Latanoprost Ophthalmic Solution - Scientific Information
|Condition:||Glaucoma, Intraocular Hypertension|
|Class:||Ophthalmic glaucoma agents|
|Form:||Eye drops (ophthalmic)|
|Ingredients:||Latanoprost, benzalkonium chloride, dibasic sodium phosphate (anhydrous), monobasic sodium phosphate (monohydrate) sodium chloride, water for injection|
|Chemical Names||1) Isopropyl-(Z)-7[(1R,2R,3R,5S)3,5-dihydroxy-2-[(3R)-3hydroxy-5-phenylpentyl]cyclopentyl]-5-heptenoate 2) 13,14-dihydro-17-phenyl-18,19,20-trinor-PGF2 α-isopropyl ester|
Colourless to slightly yellow oil.
|Solubility||Very soluble in acetonitrile and freely soluble in acetone, ethanol, ethyl acetate, isopropanol, methanol and octanol, and practically insoluble in water|
Each mL of Latanoprost Ophthalmic Solution contains 50 μg latanoprost, including the following inactive ingredients benzalkonium chloride (as a preservative), dibasic sodium phosphate (anhydrous), monobasic sodium phosphate (monohydrate), sodium chloride, and water for injection. Latanoprost Ophthalmic Solution is buffered to a pH of approximately 6.7 and is isotonic with lacrimal fluid.
Stability and Storage Recommendations
Store unopened bottle under refrigeration (2 to 8°C). Protect from light. During shipment, the bottle may be maintained at temperatures up to 40°C (104°F) for a period not exceeding 8 days. Once opened, bottle may be stored at room temperature up to 25°C, for up to six weeks.
Availability of Dosage Forms
Latanoprost Ophthalmic Solution (latanoprost) is a sterile, isotonic, buffered aqueous solution of latanoprost 50 μg/mL. One drop contains approximately 1.5 μg of latanoprost. Latanoprost Ophthalmic Solution is intended for topical administration on the eye.
Latanoprost Ophthalmic Solution is supplied in Alcon’s standard LDPE DROP-TAINER bottles with a fill volume of 2.5 mL (in the 4 mL bottle) with natural LDPE dispensing plug and a polypropylene (PP) closure. Tamper evidence is provided by a polyvinyl chloride (PVC) shrink band around the neck and closure of the DROP-TAINER.
Each bottle contains 2.5 mL of Latanoprost Ophthalmic Solution corresponding to approximately 80 drops of solution.
Latanoprost has been shown to lower IOP in primates, with minimal acute irritation of the eye. Results from studies show large species differences in pharmacologic responses which probably depend on the variation in prostaglandin receptor distribution between species.
Reduction of IOP - Topical administration of doses of 0.3-3 μg/eye in the cat had very little IOP reducing effect. In the cynomolgus monkey, topical doses of 1-9.5μg caused dose-related reduction in IOP. The onset of effect was slow, giving a maximum reduction 4 to 6 hours after the dosing. Repeated administration of 1-3 μg latanoprost daily for 5 days, lowered IOP effectively.
Aqueous Humour dynamics mode of action - The effect of topical treatment of latanoprost on aqueous humour dynamics was studied in cynomolgus monkeys. Latanoprost (3 µg) was applied once daily for five days, and on the fifth day of treatment the aqueous humour dynamics was determined using iodine labelled albumin as tracer. In the same experiments outflow facility was measured using a two level constant pressure infusion. Latanoprost increased the uveoscleral outflow by about 50% whereas the trabecular outflow and the outflow facility were unchanged. The total outflow tended to increase. The main mechanism for pressure reduction after treatment with latanoprost thus seems to be an increased uveoscleral outflow of aqueous humour. These results are in agreement with earlier studies with PGF2α-IE demonstrating the same main mechanism to lower IOP.
Other pharmacologic effects in the eye - In cats latanoprost had a marked pupillary constrictive effect. Topical application of 0.3-3 µg gave a dose dependent reduction of the pupillary diameter with a maximum response 2-3 hours after treatment. The miotic effect observed in cats and dogs is most probably a result of a direct effect on prostaglandin receptors in the iris sphincter muscle. In cynomolgus monkeys no miosis or a slight dilation of the pupil was seen after latanoprost treatment, and in clinical studies no change in pupil diameter has been observed during latanoprost treatment. The difference between species is probably due to different distribution of prostaglandin receptors.
