Dimethyl sulfoxide

Endpoint summary

Description of key information

DMSO is of low toxicity by repeated administration. In a 13-week inhalation toxicity study, the NOAEC could be established at ca. 1.0 mg/l for respiratory tract irritation and ca. 2.8 mg/l (the highest concentration tested) for systemic toxicity. 
Other repeated dose toxicity studies performed by different routes of administration and with several mammalian species have also shown that DMSO produced only slight systemic toxicity. With the exception of a decrease of the body weight gain and some hematological effects (which could be secondary to an increased diuresis) at very high dose levels, the most common finding observed in these studies is changes of the refractive power of the lens. Species in which such lens alterations readily develop include the rat, rabbit, dog and pig, while primates are not sensitive. Clinical signs of systemic toxicity and the alterations of the lens have never been observed or reported in clinical and epidemiological studies performed in humans, even after exposure to high dose level (1000 mg/kg/d for 3 months) or for a long period of time (up to 19 months). The NOAELs by oral and dermal routes in primates are 2970 and 8910 mg/kg bw/d, respectively.

Key value for chemical safety assessment

Toxic effect type:

concentration-driven

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

2 970 mg/kg bw/day

Study duration:

chronic

Species:

monkey

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEC

2 800 mg/m³

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

8 910 mg/kg bw/day

Study duration:

chronic

Species:

monkey

Additional information

The toxicity of DMSO in rats by repeated inhalation exposure has been investigated in a 13-week study compliant with the OECD guidelines. For the oral, dermal and parenteral routes, only non-guideline studies are available. Clinical and epidemiological studies are also available after dermal administration (see section "Exposure related observations in humans").

Inhalation

In a study compliant with the OECD guideline # 413 and GLP (Kenny, 2000a), three groups of rats (each of 10 males and 10 females) of the Crl:CD®BR strain were exposed to DMSO, 6 hours a day, 7 days a week, for 13 weeks using a snout-only exposure system. A fourth group, acting as control, was exposed to air only. An additional 10 male and 10 female rats concurrently exposed at the Control and High dose levels were retained following the final exposure for a further 4 weeks to assess the reversibility of any adverse findings. The study was designed to comply with OECD, US EPA OPPTS guidelines and GLP. The mean analysed chamber concentrations of DMSO were 0.310 mg/l, 0.964 mg/l and 2.783 mg/l for Groups 2 (Low dose), 3 (Intermediate dose) and 4 (High dose) respectively. Throughout the study, the animals were checked twice a day for mortality and clinical signs. Body weight and food consumption were recorded weekly. Water consumption was recorded daily. The eyes of all main and recovery group rats were examined once before the start of dosing using a Keeler indirect ophthalmoscope. Similarly, all Main and Recovery group rats in Groups 1 and 4 were examined during Week 13. Functional observations were conducted on 10 male and 10 female rats from each group, pre-treatment, on week 12 and at the end of the recovery period. Vaginal smears were prepared daily from all female rats during weeks 8 and 9 of the study for assessment of the oestrus cycle. Blood and urine samples for haematology, biochemistry and urinalysis were collected from all main group rats during week 13 of dosing. All main group animals were killed following 13 weeks of dosing and subject to a detail macroscopic examination. Sperm samples from rats from all groups were assessed for motility, sperm morphology and number. Histopathological examinations were performed on all scheduled tissues.

A high dose group male was sacrificed on humane grounds in week 13 due to the condition of the upper incisors and subsequent weight loss. Treatment-related clinical signs consisted of red staining around the nose of rats exposed to 0.964 and 2.783 mg/l. Rats exposed to 2.783 mg/l gained less weight over the exposure period compared with the controls. The trend was reversed during the recovery phase. However, the differences were small (-17% in males and -16% in females compared to controls) and in the absence of any other indications of systemic toxicity probably reflected a loss of appetite caused by the mildly irritant nature of DMSO. Differences between control and treated groups for food and water consumption were minimal and of no toxicological importance. Ophthalmic examination, functional observation battery, oestrus cycle, sperm analysis, haematology, biochemistry, urinalysis, macroscopic pathology and organ weights were unremarkable. Treatment-related microscopic changes were found in the nasal passages and pharynx of high dose males and females after treatment for 90 days, but not in rats from the low and intermediate dose groups. The pathology in the nasal passages comprised of lesions in the inferior ventral medial meatus and an increased degree of eosinophilic inclusions in the olfactory epithelium. In the pharynx, prominent goblet cells were present in the majority of high dose rats. In rats killed after the recovery period, changes were still evident in the nasal passages of high dose male and females and also in the pharynx of the females. According to these results, the no adverse effects concentrations (NOAEC) could be established at 0.964 (ca. 1.0) mg/l for respiratory tract irritation and 2.783 (ca 2.8) mg/l for systemic toxicity.

