A REPORT OF ThE CERhR AmPhETAmINES ExPERT PANEL:
2.1 Pharmacodyamics and Pharmacokinetics
2.2.1.4 Drug Abuse
Abuse. of. amphetamines. and. methamphetamines. is. associated. with. development. of. tolerance,.
psychological.dependence,.and.social.disability.(6, 8, 10)..There.are.reports.of.some.patients.greatly.
increasing.dosages.above.recommended.levels..Abrupt.withdrawal.following.prolonged.intake.of.
high.doses.can.result.in.extreme.fatigue,.mental.depression,.and.sleep.electroencephalogram.(EEG).
changes..Toxicity.associated.with.chronic.intoxication.can.include.dermatoses,.insomnia,.irritability,.
hyperactivity,.and.personality.changes..Though.rare.with.oral.intake,.psychosis.that.is.indistinguishable.
from.schizophrenia.has.been.reported..Repetitive.and.stereotypic.behavior.that.can.advance.to.self-injurious.behavior.has.been.observed.with.high.or.repeated.dosing.with.amphetamines.(reviewed.in.
(27))..Animal.models.used.to.investigate.self-injurious.behavior.in.humans.are.discussed.below.in.
Section.2.2.2.
Studies.in.humans.who.abused.methamphetamine.and.possibly.other.substances.revealed.persistent.
reductions.in.striatal.dopamine.transporter.as.observed.by.imaging.techniques.(reviewed.in.(27, 68)).
and.deficits.in.striatal.dopamine,.tyrosine.hydroxylase.activity,.and.dopamine.transporters.during.
autopsy.(reviewed.in.(27))..The.effects.in.autopsy.subjects.were.described.as.likely.markers.of.damage.
to.the.striatal.dopaminergic.system,.but.it.was.noted.that.there.were.no.obvious.behavioral.symptoms..
Dopaminergic.effects.in.humans.receiving.therapeutic.doses.of.amphetamines.are.not.known..
2.2.2 Experimental Animal
Symptoms.of.acute.amphetamine.toxicity.in.rats.and.mice.include.hyperactivity,.piloerection,.salivation,.
and. hyperpnea. (reviewed. in.(24));. dilated. pupils. and. convulsions. have. also. been. reported.(69)..
Symptoms.of.acute.methamphetamine.toxicity.in.rodents.were.reported.as.excitement,.convulsions,.
and.changes.in.seizure.threshold.(70)..The.oral.LD50.for.d-amphetamine.in.rats.is.reported.at.96.8.mg/
kg.bw..LD50.values.for.d,l-amphetamine.and.methamphetamine.in.various.species.are.summarized.
in.Table.21.and.Table.22..
Appendix II
Table 21. LD50 Values for d,l-Amphetamine Species Exposure
Route LD50 (mg/kg bw)
Mouse
oral 24a
ip 13a
iv 31.8a
sc 7a
Rat
oral 55
ip 125
sc 160
Dog oral 23
iv 6
Guinea.pig ip 50
sc 105
Rabbit iv 22
Data.from.NIOSH.(69).for.all.routes.and.from.NTP.(24) for.oral.route.
a.The.Expert.Panel.questions.the.accuracy.of.the.mouse.
LD50.data,.as.explained.in.text.below.
[The Expert Panel questions the accuracy of mouse LD50 values reported for d,l-amphetamine (Table 21). It does not make sense that the oral LD50 would be less than the iv LD50, nor that the sc LD50 would be lowest of all. The discrepancies may be due to the use of animals of different ages. In addition, while the LD50 for oral administration of d,l-amphetamine in mice is listed as 24 mg/kg in Table 21, the NTP carcinogenicity studies (24, 71) described in Section 2.4.2 used an estimated 19 (female) and 30 (male) mg/kg bw/day dose for 103 weeks and had no differences in survival of treated groups.]
