Topican

Uses

Indicated as a topical anesthetic for use on normal intact skin for local analgesia, genital mucous membranes for superficial minor surgery and as pretreatment for infiltration anesthesia

Topican is also used to associated treatment for these conditions: Acute Otitis Media, Anal Fissures, Anorectal discomfort, Arrhythmia, Back Pain Lower Back, Bacterial Vaginosis (BV), Burns, Cervical Syndrome, Earache, Hemorrhoids, Infection, Inflammatory Reaction caused by ear infection-not otherwise specified, Insect Bites, Joint Pain, Mixed Vaginal Infections, Multiple Myeloma (MM), Myringitis, Neuritis, Osteolysis caused by Bone Tumors, Osteoporosis, Otitis Externa, Pain caused by ear infection-not otherwise specified, Pain, Inflammatory, Post-Herpetic Neuralgia (PHN), Postherpetic Neuralgia, Primary Hyperparathyroidism, Rheumatic Diseases, Rheumatic Joint Disease, Sciatica, Skin Irritation, Soft Tissue Inflammation, Sore Throat, Sunburn, Susceptible infections, Trichomonas Vaginitis, Ulcers, Leg, Urethral Strictures, Vulvovaginal Candidiasis, Abrasions, Anal discomfort, Arrhythmia of ventricular origin, Cutaneous lesions, Gum pain, Minor burns, Superficial Wounds, Susceptible Bacterial Infections, Ulceration of the mouth, Viral infections of the external ear canal, Post Myocardial Infarction Treatment, Regional Anesthesia, Local anesthesia therapyLocal anesthesia therapy

How Topican works

Lidocaine is a local anesthetic of the amide type . It is used to provide local anesthesia by nerve blockade at various sites in the body . It does so by stabilizing the neuronal membrane by inhibiting the ionic fluxes required for the initiation and conduction of impulses, thereby effecting local anesthetic action . In particular, the lidocaine agent acts on sodium ion channels located on the internal surface of nerve cell membranes . At these channels, neutral uncharged lidocaine molecules diffuse through neural sheaths into the axoplasm where they are subsequently ionized by joining with hydrogen ions . The resultant lidocaine cations are then capable of reversibly binding the sodium channels from the inside, keeping them locked in an open state that prevents nerve depolarization . As a result, with sufficient blockage, the membrane of the postsynaptic neuron will ultimately not depolarize and will thus fail to transmit an action potential . This facilitates an anesthetic effect by not merely preventing pain signals from propagating to the brain but by aborting their generation in the first place .

In addition to blocking conduction in nerve axons in the peripheral nervous system, lidocaine has important effects on the central nervous system and cardiovascular system . After absorption, lidocaine may cause stimulation of the CNS followed by depression and in the cardiovascular system, it acts primarily on the myocardium where it may produce decreases in electrical excitability, conduction rate, and force of contraction .

Prilocaine acts on sodium channels on the neuronal cell membrane, limiting the spread of seizure activity and reducing seizure propagation. The antiarrhythmic actions are mediated through effects on sodium channels in Purkinje fibers.

Dosage

Topican dosage

A thick layer of Lidocaine & Prilocaine cream is applied to intact skin and covered with an occlusive dressing.

Minor Dermal Procedures: For intravenous cannulation and venipuncture, apply 2.5 grams ofLidocaine & Prilocaine cream over 20 – 25cm2 of skin surface for at least 1 hour.

Major Dermal Procedures: For more painful dermatological procedures involving a larger skinarea, apply 2grams of Lidocaine & Prilocaine cream per 10cm2 of skin and allow to remain in contact with theskin for at least 2 hours.

Adult Male Genital Skin: As an adjunct prior to local anesthetic infiltration, apply a thick layer ofLidocaine & Prilocaine cream to the skin surface for 15 minutes. Local anesthetic infiltration should beperformed immediately after removal of Lidocaine & Prilocaine cream.

Adult Female GenitalMucous Membranes: For minor procedures on the femaleexternal genitalia, such as removal of condylomata acuminata, as well as for use as pretreatmentfor anesthetic infiltration, apply a thick layer (5-10 grams) of Lidocaine & Prilocaine cream for 5 to 10 minutes.Occlusion is not necessary for absorption, but may be helpful to keep the cream in place.Patients should be lying down during the Lidocaine & Prilocaine cream application, especially if no occlusion isused. The procedure or the local anesthetic infiltration should be performed immediately afterthe removal of Lidocaine & Prilocaine cream.

