Clinical pharmacokinetics of transdermal opioids: focus on transdermal fentanyl

Validation of a fentanyl transdermal adhesion scoring tool for use in clinical practice

CONTEXT

The therapeutic efficacy of a transdermal system (TDS) is directly related to the adhesion of TDS, with partial adhesion resulting in lower plasma concentration. Currently there is no TDS adhesion scoring tool available for use in the clinical setting.

OBJECTIVES

To validate a U.S. Food and Drug Administration (FDA) scoring system for the adhesion of the fentanyl TDS in cancer patients.

METHODS

A library of images was created from photographs of fentanyl/placebo TDS placed on patients/volunteers. Thirty photographs, reflecting varying degrees of adhesion, were selected for each of series A and B, with 10 photographs common to both series. Each series was shown to 30 health professionals asked to score the photographs using the FDA scoring system. Validity was assessed using Spearman's rank correlation and reliability by Cohen's kappa (k). Photo editing software was used to assign control scores to each photograph.

RESULTS

Validity was high for both series (≥ 0.954). Inter-reliability (k) ranged from 0.327 to 0.858 (average, 0.547) and 0.433-0.910 (average, 0.620) in series A and B, respectively. The combined agreement across both series was 0.585. Intra-rater agreement (k) of the 10 common images was 0.605. No significant difference was observed between the scoring patterns for those with more than 10 years of working experience.

CONCLUSION

Overall, the TDS adhesion score determined by the participants visually in this study corresponded well to those generated by photo editing software, thus rendering the scoring system highly valid. The FDA scoring system is an adequate tool for assessing fentanyl TDS adhesion in clinical practice.

Life-threatening opioid toxicity from a fentanyl patch applied to eczematous skin

A 19-year-old man with a history of eczema was admitted to the emergency department following collapsing at home. The paramedics found him unresponsive with poor respiratory effort and a widespread erythematous rash. Anaphylaxis, thought to be secondary to flucloxacillin he had recently been prescribed, was diagnosed. Epinephrine, steroids and antihistamines were administered without clinical improvement. On arrival to hospital, constricted pupils were noted prompting the emergency physicians to consider opiate toxicity. Intravenous naloxone brought about an immediate recovery. His father subsequently disclosed that he had given his son one of his own fentanyl patches to alleviate the distressing symptoms of eczema. Although the patient had removed the patch prior to collapsing, he had suffered life-threatening opioid toxicity likely due to enhanced opiate absorption through eczematous skin. This case highlights the risks associated with fentanyl patches in patients with chronic skin conditions.

Prodrug strategies for enhancing the percutaneous absorption of drugs

The transdermal application of drugs has attracted increasing interest over the last decade or so, due to the advantages it offers, compared to other delivery methods. The development of an efficient means of transdermal delivery can increase drug concentrations, while reducing their systemic distribution, thereby avoiding certain limitations of oral administration. The efficient barrier function of the skin, however, limits the use of most drugs as transdermal agents. This limitation has led to the development of various strategies to enhance drug-skin permeation, including the use of penetration enhancers. This method unfortunately has certain proven disadvantages, such as the increased absorption of unwanted components, besides the drug, which may induce skin damage and irritancy. The prodrug approach to increase the skin’s permeability to drugs represents a very promising alternative to penetration enhancers. The concept involves the chemical modification of a drug into a bioreversible entity that changes both its pharmaceutical and pharmacokinetic characteristics to enhance its delivery through the skin. In this review; we report on the in vitro attempts and successes over the last decade by using the prodrug strategy for the percutaneous delivery of pharmacological molecules.

Dosing considerations with transdermal formulations of fentanyl and buprenorphine for the treatment of cancer pain

Opioids continue to be first-line pharmacotherapy for patients suffering from cancer pain. Unfortunately, subtherapeutic dosage prescribing of pain medications remains common, and many cancer patients continue to suffer and experience diminished quality of life. A large variety of therapeutic options are available for cancer pain patients. Analgesic pharmacotherapy is based on the patient’s self-report of pain intensity and should be tailored to meet the requirements of each individual. Most, if not all, cancer pain patients will ultimately require modifications in their opioid pharmacotherapy. When changes in a patient’s medication regimen are needed, adequate pain control is best maintained through appropriate dosage conversion, scheduling immediate release medication for withdrawal prevention, and providing as needed dosing for breakthrough pain. Transdermal opioids are noninvasive, cause less constipation and sedation when compared to oral opioids, and may improve patient compliance. A relative potency of 100:1 is recommended when converting the patient from oral morphine to transdermal fentanyl. Based on the limited data available, there is significant interpatient variability with transdermal buprenorphine and equipotency recommendations from oral morphine of 75:1–110:1 have been suggested. Cancer patients may require larger transdermal buprenorphine doses to control their pain and may respond better to a more aggressive 75–100:1 potency ratio. This review outlines the prescribing of transdermal fentanyl and transdermal buprenorphine including how to safely and effectively convert to and use them for those with cancer pain.

Transdermal fentanyl patch for postoperative analgesia in total knee arthroplasty: a randomized double-blind controlled trial

PURPOSE

To assess the efficacy of a transdermal fentanyl patch (TFP) (50 μg/hour) applied 10-12 hours before surgery versus placebo for postoperative pain control of total knee arthroplasty (TKA).