Effects on airway resistance - Airway resistance was estimated from the intrathoracic inspi-ration/expiration pressure difference. At the two highest doses (2 μg/kg and 6 μg/kg, 50 times and 150 times the clinical dose, respectively), there was an increase in pressure difference and in respiration rate. The blood flow to the lungs also decreased after the two highest doses. This indicates most likely some degree of constriction of the bronchial tree although studies in unanesthetized animals described below showed little effect.
Cardiovascular and pulmonary effects - The effects of intravenously administered latanoprost on the cardiovascular and pulmonary system in unanesthetized cynomolgus monkeys have also been evaluated. Two male and two female cynomolgus monkeys received intravenous injections of vehicle (0.9% saline) or latanoprost at doses of 1, 10, 100 and 500 µg/kg b.w. Treatment with latanoprost was in general without consistent effects on the arterial blood pressure, but dose-related increases in heart rate were recorded in 2 out of 4 animals. Dose related increases in respiration rate were recorded in all four animals following latanoprost treatment. With the highest dose the respiration rate approximately doubled, but the animals showed no signs of dyspnea. No consistent dose related changes in ECG could be detected, but minor changes in ECG waveform were recorded in 3 of the 4 animals following doses of 100 and 500 µg/kg (2500-12,500 times the clinical dose). Minor changes in ECG were also seen after vehicle administration.
The cardiovascular effects after intravenous injection of latanoprost have been studied in cynomolgus monkeys under pentobarbital anaesthesia. Latanoprost was given in escalating doses (0.6, 2 and 6 µg/kg body weight), the lowest dose corresponding to about 15 times the clinical dose in the eye (~0.04 µg/kg b.w.). At the highest dose level (150 times the clinical dose) latanoprost induced a transient increase in blood pressure and a 30% increase in cardiac output. Regional blood flow was determined with radioactive microspheres, and in most organs only minor changes in blood flow were detected. Marked increases in blood flow were detected in the temporal, parietal and frontal lobes of the brain but only with the highest dose of latanoprost. The effect on the coronary blood flow of the heart was a dose related increase. Latanoprost had no significant effect on renal blood flow. It can be concluded that any systemic effect of latanoprost on the cardiovascular system after topical application in the eye is unlikely.
A double-masked study was performed which included 20 normal volunteers and 20 patients with ocular hypertension who were treated with 60 μg/mL latanoprost in one eye and placebo in the other eye twice daily for five days. Drug effects were evaluated by comparing the two eyes. Latanoprost caused no significant effect on aqueous flow. Outflow facility was determined on the fifth day of treatment and was increased, compared to the fellow eye, from 0.33 to 0.41 μL/min/mmHg in normal eyes and from 0.20 to 0.26 μL/min/mmHg in ocular hypertensive eyes. These increases were statistically significant but they are not large enough to explain the reduction of IOP. Clinical tonography can not be used to differentiate between outflow through the trabecular meshwork or the uveoscleral route, and the increase observed in outflow facility may well be explained at least partly by increased facility of the uveoscleral outflow routes.
Toris et al. (1993) have reported an attempt to determine uveoscleral flow by an indirect technique in the human eye, and they concluded that increased uveoscleral flow was the main mechanism of action also in the human eye.
The effect of latanoprost on the nocturnal IOP has been addressed in one study. Patients were hospitalized and the nocturnal IOP was constructed from several measurements at different times of different nights. Once daily administration of latanoprost 50 μg/mL in the morning reduced the nocturnal IOP to about the same extent as daytime IOP, although the IOP-reduction of 2.3 mmHg (corrected for change in fellow eye) from a baseline IOP of 23.0 mmHg in patients also treated with timolol, and of 3.5 mmHg from a baseline of 22.0 mmHg in patients with no other IOP reducing therapy, can be considered moderate.
