Effect of topical administration of 1% morphine sulfate solution on signs of pain and corneal wound healing in dogs

Characterization of Infectious Keratitis in Opioid Users in a County Hospital Setting

Purpose

To determine risk factors and clinical course of corneal ulcers in the setting of opioid use.

Methods

A retrospective cohort study was performed of patients presenting with bacterial or fungal keratitis at a county hospital from 2010-2021. Subjects were separated into three groups: opioid drug users (heroin, methadone, fentanyl), non-opioid drug users, and non-drug users. 24 opioid users, 77 non-opioid drug users, and 38 non-drug users were included in the study. Chi-square and t-tests were used to compare hospitalization for corneal ulcer treatment; length of hospitalization; loss to follow-up; final best corrected visual acuity (BCVA); medication noncompliance; time to ulcer resolution; and visual disability (defined either by the legal limit for driving in California or the federal limit for blindness).

Results

Opioid users had higher rates of unemployment (p=0.002), homelessness (p=0.018), and psychiatric conditions (p=0.024) compared with non-opioid and non-drug users. They had more severe presentations, with worse initial BCVA of the affected eye (p=0.003), larger ulcer size (p=0.023), and higher rates of individuals below the legal vision thresholds for driving (p=0.009) and blindness (p=0.033) at initial presentation. Opioid use was associated with increased rate of hospitalization (p<0.001), higher fortified antibiotic use (p=0.009), worse final BCVA of the affected eye (p=0.020), and increased rates of BCVA worse than the legal vision thresholds for driving (p=0.043) and blindness (p<0.001) on final presentation.

Conclusions

Infectious keratitis associated with opioid use is associated with more severe presentations and poorer outcomes, including higher rates of visual disability.

Effects of commercial amniotic membrane extract on the re-epithelialization time and the early expression of matrix metalloproteinase-9 in cats with experimentally induced corneal ulcers

OBJECTIVES

To investigate whether a commercially available amniotic membrane extract (AME) can accelerate corneal wound healing and suppress the early expression of MMP-9 in the tears of cats with experimentally induced superficial ulcerative keratitis.

PROCEDURES

A total number of 16 cats were included. At the end of keratectomy, cats in the treatment group (TG, n = 8) received 40 μl of AME (EyeQ® Amniotic Eye Drops, Vetrix®) four times daily, while cats in the control group (CG, n = 8) received 40 μl of saline at the same time points. Tears were collected 24 and 48 h after keratectomy, and the total MMP-9 was quantified by ELISA.

RESULTS

The corneal re-epithelialization rate did not differ between groups (p = .26), being 0.48 ± 0.05 mm² /h in the CG and 0.41 ± 0.03 mm² /h in the TG. Similarly, the average time to achieve corneal wound healing did not differ between groups (p = .25) and was 61.50 ± 3.54 h in the CG and 70.50 ± 6.71 h in the TG. The dimensions of the ulcerated areas also did not differ at any time point between the groups (p > .05). In both groups, corneas healed without scarring, pigmentation, or vascularization. The expression of MMP-9 in the tears was similar in both groups at 24 h post-keratectomy, with a slight decrease at 48 h (p > .05).

CONCLUSIONS

The instillation of a commercial AME (EyeQ®) is safe, but it did not decrease the corneal re-epithelialization time or the early expression of MMP-9 in the tears of cats with experimentally induced superficial ulcerative keratitis in this study.

Acidic chemical corneal ulceration secondary to nail polish spill in a puppy

PURPOSE

To describe the treatment of an acidic chemical corneal ulceration in a puppy secondary to nail polish spilling on and adhering to the cornea.

CASE SUMMARY

A 12-week-old neutered male Australian Shepherd mix dog was presented to Colorado State University Veterinary Teaching Hospital's (CSU-VTH) Emergency and Urgent Care service acutely after exposure to nail polish spilling on the left eye (OS). Initial ophthalmic examination revealed nail polish adhered to approximately 80% of the cornea with moderate diffuse corneal edema and chemosis, and green nail polish adhered to the skin and fur of the periocular area. Copious flushing with eye wash was performed, but no areas of reduced nail polish adherence were noted. The patient was treated with 1 drop of topical ofloxacin 0.3% ophthalmic solution OS and hospitalized overnight, receiving hyaluronic acid ophthalmic lubrication every hour OS. The treatment plan was carried out for 6 h until time of transfer. In the morning, CSU-VTH's Ophthalmology service removed a nonadhered nail polish plaque in 1 piece using Bishop-Harmon tissue forceps. Following removal, a superficial ulcer secondary to an acidic chemical burn covering 100% of the corneal surface was noted, as well as moderate diffuse corneal edema. Following topical treatment for 8 days, the superficial ulcer healed completely, with no significant long-term consequences.

UNIQUE INFORMATION PROVIDED

This is the first report of management of an acidic chemical corneal ulceration secondary to nail polish spill in a puppy. Early assessment and vigilance in treatment was essential for a good prognosis and outcome.

