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August 23, 2010
Local & General Anesthetics
Anesthetic
It is an agent that causes partial or complete loss of sensation, with or without loss of consciousness, i.e., anesthesia.
Anesthesia
It is a partial or complete loss of sensation, with or without loss of consciousness, as a result of disease, injury, or administration of an anesthetic agent, usually by injection or inhalation.
Classification of Aesthetics
Generally there are two types of anesthetics. Such as-
Local Anesthetics
Clinically, local anesthetics are those anesthetics which are used to block pain sensation from—or sympathetic vasoconstrictor impulses to—specific areas of the body.
Local anesthetics reversibly block impulse conduction along nerve axons and other excitable membranes that utilize sodium channels as the primary means of action potential generation.
The first local anesthetic introduced into medical practice, cocaine, was isolated by Niemann in 1860 and introduced into practice by Koller in 1884 as an ophthalmic anesthetic.
Most of local anesthetic agents consist of a lipophilic group (an aromatic ring) connected by an intermediate chain (commonly including an ester or amide) to an ionizable group (usually a tertiary amine).
Local anesthetics are weak bases. For therapeutic application, they are usually made available as salts because of solubility and stability.
Factors on pKa
In the body, they exist either as the uncharged base or as a cation. According to Henderson-Hasselbalch equation the relative proportions of these two forms is given by-
log (Cationic form)/(Uncharged form)=〖pK〗_a- pH
Because the pKa of most local anesthetics is in the range of 8.0–9.0, the larger percentage in body fluids at physiologic pH will be the charged (cationic form).
[Note to know: The cationic form is the most active form at the receptor site because it cannot readily exit from closed channels. However, the uncharged form is important for rapid penetration of biologic membranes and producing a clinical effect, since the local anesthetic receptor is not readily accessible from the external side of the cell membrane. Therefore, local anesthetics are much less effective when they are injected into infected tissues because a smaller percentage of the local anesthetic is nonionized and available for diffusion across the membrane in an environment with a low extracellular pH.]
Pharmacodynamics (M/A of LA)
Local anesthetics prevent the initiation and propagation of the nerve impulse (action potential). By reducing the passage of sodium through voltage-gated Na ion channels they raise the threshold of excitability (the transmembrane potential -90 - -60mv changed to +40mv); in consequence, conduction is blocked at afferent nerve endings, and by sensory and motor nerve fibers. The fibers in nerve trunks are affected in order of size, the smallest (autonomic, sensory) first, probably because they have a proportionately greater surface area then the larger (motor) fibers. Paradoxically, the effect in the CNS is stimulation. A related flow chart is given below-
Uses of LA
LA are usually used by injection into the area of the nerve fibers to be blocked, and sometimes also topically.
Absorption
Systemic absorption of injected local anesthetics from the site of administration depends on several factors including-
[vasoconstrictor substances such as epinephrine reduce systemic absorption of local anesthetics from the depot site by decreasing regional blood flow in these area.]
Distribution
The amide local anesthetics are widely distributed after intravenous bolus administration. The distribution rate of a single dose of a local anesthetic is determined by diffusion into tissues with concentrations approximately in relation to blood flow (blood t1/2 only a few minutes).
Metabolism and Excretion
The local anesthetics are converted in the liver or in plasma to more water-soluble metabolites and then excreted in the urine. Since LA in the uncharged form diffuse readily through lipid, little or no urinary excretion of the neutral form occurs. Ester like LA hydrolyzed very rapidly in the blood by butyrylcholinesterase (pseudocholinesterase) to have very short plasma half-lives. Decreased hepatic removal of local anesthetics should also be anticipated in patients with reduced hepatic blood flow.
Basic Administration of Local Anesthetics
Topical (Surface)- skin and mucosa
Infiltration – direct injection intradermal or sc (eg. knee)
for: joint pain
Peripheral Nerve Block – injected close to nerve trunks (eg. brachial)
for: surgical procedures, severe, chronic pain (eg. cancer)
Spinal – injection into subarachnoid space near spinal cord
for: surgery
Epidural – injection just above dura surrounding spinal cord, near spinal nerve roots
for: OB, surgery
Factors Affecting the Pharmacokinetics of Local Anesthetics
Lipid solubility (hydrophobicity)
• All local anesthetics have weak bases. Increasing the lipid solubility leads to faster nerve penetration, block sodium channels, and speed up the onset of action.