In one study, 12 healthy volunteers and 11 asthmatic patients, 6 males and 5 females in each group, received three doses of escalating concentration 35, 115 and 350 μg/mL of latanoprost in each eye. No negative effect was observed on any of the respiratory parameters measured in either test group (one female was excluded from the study). In addition, latanoprost has not been found to affect pulmonary function when studied in a small number of steroid treated patients suffering from moderate asthma.
The main study providing basic pharmacokinetic data included four male volunteers between 63 and 67 years of age receiving either 3 μg labelled latanoprost topically as an eye drop or 210 μg labelled latanoprost during a 15 min i.v. infusion. From this study the fate of an ocular dose can be summarized as follows 77 to 88% is absorbed systemically, 90% is bound to plasma proteins within 3 min. A maximum plasma concentration of 64 pg/mL is reached within 40 min, and the drug and/or its metabolites is rapidly eliminated with a half-life in the ß-phase of 1.84 hrs in plasma. 88% is eliminated by the kidneys, essentially all of it within 24 hrs, and 15% through faeces with a more prolonged elimination time indicating some biliary excretion of drug or metabolites (<0.09% 144-168 hrs post-dose). Relevant corresponding figures for i.v. infusion are similar. This study is based on radio labelled latanoprost and gives no information concerning metabolism of the drug. Thus the figures should be regarded as maximal figures for active drug, before correction for protein binding. The study was performed on individuals of an age group that corresponds to glaucoma patients, but included only males.
In another study it was found that the plasma levels 5-60 min post-dose in patients treated with latanoprost for at least one year were very low. Ten patients were examined, 8 treated in both eyes, two in one eye only, all of them with a concentration of 50 μg/mL corresponding to a dose of about 1.5 μg or 3 μg latanoprost assuming total absorption of one eye drop in each eye. There were 5 males and 5 females between 64 and 81 years of age. A total of 49 blood samples were taken, five from each patient (the final 60 min sample was lacking in one patient) trough and 5, 15, 30 and 60 min values post-dose. In 30 of those 49 samples there was no measurable activity of the acid of latanoprost (< 20 pg/mL). This included all ten trough samples and the remaining four samples of three patients (two on 3 and one on 1.5 μg). In another 7 samples the detected activity was below the accepted detection limit for the technique, 30 pg/mL. The highest values observed were 5 min 67 pg/mL, 15 min 54 pg/mL, 30 min 55 pg/mL, and 60 min 42 pg/mL. Thus these data are similar to those found in the study on healthy volunteers with radio labelled latanoprost concerning maximal plasma levels.
Toxicological studies performed in mice, rats, rabbits, dogs and monkeys indicate that there is a high therapeutic index with latanoprost with respect to systemic side effects. The maximum clinical daily dose is expected to be 1.5 µg/eye/day.
Single Dose Toxicity
Oral and intravenous (i.v.) single dose toxicity was studied in mice and rats. Because of low solubility in water, the maximum concentration of latanoprost in saline was 40 μg/mL and the maximum injected dose was 2 mg/kg, approximately 50,000 times the clinical dose. No mortality was observed. For oral single dose toxicity a solution of latanoprost in oil was used to achieve a higher concentration. The highest dose employed, 50 mg/kg (approx. 1 million times the clinical dose), did not induce any toxic symptoms. In an i.v. toxicity study in dogs, no mortality occurred at doses of 170, 340 or 680 μg/kg. Clinical signs observed were similar to those reported after PGF2α.
Repeated Dose Toxicity
Topical administration on the eye - The effect of daily administration of the latanoprost formulation topically on the eye has been investigated in a subacute study in rabbits (4 weeks) and chronic studies in rabbits and cynomolgus monkeys (12 months) and rhesus monkeys (24 months).
Studies in rabbits - In the rabbit study, eye drops containing latanoprost were administered twice daily for a total of four consecutive weeks to Fauve de Bourgogne (pigmented) rabbits, the doses being 0, 1, 5 and 25 µg per administration. The total daily dose was 0, 2, 10 and 50 µg/eye. One eye was treated and the other served as control. No local ocular irritation and no effects of treatment on the pupillary or corneal reflexes were observed. No clinical changes were observed during the ophthalmological examination and no effects of treatment of toxicological significance were observed when clinical pathology parameters were examined. No treatment-related macroscopic or microscopic changes were observed.
