- Email: [email protected]
Tolerance to a lethal dose of phenacetin in phenacetin-pretreated albino rats
(1971)
TOXJCOLOGYANDAPPLIEDPHARMACOLOGY18,269-213
Tolerance to a Lethal Phenacetin-Pretreated GIOVANNA
Department
Dose
in
CARRO-CIAMPI
of Pharmacology, Kingston, Ontario, Received
of Phenacetin Albino Rats
Norember
Queen’s Canada
Uniuersit~~,
20, I969
Tolerance to a Lethal Dose of Phenacetin in Phenacetin-Pretreated Albino Rats. CARRO-CIAMPI, G. (1971). Toxicol. Appl. Pharmacol. 18, 269-273. Repeateddaily oral administration of sublethaldosesof phenacetin to malealbino rats enabledthe animalsto tolerate a lethal oral doseof phenacetin.This wasobservedat daily dosesequal to l/6, l/5, l/4, and 213 of the oral LD50CIo0daysjof phenacetinwhich is 1.12t 0.02 g/kg/day. The duration of treatment necessaryto induce tolerance varied from 5 weeks for the lower daily dosesto 2 weeksfor the highestdaily dose.Tolerancewas also demonstratedin the survivors of a group of rats treated with toxic increasingdaily dosesof phenacetinfor a period of 7 days. Tolerancedisappearedwithin 1 week of the abrupt discontinuationof daily administration of phenacetin. In his review on phenacetin, Smith (1958) stated that “there is no evidence that addiction occurs and physical dependence and withdrawal symptoms have not been demonstrated either in animals or in man.” This wasconfirmed by Boyd and Hottenroth (1968) in a study of the chronic oral toxicity of phenacetin in the albino rat. In the experiments reported by Boyd and Hottenroth (1968) and in related experiments reported by Boyd ef al. (1969), it was observed that most deaths occurred in the first weeks of daily administration of large doses of phenacetin. This suggestedthe possibility that sometype of adjustment or adaptation may develop to the lethal actions of the drug during the initial weeksof administration. The present study was undertaken to test this possibility. The project had two objectives: (a) to ascertain whether rats chronically treated with phenacetin develop a capacity to tolerate a lethal dose of phenacetin; and (b) to determine the effects on any demonstrated tolerance of the parameters involved, namely, daily dose and duration of phenacetin pretreatment.
METHODS The experiments were performed on young adult male albino rats of a Wistar strain.’ They were housed in groups of 8-10 in boarding cages22 i: 20 x 13 inches and were given a standard laboratory diet2 and water ad libitum. ’ The animalswereobtainedfrom Woodlyn FarmsLimited,Guelph,Ontario. * The diet wasRocklandMouse/RatDiet Complete from Teklad Incorporated of Winfield, Iowa. 10
269
270
CARRO-CIAMPI
Phenacetin, USP XVII, was used as a suspension in distilled water with 0.2 % gum tragacanth prepared fresh daily. It was administered orally through an intragastric cannula attached to a syringe. The volume of suspension was kept constant at 20 ml/kg body weight. A solution of 0.2 % gum tragacanth in distilled water was prepared daily and administered to control animals through an intragastric cannula at a volume of 20 ml/kg body weight. The schedule of phenacetin pretreatments is indicated in Table 1. The animals were given phenacetin daily for 5 days a week, at doses equal to 715 of those listed in Table 1 (which are calculated as given daily, 7 days a week), according to the method of Boyd and Hottenroth (1968).3 A total of 72 phenacetin-pretreated rats were distributed into 5 different dosage groups of 6-15 animals per group. The respective daily doses were approximately l/10, l/6, l/5, l/4, and 2/3.of the oral LD50000 days)of phenacetin in male rats, calculated by Boyd and Hottenroth (1968) to be equal to 1.12 & 0.02 g/kg/ day. The duration of treatment varied between 15 and 42 days (Table 1). The number of gum tragacanth controls varied from 4 to 15 per group to a total of 59 (Table 1). TABLE
1
THE SCHEDULE OF PHENACETIN-PRETREATMENT IN RATS
Daily dose of phenacetin k/W
Number of phenacetin-pretreated animals
Number of control animals
0.107
8 8 8 7 14 6 15 6
8 6 8 6 7 15 5
0.178 0.178 0.178 0.178 0.214 0.286 0.714
4
Days of pretreatment 42 21 28 35 35 (+6)b 35 35 15
E Daily doses are entered as average doses given daily, 7 days a week. As noted in the text, phenacetin was given as 715 of these doses for 5 days a week. b Thirty-five days of pretreatment were followed by 6 days in which phenacetin administration was withdrawn.