MATERIALS AND METHODS

We enrolled 40 patients undergoing elective TKA under spinal anesthesia using isobaric or hyperbaric bupivacaine. Subjects were randomized to receive a TFP (Duragesic(®) 50 μg/hour) or placebo patch applied with a self-adhesive to the anterior chest wall 10-12 hours before spinal anesthesia. Every patient was given patient-controlled morphine for postoperative pain control. Patients were evaluated every 4 hours until 48 hours.

RESULTS

Morphine consumption at 24 and 48 hours in the TFP group versus the placebo group was 15.40±12.65 and 24.90±20.11 mg versus 33.60±19.06 and 57.80±12.65 mg (P≤0.001). Numeric rating scale scores at rest and during movement over 48 hours were lower in the TFP group. Ambulation and nausea/vomiting scores were statistically greater, but not clinically significant in the TFP group. Sedation scores were low and not statistically significantly different between groups. There was no severe respiratory depression.

CONCLUSION

TFP (50 μg/hour) applied 10-12 hours before surgery can effectively and safely decrease morphine consumption and pain scores during the first 48 hours after TKA surgery.

Assisted suicide by fentanyl intoxication due to excessive transdermal application

Herein, we report a case of an assisted suicide committed by application of 34 matrix-based fentanyl-containing transdermal therapeutic systems (TTS) with different release rates. The TTS were supplied by the husband but administered by the deceased herself. Besides routine systematic toxicological analysis (STA), the concentrations of fentanyl and norfentanyl were determined in the blood (femoral and heart), urine, stomach content, brain, lung tissue, musculus iliopsoas, liver, kidney, bile and in some of the used TTS by LC-MS/MS. Blood levels of fentanyl were 60.6 μg/L in femoral blood and 94.1 μg/L in heart blood. These concentrations are in good concordance with levels described in cases with accidental or lethal suicidal fentanyl patch application. The organ distribution indicates an influence of post-mortem redistribution. The levels of residual fentanyl in the TTS were also determined. STA furthermore revealed supratherapeutic levels of bromazepam. Thus, the cause of death was a combination of fentanyl and bromazepam intoxication. However, considering the determined levels of fentanyl and norfentanyl in the entire set of specimens and the high toxicity in comparison to bromazepam, fentanyl was the leading toxic noxa.

Chronological age affects the permeation of fentanyl through human skin in vitro

AIM

To study the influence of chronological age on fentanyl permeation through human skin in vitro using static diffusion cells. Elderly individuals are known to be more sensitive to opioids and obtain higher plasma concentrations following dermal application of fentanyl compared to younger individuals. The influence of age - as an isolated pharmacokinetic term - on the absorption of fentanyl has not been previously studied.

METHOD

Human skin from 30 female donors was mounted in static diffusion cells, and samples were collected during 48 h. Donors were divided into three age groups: <30 years of age (n = 6), ≥30 and <60 years of age (n = 18) and ≥60 years of age (n = 6).

RESULTS

The youngest group had a significantly higher mean absorption (3,100 ng/cm(2)) than the two other groups (2,000 and 1,475 ng/cm(2), respectively) and a significant larger AUC (young age group: 9,393 ng; middle and old age groups: 5,922 and 4,050 ng, respectively). Furthermore, the lag time and absorption rate were different between the three groups, with a significantly higher rate in the young participants versus the oldest participants.

CONCLUSION

We demonstrate that fentanyl permeates the skin of young individuals in greater amounts and at a higher absorption rate than in middle-aged and old individuals in vitro.

Converting to transdermal fentanyl: avoidance of underdosing

BACKGROUND

Converting between the various opioid agents continues to be challenge for many practitioners. Specifically, variable recommendations for converting to the transdermal fentanyl patch may lead to confusion among clinicians and errors in dosing.

OBJECTIVE

Our aim was to describe the inconsistencies among available opioid conversions with regard to transdermal fentanyl and to provide recommendations for safe and effective utilization of this product in patients with chronic pain.

RESULTS

Available reports support the use of the morphine intravenous to oral ratio of 1:3 during the conversion to transdermal fentanyl product.

CONCLUSIONS

Underdosing is an often overlooked complication of switching to transdermal fentanyl. Current recommendations for converting to transdermal fentanyl do not reflect contemporary clinical practice and should be reevaluated.

Pharmacokinetics, Tolerability, and Performance of a Novel Matrix Transdermal Delivery System of Fentanyl Relative to the Commercially Available Reservoir Formulation in Healthy Subjects

A novel transdermal formulation of fentanyl-containing dipropylene glycol droplets dispersed in a silicone matrix with a rate-controlling membrane was developed. Healthy male subjects (n = 24) received repeated 72-hour applications of fentanyl (50 mug/h) as the novel matrix and the conventional reservoir formulations in a randomized, 2-way crossover study. Blood samples were collected, and serum concentrations of fentanyl were assayed using liquid chromatography with mass spectrometry detection. The mean area under the curve (AUCtau) and peak concentrations (C(max)) of the matrix formulation were 84 838 pg.h/mL and 1680 pg/mL, respectively. Ratio and 90% confidence intervals of AUCtau and C(max) between the 2 formulations were within 80% to 125%. Adherence of the matrix formulation was higher than the reservoir formulation (62.5 vs 56.2%, P < .0001), without affecting skin irritation. Vital signs and adverse events of the 2 formulations were similar in nature and frequency. The novel matrix formulation displayed enhanced adherence and resulted in similar pharmacokinetics and tolerability as the reservoir formulation.