In 2 range-finding studies (Kenny, 1999 and 2000b), three groups of 5 males and female Crl:CD®BR rats were exposed, by inhalation (snout only), to an atmosphere of droplets and/or vapour generated from DMSO for 6 hours each day, over a period of 14 or 28 days. The rats were killed on the day following the last exposure. The achieved study mean analysed respirable concentrations of DMSO in air were 0, 0.520 (vapour), 1.390 (> 64% of droplets 7 µm) and 5.360 mg/l (> 64% of droplets 7 µm) for the 14-day study and 0, 0.132 (vapour), 0.507 (vapour) and 1.886 (75% of droplets 7µm) mg/l for the 28-day study. In both studies, clinical signs both during exposures and at rest were monitored and recorded. Body weight was recorded twice weekly and food and water consumption was recorded daily. In the 28-day study, body rectal temperature was recorded on one occasion during the week prior the start of exposure and immediately after the 6-hour exposure on week 1 and 4 for the control and high dose animals. In the 14-day study, laboratory investigations comprising analysis of haematological and blood chemistry parameters were conducted at the end of the treatment period. In both studies, following sacrifice of the animals rats were subjected to detailed macroscopic examinations followed by preservation of tissues. Adrenals, kidneys, liver, lungs, spleen and testes were weighed and, the larynx, lungs, nasal passages, trachea, and any gross lesions were subject to histopathological examination with in addition, eyes, kidneys and liver, in the 14-day study.

There were no unscheduled deaths during these studies. There were no clinical signs attributable to the administration of DMSO. There were no treatment-related effects on body temperature. In the 14-day study, the mean body weight gain of High and Intermediate dose rats (both sexes) and Low dose female rats was lower than control values. The mean cumulative food consumption of High and Intermediate dose rats (both sexes) and Low dose female rats was lower than the concurrent controls. The mean cumulative water consumption of High dose female rats was higher than that of controls. None of these effects on the body weight gain and the food and water consumption were observed in the 28-day study. In the 14-day study, there were no findings considered to be of toxicological importance in haematology and blood biochemistry parameters investigated prior to sacrifice. There were no treatment-related macroscopic findings at necropsy and mean organ weights of all test groups were similar to control values in both studies. Aggregations of macrophages in the lungs, epithelial hyperplasia in the larynx and eosinophilic inclusions in the olfactory epithelium of the nose were detected at the High dose level in the 14-day study but not in the 28-day study. Based on the 28-day study, the NOAEC for systemic toxicity and local effects on the respiratory tract is estimated to be >1.886 mg/l.

Two groups of 32 Sprague-Dawley male rats were exposed whole-body to DMSO at concentrations of 0 or 0.2 mg/l 7 hours a day, 5 days a week for a total of 30 exposures. All animals were examined for toxic signs prior to, during, and subsequent to each exposure. Body weight was recorded prior to the first exposure and after the final exposure. Prior to the first exposure and after the final exposure, haemoglobin concentration, packed erythrocyte volume and total leukocyte and reticulocyte counts were done on all animals. At the termination, all animals were sacrificed, blood and tissue specimens were obtained for biochemical analysis (SGPT and SGOT activities, liver alkaline phosphatase activity, or liver lactate concentrations) and gross observations of the organs were made. Sections of the heart, lung, liver, spleen, and kidney were taken for histological examination.

o significant alterations were noted in the limited number of biochemical and haematological parameters. Gross and histopathologic examinations of organs and tissue were unremarkable (Fishman et al., 1969).