At the end of the pretreatment period, phenacetin-pretreated and control rats were starved overnight, and next morning they were given a lethal dose of phenacetin, 4 g/kg. Since Boyd and Krijnen (1969) noted that the susceptibility of rats to a lethal dose of phenacetin increases with increasing body weight, the body weight of treated and controls were compared by the Student’s t test (Snedecor and Cochran, 1967). RESULTS The mean body weight of phenacetin-pretreated rats, on the day when they were given 4 g/kg of phenacetin, was similar to that of the controls (Table 2), and none had 3 Boyd and Hottenroth (1968) have shown that a weekly dose divided into 5 equal parts and each part given 5 days a week had the same effect as divided into 7 equal parts and each part given 7 days a week.
271
PHENACETIN TOLERANCE TABLE 2 BODY WEIGHT OF PHENACETIN-PRETREATED RATS AND THEIR CONTROLS ON THE DAY THEY WERE GIVEN PHENACETIN IN A LETHAL DOSE OF 4 G/KG Phenacetin-pretreated Daily dose ---- (g/kg) 0.107 0.178 0.178 0.178 0.178 0.214 0.286 0.714 Total
N 8 8 8 7 14 6 15 6 72
Gum tragacanth controls
animals Mean & SD body weight (g) 252 274 307 304 304 315 308 359 301
f f i It rt & zt i f
N
23 14 18 17” 35 30 34 26 37
---
4 8 6 8 6 7 15 5 59
Mean i SD body weight (9) --260 I 28Odc 288 z 326 i 298 5 326 i 318 ir 370 * 308 rt
7 1.5 23 18 36 22 21 23 36
a The mean body weight of pretreated rats was significantly (P c 0.05) lower than that of the controls of the same group but did not differ significantly from the mean body weight of the total number of controls used. loo%80.
a
.
.
6040. 2000.107 Dose = 42 Days, Dose x Day: i-4.5
loo%t3060. 40. 20. ODose = Days, Dose x Days
0.178 21 = 3.7
. b r113
14
I.178 35 6.2
0.286
0.714
0.178 35+6 6.2
FIG. 1. Reduction in susceptibility to a lethal dose of phenacetin (4 g/kg) in phenacetin-pretreated rats. The bars indicate percent mortality values and their 95 % confidence limits. Empty bars indicate controls, and hatched bars phenacetin-pretreated animals. “Dose” indicates daily dose of phenacetin in g/kg/day; “Days” indicate number of days of pretreatment; and “Dose x Days” indicate total dose of phenacetin received during pretreatment in g/kg. A solid triangle indicates P < 0.05 > 0.02 and a solid square indicates P < 0.01. The results in the lower right columns were obtained by giving 4 g/kg of phenacetin 6 days after cessation of phenacetin-pretreatment, shown as “35 + 6”.