Opioids and Ocular Surface Pathology; A Literature Review of New Treatments Horizons

This review discusses the role of opioids in the corneal surface and the different pathways and therapeutic methods of management. A literature review was performed using PubMed database. For the database search, the main searching words “opioid” and “topical opioid treatment” were used with the descriptors “cornea”, “ocular surface”, “neuropathic corneal pain”, “corneal sensitivity” and “naltrexone”; original scientific articles and reviews were included to achieve the purpose of the review. The endogenous opioid system has relevant functions in the organism, and in daily use, opioids are used as painkillers. However, these drugs may be employed for other indications as opioid pathways have a wide spectrum. The corneal surface for topical treatment is easily accessible, hence sparing the side effects of systemic opioids. Instillation of opioid antagonist substances, such as naltrexone, increases corneal healing rates and stimulates the division of corneal epithelium cells without deleterious effects. The natural modulation of endogenous opioids controls different forms of pain, including inflammatory and neuropathic pain, both in the ocular surface and in the central nervous system. There are diverse methods in controlling pain using opioids, especially in refractory forms. This review attempts to collect the literature about corneal surface and opioid pathways to provide an overview image and a possible direction of the news treatments.

The use of topical nalbuphine in different concentrations to control pain after photorefractive keratectomy

PURPOSE

This is a randomized controlled study aiming to evaluate the safety and efficacy of two different concentrations of topical nalbuphine hydrochloride, when used to relieve pain in the first days following photorefractive keratectomy (PRK).

METHODS

This is a prospective double blinded randomized clinical trial that included 189 patients who had PRK for correction of low and moderate refractive errors. Patients were randomly assigned to three groups according to the eye drops given to relieve pain in the first three postoperative days; the first group received topical nalbuphine with a concentration of 2 mg/ml (Group A = 64 patients), the second group received topical nalbuphine in a concentration of 1 mg/ml (Group B = 69 patients) and the third group received topical artificial tears only (Group C = 56 patients).The patients were asked to rate their pain daily using a numeric rating scale and to record the number of drops instillation times/day. The time needed for complete epithelial healing, best-corrected visual acuity (BCVA) and spherical equivalent after three months were recorded in each group.

RESULTS

In the first three days, there was a statistically significant difference in pain score among the three groups with lower values in the two topical nalbuphine groups when compared with the control group receiving artificial tears. Moreover, the higher concentration group showed significantly lower pain score and less number of drops used /day in comparison with the lower concentration group.There were no statistically significant differences in epithelial healing time, BCVA and spherical equivalent after three months among the three groups.

CONCLUSION

The use of topical nalbuphine is effective in relieving pain in the first few days following PRK and this pain relief is not associated with any compromise regarding epithelial healing nor refractive outcome. The pain control with 2 mg/ml concentration is significantly higher than that with 1 mg/ml concentration of nalbuphine. Trial registration numberISRCTN21394752 https://doi.org/10.1186/ISRCTN21394752 The trial is retrospectively registered in ISRCTN registry at March 08, 2021.

The opioid peptide biphalin modulates human corneal epithelial wound healing in vitro

PURPOSE

Analgesic drugs, including nonselective opioids and non-steroidal anti-inflammatory drugs, should be used with great precautions to relieve pain after trauma to the corneal epithelium because of their unfavorable effects on wound healing. Biphalin is a synthetic opioid peptide that has been demonstrated to possess a strong analgesic effect on rodents. The purpose of this study is to investigate the effects of biphalin on human corneal epithelial wound healing.

METHODS

An immortalized human corneal epithelial cell (HCEC) culture was used to analyze the effects of biphalin on wound healing. The toxicity of biphalin at various concentrations was measured by the MTT assay. The effects of 1μM and 10μM biphalin on wound closure, cell migration and proliferation were tested in an in vitro scratch assay of HCECs. Naloxone, a non-selective competitive opioid receptor antagonist, was also used to inhibit the effects of biphalin in all experiments.

RESULTS

Biphalin did not cause any toxic effect on HCECs at concentrations lower than 100μM at various incubation time points. Biphalin significantly increased wound healing at 1μM concentration in an in vitro scratch assay of HCECs (P<0.05). It also significantly increased migration of HCECs (P<0.01). There was no significant difference between the biphalin and control groups of HCECs in the Ki67 proliferation assay.

CONCLUSION

Biphalin, which is a synthetic opioid peptide, promotes corneal epithelial wound healing by increasing cell migration. This role should be evaluated in further in vivo and clinical studies.