• The more tightly local anesthetics bind its target, the longer the duration of onset action.
• Local anesthetics have two forms, ionized and nonionized. The nonionized form can cross the membranes, but the ionized form binds more strongly to sodium channels.
pH influence
• Usually at range 7.6 – 8.9
• Decrease in pH shifts equilibrium toward the ionized form, delaying the onset action.
• Lower pH, solution more acidic, gives slower onset of action
Vasodilation
• Vasoconstrictor is a substance used to keep the anesthetic solution in place at a longer period and prolongs the action of the drug
• Vasoconstrictor delays the absorption which slows down the absorption into the bloodstream
• Lower vasodilator activity of a local anesthetic leads to a slower absorption and longer duration of action
• Vasoconstrictor used is usually epinephrine
Adverse effects (toxicity)
There are some adverse effects of LA on our different bodily mechanisms, such as-
On CNS
_ Euphoria (cocaine)
- sleepiness
- visual and auditory disturbance
- Nystagmus, shivering convulsions
- CNS depression leading to respiratory depression
On PNS
- Neurotoxicity (sensory and motor deficits)
On CVS
_ myocardial depression
- vasodilatation, hypotension
- Qunidine like action (antiarrythmic)
- hypertension (cocaine)
On blood
- Methaemoglobinaemia
Allergic
- rash
- asthma
- Anaphylactic Shock
Others
- Myasthenia gravis
- vomiting
- Mydriasis
- Pyrexia
- hallucination
- addiction etc.
General Anesthetics
General anesthetics are the agents that produce reversible unconsciousness with loss of pain and reflexes along with adequate muscle relaxation. GA do not act by any receptors because they are all nonspecific drugs and since they have got no antagonist.
Effects
The effects GAs include are-
Analgesia
Amnesia
Loss of consciousness
Inhibition of sensory and autonomic reflexes
Skeletal muscle relaxation
Types of GA
GA agents fall into following two types-
Inhalation agents or volatile anesthetics
Intravenous agents or non-volatile anesthetics
Inhalation Anesthetics
The anesthetics which enter and leave the body through the lungs are inhalation anesthetics. Anesthetics can easily cross the alveolar membrane as they are all lipid soluble molecules.
Intravenous Anesthetics
These anesthetics are administered intravenously. These produce anesthesia without excitement and produce unconsciousness in about 20 seconds.
Pre-anesthetic Medication
In addition to GA agents there are considerable numbers of drugs that are used before and during surgical operation for sedation and analgesia. This use of drugs is called pre-anesthetic medication, and the drugs are called adjuvant anesthetics.
Drugs used in Pre-anesthetic Medication
1. For sedation and amnesia
- Diazepam, Phenobarbitone
2. For suppressing respiratory and salivary secretion (anticholinergic agents) and reflex excitability
- Atropine sulphate
3. To prevent bronchospasm, hypotension and vomiting (antiemetics)
- Promethazine hydrochloride, Chlorpheneramine maleate
4. To relief pain (opioid analgesics) and production of sedation
- Inj. Pethidine, Morphine
5. Barbiturates (as sedative, hypnotic agents)
Balanced Anesthesia
Balanced anesthesia is one in which each drug being selected for one specific purpose and the whole combination providing the most effective and comfortable but the least hazardous anesthetic experience for the patient and the best operating condition for the surgeon.
An example is given below-
1. Pre-anesthetic medication with a basal anesthetic (barbiturate), a narcotic-analgesic (pethidine), and a vagal inhibitor (atropine)
2. Induction by short acting barbiturates (thiopentone, methohexitone)
3. Maintenance of unconsciousness, analgesia and reflex inhibition by an anesthetic gas (N2O with O2 and halothane) and an intravenous narcotic analgesic (pethidine)
4. Maintenance of muscle relaxation by neuromuscular blocking agents.
Patient Factors in Selection of Anesthesia
The selection of anesthesia administered preoperatively depends on two factors-
1. Status of organ system
2. Concomitant use of drugs
Status of organ system
Liver and kidney
Liver and kidneys help in distribution and clearance of various anesthetic agents , and also the target organs of toxic effects. The repeated administration of anesthetic agents cause rapid release of chloride, fluoride, bromide which affect the organs.