In a 52-week study in Dutch belted rabbits, 4 groups of 10 rabbits of each sex received 0, 10, 30 and 100 µg/day of latanoprost by two daily ocular administrations. Latanoprost eye drops or vehicle was instilled into the conjunctival sac. Control animals received vehicle in the right eye only. Treated groups received the test formulation in the right eye and the same quantity of vehicle in the left eye. Ophthalmoscopy, tonometry and pachymetry examinations were performed on all animals pre-dose and at weeks 14, 25 and 51. No evidence of local irritancy, ocular or systemic toxicity, or change in the pigmentation of iris were observed. A mild transient erythema and equivocal variations in intraocular pressure were observed. No treatment-related macroscopic or microscopic changes were seen.
Studies in monkeys - Two 12-month topical ocular studies were completed in cynomolgus monkeys. In the first study wild caught cynomolgus monkeys were divided into 4 groups receiving 0, 20, 50 and 100 µg/day by two topical administrations. Treated animals received latanoprost solution in the right eye and the corresponding vehicle in the left eye. During the study some animals developed an increase in the iris pigmentation and an increase of the palpebral fissure and the study was therefore slightly modified. These changes started to appear in some animals after 2-3 months treatment. At the end of the treatment period, two treated males and one treated female were kept for a treatment-free period of 183 days (26 weeks); in one female the treatment was stopped on day 156 to evaluate the recovery of the ocular changes (iris pigmentation and eyelid effects) until the end of the treatment period for the other animals (week 53). No treatment-related signs of toxicity were seen at any dose level. The only treatment-related findings were reversible changes in the aspect of the palpebral fissure and a non-reversible increase in the iris pigmentation. These changes were attributed to the pharmacological action of latanoprost and were without a clear dose-relationship in frequency or intensity. No pathological changes were observed in any of the intra- or extraocular tissues at microscopic examination. The iridial stroma exhibited a more intense pigmentation of the melanocytes but remained morphologically normal. These findings were further confirmed in extended morphological studies of the treated and control cynomolgus monkey eyes.
In a 52-week study in domestic bred cynomolgus monkeys, lower doses compared with the above mentioned study were used since clinical studies had indicated that the maximum human dose would be 1-2 µg/eye/day. The same experimental procedure as in the above mentioned study was employed. Two groups of five animals of each sex were treated with 2 and 6 µg/day by twice daily applications. Six monkeys served as control and received the vehicle only. Also in this study no treatment-related signs of toxicity were observed at any dose level. The only treatment-related findings were the same local ophthalmological changes in the treated eye as described above. These consisted of a change in the aspect of the palpebral fissure (one male at 6 μg/eye/day) and a slight increase in the iris pigmentation in the majority of animals. With the lower doses the changes appeared later, usually between 6-12 months of treatment.
Another chronic study was conducted in domestic bred rhesus monkeys to investigate the toxicity of latanoprost following two daily ocular administrations for 104 consecutive weeks with an intermediate sacrifice after 52 weeks of treatment. To evaluate the regression of any toxic signs, some animals treated for 52 weeks were left for a two-year treatment-free period. The monkeys were divided into 4 groups receiving 0, 1, 3 or 10 μg, by twice daily applications (i.e., 0, 2, 6 or 20 μg/day). No treatment related signs of toxicity were observed at any dose level. The only treatment related findings were local ophthalmologic changes in the treated eye confirming observations made in the cynomologus monkey: a dose-dependent reversible slight increase of the palpebral fissure (6 and 20 μg/day), and a slight increase in iris pigmentation in some animals from all dose groups without a dose-relationship in frequency and intensity, but with a trend regarding time of appearance. During the second year of treatment, new cases of pigmentation were observed only in the high dose group. Microscopic examination revealed a slight increase in frequency and intensity in animals receiving 6 and 20 μg/day. The iridial stroma exhibited a more intense pigmentation of the pigmented cells but remained morphologically normal. There were no signs of increased number of pigmented cells of the iris stroma. These changes were attributed to the pharmacological action of latanoprost, as no pathological changes were observed in any of the intra- or extraocular tissues.