Oral

Studies performed with several species and an OECD 421 study have shown that DMSO is of low toxicity after repeated oral administration.

Rats

Groups of 50 male and 50 female Sprague Dawley rats received oral daily doses of 0, 1, 3 or 9 ml/kg DMSO (50% aqueous solution), 5 days a week for a total of 18 months (78 weeks) (Noel et al., 1975). After 52 weeks, 10 males and 10 females from each were sacrificed. Animals were observed daily, weighed weekly and food intake was calculated at weekly intervals. Ophthalmoscopic examination of the eyes of all animals was made before dosing and then at regular intervals throughout the study. Haematology studies (PCV, haemoglobin, total and differential white cell count and prothrombin index), together with urinalysis and measurement of urine concentration were performed on animals from each group after 4, 12, 20, 32, 51, 60 and 72 weeks. After 78 weeks remaining animals were sacrificed and their tissues preserved. Mortalities were few and could not be related to DMSO treatment. Occasional behavioural changes, persisting for about 5 min after dosing, were observed. These consisted of stretching and arching of the back, accompanied by an in drawing of flanks and abdomen, and were attributed to abdominal discomfort. There was a dose-related depression (<10%) of weight gain in both sexes, with the exception of males receiving 1 ml/kg (in males, ca. -20% at the top dose and ca. -10% at the mid dose and in females, ca. -20% at the top dose and ca -10% at the mid and low doses). There was no accompanying reduction of food intake. A slight reduction of haemoglobin and PCV in male rats receiving 9 ml/kg was observed. Examination of the eye revealed no changes in the retina or vitreous humour. No peripheral (equatorial) opacities were seen and there was no difference in incidence of polar opacities between the test and control animals. Prominent nuclear annuli were seen in a small number of animals towards the end of the study, but there was no dose-relationship to suggest any treatment-related effects. The only relevant finding was some degree of change in the refractive index of the nuclear region in 3 rats receiving 9 ml/kg. The No Observed Adverse Effect Level (NOAEL) is 3300 mg/kg/day based on the slight depression of the body-weight gain at the low and mid dose levels and the LOAEL is 9900 mg/kg/day for the ophthalmology and haematology effects.

The potential toxic effects of Dimethylsulfoxide (DMSO) on male and female reproductive performance, such as gonadal function, mating behavior, conception, development of the conceptus and parturition was evaluated in a reproduction/developmental screening study according to the OECD Guideline No. 421 (27th July 1995) (Davies, 2007). Four groups of Sprague Dawley rats (12 males and 12 females) were treated with DMSO at 0, 100, 300, 1000 mg/kg/d as follows:

* Males: during 2w before mating, the mating period (2w) and until sacrifice.

* Females: during 2w before mating, the mating period (2w), pregnancy (3w), and lactation until day 21 pp inclusive

Mortality and clinical signs were checked twice daily. Body weight and food consumption were recorded at regular intervals. At final sacrifice of the parent, the testis and epididymides were weighed for the males and a complete macroscopic post-mortem examination was performed for both genders. A microscopic examination was performed on the ovaries, testes and epididymides of females and males, respectively.

No death was observed in the parental generation. One female treated at 300 mg/kg/day was sacrificed after the end of the pairing period as no evidence of mating has been observed. No treatment-related clinical signs were observed during the study in males and females. Females of all dose-levels gained slightly less weight (-11%, -26%, -22%) during the pre-pairing period than the controls, although weight gains during gestation and lactation were similar to the controls. Marginally higher absolute and relative liver weights were noted in the males given 1000 mg/kg/day. There were no treatment-related macroscopic findings. The NOAEL for parental toxicity was equal or higher than1000 mg/kg/day.

