Biomedical subjects

T H Maren

Publications and source records attributed to T H Maren.

At least 19 recordsLinked to original sources

PubMed1995

Effect of pH on the ocular distribution of a topical carbonic anhydrase inhibitor.

Ampholyte carbonic anhydrase inhibitors (including MK-927) have previously been shown to elicit greater intraocular pressure reduction when applied in ionized form at moderately acidic or alkaline pH compared to application of un-ionized drug at neutral pH. Since ionized solutions should be far more membrane-impermeant than un-ionized solutions, we attempted to solve this apparent paradox. We studied the distribution at 0.5-18 hr of MK-927 in eye tissues and fluid after topical instillation of one drop of a 0.5% solution at pH 4.9, 7.0 and 9.1. Measured drug concentrations at 30 min in corneal epithelium and stroma are approximately 4.5-fold greater after acidic or alkaline application than after neutral application, with the highest levels being found in corneal epithelium. The same pattern is seen in ciliary process, the site of aqueous humor production. Here drug concentration is approximately 60% of that in cornea at 30 min. Free drug concentrations in ciliary process were used to compute the time course of maximal carbonic anhydrase inhibition for the three modes of application. Drug concentration in sclera, uvea and aqueous humor at all times are all low by comparison, suggesting drug movement is from cornea to ciliary process via the corneo-scleral junction. The k(in) for proton movement across the corneal epithelium was measured (k(in) = 12.4 hr-1) from which a permeability coefficient (P = 2.7 x 10(-2) cm sec-1) was computed. Separate analysis was made of the pH status of the cornea 30 min and 1 hr following instillation of 1 drop 2% acidic (pH 4.9) and alkaline (pH 9.1) MK-927, with sodium sulfadiazine and pilocarpine.HCl as pH controls. Stromal bicarbonate at 30 min was approximately halved after acidic drops and doubled after alkaline drops consistent with pH decrease or increase of nearly 0.3 U. The results are in accord with classical schemes for amine permeation of the cornea at acidic pH when consideration is given to movement of acid equivalents and corneal pH. Thus drug inside the eye is in relatively (> 95%) lipophilic form except that trapped in the cornea shortly after acidic or alkaline applications.

Administration, Topical↗

PubMed1995

The effect of temperature on the binding of sulfonamides to carbonic anhydrase isoenzymes I, II, and IV.

We report the effect of temperature on the equilibrium dissociation constants (Kl) for a series of six sulfonamides binding to three carbonic anhydrase (CA) isoenzymes (I, II, and IV). Kl values obtained at 0 degree, 15 degrees, and 23 degrees under conditions of nearly constant and low substrate (CO2) concentration were used to calculate enthalpy and entropy changes associated with sulfonamide binding as well as to provide estimates of inhibitory potency of sulfonamides at 37 degrees. We studies four classic sulfonamide (methazolamide, benzolamide, ethoxzolamide, and sulfanilamide) and the novel sulfonamides MK-507 (dorzolamide) and CF3SO2NH2. In all cases, the Kl was observed to increase with increasing temperature, which is consistent with a negative enthalpy of sulfonamide binding. The extrapolated increase in Kl over the 0-37 degrees temperature range varied from 4-fold for sulfanilamide binding to CA l to 14-fold for CF3SO2NH2 binding to CA IV, corresponding to binding enthalpy values of -7.2 to -11.7 kcal/mol. For CA II and I, entropy changes associated with sulfonamide binding were in general modest and ranged from -5.3 to +4.1 entropy units (eu) for five of the compounds tested. In contrast, ethoxzolamide binding was associated with a relatively large positive entropy change. Also, the variatione in k(on) and k(off) with temperature were studied for three sulfonamides binding to CA II. The association rate constants for methazolamide, benzolamide, and ethoxzolamide binding showed increases of 2-fold or less, whereas dissociation constants increased 3-9-fold over the range of 0-37 degrees. Thus, the temperature effect in increasing Kl is in large part due to a faster rate of sulfonamide dissociation. Apparent activation parameters at 23 degrees for k(on) were delta H++ = -2.35 to 3.8 kcal/mol, delta G++ = 7.3 to 8.6 kcal/mol, and delta S++ = -16.2 to -32.7 entropy units. For k(off), the corresponding values were delta H++ = 5.6 to 14.5 kcal/mol, delta G++ = 19.0 kcal/mol, and delta S++ = -14.8 to -45.7 entropy units.