Multicenter clinical study for evaluation of efficacy and safety of transdermal fentanyl matrix patch in treatment of moderate to severe cancer pain in 474 chinese cancer patients

OBJECTIVE

Although a new matrix formulation fentanyl has been used throughout the world for cancer pain management, few data about its efficacy and clinical outcomes associated with its use in Chinese patients have been obtained. This study aimed to assess the efficacy and safety of the new system in Chinese patients with moderate to severe cancer pain.

METHODS

A total of 474 patients with moderate to severe cancer pain were enrolled in this study and were treated with the new transdermal fentanyl matrix patch (TDF) up to 2 weeks. All the patients were asked to record pain intensity, side effects, quality of life (QOL), adherence and global satisfaction. The initial dose of fentanyl was 25 μg/h titrated with opioid or according to National Comprehensive Cancer Network (NCCN) guidelines. Transdermal fentanyl was changed every three days.

RESULTS

After 2 weeks. The mean pain intensity of the 459 evaluated patients decreased significantly from 5.63±1.26 to 2.03±1.46 (P<0.0001). The total remission rate was 91.29%, of which moderate remission rate 53.16%, obvious remission rate 25.49% and complete remission rate 12.64%. The rate of adverse events was 33.75%, 18.78% of which were moderate and 3.80% were severe. The most frequent adverse events were constipation and nausea. No fatal events were observed. The quality of life was remarkably improved after the treatment (P<0.0001).

CONCLUSION

The new TDF is effective and safe in treating patients with moderate to severe cancer pain, and can significantly improve the quality of life.

A double-blind, placebo-controlled study on the effect of buprenorphine and fentanyl on descending pain modulation: a human experimental study

OBJECTIVES

The descending pain inhibitory system is impaired in chronic pain and it is important to know how analgesics interact with this system. The aim of this human experimental pain, double-blind, randomized, placebo-controlled, 3 way cross-over study was to investigate the effect of 2 different opioids on descending pain inhibition using conditioning pain modulation (CPM) as a screening tool.

METHODS

Twenty-two healthy male volunteers were randomized to 72 hours of treatment with transdermal patches of fentanyl (25 μg/h), buprenorphine (20 μg/h), or placebo. The CPM was induced by immersing the hand into cold (3.0 ± 0.3°C) water and the evoked pain was continuously rated on a visual analogue scale (VAS). The test stimulus [pressure pain tolerance threshold (PPTol)] was applied to the contra-lateral arm. The CPM test was performed at baseline, 24, 48, and 72 hours after application of the patches.

RESULTS

The opioid treatments did not significantly (F=2.249; P=0.07) modulate the PPTol over the treatment period compared with placebo. The CPM-evoked PPTol increases (percentage increase from what was obtained at the baseline before patch application) were significantly enhanced by buprenorphine (P=0.004) and fentanyl (P=0.005) compared with placebo, with no differences between the 2 active drugs. Fentanyl significantly attenuated the time to cold water-evoked VAS peak compared with placebo (P=0.005), and the same trend was observed for buprenorphine (P=0.06). The VAS pain intensity was not affected.

DISCUSSION

The opioids buprenorphine and fentanyl significantly potentiate the effect of descending pain inhibition in healthy volunteers.

Interindividual variation in transdermal and oral drug deliveries

It is generally assumed that the topical absorption of drugs is subject to more interindividual variation than the oral absorption of drugs. To date, we are unaware of any clinical studies or meta-analyses that compare the interindividual variation of transdermal and oral drug deliveries for a large number of medications. In this research article, the absorption data for 10 medications that can be used as an oral medication or a transdermal patch were compiled, and from the collected data, the interindividual variance was calculated for topical and oral absorption as an overall average and by drug. This research article also briefly reviews the pharmacokinetics and pharmacodynamics of transdermal and oral drug absorption. Our results indicate that there is considerable interindividual variation in topical and oral absorption for the 10 medications investigated. Yet, surprisingly, the calculated overall mean and median coefficient of variation (CV) for topical and oral absorption were comparable (within 10% of each other). Therefore, the interindividual variation in topical and oral absorption may not be as divergent as assumed previously. In a drug-by-drug comparison, certain medications demonstrated considerably more variation when absorbed orally versus topically and vice versa. It is unclear why certain drugs had less variation in absorption when delivered topically versus orally (or vice versa). However, patterns in drug molecular weight (MW) or octanol partition coefficient (log K(OCT) ) could not totally explain these findings. In our analysis, the previously reported correlation between MW or log K(OCT) and interindividual variation in absorption could only be replicated when plotting the topical absorption CV and MW. What became clear from our analysis is that the drug itself is an important variable when considering which route of delivery (oral or topical) will provide the least amount of interindividual variation. Our study had many limitations because of study design, which may have affected our calculations and conclusions. Further experimentation is needed to support and reveal the basic science of skin or drug chemistry that can further explain these findings.

