This is the answer that matters
	Easily subjected to statistical testing	Host factors are integrated
	Easy to vary technical factors	Resistant isolates can sometimes be tested
	Easy to test multiple isolates	Quantitative endpoints (tissue burden, rate of clearance) can be tested
	Easy to test isolates with defined types of resistance	A range of doses and dose combinations can be tested
Weaknesses	Relevance of in vitro methods not always clear	Infection models are often poor mimics of human disease	Subjects and infecting isolates are heterogeneous
	Host factors are ignored	Pharmacokinetic and toxicological behavior of test drugs (and their pharmacological effects on each other) may not mimic that seen in humans	No ability to control nature of infecting isolate
	Pharmacokinetic factors are ignored	Only limited numbers of isolates can be tested	Underlying disease cannot be controlled
		Only limited numbers of repetitions are possible	Lack of quantitative endpoints for many diseases
		Resistant isolates sometimes have reduced virulence	Limited ability to study a range of doses
			Very expensive
			Slow

TABLE 3.

Summary of key findings reported in studies of C. neoformans with combinations of clinically relevant antifungal agents^a

Combination	Settings studied	General findings	Comments
5FC + AmB	In vitro (40, 63, 74, 78, 80, 92, 126, 140, 156, 189)	Indifference (63, 74, 78, 80, 140, 156, 189) synergy (40, 126), antagonism with 5FC-resistant strain (80)	AmB reduces development of resistance to 5FC; 5FC-resistant strains have been used in numerous studies (80, 126, 189) and produce various results
	Mice (16, 27, 60, 80, 158) Rabbits (150)	Improved survival (16, 27, 158) Reduced tissue burden (16, 150)	Survival (27) or reduction in tissue burden (150) not necessarily better than results with AmB alone (60); combination more effective than AMB and 5FC alone against 5FC-resistant strains (158)
	Humans (24, 42, 43, 55, 103, 144, 213)	Similar (213) or improved (24, 171) clinical success overall, improved sterilization of CSF (24, 213)	Addition of 5FC leads to earlier sterilization of CSF (24); clinical success rates were similar between AmB + 5FC and AmB alone (73 vs. 83%) after 2 weeks of therapy (213); relapse has been associated with no use of 5FC during initial 2 weeks (171)
5FC + triazoles	In vitro FLC (3, 138, 140), KTC (31, 140), ITC (12), PSC (14)	FLC: synergy (138) KTC: indifference (31, 89) ITC, PSC: indifference or synergy (12, 14)	Synergy in 62% of 50 strains studied for FLU-5FC (138); various doses may be necessary to achieve greatest effect; addition of 5FC helped prevent emergence of 5FC-resistant mutants
	Animal studies FLC: mice (3, 60, 61, 101, 139, 157)^b KTC: mice (50, 78, 158) and rabbits (150) ITC: mice (157), hamsters (89), and guinea pigs (212) PSC: mice (14)	Improved (3, 50, 61, 157), similar (14, 50, 60, 212), or worse (89) survival Reduced tissue burden (50, 78, 101, 212)	Combination associated with better survival than monotherapy and was consistent over a range of doses (3); effects more pronounced at lower doses (101), and single agents were very effective at higher doses alone; 5FC + KTC rarely cleared tissues better than either agent alone (150); hamsters with combination did worse than with ITC alone (89); ITC + 5FC performed similarly to ITC + AmB and better than ITC or 5FC monotherapy in guinea pigs (212); with 10 days of treatment of mice, combination prolonged survival more than either agent alone but not when treatment was limited to 5 days (157); PSC combination not better than monotherapy in terms of survival but better than monotherapy in reducing fungal counts in brain tissue (14)
	Humans FLC (48, 102, 124, 193, 223)	Good clinical success (48, 102, 193, 223) Increased survival (124)	63% success rate in cryptococcal meningitis (95% confidence interval, 48-82%) (102); improved survival (32%) versus FLC alone (12%) at 6 months in AIDS-associated cryptococcal meningitis (124)
AmB + triazoles	In vitro FLC (13, 74), KTC (78, 140, 150, 161), ITC (13), PSC (13)	Indifference (13, 78, 140)	FLC: indifference in 10/15 strains tested, indifference in 4/15, and synergy in 1/15 with NCCLS methods (13); indifference among 3 strains using an inoculum of 104 CFU/ml on yeast nitrogen base broth and response surface plots (74); KTC: no antagonism observed (78, 140, 150); synergy reported with one strain in two studies using nonstandard methodologies (140, 161); ITC: 14/15 strains indifferent; 1/15 synergistic (13); PSC: 8/15 strains indifferent; 5/15 synergistic; 2/15 indifferent in one study (13)
	Animal models FLC: mice (2, 13)^b KTC: mice (50, 78, 158) and rabbits (150) ITC: mice (157) and guinea pigs (212)	FLC/KTC: improved survival compared to results with azole (2, 13, 78, 158)^b and/or AmB (2, 158) ITC: did not improve or worsened survival (157) Reduced tissue burden (2, 13, 78, 212)	FLC: addition of AmB to FLC had dramatic impact on yeast burden in brain tissue^b, but survival with AmB was 100%; effects on survival were greatest at highest dosages of azole-AMB (2, 158); improved survival at lower doses of ITC + AmB, but survival was worse when higher doses were used (157); FLU preexposure did not reduce subsequent AmB activity (13)
	Humans—case report (47)		Case report of a woman with meningitis who responded to this combination after failing AmB
Caspofungin or anidulafungin + AmB	In vitro (71)	Synergy	Used higher levels of caspofungin than would be used for humans
Caspofungin or anidulafungin + FLC	In vitro (71, 169)	Indifference (71, 169) or synergy (71)	One study showed that echinocandins were no better than FLC monotherapy (169); no antagonism (71, 169)
ITR + FLC	Guinea pigs (212)	Reduced tissue burden	Survival was 100% in all treatment groups; improved sterilization of tissues compared to FLC but not ITC