Topical treatment with a mu opioid receptor agonist alleviates corneal allodynia and corneal nerve sensitization in mice

Corneal pain is considered to be a core symptom of ocular surface disruption and inflammation. The management of this debilitating condition is still a therapeutic challenge. Recent evidence supports a role of the opioid system in the management of corneal nociception. However, the functional involvement of the mu opioid receptor (MOR) underlying this analgesic effect is not known. We first investigated the expression of the MOR in corneal nerve fibers and trigeminal ganglion (TG) neurons in control mice and a mouse model of corneal inflammatory pain. We then evaluated the anti-nociceptive and electrophysiological effects of DAMGO ([D-Ala²,N-Me-Phe⁴,Gly⁵-ol] enkephalin), a MOR-selective ligand. MOR immunoreactivity was detected in corneal nerve fibers and primary afferent neurons of the ophthalmic branch of the TG of naive mice. MOR expression was significantly higher in both structures under conditions of inflammatory corneal pain. Topical ocular administration of DAMGO strongly reduced both the mechanical (von Frey) and chemical (capsaicin) corneal hypersensitivity associated with inflammatory ocular pain. Repeated instillations of DAMGO also markedly reversed the elevated spontaneous activity of the ciliary nerve and responsiveness of corneal polymodal nociceptors that were observed in mice with corneal pain. Finally, these DAMGO-induced behavioral and electrophysiological responses were totally blunted by the topical application of naloxone methiodide, an opioid receptor antagonist. Overall, these results provide evidence that topical pharmacological MOR activation may constitute a therapeutic target for the treatment of corneal pain and improve corneal nerve function to alleviate chronic pain.

Analgesic effect of topical and subconjunctival morphine in dogs after phacoemulsification: A pilot study

OBJECTIVE

To determine the efficacy of a single treatment of topical and subconjunctival 0.1% preservative-free morphine sulfate (PFMS) in providing analgesia following phacoemulsification in dogs.

ANIMALS STUDIED

Ten diabetic and ten non-diabetic client-owned dogs treated with bilateral phacoemulsification.

PROCEDURES

A prospective, randomized, masked, negative-controlled clinical trial was performed. All dogs received topical (0.2 mL) and subconjunctival (0.1 mL) 0.1% PFMS in one eye following phacoemulsification. The other eye received an equal volume and mode of administration of balanced salt solution (BSS). Ophthalmic examination, blinking rates, tearing, conjunctival hyperemia, aqueous flare, and central corneal esthesiometry (CCE) were evaluated in all eyes 1 day prior to surgery and at 4, 24, and 48 hours after surgery. Complete physical examination, ocular ultrasound, electroretinogram, hemogram, and serum biochemistry panel were performed in all dogs prior to phacoemulsification. All dogs received the standard of care treatment before and after surgery, including uniform anesthetic protocol.

RESULTS

Baseline ophthalmic exams were unremarkable, except for the presence of cataracts, in all dogs. The mean CCE (±SD) at 4 hours post-operatively was 1.76 ± 1.27 g/mm² and 1.85 ± 1.5 g/mm² for the negative control and PFMS groups, respectively. There were no statistical differences in blepharospasm, conjunctival hyperemia, tearing, aqueous flare, blinking rates, CCE, or intraocular pressure (IOP) between the treatment groups for any of the time points for the non-diabetic and diabetic dogs, or for all dogs combined (P > .05).

CONCLUSIONS

Topical and subconjunctival 0.1% PFMS did not affect the evaluated parameters after phacoemulsification in the study dogs at the timepoints assessed.

Delta Opioids: Neuroprotective Roles in Preclinical Studies

Since ancient times, opioids have been used clinically and abused recreationally. In the early stages (about 1,000 AD) of opium history, an Arab physician, Avicenna, administered opioids to control diarrhea and eye diseases. ¹ Opioids have very strong pain relieving properties and they also regulate numerous cellular responses. Opioid receptors are expressed throughout the body, including the nervous system, heart, lungs, liver, gastrointestinal tract, and retina. ^2-6 Delta opioid receptors (DORs) are a very attractive target from the perspective of both receptor function and their therapeutic potential. Due to a rapid progress in mouse mutagenesis and development of small molecules as DOR agonist, novel functions and roles of DORs have emerged in recent years. This review article focuses on the recent advances in the neuroprotective roles of DOR agonists in general and retina neuroprotection in particular. Rather than being exhaustive, this review highlights the selected studies of DOR function in neuroprotection. We also highlight our preclinical studies using rodent models to demonstrate the potentials of DOR agonists for retinal neuroprotection. Based on existing literature and our recently published data on the eye, DOR agonists possess therapeutic abilities that protect the retina and optic nerve injury against glaucoma and perhaps other retinopathies as well. This review also highlights the signaling events associated with DOR for neuroprotection in the eye. There is a need for translational research on DORs to recognize their potential for clinical application such as in glaucoma.

Dual enkephalinase inhibitor PL265: a novel topical treatment to alleviate corneal pain and inflammation