Continuous ropivacaine infusion vs transdermal fentanyl for providing postoperative analgesia following temporomandibular joint interpositional gap arthroplasty

AIM

The purpose of this study was to evaluate the postoperative pain control and mouth opening in patients undergoing temporomandibular joint interpositional gap arthroplasty by either placing an epidural catheter in the incision wound and infusing ropivacaine 0.25% or by using a transdermal fentanyl patch.

MATERIALS AND METHODS

The study was prospective, randomized and double blind. Eighty patients belonging to American Society of Anesthesiologists grade I and II, 18-32 years of age, scheduled for temporomandibular joint interpositional gap arthroplasty were randomized into 2 groups; ropivacaine group (G rop): to receive 0.25% ropivacaine infusion and transdermal fentanyl group (G tf): to receive transdermal fentanyl patch. For postoperative pain (Visual Analog Score [VAS]) and analgesic requirements were assessed 2, 4 and 8 h after surgery and each morning, until and 4 days after surgery.

RESULTS

Time to first analgesic requirement was found to be significantly (P < 0.0001) higher in G rop (49 ± 6.7) as compared with G tf (32 ± 9.1) VAS were also significantly lower in G rop throughout the postoperative period. Postoperatively, mouth opening was better in G rop as compared with G tf, which was statistically significant.

CONCLUSION

It was concluded that by placing an epidural catheter at the incision wound and continuously infusing with ropivacaine 0.25% effectively controls the postoperative pain in patients undergoing temporomandibular joint interpositional gap arthroplasty and provides better postoperative mouth opening.

Effect of transdermal opioids in experimentally induced superficial, deep and hyperalgesic pain

BACKGROUND AND PURPOSE

Chronic pain and hyperalgesia can be difficult to treat with classical opioids acting predominately at the µ-opioid receptor. Buprenorphine and its active metabolite are believed to act through µ-, κ- and δ-receptors and may therefore possess different analgesic and anti-hyperalgesic effects compared with pure µ-receptor agonists, for example, fentanyl. Here, we have compared the analgesic and anti-hyperalgesic effects of buprenorphine and fentanyl.

EXPERIMENTAL APPROACH

Twenty-two healthy volunteers were randomized to treatment with transdermal buprenorphine (20 µg·h(-1), 144 h), fentanyl (25 µg·h(-1), 72 h) or placebo patches in a double-blind, cross-over experimental pain study. The experimental pain tests (phasic pain, sensitization) involved pressure at the tibial bone, cutaneous electrical and thermal stimulation, intramuscular nerve growth factor, UVB light burn injury model and intradermal capsaicin-induced hyperalgesia. Pain testing was carried out at baseline, 24, 48, 72 and 144 h after application of the drugs.

KEY RESULTS

Compared with placebo, buprenorphine, but not fentanyl, significantly attenuated pressure at the tibial bone as well as pressure pain in the primary hyperalgesic area induced by UVB light The two drugs were equipotent and better than placebo against cutaneous thermal pain stimulation), but failed to show significant analgesic effect to cutaneous electrical stimulation, nerve growth factor-induced muscle soreness and to capsaicin-induced hyperalgesia.

CONCLUSIONS AND IMPLICATIONS

Buprenorphine, but not fentanyl, showed analgesic effects against experimentally induced, bone-associated pain and primary hyperalgesia compared with placebo. These tissue- and modality-differentiated properties may reflect the variable effects of opioid drugs observed in individual patients.

Evaluation of transdermal fentanyl patch attachment in dogs and analysis of residual fentanyl content following removal

OBJECTIVE

To investigate whether the method used to attach matrix-type fentanyl patches influences the degree of skin attachment and the amount of active drug remaining in patches after use.

STUDY DESIGN

Prospective, randomised clinical study.

STUDY POPULATION

Fifteen adult dogs of mixed breeds.

METHODS

Two equally sized matrix-type fentanyl patches were attached to the dorsal third of the lateral thorax of fifteen dogs for 72 hours. The two patches were attached using different techniques: Method AD used an adhesive dressing in combination with a transparent film. Method TG used tissue adhesive applied to the edges of the patch. After 72 hours the patches were removed and the proportion of the patch attached at this time calculated. The residual content of the patches was analysed using a validated gas chromatography-mass spectrometery (GC-MS) analysis technique.

RESULTS

After 72 hours of continuous attachment, the mean proportion of drug uptake for method AD was 17.2 (SD ± 11.1)% and for method TG this was 16.9 (SD ± 7.3)%. The median proportion of attachment for method AD was 100% and for method TG was 95.6%.

CONCLUSIONS

The method of attachment did not significantly influence the uptake of fentanyl from matrix-type patches. The method of attachment resulted in a significant difference in the proportion of the patch attached 72 hours after placement, with method AD resulting in a greater median proportion of attachment than TG.

CLINICAL RELEVANCE

The method used to attach matrix-type fentanyl patches to dogs should not interfere with drug uptake. The residual fentanyl content remaining in these patches after 72 hours of continuous application is significant and could lead to intoxication if ingested by humans.

Is morphine still the best reference opioid?