Iris pigmentation - A number of studies have been performed to investigate the mechanism of latanoprost induced iris pigmentation. It is of particular interest that naturally occurring prostaglandins such as PGF2α and PGE2 also cause increased pigmentation of the iris. The effect is a class effect of prostaglandins. It has been shown that the human iridial melanocytes express FP receptors in their cell membrane, and since latanoprost is a very selective FP receptor agonist, it implies that the effect is mediated by FP receptors in the melanocytes. Latanoprost binds only to a very small extent to melanin.
Morphometrical analysis of irides from monkeys in the chronic toxicity studies has demonstrated that there was no increase in the number of iridial melanocytes in the treated eyes compared to controls nor was latanoprost-induced increased iris pigmentation in sympathectomized rabbits associated with any increase in the number of stromal melanocytes or other cells in the iris. No proliferative effect of latanoprost acid has been demonstrated in in vitro studies on cultured human melanocytes and epidermal melanocytes and there was no uptake of 5bromodeoxyuridine (5-BrU) or tritiated thymidine into melanocytes incubated with latanoprost acid, which strongly indicate that DNA synthesis has was not initiated during exposure to latanoprost. Additionally, latanoprost had no proliferative effect on human cultured uveal and cutaneous melanoma cell lines, implying that latanoprost does not enhance proliferation of malignant melanoma cells. The results of these in vivo and in vitro studies on monkey and human melanocytes clearly show that latanoprost has no proliferative effect on ocular melanocytes.
The melanogenic effect of latanoprost has been investigated in several studies. It has been shown that the eumelanin (physiological brown melanin) content of the iris stroma increased significantly during latanoprost treatment in cynomolgus monkeys, whereas the normally predominant pheomelanin (cystein-containing yellowish melanin) was unaffected by treatment. Since pheomelanin cannot be converted to eumelanin, the only possibility is the new syntheses of eumelanin.
A morphometrical analysis of iridial melanocytes from rhesus monkeys treated for two years with latanoprost demonstrated that there was an increase in the number of melanosomes and the area covered by melanosomes of the cytoplasm in the treated eye compared to the contralateral control eye.
Latanoprost has been shown to increase the transcription of tyrosinase, the rate-limiting enzyme in the biosynthesis of melanin, in iridial melanocytes in vivo in monkeys and also in cultured human melanocytes from mixed colour (hazel) and brown irides. These results also suggest that the basal transcription of tyrosinase may be of importance whether latanoprost treatment leads to an increase in tyrosinase expression and that latanoprost probably contributes to the variability of the latanoprost-induced iris pigmentation change. This may explain why increased pigmentation in blue eyed persons during latanoprost treatment only rarely is seen or is very slow.
Latanoprost has no melanogenic effect on melanocytes in the iridial and retinal pigment epithelium of the monkey eye.
The available data demonstrate that latanoprost induces melanogenesis thereby increasing the melanin content of the iridial melanocytes and exclude that proliferative changes occur during pigmentation. Decreased catabolism of melanin in the iridial melanocytes is considered an unlikely mechanism behind the latanoprost-induced increased iridial pigmentation, since there seems to be no or minimal catabolism of melanin in iridial melanocytes.
Light microscopical and ultrastructural examinations of human iridectomy and trabeculectomy specimens have demonstrated that the latanoprost-induced pigmentation change is not associated with any proliferative, inflammatory or degenerative changes in latanoprost-treated irides or hyperpigmentation in the trabecular meshwork.
Oral repeated dose administration - Subchronic oral administration of latanoprost was performed in mice and rats with latanoprost dissolved in saline and oil (neutral oil TG/10). Due to low solubility the maximum dose of latanoprost in saline was 200 µg/kg/day, approximately 5000 times the clinical dose, and the maximum dose in oil solutions was 10 mg/kg/day, approx. 250,000 times the clinical dose. The studies in mice and rats were 28 days and 13 weeks, respectively. No toxic effects were seen.