Dogs

Groups of 5 males and 5 females pure-bred Pembrokeshire Corgis dogs were dosed orally with 0, 1, 3 and 9 ml/kg of a 50% aqueous solution of DMSO, once per day, 5 days a week, for approximately 2 years (Noel et al., 1975). After 18 weeks, unexpected eye changes were observed. Dosing was continued for half the dogs in each group for the remaining 86 weeks; the other half was not treated but observed for signs of recovery. The total interval of dosing was 2 years. Clinical signs were recorded daily; food intake was measured twice daily. All animals were subject to regular examination, including ophthalmoscopy. ECG, clinical chemistry, haematology, and urinalysis monitoring was conducted before and at regular intervals during the study. At the end of the study, all animals were sacrificed and subjected to detailed necropsy. Principal organs were weighed and tissues taken for histopathological examination. Eyes were examined and the lenses removed and weighed; the volume of aqueous humour was measured. There were no marked clinical signs and only one accidental death occurred. Occasional isolated bouts of vomiting were seen at 9 ml/kg/day and transitory "head shaking" was temporarily observed during weeks 11 and 12 at this and the 3 ml/kg/day level. No adverse effects on bodyweight and food intake were recorded. ECG records were normal throughout except for a transient, minimal slowing of the heart rate in recordings made after 4 weeks. Terminal radiology of excised bone showed no evidence of osteoporosis. Laboratory investigations confirmed the persistence of diuresis in dogs receiving 3 ml/kg and above but no renal damage resulted. Persistently increased PCV, haemoglobin levels, and total red cell count were observed at 9 ml/kg. The red cells had normal haemoglobin concentrations (MCHC) and were of normal size (MCV). Bone marrow examination prior to termination revealed no evidence of toxic changes. It seemed possible that the constant diuresis had resulted in a balance with a slightly higher degree of haemoconcentration than is normally found. Ocular effects were observed after 5-10 weeks dosing in the dogs receiving 9 ml/kg including central (nuclear) lenticular changes with alteration of the refractive index (myopia) and by the fifth month, transitory equatorial opacities, central (nuclear) opalescence, and changes in the vitreous humour. Similar effects were observed in dogs receiving 3 and 1 ml/kg but they occurred more slowly, respectively after 16 and 31 weeks of treatment. No abnormalities, other than those in the eye, were detected during macroscopic or microscopic examination of organs. Consequently, the NOAEL for the systemic effects, excluding the ocular effects, is 1100 mg/kg bw/day. The LOAEL for the ocular effects is 1100 mg/kg bw/day and the LOAEL for the other systemic effects is 3300 mg/kg bw/day based on clinical signs, heamatological changes and increased diuresis.

Monkeys

Daily doses of 1, 3, or 9 ml/kg b.w. of a 90% aqueous DMSO solutions (990, 2970 and 8910 mg/kg bw/d) was administered intragastrically to rhesus monkeys (3-6 animal/group) over an 18-month period (Vogin et al., 1970). Body weight, blood pressure, heart rate, respiratory rate, body temperature, water consumption, neurological reflexes, and ophthalmologic characteristics were observed. Electrocardiograms, haematological studies, and chemical analyses of blood (SGPT, serum alkaline phosphatase, BUN, glucose, 45-minute sulfobromophthalein (BSP) retention, and endogenous creatinine clearance) and urine (specific gravity, pH, albumin, glucose, occult blood, ketone bodies, and microscopic examination of the sediment) also were done in all animals. Gross and histomorphologic examinations were made at terminal sacrifice. The following organs were weighed: liver, kidneys, heart, brain, gonads, prostate or uterus, adrenals, thyroid, pituitary, and lungs. Histomorphologic examinations were performed on the following hematoxylin/eosin-stained sections of formalin-fixed tissues: liver, spleen, stomach (including fundus and pyloric regions), small intestine (including duodenum, jejunum, and ileum), large intestine (including colon and cecum), pancreas, kidneys, bladder, adrenals, gonads, thyroid, pituitary, thymus, salivary glands, lymph nodes (including cervical and mesenteric), heart, lungs, femoral bone marrow, skin, skeletal muscle, spinal cord, brain, gallbladder, epididymis, seminal vesicles, prostate, uterus, aorta, larynx, trachea, peripheral nerve, diaphragm, and lacrimal glands. The eyes were fixed in formalin or Zenker's fixative. Bone marrow smears were stained with Wright's stain. Animals could not tolerate 9 ml/kg, and died between weeks 15 and 53 of the study. The principal clinical signs included ptyalism and emesis. These signs occurred sporadically and did not appear to be related to the dose except in the group receiving 9 ml/kg. Monkeys given 1 and 3 ml/kg orally, showed slightly less gain in mean body weight compared to the respective control animals during the study. However, no biological significance is attached to these differences because of the Iimited number of animals per group and the wide range of initial weights. Marked losses in body weight occurred in animals given 9 ml/kg. No DMSO-related changes were found in the treated monkeys during physical examinations. No significant differences were found between the DMSO-treated and control monkeys in any of the haematological or biochemical parameters evaluated. Further, no significant differences were seen in erythrocyte sedimentation rate (ESR), BSP retention, creatinine clearance and urinalysis between the treated and control animals. No significant differences were seen in absolute or relative organ weights between the treated and control animals. No significant lesions attributable to DMSO were found upon gross examination at necropsy. Histologically, atelectasis and emphysema were the only pathologic changes. Some regurgitation and/or tracheal inspiration of DMSO might have occurred. Ophthalmoscopic examinations revealed no evidence of ocular toxicity. No toxicological or pathological changes attributable to oral administration of 1 or 3 ml/kg of DMSO were found. Consequently, the NOAEL for the systemic effects is 2970 mg/kg bw/day and the LOAEL is 8910 mg/kg bw/day based on effects on food consumption (anorexia) and body weight gain, ptyalism and emesis.