Table 22. LD50 Values for Methamphetamine Species Exposure
Route
LD50 (mg/kg bw) Mouse
ip 15.
iv 6.3
sc 7.56
Rat sc 10.93
Guinea.pig oral 90
Data.from.Registry.of.Toxic.Effects.of.Chemical.Substances.
(RTECS).database.(70).
Appendix II
Continuous.iv.infusion.of.rats.with.amphetamines.1.mg/kg.bw/hour.for.12.days.resulted.in.reduced.
brain.norepinephrine.and.cardiac.catecholamine.levels.and.increased.motor.activity.and.stereotypic.
behaviors,.manifested.as.grooming,.scratching,.rearing,.limb.flicks,.and.biting.(reviewed.in.(24))..
Behavioral.effects.were.reversed.upon.cessation.of.dosing..Amphetamine.effects.following.repeated.
oral. dosing. are. reported. below. in. the. description. of. an. NTP. study.. Repeated. parenteral. dosing.
of.rodents.with.methamphetamine.has.caused.excitement,.weight.loss.or.decreased.weight.gain,.
alteration.in.classical.conditioning,.changes.in.pancreas,.and.hemorrhage.(70)..Higher.doses.[not specified].of.amphetamines.were.reported.to.induce.brain.lesions.such.as.hyperemia,.hemorrhage,.
and.glial.proliferation.in.monkeys.and.enlarged.and.chromatolytic.medulla.oblongata.neurons.in.cats.
(reviewed.by.(71))..
A.review.by.Kita.et.al..(27).reported.that.parenteral.dosing.with.methamphetamine.or.amphetamine.
concentrations. exceeding. therapeutic. levels. has. resulted. in. persistent. regional. (mainly. striatal).
depletion.of.brain.dopamine.levels.in.rats,.mice,.cats,.guinea.pigs,.and.monkeys,.and.decreased.
tyrosine.hydroxylase.activity.in.rats.and.cats..Decreased.numbers.of.dopamine.transport.pumps.were.
reported.in.mice.and.rats..Catecholamine.turnover.was.found.to.be.increased.in.rats..Reductions.in.
brain.norepinephrine.levels.were.observed.in.monkeys.and.cats..Decreases.in.serotonin.concentration.
and.tryptophan.hydroxylase.activity.were.reported.in.rats.and.cats.and.reduced.numbers.of.serotonin.
transporter. pumps. were. reported. in. one. rat. study.. Some. recovery. of. neurotransmitter. levels. was.
observed.at.lower.doses.in.monkeys.(~2.0.mg/kg.bw).and.rats.(≤.12.5.mg/kg.bw),.but.at.higher.doses,.
the.effects.persisted.for.months..Studies.examining.effects.of.amphetamines.on.neurochemical.indices.
in.developing.animals.are.discussed.in.detail.in.Section.3.2.3..
Neuroanatomical.evidence.of.amphetamine-induced.toxicity.was.also.reported..Swollen.nerve.fibers.
and.terminals.were.observed.in.rats.and.mice.dosed.with.amphetamine.or.methamphetamine.(reviewed.
in.(27))..Methamphetamine.treatment.has.resulted.in.reductions.of.brain.dopaminergic.axons.and.axon.
terminals.in.rats.and.monkeys.and.serotonergic.axons.and.axon.terminals.in.rats.(reviewed.in.(72))..
Development.of.neurotoxicity.depends.on.dose,.number.of.exposures,.intervals.between.dosing,.and.
duration.of.neuron.exposure.(reviewed.in.(72))..It.has.been.reported.that.administration.of.reuptake.
blockers.with.amphetamines.prevents.neuronal.damage.(reviewed.in.(27, 72))..Apoptosis.was.reported.
as.a.possible.mechanism.of.neurotoxicity.in.mice.and.rats.(reviewed.in.(27))..