Respiratory system
The RS is affected when inhalation anesthetics are administered. It becomes complicated for a patient of asthma or perfusion abnormalities. Because, it depress the RS; additionally, they are bronchodilators.
CVS
Ischemic injury of tissues reduces perfusion pressure because of the hypotensive effect of the most anesthetics. If a hypotensive condition necessitates treatment during operation, a vasoactive agent is administered considering the possibility of sensitization of heart to the arrhythmogenic effects.
Nervous system
Various neurologic disorders, i.e., epilepsy or myasthenia gravis demand the right selection of an anesthetic, even having sensitivity to halogenated hydrocarbon-induced malignant hyperthermia, too.
Pregnancy
Selecting an anesthetic is very sensitive for a pregnant woman. There is a report that transient use of nitrous oxide can cause aplastic anemia in the unborn child. Oral clefts have occurred in the fetuses of women who have received benzodiazepines. Diazepam should not be used routinely during labor, because it results in temporary hypotonia and altered thermoregulation in the newborn.
Concomitant use of drug
- Multiple adjunct agents
Commonly surgical patients receive one or more preanesthetic medications , such as – antiemetic agents, anticholinergic agents, antiallergic agents, analgesics etc. to facilitate smooth induction of anesthesia. Such coadministration can also enhance undesirable anesthetic effects (i.e., hypoventilation), and it may produce negative effects that are not observed when each drug is given individually.
- Concomitant use of additional non-anesthetic drugs
Surgical patients may be chronically exposed to agents for the treatment of the underlying disease as well as to drugs of abuse that alter the response to anesthetics.
Stages of Anesthesia
Surgical anesthesia classically divided in four well-defined stages when a slowly acting anesthetic (such as ether) is used. The stages are-
Stage 1- Analgesia
Analgesia is partial until stage 2 is about to be reached. Consciousness and sense of touch are retained and sense of hearing is increased.
Stage 2-Excietment
The patient experiences delirium and possibly violent, combative behavior.
There is a rise or irregularity in blood pressure.
The respiratory rate may increase.
To avoid this stage, a short-acting barbiturate (such as thiopental) is given intravenously before inhalation anesthesia is administered.
Stage 3- Surgical Anesthesia
Regular respiration and relaxation of the skeletal muscles occur in this stage.
Eye reflexes decrease progressively, until the eye movements cease and the pupil is fixed.
Surgery may proceed during this stage.
Stage 4- Medullary Paralysis
Severe depression of the respiratory and vasomotor centers occur during this stage.
All reflexes activities lost and pupil widely dilated.
Death can rapidly ensue unless measures are taken to maintain circulation and respiration.
Induction, Maintenance and Recovery from Anesthesia
Anesthesia can be divided into three major stages-
Induction
It is defined as the period of time from the onset of administration of the anesthetic to the development of effective surgical anesthesia in the patient. During induction, it is essential to avoid the dangerous excitatory phase (delirium). GA is normally induced with an I/v anesthetic like thiopental, which produces unconsciousness within 25 seconds after injection. Then additional proper anesthetic combination can be administered to get desired surgical stage of anesthesia (stage iii). For children, without intravenous access, nonpungent agents, such as halothane or sevoflurane, are used to induce GA. This is termed inhalation induction.
Maintenance
It is the period during which the patient is surgically anesthesized. Then the anesthesiologist monitors the patient during the whole period of surgical procedure to balance the amount of drug inhaled and/or infused with the depth of anesthesia. Anesthesia is usually maintained by the administration of volatile anesthetics, because these agents offer good minute-to-minute control over the depth of anesthesia. Opioid, such as fentanyl, are often used for pain along with inhalation agents.
Recovery
Postoperatively, the anesthesiologist withdraws the anesthetic mixture and monitors the patient carefully until he/she is fully recovered from unconsciousness. Patients are observed for the delayed toxic reactions, such as hepatotoxicity caused by halogenated hydrocarbons.
Depth of Anesthesia
It has been divided into four sequential stages. Each stage characterized by increased CNS depression, which is caused by accumulation of the anesthetic drug in the brain. The stages are-
1. Stage 1- Analgesia
2. Stage 2-Excietment
3. Stage 3- Surgical Anesthesia
4. Stage 4- Medullary Paralysis
It is an agent that causes partial or complete loss of sensation, with or without loss of consciousness, i.e., anesthesia.