272
CARRO-CIAMPI
died as a result of pretreatment alone. The time to death, after 4 g/kg of phenacetin, varied from 24 to 72 hr. Percentage mortality values and their 95 ‘A confidence limits are represented in Fig. 1. In phenacetin-pretreated rats mortality rates were lower than those of controls. In order to test the statistical significance of the differences, chi square was calculated in each group by means of a 2 x 2 contingency table (Snedecor and Cochran, 1967). Groups in which the reduction in mortality was found not to be statistically significant were those treated with either too low a daily dose of phenacetin (0.107 g/kg/day for 42 days) or too short a duration of pretreatment (0.178 g/kg/day for 21 and 28 days). At the daily dose of 0.178 g/kg, decreased susceptibility to the lethal effect of 4 g/kg was not present when pretreatment had been withdrawn for 6 days (Fig. 1). In addition, it can be seen from Fig. 1, that a maximal tolerance was observed when a total dose of about 10-l 1 g/kg had been administered over a period of 15-35 days, suggesting that the duration of pretreatment could be considerably shortened without a loss of effect by using larger daily doses. To test this hypothesis an experiment was performed in which duration of pretreatment was reduced to 7 days. Nine rats were given daily, for 6 days, increasing doses of phenacetin of 1.O, 1.25, 1.56, 1.95,2.44, and 3.05 g/kg, which amounted to a total dose of 11.7 g/kg. The day after the last administration, 2 animals died. The next day the 7 survivors together with 5 controls of the same body weight were starved overnight and given 4 g/kg of phenacetin. All the controls died, and all the phenacetin-pretreated animals survived; the difference was statistically significant (P < - 0.05). DISCUSSION These experiments indicate that tolerance toward the lethal effects of phenacetin is produced by the previous repeated oral administration of phenacetin as suggested by the data of Boyd and Hottenroth (1968) and Boyd et al. (1969). Tolerance develops from relatively low, nontoxic daily doses of phenacetin as well as from higher doses which have severely toxic effects. The duration of administration necessary to obtain tolerance varies inversely with the daily dose of phenacetin used. The tolerance appears to be short-lived. These results and data reported in the literature indicating that phenacetin does not lead to habituation or physical dependence (Smith, 1958 ; Boyd and Hottenroth, 1968) suggest that metabolic factors might be the basis of the demonstrated tolerance. Decreased toxicity of a drug in the course of long-term chronic toxicity studies as well as that which results from previous administration of other drugs, has been demonstrated to be due to enhanced metabolism of the drug (Conney, 1965; Burns et al., 1965). Tolerance could also be due to the “receptors” becoming resistant. Reports were found in the literature which indicated that liver microsomal enzymes responsible for phenacetin metabolism are increased by a number of drugs. In citro O-dealkylation of phenacetin by rat liver microsomes is accelerated by previous administration to the intact animal of a single dose of alpha, beta, and gamma benzene hexachloride, dicophane, or dieldrin (Ghazal et al., 1964) and of 3-methylcholanthrene (Conney et al., 1966). Phenobarbital pretreatment of rats stimulates in ciao O-dealkylation and N-hydroxylation of phenacetin (Biich et al,, 1967). The ability of phenacetin to induce its own metabolism is not known. However, it has been demonstrated that,
PHENACETIN
TOLERANCE
173
when administered in a single dose to rats and guinea pigs, phenacetin fails to stimulate ill vitro hydrolysis of acetylsalicylic acid by liver microsomal enzymes (Howes and Hunter, 1968). ACKNOWLEDGMENTS The author wishesto acknowledgethe assistance and advice of Dr. Eldon M. Boyd and the receipt of a studentshipfrom the Medical ResearchCouncil of Canada. This project wasaidedfinancially by CharlesE. Frosst and Company of Montreal. REFERENCES BOYD,E. M., and HOTTENROTH, S. M. H. (1968).The toxicity ofphenacetin at the rangeof the oral LD50clo~ daysjin albino rats. Toxicol. Appl. Pharmacol. 12, 80-93. BOYD, E. M., and KRIJNEN, C. J. (1969). Tolerated dosesof phenacetinin relation to body weight and organ weights. Jap. J. Pharmacol. 19, 386-394. BOYD, E. M., CARRO-CIAMPI, G., and KRIJNEN, C. J. (1969).lntragastric versusdietary administration of phenacetin.Pharmacol. Res. Commun. 1, X9-264. B&H, H., GERHARDS, W., PFLEGER, K., R~~DIGER, W., and RUMMEL, W. (1967).Metabolische Umwandlung von Phenacetin und N-Acetyl-p-Aminophenol nach Vorbehandlung mit Phenobarbital.Biochem. Pharmacol. 16, 1585-1599. BURNS, J. J., CUCINELL, S. A., KOSTER, R., and CONNEY, A. H. (1965).Application of drug metabolismto drug toxicity studies.Ann. N. Y. Acad. Sci. 123, 173-286. CONNEY, A. H. (1965).Enzymeinduction and drug toxicity. Proc. Itlt. Pharmacol. Meet., 2t11l. 1963, Vol. 4, pp. 217-297. CONNEY, A. H., SANSUR, M., SOROKO, F., KOSTER, R., and BURNS, J. J. ( 1966).Enzymeinduction and inhibition in studies on the pharmacological actions of acetophenetidin. J. Pharmacol.
