CLINICAL PHARMACOLOGY & PHARMACOTHERAPEUTICS

ByG.Sudheer Babu M.pharm

RHEUMATOID ARTHRITIS

CONTENTS1. Introduction

2. Definition 3. Epidemiology 4. Etiology 5. Risk factors 6. Symptoms 7. Diagnosis8. Pathophysiology9. Treatment10. Conclusion

introduction

BONE STRUCTURE

1. It consists of a diaphysis or shaft and two epiphysis or extremities.

2. The diaphysis is composed of central medullary canal containing yellow bone marrow.

3. Periosteum is a vascular membrane which covers the bone & it has two layers

4. The outer layer is tough and fibrous and the inner layer consists of osteoblasts and osteoclasts.

5.The epiphysis consists of cancellous or spongy bone made of red bone marrow.

6. Epiphysis also consists of articular (hyaline) cartilage.

MICROSCOPIC STRUCTURE OF BONE

Large number of tube shaped units – OSTEONS, containing a central canal.(cc)

The central canal consists of BV, nerves & each CC is linked with other CC through PERFORATING CANAL

Cylindrical plates arranged around each central canal – LAMELLAE

Between the lamellae string like cavities called LACUNAE are present containing an osteocyte

The lacunae are interconnected by CANALICULI which allows the circulation interstitial fluid

Functions of bones

1. Haemopoiesis, the production of blood cells.

2. Forming the boundaries of the cranial, thoracic and pelvic cavities, protecting the organs they contain.

3. Giving attachment to the muscles and tendons.

4. Mineral storage, especially cal. Phosphate

5. Allowing movements of the body.

6. Giving particular shape to the body.

TYPES OF BONES

Bones are classified as: 1. Long bones: consist of a shaft and two extremitiese.g. femur, tibia and fibula.

2. Short bones: carpals (wrist)

3.Irregular bones: vertebrae & some skull bones.

4. Flat bones: sternum, ribs & most skull bones.

5. Sesamoid bones: patella (knee cap)

Stages of development of a bone

Synovial joint

1. It is characterised by the presence of capsule between the articulating bones and the capsule is lubricated with synovial fluid.

2. Synovial membrane forms the lining of capsule.

3. Synovial fluid is a thick sticky fluid secreted by synovial membrane into the synovial cavity.

1. it contains phagocytes which removes microbes and cellular debris.

2. acts as lubricant.

3. maintains joint stability.

4. Synovial fluid act as cushion by preventing the friction between the bones.

RHEUMATOID ARTHRITIS1. This is a chronic progressive inflammatory autoimmune disease mainly affecting synovial joints.2. It is more common in females than in males.3. It is a systemic disorder where it affects not only joints but also other sites including the heart, blood vessels and skin.4. Immune complexes composed of IgM activate and release cytokines (mainly TNF alpha and IL1)5. These TNF & IL1 are chemotactic to neutrophils and secrete lysosomal enzymes which damage cartilage and erode bone, while the PG’s produced in the process cause vasodilation and causes pain.

Other variant forms of RA:1. FELTY’S SYNDROME:

It is a combination of rheumatoid arthritis along with splenomegaly & consequent haematologic derangements.

2. JUVENILE RA:

occurs below 16 years of age

characterised by acute onset of fever & pain at the site of knees & ankles.

OA VS RA

Osteoarthritis Rheumatoid ArthritisType of disease degenerative inflammatory and autoimmune

Tissue affected articular cartilage synovial membrane

Age of onset late middle age any age, mainly 30 to 55 years

occasionally children

Joints affected weight bearing areas small joints e.g. hands, feet

e.g. hip, knee; often often many joints

only a single joint

EPIDEMIOLOGY

1. The prevalence rate is 1%, women are affected three to five times as often as men.

2. It is 4 times more common in smokers than non smokers.

3. The incidence of rheumatoid arthritis is 3 cases per 10,000 population per annum.

ETIOLOGY

1. The exact causes of rheumatoid arthritis are unknown.

2. Abnormal autoimmune response.

3. Genetic susceptibility.

4. Environmental factors.

RISK FACTORS

According to National Rheumatoid Arthritis Society (NRAS), RA affects about 1.3 million Americans.

AGE : RA can occur at any age from childhood to old age, onset usually begins between the ages of 30-50.

GENDER : Women are more likely to develop RA than men.

SMOKING : Heavy long-term smoking is a very strong risk factor for RA.

Symptoms1. Morning stiffness

2. Joint pain

3. Fatigue

4. Low grade fever

5. Loss of appetite

6. Presence of rheumatoid nodules

7. Myalgia and synovitis

DIAGNOSIS

DIAGNOSIS

1. Anti-CCP Antibody Test :

The presence of antibodies to cyclic citrullinated peptides (CCP) can identify RA years before symptoms develop.

2. C-Reactive Protein :

High levels of C-reactive protein (CRP) are also indicators of active inflammation.

3. Rheumatoid Factor :

In RA, antibodies that collect (anti IgG antibodies) in the synovium of the joint are known as Rheumatoid factor. In about 80% of cases of RA, blood tests reveal rheumatoid factor.

PATHOGENESIS OF RHEUMATOID ARTHRITIS

Genetic susceptibility

(MHC Class –II) Joint deformities

Antigenic stimulation

CD4+ T- cells

Destruction of bone, cartilage

Cytokines fibrosis, ankylosis

(TNF-α, INF-γ, IL-1)

activate activate activate Inflammatory damage to synovium,

small vessels, collagen

B-cells Endothelial Macrophages

cells

anti-IgG release of cytokines, Formation of immune complex,

antibody adhesion proteases inflammatory cells, pannus

molecules

PATHOGENESIS OF RHEUMATOID ARTHRITIS

1. due to antigenic exposure ( e.g. infectious agent ) CD4 T-cells , MHC class II ( HLA-DR) cells are activated.