It is a partial or complete loss of sensation, with or without loss of consciousness, as a result of disease, injury, or administration of an anesthetic agent, usually by injection or inhalation.
Generally there are two types of anesthetics. Such as-
- Local anesthetics
- General anesthetics
Chemistry of LA
- LA is generally used when loss of consciousness is neither necessary nor desirable and also as an adjunct to major surgery to avoid high dose of GA.
- It can be used for major surgery, with sedation, though many patients prefer unconsciousness.
- It can also be used topically for short periods to give relief from local pain or itching (but skin allergy is common).
Pharmacokinetics
- Dosage
- Site of injection
- Drug-tissue binding
- Presence of vasoconstricting substances
- Physicochemicals and pharmacologic properties of drug
March 30, 2010
A Patient with Depression
Case: A 46-years-old gentleman presented in the outpatients clinic with a 6 months history of generalised un wellbeing, weakness and lethargy, loss of weight, poor appetite, insomnia and extreme tiredness. He lost his wife 2 years back and did not have any children and also suffered from diabetes mellitus. He has consulted many physicians and underwent a battery of tests without any conclusive diagnosis. His diabetic status was well under control with oral hypoglycaemic drugs. Routine biochemical parameters (LFT, TFT, auto immune screening, cortisol, electrolytes, CRP) haematological parameters (Hb, TC, DC, platelet ESR), virological screening (Hepatitis B, Hepatitis C, HIV) were all satisfactory. X-ray and ECG were normal. CT brain was normal.
Diagnosis : Depressive illness
Discussion :
Depression is a major problem in primary care. At least 30% of patients attending clinic, has major depression. However, majority of them are unrecognised or inappropriately treated leading to loss of Productivity, functional decline and increased mortality.
Diagonising depression can be difficult as patients rarely present with symptoms that fit neatly into diagnostic taxonomies.
Patients in medical settings usually present with physical social and psychological problems along with somatic symptoms and the consulting doctor has to find out depressive illness from the above mentioned presenting problems.
Consulting styles also influence whether depression is recognised. It has been found that doctors who ask open question initially (like enquiring about sleep pattern, mood etc.), give more time, are more empathic, make more eye contact and interrupt less are more likely to detect depression.
When to consider depression in the differential diagnosis :
The patients usually complain of :
depressed mood, diminished interest or pleasure in all activities, unintentional weight loss or weight gain, insomnia or hypersomnia nearly every day, early morning waking or interrupted sleep, feeling of guilt, worthlessness, loss of energy, lack of concentration and in severe cases thoughts of death and suicide.
In addition, there are certain co-morbid medical condition, where depression is common and clinician should positively look for evidence of depression if suggestive symptoms are present in such cases - these conditions are :
n cancer
n Parkinson disease
n cerebrovascular accidents
n old MI, chronic pain
n diabetes mellitus
n old age
Depression is a major problem in primary care. At least 30% of patients attending clinic, has major depression. However, majority of them are unrecognised or inappropriately treated leading to loss of Productivity, functional decline and increased mortality.
Diagonising depression can be difficult as patients rarely present with symptoms that fit neatly into diagnostic taxonomies.
Patients in medical settings usually present with physical social and psychological problems along with somatic symptoms and the consulting doctor has to find out depressive illness from the above mentioned presenting problems.
Consulting styles also influence whether depression is recognised. It has been found that doctors who ask open question initially (like enquiring about sleep pattern, mood etc.), give more time, are more empathic, make more eye contact and interrupt less are more likely to detect depression.
When to consider depression in the differential diagnosis :
The patients usually complain of :
depressed mood, diminished interest or pleasure in all activities, unintentional weight loss or weight gain, insomnia or hypersomnia nearly every day, early morning waking or interrupted sleep, feeling of guilt, worthlessness, loss of energy, lack of concentration and in severe cases thoughts of death and suicide.
In addition, there are certain co-morbid medical condition, where depression is common and clinician should positively look for evidence of depression if suggestive symptoms are present in such cases - these conditions are :
n cancer
n Parkinson disease
n cerebrovascular accidents
n old MI, chronic pain
n diabetes mellitus
n old age
Anxiety disorder like phobia, panic disorder, obsessive compulsive state, generalised severe anxiety are quite common presentation in general practice. These patients are also more vulnerable to depression and the clinician should be aware of this. Somatization is also an integral part of the presentation in depression. As the psychiatric definition of depression does not take into account somatic presentation, an astute clinician should be aware of this fact and try to find out whether depression is underlying cause for the somatization.