Ocular pain is a core symptom of inflammatory or traumatic disorders affecting the anterior segment. To date, the management of chronic ocular pain remains a therapeutic challenge in ophthalmology. The main endogenous opioids (enkephalins) play a key role in pain control but exhibit only transient analgesic effects due to their rapid degradation. The aim of this study was to explore the antinociceptive and anti-inflammatory effects of topical administration of PL265 (a dual enkephalinase inhibitor) on murine models of corneal pain. On healthy corneas, chronic PL265 topical administration did not alter corneal integrity nor modify corneal mechanical and chemical sensitivity. Then, on murine models of corneal pain, we showed that repeated instillations of PL265 (10 mM) significantly reduced corneal mechanical and chemical hypersensitivity. PL265-induced corneal analgesia was completely antagonized by naloxone methiodide, demonstrating that PL265 antinociceptive effects were mediated by peripheral corneal opioid receptors. Moreover, flow cytometry (quantification of CD11b+ cells) and in vivo confocal microscopy analysis revealed that instillations of PL265 significantly decreased corneal inflammation in a corneal inflammatory pain model. Chronic PL265 topical administration also decreased Iba1 and neuronal injury marker (ATF3) staining in the nucleus of primary sensory neurons of ipsilateral trigeminal ganglion. These results open a new avenue for ocular pain treatment based on the enhancement of endogenous opioid peptides' analgesic effects in tissues of the anterior segment of the eye. Dual enkephalinase inhibitor PL265 seems to be a promising topical treatment for safe and effective alleviation of ocular pain and inflammation.

Pharmacokinetic evaluation and safety of topical 1% morphine sulfate application on the healthy equine eye

OBJECTIVE

To determine if corneal epithelial cell integrity is detrimentally affected by short-term administration of 1.0% morphine sulfate. Additionally, we sought to determine if topical 1.0% morphine applied to the equine cornea would result in ocular or systemic absorption.

ANIMAL STUDIED

Six healthy horses.

PROCEDURE

Morphine sulfate (1.0%) was applied topically to one eye every four hours for 72 h before horses were euthanized. Serum samples were collected at varying time points during the study and aqueous and vitreous humor were collected immediately after euthanasia. Morphine quantification in serum, aqueous, and vitreous humor was performed by ELISA. Treated and control corneas were submitted for histopathology. Horses were monitored for adverse ocular and systemic effects throughout the study period.

RESULTS

All horses developed mild mucoid ocular discharge in the treated eye. One horse developed a fever during treatment. Morphine was detected in the aqueous humor of the treated eye for all horses with mean ± standard deviation of 165.18 ng/mL ± 87.69 ng/mL. Morphine was detected in vitreous humor of the treated eye of 5 of 6 horses with mean ± standard deviation of 4.87 ± 4.46 ng/mL. Morphine was detected in the serum of 5 of 6 horses at varying time points. Maximum systemic concentration reached in a single horse was 6.98 ng/mL. Corneal histopathology revealed no difference in microscopic appearance between morphine-treated and control corneas.

CONCLUSIONS

Topical administration of 1.0% morphine sulfate did not appear to cause any significant ocular or systemic adverse effects. Topical ophthalmic morphine application resulted in both ocular and systemic absorption.

Effects of topical flurbiprofen sodium, diclofenac sodium, ketorolac tromethamine and benzalkonium chloride on corneal sensitivity in normal dogs

To evaluate corneal sensitivity by using the Cochet-Bonnet® esthesiometer in normal canine eyes at different time points following instillation of three different topical non-steroidal anti-inflammatory drugs (flurbiprofen sodium 0.03%, diclofenac sodium 0.1% and ketorolac tromethamine 0.5%) and benzalkonium chloride 0.01%. Six healthy mixed breed dogs from the same litter were used in two different stages. First, one drop of flurbiprofen sodium 0.03% and diclofenac sodium 0.1% in each eye; second, one drop of ketorolac tromethamine 0.5% and benzalkonium chloride 0.01% in each eye. Baseline esthesiometry was obtained before eye drop application and every 15 minutes thereafter until a total of 105 minutes of evaluation time. A one-week interval was allowed between the two treatment phases. Statistical analysis was used to compare means according to time of evaluation and drug used. Diclofenac sodium 0.1% decreased corneal sensitivity at 75 and 90 minutes (P > 0.015) with possible interference on neuronal nociceptive activity and analgesic effect while ketorolac tromethamine 0.5% did not show any variation for esthesiometry means along the evaluation. Flurbiprofen sodium 0.03% resulted in increased esthesiometry values 30 minutes after instillation (P > 0.013), increasing corneal sensitivity and possibly producing a greater irritant corneal effect over its analgesic properties. Benzalkonium chloride 0.01% significantly increased corneal sensitivity at 15 minutes of evaluation (P > 0.001), most likely resulting from its irritating effect. Esthesiometry did not allow a definite conclusion over the analgesic effect of the NSAIDs tested; however it was effective in detecting fluctuations in corneal sensitivity.

Effect of topical administration of tramadol on corneal wound healing in rats

In this study, we aimed to investigate the effects of topical tramadol administration on corneal wound healing, and examine ophthalmic structures and intraocular pressure 7 days after tramadol administration. The experiments were conducted on eight male Wistar rats (250-300 g). After ophthalmic examination, epithelial cell layers in the central cornea were wounded. Rats received 30 μL of tramadol hydrochloride in one eye (Group Tramadol) and the same volume of vehicle in the other (Group Control) every 12 h for 7 days. Both eyes were stained with fluorescein dye, photographed, and wound area was calculated every 8 h until complete healing was observed. Eye blink frequency and corneal reflex tests were measured before and after drug administrations. After 7 days, slit lamp biomicroscopy, fundoscopy, Goldmann applanation tonometry, and histological evaluation were performed. There was no difference in the corneal wound healing rates between the tramadol and control groups. Reduction in wound area over time was also similar; group-time interaction was insignificant (F = 738.911; p = 0.225). Tramadol application resulted in blinking and blepharospasm for 30 s, but vehicle did not. Corneal reflex was intact and eye blink frequency test results were similar in all measurement times in both groups. Slit lamp biomicroscopy, fundoscopy, and intraocular pressures were within normal range. Corneal cells appeared unaffected by the repeated doses of tramadol for 7 days. Topical tramadol application on the cornea did not cause any side effect, except for initial temporary blinking and blepharospasm. Corneal wound healing was not affected, either.

