Pilocarpine Solution Research Articles

Effect of pH and buffer on the precorneal disposition and ocular penetration of pilocarpine in rabbits

An in vivo technique was utilized to study the effect of pH and buffer capacity on the precorneal disposition and ocular penetration of pilocarpine in the rabbit eye. Tear film pH, tear drug concentration and aqueous humor levels were measured at various times following the instillation of 25 μl of a 1 × 10−2 M isotonic pilocarpine solution. Test solutions were prepared in 0.0667 M phosphate buffer at various pHs (4.5, 6.0, 7.2) and at various phosphate buffer concentrations (0 M, 0.00667 M, 0.0667 M, 0.1 M) at pH 4.5. It appears that following the instillation of pilocarpine nitrate solutions buffered below the physiological pH of the lacrimal fluid, the extent of depression of the tear film pH and the tear pH re-equilibration time depends not only on the pH of the solution, but also on the precorneal fluid dynamics, and the buffer capacities of the instilled solution and that of the tears. As the buffer capacity of the instilled solution is increased, the ability of incoming tears to raise the pH in the precorneal area to its physiological value is reduced. The increase in the drainage rate due to reflex tear production is an effective mechanism by which the tear film pH re-equilibrates and is also responsible for the large reduction in the drug concentration in the precorneal area. This study examines this mechanism in detail.The depression in the tear film pH can also reduce the ocular penetration of pilocarpine by reducing its corneal permeability. Buffering of the pilocarpine nitrate solution with 0.0667 M phosphate buffer at pH 4.5 causes a two-fold reduction in the aqueous humor level as compared to an unbuffered solution at the same pH. Such a decrease is also predicted based on tear pH-time and tear concentration-time measurements of pilocarpine. This study shows the practical utility of such information in estimating the ocular penetration of drugs. Based on such information it is expected that at least a two-fold reduction in pilocarpine absorption may be caused by reflex tear production. In order to ensure optimum ocular penetration of pilocarpine, the system should not depress the tear film pH appreciably, and should allow rapid tear pH re-equilibration.

Lack of effect of pilocarpine on corneal epithelial wound healing.

The effect of a commercially available pilocarpine preparation on corneal epithelial healing rates was evaluated in rabbit eyes. Epithelial defects were created with filter paper discs soaked in n-heptanol. After creation of the defects, the corneas were stained with fluorescein and photographed using a Wratten blue filter. Follow-up examinations, drop administration, and photography were carried out every six hours for three days. Defect size was determined by computerized planimetry. The first phase of this study compared the effects of non-preserved saline and a commercially available methylcellulose preparation. The second phase compared a commercially available 2% pilocarpine preparation with 2% pilocarpine solution in non-preserved saline. We found that 2% pilocarpine had no significant effect on corneal epithelial healing rates.

Effect of poloxamer 407 gel on the miotic activity of pilocarpine nitrate in rabbits

This study was designed to evaluate poloxamer 407 gel, relative to its suitability for use as a vehicle for ophthalmic drug delivery. Pilocarpine nitrate was incorporated into 25% poloxamer gel and the formulation was administered topically to rabbit eyes. The ocular activity of pilocarpine was assessed using the pharmacological response of miosis. The change in pupillary diameter versus time curve was compared to that obtained with an aqueous pilocarpine solution, dosed under similar conditions. As indicated by the miotic response, the gel formulation appeared to enhance the activity of pilocarpine when compared to the aqueous solution.

Disposition of pilocarpine in the pigmented rabbit eye

The disposition of pilocarpine in the pigmented rabbit eye following instillation of a pilocarpine solution was studied using radiotracer techniques. The results suggest that a topically applied pilocarpine solution was removed as efficiently from the tear chamber of the pigmented rabbit as from that of albino rabbit. Nevertheless, a larger fraction of the applied dose was recovered in the pigmented rabbit eye, possibly due to the combined effect of improved corneal permeability, metabolism of the drug in the cornea, and metabolism and binding of the drug in the iris-ciliary body. Based on the area under the drug concentration vs time curve, about 10 times as much pilocarpine was found in the iris-ciliary body of the pigmented than the albino rabbit. Despite this drug accumulation in the iris-ciliary body, which presumably derived its drug supply from the aqueous humor, the pilocarpine concentration in the aqueous humor of the pigmented rabbit was virtually indistinguishable from that in the albino rabbit.