Carbon Dioxide↗

PubMed1994

Physiological and immunocytochemical evidence for a putative H-K-ATPase in elasmobranch renal acid secretion.

The mechanism of renal acid secretion in marine fish is largely unknown. We explored whether H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase) is present and functional in acid secretion in the kidney of the elasmobranch spiny dogfish shark, Squalus acanthias. In whole animal studies, a specific inhibitor of mammalian H(+)-K(+)-ATPase, Sch-28080, abolished greater than 87% of basal (62 mg/kg) and 75% of imidazole-stimulated titratable acid excretion (5 and 62 mg/kg). Antibodies directed against the COOH-terminus hog gastric H(+)-K(+)-ATPase alpha-subunit stained specific subdivisions of the neck, early and late proximal tubule, late intermediate tubule, both segments of the distal tubule, and the early collecting duct of the renal tubule of these fish. These findings are consistent with a major role for a protein similar to the mammalian gastric H(+)-K(+)-ATPase in elasmobranch renal acid secretion.

Animals↗

PubMed1993

A new class of carbonic anhydrase inhibitor.

Aliphatic sulfonamides, as CH3SO2NH2, are very weak inhibitors of the carbonic anhydrases (KI congruent to 10(-4) M) and are extremely weak acids (Ka congruent to 10(-10.5) M). We now find CF3SO2NH2 a very potent inhibitor of carbonic anhydrase II (KI = 2 x 10(-9) M) and a much stronger acid (Ka = 10(-5.8) M). It freely dissolves in water, a 2% solution yielding pH 3.7, the strongest known sulfonamide acid. CHCl3/aqueous partition with this solution is very low, 0.006. The plot of CH3SO2NH2 and eight hydrophilic halo-alkyl congeners gives a linear relation over 5 orders of magnitude, pKI increasing as pKa declines. Transcorneal permeability of CF3SO2NH2 in rabbits is very high; from one drop on the cornea it rapidly gains access to the ciliary process, where it fully inhibits carbonic anhydrase and gives the maximum pressure drop (for any drug) of 6 mm Hg at 30-60 min. Action is short due to rapid disappearance of free drug from the eye at the rate of aqueous humor flow. Analyses are made of binding of CF3SO2NH2 to carbonic anhydrase and melanin in ciliary process. CF3SO2NH2 is not attacked by glutathione, is 75% bound to plasma protein, and is not taken into the renal secretory system. Excretion rate follows from glomerular filtration and tubular reabsorption. Intravenous injection thus leads to prolonged plasma levels (half-life, 24 h), a general diffusion into tissues and alkalinization of the urine, as with "classic" inhibitors. Drug is bound to carbonic anhydrase in red cells and decays with half-life of 4 days. The rapid and effective binding to carbonic anhydrase of this small hydrophilic molecule shows that complex lipophilic structures are not necessary for powerful inhibition of the enzyme. It does not appear essential for a sulfonamide to occupy a "hydrophobic pocket" in the active site cavity to react effectively at the zinc center.

Animals↗

PubMed1993

A comparison between the effect of topical and systemic carbonic anhydrase inhibitors on aqueous humor secretion.

We have assessed the onset and duration of decreased intraocular pressure and aqueous humor flow contrasting systemic and topical administration of carbonic anhydrase inhibitors. The relationship between physiological effects and fractional activity of carbonic anhydrase isoenzymes in the eye was also investigated. Experiments were performed in normotensive New Zealand white rabbits. Intraocular pressure was determined manometrically or tonometrically and aqueous humor flow by sulfacetamide clearance. We studied methazolamide (25 mg kg-1), ethoxzolamide (4 mg kg-1), and MK-927 (2% in 0.5% hydroxyethylcellulose, topical, pH 4.8). There is an immediate reduction in intraocular pressure (1.2 and 1.8 mmHg by 2 min) and aqueous flow (33% and 40% by 5 min) following intravenous dosing with either methazolamide or ethoxzolamide. This correlates with rapid appearance of drug in the anterior uvea and very low fractional activity of ocular carbonic anhydrase isoenzymes II (cytosolic) and IV (membrane bound). Peak intraocular pressure reduction averaged 4.2 +/- 0.68 mmHg and 4.5 +/- 0.8 mmHg for methazolamide and ethoxzolamide at 60 and 45 min, respectively. Peak flow reduction was 38% for methazolamide and 40% for ethoxzolamide, at 5 min. Aqueous flow and intraocular pressure returned to baseline at 7 and 4 hr following methazolamide and ethoxzolamide, respectively. This corresponds to decay of drug from ocular tissues and significant increases in fractional activity of carbonic anhydrase isoenzymes. Topical MK-927 resulted in a 1.2 mmHg decrease in pressure by 5 min. This correlated with the early appearance of drug in the anterior uvea prior to its appearance in aqueous humor and very low fractional activity of carbonic anhydrase isoenzymes. Intraocular pressure decreased 3.6 +/- 0.35 mmHg at 1 hr and returned to baseline by 6 hr. Aqueous flow was reduced 12% by 5 min and 35% at 1 hr. The appearance of MK-927 in the anterior uvea prior to detection in aqueous suggests a significant non-corneal route of absorption following topical administration. Topical MK-927 results in a more gradual reduction in intraocular pressure and flow, although peak effects are not statistically different from systemic carbonic anhydrase inhibitors. The time of pressure return to baseline is also comparable to systemic carbonic anhydrase inhibitors. Because the relations between carbonic anhydrase II and carbonic anhydrase IV in the ciliary process are not yet clear and since the drugs have different affinities for the isozymes, the precise degree of fractional inhibition necessary for pharmacological effect is not certain, but based on drug concentration in the anterior uvea, may take 98% inhibition for full intraocular pressure reduction.