Dermal

Studies performed with several species have shown that DMSO is of low toxicity after repeated dermal administration.

Rabbits

Groups of males and females New Zealand white rabbits received daily applications of 50% or 90% aqueous solution of DMSO to normal and abraded skin at volumes equivalent to 0, 1.5, 2,7, 4.5 or 8.1 ml undiluted DMSO per kg (0, 1,650, 2,970, 4,950, 8,910 mg/kg bw/d, respectively). Treatments continued for 6 months; animals were kept under observation for an additional 12 weeks after treatment was terminated. Each rabbit was observed daily, weighed weekly and its water consumption was recorded during week 26. Ophthalmoscopic examination was performed on all animals before dosing commenced and then after 5, 8, 14, 20, 22, 28 and 33 weeks. Haematological investigations comprising PCV, haemoglobin, total and differential white cell count, and ESR, were performed initially and at 4, 12, 26 and 32 weeks. At termination, each animal was subjected to a post mortem examination, with subsequent organ weight analysis and histopathology. Rabbits received dermal applications of DMSO to normal and abraded skin for a period of 23 weeks, when ocular changes were observed. Treatment was withheld from animals showing ocular changes; the remaining animals continued to receive DMSO applications for the scheduled 26 weeks (6 months). Mortality was high in all groups, however there was no significant difference in mortality between groups. Bodyweight records were complete for the first 8 weeks of treatment, during which period bodyweight was reduced in female receiving 8.1 and 4.5 ml/kg. There were no clinical signs to suggest systemic toxicity. Local dermal reactions of slight erythema and mild edema were observed following each application. The degree of reaction was similar in all groups. Abrasion of the skin did not increase the reaction. Water consumption, measured during week 26, was markedly increased in animals receiving 8.1 m/kg; a lesser increase in water consumption was noted for other groups receiving DMSO. Macroscopic and hematological examinations, organ weight analysis, and histopathology did not reveal any adverse effects. There were no changes in dermal morphology except for random occurrences of inflammatory reaction. After 23 weeks of treatment, adverse ocular (lenticular) effects were observed at all dose levels (1, 5, 3 and 8 rabbits with a normal skin and 3, 7, 4 and 11 rabbits with an abraded skin, respectively at 1.5, 2.7, 4.5, and 8.1 ml/kg). These were restricted to the lens, and consisted of nuclear refractive changes. There was no effect on the peripheral lens, vitreous humour, or retina (Noel et al., 1975). Consequently, the NOAEL for the systemic effects, excluding ocular changes, is 2970 mg/kg bw/day, and the associated LOAEL is 4950 mg/kg bw/day, based on decreased mean body weight (females) and increased water consumption at higher dose levels. The LOAEL is 1650 mg/kg bw/day for the ocular changes and the skin irritation.