2. now the cytokines are activated , which results in the formation of TNF-α, interferon γ, IL-1 & IL-6.

3. these cytokines activate endothelial cells, B lymphocytes and macrophages.

4. activation of B-cells releases IgM antibody against IgG (i.e., anti- IgG); this molecule is termed as Rheumatoid Factor (RF)

5. IgG & IgM immune complexes trigger inflammatory damage to the synovium, small vessels and collagen.

6. endothelial cells stimulate adhesion molecules which stimulate the inflammatory cells.

7. activation of macrophages releases proteases which causes damage to the joint tissues leading to Pannus formation., which causes destruction of bone & cartilage

PANNUS FORMATION

Activation of macrophages releases proteases , collagenase, acid hydrolases, which causes degradation of cartilage by the formation of Pannus

The restriction in the movements of synovial joints is due to the formation of fibrous tissue a condition known as Ankylosis

treatment

CLASSIFICATION OF ANTIRHEUMATOID DRUGS

A. Disease modifying antirheumatic drugs (DMARD’s):

1. Immunosuppressants: methotrexate, azathioprine, cyclosporine

2. sulfasalazine

3. chloroquine

4. Leflunomide

5. Gold compounds

6. d-penicillamine

B. Biologic response modifier’s (BRM’S) :

1. TNFα inhibitors : Etanercept, Infliximab, Adalimumab

2. IL-1 antagonist : Anakinra

c. Adjuvant drugs :

Prednisolone & other corticosteroids.

DMARD’s

Methotrexate: (Mtx) immunosuppressant

Mechanism of action:

Mtx in RA mainly acts by inhibiting the enzyme Aminoimidazole carboxamide ribonucleotide transformylase (AICAR) & thymidylate synthetase enzyme, which results in the inhibition of cytokine production.

Pharmacokinetics: Oral absorption : 70% Half life : 6-9 hours Excretion : urine (70%) & bile (30%)

Adverse effects: nausea and mucosal ulcers. In some patients liver damage leading to cirrhosis.

Azathioprine : (purine antagonist)

Mechanism of action:

Azathioprine

Thiopurine methyl transferase (TPMT)

6- thioguanine ( active metabolite)

It acts by suppressing B-cell and T-cell function, immunoglobulin production & IL-2 secretion.

Adverse effects: Bone marrow depression G.I disturbances Acute allergic reactions

Cyclosporine: Sulfasalazine:Mechanism of action: Mechanism of action:

It inhibits IL-1 & IL-2 production. It is metabolised in the body to sulfapyridine

& 5-Aminosalicylic acid.

Pharmacokinetics: sulfapyridine is the active moiety which Bioavailability : 20-30% suppress the superoxide radicals and Metabolism : CYP3 enzymes cytokine production.

Adverse effects: Adverse effects: Hypertension Reversible infertility occurs in men Hyperkalemia nausea, vomiting, headache & rashes Hirsutism

Leflunomide:Mechanism of action Leflunomide

body

A77-1726 (act. Metabolite)

This metabolite inhibits the enzyme Dihydro orotate dehydrogenase & pyrimidine synthesis.

hence there is no T-cell proliferation

Pharmacokinetics: adverse effects:completely absorbed orally loss of hair

Half life is 19 days leucopenia

GOLD:Mechanism of action:

It reduces the chemotaxis, phagocytosis , macrophage & lysosomal activity.

It prevents the joint destruction, may induce the healing of bony erosions.

Gold is heavily bound to plasma & tissue proteins ; it stays in the body for years.

It is rarely used now because it causes

kidney & liver damage,

bone marrow depression &

hypotension

d- penicillamine:

It is copper chelating agent with gold like action. It is having adverse effects similar to gold, hence its use is obsolete now.

Corticosteroids:

They have immunosuppressant and anti inflammatory activity. They are often administered with NSAIDS to have better action. Long term use of corticosteroids causes serious adverse effects, hence low doses

(5-10mg prednisolone) are used.

Biological response modifiers (BRM):

TNFα inhibitors: ( etanercept, infliximab & adalimumab) Mainly suppress macrophage & T-cell function. Inflammation in the joints gradually decreases. New bone erosions are slowed. Quick response than DMARDS. BRM are often combined with methotrexate for better action. All are very expensive drugs.

IL-1 antagonist:

Anakinra: it is less effective than TNFα inhibitors. dose : 100mg S.C. daily.

Etanercept :

Route & dose: S.C. injection 50mg weekly.

S/E: pain, redness, swelling & itching occurs at the site of infection.

Infliximab: Route & dose: I.V. 3-5mg is infused for every 4-8 weeks.

S/E: increasing respiratory infections, worsening CHF.

Adalimumab: Route & dose: S.C. injection 40mg for every 2 weeks.

S/E: pain, redness, swelling & itching occurs at the site of infection.

MethotrexateTREXALL 15mg tablets

SulfasalazineAZULFIDINE500mg tablets

Adalimumab

surgery

OSTEOTOMY The knee is opened. A debridement (removal of damaged tissue) is performed in the joint to

eliminate the loose or torn fragments that are causing pain and inflammation. The bone is then reshaped to remove the deformity.

conclusionThere is no cure for rheumatoid arthritis. Maintaining proper diet with regular medication is the only way to avoid the progression of the disease.

References

• 1. Ross & Wilson's., Anatomy & physiology

• 2. Harsh Mohan’s., Textbook of pathology

• 3. Rang and Dale’s., Pharmacology

• 4. K.D. Tripathi., Essentials of medical pharmacology