Efficacy and safety of pain relief medications after photorefractive keratectomy: review of prospective randomized trials

The objective of this review was to provide a comprehensive overview and comparison of results from all prospective randomized trials published to date of medications used to treat pain after photorefrative keratectomy (PRK). A PubMed database search revealed 23 prospective and randomized studies. They included the following classes of medications: nonsteroidal antiimflammatory drugs (NSAIDs), anesthetics, opiates, acetaminophen, gabapentin, and pregabalin. The studies found that although the efficacy of drugs tended to be similar, tetracaine 1% and nepafenac 0.1% tended to have the most analgesic effect. Delayed corneal reepithelialization was a common side effect of both topical anesthetics and topical NSAIDs. Tetracaine 1% resulted in the most significant delay in reepithelialization when tested against placebo control compared with other topical medications tested against placebo. Concomitant use of topical NSAIDs and topical anesthetics, especially tetracaine, may have to be avoided to minimize the risk for delayed corneal healing.

FINANCIAL DISCLOSURE

Neither author has a financial or proprietary interest in any material or method mentioned.

Effect of once daily topical 0.3% naltrexone on tear parameters and corneal sensitivity in dogs with uncontrolled keratoconjunctivitis sicca: a double-masked randomized placebo-controlled clinical trial

OBJECTIVE

To determine the effect of once daily topical 0.3% naltrexone (NTX) on tear production, tear film breakup time (TFBUT), and corneal sensitivity in dogs with uncontrolled keratoconjunctivitis sicca (KCS).

ANIMALS STUDIED

Sixteen dogs with uncontrolled KCS.

PROCEDURES

A randomized placebo-controlled trial was performed in 16 dogs with topical 0.3% NTX once daily or topical saline solution drops once daily. A baseline was obtained at week 0 for tear production (Schirmer tear test 1 and 2-STT1, STT2), TFBUT, and corneal sensitivity. STT1, STT2, and TFBUT were then subsequently measured at weeks 1, 2, and 4 while on NTX or saline drops. Corneal sensitivity measures were repeated at week 4. The drops were subsequently discontinued and all parameters rechecked at week 5.

RESULTS

There was no statistically significant difference in tear parameters or corneal sensitivity between the NTX-treated and the saline-treated groups.

CONCLUSION

Topical 0.3% NTX given as a once daily dose over 4 weeks did not alter tear production, tear film stability, or corneal sensitivity in dogs with uncontrolled KCS.

Evaluation of corneal anaesthesia after the application of topical 2 per cent lidocaine, 0.5 per cent bupivacaine and 1 per cent ropivacaine in dogs

The objective of this study was to describe and compare the efficacy and duration of topical anaesthesia induced by 2 per cent lidocaine (L), 0.5 per cent bupivacaine (B) and 1 per cent ropivacaine (R) in the dog using 24 clinically healthy beagles with normal ocular examination. Dogs were randomly divided into three groups: 2 per cent lidocaine (n=8), 0.5 per cent bupivacaine (n=8) and 1 per cent ropivacaine (n=8). The baseline corneal touch threshold (CTT) was measured using a Cochet-Bonnet aesthesiometer. Following baseline CTT measurement, a single drop of the assigned anaesthetic was applied to each eye and the CTT was measured bilaterally within one minute after administration and every five minutes until the basal CTT value was restored. Data were analysed with non-parametric analysis of variance models and Dunnet's test for post hoc analysis. One per cent ropivacaine was the most effective drug (LCTTmax=3 cm, BCTTmax=2 cm, RCTTmax=0 cm; P<0.001), and had the shortest latency (LLatency=5 minutes, BLatency=5 minutes, RLatency=1 minute; P<0.001) and the smallest AUC (LAUC=80 cm×minute, BAUC=68.25 cm×minute, RAUC=36.88 cm×minute; P<0.001). There was no statistical difference in the duration of corneal anaesthesia between the groups (P=0.09) and all topical anaesthetics tested reduced corneal sensitivity, although 1 per cent ropivacaine had the maximal and quickest anaesthetic effect. This drug could be used for specific diagnostic procedures where quick and short, but effective, corneal anaesthesia is needed.

Analysis of the transport of and cytotoxic effects for nalbuphine solution in corneal cells

OBJECTIVE

To assess the in vitro effects of various nalbuphine concentrations on viability and wound healing ability of corneal cells and potential drug transport through the corneal epithelium.

SAMPLE

Cultured canine and human corneal epithelial cells (CECs) and cultured canine corneal stromal fibroblasts.