Exp. Therap. 151, 133-138.
A., KORANSKY, W., PORTIG, J., WOHLAND, H. W., and KLEMPAN, 1. (1964). Beschleunigung von Entgiftungsreaktionen durch verschiedeneInsecticide. !Vnllr!vn-Scl7mierf~~berg’s Arch. Exp. Pathol. Pharmakol. 249, I-10. HOWFS, J. F., and HUNTER, W. H. (1968). The hydrolysis of acetylsalicyclic acid by liver microsomes.J. Pharm. Pharmacol. 20, 107-l 10. SMITH, P. K. (1958). Acetophenetidin, a Critical Bibliographic RelVew, pp. 1388140.Wiley (Interscience),New York. SNEDECOR, G. W., and COCHRAN, W. J. (1967).Statistical Methods. 6th ed. Iowa State Univ. Press,Ames, Iowa. GHAZAL,
TOXJCOLOGYANDAPPLIEDPHARMACOLOGY18,269-213
Tolerance to a Lethal Phenacetin-Pretreated GIOVANNA
Department
Dose
in
CARRO-CIAMPI
of Pharmacology, Kingston, Ontario, Received
of Phenacetin Albino Rats
Norember
Queen’s Canada
Uniuersit~~,
20, I969
Tolerance to a Lethal Dose of Phenacetin in Phenacetin-Pretreated Albino Rats. CARRO-CIAMPI, G. (1971). Toxicol. Appl. Pharmacol. 18, 269-273. Repeateddaily oral administration of sublethaldosesof phenacetin to malealbino rats enabledthe animalsto tolerate a lethal oral doseof phenacetin.This wasobservedat daily dosesequal to l/6, l/5, l/4, and 213 of the oral LD50CIo0daysjof phenacetinwhich is 1.12t 0.02 g/kg/day. The duration of treatment necessaryto induce tolerance varied from 5 weeks for the lower daily dosesto 2 weeksfor the highestdaily dose.Tolerancewas also demonstratedin the survivors of a group of rats treated with toxic increasingdaily dosesof phenacetinfor a period of 7 days. Tolerancedisappearedwithin 1 week of the abrupt discontinuationof daily administration of phenacetin. In his review on phenacetin, Smith (1958) stated that “there is no evidence that addiction occurs and physical dependence and withdrawal symptoms have not been demonstrated either in animals or in man.” This wasconfirmed by Boyd and Hottenroth (1968) in a study of the chronic oral toxicity of phenacetin in the albino rat. In the experiments reported by Boyd and Hottenroth (1968) and in related experiments reported by Boyd ef al. (1969), it was observed that most deaths occurred in the first weeks of daily administration of large doses of phenacetin. This suggestedthe possibility that sometype of adjustment or adaptation may develop to the lethal actions of the drug during the initial weeksof administration. The present study was undertaken to test this possibility. The project had two objectives: (a) to ascertain whether rats chronically treated with phenacetin develop a capacity to tolerate a lethal dose of phenacetin; and (b) to determine the effects on any demonstrated tolerance of the parameters involved, namely, daily dose and duration of phenacetin pretreatment.