Treatment :
Majority of the depressive illness can be treated at primary care level (if the clinician is willing). However some alarm signs should prompt the physicians for a prompt psychiatric referral.
Majority of the depressive illness can be treated at primary care level (if the clinician is willing). However some alarm signs should prompt the physicians for a prompt psychiatric referral.
Drug Therapy :
If used appropriately, drugs are successful in more than 70% of cases. However, selection of medication is important.
It was recognised in the 50's that the depression was mediated mainly the deficiency of monoamine neurotransmitter like serotonin, nor-adrenaline and dopamine."
The major pharmacological manoeuvre involves increasing the level of these monoamines in the brain by either inhibiting the enzyme monoamine-oxidase, blockage of auto receptors that generate negative feed back on the release of neurotransmitters and blockage of the reuptake of the transmitter back into the nerve cell.
If used appropriately, drugs are successful in more than 70% of cases. However, selection of medication is important.
It was recognised in the 50's that the depression was mediated mainly the deficiency of monoamine neurotransmitter like serotonin, nor-adrenaline and dopamine."
The major pharmacological manoeuvre involves increasing the level of these monoamines in the brain by either inhibiting the enzyme monoamine-oxidase, blockage of auto receptors that generate negative feed back on the release of neurotransmitters and blockage of the reuptake of the transmitter back into the nerve cell.
Monoamine oxidase inhibitors :
The initial drugs were mono-amineoxidase inhibitors. However because of their side effect profile and drug interactions they are not used at least at the primary care level.
The initial drugs were mono-amineoxidase inhibitors. However because of their side effect profile and drug interactions they are not used at least at the primary care level.
Nonselective serotonin and noradrenaline reuptake inhibitors:
The second group of drugs to come were tricyclic anti depressant (non selective serotonin and noradrenaline uptake inhibitors) which are being still used very commonly in the clinical practice. The problem with them is the non-selective nature of their recepter blockage and the resultant side effect profile. Commonly used drugs are :
1. Amitriptyline- Special indication if there is associated insomnia, chronic pain, migraine, post herpetic neuralgia.
2. Imipramine - Enuresisis, insomnia, panic disorder, post traumatic stress disorder, obsessive compulsive state.
These drugs have adverse effect on cardiac function and should be avoided in patients with cardiac problems. They have prominent anticholinergic side effects.
The second group of drugs to come were tricyclic anti depressant (non selective serotonin and noradrenaline uptake inhibitors) which are being still used very commonly in the clinical practice. The problem with them is the non-selective nature of their recepter blockage and the resultant side effect profile. Commonly used drugs are :
1. Amitriptyline- Special indication if there is associated insomnia, chronic pain, migraine, post herpetic neuralgia.
2. Imipramine - Enuresisis, insomnia, panic disorder, post traumatic stress disorder, obsessive compulsive state.
These drugs have adverse effect on cardiac function and should be avoided in patients with cardiac problems. They have prominent anticholinergic side effects.
Selective serotonin and noradrenalin uptake inhibitors:
Venlafaxine :
This is a comparatively new class of drug - devoid of cardiac side effects and has quick onset of action. This is also emerging as an effective treatment for anxiety disorder (so commonly associated with depression).
Venlafaxine :
This is a comparatively new class of drug - devoid of cardiac side effects and has quick onset of action. This is also emerging as an effective treatment for anxiety disorder (so commonly associated with depression).
Special indications :
Anxiety, neuropathic pain, obsessive compulsive disorder. It can cause sedation and anticholinergic side effects are less common.
Anxiety, neuropathic pain, obsessive compulsive disorder. It can cause sedation and anticholinergic side effects are less common.
Selective serotonin re-uptake inhibitors : (SSRI)
1. Citalopram - particularly helpful in post CVA depression, diabetic neuropathy panic disorder, obsessive compulsive disorders.
2. Escitalopram - It is a new drug (isomer of citalopram) and has a very quick onset of action (compared to citalopram).
3. Fluoxetine
4. Paroxetine
5. Sertraline
They usually do not cause sedation. These group of drugs can both cause weight loss and weight gain. These are cardiac friendly drugs and can be safely prescribed in cardiac patients.