SUMMARY Cancer and noncancer pain can usually be managed according to the WHO analgesic ladder and, in many countries, morphine remains the first-line opioid of choice for chronic severe pain. There have been many advances in the use of opioids for moderate-to-severe pain control in recent years. Consequently, the position of morphine as the gold standard became gradually more questioned, mostly because of serious adverse effects and the availability of different opioids and new formulations. The place of morphine as the first-line option is based on reasons of familiarity, availability or cost rather than medical advantages. In recent years, a number of systematic reviews failed to demonstrate superiority of morphine over other opioids in terms of efficacy or tolerability. Moreover, some strong opioids have shown improved tolerability or convenience. Currently, morphine might still be considered as a reference drug for equivalent dosing, but not for strategic healthcare decisions, as it has not demonstrated clinical or pharmacological superiority over other opioids. Therefore, there is a lack of evidence to sustain the role of morphine as the gold standard in the treatment of chronic severe pain.

In-vitro and in-vivo transdermal iontophoretic delivery of tramadol, a centrally acting analgesic

Objectives

The feasibility of transdermal delivery of tramadol, a centrally acting analgesic, by anodal iontophoresis using Ag/AgCl electrodes was investigated in vitro and in vivo.

Methods

To examine the effect of species variation and current strength on skin permeability of tramadol, in-vitro skin permeation studies were performed using porcine ear skin, guinea-pig abdominal skin and hairless mouse abdominal skin as the membrane. In an in-vivo pharmacokinetic study, an iontophoretic patch system was applied to the abdominal skin of conscious guinea pigs with a constant current supply (250 µA/cm2) for 6 h. An intravenous injection group to determine the pharmacokinetic parameters for estimation of the transdermal absorption rate in guinea pigs was also included.

Key findings

The in-vitro steady-state skin permeation flux of tramadol current-dependently increased without significant differences among the three different skin types. In the in-vivo pharmacokinetic study, plasma concentrations of tramadol steadily increased and reached steady state (336 ng/ml) 3 h after initiation of current supply, and the in-vivo steady-state transdermal absorption rate was 499 µg/cm2 per h as calculated by a constrained numeric deconvolution method.

Conclusions

The present study reveals that anodal iontophoresis provides current-controlled transdermal delivery of tramadol without significant interspecies differences, and enables the delivery of therapeutic amounts of tramadol.

Clinical pharmacology of analgesic medicines in older people: impact of frailty and cognitive impairment

Pain is highly prevalent in frail older people who often have multiple co-morbidities and multiple medicines. Rational prescribing of analgesics in frail older people is complex due to heterogeneity in drug disposition, comorbid medical conditions, polypharmacy and variability in analgesic response in this population. A critical issue in managing older people with pain is the need for judicious choice of analgesics based on a comprehensive medical and medication history. Care is needed in the selection of analgesic medicine to avoid drug-drug or drug-disease interactions. People living with dementia and cognitive impairment have suboptimal pain relief which in part may be related to altered pharmacodynamics of analgesics and challenges in the systematic assessment of pain intensity in this patient group. In the absence of rigorously controlled trials in frail older people and those with cognitive impairment a pharmacologically-guided approach can be used to optimize pain management which requires a systematic understanding of the pharmacokinetics and pharmacodynamics of analgesics in frail older people with or without changes in cognition.

Complications of oral exposure to fentanyl transdermal delivery system patches

PURPOSE

Fentanyl is a synthetic opioid available therapeutically as an intravenous, transbucal, or transdermal preparation. It is also used as a drug of abuse through a variety of different methods, including the oral abuse of transdermal fentanyl patches. This is a series of patients with oral fentanyl patch exposure reported to our center and represents the first series of oral fentanyl patch exposures collected outside of the postmortem setting.

METHODS

In this series, we examined the New York Poison Control Center database for all cases of oral abuse of fentanyl reported between January 2000 and April 2008.

RESULTS

Twenty cases were reported, nine were asymptomatic or had symptoms of opioid withdrawal; 11 had symptoms of opioid intoxication. Eight patients were administered naloxone and all showed improvement in clinical status. Only one case resulted in a confirmed fatality-this patient had an orally adherent patch discovered at intubation.

CONCLUSIONS

Oral exposure may result in life-threatening toxicity. Patients should be closely assessed and monitored for the opioid toxidrome, and if symptomatic, should be managed with opioid antagonists and ventilatory support.

Intranasal fentanyl: from pharmacokinetics and bioavailability to current treatment applications

Fentanyl, a short-acting synthetic pure opiate, offers an excellent option for the treatment of cancer and chronic pain. While oral administration is not an option, its high potency and lipophilicity have made intranasal administration feasible. Intranasal fentanyl has a bioavailability of 89%, with a short onset of action ( approximately 7 min) and duration times ( approximately 1 h). It bypasses the oral/gastrointestinal route, delivers the analgesic dose in a volume of 150 microl that can be adequately absorbed and, with a pH of 6.4, avoids local irritation. Intranasal fentanyl has been investigated to assess its potential as a well-tolerated acute postoperative breakthrough pain relief medication. It has been shown to be superior to oral transmucosal fentanyl for the treatment of cancer breakthrough pain. Similar analgesic effects to fentanyl or morphine intravenously and orally, with a similar safety profile, have been reported for postoperative or acute pain treatment of children and adults in the prehospital and hospital settings.