Investigations of the efficacy and bio-availability of different pilocarpine eye drops

The efficacy of three pilocarpine preparations in different concentrations (pilocarpine borate 0.5%, 1%, 2%; pilocarpine hydrochloride 0.5%, 1%, 2%; pilocarpine nitrate 1%, 2%) was investigated in 57 glaucomatous patients. Pilocarpine borate reduced intraocular pressure more effectively than either of the other pilocarpine solutions. The 2% concentration had a particularly prolonged effect. This finding corresponded well with pilocarpine levels in the aqueous humour of rabbits, as determined by spectrophotometric analysis. Pilocarpine borate 2% revealed an almost two-fold amount of drug compared to the 2% hydrochloride and nitrate solutions, and a detectable pilocarpine level was present for a longer period as well.

Analysis of Pilocarpine and Isopilocarpine in Ophthalmic Solutions by uv Spectrophotometry-Polarimetry

An improved analytical method was developed that simultaneously quantitates pilocarpine and isopilocarpine in the presence of each other and pilocarpic acid. Pilocarpine and isopilocarpine are first separated from any pilocarpic acid present in the sample by eluting with water-washed chloroform through a column packed with acid-washed diatomaceous earth. The concentrations of pilocarpine and isopilocarpine then are determined by a combination of UV spectrophotometric and polarimetric measurements. UV absorbance is measured at the absorption maximum (215 nm), and optical rotation is measured at the 254-nm line of mercury. Standard curve and standard recovery data are presented. The method is applicable to several commercially available ophathalmic solutions of pilocarpine and is compared to both the USP colorimetric method and a high-performance liquid chromatographic method.

Comparison of the ocular effects of topical etomidate and pilocarpine in rabbits

Etomidate, (R-(+) ethyl-1-(phenylethyl) 1H-imidazole-5-carboxylate), when administered as drops to the eyes of normal New Zealand white rabbits in concentrations of 2%, 4% and 8% in arachis oil has been shown to significantly lower the intraocular pressure in these animals. The intraocular pressure was measured with the Perkins handheld applanation tonometer. The intraocular pressure reducing effect of the 2% and 4% were better than that of 1% pilocarpine; the two per cent etomidate solution reduced intraocular pressure from a pretreatment mean of 13.6mm Hg to a new mean of 7.7mm Hg after three weeks treatment, while the 4% etomidate solution lowered the intraocular pressure from a pretreatment mean of 14.4mm Hg to a new mean of 7.3mm Hg also after three weeks treatment. Pilocarpine (1%) reduced the intraocular pressure from a pretreatment mean of 13.7mm Hg to 10.7mmHg after three weeks treatment in the same group of rabbits. Etomidate (8%) solution also showed a more significant reduction of intraocular pressure than the 2% solution of pilocarpine. The eight percent etomidate reduced the pretreatment mean intraocular pressure of 14.0mm Hg to a new mean of 6.5mm Hg after three weeks treatment while 2% pilocarpine lowered a pretreatment mean of 13.9mm Hg to 9.0mm Hg after three weeks treatment in the same group of rabbits. There was a persistence of the low intraocular pressure produced by the various concentrations of etomidate in arachis oil after treatment with these drops was stopped. However, this feature was also shown by the two concentrations of pilocarpine used but not in as marked an extent as the etomidate solutions with regard to duration of effect and height of reduction of the intraocular pressure. During a three week period of topical application of drops to the rabbits eyes, the etomidate solutions were found to have no effect in the iris sphincter.

Intraocular pressure reduction in chronic simple glaucoma by continuous infusion of dilute pilocarpine solution.

Ten hospital outpatients with bilateral chronic simple glaucoma received a single drop of 2% pilocarpine to one eye and a continuous infusion of 0.1 % pilocarpine at a flow rate of 0.01 ml/min to the other eye (both solutions were at pH 7.2). On another occasion the treatments were reversed. Measurements of intraocular pressure (IOP) and pupil diameter were made at 30 min intervals for 2 hours. The continuous infusion of dilute solution was as effective as the single drop of more concentrated solution in reducing IOP and in constricting the pupil; the drop was somewhat faster in producing its effect.

