Causes
The most common cause of temporary lymphocytopenia is a recent infection, such as the common cold.Lymphocytopenia, but not idiopathic CD4+ lymphocytopenia, is associated with corticosteroid use, infections with HIV and other viral, bacterial, and fungal agents, malnutrition, systemic lupus erythematosus, severe stress, intense or prolonged physical exercise (due to cortisol release),   rheumatoid arthritis, sarcoidosis, multiple sclerosis, and iatrogenic (caused by other medical treatments) conditions. Lymphocytopenia is a frequent, temporary result from many types of chemotherapy, such as with cytotoxic agents or immunosuppressive drugs. Some malignancies that have spread to involve the bone marrow, such as leukemia or advanced Hodgkins disease, also cause lymphocytopenia. Another cause is infection with Influenza A virus subtype H1N1 (and other subtypes of the Influenza A virus) and is then often associated with Monocytosis; H1N1 was responsible for the Spanish flu, the 2009 flu pandemic and in 2016 for the Influenza-epidemic in Brazil. The SARS disease caused lymphocytopenia. Among patients with laboratory-confirmed COVID-19 in Wuhan China through January 29th, 2020, 83.2 percent had Lymphocytopenia at admission.Large doses of radiation, such as those involved with nuclear accidents or medical whole body radiation, may cause lymphocytopenia. Diagnosis
Lymphocytopenia is diagnosed when the complete blood count shows a lymphocyte count lower than the age-appropriate reference interval (for example, below 1.0 x 10(9)/L in an adult). Prognosis
Lymphocytopenia that is caused by infections tends to resolve once the infection has cleared.
Prescribers should be cautious in the use of labetalol for nursing mothers.Pediatric: no studies have established safety or usefulness in this population.Geriatric: the elderly are more likely to experience dizziness when taking labetalol. Labetalol should be dosed with caution in the elderly and counseled on this side effect. Side effects
Common
Neurologic: headache (2%), dizziness (11%)
Gastrointestinal: nausea (6%), dyspepsia (3%)
Cholinergic: nasal congestion (3%), ejaculation failure (2%)
Respiratory: dyspnea (2%)
Other: fatigue (5%), vertigo (2%), orthostatic hypotensionLow blood pressure with standing is more severe and more common with IV formulation (58% vs 1%) and is often the reason larger doses of the oral formulation cannot be used. Rare
Fever
Muscle cramps
Dry eyes
Heart block
Hyperkalemia
Hepatotoxicity
Drug eruption similar to lichen planus
Hypersensitivity - which may result in a lethal respiratory distress

Contraindications
Labetalol is contraindicated in people with overt cardiac failure, greater-than-first-degree heart block, severe bradycardia, cardiogenic shock, severe hypotension, anyone with a history of obstructive airway disease including asthma, and those with hypersensitivity to the drug. Chemistry
The minimum requirement for adrenergic agents is a primary or secondary amine separated from a substituted benzene ring by one or two carbons. This configuration results in strong agonist activity. As the size of the substituent attached to the amine becomes greater, particularly with respect to a t-butyl group, then the molecule typically is found to have receptor affinity without intrinsic activity, and is, therefore, an antagonist. Labetalol, with its 1-methyl-3-phenylpropyl substituted amine, is greater in size relative to a t-butyl group and therefore acts predominantly as an antagonist. The overall structure of labetalol is very polar.