METHODS The experiments were performed on young adult male albino rats of a Wistar strain.’ They were housed in groups of 8-10 in boarding cages22 i: 20 x 13 inches and were given a standard laboratory diet2 and water ad libitum. ’ The animalswereobtainedfrom Woodlyn FarmsLimited,Guelph,Ontario. * The diet wasRocklandMouse/RatDiet Complete from Teklad Incorporated of Winfield, Iowa. 10
269
270
CARRO-CIAMPI
Phenacetin, USP XVII, was used as a suspension in distilled water with 0.2 % gum tragacanth prepared fresh daily. It was administered orally through an intragastric cannula attached to a syringe. The volume of suspension was kept constant at 20 ml/kg body weight. A solution of 0.2 % gum tragacanth in distilled water was prepared daily and administered to control animals through an intragastric cannula at a volume of 20 ml/kg body weight. The schedule of phenacetin pretreatments is indicated in Table 1. The animals were given phenacetin daily for 5 days a week, at doses equal to 715 of those listed in Table 1 (which are calculated as given daily, 7 days a week), according to the method of Boyd and Hottenroth (1968).3 A total of 72 phenacetin-pretreated rats were distributed into 5 different dosage groups of 6-15 animals per group. The respective daily doses were approximately l/10, l/6, l/5, l/4, and 2/3.of the oral LD50000 days)of phenacetin in male rats, calculated by Boyd and Hottenroth (1968) to be equal to 1.12 & 0.02 g/kg/ day. The duration of treatment varied between 15 and 42 days (Table 1). The number of gum tragacanth controls varied from 4 to 15 per group to a total of 59 (Table 1). TABLE
1
THE SCHEDULE OF PHENACETIN-PRETREATMENT IN RATS
Daily dose of phenacetin k/W
Number of phenacetin-pretreated animals
Number of control animals
0.107
8 8 8 7 14 6 15 6
8 6 8 6 7 15 5
0.178 0.178 0.178 0.178 0.214 0.286 0.714
4
Days of pretreatment 42 21 28 35 35 (+6)b 35 35 15
E Daily doses are entered as average doses given daily, 7 days a week. As noted in the text, phenacetin was given as 715 of these doses for 5 days a week. b Thirty-five days of pretreatment were followed by 6 days in which phenacetin administration was withdrawn.
At the end of the pretreatment period, phenacetin-pretreated and control rats were starved overnight, and next morning they were given a lethal dose of phenacetin, 4 g/kg. Since Boyd and Krijnen (1969) noted that the susceptibility of rats to a lethal dose of phenacetin increases with increasing body weight, the body weight of treated and controls were compared by the Student’s t test (Snedecor and Cochran, 1967). RESULTS The mean body weight of phenacetin-pretreated rats, on the day when they were given 4 g/kg of phenacetin, was similar to that of the controls (Table 2), and none had 3 Boyd and Hottenroth (1968) have shown that a weekly dose divided into 5 equal parts and each part given 5 days a week had the same effect as divided into 7 equal parts and each part given 7 days a week.