Medical grade DMSO was applied daily to the shaved backs of groups of 10 rabbits for 30 days at the dose of 0, 1 & 5 g/kg. Blood was drawn by cardiac puncture from each rabbit 1 and 7 days prior to treatment, and on treatment days 1, 7, and 30. Serum chemistry, serum enzyme levels and liver alcohol dehydrogenase levels were evaluated. Eye lenses of each rabbit were examined with a biomicroscope before and during treatment. At the end of the study, all rabbits were autopsied and examined for gross pathology. There was no mortality. At both 1 and 5 g/kg/day of DMSO administration resulted in elevated values for serum LDH. Transient elevations of the serum haemoglobin values were observed at 1 g/kg, as well as serum hemoglobin, total bilirubin and glucose at 5 g/kg. There were no gross lesions in DMSO or control animals examined at the end of the study. None of the animals treated with 1 g/kg/day displayed lenticular changes. All of the rabbits treated with 5 g/kg/day displayed microscopic ocular changes, which were first detected after 10-15 days treatment (Wood et al., 1971). Consequently, the NOAEL for the systemic effects is 1000 mg/kg bw/day, and the associated LOAEL is 5000 mg/kg bw/day, based on increased serum LDH, Hb, total bilirubin and glucose levels and lenticular changes.

Dogs

Twenty beagles dogs, five groups of two males and two females were treated dermally for 26 weeks with 1 ml/kg of 100% DMSO (3.3 g/kg) or 3 ml/kg of 60% DMSO (5.9 g/kg) and 100% DMSO (9.9 g/kg), 3 times a week; or with 6 ml/kg of 60% DMSO (19.8 g/kg) and 100% (33.0 g/kg) DMSO, 5 times a week. One-half of the animals in each group were necropsied at the end of treatment while the remaining animals in each group were necropsied after a recovery period of four to five weeks. Haematological analyses included hematocrit, haemoglobin, red blood cell and reticulocyte counts, platelet counts, and total and differential white blood cell counts. Hemochemical analyses included bromosulfonphthalein retention, serum alkaline phosphatase activity, blood urea nitrogen, prothrombin time, serum sodium, potassium, and chloride, blood sugar, serum bilirubin, and SGOT and SGPT activity. Sulfhemoglobin and methemoglobin determinations were done but only on a few animals from each group and then not as part of every examination. Urine obtained in metabolism cages was analysed for specific gravity, pH, sugar, and protein and examined microscopically. The following organ weights were obtained: adrenal glands, heart, kidneys, liver, lungs, ovaries, pituitary, prostate gland, seminal vesicles, spleen, testes, thyroid and parathyroid glands together, and uterus. These and the following tissues were examined both grossly and microscopically: aorta, bone marrow, cecum, cerebellum, cerebrum, colon, diaphragm, duodenum, esophagus, eye, gallbladder, hypothalamus, ileum, jejunum, mesenteric lymph node, optic nerve, pancreas, parotid gland, pons, skin, spinal cord, stomach, submaxillary gland, thymus gland, trachea, and urinary bladder. No systemic toxicity was observed except one dog, which had received 19.8 g/kg per week that died on day 26 of the study. However, all animals developed a distinct and persistent malodorous breath and the skins of these dogs became transiently reddened and warm upon application of DMSO. Within three weeks desquamation of the epidermis began in all dogs at the site of application and persisted throughout the period of treatment. The skin changes consisted of a membranous desquamation followed by a persistent or continuous furfuraceous desquamation. No changes were seen when haematology and hemochemistry were examined during weeks 4, 8, 12, 16, 25, and 26 or when urinalyses were performed during weeks 21 and 25. Necropsies performed upon one-half of the dogs at the end of the treatment period revealed no obvious changes in organ weights, and the only DMSO-related effects found upon gross and microscopic examination of the organs involved the skin at the site of administration; the histology of the skin at these sites was normal except for the desquamating epidermis. No skin lesions were present when the remainder of the animals were necropsied four to five weeks later (Smith et al., 1968). Consequently, the NOAEL for the systemic effects is 6600 mg/kg bw/day based on halitosis, no systemic toxic effects and no histological changes of the eyes. The LOAEL for skin irritation is 660 mg/kg bw/day based on desquamating epidermis.