A.review.by.Kita.et.al..(27).discusses.the.animal.literature.and.modeling.that.supports.self-injurious.
behaviors.in.humans..Kita.et.al..state.“The.acute.appearance.of.self-injurious.behavior.associated.
with.administration.of.amphetamines.to.rodents.may.accurately.predict.the.later.neurotoxicity.and.at.
the.same.time.serve.as.a.model.for.the.study.of.this.disabling.symptom.in.humans.”.Animal.literature.
does.not.provide.a.neurochemical.basis.for.self-injurious.behavior.although.it.points.to.involvement.
of.central.dopamine.neurons..Reversal.of.some.self-injurious.behaviors.by.dopamine.antagonists.
provides.evidence.of.dopaminergic.involvement.
NTP.toxicity.studies.were.reviewed.in.detail.because.reproductive.organs.were.examined.in.a.subchronic.
and.a.carcinogenicity.study.and.growth.was.measured.in.the.subchronic.study..The.carcinogenicity.
study.is.described.in.Section.2.4.2.
Appendix II
sulfate. in. F344/N. rats. and. B6C3F1. mice.. Rats. and. mice. were. randomly. assigned. to. groups. and.
administered. USP. grade.d,l-amphetamine. sulfate. (99%. purity). through. feed.. Drug. stability. and.
concentration.in.feed.were.verified..Survival.data.were.analyzed.using.Kaplan.Meier,.Cox,.or.Tarone.
life.table.test.methods..Continuous.data.were.analyzed.using.Dunn,.Shirley,.or.Jonckheere.tests..
In.the.14-day.study,.7-week-old.rats.(5/sex/group).were.fed.diets.containing.0,.47,.94,.188,.375,.or.
750.ppm.d,l-amphetamine.sulfate..Nine-week-old.mice.(5/sex/group).were.fed.diets.with.0,.125,.250,.
500,.1000,.or.2000.ppm.d,l-amphetamine.sulfate..Animals.were.observed.daily.and.weighed.before,.
during,.and.after.the.study..Following.kill,.animals.were.necropsied.and.organ.weights.were.measured..
Major.organs.were.fixed.in.10%.neutral.buffered.formalin.for.a.histological.analysis..Included.among.
organs.analyzed.were.mammary.gland,.prostate,.testis,.seminal.vesicle,.ovary,.and.uterus..Doses.at.
which.histological.evaluation.was.conducted.in.each.species.are.discussed.below..
In.the.14-day.study,.all.rats.survived..Final.mean.body.weights.in.the.375.and.750.ppm.groups.were.
7.–.9%.lower.for.males.and.5.–.16%.lower.for.females.compared.to.controls..Reduction.in.final.body.
weight.was.statistically.significant.for.females.at.750.ppm..Feed.intake.was.reduced.in.groups.exposed.
to.≥94.ppm.during.the.first.week.of.the.study.and.was.marginally.reduced.in.males.from.the.750.ppm.
group.during.the.second.week.of.the.study..Hyperactivity.[determined by general observations, not standard measures].was.observed.in.rats.exposed.to.≥375.ppm..According.to.the.results.section,.
absolute.heart.weight.was.reduced.in.females.exposed.to.≥375.ppm..[The only organ weight effect data shown in Table J1 of the NTP study are for liver. According to that table, relative (to body weight) liver weights were increased in males exposed to 750 ppm and females exposed to ≥188 ppm.].Histopathologic.evaluation.was.conducted.on.animals.from.the.control.and.750.ppm.groups;.
no.lesions.were.observed.[data not shown].
Four.males.in.the.1000.ppm.group.and.1.male.in.the.2000.ppm.died.in.the.14-day.mouse.study..