Pitfalls with the "chest compression-only" approach: the challenge of an unusual cause

Chest compression-only (CC-only) is now incorporated in the Norwegian protocol for dispatch guided CPR (cardiopulmonary resuscitation) in cardiac arrest of presumed cardiac aetiology.We present a case that is unique and instructive as well as unusual. It reminds us of the challenges that face bystanders, dispatch centres and ambulance services when faced with possible cardiac arrest.This case report describes a 50 year old man in a rural community. He had suffered a heart attack 8 months previously, and was found unconscious with respiratory arrest in his garden one morning. Due to the proximity to the ambulance station, the paramedics were on the scene within three minutes. A chain-saw was lying beside him, but no external injuries were seen. The patient had no radial pulse, central cyanosis and respiratory gasps approximately every 30 seconds. Ventilation with bag and mask was given, and soon a femoral pulse could be palpated. Blood sugar was elevated and ECG (electrocardiogram) was normal. GCS (Glasgow Coma Scale) was 3. Upon arrival of the physician staffed air ambulance, further examination revealed bilateral miosis of the pupils and continuing bradypnoea. Naloxone was given with an immediate effect and the patient woke up. The patient denied intake of narcotics, but additional information from the dispatch centre revealed that he was hepatitis C positive. After a few hours, the patient admitted to have obtained a fentanyl transdermal patch from an acquaintance, having chewed it before falling unconscious. This case report shows the importance as well as the challenges of identifying a non-cardiac cause of possible cardiac arrest, and the value of providing causal therapy.

Formulations of fentanyl for the management of pain

Fentanyl is an opioid initially developed for parenteral administration. While oral administration is not an option due to a high first-pass metabolism, its high potency and lipophilicity have made a number of new routes of administration feasible. The transdermal therapeutic system offers an excellent option for long-term treatment of cancer and chronic pain, achieving stable plasma concentrations over the treatment period. The recent change from reservoir to matrix systems has made these systems more convenient to wear and safer to use, while being bioequivalent. In contrast, the patient-controlled iontophoretic transdermal system has been developed to enable on-demand delivery of transdermal bolus doses of fentanyl to treat postoperative pain. It offers a needle-free system to provide patient-controlled analgesia otherwise offered by intravenous pumps. However, due to technical difficulties the system is currently not clinically available. Oral transmucosal fentanyl utilizes the rapid uptake through the buccal mucosa to achieve high plasma concentrations rapidly and is indicated to treat breakthrough pain in patients who are not opioid-naive. The recently introduced fentanyl buccal tablets offer slightly better pharmacokinetics for the same indication. The intranasal route is another option to achieve rapid uptake of fentanyl, and is currently being investigated to provide acute and breakthrough pain relief. Transpulmonary administration of fentanyl remains experimental and this route of administration is not yet in clinical use. Overall, the specific pharmacological and physicochemical properties of fentanyl have made this compound highly suitable for novel routes of administration in a range of clinical indications.

Ester prodrugs of morphine improve transdermal drug delivery: a mechanistic study

Two alkyl esters of morphine, morphine propionate (MPR) and morphine enanthate (MEN), were synthesized as potential prodrugs for transdermal delivery. The ester prodrugs could enhance transdermal morphine delivery. The mechanisms of this enhancing effect were elucidated in this study. Both prodrugs were more lipophilic than their parent drug as evaluated by the skin/vehicle partition coefficient (log P) and capacity factor (log K′). The in-vitro skin permeation of morphine and its prodrugs from pH 6 buffer was in the order of MEN &gt; MPR &gt; morphine. MPR and MEN respectively enhanced the transdermal delivery of morphine by 2- and 5-fold. A contrary result was observed when using sesame oil as the vehicle. The prodrugs were stable against chemical hydrolysis in an aqueous solution, but were readily hydrolysed to the parent drug when exposed to skin homogenate and esterase. Approximately 98% MPR and ∼75% MEN were converted to morphine in an in-vitro permeation experiment. The viable epidermis/dermis contributed to a significant resistance to the permeation of ester prodrugs. According to the data of skin permeation across ethanol-, α-terpineol-, and oleic acid-pretreated skin, MEN was predominantly transported via lipid bilayer lamellae in the stratum corneum. The intercellular pathway was not important for either morphine or MPR permeation.

Transdermal fentanyl: pharmacology and toxicology

OBJECTIVE

To evaluate the underlying pharmacology, safety, and misuse/abuse of transdermal fentanyl, one of the cornerstone pharmacotherapies for patients with chronic pain.

METHODS

Literature was identified through searches of Medline (PubMed) and several textbooks in the areas of pharmacology, toxicology, and pain management. A bibliographical review of articles identified by these searches was also performed. Search terms included combinations of the following: fentanyl, transdermal, patch, pharmacology, kinetics, toxicity, and poisoning. All pertinent clinical trials, retrospective studies, and case reports relevant to fentanyl pharmacology and transdermal fentanyl administered by any route and published in English were identified. Each was reviewed for data regarding the clinical pharmacology, abuse, misuse, and safety of transdermal fentanyl. Data from these studies and information from review articles and pharmaceutical prescribing information were included in this review.