PROCEDURES

CECs and stromal fibroblasts were exposed to nalbuphine (concentration of solutions ranged from 0% to 1.2%) for up to 30 minutes, and viability was assessed with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. A standard scratch test technique was used. Wound healing of CECs and stromal fibroblasts was evaluated following treatment with nalbuphine solutions < 0.1%. Liquid chromatography-mass spectrometry-mass spectrometry analysis was used to evaluate drug transport across a monolayer and a multilayer of human CECs.

RESULTS

A progressive decrease in viability was detected in canine CECs for all nalbuphine treatment groups, whereas treatment with only 0.5% or 1.2% nalbuphine significantly reduced corneal stromal fibroblast viability, compared with results for control cells. Within 24 hours, treatment with 0.1% nalbuphine solution significantly altered the healing rate of both canine CECs and stromal fibroblasts. Continuous increases in transport rates of nalbuphine were detected with time for both the monolayer and multilayer of human CECs.

CONCLUSIONS AND CLINICAL RELEVANCE

In vitro, nalbuphine potentially could penetrate through corneal tissue, but it may cause damage to the corneal epithelium and stromal fibroblasts. Therefore, nalbuphine potentially may impair corneal wound healing.

Effect of topical administration of 0.8% nalbuphine on the cornea in dogs after phacoemulsification

It is suggested that topical application of opioids may provide localized analgesia without delay in corneal wound healing. This study was designed to evaluate the effect of topical application of 0.8% nalbuphine on post-operative ocular pain in dogs. Twelve eyes from 11 dogs undergoing phacoemulsification cataract surgery were divided into a nalbuphine group (n=6) and saline group (n=6). Postoperatively, the nalbuphine group received 0.1 ml of topical 0.8% alkalinized nalbuphine (pH 5.6) every 8 hr, and the saline group received 0.1 ml of topical saline (pH 5.9) as a placebo. All dogs received systemic postoperative pain managements with oral tramadol (4 mg/kg) and prednisolone (0.5 mg/kg) every 8 hr. All dogs received pre- and post-ophthalmic examinations. Pain was scored in the dogs using a pain scoring system modified from the University of Melbourne pain scale at 15, 30 and 60 min following the topical treatment on days 1 and 2 (24 and 48 hr after surgery). Eye blink frequency and corneal touch threshold (CTT) were recorded at the same time. There was no statistical difference in the pain score between groups. Significant decreases in CTT, blepharospasm and eye blink frequency were observed after the topical nalbuphine treatment. This indicated that topical application of 0.8% nalbuphine solution can produce a rapid reduction of corneal discomfort in dogs.

Should topical opioid analgesics be regarded as effective and safe when applied to chronic cutaneous lesions?

Objectives

The induction of analgesia for many chronic cutaneous lesions requires treatment with an opioid analgesic. In many patients suffering with these wounds such drugs are either contraindicated or shunned because of their association with death. There are now case reports involving over 100 patients with many different types of chronic superficial wounds, which suggest that the topical application of an opioid in a suitable gel leads to a significant reduction in the level of perceived pain.

Key findings

Some work has been undertaken to elucidate the mechanisms by which such a reduction is achieved. To date there have been no proven deleterious effects of such an analgesic system upon wound healing. Although morphine is not absorbed through the intact epidermis, an open wound provides no such barrier and for large wounds drug absorption can be problematic. However, for most chronic cutaneous lesions, where data has been gathered, the blood levels of the drug applied ranges from undetectable to below that required for a systemic effect.

Summary

If proven, the use of opioids in this way would provide adequate analgesia for a collection of wounds, which are difficult to treat in patients who are often vulnerable. Proof of this concept is now urgently required.

Histologic evaluation of the immediate effects of diamond burr debridement in experimental superficial corneal wounds in dogs

PURPOSE

To evaluate the corneal changes immediately after diamond burr debridement of superficial corneal wounds in dogs. Spontaneous chronic corneal epithelial defects (SCCEDs) are the most common form of canine recurrent corneal ulcers. The diamond burr has been used in the management of corneal lesions in humans since 1983. Recently, it has been successfully used in the treatment of SCCEDs in dogs; however, little has been documented as to its mechanism of action.

METHODS

Five adult female research dogs euthanized for reasons unrelated to the study were included, providing 10 normal eyes. An excimer laser spatula was used for epithelial removal after delineation with an 8 mm punch biopsy trephine. Diamond burr debridement was performed for 30 and 45 s in five eyes each (groups 1 and 2 respectively). The procedure was performed on the ventral half of the experimental defect as well as ventral normal cornea, immediately after euthanasia, and prior to enucleation. Samples were processed routinely for histologic evaluation and stained with periodic acid-Schiff.

RESULTS

No stromal defects could be identified under light microscopy. In experimental corneal wounds, multi-focal areas remained covered by the epithelial basement membrane (BM) after diamond burr treatment in both groups (group 1 = 48% ± 16SD, group 2 = 26% ± 12SD). Removal of BM on group 2 was significantly higher than group 1 (P < 0.05). CONCLUSIONS : The diamond burr allows a safe method of debridement and does not create defects beyond the epithelial BM in corneal wounds in normal dogs. Evaluation of the diamond burr debridement in cases of SCCEDs is warranted.