Pediatric Patients: The following are the maximum recommended doses, application areas andapplication times for Lidocaine & Prilocaine cream based on a child’s age and weight:

• 0 to 3 months or <5 kg: Maximum Total Dose1 gm,Maximum Application Time: 1 hour
• 3 to 12 months and >5 kg:Maximum Total Dose 2 gm, Maximum Application Time 4 hour
• 1 to 6 years and >10 kg:Maximum Total Dose 10 gm, Maximum Application Time 4 hour
• 7 to 12 years and >20 kg:Maximum Total Dose 20 gm, Maximum Application Time 4 hour

Side Effects

Nervousness, dizziness, blurred vision, tremors, drowsiness, convulsions, unconsciousness, respiratory arrest, hypotension, myocardial depression, bradycardia, cardiac arrest and anaphylactoid reactions (cutaneous lesion, urticaria, oedema).

Toxicity

Symptoms of overdose and/or acute systemic toxicity involves central nervous system toxicity that presents with symptoms of increasing severity . Patients may present initially with circumoral paraesthesia, numbness of the tongue, light-headedness, hyperacusis, and tinnitus . Visual disturbance and muscular tremors or muscle twitching are more serious and precede the onset of generalized convulsions . These signs must not be mistaken for neurotic behavior . Unconsciousness and grand mal convulsions may follow, which may last from a few seconds to several minutes . Hypoxia and hypercapnia occur rapidly following convulsions due to increased muscular activity, together with the interference with normal respiration and loss of the airway . In severe cases, apnoea may occur. Acidosis increases the toxic effects of local anesthetics . Effects on the cardiovascular system may be seen in severe cases . Hypotension, bradycardia, arrhythmia and cardiac arrest may occur as a result of high systemic concentrations, with potentially fatal outcome .

Pregnancy Category B has been established for the use of lidocaine in pregnancy, although there are no formal, adequate, and well-controlled studies in pregnant women . General consideration should be given to this fact before administering lidocaine to women of childbearing potential, especially during early pregnancy when maximum organogenesis takes place . Ultimately, although animal studies have revealed no evidence of harm to the fetus, lidocaine should not be administered during early pregnancy unless the benefits are considered to outweigh the risks . Lidocaine readily crosses the placental barrier after epidural or intravenous administration to the mother . The ratio of umbilical to maternal venous concentration is 0.5 to 0.6 . The fetus appears to be capable of metabolizing lidocaine at term . The elimination half-life in the newborn of the drug received in utero is about three hours, compared with 100 minutes in the adult . Elevated lidocaine levels may persist in the newborn for at least 48 hours after delivery . Fetal bradycardia or tachycardia, neonatal bradycardia, hypotonia or respiratory depression may occur .

Local anesthetics rapidly cross the placenta and when used for epidural, paracervical, pudendal or caudal block anesthesia, can cause varying degrees of maternal, fetal and neonatal toxicity . The potential for toxicity depends upon the procedure performed, the type and amount of drug used, and the technique of drug administration . Adverse reactions in the parturient, fetus and neonate involve alterations of the central nervous system, peripheral vascular tone, and cardiac function .

Maternal hypotension has resulted from regional anesthesia . Local anesthetics produce vasodilation by blocking sympathetic nerves . Elevating the patient’s legs and positioning her on her left side will help prevent decreases in blood pressure . The fetal heart rate also should be monitored continuously, and electronic fetal monitoring is highly advisable .

Epidural, spinal, paracervical, or pudendal anesthesia may alter the forces of parturition through changes in uterine contractility or maternal expulsive efforts . In one study, paracervical block anesthesia was associated with a decrease in the mean duration of first stage labor and facilitation of cervical dilation . However, spinal and epidural anesthesia have also been reported to prolong the second stage of labor by removing the parturient’s reflex urge to bear down or by interfering with motor function . The use of obstetrical anesthesia may increase the need for forceps assistance .

The use of some local anesthetic drug products during labor and delivery may be followed by diminished muscle strength and tone for the first day or two of life . The long-term significance of these observations is unknown . Fetal bradycardia may occur in 20 to 30 percent of patients receiving paracervical nerve block anesthesia with the amide-type local anesthetics and may be associated with fetal acidosis . Fetal heart rate should always be monitored during paracervical anesthesia . The physician should weigh the possible advantages against risks when considering a paracervical block in prematurity, toxemia of pregnancy, and fetal distress . Careful adherence to the recommended dosage is of the utmost importance in obstetrical paracervical block . Failure to achieve adequate analgesia with recommended doses should arouse suspicion of intravascular or fetal intracranial injection . Cases compatible with unintended fetal intracranial injection of local anesthetic solution have been reported following intended paracervical or pudendal block or both. Babies so affected present with unexplained neonatal depression at birth, which correlates with high local anesthetic serum levels, and often manifest seizures within six hours . Prompt use of supportive measures combined with forced urinary excretion of the local anesthetic has been used successfully to manage this complication .

It is not known whether this drug is excreted in human milk . Because many drugs are excreted in human milk, caution should be exercised when lidocaine is administered to a nursing woman .

Dosages in children should be reduced, commensurate with age, body weight and physical condition .

The oral LD 50 of lidocaine HCl in non-fasted female rats is 459 (346-773) mg/kg (as the salt) and 214 (159-324) mg/kg (as the salt) in fasted female rats .