Administration, Topical↗

PubMed1993

Chemical properties of carbonic anhydrase IV, the membrane-bound enzyme.

The carbonic anhydrase (CA) isozyme (IV) in microsomes is thought to have a dominant role in secretory processes. Using microsomes from bovine kidney and lung (which had the same activity), we have measured the Km and kcat for CO2 hydration and compared these numbers with those for CA I (red blood cells and gut), CA II (red blood cells and secretory cells), and CA III (muscle). For kidney CA IV, Km is 10 mM and kcat is 170,000 sec-1 at 0 degree, approaching the rate for CA II but much greater than those for CA I or III. The Ki values for 11 sulfonamides with CA IV were measured and in all cases showed less binding (averaging 17-fold) than to CA II. This is the result of reduction of the association rate constants (k(on)), whereas the dissociation constants of the drug-enzyme complexes (k(off) are similar between CA II and IV. Based on these data, full physiological effects may be expected when inhibition of CA IV is about 99%. Anion inhibition of CA IV is similar to that of CA II and less than that of CA I or CA III. Data are compatible with the proposed role of CA IV in physiological events, i.e., HCO3- formation and secretion at one cell border and H+ separation and excretion at the other.

Animals↗

PubMed1993

pH and drug ionization affects ocular pressure lowering of topical carbonic anhydrase inhibitors.

PURPOSE: To evaluate the effect of drug ionization on the ocular hypotensive activity of topical carbonic anhydrase inhibitors. METHODS: Ocular normotensive New Zealand albino and ocular hypertensive Dutch Belted pigmented rabbits were used. Tonometric intraocular pressure levels were taken after topical application of 50 microliters of drug (at various concentrations and pH values) to one eye with the contralateral eye used as an untreated control. The drugs tested were MK-927, L-662,583, and AHR-16329. Eye tissues were analyzed for drug by our enzymatic methods. RESULTS: In all cases, the more ionized the applied drug the greater the ocular hypotensive activity. Tissue distribution studies showed that there was more drug found in the eye after the ionized form of a drug was applied than that found after application of the less ionized forms. CONCLUSIONS: Increasing the ionization of three ampholyte topical carbonic anhydrase inhibitors increases their ocular hypotensive activity. These data taken with ocular disposition data suggest that ionized compounds of this type are more readily sequestered in the cornea, which serves as a drug depot for prolonged drug delivery and activity.

Animals↗

PubMed1993

Carbonic anhydrase inhibitory activity and ocular pharmacology of organic sulfamates.

Organic sulfamates are a new variation to the carbonic anhydrase (CA) inhibitor structure-action relationship. Inhibitory activity is conferred by the classic sulfonamide group, but through linkage to the benzene ring by an oxygen. AHR-16329, a representative sulfamate, has an acidic (sulfonamide, pKa 8.9) and basic (imidazole, pKa 6.0) group and has desirable physicochemical properties for topical intraocular pressure lowering: good water solubility below pH 6.0, a CHCl3/buffer ratio of 0.5 at pH 7.0 and a Kl against CA-II of 7 nM. Inhibition of CO2 hydration is noncompetitive. When applied locally to the eye, AHR-16329 reaches significant levels in ocular tissues and fluids and reduces significantly intraocular pressure. Five percent concentration gives the greatest reduction, equivalent to systemic inhibitors; 2 and 5% have similar pressure x time duration. These studies expand structure-action relations in the field of CA inhibitors and the validity of developing topical CA inhibitors for treatment of glaucoma.