Intravenous repeated dose administration - The studies were performed in rats and dogs, the duration of treatment being 4 and 13 weeks in each species. Latanoprost was dissolved in saline and in the 4 week study in rats injected in doses of 1, 10, 100 and 340 µg/kg/day. In the 13 week study in rats the doses were 5, 35 and 250 µg/kg/day. In the intravenous studies some mortalities occurred in rats given 250 µg/kg/day (> 5000 times the clinical dose per body weight). The mortalities were most likely due to acute cardiovascular effects.
In the 4 week dose-finding study in the dog in which doses of 1, 10, 100 and 340 µg/kg/day were tested, doses of 100 and 340 µg/kg caused vomiting, hypersalivation and miosis. The doses selected for the 13 week study were 1, 10 and 100 µg/kg/day. Hypersalivation and miosis were seen at the dose of 10 and 100 µg/kg/day, and vomiting at the dose of 100 μg/kg. No pathological changes were observed. It is evident that a doses of 250 µg/kg/day causes some deaths due to cardiovascular effects in rats. The high doses employed are considerably higher (5000 - 10,000 times) than the clinical dose.
Reproduction and Teratology
In order to reveal potential adverse effects on reproduction, latanoprost has been administered i.v. to male and female rats before and during pregnancy to study its effect on fertility, teratology and peri- and postnatal development. All studies were performed with intravenous injection of latanoprost since this route of administration was considered to give the highest systemic exposure. The duration of administration of latanoprost was selected to cover the periods where reproductive performance/fertility, embryogenesis and peri/postnatal development are known to be sensitive to drug effects in the respective species. The doses were selected based on dose-range finding studies in rats and rabbits and on the results from preliminary systemic toxicity studies in rats.
The fertility and the general reproductive performance were not affected in female or male rats. In the dose range study for peri- and postnatal toxicity, pup mortality was increased in the groups given 10 µg/kg or more and this effect was particularly marked in the 100 µg/kg/day group. The high dose selected was 10 µg/kg in the main peri- and postnatal study in the rat. This study showed no treatment-related effects on peri- and postnatal development at the selected dose levels (1-10 µg/kg/day) of latanoprost.
In the embryotoxicity study in rats, no embryotoxicity was observed at the doses (5, 50 and 250 µg/kg/day) of latanoprost used. However, latanoprost induced embryolethal effects in rabbits in doses above 5 µg/kg/day. The dose level of 5 µg/kg/day caused a slight increase in foetal resorption and was selected as the high dose in the main study. This dose caused significant embryo-foetal toxicity characterized by increased incidence of late resorption and abortion and by reduced foetal weight. No consistent indications of embryo fetal toxicity were observed with the low and intermediate doses of 0.2 and 1 µg/kg/day. The effects on the foetal development are probably due to a pronounced luteolytic effect in the rabbit which has been described as a pharmacologic property of prostaglandin F2α and its analogues and has been reported in several research and review papers.
The feto-placental transfer and lacteal secretion of latanoprost was investigated in rats. The concentrations of radioactivity of latanoprost and PhXA85 (acid of latanoprost) were measured in plasma and milk. The concentration of radioactivity was analysed in tissues after single intravenous administration of tritium labelled latanoprost at a dose of 200 μg/kg to pregnant or lactating rats. On the 12th-gestation day, the concentration of radioactive latanoprost in the fetus was 0.00006% of the dose at 1 hour. The value of radioactivity in the fetus at 24 hours was below the limit of detection. On the 18th gestation day, the concentration of radioactive latanoprost in the fetus was 0.018% (at 1 hour) and 0.005% (at 4 hour). Again, at 24 hours there was no radioactivity measured. In the milk the concentration of radioactive latanoprost was shown to be eliminated more slowly than for plasma. Of the low levels remaining in milk at 2 hours and 8 hours, only 5.5% and 15% respectively was the acid of latanoprost. The more polar metabolites formed the rest of the radioactivity in the milk.
Studies on the mutagenic potential of latanoprost have been performed by using in vitro and invivo methods.