Precaution

Absorption from wound surfaces and mucous membranes is relatively high, especially in the bronchial tree. This cream should be used with caution in patients with traumatised mucosa and/or sepsis in the region of the proposed application. If the dose or site of administration is likely to result in high blood levels, cream should be used cautiously in patients with epilepsy, impaired cardiac condition, bradycardia, impaired hepatic function and in severe shock. The use of oropharyngeal topical anesthetic agents may interfere with swallowing and thus enhance the danger of aspiration. This is particularly important in children because of their frequency of eating. Numbness of the tongue or buccal mucosa may increase the danger of biting trauma.

Interaction

Cream should be used with caution in patients receiving antiarrhythmic drugs, such as tocainide, since the toxic effects are additive.

Volume of Distribution

The volume of distribution determined for lidocaine is 0.7 to 1.5 L/kg .

In particular, lidocaine is distributed throughout the total body water . Its rate of disappearance from the blood can be described by a two or possibly even three-compartment model . There is a rapid disappearance (alpha phase) which is believed to be related to uptake by rapidly equilibrating tissues (tissues with high vascular perfusion, for example) . The slower phase is related to distribution to slowly equilibrating tissues (beta phase) and to its metabolism and excretion (gamma phase) .

Lidocaine's distribution is ultimately throughout all body tissues . In general, the more highly perfused organs will show higher concentrations of the agent . The highest percentage of this drug will be found in skeletal muscle, mainly due to the mass of muscle rather than an affinity .

Elimination Route

In general, lidocaine is readily absorbed across mucous membranes and damaged skin but poorly through intact skin . The agent is quickly absorbed from the upper airway, tracheobronchial tree, and alveoli into the bloodstream . And although lidocaine is also well absorbed across the gastrointestinal tract the oral bioavailability is only about 35% as a result of a high degree of first-pass metabolism . After injection into tissues, lidocaine is also rapidly absorbed and the absorption rate is affected by both vascularity and the presence of tissue and fat capable of binding lidocaine in the particular tissues .

The concentration of lidocaine in the blood is subsequently affected by a variety of aspects, including its rate of absorption from the site of injection, the rate of tissue distribution, and the rate of metabolism and excretion . Subsequently, the systemic absorption of lidocaine is determined by the site of injection, the dosage given, and its pharmacological profile . The maximum blood concentration occurs following intercostal nerve blockade followed in order of decreasing concentration, the lumbar epidural space, brachial plexus site, and subcutaneous tissue . The total dose injected regardless of the site is the primary determinant of the absorption rate and blood levels achieved . There is a linear relationship between the amount of lidocaine injected and the resultant peak anesthetic blood levels .

Nevertheless, it has been observed that lidocaine hydrochloride is completely absorbed following parenteral administration, its rate of absorption depending also on lipid solubility and the presence or absence of a vasoconstrictor agent . Except for intravascular administration, the highest blood levels are obtained following intercostal nerve block and the lowest after subcutaneous administration .

Additionally, lidocaine crosses the blood-brain and placental barriers, presumably by passive diffusion .

Half Life

The elimination half-life of lidocaine hydrochloride following an intravenous bolus injection is typically 1.5 to 2.0 hours . Because of the rapid rate at which lidocaine hydrochloride is metabolized, any condition that affects liver function may alter lidocaine HCl kinetics . The half-life may be prolonged two-fold or more in patients with liver dysfunction .

Clearance

The mean systemic clearance observed for intravenously administered lidocaine in a study of 15 adults was approximately 0.64 +/- 0.18 L/min .

Elimination Route

The excretion of unchanged lidocaine and its metabolites occurs predominantly via the kidney with less than 5% in the unchanged form appearing in the urine . The renal clearance is inversely related to its protein binding affinity and the pH of the urine . This suggests by the latter that excretion of lidocaine occurs by non-ionic diffusion .

Prilocaine is metabolized in both the liver and the kidney and excreted via the kidney.

Pregnancy & Breastfeeding use

There is no, or inadequate, evidence of safety of the drug in human pregnancy but it has been in wide use for many years without apparent ill consequence. If drug therapy is needed in pregnancy, this drug can be used if there is no safer alternative. Cream enters the mothers milk, but in such small quantities that there is generally no risk of affecting the child at therapeutic dose levels.

Contraindication

Hypersensitivity to local anaesthetics of the amide type or to any other component of the product.

Special Warning

Hepatic Impairment Parenteral: Dosage reduction may be needed.

Acute Overdose

Toxic levels of lidocaine (>5 µg/ml) and/or prilocaine (>6 µg/ml) may decrease cardiac output, total peripheral resistance and mean arterial pressure. These changes are due to direct depressant effects of these local anaesthetic agents on the CVS.

Storage Condition

Store in a cool and dry place, protected from light

Innovators Monograph

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