Serotonin antagonists:
Mirtazapine
This is particularly helpful in anxiety and insomnia. It can also cause weight gain. It has got sedative potential.
1. Citalopram - particularly helpful in post CVA depression, diabetic neuropathy panic disorder, obsessive compulsive disorders.
2. Escitalopram - It is a new drug (isomer of citalopram) and has a very quick onset of action (compared to citalopram).
3. Fluoxetine
4. Paroxetine
5. Sertraline
They usually do not cause sedation. These group of drugs can both cause weight loss and weight gain. These are cardiac friendly drugs and can be safely prescribed in cardiac patients.
Serotonin antagonists:
Mirtazapine
This is particularly helpful in anxiety and insomnia. It can also cause weight gain. It has got sedative potential.
Noradrenaline and dopamine reuptake inhibitors :
Bupropion - Particularly helpful in smoking cessation and post traumatic stress disorder.
Serotonin antagonist and re-uptake inhibitors :
Nefazadone - } Panic disorder
} post traumatic stress disorder
Trazodone -. } Insomnia
Bupropion - Particularly helpful in smoking cessation and post traumatic stress disorder.
Serotonin antagonist and re-uptake inhibitors :
Nefazadone - } Panic disorder
} post traumatic stress disorder
Trazodone -. } Insomnia
Few points to remember
n Anti depressants will be effective in approximately 70% of case.
n It may take 4-6 weeks before it may be fully effective.
n If within 6 weeks therapy there is no appreciable change, one drug can be substituted for another.
(Failure of one drug does not necessarily mean that the ot her drug of the same group may not be effective).
n Wash out period is not necessary while changing from SSRI to another drug like venlafaxine or mirtazapine. (However abrupt withdrawal of SSRI may cause symptoms).
n SSRI should not be coprescribed with sibutramine (appetite suppressants).
n All anti-depressants should be used with caution in hepatic disorders.
n If no appreciable changes is noted with the 2nd drug - psychiatric opinion will be needed. In anxiety disorders, although benzodiazepines are the most effective. drugs, they should only be used for a very brief period because of dependance potential. One of the antidepressants with prominent anti anxiety effect should therefore be chosen for long term treatment of primary anxiety disorders.
n Anti depressants will be effective in approximately 70% of case.
n It may take 4-6 weeks before it may be fully effective.
n If within 6 weeks therapy there is no appreciable change, one drug can be substituted for another.
(Failure of one drug does not necessarily mean that the ot her drug of the same group may not be effective).
n Wash out period is not necessary while changing from SSRI to another drug like venlafaxine or mirtazapine. (However abrupt withdrawal of SSRI may cause symptoms).
n SSRI should not be coprescribed with sibutramine (appetite suppressants).
n All anti-depressants should be used with caution in hepatic disorders.
n If no appreciable changes is noted with the 2nd drug - psychiatric opinion will be needed. In anxiety disorders, although benzodiazepines are the most effective. drugs, they should only be used for a very brief period because of dependance potential. One of the antidepressants with prominent anti anxiety effect should therefore be chosen for long term treatment of primary anxiety disorders.
When to refer to a Psychiatrist :
If the patient needs specific therapy like prolonged counselling, conditioned behaviour therapy, opinion of a psychiatrist should be taken -
1. If the patient is not responding to the use of two successive anti depressant over a period of 2-3 months.
2. If the patients have evidence of psychosis like hearing voice or visual hallucination, have manic symptoms or judged to have high risk for suicide.
If the patient needs specific therapy like prolonged counselling, conditioned behaviour therapy, opinion of a psychiatrist should be taken -
1. If the patient is not responding to the use of two successive anti depressant over a period of 2-3 months.
2. If the patients have evidence of psychosis like hearing voice or visual hallucination, have manic symptoms or judged to have high risk for suicide.
Once the treatment has been successfully instituted, it should be carried out for atleast 6 months. If the patient has a high risk of relapse (i.e., past history of recurrent depression), the treatment should be continued for at least 2 years.