Animals↗

PubMed1992

Synthesis and physicochemical properties of sulfamate derivatives as topical antiglaucoma agents.

Several imidazolylphenyl sulfamate and (imidazolylphenoxy)alkyl sulfamate derivatives were synthesized and evaluated as topically active carbonic anhydrase inhibitors. Water solubility, pKa, carbonic anhydrase inhibition, and partition coefficient for the compounds were measured. Sulfamic acid 2-[4-(1H-imidazol-1-yl)phenoxy]ethyl ester monohydrochloride (16) has the best combination of properties and showed excellent topical activity in lowering the intraocular pressure in New Zealand white rabbits.

Administration, Topical↗

PubMed1992

Relations among IOP reduction, ocular disposition and pharmacology of the carbonic anhydrase inhibitor ethoxzolamide.

We have measured sequentially the concentrations of ethoxzolamide (6-ethoxybenzothiazole-2-sulfonamide) in ocular tissues following its intravenous or topical administration to normal albino rabbits. This was done in parallel with determinations of intraocular pressure (IOP) measured by tonometer or direct manometry. Ethoxzolamide was used because of its very high activity against carbonic anhydrase and experience showing that there is little or no other receptor in tissues. During the course of these experiments it was discovered that the lipid-soluble ethoxzolamide is converted in vivo to a water-soluble metabolite, while retaining high activity against the enzyme. Presumably this is the 6-O-glucuronide adduct. At the minimal dose for maximal effect (4 mg kg-1 i.v. at 45 min) the IOP lowering was 4.2 mmHg, the concentration in anterior uvea was 2.5 mumol kg-1, and the fractional inhibition of the enzyme (i) was 0.9995. The effect of free drug in the anterior uvea and other tissues. Following topical administration i was measured as a function of drug and enzyme in ciliary process. IOP lowering at 1 hr was -1.9 mmHg and i = 0.9993. By 4 hr i = 0.9980 and the pharmacological effect disappeared. At 8 hr the concentration of ethoxzolamide in the ciliary process is 0.4 mumol kg-1, essentially that of enzyme, with no free drug present: drug is now a marker for enzyme. Ethoxzolamide also labels the red cell carbonic anhydrases in the rabbit as well as other species including man. There appears to be no ethoxzolamide receptor other than carbonic anhydrase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

The microchemical detection of carbonic anhydrase in corneal epithelia.

Carbonic anhydrase (CA) activity has been detected and quantified in the corneal epithelia of various mammalian species using a microchemical assay. The highest levels were found in the rabbit, followed by man, dog, sheep, and cat. Enzyme levels in the rabbit epithelium were approximately one-third the amount found in the endothelium, perhaps explaining earlier failures to find CA in the epithelium. Selective inactivation of CA-II in tissue homogenates with bromopyruvic acid allowed determination of CA-I/CA-II ratios. The ratios in corneal epithelia from two species (rabbit and dog) approximated that in the erythrocyte. Although CA levels in the epithelium are low they are perhaps functional in the transfer of CO2 across the cornea.

Animals↗

PubMed1992

Renal acid-base physiology in marine teleost, the long-horned sculpin (Myoxocephalus octodecimspinosus).

We have sought to define urinary acid-base excretion in the marine teleost using the long-horned sculpin, Myoxocephalus octodecimspinosus. Urine flow (1.7 ml.h-1.kg-1) is relatively high, and glomerular filtration rate is very low (2.9 ml.h-1.kg-1). The urine-to-plasma ratio of inulin is 2. Renal clearance of p-aminohippurate is very high (108 ml.h-1.kg-1); phosphate and divalent cations are also secreted. In this framework we found urinary pH to average 6.6, but infusion of acid or alkali elicited a pH range of 6.1-7.8. Untreated fish may also have alkaline urine; so it is not surprising that precipitates of calcium or magnesium phosphate are sometimes found in bladder. These are of fine sandy quality and never cause blockage. Infusion of buffer (imidazole) increased the concentration of titratable acid 11-fold and output 2.5-fold. Carbonic anhydrase inhibitors had no effect on any urinary component, and histochemical studies revealed that cytoplasm and membranes did not yield the specific cobalt stain for the enzyme. An alkaline load (NaHCO3) is rapidly dissipated by gill excretion, mediated in part by carbonic anhydrase. An acid load (HCl) is rapidly dissipated by gill excretion, not dependent on carbonic anhydrase, and some renal excretion. Comparison and contrast of the low rates of HCO3- reabsorption in the marine teleost (and elasmobranch) with those of mammals suggest strongly that renal carbonic anhydrase evolved in connection with these high reabsorptive rates beginning in freshwater fish and continuing through amphibia and birds.