271
PHENACETIN TOLERANCE TABLE 2 BODY WEIGHT OF PHENACETIN-PRETREATED RATS AND THEIR CONTROLS ON THE DAY THEY WERE GIVEN PHENACETIN IN A LETHAL DOSE OF 4 G/KG Phenacetin-pretreated Daily dose ---- (g/kg) 0.107 0.178 0.178 0.178 0.178 0.214 0.286 0.714 Total
N 8 8 8 7 14 6 15 6 72
Gum tragacanth controls
animals Mean & SD body weight (g) 252 274 307 304 304 315 308 359 301
f f i It rt & zt i f
N
23 14 18 17” 35 30 34 26 37
---
4 8 6 8 6 7 15 5 59
Mean i SD body weight (9) --260 I 28Odc 288 z 326 i 298 5 326 i 318 ir 370 * 308 rt
7 1.5 23 18 36 22 21 23 36
a The mean body weight of pretreated rats was significantly (P c 0.05) lower than that of the controls of the same group but did not differ significantly from the mean body weight of the total number of controls used. loo%80.
a
.
.
6040. 2000.107 Dose = 42 Days, Dose x Day: i-4.5
loo%t3060. 40. 20. ODose = Days, Dose x Days
0.178 21 = 3.7
. b r113
14
I.178 35 6.2
0.286
0.714
0.178 35+6 6.2
FIG. 1. Reduction in susceptibility to a lethal dose of phenacetin (4 g/kg) in phenacetin-pretreated rats. The bars indicate percent mortality values and their 95 % confidence limits. Empty bars indicate controls, and hatched bars phenacetin-pretreated animals. “Dose” indicates daily dose of phenacetin in g/kg/day; “Days” indicate number of days of pretreatment; and “Dose x Days” indicate total dose of phenacetin received during pretreatment in g/kg. A solid triangle indicates P < 0.05 > 0.02 and a solid square indicates P < 0.01. The results in the lower right columns were obtained by giving 4 g/kg of phenacetin 6 days after cessation of phenacetin-pretreatment, shown as “35 + 6”.
272
CARRO-CIAMPI
died as a result of pretreatment alone. The time to death, after 4 g/kg of phenacetin, varied from 24 to 72 hr. Percentage mortality values and their 95 ‘A confidence limits are represented in Fig. 1. In phenacetin-pretreated rats mortality rates were lower than those of controls. In order to test the statistical significance of the differences, chi square was calculated in each group by means of a 2 x 2 contingency table (Snedecor and Cochran, 1967). Groups in which the reduction in mortality was found not to be statistically significant were those treated with either too low a daily dose of phenacetin (0.107 g/kg/day for 42 days) or too short a duration of pretreatment (0.178 g/kg/day for 21 and 28 days). At the daily dose of 0.178 g/kg, decreased susceptibility to the lethal effect of 4 g/kg was not present when pretreatment had been withdrawn for 6 days (Fig. 1). In addition, it can be seen from Fig. 1, that a maximal tolerance was observed when a total dose of about 10-l 1 g/kg had been administered over a period of 15-35 days, suggesting that the duration of pretreatment could be considerably shortened without a loss of effect by using larger daily doses. To test this hypothesis an experiment was performed in which duration of pretreatment was reduced to 7 days. Nine rats were given daily, for 6 days, increasing doses of phenacetin of 1.O, 1.25, 1.56, 1.95,2.44, and 3.05 g/kg, which amounted to a total dose of 11.7 g/kg. The day after the last administration, 2 animals died. The next day the 7 survivors together with 5 controls of the same body weight were starved overnight and given 4 g/kg of phenacetin. All the controls died, and all the phenacetin-pretreated animals survived; the difference was statistically significant (P < - 0.05). DISCUSSION These experiments indicate that tolerance toward the lethal effects of phenacetin is produced by the previous repeated oral administration of phenacetin as suggested by the data of Boyd and Hottenroth (1968) and Boyd et al. (1969). Tolerance develops from relatively