Three groups of 2 beagle dogs receiving daily dermal applications of 1.1, 3.3 and 11 g/kg/d DMSO for 118 consecutive days exhibited no adverse, haematological or macroscopic effects. Dogs exhibited malodorous breath and desquamation at the treatment site. At all dose levels, treatment produced slowly developing changes in the eye, manifested by myopia and lenticular changes. The eye changes continued to progress even after cessation of treatment. (Smith et al., 1969). Consequently, the NOAEL and LOAEL for the systemic effects, other than the ocular effects, is 3300 and 11000 mg/kg bw/day, respectively, based on increased diuresis. The NOAEL and LOAEL for the ocular changes are 1100 and 3300 mg/kg bw/day, respectively. The LOAEL for skin irritation is 1100 mg/kg bw/day.

Monkeys

Daily doses of 0, 1, 3, or 9 ml/kg b.w. of a 90% aqueous DMSO solution were administered dermally to 4 groups of rhesus monkeys, 7 days per week, over an 18-month period. Dosages administered were equivalent to 990, 2970, and 8910 mg/kg bw/d. There were 2 males and 1 female in the control group, 2 animals of each sex in the groups treated with 1 and 3 ml/kg, and 3 animals of each sex in the groups receiving 9 ml/kg per day of DMSO. Physical signs, behaviour, and survival time were recorded daily. Examinations included 48-hour water consumption, electrocardiogram, neurology (reflexes), heart rate, body weight, blood pressure, body temperature, respiratory rate (on weeks 1, 4, 7, 12, 24, 37, 51, and 73 of study) and ophthalmology. Complete blood counts, SGPT, serum alkaline phosphatase (SAP), BUN, blood glucose, 45-minute sulfobromophthalein (BSP) retention, and endogenous creatinine clearance were measured in all animals. Urinalysis consisted of specific gravity, pH, albumin, glucose, occult blood, ketone bodies, and microscopic examination of the sediment. All animals that died or were sacrificed were submitted to a detailed necropsy. The following organs were weighed: liver, kidneys, heart, brain, gonads, prostate or uterus, adrenals, thyroid, pituitary, and lungs. Histomorphologic examinations were performed on the following tissues: liver, spleen, stomach (including fundus and pyloric regions), small intestine (including duodénum, jejunum, and ileum), large intestine (including colon and cecum), pancreas, kidneys, bladder, adrenals, gonads, thyroid, pituitary, thymus, salivary glands, lymph nodes (including cervical and mesenteric), heart, lungs, femoral bone marrow, skin, skeletal muscle, spinal cord, brain, gallbladder, epididymis, seminal vesicles, prostate, uterus, aorta, larynx, trachea, peripheral nerve, diaphragm, and lacrimal glands. All animals treated topically with DMSO exhibited scaling and flaking of the skin in the area of drug application during the initial phases of the study. There were no apparent differences among the various treatment groups. Although several animals had erythema of the skin, it did not appear to be related to dose, and did not occur at regular internals. No other adverse behavioural or physical signs were seen that could be attributed to topical application of DMSO. No DMSO-related changes were found in the treated monkeys during physical examinations. No evidence of refractoriness to Tropicamide mydriasis was seen in any of these monkeys. The typical DMSO lenticular changes described in other species were not visible in any monkey during the course of the experiment. No significant differences were found between the DMSO-treated and control monkeys in any of the haematological or biochemical parameters evaluated. Further, no significant differences were seen in erythrocyte sedimentation rate (ESR), BSP retention, creatinine clearance and urinalysis between the treated and control animals. No significant differences were seen in absolute or relative organ weights between the treated and control animals. No significant lesions attributable to DMSO were found upon gross examination at necropsy. No histological changes were visible in the lenses of treated animals with the exception of a monkey that had retinal detachment. The authors concluded that Rhesus monkeys can tolerate DMSO at doses up to 9 ml/kg/day administered dermally for approximately 18 months y (Vogin et al., 1970). Consequently, the NOAEL for the systemic effects is higher than 8910 mg/kg bw/day based on the lack of systemic toxicity and changes in the lens of the eyes. The LOAEL for skin irritation is 990 mg/kg bw/day.