Vehicle Effects on Ocular Drug Bioavailability III: Shear-Facilitated Pilocarpine Release from Ointments

Pilocarpine release from water-in-oil emulsion ointments was studied in vitro and in vivo, using albino rabbits. Pilocarpine release from the vehicle to the ocular fluids was dependent on shear, i.e., blinking, and the dosing system emulsifying efficiency. A mechanical shearing component was vital for correlating corneal drug penetration and the in vitro pilocarpine release pattern. Simple diffusion studies with the vehicles did not predict drug in vivo release, but the ointment systems were all superior to an aqueous pilocarpine solution. Incorporation of a mechanical shearing component to mimic blinking gave good correlation of in vitro and in vivo results. Also, increasing the vehicle emulsifying efficiency by surfactant addition decreased shear-facilitated drug release and in vivo performance. Finally, increasing the internal aqueous phase volume fraction decreased in vivo performance and was linked to the influence of effective drug concentration in the vehicle.

Stereoselective epimerization of pilocarpine in aqueous solution as determined by 13C nuclear magnetic resonance spectroscopy

Cleavage and recyclization of the lactone ring of pilocarpine (1) and of isopilocarpine (2) in D2O with varying pD have been studied by 13C nmr spectroscopy. Alkaline treatment (pD 10–13) results in rapid epimerization of pilocarpine to form isopilocarpine (28 ± 3% at 30 °C) and hydrolysis of the parent compound(s) to form the open chain pilocarpinate (isopilocarpinate). By contrast, isopilocarpine does not epimerize to pilocarpine under similar treatment. A mechanism is discussed for the epimerization of pilocarpine and the nonepimerization of the isopilocarpine is rationalized. pKa values of 5.7 and 8.5, respectively, have been determined for pilocarpinic acid and for the dissociation of the protonated quaternary nitrogen of the imidazole ring of pilocarpine. A basis for assay of degradation products in aqueous pilocarpine solutions utilizing differences in 13C chemical shift for C-8 is discussed.

Simultaneous determination of pilocarpine and isopilocarpine in pharmaceutical preparations by liquid chromatography

A liquid chromatographic assay method is described for the simultaneous determination of pilocarpine and isopilocarpine in pharmaceutical preparations. The method involves separation of the isomers on a high‐resolution ion‐exchange column, followed by detection of pilocarpine and isopilocarpine by UV absorption in the 217‐nm region. The specificity of the method is such that pilocarpine and isopilocarpine can be assayed separately in the presence of one another and in the presence of the excipients commonly found in commercial pilocarpine solutions. Its sensitivity for isopilocarpine is at least 25 ppm (independent of the concentration of pilocarpine). In contrast, USP methods lack both specificity and sensitivity. It is concluded that this method is applicable to the routine analysis of commercial pilocarpine preparations and is an improvement over the official methods.

Hydrolysis and Epimerization Kinetics of Pilocarpine in Aqueous Solution

The kinetics of the hydroxide-ion-catalyzed hydrolysis and epimerization of pilocarpine in aqueous solution were investigated utilizing pH-stat titrimetry and NMR spectroscopy. The mechanism of epimerization involves formation of a carbanion stabilized by resonance with the enolate hybrid. Both hydrolysis and epimerization follow pseudo-first-order kinetics, and the appropriate rate constants and energies of activation were calculated. Epimerization was found to occur to a greater extent than previously assumed and must be considered as a major pathway of degradation and inactivation of pilocarpine. The rate of hydroxide-ion-catalyzed epimerization increases more rapidly with temperature than does the rate of hydrolysis, a fact that should be considered if ophthalmic solutions of pilocarpine are sterilized by heat. It is suggested that isopilocarpine may not be a genuine jaborandi alkaloid but an artifact produced by epimerization of pilocarpine during drying, storage, and extraction of the plant material.

Astigmatism of the lens by asymmetric contraction of the ciliary muscle.

A solution of pilocarpine was applied with a cotton wool pledget to the surface of the bulbar conjunctiva. This resulted in astigmatism by asymmetric contraction of the ciliary muscle. This seems to confirm that the ciliary muscle belongs to the multiple unit class of smooth muscles.

Sterility and Concentration of Pilocarpine Solutions

Sterility and Concentration of Pilocarpine Solutions

The effect of parasympatheticotropic drugs on the phagocytic power of the leukocytes in cancer patients

In 12 cancer patients the phagocytic activity of leukocytes was studied after subcutaneous injection of 1% pilocarpine solution (0.5 ml). In 9 of the 12 patients investigated the phagocytic reaction proved to be perversed, i.e., the leukocytic activity increased greatly in response to pilocarpine administration. The data obtained made it possible to assume that in cancer patients disturbance of the functional atate of leukocytes was evidently provoked by the main pathological process-cancer intoxication causing a specific and maybe sensitizing action on the leukocyte activity. A possibility is also not excluded that in cancer patients the phagocytic activity of leukocytes in response to the administration of parasympathicotropic substance may depend on the extent, form, and stage of cancer process.