Acid-Base Equilibrium↗

PubMed1992

Direct measurements of the rate constants of sulfonamides with carbonic anhydrase.

Kinetic values for 14 sulfonamides and carbonic anhydrase (equivalent of isozyme II) were determined directly by measurement of association rate constants (kon) and equilibrium constants (KI), yielding dissociation rate constants, koff. Values for kon (in liter/mol sec-1) ranged from 0.003 to 31 x 10(6), whereas KI ranged from 0.7 to 17,000 x 10(-9) M. The koff range was very small, 0.01-0.05 sec-1. Thus, the activity, which is usually thought of as reflecting KI, is entirely a function of the association rate. This is not the common situation in enzyme-inhibitor reactions. The koff range is faster by several orders of magnitude than drug decay from plasma, so equilibrium is always achieved at the enzyme site in vivo, after parenteral administration of acetazolamide, methazolamide, or ethoxzolamide. For topical administration, as for MK-927 to reduce intraocular flow and pressure, the quantitative relation between free drug in tissue and that bound to enzyme in ciliary process is not so clear. Thus, koff might be an independent factor in pharmacological activity. The reaction of anions with carbonic anhydrase is entirely different, in that variations in KI are chiefly determined by koff.

Animals↗

PubMed1991

Localization and activity of renal carbonic anhydrase (CA) in CA-II deficient mice.

A null allele at the mouse Car 2 locus was induced by ethylnitrosurea; mice homozygous for the new allele lack the carbonic anhydrase (CA)-II isoenzyme. The expression of this genetic lesion was investigated by: (1) using tissue fractionation techniques to determine localization and activity of CA in the kidney, and (2) examining renal response to CA inhibition in CA-II deficient mice (CAD), in normal (N) mice and in heterozygous litter mates (LM). N and LM mice had CA activity in proximal tubule brush border membranes and cytosol. CA activity was also localized to membranes and cytosol of the outer medullary region. CAD mice lacked cytosolic activity but had normal CA activity in all membranes examined. All membrane associated CA had 2-8-fold lower sulfonamide sensitivity than cytosolic CA. These inhibition characteristics suggest that the membrane enzyme is CA-IV. Baseline urinary excretion of Na+, K+, and HCO3- was similar in all groups. Urine pH and Cl- excretion were higher and titratable acid output was lower in CAD mice. Inhibition of CA (methazolamide, 25 mg/kg) led in all groups to equivalent increments of urine pH, urine flow, and HCO3-, Na+, and K+ excretion. Cl- excretion was unchanged. Thus the extent of the genetic deficiency of CA-II mice extends to the kidney cytosol but does not alter membrane localization or levels of CA, probably CA-IV. The similar response to CA inhibition in CAD mice suggests that CA-IV, the membrane bound isoenzyme is the important isoenzyme in proximal tubule HCO3- reabsorption.

Animals↗

PubMed1990

Chemical and pharmacological properties of MK-927, a sulfonamide carbonic anhydrase inhibitor that lowers intraocular pressure by the topical route.

A large number of sulfonamides have now been tested by the topical route for the lowering of intraocular pressure in the normal albino rabbit. Certain compounds with favorable balance between lipid and water solubility, and high activity against carbonic anhydrase, do lower pressure as much as 3 mmHg. MK-927, a thienothiopyrane-2-sulfonamide carrying an alkylamino group of pK 5.8, has desirable physicochemical properties: good water solubility below pH 5.8, a CHCl3/buffer ratio of 0.6 at pH 5.4, and a KI value against carbonic anhydrase of 2-7 nM, depending on assay conditions. Inhibition of CO2 hydration is non-competitive. By comparison with other candidate topically active sulfonamides, it is the most effective in terms of pressure lowering times duration of action. There are no apparent systemic effects or ocular toxicity. The concentration of drug reaching the ciliary process and aqueous humor is of the same order as that following parenteral sulfonamides, so that inhibition of the enzyme exceeds 99%. MK-927 is therefore a candidate for the clinical treatment of glaucoma.