Key Points:
n Depression is a common presentation in clinical practice.
n A positive approach and leading question from the clinician will help in diagonising depression.
n Most of the illnesses may be treated at primary care level.
n Choosing the right drug will depend on the clinical circumstances and the presence of other associated conditions like anxiety disorders, presence of cardiac problem and sleep disturbance.
n In high risk patients, the patients should be referred to psychiatrists. n
n Depression is a common presentation in clinical practice.
n A positive approach and leading question from the clinician will help in diagonising depression.
n Most of the illnesses may be treated at primary care level.
n Choosing the right drug will depend on the clinical circumstances and the presence of other associated conditions like anxiety disorders, presence of cardiac problem and sleep disturbance.
n In high risk patients, the patients should be referred to psychiatrists. n
Source: “Experience with Evidence in Clinical Practice,” Dr. Subrata Maitra, Soma Book Agency.
Courtesy: Advocate Monzurur Rahman Ruskin.
Courtesy: Advocate Monzurur Rahman Ruskin.
February 26, 2010
Dental Products
The agents, which are used in the prevention of caries, polishing agents and desensitizing agents, called dental products.
A wide variety of inorganic compounds used in dentistry are of interest to pharmacists. These include-
1. Polishing
2. Cleaning
3. Anticaries agents
Anticaries agents (Fluorides)
Products of fluorides are-
1. Fluoridated water
2. Fluoride drops
3. Topical fluoride application to teeth
4. Fluoride-containing vitamins
5. Fluoride dentifrices
Problems associated with antibiotic-containing dentifrices
1. Sensitization of a significant portion of the population to the antibiotic and
2. Development of antibiotic-resistant microorganisms. Chemical composition of dentifrice-
CH3¾NCH2CO2Na
|
C(CH2)10CH3
||
O
Sodium N-lauroyl sarcosinate
The mechanism by which fluoride inhibits caries formation
The mechanism by which fluoride inhibits caries formation is still to be completely elucidated. There are two current hypotheses:
1. Decreased acid solubility of enamel and
2. Bacterial inhibition
Decreased acid solubility of enamel
We came to know that fluoride decreases the solubility of enamel in acid. This lowering of solubility is more pronounced in enamel already attacked by caries. Caries lesions cause the enamel to become more permeable to fluoride which, along with the lower pH found in a caries lesion, favors fluoride uptake by hydroxyapatite. Enamel already showing carious changes may be 20% less soluble than intact enamel in the same teeth. Even if one assumes that fluorapatite is less soluble than hydroxyl apatite, the outer enamel will have at the most only one hydroxyl in 50 replaced by fluoride, which would not affect the overall decrease in observed solubility. Other mechanisms that have been postulated as to how fluoride might decrease enamel solubility include:
(1) Reduction of the number of defects in apatite crystals; and
(2) Competition with carbonate during apatite formation
Bacterial inhibition
This hypothesis is based on the enzyme inhibitory properties of fluoride. This in itself is difficult to justify, as a fluoride concentration of 10 ppm is needed for any significant inhibition of many of the oral bacteria. Though plaque fluoride is bound fluoride, it still seems to reduce acid production in the plaque. In contrast, topically applied sodium fluoride loses its ability to inhibit acidogenesis within one week of application indicating that fluoride reduces the incidence of caries by some other mechanism. While it might appear that the fluoridated plaque is beneficial. Its presence still promotes inflammation of the gingivae (gums), making its removal desirable.
Mechanisms of fluoride decrease enamel solubility include:
(1) Reduction of the number of defects in apatite crystals; and
(2) Competition with carbonate during apatite formation
Adjusted allowance of fluoride
| Water fluoride (ppm) | Sodium fluoride (mg per day) | Provide fluoride ion (mg per day) |
| 0.0 | 2.2 | 1.0 |
| 0.2 | 1.8 | 0.8 |
| 0.4 | 1.3 | 0.6 |
| 0.6 | 0.9 | 0.4 |
Stability of stannous fluoride solution
1. The stability is increased with increasing stannous fluoride concentration.
2. The rate of turbidity formation is temperature-dependent.
3. The loss of stannous cation is both pH-dependent and dependent upon the buffer or complexing agent used.
Official products
Sodium fluoride
Sodium fluoride (NaF) U. S. P. is a compound having molecular weight 41.99.
Properties
1. It is a white odorless powder
2. It is soluble in water and insoluble in alcohol.
Application
1.5 to 3 ppm in drinking water; topically, as a 2% solution to the teeth
Usual dose: 2.2 mg once a day
Stannous Fluoride (SnF3)
It is a topical product having mol. wt. 156.69.