Eight rhesus monkeys (Macaca mulatta), 4 groups of 1 males and 1 females each were treated dermally for 26 weeks with 1 ml/kg (3.3 g/kg) or 3 ml/kg (9.9 g/kg) of 100% DMSO, 3 times a week, or 6 ml/kg of 60% (19.8 g/kg) or 100% (33.0 g/kg) DMSO, 5 times a week. One monkey from each group was necropsied at the end of treatment while the remaining animals in each group were necropsied after a recovery period of four or 14 weeks. The same haematological, hemochemical, gross pathological and microscopical examinations were performed as in the previous dog study (Smith et al., 1968). No systemic toxicity was observed, although shortly after the start of treatment a malodorous breath was present, and membranous followed by furfuraceous desquamation developed at the site of treatment. Both persisted throughout the treatment period. No changes in hematology and hemochemistry were seen in examinations conducted during weeks 5, 8, 12, 20, and 25, or in urinalysis conducted during week 25. Necropsy at the end of treatment revealed no abnormal organ weights or gross or microscopic morphology other than that involving the desquamating epidermis. Examination of the remainder of the animals 4 or 14 weeks later revealed no alteration in hematology, hemochemistry, urinalysis and no microscopically abnormal organs, including the skin (Smith et al., 1968). Consequently, the NOAEL for the systemic effects, including the ocular effects, is higher than 6600. The LOAEL for skin irritation (without associated microscopic changes) is 660 mg/kg bw/day.

Three groups of 8 rhesus monkeys received daily dermal applications of 1.1, 3.3 and 11 g/kg/d DMSO (as a 90% solution) for 185 to 200 days. The treatment induced malodorous breath and skin lesions but did not have no effect on the behavior or body weight of the animals. Retinoscopic examinations and slit-lamp biomicroscopic examinations revealed no visible alterations in the eyes of these monkeys. Hematologic and hemochemical determinations revealed no abnormal values. Urinalyses revealed some DMSO-related increases in 24-hour urine volume and hydroxyproline excretion at 11 g/kg; at the same time, both specific gravity and urinary pH were lowered in some cases. Further examination did not reveal the presence of sugar, protein or abnormal numbers of formed elements. No treatment related differences existed between the groups of monkeys with respect to final body weight or the organ weights (Smith et al., 1969). Consequently, the NOAEL and LOAEL for the systemic effects, including the ocular effects, are 6600 and 11000 mg/kg bw/day, respectively, based on increased 24-hour urine volume and hydroxyproline excretion. The LOAEL for skin irritation is 3300 mg/kg bw/day.

Pigs

DMSO was applied dermally, 5 days par week, to groups of 4 male and 4 female pigs for 18 or 58 weeks. Fifty percent and 90% aqueous solutions were used to give levels equivalent to 8.1, 4.5, 2.7 or 1.5 ml DMSO/kg/day, divided into two applications/day for pigs. Clinical observations, food intake, recording of body weight, laboratory investigations, and macroscopic and microscopic post mortem examinations were conducted and recorded in essentially the same way as described for the oral study with dogs (Noel et al., 1975), except that the eyes were not examined biochemically or histologically. No mortalities or clinical changes were observed. Weight gain was reduced in the group receiving 8.1 ml/kg during the first 18 weeks of dosing. Laboratory investigations and terminal macro- and microscopic examinations revealed no adverse effects apart from an increase in absolute and relative spleen weight from all dosage groups treated for 1 year. Lenticular changes were observed in all dosage groups after one year and ranged from mild at 1.5 ml/kg to severe at 8.1 ml/kg. No ocular effects were observed in pigs receiving dermal applications of 1.5 ml/kg for only 18 weeks (Noel et al., 1975). Consequently, the NOAEL and LOAEL after 18 weeks of exposure are 1650 and 2970 mg/kg bw/day, based on decreased body weight gain and refractive change in the lens. The LOAEL after 58 week of exposure is 1650 mg/kg bw/day, based on decreased body weight gain, increased spleen weight and changes in the lens of eye

Justification for classification or non-classification

Based on the available data, no classification for repeated toxicity has to be applied for DMSO according to EU Directive 67/584/EEC and EU regulation (EC) No 1272/2008 (CLP).