Lymphocytosis is an increase in the number or proportion of lymphocytes in the blood. Absolute lymphocytosis is the condition where there is an increase in the lymphocyte count beyond the normal range while relative lymphocytosis refers to the condition where the proportion of lymphocytes relative to white blood cell count is above the normal range. In adults, absolute lymphocytosis is present when the lymphocyte count is greater than 5000 per microliter (5.0 x 109/L), in older children greater than 7000 per microliter and in infants greater than 9000 per microliter. Lymphocytes normally represent 20% to 40% of circulating white blood cells. When the percentage of lymphocytes exceeds 40%, it is recognized as relative lymphocytosis. Causes
Lymphocytosis is a feature of infection, particularly in children. In the elderly, lymphoproliferative disorders, including chronic lymphocytic leukemia and lymphomas, often present with lymphadenopathy and a lymphocytosis.Causes of absolute lymphocytosis include:

acute viral infections, such as infectious mononucleosis (glandular fever), hepatitis and Cytomegalovirus infection
other acute infections such as pertussis
some protozoal infections, such as toxoplasmosis and American trypanosomiasis (Chagas disease)
chronic intracellular bacterial infections such as tuberculosis or brucellosis
chronic lymphocytic leukemia
acute lymphoblastic leukemia
lymphoma
post-splenectomy state
CARD11-related congenital B cell lymphocytosis (rare, also known as BENTA disease)Causes of relative lymphocytosis include:

age less than 2 years;
acute viral infections;
connective tissue diseases,
thyrotoxicosis,
Addisons disease,
splenomegaly with splenic sequestration of granulocytes. Diagnosis
Lymphocytosis is usually detected when a complete blood count is obtained. If not provided the lymphocyte count can be calculated by multiplying the total white blood cell (WBC) count by the percentage of lymphocytes found in the differential count.
Pharmacology
Mechanism of action
Alvimopan is a competitive antagonist of the μ-opioid receptors (MOR) in the gastrointestinal tract, with a Ki of 0.2 ng/mL. Activation of these receptors by endogenous or exogenous agonists reduces gastrointestinal motility, and alvimopan blocks this effect. Like most other peripherally-selective MOR antagonists, such as naloxegel and methylnaltrexone, alvimopan is selective for peripheral receptors because is effluxed by P-glycoprotein, which  reduces its ability to cross the blood-brain barrier and affect the central nervous system. Pharmacokinetics
Absorption
Peak plasma concentration (Cmax) of alvimopan is reached approximately 2 hours after oral dosing, while the Cmax for metabolite occurs 36 hours after an oral dose. Alvimopans high affinity for the peripheral μ-receptor results in an absolute bioavailability less than 7%. Distribution
80% to 90% of systemically available alvimopan is bound to plasma protein. At steady state, the volume of distribution is approximately 30 liters. Metabolism
Alvimopan undergoes no significant hepatic metabolism, but is metabolized by intestinal flora. Gut metabolism produces an active metabolite with no clinically significant contribution to drug effect. Elimination
Alvimopan undergoes 35% renal excretion and greater than 50% biliary excretion. Drug metabolized by intestinal flora is excreted in the feces. Alvimopans half-life of elimination is 10 to 17 hours, while that of the gut metabolite is 10 to 18 hours. Dosing and administration
Alvimopan is required by the FDA to participate in Risk Evaluation and Mitigation Strategy (REMS) to ensure safe use. Alvimopan is only approved for short term use of no more than 15 doses.