According.to.study.authors,.the.deaths.were.not.clearly.related.to.treatment..Weight.loss.occurred.
in.males.exposed.to.≥500.ppm..Mean.final.body.weights.of.females.exposed.to.≥250.ppm.were.
significantly.lower.than.controls.by.12.–.13%..Feed.intake.was.similar.in.all.groups,.although.it.was.
noted.that.the.2000.ppm.males.scattered.their.feed..Mice.in.the.1000.ppm.group.were.either.hyperactive.
or.lethargic.and.hyporesponsive..According.to.the.results.section,.relative.liver.weights.were.increased.
in.males.exposed.to.≥.250.ppm.and.females.from.the.2000.ppm.group..Other.significant.organ.weight.
changes.listed.in.Table.J3.of.the.NTP.report.included.decreased.absolute.brain.and.thymus.weight.
and.increased.relative.kidney.weights.in.males.of.the.2000.ppm.group;.absolute.heart.weight.was.
increased.in.females.exposed.to.≥125.ppm..Histopathologic.evaluation.was.conducted.in.controls,.the.
2000.ppm.group,.and.males.in.the.1000.ppm.group..No.lesions.were.observed.[data not shown].
The.13-week.studies.were.conducted.according.to.FDA.Good.Laboratory.Practice.(GLP).procedures..
At.7.–.8.weeks.of.age,.10.rats/sex/dose.were.fed.diets.containing.0,.47,.94,.188,.375,.or.750.ppm.d,l-amphetamine.sulfate..At.8.–.9.weeks.of.age,.10.mice/sex/group.were.fed.diets.containing.0,.125,.250,.
500,.1000,.or.2000.ppm.d,l-amphetamine.sulfate..Doses.were.based.upon.results.observed.in.the.14-day.studies..Animals.were.observed.daily.and.weighed.before,.during,.and.after.the.study..Following.
kill,.animals.were.necropsied.and.organs.were.weighed..Major.organs.were.fixed.in.10%.neutral.
buffered.formalin.for.histological.analysis..Included.among.organs.analyzed.were.mammary.gland,.
prostate,.testis,.ovary,.and.uterus..Doses.at.which.histologic.evaluation.was.conducted.in.each.species.
Appendix II
are.discussed.below..Thymus.and.spleen.were.also.examined.in.some.rats.from.lower.dose.groups.
All.rats.survived.in.the.13-week.study..Final.body.weights.were.significantly.reduced.in.both.sexes.
of.all.treated.groups..Final.mean.body.weights.in.the.188,.375,.and.750.ppm.groups.were.11,.18,.and.
38%.lower.in.males.and.15,.26,.and.32%.lower.in.females..Feed.intake.by.the.750.ppm.males.was.20%.
lower.than.controls..Hyperactivity.was.observed.in.all.dose.groups.and.severity.increased.according.
to.dose..According.to.study.authors,.organ.weight.changes.were.due.to.body.weight.reductions..
[The study authors’ statement is confirmed by dose-related reductions in absolute weight and increases in relative organ weights observed in many organs. The exceptions that appeared to be dose-related were an increase in absolute brain weight (≥94 ppm females) and decreases in relative (to body weight) liver (750 ppm males) and thymus (≥94 ppm males, ≥375 ppm females) weights.].A.histopathological.examination.was.conducted.in.controls.and.the.750.ppm.group..No.
treatment-related.lesions.were.observed.[data not shown]..
In.the.13-week.mouse.study,.8.males.of.the.500.ppm.group.died,.3.males.of.the.1000.ppm.group.died,.
and.7.females.and.6.males.from.the.2000.ppm.group.died..Mean.final.body.weights.of.all.treated.
groups.were.lower.than.controls..At.doses.≥250.ppm,.body.weights.were.18.–.30%.lower.than.controls.
in.males.and.13.–.19%.lower.than.controls.in.females..All.treated.mice.were.hyperactive.and.severity.
increased.according.to.dose..Fighting.was.observed.in.males.exposed.to.≥250.ppm..According.to.study.
authors,.increases.in.relative.organ.weights.were.due.to.reduced.body.weights..[Decreases in absolute organs weights were also consistent with reduced body weights.] A.histological.evaluation.was.
conducted.in.the.control.and.2000.ppm.groups,.males.in.the.1000.ppm.group,.and.all.mice.that.died.
during.the.study..No.treatment-related.lesions.were.observed.[data not shown].