Administration, Topical↗

PubMed1989

The permeability of hydrophobic membranes to 22Na salts and 14CO2 in low dielectric media.

The one-way fluxes of 14CO2 and a series of 22Na (Cl, Br, HCO3, ClO4, I) salts across n-hexadecane-impregnated solid-support liquid membranes have been measured in water and low dielectric media (50-90 vol% dioxane/water). One-way fluxes for 14CO2 (J14CO2) were 0.84 and 1.03 x 10(-9) mol cm-2 s-1 in 75% dioxane (aq.) and water, respectively, across both impregnated cellulose and teflon membranes. 22Na fluxes across impregnated cellulose membranes in 75% dioxane (aq.) ranged from 1.8 to 11.4 x 10(-10) mol cm-2 s-1 and had the order NaCl less than NaBr less than NaHCO3 less than NaClO4 less than Nal. 22Na fluxes across impregnated teflon membranes were slightly smaller, 1.5-7.1 x 10(-10) mol cm-2 s-1, but had the same order for the anions tested. No measurable 22Na fluxes were observed in aqueous media. For NaI and NaClO4 there was a 3-6-fold enhancement of fluxes in 90% dioxane (aq.) compared to 75% dioxane (aq.). The corresponding enhancement for fluxes of NaHCO3, NaBr and NaCl was 1.5-fold. The results are discussed in terms of ion-paired salt transport in low dielectric media.

Alkanes↗

PubMed1989

Measurement of aqueous humor flow following scleral injection of sulfacetamide as marker: effect of methazolamide, timolol, and pilocarpine.

A simple technique for rapid determination of the flow of aqueous humor (AH) in rabbits is described. Data from control eyes and eyes treated with known inhibitors of aqueous humor production are presented as evidence of the suitability of the technique for comparing the influence of other drugs on aqueous flow. The flow measurement depends on marker dilution by fluid turnover during the first 30 min after 5 microliters marker solution is delivered to the anterior chamber. This is done by passing a needle through the sclera and behind the iris. The advantage of this route is that it permits withdrawal of the needle after delivery without leakage of marker or aqueous humor. Sulfacetamide (SAC), a sulfonamide with low lipid solubility and pKa 5.4, is the marker of flow used here. Control flow data from SAC, fluorescein (FL), reactive blue-2, and 14C-inulin as markers were compared. The control flow measured with SAC in two independent groups is 3.91 and 3.40 microliters/min or 3.69 +/- 0.37 S.E. overall. The data show that inhibition of carbonic anhydrase (CA) in ciliary processes by systemic methazolamide reduces flow 38%. Topical timolol reduces flow 35%. Pilocarpine, which is known to decrease IOP largely by increasing outflow facility, did not significantly reduce flow. This system for measuring AH flow allows rapid accumulation of data for topical, intracameral or systemic treatments.

Animals↗

PubMed1989

Ocular hypotensive activity and disposition of the topical carbonic anhydrase inhibitor 6-hydroxy-benzo[b]thiophene-2-sulfonamide, L-650,719, in the rabbit.

The carbonic anhydrase (C.A.) inhibitor, L-650,719 (6-hydroxy-benzo[b]thiophene-2-sulfonamide) is an advance over the corresponding 6-OH benzothiazole-2-sulfonamide in increased water solubility (4 mM) and CHCl3/buffer partition (0.05). KI vs CA is 10(-8) M. Topical treatment with 1 drop of 0.15-8% suspensions (in hydroxyethylcellulose-HEC) lowered intraocular pressure (IOP) up to 2.6 mmHg, with a plateau at 2%. Two hours after 2% treatment ocular drug distribution showed (microM or mumole/kg): cornea, 115, anterior aqueous 27, posterior aqueous 4, ciliary processes 15. Calculated inhibition of C.A. is 99.7%. IOP lowering effect disappeared at 6 hrs. L-650,719 was also given in solution (17 mM, pH 9.3). One drop every 5 min x 5 or 10 min residence on cornea of this solution produced an IOP lowering and drug distribution similar to that of the 2% suspension. Increasing HEC concentration in the single drop solution from 0 to 1%, led to a 3-fold increase in anterior aqueous drug levels and an improved delta IOP. The pressure lowering is somewhat less than achieved with parenteral sulfonamides in the rabbit. Clinical trials showed modest activity, so L-650,719 is not being developed further. It is evident, however, that sulfonamides with a variety of chemical and pharmacological properties are conducive to development for topical treatment of glaucoma.

Animals↗