Co-administration of δ- and μ-opioid receptor agonists promotes peripheral opioid receptor function

Enhancement of peripheral opioid analgesia following tissue injury or inflammation in animal models is well-documented, but clinical results of peripheral opioid therapy remain inconsistent. Previous studies in the central nervous system have shown that co-administration of μ- and δ-opioid receptor agonists can enhance analgesic outcomes; however, less is known about the functional consequences of opioid receptor interactions in the periphery. The present study examines the effects of intraplantar injection of the μ- and δ-opioid receptor agonists, morphine and deltorphin, alone and in combination on behavioral tests of nociception in naïve rats and on potassium-evoked release of CGRP from sciatic nerves of naïve rats. Neither drug alone affected nociceptive behaviors or CGRP release. Two separate measures of mechanical nociceptive sensitivity remained unchanged after co-administration of the two drugs. In contrast, when deltorphin was co-injected with morphine, dose-dependent and peripherally restricted increases in paw withdrawal latencies to radiant heat were observed. Similarly, concentration-dependent inhibition of CGRP release was observed when deltorphin and morphine were administered in sequence prior to potassium stimulation. However, no inhibition was observed when morphine was administered prior to deltorphin. All combined opioid effects were blocked by co-application of antagonists. Deltorphin exposure also enhanced the in vivo and in vitro effects of another μ-opioid receptor agonist, DAMGO. Together, these results suggest that under normal conditions, δ-opioid receptor agonists enhance the effect of μ-opioid receptor agonists in the periphery, and local co-administration of δ- and μ-opioid receptor agonists may improve results of peripheral opioid therapy for the treatment of pain.

Effect of topical 0.5% morphine on postoperative pain after photorefractive keratectomy

PURPOSE

To investigate safety and efficacy of 0.5% morphine drops for pain control after photorefractive keratectomy (PRK).

METHODS

In a double-blind prospective study, 40 patients were randomized to either 0.5% morphine drops (n=20) or vehicle control (n=20). Treatment occurred every 2 hours following PRK on the day of the procedure, then four times daily on postoperative days 1 through 3. Patients completed pain assessment questionnaires (visual descriptor, numerical rating, visual analog scales, and oral analgesic consumption) every 2 hours while awake during the treatment period. Daily average and maximum scores were compared between the two groups. Patients were examined daily for 4 days after PRK, weekly for 4 weeks, then monthly for 3 months. Epithelial healing, corneal haze, and refractive outcomes were compared.

RESULTS

Both average and maximum pain scores were lower in the morphine group than in the vehicle control group on all scales and during all 4 days after PRK. Statistical significance (P<.05) was reached on numeric rating scale on procedure day and on postoperative day 1. The difference between the groups on the visual analog scale was statistically significant on procedure day, and on postoperative days 1 and 2. Oral analgesic consumption was higher in the vehicle control group on postoperative day 2. No difference between groups was noted in epithelial healing or refractive outcomes. Stromal haze scores were lower in the morphine group, but the difference was not statistically significant.

CONCLUSIONS

Topical 0.5% morphine may be an effective and safe method of pain control after PRK.

Topical fentanyl in a randomized, double-blind study in patients with corneal damage

OBJECTIVES

Corneal damage causes severe pain. This study investigated whether peripheral opioid receptors are present in the human cornea and assessed the efficacy of topical fentanyl in patients with corneal erosion.

METHODS

Immunohistochemical staining experiments were performed to examine the presence of both mu and delta-receptors on peripheral nerve fibers within human corneal tissue. In a randomized, double-blind clinical trial dexpanthenol (n=20) or dexpanthenol plus 10 microg fentanyl (n=20) were topically applied every 4 hours to the eye of patients with a surgical intervention of corneal damage and subjective pain intensity was determined by a numerical rating scale.

RESULTS

Immunohistochemical staining identified peripheral nerve fibers in human cornea expressing both mu and delta-opioid receptors. In patients with corneal damage the ophthalmic intervention in local anesthesia decreased the subjective pain intensity significantly. At 4-hour intervals after the ophthalmic intervention, moderate pain intensity levels were not altered by the application of dexpanthenol with or without fentanyl. At 24 hours pain intensity dropped significantly, most likely owing to a natural decrease in pain, because the erosion was almost healed.

DISCUSSION

Both mu and delta-receptors are localized on nerve fibers within the cornea, which are accessible for topical opioid treatment. However, our formulation and dose of topical fentanyl in combination with dexpanthenol did not show any benefit in relieving pain from corneal erosion. Future studies are planned to determine the optimal protocol and dose of topical opioid treatment.