Properties
1. It is a white, crystalline powder.
2. It has a bitter, salty taste.
3. It melts at about 2130 C.
4. It is freely soluble in water and is practically insoluble in alcohol, ether and chloroform.
Use: It has topical use only.
Phosphate
Dentifrices
1. Anticaries agents
2. Polishing agents
3. Thickening agents
4. Surfactants
5. Humectants
Composition of Crest, a stannous fluoride tooth paste
| Chemical Constituents | Amount (%) |
| Stannous fluoride | 0.4 |
| Stannous pyrophosphate | 1 |
| Calcium pyrophosphate | 39 |
| Glycerin | 10 |
| Sorbitol (70% solution) | 20 |
| Water | 29.6 |
| Miscellaneous formulating agents | |
Composition of Colgate, an MFP fluoride tooth paste
| Chemical Constituents | Amount (%) |
| Sodium monofluorophosphate (MFP) | 0.76 |
| Insoluble sodium metaphosphate | 41.85 |
| Anhydrous dicalcium phosphate (CaHPO4) | 5 |
| Sorbitol | 11.9 |
| Glycerol | 9.9 |
| Sodium N-lauroyl sarcosinate | 2 |
| Water | 24.4 |
| Miscellaneous formulating agents | 4.2 |
Test of degree of abrasiveness
In vitro test
1. Brushing machines that evaluated wear on a tooth surface
2. Loss of tooth surface as measured by radiotracer techniques
3. Enamel-polishing capability as measured by a reflectometer
In vivo test
1. Measuring the degree of stain buildup or removal over a period of time
2. The degree of abrasiveness on acrylic surfaces of veneer crowns
Cleaning agents
Some common cleaning agents are as follows.
1. Insoluble Sodium metaphosphate (NaPO3)
2. Anhydrous and hydrous calcium monohydrogen phosphate (dicalcium phosphate; CaHPO4 and CaHPO4.2H2O)
3. Calcium pyrophosphate (Ca2P2O7)
4. Calcium carbonate (CaCO3)
5. Pumice
Cosmetic dentifrices
| Brand | Composition | Abrasivity |
| Close Up | Silicas of controlled particle size | Moderate |
| Excitement | CaHPO2. 2H2O | Low |
| Macleans | CaHPO4. 2H2O | Moderate |
| Pearl Drops Tooth Polish | Hydrated AlPO4 and CaHPO4. 2H2O | Moderate |
| Plus White | CaHPO4 and CaHPO4. 2H2O | Moderate to high |
| Plus White Plus | CaHPO4 and CaHPO4. 2H2O | Moderate to high |
| Ultra Brite | CaHPO4 and CaHPO4. 2H2O | Moderate |
| Vote | Silica | Moderate to high |
Official product
Pumice
Pumice is a substance of volcanic origin, consisting chiefly of complex silicates of aluminum, potassium and sodium.
Properties
1. It occurs as very light, hard, rough, porous, grayish masses, or as a gritty, grayish powder.
2. It is odorless and tasteless, and stable in air.
3. It is practically insoluble in water, and is not attacked by acids.
Desensitizing agents
1. Sensodyne (contains strontium chloride)
2. Thermodent (contains formalin)
3. Ammoniacal Silver Nitrate Solution
Official products
Zinc Chloride
Zinc Chloride U.S.P. is an astringent and dentin desensitizer. It is topical to the teeth as a 10% solution; to the skin and mucous membranes, as a 0.5% to 2% solution.
Properties
1. It is a white or practically white, odorless, crystalline powder or white or practically white crystalline granules.
2. It may also have porcelain-like masses or be molded into cylinders.
3. A 1 in 10 solution is acid to litmus.
4. It is very soluble in water and freely soluble in alcohol and glycerin.
5. Its solution in water or in alcohol is usually slightly turbid, but it is disappeared after adding a small quantity of hydrochloric acid.
Zinc-Eugenol Cement
Zinc-Eugenol Cement N.F. consists of some powders (zinc acetate, zinc stearate, zinc oxide, rosin); and liquids (Eugenol and cottonseed oil).
Property
To use the cement, a thick paste is prepared immediately before use by mixing up ten parts of the powder with one part of the liquid.
Use
It is widely used by dentists for their sedative effect on pulpal pain, particularly when restoring teeth with deep carious lesions.
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