The in vitro mutagenic potential was tested in bacteria (Salmonella typhimurium and Eschericia coli) and in the mouse lymphoma cells. No mutagenic effect was observed in these systems. Invitro chromosome aberration studies in human lymphocytes showed an increase in numbers of aberrant cells at concentrations of 130 and 160 µg/mL in the absence of S9. Treatment of cultures with latanoprost in the presence of S9 were negative. Normal frequencies of cells with aberrations were seen at a concentration of 100 µg/mL. The cytotoxic effects of latanoprost were clearly reflected by the poor yield of cells from cultures receiving 160 µg/mL in the absence of S9.
The in vivo micronucleus test in mice showed no signs of chromosome aberrations. As the aberrations in the mouse lymphoma occur predominantly in the absence of S9, the performed micronucleus test constitutes an appropriate in vivo assessment.
In order to further elucidate a potential genotoxic effect, an in vitro/in vivo unscheduled DNA test (UDS) was performed. This study did not indicate any mutagenic potential of latanoprost and as the test is a validated method it can be concluded that latanoprost has no mutagenic potential.
For the evaluation of the carcinogenic potential, latanoprost dissolved in physiological saline was administered by gavage route to mice and rats. The duration of the study in mice was intended to be 80 weeks. However, owing to the good survival rate of the animals, the duration of the study was extended until survival had reached approximately 50% for each sex. The males were necropsied week 88, and the females week 92. The dose levels (2, 20 and 200 µg/kg/day) were chosen based on the human therapeutic dose level and previous toxicity and pharmacokinetic studies. The highest dose is approx. 5000 times the human therapeutic dose when normalized for body weight and approaches the limit of solubility of latanoprost in water. In a toxicokinetic study in the same strain of mouse, latanoprost administered at 200 µg/kg/day once daily by oral gavage resulted in a mean maximal plasma concentration of the acid of latanoprost 5 min after the last dose about 50 times higher than the maximal human plasma concentration after a clinical dose in both eyes.
There were no clinical signs attributable to treatment and no evidence to suggest that treatment had any effect on the incidence of palpable masses. Survival was not affected by treatment with the test article. The incidence and causes of morbidity and mortality in all groups were consistent with the expected profile in this strain of mouse. Body weight for high dose females tended to be slightly lower than for those of the control throughout the study. There was no indication that red or white blood cell counts were affected by treatment. The spectrum of necropsy findings in treated animals was generally similar to that in controls. There were no non-neoplastic findings of unusual nature or incidence attributable to the test article. There were no unusual tumour types or increased incidence of tumours attributable to the test article. It is therefore evident that the latanoprost has no carcinogenic potential in the mouse.
The design of the carcinogenicity study in rats was the same as in mice but with longer duration of the study. The dose levels were based on the human therapeutic dose level and previous toxicity and pharmacokinetic studies. The high dose, 200 µg/kg/day, was approximately 5000 times the human therapeutic dose and approaches the limit of latanoprost solubility in water. In a toxicokinetic study in the same strain of rats, latanoprost was administered at 200 µg/kg/ day once daily by oral gavage route, the maximal plasma concentration of the acid of latanoprost was about 13-17 times higher than the maximal human plasma concentration after a clinical dose on both eyes. Therefore in the rat a sufficient dose level was used.
There were no clinical signs attributable to treatment and no evidence to suggest that treatment had any effect on the incidence of palpable masses. There was no indication that survival had been adversely affected by treatment. The incidence and causes of morbidity and mortality in all groups were consistent with the expected profile in this strain of rat. Body weight and food consumption were not affected by treatment. There was no indication that red or white blood cell counts were affected by treatment. The spectrum of necropsy findings in treated animals was generally similar to that in controls. There were no unusual non-neoplastic findings or increased incidence of tumours attributable to the test article. It can therefore be concluded that the oral administration of latanoprost to the rat, for the major part of its life span, at dose levels up to 200 µg/kg/day was well tolerated and produced no evidence of toxicity. There were no unusual tumour types attributable to the test article. Therefore in the rat no carcinogenic potential was observed.
An eye irritation test was conducted in rabbits in order to study whether changes in the formulation of the eye drops resulted in any local irritating effect. The two formulations tested were non-irritant. It can be stated that the formulations have been well tolerated in all the topical eye studies.
The anaphylactic and sensitization studies in the guinea pig demonstrated that latanoprost did not have any sensitization properties.