low, nontoxic daily doses of phenacetin as well as from higher doses which have severely toxic effects. The duration of administration necessary to obtain tolerance varies inversely with the daily dose of phenacetin used. The tolerance appears to be short-lived. These results and data reported in the literature indicating that phenacetin does not lead to habituation or physical dependence (Smith, 1958 ; Boyd and Hottenroth, 1968) suggest that metabolic factors might be the basis of the demonstrated tolerance. Decreased toxicity of a drug in the course of long-term chronic toxicity studies as well as that which results from previous administration of other drugs, has been demonstrated to be due to enhanced metabolism of the drug (Conney, 1965; Burns et al., 1965). Tolerance could also be due to the “receptors” becoming resistant. Reports were found in the literature which indicated that liver microsomal enzymes responsible for phenacetin metabolism are increased by a number of drugs. In citro O-dealkylation of phenacetin by rat liver microsomes is accelerated by previous administration to the intact animal of a single dose of alpha, beta, and gamma benzene hexachloride, dicophane, or dieldrin (Ghazal et al., 1964) and of 3-methylcholanthrene (Conney et al., 1966). Phenobarbital pretreatment of rats stimulates in ciao O-dealkylation and N-hydroxylation of phenacetin (Biich et al,, 1967). The ability of phenacetin to induce its own metabolism is not known. However, it has been demonstrated that,
PHENACETIN
TOLERANCE
173
when administered in a single dose to rats and guinea pigs, phenacetin fails to stimulate ill vitro hydrolysis of acetylsalicylic acid by liver microsomal enzymes (Howes and Hunter, 1968). ACKNOWLEDGMENTS The author wishesto acknowledgethe assistance and advice of Dr. Eldon M. Boyd and the receipt of a studentshipfrom the Medical ResearchCouncil of Canada. This project wasaidedfinancially by CharlesE. Frosst and Company of Montreal. REFERENCES BOYD,E. M., and HOTTENROTH, S. M. H. (1968).The toxicity ofphenacetin at the rangeof the oral LD50clo~ daysjin albino rats. Toxicol. Appl. Pharmacol. 12, 80-93. BOYD, E. M., and KRIJNEN, C. J. (1969). Tolerated dosesof phenacetinin relation to body weight and organ weights. Jap. J. Pharmacol. 19, 386-394. BOYD, E. M., CARRO-CIAMPI, G., and KRIJNEN, C. J. (1969).lntragastric versusdietary administration of phenacetin.Pharmacol. Res. Commun. 1, X9-264. B&H, H., GERHARDS, W., PFLEGER, K., R~~DIGER, W., and RUMMEL, W. (1967).Metabolische Umwandlung von Phenacetin und N-Acetyl-p-Aminophenol nach Vorbehandlung mit Phenobarbital.Biochem. Pharmacol. 16, 1585-1599. BURNS, J. J., CUCINELL, S. A., KOSTER, R., and CONNEY, A. H. (1965).Application of drug metabolismto drug toxicity studies.Ann. N. Y. Acad. Sci. 123, 173-286. CONNEY, A. H. (1965).Enzymeinduction and drug toxicity. Proc. Itlt. Pharmacol. Meet., 2t11l. 1963, Vol. 4, pp. 217-297. CONNEY, A. H., SANSUR, M., SOROKO, F., KOSTER, R., and BURNS, J. J. ( 1966).Enzymeinduction and inhibition in studies on the pharmacological actions of acetophenetidin. J. Pharmacol.
Exp. Therap. 151, 133-138.
A., KORANSKY, W., PORTIG, J., WOHLAND, H. W., and KLEMPAN, 1. (1964). Beschleunigung von Entgiftungsreaktionen durch verschiedeneInsecticide. !Vnllr!vn-Scl7mierf~~berg’s Arch. Exp. Pathol. Pharmakol. 249, I-10. HOWFS, J. F., and HUNTER, W. H. (1968). The hydrolysis of acetylsalicyclic acid by liver microsomes.J. Pharm. Pharmacol. 20, 107-l 10. SMITH, P. K. (1958). Acetophenetidin, a Critical Bibliographic RelVew, pp. 1388140.Wiley (Interscience),New York. SNEDECOR, G. W., and COCHRAN, W. J. (1967).Statistical Methods. 6th ed. Iowa State Univ. Press,Ames, Iowa. GHAZAL,