↵ a AmB, amphotericin B; CLT, clotrimazole; FLC, fluconazole; 5FC, flucytosine; KTC, ketoconazole; ITC, itraconazole; PSC, posaconazole; RVC, ravuconazole; SPC, saperconazole; TRB, terbinafine; VRC, voriconazole.
↵ b Larsen et al., Abstr. 5th Int. Conf. Cryptococcus Cryptococcosis, abstr. P3.1, 2002.

TABLE 4.

Summary of key findings reported in studies of Candida spp. with combinations of clinically relevant antifungal agents^a

Combination	Settings studied	General findings	Comments
5FC + AmB	In vitro (21, 40, 63, 74, 92, 105, 122, 133, 140, 156, 161, 178, 191)	Synergy (40, 105, 133, 178, 191) or indifference (21, 74, 92, 122)	Addition of AmB helps prevent emergence of 5FC resistance
	Mice (157, 164, 191, 209) and rabbits (208)	Improved survival (164) Reduced tissue burden (164, 208, 209)	Most effective combination in one study when compared with results for AmB-rifampin, 5FC-KTC, and these agents alone (208); reduced dosages of the agents were possible in combinati on while maintaining efficacy (209)
	Humans with invasive disease (1, 36, 100, 155)	Good clinical success	AmB + 5FC cleared cultures faster than fluconazole in humans with peritonitis (100)
5FC + azoles	In vitro Econazole (63), miconazole (63, 191) CLT (22), KTC (19, 20, 140), FLC (74, 105, 129)	No consensus Synergy (129), indifference (19, 105), antagonism (74, 140)	Extended duration of postantifungal effect was reported in one study with fluconazole-flucytosine (129), low concentrations of 5FC-KTC appeared antagonistic for C. parapsilosis (19) contour surface plot methodology suggested negative interaction between fluconazole and flucytosine over a range of concentrations (74)
	KTC: mice (158) and rabbits (208) ITC: mice (157) FLC: mice (180) and rabbits (115)	Improved survival (157, 158) Reduced tissue burden (115, 208)	FLC doses in rabbits were equivalent to 1,600 mg/day in humans (115); 5FC-KTC appeared to prolong survival against some C. albicans strains in a murine model more than either agent alone (even in higher concentrations) but against other strains had no survival benefit over a single agent (158); effects most apparent with 5FC-resistant C. albicans strains; in rabbits (115) FLC-AmB combination sterilized cardiac vegetations faster than FLC but performed similarly to FLC in kidney
	Humans (181)		Case report of sepsis due to C. albicans that was treated successfully with 5FC plus FLC (181)
AmB + azoles	In vitro FLC (67, 74, 105, 107, 122, 154, 161, 175, 185, 186, 214, 216, 217),^b sequential (67, 105, 107, 175) Miconazole (31, 49, 63, 154, 191)^c CLT (22, 49) KTC (31, 140, 154, 161, 183, 198) ITC (154, 161, 184, 185)	Antagonism	One study suggested indifferent effects for AmB-FLC against C. albicans over a wide range of concentrations (74) Slight synergy with higher concentrations of KTC and AmB (161); short-term exposure with miconazole resulted in antagonism, long-term exposure resulted in positive effects (31)
	FLC: mice (113, 176, 199, 202) and rabbits (115, 176) ITC: mice (157, 203) KTC: mice (158) and rabbits (208) PSC: mice^d SPC: mice (206) Sequential: mice (202, 203, 216)	Improved (FLC, PSC, SPC) (113, 157, 176, 202) or similar to worse (ITC, KTC) (157, 203) survival Reduced tissue burden (FLC, KTC) (115, 208) but ITC-AmB had poorer clearance of tissues (kidney) (203) with combination	AmB-FLC effects not as profound in a less-acute model of infection (202); in rabbits, combination was not better than AMB alone in sterilizing cardiac vegetations and kidneys (115). Rabbit model used FLC doses equivalent to 1,600 mg/day in humans (115). In mice, the combination resulted in worse survival and kidney fungal burden compared to AmB alone (113) against FLC-susceptible and low-level resistance (MIC, 64 to 125 μg/ml) strains AmB-FLC gave better survival than AmB but not FLC (199) and in another study gave better survival than FLC but not AmB (176). IT C-AmB resulted in 100% mortality in mice, while 90% of amB- treated mice survived; in neutropenic rabbits AmB-KTC improved sterilization rates in kidneys (208) relative to either agent alone but not as much as AmB-5FC combination; AmB-KTC prolonged survival against one C. albicans strain but not 2 others (158); combinations of AmB-KTC against 2 C. albicans strains were generally not better than AmB alone in prolonging survival in infected mice (158)
	Humans with candidemia (166)	Good clinical success	Comparable clinical cure rates to FLC alone, faster bloodstream sterilization with the combination regimen
AmB + nystatin	In vitro (31)	Indifference	/PICK>
Caspofungin or anidulafungin + FLC	In vitro (169)^b	Indifference	FLC reduced caspofungin activity against C. albicans biofilms^b; in mice no additional benefit of combination therapy was observed with low doses of FLC and caspofungin on clearance of yeasts from kidneys^e
	Mice (77)	Improved or similar tissue burden	Caspofungin + FLC over 4 dosing schemes did not improve tissue clearance of C. albicans from kidney tissue compared to FLC alone but not caspofungin alone
TRB + FLC or ITC	In vitro (10, 11)	Indifference (10, 11) or synergy (10, 11)	No antagonism observed (10, 11)
	Humans (73)		Case report of successful therapy of oropharyngeal candidiasis due to azole- and terbinafine-resistant C. albicans with TRB + FLC therapy
TRB + AmB	In vitro (10)	Indifference or synergy	No antagonism observed
AmB + rifampin	In vitro (23)	Synergy	Synergy in 6 of 8 strains tested; used method of Jawetz (90) to define synergy
	Neutropenic rabbits (208)	Similar or worse tissue burden	Worse clearance of yeasts from splenic tissue than with AmB alone but similar clearance in kidney, liver, and lung
TRB + cyclosporine A or tacrolimus	In vitro (142)	Synergy	Synergistic against C. albicans as well as C. glabrata and C. krusei; dependent on calcineurin
FLC + cyclosporine	In vitro (120)	Synergy or indifference	Results varied with endpoint used
	Rats (119)	Reduced tissue burden	FLC approximated high doses used in humans, but cyclosporine concentrations were higher than that used in humans; combination was the most effective regimen in clearing cardiac vegetations and kidneys even compared to AmB

↵ a See Table 3 for drug name abbreviations.
↵ b Also Bachman et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-1813, 2002.
↵ c Also Schacter et al., letter.
↵ d Cacciapuoti et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-1814, 2002.
↵ e Bocunegra, L.K. Navjar, S. Hernandez, R.A. Larsen, and J.R. Graybill, Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-864, p. 387, 2002.

TABLE 5.

Summary of key findings reported in studies of Aspergillus spp. with combinations of clinically relevant antifungal agents^a

Combination	Settings studied	Findings	Comments
AmB + 5FC	In vitro (58, 87, 95, 104, 140)^b	No consensus Synergy^b; synergy or indifference (95); indifference (87, 104); antagonism or synergy (58)	Results differ between studies and are variable amongst strains in same study (58, 95), different methodologies and doses employed