Deletion of delta-opioid receptor in mice alters skin differentiation and delays wound healing

In addition to their well-known antinociceptive action, opioids can modulate non-neuronal functions, such as immune activity and physiology of different cell types. Several findings suggest that the delta-opioid receptor (DOR) and its endogenous ligands (enkephalins) are important players in cell differentiation and proliferation. Here we show the expression of DOR in mouse skin and human skin cultured fibroblasts and keratinocytes using RT-PCR. In DOR knock-out (KO) mice, a phenotype of thinner epidermis and higher expression of cell differentiation marker cytokeratin 10 (CK 10) were observed compared with wild type (WT). Using a burn wound model, significant wound healing delay (about 2 days) and severe epidermal hypertrophy were shown at the wound margin of DOR KO mice. This wound healing delay was further investigated by immunohistochemistry using markers for proliferation, differentiation, re-epithelialization, and dermal repair (CK 6, CK 10, and collagen IV). The levels of all these markers were increased in wounds of KO mice compared with WT. During the wound healing, the epidermal thickness in KO mice augments faster and exceeds that of the WT by day 3. These results suggest an essential role of DOR in skin differentiation, proliferation, and migration, factors that are important for wound healing.

Corneal Safety of Topically Applied Naltrexone

PURPOSE

Naltrexone (NTX), an opioid antagonist, accelerates wound healing of corneal epithelium in normal and diabetic animals. This study examined the safety of NTX by topical application in the cornea.

METHODS

NTX in concentrations of 10(-3), 10(-4), 10(-5), 10(-6), or 10(-7) M was administered topically 4 times/daily for 7 d to the eye of Type 1 diabetic rats (glucose levels >400 mg/dL) (DB), DB animals receiving insulin to maintain normoglycemia (DB-IN), and normal (nondiabetic) (Normal) subjects beginning 8 weeks after onset of diabetes.

RESULTS

No differences in intraocular pressures, corneal thickness, endothelial cell number, or epithelial apoptosis, necrosis, or organization were observed between DB, DB-IN, and Normal groups with and without treatment with NTX. The DB group had a twofold decrease in corneal sensitivity from the Normal and DB-IN groups prior to NTX treatment but were comparable to the Normal and DB-IN groups for at least 2 weeks after chronic exposure to 10(-3) to 10(-7) M NTX was terminated. No differences between Normal and DB-IN groups were noted.

CONCLUSIONS

Topical application of NTX over a 10,000-fold range of dosage had no overt toxicity for the parameters studied, indicating that efficacy studies for the use of NTX in corneal wound healing are warranted.

[Potential applications and significance of peripheral opioid analgesia]

Recently, the local application of analgesic substances has attracted much interest and has become increasingly relevant in daily clinical practice. The lack of the well-known therapy-limiting central side effects of systemically administered opioids is a clear advantage of "peripheral opioid analgesia". Important prerequisites for the occurrence of peripheral analgesic effects of opioids are good accessibility of the painful site, presence of clinically relevant pain, signs of a local inflammation, exclusion of a fast systemic absorption, and adequately potent analgesic substances. This review gives an outline of recent experience with various clinical applications of "peripheral opioid analgesia".

Topische Applikation von Morphingel bei entzündlichen Haut- und Schleimhautläsionen

AIM

The aim of this study was to demonstrate a peripheral local opioid effect using case examples involving inflammatory mucosal and cutaneous lesions.

METHODS

A 0.1% morphine gel, mixed in the hospital pharmacy, was applied several times daily to inflammatory mucosal lesions (oral, anogenital and in one patient to a skin ulcer). The effects and side effects were documented.

RESULT

All patients experienced a significant reduction in pain with the use of topical morphine gel and no side effects were seen.

CONCLUSION

Topical peripheral application of morphine gel is a simple, effective method that can be carried out by patients several times a day with few side effects.

Peripheral opioid analgesia: Clinical applications

Peripheral opioid analgesia is undoubtedly of clinical relevance, especially considering that systemic opioid therapy often is hampered by central side effects. Despite some clinical studies that do not show peripheral opioid-mediated pain control, mostly because of methodologic shortcomings, studies evaluating inflammatory pain conditions show clear evidence and the number and the sites of applications are increasing. The intention of this paper is to give insight into the recent experience with the clinical applications of peripheral opioid analgesia.

Standing sedation and pain management for ophthalmic patients

Several ocular procedures, including examination, removal of corneal foreign bodies, nictitans surgery, eyelid repair, and tumor excision,can be successfully performed in the appropriately restrained and sedated standing horse. Sedation is best achieved with xylazine,with or without the addition of acepromazine. Additional analgesia can be provided with appropriate local anesthetic blocks. Surgical conditions are greatly improved by using an auriculopalpebral and supraorbital block and topical anesthetics. More elaborate standing sedation involving continuous rate infusions of lidocaine or detomidine combined with butorphanol may facilitate more involved surgery with appropriate support staff and equipment in animals that are at high risk for general anesthesia or when the latter is not an option. Short-term or long-term analgesia is most commonly provided with nonsteroidal anti-inflammatory drugs, but several newer techniques, including lidocaine and butorphanol infusions, may be effective. Topical treatment with opioids to provide analgesia and opioid antagonists to enhance corneal healing is an exciting new development that may revolutionize our approach to corneal ulcer therapy in the future if current research findings are supportive.