The Effect of Methyl-Cellulose on Responses to Solutions of Pilocarpine

The Effect of Methyl-Cellulose on Responses to Solutions of Pilocarpine

A Control for the Direct Manipulation of the Fractional Anticipatory Goal Response

The fractional anticipatory goal response (r,) has carried a heavy burden in recent theorizing. Because of its importance it has seemed reasonable to attempt to manipulate it directly. The r, is usually conceived of as a small part of the terminal goal response. This fractional part of the goal response becomes evocable by stimuli at the start of whatever apparatus is being used and leads to an important part of the stimuli (so) initiating the instrumental response. There are undoubtedly many components to the r,, but the one most frequently mentioned is salivation. It has seemed reasonable, therefore, to attempt direct manipulation of r, through salivation. Lewis, Butler, and Diamond (1958) suggested that they had directly manipulated the r, using two drugs. One of the drugs was chlorbutinal plus benzocaine, 20 gr. per fluid oz., in alcohol 64% by volume. It is a mild anesthetic and was sprayed directly into S's mouth. The assumption was that the afferent consequences of a salivary r, would thus be reduced or eliminated. The second drug, the function of which was to increase salivation, was pilocarpine in solution, 1/2 gr. in 2 oz. distilled water. In addition, a control group, given plain distilled water, was used. All animals were given identical training in a T maze, following which the oral solutions were administered. Activity measurements indicated no differential effect as a function of the three solutions, although activity was depressed by all three treatments. Running speed measures indicated that both pilocarpine and water resulted in increased performance, relative to chlorbutinal plus benzocaine. Although inconclusive, these effects were believed to be in line with r,-s, theory. One reason the results were inconclusive was because of the remaining possible differential side effects of the solutions. The chlorbutinal plus benzocaine had an alcohol base and the pilocarpine had a distilled water base, each of which may have introduced different side effects. The third group was a control only for the effects of water. Specific controls are needed for the effects of alcohol on activity.

THE NODE

was the size of a pinpoint. The ophthalmologist who referred the patient to us stated that he had first examined her one year previously, when she presented glaucoma simplex of the right eye and absolute hemorrhagic glaucoma of the left eye. The left eye was removed, and she was instructed to use 3 drops of a solution containing J4 grain (0.03 Gm.) of physostigmine salicylate to the ounce (28 cc.) of distilled water in the right eye. The tension in the eye was 35, and vision was 20/40. This condi¬ tion was controlled by this medication. Suspecting physostigmine salicylate as a causative factor, we instructed the patient to supplant its use with that of a 1 per cent solution of pilocarpine and to apply a modification of calamine lotion locally. In a few days she was well. Patch tests with the physostigmine salicylate and the pilocarpine solution showed

DERMATITIS VENENATA FROM USE OF PHYSOSTIGMINE SALICYLATE IN THE EYE

was the size of a pinpoint. The ophthalmologist who referred the patient to us stated that he had first examined her one year previously, when she presented glaucoma simplex of the right eye and absolute hemorrhagic glaucoma of the left eye. The left eye was removed, and she was instructed to use 3 drops of a solution containing J4 grain (0.03 Gm.) of physostigmine salicylate to the ounce (28 cc.) of distilled water in the right eye. The tension in the eye was 35, and vision was 20/40. This condi¬ tion was controlled by this medication. Suspecting physostigmine salicylate as a causative factor, we instructed the patient to supplant its use with that of a 1 per cent solution of pilocarpine and to apply a modification of calamine lotion locally. In a few days she was well. Patch tests with the physostigmine salicylate and the pilocarpine solution showed

Some Interesting Experiences in the Clinical Pharmacology of the Eye

Four interesting experiences are recounted in each of which a prescription properly prepared from chemicals conforming to required standards as proven by subsequent tests produced unexpected results in the eyes of the patient. A solution of pilocarpine 2% with eserine ½% produced mydriasis. A solution of homatropine hydrobromide producing extreme and prolonged mydriasis was found to be contaminated with atropine. Pharmacologic tests were necessary in this connection, being much more delicate than any chemical test. A pilocarpine solution of high purity was found irritating to the eyes of a patient because of unusual sensitization to small differences in hydrogen ion concentration. Read before the Ophthalmological Section of the Baltimore City Medical Society Feb. 26, 1931.