RESULTS

Fentanyl is a high-potency opioid that has many uses in the treatment of both acute and chronic pain. Intentional or unintentional misuse, as well as abuse, may lead to significant clinical consequences, including death. Both the US Food and Drug Administration (FDA) and Health Canada have warned of potential pitfalls associated with transdermal fentanyl, although these have not been completely effective in preventing life-threatening adverse events and fatalities related to its inappropriate use.

CONCLUSIONS

Clinically consequential adverse effects may occur unexpectedly with normal use of transdermal fentanyl, or if misused or abused. Misuse and therapeutic error may be largely preventable through better education at all levels for both the prescriber and patient. The prevention of intentional misuse or abuse may require regulatory intervention.

The use of transdermal fentanyl in cancer pain--a compliance study of outpatients in Taiwan

The aim of this study is to investigate cancer patients' response and side effects associated with transdermal therapeutic fentanyl (TTS-F), whose pain was hardly controlled by nonweak/weak opioids in Taiwan. From 2005 to 2006, 822 outpatients received TTS-F to collect pain assessment forms and diaries for 4 weeks. Most (78.7%) patients were initially prescribed 25 microg/h TTS-F. Doses were adjusted weekly at clinicians' discretion, according to pain assessment and side effects. Patients receiving 50 microg/h, 75 microg/h, and > 75 microg/h TTS-F had increased from 17.5% to 32.1%, 1.8% to 3.4%, and 1.9% to 2.2%, respectively, by week 2; further small increases were found in weeks 3 and 4. Pain palliation improved from 60.6% during week 1 to 78.6% at week 4. The common adverse effects were nausea/vomiting. Patient's compliance was >90%. This study found that the TTS-F is effective and well tolerated.

Fatal overdose due to prescription fentanyl patches in a patient with sickle cell/beta-thalassemia and acute chest syndrome: A case report and review of the literature

Introduced into clinical practice in the 1960s, the analgesic fentanyl is 100 times more potent than morphine. Various methods of administration exist including the transdermal Duragesic patch system, widely used in chronic pain and palliative care settings. Numerous, often imaginative methods of abuse of fentanyl patches have been reported; the majority of fatal fentanyl overdose cases resulting from deliberate abuse or suicide. We describe the accidental overdose of a young black male with sickle cell/beta-thalassemia who had been using the Duragesic system for almost 2 years.At autopsy the macroscopic findings were of nonspecific opiate overdose with congested heavy lungs. Histopathological examination revealed severe sickling of red blood cells in the lungs (acute chest syndrome). Toxicological examination revealed blood and urine fentanyl levels of 40 microg/L and 400 microg/L (10 fold and 100 fold higher than therapeutic levels). The mast cell tryptase was also significantly elevated at 76 microg/L, (Normal 2-14 microg/L). We discuss the relevance of these findings with regard to the cause of death, and stress the need to consider fentanyl when confronted with nonspecific signs of opiate overdose as it is not detected in routine toxicological drug screens.

Fentanyl inhibits glucose-stimulated insulin release from β-cells in rat pancreatic islets

AIM: To explore the effects of fentanyl on insulin release from freshly isolated rat pancreatic islets in static culture.

METHODS: Islets were isolated from the pancreas of mature Sprague Dawley rats by common bile duct intraductal collagenase V digestion and were purified by discontinuous Ficoll density gradient centrifugation. The islets were divided into four groups according to the fentanyl concentration: control group (0 ng/mL), group I (0.3 ng/mL), group II (3.0 ng/mL), and group III (30 ng/mL). In each group, the islets were co-cultured for 48 h with drugs under static conditions with fentanyl alone, fentanyl + 0.1 μg/mL naloxone or fentanyl + 1.0 μg/mL naloxone. Cell viability was assessed by the MTT assay. Insulin release in response to low and high concentrations (2.8 mmol/L and 16.7 mmol/L, respectively) of glucose was investigated and electron microscopy morphological assessment was performed.

RESULTS: Low- and high-glucose-stimulated insulin release in the control group was significantly higher than in groups II and III (62.33 ± 9.67 μIU vs 47.75 ± 8.47 μIU, 39.67 ± 6.18 μIU and 125.5 ± 22.04 μIU vs 96.17 ± 14.17 μIU, 75.17 ± 13.57 μIU, respectively, P < 0.01) and was lowest in group III (P < 0.01). After adding 1 μg/mL naloxone, insulin release in groups II and III was not different from the control group. Electron microscopy studies showed that the islets were damaged by 30 ng/mL fentanyl.

CONCLUSION: Fentanyl inhibited glucose-stimulated insulin release from rat islets, which could be prevented by naloxone. Higher concentrations of fentanyl significantly damaged β-cells of rat islets.

The combined analgesic effect of gabapentin and transdermal fentanyl patch on acute and chronic pain after maxillary cancer surgeries

Purpose of this study was to evaluate the combined analgesic effect of gabapentin and transdermal fentanyl patch, on acute and chronic pain after surgery for maxillary cancer.