	Mice (6, 157) and rats (187)	Improved survival (6, 157)	Improved survival with 5FC + AmB in mouse model (6). No survival benefit with 5FC + AmB vs. AmB alone in steroid-suppressed rats (187).
AmB + rifampin	In vitro (95)	Synergy (95); indifference or synergy (46, 58, 87)	Antagonism not observed in any study
	Mice (6) and rats (187)	No consensus	No survival benefit with rifampin + AmB vs. AmB alone in steroid-suppressed rats (187).
			Improved survival with rifampin + AmB in mouse model (6).
AmB + azoles	In vitro (58, 87, 97, 118, 140, 207)^b^,^c^,^d^,^e	No consensus	Pretreatment with KTC (118) or ITC (97, 118) strongly attenuates effect of AmB; simultaneous treatment less antagonistic to indifferent; AmB then KTC weakly synergistic (118); no antagonism for AmB then ITC; indifferent effects with simultaneous ITC-AmB^e. Studies using colorimetric analysis and response surface modeling demonstrated ITC-AmB antagonism with simultaneous use (207).^b
		Synergy (58, 140), antagonism, (118, 140, 207)^c^,^b or indifference (58, 87)^d
	ITC: Mice (179)^f KTC: mice (157, 180) and rats (187) PSC: mice^g	Concurrent: no survival benefit (ITC)^f or worse survival (KTC) (157, 187)	Neutropenic mice had significantly worse survival when pretreated with KTC before AmB or AmB + KTC (180). Steroid-suppressed rats given simultaneous KTC and AmB had worse survival than with AmB alone (187). Mice pretreated with ITC before AmB or AmB + ITC had lower survival than without pretreatment (179). Neutropenic mice with CNS infection had equal survival with either agent or combination vs. no treatment^f but nonneutropenic mice challenged intravenously had reduced survival times with combination therapy (157). In mice, no sequential antagonism of PSC by pretreatment with AmB^g.
		Sequential: no survival benefit with or worse survival (179) compared to AmB results alone
AmB + echinocandins	In vitro Caspofungin (5, 15)^e Anidulafungin or micafungin^h	Synergy (5),^e indifference or synergy (15)^h	No antagonism seen. Eagle-like effect (antagonism at high doses) seen in one study^h.
	Mice Caspofunginⁱ or micafungin^j^,^k	Improved survival^j^,^k Reducedⁱ^,^k or similarⁱ tissue burden	Neutropenic mice, fungal burden in kidneys at 4 days reduced (10/16 groups) or equivalent (6/16) with combination therapy vs. either agent alone. Increased survival, reduced fungal lung burden, reduced serum galactomannan titer with combination vs. monotherapy^j. Steroid-immunosuppressed mice had 100% survival with combination therapy vs. 61% with micafungin and 53% with AmB.
Triazoles + caspofungin or micafungin	In vitro ITC-caspofungin^e^,^l^,^m or micafungin^j PSC-caspofungin^m RVC-caspofungin^m VRC-caspofungin or micafungin^d^,^m^,ⁿ	Indifference or synergy^d^,^j^,^l^,^m^,ⁿ or synergy^e^,^m	No antagonism seen in most studies; increased susceptibility with preexposure to either agent^l. VRC-caspofungin: indifference against caspofungin- or micafungin-resistant-strains,^d ITC and PSC demonstrated synergy with caspofungin^m; RVC and VRC demonstrated indifference with caspofungin^m.
	ITC-caspofungin: guinea pigs^o ITC-micafungin: mice (117) KTC-micafungin: mice (117) RVC-micafungin: rabbits^p VRC-guinea pigs (94)	Improved (117)^p (94) survival or similar Reduced tissue burden (94)^o.	Fungal burden in kidneys at day 4 undetectable in 9/9 animals receiving ITC-caspofungin therapy^o. RVC-micafungin increased survival with combination (9/12) vs. revuconazole alone (2/8) or micafungin alone (0/8)^p.

↵ a See Table 3 for drug name abbreviations.
↵ b Also see Te Dorsthorst et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-850, 2002.
↵ c Also see Gavalda et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-1817, 2002.
↵ d Also see M. A. Ghannoum, N. Isham, and D. Sheehan, Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-855, p. 385, 2002.
↵ e Also see Manavathu et al., Abstr. 40th Intersci. Conf. Antimicrob. Agents Chemother., abstr. 931, 2000.
↵ f Also see Chiller et al., Abstr. 41st Intersci. Conf. Antimicrob. Agents Chemother., abstr. J-1614, 2001.
↵ g Najvar et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-1818, 2002.
↵ h Ostrosky-Zeichner et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-1816, 2002.
↵ i Douglas et al., Abstr. 41st Intersci. Conf. Antimicrob. Agents Chemother., abstr. J-1836, 2001.
↵ j Kohno et al., Abstr. 40th Intersci. Conf. Antimicrob. Agents Chemother., abstr. 1686, 2000.
↵ k Nakajima et al., Abstr. 40th Intersci. Conf. Antimicrob. Agents Chemother., abstr. 1685, 2000.
↵ l Kontoyiannis et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-851, 2002.
↵ m Manavathu et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-854, 2002.
↵ n O'Shaughnessy et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-856, 2002.
↵ o Douglas et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-1819, 2002.
↵ p Petraitiene et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-857, 2002.