STUDY DESIGN

The Study was double blind and prospective. 100 subjects belonging to ASA grade I and II, 30-50 years age group, scheduled for maxillary cancer surgery were randomized into two groups; treatment group (GT): to receive gabapentin, transdermal fentanyl patch or control group ©: two placebos. For acute postoperative pain (Visual Analogue Score) and analgesic requirements were assessed 2, 4, 8 hours and 7 days after surgery. Subjects were also assessed for chronic pain 2, 4, 6 months later.

RESULTS

Subjects in treatment group required lesser dose of analgesic, as compared to control group, in the post operative period. Visual Analogue Scores were also significantly lower in the treatment group throughout the post operative period. Occurrence of side effects was non significant between both groups. 2, 4 and 6 months after surgery, 40, 35 and 28 subjects respectively, out of total 45 subjects of the control group, reported chronic pain. In comparison, 25, 10 and 4 subjects out of 42 subjects in the treatment group reported chronic pain 2, 4, 6 months respectively after surgery. 15, 10 and 6 out of 45 of the control group required analgesics, whereas 2, 0 and 0 out of 42 in the treatment group, required analgesics respectively 2, 4 and 6 months after surgery

CONCLUSION

Acute and chronic pain after maxillary cancer surgery is significantly reduced by multimodal analgesia.

Estimating skin permeability from physicochemical characteristics of drugs: a comparison between conventional models and an in vivo-based approach

This study evaluates the correlation of some widely used skin permeability predictive models with a recently proposed empirical model based on human in vivo dermatopharmacokinetic data. Drug fluxes through the skin have been calculated using in vitro- and in vivo-based models, and observed in vivo data, and the values compared. Most in vitro-based models underestimate the in vivo data by 1-100-fold. The discrepancy between observed data and prediction reaches the maximum (1000-10,000-fold underestimation) for nicotine (with the smallest molecular weight and logK(oct)), nitroglycerin (with the largest number of hydrogen bond acceptor groups), and for oxybutynin (with the largest molecular weight and logK(oct)) where there was a 1000-fold flux overestimation. However, most models correlated well with the in vivo data and the in vivo-based model (p<0.05). The vehicle effect and using non-steady state in vivo data in the flux calculations partly account for the observed discrepancies between predicted and observed values. Nevertheless, these results reveal the need for further refinement of skin permeability predictive equations, using the steady state in vivo data, and consideration of formulation effect.

Multiscale modeling framework of transdermal drug delivery

This study addresses the modeling of transdermal diffusion of drugs to better understand the permeation of molecules through the skin, especially the stratum corneum, which forms the main permeation barrier to percutaneous permeation. In order to ensure reproducibility and predictability of drug permeation through the skin and into the body, a quantitative understanding of the permeation barrier properties of the stratum corneum (SC) is crucial. We propose a multiscale framework of modeling the multicomponent transdermal diffusion of molecules. The problem is divided into subproblems of increasing length scale: microscopic, mesoscopic, and macroscopic. First, the microscopic diffusion coefficient in the lipid bilayers of the SC is found through molecular dynamics (MD) simulations. Then, a homogenization procedure is performed over a model unit cell of the heterogeneous SC, resulting in effective diffusion parameters. These effective parameters are the macroscopic diffusion coefficients for the homogeneous medium that is "equivalent" to the heterogeneous SC, and thus can be used in finite element simulations of the macroscopic diffusion process. The resulting drug flux through the skin shows very reasonable agreement to experimental data.

[Management of transdermal therapeutics in perioperative care]

OBJECTIVE

To provide guidance on perioperative management of most frequently encountered transdermal therapeutics in anaesthesiology: nicotine, fentanyl, nitroglycerin, scopolamine and estradiol.

DATA SOURCES

A review of the last decade literature was carried out on the Pubmed database using the following keywords (transcutaneous or percutaneous or transdermal or transdermic or skin or dermal) and (drug delivery systems or therapeutic systems or drug administration) grouped under the Mesh terms cutaneous administration, perioperative care, surgery, pharmacokinetics, nicotine, fentanyl, nitroglycerin, scopolamine, estradiol.

STUDY SELECTION

Original articles, general articles reviews, guidelines, letters to the editor and case reports have been selected.

DATA EXTRACTION

Articles were analyzed for each transdermal treatment in terms of pharmacokinetics as well as anaesthetics and surgical interactions.

DATA SYNTHESIS

Transdermal nicotine must be removed before anaesthesia of patients with coronary disease or with high risk of inhalation and in case of reconstructive surgery. Transdermal fentanyl must be maintained during the perioperative period and associated with preventive treatments of hyperalgesia. Transdermal administration of fentanyl by iontophoresis is a promising system for postoperative analgesia. Transdermal nitroglycerin must be maintained before scheduled surgery of a coronary patient. Transdermal scopolamine must be removed the day before surgery because of its side effects. It could have an interest in the prevention of postoperative nausea and vomiting, but its therapeutic method remain to be defined. Transdermal estradiol can be maintained during the perioperative period.

CONCLUSION

The management of transdermal therapeutics in peri operative care can be adapted for each treatment and for each patient by knowing pharmacokinetics as well as anaesthetics and surgical interactions. In emergency situations, the actions to be taken do not generally differ, but one must be aware that the effects of trandermal treatments do not disappear immediately when removed, due to their pharmacokinetics properties.